28. Compression Testing of Micro-Scale Unidirectional Polymer Matrix Composites

This project builds on work done by Lu et al. An experimental study is carried out to characterize the failure behavior of a fiber reinforced polymer matrix composite at the micro-scale using the same test methodology. In order to address the issue of catastrophic failure observed in the previous effort, a physical stop for the indenter that limits maximum displacement to a predetermined value is integrated into the specimen design. Micron-sized specimens of IM7/BMI unidirectional composite with an integrated indenter displacement control were fabricated using Focused Ion Beam (FIB) milling. The specimens were compression tested using a custom built, SEM-based in-situ micro-testing device. During compression, SEM images are acquired continuously between displacement intervals so the deformation phenomena can be observed. Initial results showed that the integrated indenter displacement control prevents complete destruction of the specimen after the onset of failure. Damage observed includes interface failure, broken fibers, and general crushing. Parallel efforts on larger-scale compressive testing are conducted on millimeter-sized specimens using an in situ mechanical test frame located in an X-ray micro computed tomography (μCT) system. Failure response includes longitudinal splitting or brooming and kinking. A quantitative comparison of the compressive strength and modulus obtained from the two size scales specimen shows that there is no indication of a size effect. The experimental results will be used to validate the numerical models of micro-compression behavior.