Composite materials are the advanced materials which are widely used in manufacturing industries. The most commonly used composite materials are metal matrix composites. Due to the presence of abrasive reinforcing particles, traditional machining of these causes severe tool wear and hence reduces the life of cutting tool. Wire electrical discharge machining (WEDM) is quite successful for machining of metal matrix composites. Wire Electrical Discharge machining is a specialized thermal machining process capable of accurately machining parts of hard materials with complex shapes. The selection of process parameters in WEDM to obtain greater accuracy or cutting efficiency is still not fully solved due to the complicated stochastic process mechanisms with the most recent CNC wire cut EDM. One of the main research fields in WEDM is related to the improvement of the process productivity by avoiding wire breakage. The different factors viz., decrease in flushing pressure, inefficient removal of erosion debris and some other types of stochastic phenomena that occur during the machining process can lead to the breakage of wire electrode. In such cases, the wire has to be looped again by stopping the machining process, which leads to an undesired time waste. Before wire breaks, wire breakage has to be predict by diagnosing in advance low quality cutting regimes in order to perform an on line readjustment of the machine parameters. Worn electrode state dramatically affects the texture of the machined surface. Wire electrical discharge machining has been found to be a promising machining technique for obtaining desired dimensional accuracy and surface finish on hard and tough materials. Wire electrodes used in WEDM are the core of the system. WEDM is extensively used in machining of conductive material. In this study the effect of different wire electrode materials on dimensional accuracy and surface finish for wire electrical discharge machining of metal matrix composite material were investigated. The experiments were conducted under the following process parameters viz., pulse on-time, pulse off-time, current and wire feed speed. For the experiment the aluminium 6061 alloy with 0%, 5%, and 10 % of silicon carbide (SiC) reinforcement material was used. To conduct the experiment CNC wire EDM machine with two different wires viz., molybdenum and brass wire was used. L9 Taguchi orthogonal array technique was used to design the experiment. Experimental results indicate that for better surface finish and dimensional accuracy of Al6061 alloy, the brass wire is more suitable. Good surface finish and dimensional accuracy can be obtained with molybdenum wire in Al-SiC composite material. Increasing percentage of silicon carbide in aluminium 6061 alloy increases the variation in surface finish and dimensional accuracy. Wire wear rate of both brass and molybdenum wire is increased with increase in percentage of silicon carbide.


Effect of Wire Electrode Materials on Performance Characteristics for Wire Electrical Discharge Machining of Metal Matrix Composite Material

Thermo-acoustic systems are being considered as a potential sustainable solution for electricity generation where the sound waves can be used for electricity generation through a linear alternator. Thermo-acoustic is actually a field of science that is concern with the interaction between thermal energy (heat) and acoustic energy (sound) with the purpose of inducing cooling or generate electricity. Recently, there have been a significant increase in the development of thermo-acoustic refrigerators as well as thermo-acoustic generators with limited to no moving parts involved. Travelling wave devices have exhibited promising results with respect to their performance whilst working at very lower temperatures. This work describes the construction of a two-stage travelling-wave thermo-acoustic generator. In addition, an experimental investigation into the effect of the heat source on the potential of the device for electricity generation has been conducted in order to evaluate the device performance. The effect of the geometric configurations of the thermo-acoustic engines is examined for series and parallel arrangement. The prototype consists of two thermo-acoustic engine connected through Polyvinyl chloride (PVC) pipes forming a loop for the waves to travel through. A commercial loudspeaker was used as linear alternator in order to assess the potential for sound-to-electricity conversion of the system. Each engine consists of the regenerator, a cold heat exchanger and a hot heat exchanger. The magnitude of the sound generated by the engines, the onset time and the magnitude of electricity generated by the linear alternator have been considered as performance indicators for the device developed. Clear trends showing the effect of inputs parameters on device performance have been presented. The prototype was developed and thenceforth evaluated. It proved to perform better with the parallel configuration, and achieved a faster onset time than with series configuration. A minimum onset time of 3.15 minutes to produce a sound was recorded. The average minimum/maximum amount of heat that has produced a sound was 340/635^o^C corresponding to sound of 114.1/126.4 dB and a voltage of 387/486 mV respectively. Although the efficiency of the sound-to-electricity conversion was low, this work proves the viability of thermo-acoustic as the alternative solution for electricity generation. Research attention can be invested more on geometric arrangements and configurations of the multistage thermoacoustic devices i.e. the use of a suitable sound-to-electricity convertor, the best location for the alternator as well as whether single or multiple alternators produces better results. This paper provides clarity on the potential for thermo-acoustic system for sound-to-electricity conversion.


Construction and Performance Analysis of a Two-Stage Travellng-Wave Thermo-Acoustic Generator

Abstract:

Utilizing nanofluid in heat exchanger is extensively interested in petrochemical and power plant industries due to the durability provided to the exchanger long-life operation.   In the present research, an experimental investigation is carried out to study the influence of copper and aluminum oxide nanofluids on the performance of shell and tube type heat exchanger. Comparsion with theoretical outcome is also conducted.  Implementation of the experiments was performed using counter-flow double-pipe heat exchanger. The heat exchanger consists of 21 tubes through which the hot fluid flows. The 7 thermocouples are positioned along the hot and cold circuits so as to facilitate the measurement of temperatures at the inlet, exit and intermediate points of the exchanger. pure water is heated by means of an electric heating element to a specified temperature and is then pumped into the tubes of the heat exchanger unit. The second fluid (the nanofluid), stored in the cold fluid tank, is pumped into the heat exchanger unit by means of another impeller pump. The nanofluid flows in the annular space around the tubes. Although parallel and counter flow configurations can easily be established by making use of the four ball valves placed along the cold circuit, only counter flow configuration was setup for operation in the present study. Various volume fractions ranging from 0.26% - 0.83% were tested to assess the morphology of nanoparticle and volume fraction on the exchanger efficiency. It was observed that the volume fraction of nanofluid has a direct relationship to the heat exchanger effectiveness. As the volume fraction was increased, the effectiveness was found to increase by 7% and 10% for Al~2~O~3~ and Cu nanofluids, respectively.  Further, the effect of mass flow rate of cold-side nanofluid was investigated. The Reynolds number for the cold nanofluid was varied in the range 7000 - 15000. It was observed that the mass flow rate of cold nanofluid has a direct relationship with the Nusselt number. A significant enhancement in Nusselt number by 13% and 23% was observed for Al~2~O~3~ and Cu nanofluids, respectively. The effect of varying inlet temperature of hot fluid was also investigated.  Results indicate an enhancement in performance for higher inlet temperatures of hot fluid. Moreover, the heat leak from the shell side to the ambience was estimated for each case. Al~2~O~3~ nanofluid was observed to have greater heat leak in comparison to Cu nanofluid.


