Carbon fiber reinforced polymers (CFRP) are crucial for many engineering applications due to their superior material properties. CFRPs have strength and toughness that are comparable to metals but with the advantage of having lighter weight and higher corrosion resistance. Typically, structural parts are joined by bolts and rivets that would result in difficulties keeping the integrity of these joints. The main issue with rivets, screw holes, etc., especially in CFRP, is that they become stress concentration sites that may develop cracks, splits and delamination. Therefore, adhesive bonding is an attractive alternative that can be used as a joining method for CFRP substrates to overcome the disadvantages bolts and rivets.

Structural parts are usually subjected to cyclic loading in engineering applications. Therefore, fatigue is considered as a major design tool for the life of these parts. Finite element analysis (FEA) is a powerful tool for modeling damage in components. This work presents an approach to simulate fatigue crack growth in adhesively bonded CFRP composite substrates using a double cantilever beam (DCB) specimen.

Extended finite element method (XFEM) is utilized to simulate the crack path within the interface between the DCB using the enrichment technique to assign elements to the crack path. The model calculates the stress intensity factor (SIF) based on the domain integral evaluated over the contour around the crack tip. Then, the SIF is converted at each sub-step to the energy release rate (ERR), which includes a correction factor estimated from the cohesive zone (CZ) stiffness and damage parameters. The model is idealized as a 2D geometry as the crack is assumed to be a through-thickness crack, with the nodes at the unloaded edge and the corner being constraining in the longitudinal and the tangential directions, respectively. Displacement was applied at the other end of the specimen separating the two beams in a mode I condition. Finally, the number of cycles is estimated from Paris law. This study shows that mesh size, which is the main determinant of crack extension, has a major influence on estimating the number of cycles.

To verify the proposed model, fatigue crack growth (FCG) tests were performed on an 8-layer unidirectional CFRP laminates (HexPly T700/M21) fabricated into DCB specimens. The substrates were pretreated using a Teflon material as the baseline surface treatment before the application of an aerospace grade adhesive (Araldite 420). The estimated energy release rate (ERR) using the developed finite element model is within 90% or more of that determined experimentally.


Modeling Fatigue Crack Growth in CFRP Adhesively Bonded Substrate Using XFEM

Division / Sponsors: 
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

IMECE2020 - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.