【摘要】 用超声波断口图和扫描电镜(SEM)研究了聚甲基丙烯酸甲酯(PMMA)的失稳断裂与断口形态,发现了两个断裂临界速度。当裂纹速度达到第一临界值时,出现二次曲线记号;裂纹扩展速度超过第二临界速度时,断口表面留下二级微裂纹丛。这两个临界速度都是试件厚度的函数。更多还原

【Abstract】 Ultrasonic fractography and scanni ng eletronic microscopy(SEM)are used to study the instability fra cture and fractogra-phy of polymethylmethacrylate(PMM).Two Critical Crack velocities are f ound for the fracture.Conic markings will appear when the crack speed reaches the first critical speed.Crack propagating at sp eed beyond the second critical speed leaves a thicket of small branches penetrating the surface behind them.Both Critical speed s are function of the thickness of the specimens.更多还原