Displacement Rate Effects on the Mode II Shear Delamination Behavior of Carbon Fiber/Epoxy Composites

Abstract

This paper studies the influence of displacement rate on mode II delamination of unidirectional carbon/epoxy composites. End-notched flexure test is performed at displacement rates of 1, 10, 100 and 500 mm/min. Experimental results reveal that the mode II fracture toughness GIIC increases with the displacement, with a maximum increment of 45% at 100 mm/min. In addition, scanning electron micrographs depict that fiber/matrix interface debonding is the major damage mechanism at 1 mm/min. At higher speeds, significant matrix-dominated shear cusps are observed contributing to higher GIIC. Besides, it is demonstrated that the proposed rate-dependent model is able to fit the experimental data from the current study and the open literature generally well. The mode II fracture toughness measured from the experiment or deduced from the proposed model can be used in the cohesive element model to predict failure. Good agreement is found between the experimental and numerical results, with a maximum difference of 10%. The numerical analyses indicate crack jump occurs suddenly after the peak load is attained, which leads to the unstable crack propagation seen in the experiment.

Lightweight Glass Fiber-Reinforced Polymer Composite for Automotive Bumper Applications: A Review

“…The mechanics and mechanisms of composite failure under impact loading are divided into five main stages as follows: (1) cracking of matrix phase that leads to fiber/matrix interface debonding mode due to high shear stress, (2) transverse bending crack that is generally due to the high flexural stress in the bottom layers, (3) mesoscale interlaminar damage that appears as multiple delaminations due to the diversion of cracks in the interface area, (4) fiber breakage which is a failure damage mode under tension as well as fiber micro-buckling that normally occurs under compressive loads, and (5) penetration [ 209 ]. In stage 1, a rapid increase in load without noticeable damage is followed by matrix cracking [ 210 ]. In stage 2, the rapid spread of matrix cracking leads to interlaminar delamination (interfacial debonding) [ 211 ].…”

Fiber bridging mechanism in moisture‐induced mode I delamination in carbon/epoxy composites: Finite element analysis and experimental investigation

“…Here, E m is taken as 4.5 GPa and h ce is 10 μm. [15,16,41,42] Thus, K nn is estimated to be 4.5 Â 10 5 MPa/mm. This is also within the range commonly used (9.4 Â 10 3 to 3 Â 10 6 MPa/mm).…”

“…This was found to be sufficient to simulate the bending behavior of the specimen, which was done by comparing the linear-elastic region of the global force-displacement curves obtained from the experiment and the one obtained from the FE model. [15,16,41,42] The delamination zone of interest was meshed using elements with a predetermined length of 0.1 mm. The elements outside the delamination zone of interest were set to a length of 2 mm.…”

“…The width of the entire specimen was meshed using 0.5-mm elements. This discretization approach has been reported to be sufficient to provide stable crack growth behavior for mode I [15] and mode II [41] cases of the same unidirectional carbon/epoxy composite at different displacement rates. With regard to boundary conditions, the bottom of the left end was fixed, and the top of the left end was subjected to a vertical displacement.…”

“…The mode I penalty stiffness K nn is estimated using Equation (), where E m is the Young's modulus of the epoxy resin and h ce is the thickness of the cohesive element (10 μm). This approach has been successfully applied in several studies, for example, to simulate the mode II delamination of three quasi‐isotropic quasi‐homogeneous woven glass/polyester composites, [ 20 ] mode II delamination of unidirectional carbon/epoxy composites subjected to moisture effects, [ 16 ] mode I, [ 15 ] mode II [ 41 ] and mixed‐mode I/II [ 42 ] delamination of unidirectional carbon/epoxy composite with displacement rate effects. Here, E m is taken as 4.5 GPa and h ce is 10 μm.…”