In-situ observation of microscopic fracture process around an open hole in short glass fiber reinforced thermoplastic GFRTP composites is conducted. The specimens with four different fiber surface treatments are used. In all the material systems, the first damage observed is fiber/matrix interfacial debonding at the fiber ends. It is observed that there is a difference in fracture process between the materials with higher and lower interfacial strength. In a material system with lower interfacial strength, debonding propagates along the fiber to the fiber center and fiber break is not observed. In a material system with higher interfacial strength, extensive debonding propagation is not observed and fiber break is observed. The micro-grid method is applied to measure the fiber displacement distribution. The shear-lag prediction is compared with the experimental results. The fiber displacement distribution obtained by the micro-grid method is found to agree well with the shear-lag prediction until extensive interfacial debonding occurs.