Evaluating the Influence of Nanofluid Type and Volume Fraction on the Performance of Heat Exchanger

Natural convection has a great its importance in several practical applications. In particular, the configuration of two horizontal parallel walls, with heated upper plate and open cavities, gets considerable attention in many thermal engineering applications, such as cooling of electronic components and devices, chemical vapor deposition systems and solar energy systems. The flow motion is strongly affected by the location of the heated surface, positioned on the upper or the lower wall of the horizontal channel. The main flow in natural convection is caused by the low heat exchanged between flow and walls, and one of the techniques to enhance the heat transfer is expanding the exchange surfaces. Porous media provided with high thermal conductivity, like metal foams, are an adequate method of heat transfer enhancement due to their large surface area to volume ratio and to intense mixing of the flow. In this work, a numerical investigation on two-dimensional steady state natural convection in a horizontal channel partially filled with a porous medium and heated at uniform heat flux from above is carried out. The lower plate is adiabatic. The porous medium is modeled using the Brinkman–Forchheimer-extended Darcy model and the local thermal equilibrium (LTE) hypothesis is assumed. The structure of the porous medium is homogenous and isotropic, the thermophysical properties of the air and the porous medium are temperature independent and the fluid flow is laminar and incompressible. The governing equations in the two-dimensional model is realized and solved by means of the ANSYS-FLUENT code. The computational domain is made up of the principal channel and two lateral extended reservoirs at the open vertical sections. The channel has dimensions L equal to 400 mm and the distance between the two horizontal plates, b, is equal to 40 mm. The two external reservoirs allow to simulate the external ambient and to assign at the boundary of the reservoirs a velocity equal to zero and the ambient temperature. Furthermore, a porous plate is considered near the upper heated plate and it has a thickness equal to 20 mm whereas the length and the width are the same of the channel. The aluminum foam has 10, 20 and 40 PPI and its porosity ranges from 0.89 and 0.97. Rayleigh number values are examined, from 10 to 1000. The main aim of the present study is to analyze the effect of pores per inch and porosity. The numerical simulations are performed with working fluid air. Different values of assigned wall temperatures are considered. Results are presented in terms of velocity and temperature fields, and both temperature and velocity profiles at different significant sections are shown, to obtain a description of the natural convection inside the open-ended cavity. Finally, Average Nusselt number values are evaluated.


Study on Natural Convection in Horizontal Parallel Plate Channels Heated on Upper Wall and Partially Filled With Metal Foam

A new design of an intercept valve assembly of the intermediate-pressure turbine part of greater power output is investigated in terms of pressure losses and flow fluctuations by using measurement on an experimental valve model. In addition, numerical simulations are used to further clarify measured phenomena. For such valve assemblies, it is important to exactly predict pressure losses and avoid danger of vibrations, which are caused by undesirable flow fluctuations, in order to guarantee valve´s efficiency and operational reliability. For this type of valve, it is especially important for turbine operations in partial loads (off-design conditions). Measurements were carried out in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences (IT) in a modular aerodynamic tunnel. Numerical simulations were carried out in the Doosan Skoda Power Company (DSP) by using a package of ANSYS software tools. The experimental valve model is a scaled model of a real valve assembly. It consists of an inlet pipeline, a stop valve and a control valve including its diffuser and outlet pipeline. Measured regimes were defined by a mass flow rate and a control valve lift which can be precisely changed. In order to investigate pressure loses, total and static pressures at valve characteristic locations were measured by using Prandtl probes and wall static pressure taps. In order to measure pressure fluctuations, Kulite fast response pressure transducers were used. They were situated near the valve throat where the flow fluctuations, which are strongly related to a flow separation, are the most visible and influential. Measurement results are compared with numerical results and locations with a flow separation were found. In order to reduce this phenomenon, different valve seat angles were also tested. As a result, a valve design could be optimized and, for a pressure loss prediction, a pressure loss model for this new intercept valve assembly could be created. Therefore, pressure losses in similar valve assemblies can be predicted with required accuracy for each new turbine where modern intercept valves are used. This helps to increase steam turbine efficiency and reduce fuel consumption. Based on pressure fluctuations results, operating conditions at which dangerous flow instabilities occur were identified. It was concluded that there is an operating condition border where the flow field starts to be unstable. As a result, the areas of safe and dangerous operating conditions can be predicted so that the operational reliability of the valve can be guaranteed.


