A methodology for in-situ micro-compression testing of fiber composites

A methodology for in-situ micro-compression testing of fiber composites has been developed. The tests were performed on carbon fiber reinforced bismaleimide matrix unidirectional composite, IM7/BMI 5250-4. Micro-size specimens were prepared from the bulk composite plaque through a two-step micro-fabrication process and then tested by using a micro-mechanical testing device placed inside the scanning electron microscope chamber. Results show that the fundamental properties (modulus and strength) of the fiber composites obtained from micro-size specimens are consistent with the theoretical estimations and significantly higher than those from macro-size specimens, which may have revealed the presence of size-scale effects in composite materials. The in-situ testing shows that the overall failure mode of the present composite is caused by "micro-buckling" of fibers in shear-mode. High shear strains are seen to occur at the fiber-matrix interfaces, which lead to the micro-cracking and ultimate failure of the composite.