Abstract
Recently, polymers widely used as machine parts and structural members, and their conditions used become severe. Therefore understand of fracture phenomena characteristic to polymers is important for making better reliability of machines and structures, and preventing any accidents caused by their fracture.
Many theoretical and experimental studies have stated that local strains near the notch-root and the crack-tip strongly affect initiation and propagation of fatigue cracks, respectively. However in spite of their studies, fatigue crack initiation and propagation at the notch-root have been recognized to be very complicated. The difficulties and limitation in cvaluating the small crack propagation behaviors with continuum analysis of fracture mechanics parameter of ΔK are also pointed out.
In this paper, local strain at the notch-root during process of crack initiation and local strain at the crack-tip during process of crack propagation in polymer are measured in real time under low cycle fatigue tests by the fine grid method, the relations between local strain and crack initiation and crack propagation are investigated, and a more accurate approach for fatigue life estimation is discussed. In addition, a real-time measurement system of local strain at the fatigue crack tip using image processing is described.