Investigation of Pressure Losses and Flow Fluctuations in an Intercept Valve Assembly of an Intermediate-Pressure Turbine Part

In the near future, the world’s transportation system should be powered by less-pollutant or completely non-pollutant energy sources. The rationale behind these systems is the protection of the planet and all forms of lives. The transportation sector produces 15 to 20 % of greenhouse gas emissions. Many renewable energy sources are being explored for the transportation sector. But the technologies are less popular because of their infancy stages, as well as the cost associated with their use. Solar energy, compressed air, hydrogen, electric battery etc. are few examples of the clean and renewable energy sources which are prominent for powering the transportation of the future. Compressed air is one of the plausible solutions to solving the energy problem, considering the fact that air is readily available. But the problem in the usage of the compressed air energy has been the storage system. In this paper, the performance of two distinct compressed air reservoirs for energy storage in small scale systems was investigated. Physical experiments were conducted, and simulations were performed. The analysis performed in this work was focusing on the results trends. Two air compressors were utilized for the experiment and they were both of reciprocating type. The first air compressor was driven by an internal combustion engine (ICE) and the second was driven by an electric motor. The decision regarding which results to consider was made based on the data collected. The experimental results were used to provide a frame of reference for the computer (MATLAB) simulation. Additionnaly, the performance of the dynamic reservoir was analysed for three spring stiffnesses. In summary, this study shows that the maximum pressure that can be stored in any dynamic reservoir depends largely on the capacity of the compressor. The quick rise in pressure during the charging process and the quicker exit during the discharging period clearly indicated that something unusual took place. It appears that the spring has a beneficial impact on the working of compressed air reservoir. The piston and the spring represent the heart of the dynamic reservoir. During charging they convert the pressure to force and the force to strain energy respectively. During discharge, they reverse the charging process by converting the strain energy to force and the force to pressure. Thus, ensuring a consistent performance of the dynamic reservoir. The dynamic reservoir offers the capacity to store a high quantity of compressed air in a relatively small volume. It offers a better mass flow rate during discharge, because the spring pushes the gas out of the reservoir, making a steady flow possible. The rapid pressure rise inside the dynamic reservoir and the constant pressure supply during discharge will improve the performance of compressed air powered applications and will help those to become more reliable.


Development and Performance Evaluation of a Dynamic Compressed Air Energy Storage System

The use of composite joints has been increased in recent years in structural applications such as aircraft, civil engineering structure, ship structure, wind energy sector, and automotive industry. All previous efforts focused on bolted and riveted connections loaded in shear (in-plane loading) either in single or double lap joints. No work in literature that addresses the analysis of bolted connection in glass fibre reinforced plastics loaded in tension. Such joint configuration is essential in connections of wind turbine blades, in particular for vertical axis wind turbine blades, where the blade is connected to the rotor in bolted connections loaded in tension. In this paper, the behaviour of composite bolted connection joints under out of plane loading was investigated. A parametric study was conducted to study the joint stiffness variation with different parameters such as the ratio between edge distance (e) and bolt diameter (D), e/D, plate width (W) to bolt diameter ratio, W/D, stacking sequence and bolt load. The effect of the fillet radius also investigated to determine the minimum radius which prevents the onset of delamination between stacked layers. The experimental work was conducted on GFRP tension clips (L-angle) joint specimens manufactured by the vacuum infusion technique. Large samples of dimensions 1 m long were first produced and then cut into different specimen sizes. Holes are then drilled carefully at specific locations to avoid inducing damage to the specimen before testing. In the present work, three types of laminates were used; a unidirectional laminates with an areal density of 1050 gm/m2, biaxial laminates, triaxial laminates 0 / +45  / -45 with an areal density of 1200 g/m2, triaxial laminates 90 / +45 / -45 with an areal density of 900 g/m2. A 3D finite element (FE) model was developed to study the effect of joint parameters on its stiffness and the resulting failure modes. Finite element models were constructed and the experimental results were used to validate these finite element models. The finite element model was based on continuum shell elements and was used in conjunction with Hashin’s failure criteria for fibre reinforced polymer composites. The finite element results were validated against experimental results. The analysis concluded that the failure load increases when the edge distance to bolt diameter ratio (e/D) increases and the biaxial stacking sequence is better than unidirectional and the fillet radius affect significantly in the onset of delamination. The (e/D) ratio, stacking sequence, and fillet radius are very significant parameter.


Analysis of Composite Bolted Connection Joints Under Out of Plane Loading

This work describes the design and construction of a four-stage travelling-wave thermo-acoustic system for electricity generation. Thermo-acoustic devices are systems which utilized what is known as thermo-acoustic effect to convert thermal energy to acoustic energy or vice versa. Thermo-acoustic conversion consists of using a sound-wave for the transfer of heat from a low to high temperature medium or the use of heat energy to generate a sound wave. Both the absence of moving parts and simplicity of thermo-acoustic systems demonstrate that they have the potential for developing low-cost power generators. Many existing studies have pointed out the acoustic-to-electric potential of thermo-acoustic systems. Hence in this work, a thermo-acoustic system have been developed in order to get an insight into the designing of the system with respect to the geometrical configuration. The thermo-acoustic system core consists of three crucial parts: hot heat exchanger, regenerator and cold heat exchanger, where the thermo-acoustic processes take place. The total length of the travelling-wave system is 3560 mm and each engine stage is placed at a mutual distance of 640 mm. The engine stage is having four cartridge heaters connected in parallel at one side of the regenerator. Heat is transferred to the regenerator by conduction through copper strip. Between the hot heat exchanger and the regenerator, there is some holes where thermocouples can be placed for temperature measurements. The maximum operating temperature for the hot heat exchanger is between 650 and 1000. Copper strip has been selected because of its high thermal conductivity properties. Copper strips is cut into 200 mm, folded around a bench vice to obtain a 90º angle, drilled and placed over the cartridge heaters inside the regenerator tube. Water with ambient temperature is used to cool the system which is fed to the ambient heat exchanger. The circulation water used for the ambient heat exchanger is supplied from a tape through tubing transparent pipes of 6 mm. Copper strips (5×20×80 mm) are drilled and placed over the tubes touching the regenerator to ensure proper heat conduction from the regenerator to the water flow. The honeycomb ceramic has been selected for this design, due to its good thermal contact, availability and low thermal conductivity. The honeycomb ceramic in the square shape is cut by (85 × 95 mm) and sandwiched between both heat exchangers. The honeycomb ceramic regenerator used in this experimental research has 400 CPSI, with square spores. The engine core has four flanges. Each side of the regenerator tube has two flanges that are connect by four bolts and between these flanges there is a gasket of 5 mm in thickness. Flange gasket are used to create a static seal between two flanges faces, at various operating conditions, with varied pressure and temperature ratings. This gasket fills the microscopic spaces and irregularities of the flange faces, and then it forms a seal th

