摘要
用手制动拉索和制动器螺栓将装运的面包车固定在平板车上,到达目的地后发现制动器螺栓出现松动和断裂现象。在运输过程中,制动器螺栓不仅承受上下振动方向高频率低应力而形成的双向弯曲状态,而且又要承受前后方向的低频率高应力而形成的单向弯曲状态。通过受力分析并结合扫描电镜对断口形貌和显微组织的观察,在螺栓齿根发现多处疲劳源,在扩展阶段,出现疲劳辉纹和大量二次裂纹,最终在拉应力作用下形成撕裂台阶而断裂。
Brake studs loosened and fractured at the terminal when cables were locked during the delivery of minibuses in a flatbed. The material of studs were checked and confirmed to be normal by means of microstructure examination, chemical composition analysis and hardness testing. Due to locked cables, bending and torsional stresses firstly concentrated on the studs, which linked the wheel and the brake, and forced them to work in static condition. Stress analysis and observations of fracture morphology and microstructure led to the conclusion that improper delivery manner gave rise to compound stress which caused the studs looseness, or rupture. Up-down vibration generated low stress on high frequency to form the crack source in opposite bending directions and leave fatigue striation and massive secondary cracks. More restrictions against semi-dependent suspension in driving direction, as well as greater braking impact than start-up impact, generated low frequency high stress, which made studs to bend in driving direction. Strain damage formulated a crack after cumulative cycles and propagated to be a split step under tensile stress before the final fracture.
出处
《理化检验（物理分册）》
CAS
2004年第3期145-147,共3页
Physical Testing and Chemical Analysis(Part A:Physical Testing)
