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采用外观检查、扫描电镜(SEM)断口观察、金相(OM)检验等方法分析了TB8钛合金紧固件疲劳断裂后的断口形貌和显微组织,并对紧固件头部附近的受力情况进行了有限元模拟分析。研究结果表明,疲劳试验后头部完全断裂的TB8钛合金紧固件均为多源疲劳开裂,同时可见三块疲劳区域,主疲劳区扩展相对较充分,但疲劳裂纹扩展距离均较短。不同疲劳试验结果的TB8钛合金紧固件显微组织均由等轴初生α相和β转变组织组成,再结晶后的β晶粒较小,且没有形成明显的晶界;而通过有限元模拟计算可知,当挤头部圆角半径(R)接近于1.0mm,同时紧固件抛物线流线离倒角较远时,紧固件头部的疲劳性能较好,这与疲劳试验结果相一致。因此,通过减小镦制时丝材端面与模具型面的摩擦力,以控制TB8钛合金紧固件挤头部区域的流线形态,同时在满足技术要求的前提下尽量减小R的尺寸,可以获得较高的疲劳强度。
The appearance and microstructure of the fracture of the TB8 titanium alloy fastener after fatigue fracture were analyzed by visual inspection, scanning electron microscope (SEM) fracture observation and metallographic examination (OM) Force situation of the finite element simulation analysis. The results show that the TB8 titanium alloy fasteners with completely broken head after fatigue test are all multi-source fatigue cracking, and three fatigue zones are visible at the same time. The main fatigue zone expands relatively well, but the fatigue crack propagation distance is short. The results of different fatigue tests showed that the microstructure of TB8 titanium alloy fasteners consisted of primary α-phase and β-transformed tissue, and the β grains after recrystallization were smaller and no obvious grain boundaries were formed. However, by means of finite element simulation Calculations show that the fatigue performance of the fastener head is better when the fillet radius (R) is close to 1.0 mm and the fastener parabolic flow line is further from the chamfer, consistent with the fatigue test results . Therefore, by reducing the friction when the upsetting wire end face and the mold surface to control the TB8 titanium alloy fastener extrusion head streamline region shape, while meeting the technical requirements of the premise to minimize the size of R , You can get a higher fatigue strength.