Design and Construction of a Four-Stage Travelling-Wave Thermo-Acoustic System for Power Generation

There has been a growing interest in solid-state thermoelectric (TE) materials over the past few decades due to their applications in harvesting industrial waste heat. TE figure of merit (ZT), a dimensionless parameter commonly used to assess the efficiency for TE energy conversion, is inversely related to the thermal conductivity of material. In most TE materials, thermal transport is mainly contributed by phonons and the ZT can be largely improved by suppressing the lattice thermal transport, without degrading the electron transport. Along this line, phonon scattering at boundaries/interfaces is a common approach to dramatically reduce the lattice thermal conductivity. Confining phonons to nanosized structures/films nullifies their contribution to the thermal transport thereby decreasing the materials thermal conductivity. Knowledge of spectral phonon mean free paths is critical for evaluating the thermal conductivity reduction using classical phonon size effects. Numerous reports have been published that demonstrate lowering of thermal conductivity in conventional TE materials. Despite the thermal conductivity reduction, the ZT for existing TE materials is still subpar to be considered for solid-state TE power harvesting devices. Using the nanostructuring approach, bismuth telluride (Bi~2~Te~3~) has shown remarkable improvements in the ZT value. The electronic properties for Bi~2~Te~3~ are comparatively straightforward to measure and have been extensively reported but current understanding of thermal properties is still lacking. This is partly due to limited reports on accurate thermal conductivity measurements and challenges in preparing high-quality single-crystal Bi~2~Te~3~ thin films. In this regard, the present work is geared towards understanding the room temperature thermal transport in Bi~2~Te~3~ thin films. High-quality Bi~2~Te~3~ thin films have been prepared using chemical vapor deposition on a SiO2/Si substrate. Thickness-dependent thermal conductivity has been studied with the aim of assessing spectral phonon mean free paths in the material. The through-thickness thermal conductivities of Bi~2~Te~3~ thin films with thicknesses ranging from 20 nm – 300 nm has been experimentally measured using the time domain thermoreflectance (TDTR) method, which is a widely accepted and accurate method for thermal conductivity characterization of thin films. The thickness of the films has been confirmed using the atomic force microscopy. TDTR experiments have been performed at two different modulation frequencies to decouple the effect of the interfacial conductance. The measured room-temperature thermal conductivity values stay close to the bulk value of 0.45 W m^-1^ K^-1^ for all the thin films, suggesting that mean free path of most phonons is smaller than 20 nm, which agrees well with the first-principles predictions. This result sheds light on potential thermal conductivity reduction in Bi~2~Te~3~ thin films as TE materials.


Through-Thickness Thermal Conductivity of Bi2Te3 Thin Films Grown by Chemical Vapor Deposition

A rapid increase in energy demand has strained natural resources. As such, there is an urgent need to develop novel materials with higher performance capabilities and promote green technology. In this regard, advanced manufacturing and tribological characterization of novel and green materials are of high importance. The conventional materials used in energy storage devices, such as batteries and supercapacitors, suffer from problems of electric wastes, high-cost, toxicity, and non-biodegradability. There is an impending need to find novel energy storage materials that can provide high electrochemical performance while being environmentally sustainable. Lignin is a naturally occurring source of carbon that holds a high promise for energy storage applications due to its abundance, low-cost, and bio-degradability. However, unprocessed lignin has several issues that limit its electrochemical performance. Uneven pore size and distribution, highly complex surface chemistry, largely unknown surface functional groups, and an intricate 3D network of chains in unprocessed lignin, create hindrance to charge transport and ion mobility. As a result, the lignin-based electrochemical devices are prone to instability, poor performance, and low cycle life. Hence, it is of utmost importance to understand the surface morphology and characteristics of lignin electrodes in detail. In this research, MnO~2~ deposited alkali lignin-based electrode is synthesized for application in a flexible supercapacitor. MnO~2~ particles deposited on alkali lignin, via hydrothermal treatment, was used as the electroactive material with an Al substrate. An asymmetric supercapacitor, with Al/lig/MnO~2~ as the anode, was assembled using an aqueous gel electrolyte of PVA/H~3~PO~4~ and Al/AC as the cathode. To study the morphology and microstructure of the electrode, synchrotron X-ray microtomography was employed. Data analysis was performed using image processing and several surface parameters were calculated and compared. The 3D concatenated images revealed details on surface morphology, surface packing density, roughness, chain length, and 3D structure of chains. The electrochemical system performance was assessed using cyclic charge-discharge (CCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Three varying ratios of lignin and MnO~2~ were tested and analyzed to achieve optimal performance. The highest specific capacitance obtained was 379 mF cm^-2^ at a current density of 40 mA g^-1^, which is 900 times greater than currently reported. The supercapacitor exhibited high capacitance retention of 80%, an energy density of 6 Wh kg^−1^, and a power density of 355 W kg^−1^. The exhibited remarkable performance makes this supercapacitor suitable for several applications. Thus, this work utilizes synchrotron tomography in revealing several important surface characteristics of a novel and green supercapacitor electrode. The electrode is of high performance and s

