Fracture characterization of overmold composite adhesion

Abstract

A general testing approach is presented via a fracture mechanics study on the interfacial delamination behavior in overmolded composite materials using a variant of the double cantilever beam (DCB) geometry. Overmolding, a common injection molding process, is used to fabricate asymmetric DCB test specimens with Lexan™ 3414 resin overmolded onto commercially available TenCate Cetex® FST woven glass fiber/polycarbonate laminates. An analytical beam theory model is employed to partition the planar fracture modes at the overmold interface into mode I and mode II components, which are functions of material properties and relative beam thicknesses. Specimen curvature measurements are integrated into the beam theory model to estimate the residual stress effects on fracture mode mixity. We use the overmold thickness as a tunable variable to control fracture mode mixity, and target near mode I fracture conditions, where we find mode I fracture energy ( G Ic) values of approximately 1 kJ/m2. Fiber bridging across the failure interface is observed, which is not expected at the nominal polymer/polymer overmold interface. Complementary scanning electron microscopy images of the failure surfaces indicate crack initiation at the overmold interface, followed by a change in locus of failure to the nearby polymer/glass fiber interface in the top layer of the composite laminate. Fiber bridging is observed in all specimens tested over a modest range of mode mixity, including specimens modified to the single leg bending geometry, suggesting that the polymer/glass interface is more susceptible to crack propagation than the desired overmold interface, which likely derives its strength from molecular interdiffusion during the overmolding process.

Numerical Simulation and Experimental Validation of Hybrid Injection Molded Short and Continuous Fiber-Reinforced Thermoplastic Composites

“…Thus, a variety of acceleration techniques have been developed over the years to solve the computing capacity issues related to the solution of finite element static problems involving two-scale homogenization approaches (FE2 analyses) [20], among them reduced order models [21,22], the (non-uniform) transformation field analysis [23], response surface models [24,25] and machine learning approaches such as neural networks [26,27]. However, while these homogenization techniques can be used to describe the material behavior dependent on the specific local microstructure, further modeling and numerical challenges arise after the onset of failure (e.g., cracking, fiber bridging, and delamination mechanisms) occurring in the composite component at higher deformations [28][29][30]. Capturing the details of such nonlinear post failure behavior is still the subject of different research investigations and is neglected in this work.…”

Effects of the Injection Material and Resin Layer on the Mechanical Properties of Carbon Fiber-Reinforced Thermoplastic (CFRTP) Press and Injection Hybrid Molded Parts

“…Press and injection hybrid molded structural parts are now commercially available and displayed as prototypes at many exhibitions. On the other hand, academic papers are usually focused on the interfacial bond properties between the surface material and the injection material [16][17][18], which represent an issue in actual structural parts. Quantitatively evaluated mechanical properties (stiffness, strain distribution, etc.)…”

Development of Carbon Fiber-Reinforced Thermoplastics for Mass-Produced Automotive Applications in Japan

“…Moreover, introducing thermoplastics into high-performance discontinuous CFRPs offers a solution for high-cycle manufacturing with compression molding and stamp molding. Moreover, continuous CFRPs with additive injection-molded discontinuous CFRPs [17][18][19][20] (also denoted as "overmolding") have been developed to fulfill the new application requirements.…”

“…into high-performance discontinuous CFRPs offers a solution for high-cycle manufacturing with compression molding and stamp molding. Moreover, continuous CFRPs with additive injection-molded discontinuous CFRPs [17][18][19][20] (also denoted as "overmolding") have been developed to fulfill the new application requirements. A national project focusing on the systematic development of lightweight CFRTP applications for automotive mass production was launched by the Japanese Ministry of Economics and Trade and Industries (METI) in the 2008-2012 financial years.…”