(Abstract:) This study investigated the crack growth behavior of porous polymer membranes, experimentally and numerically to clarify the criterion of crack growth. A notch was introduced into the membrane (as an initial crack) and a uniaxial loading was applied for the crack propagation. During the test, crack propagation behavior was observed using a CCD camera and Digital Image Correlation (DIC) method. The strain around the pre-crack tip whenat the start of crack propagation was measured experimentally using DIC method. Using DIC method, it was clarified that large-scale yield developed before starting of crack growth. The stable growth of the crack was observed during the tensile test. In parallel, a homogenized model that mimicked a pre-cracked porous polymer membrane was created. Based on the material properties obtained from uniaxial tensile tests and yield criteria for porous materials, a uniaxial tensile load was applied to the model and the stress (and strain) field around the crack tip was investigated. Such a local strain distribution was compared with the experiment, showing a good agreement each other. By using strain distribution from DIC method, J-integral value was calculated to investigate criterion of crack growth. Regardless of the initial crack length, it is found that the J-integral value at the initiation of crack growth becomes constant for all tests. Therefore, Tthe criterion of crack propagation could be determined by J-integral values. Our study using DIC experiment and FEM computation thus reveals the crack growth behavior of porous polymer membrane and determines the criterion of crack growth.

(Methods: ) First, a uniaxial tensile test was performed using dumbbell-shaped specimens to obtain stress-strain curve and the material properties such as Young's modulus and yield stress and the elasto-plastic constitutive law. Next, a notch (as initial crack) was introduced in the membrane and uniaxial loading was applied in order to propagate a crack stably. During the test, the crack propagation behavior was observed using CCD camera and digital image correlation (DIC) method. This study investigated several samples with different pre-crack length. In parallel, a homogenized model imitating a porous polymer membrane with pre-crack was created. Based on the material properties obtained from the uniaxial tensile test and yield criterion of porous materials \[1\], a uniaxial tensile loading was applied to the model to investigate stress (and strain) field around the crack tip. Subsequently, the strain at crack tip just before crack propagation was experimentally measured by using DIC method. Such local strain distributions were compared with that FEM computation. To elucidate criterion of crack growth of polymer membrane. The stress field around the crack tip was analyzed and evaluated by J-integral.

(Results: ) Uniaxial tensile test provides constitutive equation of elastoplastic deformation of the membrane. Next, pre-crack specimen was investigated and was found that the crack progressed stably, resulting in membrane fracture. The force – displacement curves are dependent on the length of initial crack. Using DIC method, it was clarified that large-scale yield developed before starting of crack growth. This strain distribution is very similar with our FEM computation. By using strain distributionof from DIC, J-integral value was calculated. Regardless of the initial crack length, it is found that the J-integral value at the initiation of crack growth was constant for all tests. This value indicates same order with that of porous polymer in the previous study. The detailed mechanism of stable crack growth was examined by SEM (scanning electron microscope) observations.

(Conclusions: ) In this study, the crack propagation characteristics of the porous polymer membrane were examined from experiments and FEM computations. The stable growth of the crack was observed due to large-scale yielding owing to inherent pore structure and polymer strut. The criterion of the initiation of crack propagation could be determined by J-integral values. Our study using DIC experiments and FEM computations reveal crack growth behavior of porous polymer membrane and determine the criterion of crack growth.


Characterizations of Crack Growth Behavior of Porous Polymer Membranes Using Digital Image Correlation and Finite Element Method

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

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