Tribological Characteristics of Green Supercapacitors

Offshore wind turbines are considered as a reliable source of electricity generation. However, due to the large cost of the construction, installation and maintenance of offshore wind turbines, most offshore wind turbines are designed to operate for more than 20 years. One of the biggest issues which causes a severe damage to the construction of offshore wind turbines is the existence of a very corrosive environment including large mechanical loads applied to the construction by the waves, as well as the high concentration of salt and other chemicals in the sea water. The construction of offshore wind turbine can be divided into four main regions based on the types of exposure to the water and the corrosive environment, including submerged zone, tidal zone, splash zone, and atmospheric zone. Corrosion occurs due to bacterial growth, chemicals, PH level, and salt content of the water, while abrasive action of waves expedite the failure rate of the coatings. The corrosion rate at different zones varies due to the unbalanced participation of different corrosive factors in the degradation process. In this study, experiments were conducted to compare the impact of impingement flow of 3.5 w.t. %  NaCl solution on the epoxy coating samples to the exposure of the same type of samples to a stationary 3.5 w.t.% NaCl solution. Those two exposure conditions correspond to the environments at the top part and the bottom part of the submerged zone of offshore wind turbines respectively. Electrochemical Impedance Spectroscopy (EIS) method was used  to monitor the degradation of organic coatings. Equivalent circuit models are employed to interpret the EIS spectra. Atomic Force Microscopy (AFM) was employed to study the influence of fluid flow on the surface topology of the coating samples. The roughness of the coated surfaces before and after the exposure was compared. For the two different flow conditions, i.e. impingement flow and stationary immersion, significant differences have been discovered from the EIS results and AFM results. We observed a more severe degradation in the epoxy coatings in impingement flow, and a rougher surface is formed for coating samples subjected to impingement flow. The influence of flow conditions on coating thickness has been monitored. The thickness of the coated samples exposed to the stationary fluid increased after the exposure period. On the other hand, the thickness of the samples decreased after the exposure to the impingement flow. Discussions have been carried out to explain this phenomenon.  


Comparison of Epoxy Coating Degradations Under Impingement Flow and Stationary Immersion

Aluminum alloys exhibit excellent strength to weight ratio and other useful mechanical properties desirable in aircraft industries. It is a common practice to use riveted holes to join these parts together. Cold expansion is a highly popular technique of extending fatigue crack initiation and propagation life of these holes. Earlier, various studies on fatigue crack growth and life estimation of aluminum alloys were conducted. Studies included the variation of crack growth life with changes in stress ratio, changes of fatigue life in comparison with plain holes with cold expanded holes, environmental effects, low and high cycle fatigue behavior, etc. Some of the studies were also conducted on pre-cracked cases along with cases considered for short edge margin holes. But in this parametric study, a numerical investigation is carried out to find the variation of fatigue crack initiation and propagation life in variation with material property specifically of different yield strengths with varying the rate of hole cold expansion. Here, 2024-T351 aluminum alloy is chosen as the test material. The design of the numerical setup consists of nine different cases by varying three different yield strengths from different manufacturing lots along with three different rates of cold expansion. For the combinations of highest yield strength and the highest percentage of cold expansion, fatigue crack initiation delays and at the same time crack growth rate delays significantly. For the combinations of lowest yield strength and the lowest percentage of cold expansion, both crack initiation life and crack growth life become shorter compared with highest ones. The maximum strain appears at the mandrel entry side of the hole when the model geometry is pulled with tensile load. From this strain pattern, 0.2mm entry hole corner type crack is defined as the initial crack size. When comparing with the baseline model, it is found that the fatigue lifespan for baseline is significantly shorter in terms of maximum allowable crack size with applied cyclic stress range between 206 MPa to 10.3 MPa. The baseline model fails only with a through-thickness crack size of 0.7mm while for the cases of parametric study, model even with the lowest yield strength and lowest cold expansion percentage, doesn’t fail below a crack size 3mm. It is observed that the variation of material yield strength can contribute in a notable manner when accompanied with different rate of hole cold expansion. This study can be useful to applications where variation of material strength exists with a lot to lot and at the same time improved fatigue crack growth rate prediction is desired from cold expanded holes.


Effect of Material Property and Hole Cold Expansion Rate on Fatigue Crack Initiation and Propagation on 2024-T351 Aluminum Alloy Holes

In the recent years, biomass, such as plant protein, have gain more and more attentions as alternatives to the fossil fuel-based synthetic polymer materials. Soy protein, as a low cost and abundant natural resources, is a promising candidate to be used as a functional material. Soy protein consists of various amino acid residues with different inter/intra molecular interactions, e.g. hydrogen bonds, ionic interactions, hydrophobic interactions and disulfide bonds, etc. The complicated microstructures offer great potentials for soy protein as functional modifier for polymers. Soy protein-based products, such as plastics, adhesives and coatings, have been extensively utilized in industrial and biomedical fields. In our previous studies, we have demonstrated that, by controlling the denaturation conditions and the weight fractions, soy protein could possess different morphologies and properties, therefore, form various interactions with the polymer molecules, and eventually modify their performances. Besides, both experimental and numerical simulation approaches were adopted to analyze the underlying mechanisms of the protein-polymer interactions. In this study, we use denatured soy protein as modifier to alter the crystallinity and properties of Poly(vinylidene fluoride) (PVDF) polymer; the effects of fabrication parameters of the polymer/soy protein blends, including denaturation conditions and weight fractions of protein phase, are evaluated to provide insights for the optimized designs of the functional modifier.

