EXPERIMENTAL AND ANALYTICAL SIMULATION FOR DYNAMIC BRITTLE FRACTURE OF STRUCTURAL MEMBERS

结构构件剪切脆性断裂具有瞬间破坏的特点，是一种较为严重的断裂现象，在阪神-浅地地震中，钢筋混凝土桥墩等结构发生脆性断裂的例子较多。发生脆性断裂类型的一个重要因素是作用在结构上的动荷载，即地震冲击，如阪神-川地地震。本研究的目的是研究脆性断裂的动态断裂过程和力学特征，明确断裂中的剪切作用。研究结果如下：横向冲击载荷作用下脆性梁模型断裂力学特性研究：采用动态光弹性方法对环氧树脂梁模型的裂纹扩展过程和应力动态状态进行了评价。在冲击载荷作用下，由冲击载荷引起的弯曲波引起的初始裂纹从梁的下缘向外扩展。当冲击点与缺口在同一梁截面时，裂纹沿梁轴线垂直扩展，而当冲击点与缺口不在同一截面时，裂纹向冲击点方向或反向扩展。后一种情况的原因是由于挠曲波在梁内传播所引起的剪切应力的影响。裂纹扩展方向的变化受裂纹向中性轴扩展时梁内弯曲应力大小的影响，而不受冲击位置或缺口位置的影响。裂缝扩展方向向与剪应力相对应的受弯应力较大的梁段方向变化。横向冲击作用下RC梁的冲击断裂特性研究：对RC梁模型进行了落重冲击断裂实验。在试验中，考虑剪力作用，选择了梁的中心跨和1/4跨两种冲击位置。在梁的1/4跨情况下，断裂方式为冲剪断裂，在梁的中心跨情况下，断裂方式为塑性铰断裂。两种类型的梁在弯曲波传播作用下，上边缘均产生少量裂缝。压焊钢筋的抗拉强度在残余少量氧化表面的情况下，虽然其抗拉强度与正常焊接钢筋相当，但其延性严重下降，焊接表面出现脆性断裂。少

Generally, the brittle fracture by a shearing force of structural members is a serious fracture phenomena because of its instant failure characteristics, In the Hanshin-Awaji Earthquake, there are many examples of this types of failures to such structures as reinforced concrete bridge piers. One of the important factors which the types of brittle fracture occur are the dynamic loads called earthquake shock acting to the structures as in the Hanshin-Awaji Earthquake.The objective of this research is to study dynamic fracture process and mechanical characteristics of brittle fracture, and to clear the shearing effects in the fracture, The following results were obtained from the research.1. On the mechanical characteristics of the fracture for brittle beam model subjected to lateral impact loads :The dynamic photoelasticity method was applied to evaluate the crack propagation process and the dynamic states of stress of the epoxy beam model. An initial crack propagating from the lower edg … More e of the beam with a notch subjected to impact load is initiated by the flexural wave induced by the impact load. The crack propagates vertically to the beam axis when the impact point and the notch are same cross-section of the beam, but the crack changes the propagation direction towards the impact point or reverse direction when the impact point and the notch are not same cross-section. The reasons of the latter case are the effects of shearing stress due to the flexural wave propagation in the beam. The change of the crack propagation direction is governed by the magnitude of flexural stress in the beam when the crack propagates to the neutral axis and not by the impact position or the notch position. The crack propagation direction changes towards the part of beam growing larger flexural stress corresponding to the shear stress.2. On the impact fracture properties of RC beam subjected to lateral impact :The impact fracture experiments were carried out for the RC beam model by falling weight. In the experiment, two type of impact positions which were center span and 1/4 span of the beam were selected considering the shear force effects. In the case of 1/4 span of beam the fracture mode was a type of punching shear, and in the center span of beam the fracture mode was a type of plastic hinge. Also, in both types a few cracks were generated on the upper edge of the beam by the flexural wave propagation.3. On the tensile strength of a pressure welded reinforcing barIn the case that the pressure weld was done remaining a little oxidized surface, although the tensile strength of the bar was much the same with normally welded bar, the ductility of the bar decreased seriously and the brittle fracture occurred at welded surface. Less