In addition, for the purpose of screening high-performance material formulas, and predicting the quantitative structure-property relationships, a machine learning assisted surrogate model is developed in this work. With the machine learning algorithms, we could efficiently optimize the fabrication parameters of polymer/soy protein blends with improved properties, rather than ‘exhaustive searching’ all the blends from different fabrication parameters through experiments. We herein compare several data-driven machine learning algorithms to design polymer/soy protein blends with optimized dielectric constants/loss. The process includes three steps: learning step, prediction step and reversing step. We firstly train different machine learning algorithms using the experimental dataset. The correlation within fabrication parameters and between crystal structure and dielectric properties can be revealed. Second step is to compare the prediction results from various machine learning models with experimental data to find the best algorithm based on the prediction accuracy and judging criterion R2 (the coefficient of determinant). Lastly, the reversing engineering model is constructed based on the suggestion-test approach: several new blends with the best dielectric properties and their corresponding fabrication parameters are estimated; afterwards, the candidate blends are experimentally fabricated based on the fabrication parameters, and their

Machine Learning Assisted Design for Active Cathode Materials

Self-pierce riveting (SPR) is one of the commonly used joining technologies in the automotive industry. Compared to other joining approaches, the SPR could deliver permanent connections by piercing in a single operation, which is particularly useful to assembly dissimilar materials that are difficult to weld, such as aluminum with steel. However, SPR joint results in the direct contact between two different materials, e.g. Al-Fe, which will greatly increase the potential of corrosion phenomena in the presence of electrolyte, due to the galvanic effect between dissimilar metals. The crevices between joining metals and metal-rivet, serve as the active sites for the initiation of the corrosion phenomena in corrosive environments. The corrosion often plays an important role in fatigue failures of the joints and reduces their useful life; the corrosion products could also cover the metal surface, leading to the change of the geometry and internal loading of the joint, causing unexpected stress concentrations and damages.

A comprehensive understanding on localized corrosion is necessary for both corrosion prognosis and corrosion protection for the SPR joint. The initiation and propagation of localized corrosion have been extensively investigated through experimental methods. However, it can be challenging to accurately detect the electrochemical kinetics of the localized corrosion using experimental methods due to the practical limitations of measurements, especially when considering the micro/crystal structures of the metals. Numerical simulation methods have been adopted in the recent decades to rationalize and quantify the corrosion phenomena. The numerical simulation models can be used to estimate the dissolution of metals and investigate the effects of various influencing factors and environmental conditions, e.g. geometric structures, microstructures and pH value, etc., based on the chemical and electrochemical theories. Nevertheless, in these models, the spatial and time dependences of the corrosion nucleation need to be provided prior to the simulation, which can be difficult to be predetermined sometimes.

In this study, a hybrid model is developed to simulate the corrosion process of the Al-Fe SPR joints, which consists of both stochastic corrosion nucleation information and finite element (FE) model-based corrosion evaluating prediction. The stochastic corrosion nucleation variables, including the location of the nucleation sites and their corrosion trigger time, are obtained through statistical analysis of the experimental samples. Then, these variables are imported into the physics-based FE model, and various corrosion scenarios are generated. The simulation results are statistically analyzed and validated with experiments. It is found that, the proposed hybrid model can reasonably predict the localized corrosion results of the SPR joints. In addition, parametric studies are conducted on different geometric and environmental parameters, e

Corrosion Modeling and Prognosis of the Al-Fe Self-Pierce Riveting Joints

Natural bactericidal surfaces are found on the wings of cicada and dragonfly that compose of nanopatterns such as nanopillar arrays. It has been observed that the nanopillars can penetrate into the bacterial walls or stretch them, which results in the death of bacteria cells. It was reported that, in the case of orthopaedic implants, implant-associated infections (IAIs) are on the major factors limiting the longevity of implants. The nanopatterned surface offers an attractive “chemical-free” and wide-spectrum strategy to fight against bacteria-related infections and fouling. Efforts have been made to fabricate surfaces decorated with similar types of nanopatterns by researches, which are demonstrated to exhibit bactericidal behavior. Although the bio-inspired nanostructured surface has the great potential to mitigate the risk of infection for implants through wide-spectrum antimicrobial capability. However, the fundamental bactericidal mechanisms of nanopatterned surface is not clear, which prevent the rational design and wide application of such kind bio-inspired surface. One critical research question needs to be answered to realize its full potential: how the bacteria cell response to the nanopatterns, which determines the bactericidal performance of the nanostructured surface. Considering the length and temporal scales of the bactericidal phenomena, it is extremely challenging to observe the cell-nanostructure interaction directly through experimental study. In this work, we will develop mechanical single cell model of bacteria based on finite element analysis to simulate the interactions between different strains of bacteria and the nanostructured surface. The nanostructured surface contains nanopillar arrays, which are made of polymer materials. For the bacteria models, the cell mass density and shapes are directly determined from experimental data in the literature. The cell wall is considered as elastic while the cytoplasm is considered as nonlinear viscoelastic, which is suggested by atomic force microscopy measurements. Different strains of bacteria are simulated by adopting the corresponding geometry and material properties from experimental values. The mechanical response of the bacteria cell on the nanopillar arrays will be studied based on estimated stress and strain distributions within the cell. The bactericidal efficiency of the nanopillars will be determined by the induced maximum stress and strain in the cell. A systematic study will be conducted to investigate the effects of heights, width and spacing of nanopillars on the mechanical deformation of bacteria cells. In addition, the bactericidal efficiency of nanopillars for gram-negative and gram-positive bacteria will be investigated, respectively. We expect to establish quantitative structure-performance relationship of the nanostructured surface in terms of the bactericidal efficiency, which can help the design of such bio-inspired antibacterial surface for a wide range of a

Numerical Study on Antibacterial Effects of Bio-Inspired Nanostructured Surface

Recently, the controlled drug delivery technology has been widely investigated to address and treat challenging diseases such as cancer, ADIS etc. Nanoparticle-based drug delivery systems are extensively explored and found to possess certain advantages over traditional delivery systems, such as greater stability during storage, stability in vivo after administration and ease of scale-up during manufacture. While the techniques have proven beneficial in disease treatment and diagnostics, there are still grand needs to develop different nanoparticle systems for various drugs.

Bio-based materials, such as plant protein, have gained great attention as drug delivery vehicles among the available potential colloidal carrier systems, due to their low cytotoxicity, abundance, renewability, diverse functional groups and interactions, and high drug loading capacity, etc. Soy protein is one of the promising candidates that can be extensively used as carrier for various drugs, because of its highly diverse molecule structures and interactions, e.g. polar/non-polar residues, hydrogen bonds, ionic interactions, hydrophobic interactions, disulfide bonds, etc. Although previous experimental results have demonstrated the potential of the protein as drug carrier, the underlying mechanisms of the attachment and release of drugs remain unclear, which is challenging to study directly through experimental approaches. Atomic-resolution molecular dynamics (MD) simulations is a powerful tool in the community of physics, chemistry and material science and can provide insights in understanding the molecular interactions between proteins and drugs.

In this study, MD simulations are adopted to study the mechanisms of the 11S molecule of soy protein as drug delivery vehicle. Two types of anticancer drugs are selected as the drug systems, i.e. allyl isothiocyanate (AITC) and doxorubicin (DOX). The adsorption processes of drugs on the protein are explored. The intermolecular interaction energies are analyzed to reveal the fundamental interactions that control the drug adsorption behaviors, and to determine the active sites on the protein surface. The loading efficiencies are calculated and compared with experiments. Furthermore, two types of denaturation conditions, including heat denaturation and breaking of disulfide bonds, are utilized to vary the microstructures of the protein carrier and improve their loading properties.

It is found that, for the AITC system, both nonpolar and polar residues of protein have the ability to adsorb AITCs; particularly, the polar residues serve as the primary active sites for the stable attachment of the drug molecules through the electrostatic (dipole-dipole) interactions. For the DOX system, however, the main driving force become the π-π stacking (the van der Waals interactions) among the aromatic rings of DOX and protein. In addition to pristine protein, two different denaturation processes, including heat denaturation and the breaking of

Molecular Dynamic Simulation Study on Soy Protein As Drug Delivery Vehicle

Glass Fiber Reinforced Plastics (GFRP) have been used increasingly in many fields such as aerospace, automotive and wind energy sectors. This increase is primarily due to their superior strength-to-weight ratio and excellent fatigue resistance compared to traditional materials. During the manufacturing process of glass fibre reinforced plastics using vacuum assisted resin infusion, some defects such as dry spots and air pockets may develop in the impregnated fabric, especially, when metallic inserts are used. This is particularly true for large and complex structures produced by vacuum assisted resin infusion. While computer simulations can be used to determine the flow and vacuum lines in the infusion process to eliminate such defects, they still can form in special circumstances, such as improper curing, interrupted flow, or the presence of metallic layers. These dry spots can be repaired either by re-infusion or hand wetting rather than scrapping the whole structure. To evaluate the interface between the original and repaired part, an experimental investigation was performed to study its effect on the mechanical properties and structural integrity. Experimental work based on partially infused and repaired samples was conducted. In this case, samples with dimensions of 50x50 cm with different laminates having different areal densities were prepared for vacuum assisted resin infusion. In the present work, three types of laminates were used; a unidirectional laminates with an areal density of 1050 gm/m2, triaxial laminates 0 / +45  / -45 with an areal density of 1200 g/m2, triaxial laminates 90 / +45 / -45 with an areal density of 900 g/m2. The fabrication process was then interrupted and the resulting sample was then re-infused (repaired) after complete curing of the first infusion. Samples from the first infused sample (intact) and re-infused sample are cut into standard tensile and bending specimens. To compare the response of the re-infused (repaired) and intact samples, several tensile and bending tests were performed for uniaxial, biaxial, and triaxial reinforcing fabrics with different interfaces. The results showed that the re-infusion had a minor effect on the ultimate tensile strength, particularly when the parent and repair laminates have almost the same quality. Based on visual inspection of intact samples, it is noted that each type of interface has a typical dominant failure mode. For the re-infused samples, the properties of parent and repair laminates determined the failure location. Furthermore, to quantify the role of the interface angle between the intact and repaired parts, samples with designed interface inclination were prepared using hand wetting techniques on two curing steps. The results obtained are expressed in terms of the interface angle and the type of the fabric.


Evaluation of the Mechanical Properties of Repaired Composite Panels Using Resin Re-Infusion Process

Conjugate mixed convection in a lid-driven differentially heated square cavity with two heat conducting cylinders made of SS 304 is numerically investigated by using the finite element method. Both the heat conducting cylinders are assumed to be rotating in counter clockwise direction. The right and the left vertical walls of the cavity are maintained at a constant higher temperature (T~h~) and lower temperature (T~c~) while keeping the horizontal walls adiabatic. The left vertical wall is maintained at constant lower temperature and is moving downwards with a constant velocity (u~l~). The two-dimensional mathematical model includes the system of four partial differential equations: which are continuity, linear momentum equations and energy equation. The cavity is filled with air (*Pr* = 0.71). No slip boundary conditions are imposed on the cavity walls. The investigation is performed for six different diameter ratios of the rotating cylinders keeping D~1~/D~2~ = 0.5, 1.0 and 2.0. Flow and thermal field patterns are presented via streamline and isotherm contours. The average Nusselt number is calculated along the right vertical heated wall. Parametric simulation is performed with the variation of Nusselt number with respect to the Reynolds number based on the velocity of the vertical lid. The cylinder Reynolds number (*Re~c~*) is defined based on the peripheral velocity of rotating cylinder. The ratio of cylinder Reynolds number and the Reynolds number based on velocity of the vertical lid is denoted by Ω and is defined as Ω = *Re~c~*/ *Re*. Laminar simulation is performed in the range of 10 ≤ *Re* ≤ 2000 as beyond *Re* = 2000, the fluid flow becomes turbulent. A turbulent simulation is also performed in the range of 10 ≤ *Re* ≤ 5000. For turbulent simulation, Turbulent k-ε model has been used. The computational results show that the diameter ratio (D~1~/D~2~) = 0.1 shows improved heat transfer performance among the six diameter ratios. Based on this diameter ratio further simulation is done for varying the Reynolds number of the lid in the range of 10 ≤ *Re* ≤ 10000 with six different Reynolds numbers for the cylinders (*Re~c~*) varying from 5 to 50. The observation shows that up to Reynolds number 500 of the moving lid, the heat transfer increases with the increment of rotational speed of cylinders. Beyond this range, the heat transfer remains unaffected with the change in rotational speed of the cylinders. The Richardson number (Ri) is fixed at unity ensuring pure mixed convection phenomena. Finally, combined effects of both Reynolds number and Grashof number on heat transfer performance have been investigated keeping the Richardson number in the range of 0.1≤ Ri ≤10 ensuring laminar mixed convection region. Boussinesq approximation was used where the properties of the air are considered to be constant except for the density variation as a function of temperature.


Conjugate Mixed Convection in a Differentially Heated Lid-Driven Square Cavity With Rotating Cylinders

Open pored metallic nanostructures have been widely studied due to their excellent tribological performance, superior mechanical properties, favorable electrical conductivity, potential catalytic capability and large surface areas. Through nanomanufacturing, various types of nanofabricated open pore metallic structures can be generated with well defined geometry and dimension. Among those, nickel (Ni)-based nanofabricated open pore metallic structures have distinct and exclusive properties due to their remarkable structural and surface stability. The tribological and mechanical properties of Ni-based nanofabricated open pore metallic structures must be investigated in order to design durable functional nanofabricated open pore metallic structure-based micro devices and nanosystems.

In present work, the electrical potential induced frictional behavior of nanofabricated open pore metallic structures has been studied. Open pore structural and electrical potential effects on the mechanical and tribological properties of Ni-based nanofabricated open pore metallic structures have been studied. Ni-based nanofabricated open pore metallic structures were prepared to investigate the relation between tribological properties and the pore size of the nanofabricated open pore metallic structures by using atomic force microscope (AFM). Moreover, the effects of electrical potential on tribological properties was also determined by applying various electrical potential condition on Ni-based nanofabricated open pore metallic structures.

In order to build mechanically durable functional micro/nano devices, which are influenced by electric potential, the relation between electric potential and the mechanical/ tribological behaviors of the Ni-based nanofabricated open pore metallic structures need to be investigated. The mechanical behaviors of Ni-based nanofabricated open pore metallic structures by conducting a nanoindentation experiment with a nanoindenter. Specifically, the mechanical properties of Ni-based nanofabricated open pore metallic structures were determined in order to investigate the effect of electric potential on the indentation modulus of the nanofabricated open pore metallic structures with applying an electric potential.

We observed that the tribological properties of Ni-based nanofabricated open pore metallic structures were able to be controlled by applying electrical potential. The nanofabricated open pore metallic structures showed the decreased frictional properties with increasing electrical potential. The electrical potential can influence to the mechanical properties of Ni-based nanofabricated open pore metallic structures. We found that increasing electrical potential decreases contact area between AFM tip and Ni-based nanofabricated open pore metallic structures due to the improvement of the mechanical properties of the nanofabricated open pore metallic structures.

The findings of this study would be useful for design mechanically ro

Nanofabricated Open-Pore-Metallic Structures for Friction Control

Fiber reinforced composites (FRCs) make up a large part of modern aircraft structures today and will continue this trend in the future aircraft, leading to increasingly significant fuel savings. One of the most attractive characteristics of FRC is the ability to tailor its mechanical properties with different composite layup designs. For a composite laminate with multidirectional plies, matrix cracking within off-axis plies is usually the first failure event upon loading. Historically, matrix cracking has often been investigated at a ply level with homogenized material properties. While such approach has its own value, it provides little insight into the mechanisms at the microscale where failure actually initiates and progresses. There are three stages of matrix cracking in general: the initiation, the intermediate stage when macro-sized crack forms through coalescence of individual micro cracks and final stage when macrocrack propagates towards ply interface. Realizing the limitation of traditional approaches discussed above, significant research efforts have recently been devoted to investigating matrix cracking at the constituent level mostly through the utilization of representative volume elements (RVEs). Despite the progress made, however, most of these studies focus on the initial and intermediate stages of the matrix cracking process, leaving unknown the behavior at the subsequent stage when a matrix crack approaches a ply interface. Existing fracture analyses based on homogenizing the plies into orthotropic layers typically predict a straight-line path of the transverse ply crack, which is in contradiction with the experimental findings where matrix crack branching and deflection near ply interfaces is often observed.

The present work aims to close the gap by investigating the behavior when macro-sized matrix crack approaches a ply interface and by clarifying the underlining mechanism governing the potential crack branching and deflection, with a focus on how microstructural nonuniformity affects the crack progression. In the current study, a cross-ply laminate \[0/90\]~s~ is modeled in a 2-D finite element (FE) model. An initial matrix crack is introduced in the 90° layers away from the 0/90 interface. The initial matrix crack is allowed to propagate towards either of the two interfaces. The 0° layers and a part of the initial matrix crack are modelled using homogenized layer properties to simplify the model. The nonuniformly distributed fibers are modeled explicitly close to the 0/90 interface in order to focus on the influence of this nonuniformity on the crack deflection process. Existing experimental findings have shown that the matrix cracking process is essentially the coalescence of individual fiber/matrix interfacial debond cracks. In the current study, a fracture mechanics-based approach is adopted to simulate the fiber/matrix interfacial debonding and the coalescence of individual debonds. The fiber/matrix interfacial debond

Crack Deflection Near a Ply Interface in a Composite Laminate

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Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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