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采用200毫米宽的中心裂纹试样测量了焊接接头和基体金属的疲劳裂纹扩展速率和门槛应力强度因子。业已发现,不管裂纹在哪种区域扩展(即热影响区和焊缝金属区)和采用何种焊接工艺(埋孤焊和金属极气体保护电孤焊),焊接接头的疲劳裂纹扩展速率都是相似的。然而,焊接接头的疲劳裂纹扩展性能要比基体金属的差。通过对裂纹闭合情况的观察,揭示了这样的事实:疲劳裂纹在整个加载过程中是完全张开的,这是由于焊接接头中间部分的残余应力分布处于拉伸状态之故。这种观察也解释了应力比对焊接接头疲劳裂纹扩展性能的影响不大及以焊接接头的疲劳裂纹扩展性能之所以比基体金属的差的原因。
The fatigue crack growth rate and the threshold stress intensity factor of the welded joint and the base metal were measured with 200 mm wide central crack specimens. It has been found that the fatigue crack growth rate of welded joints is both no matter in which region the crack propagates (ie, the heat affected zone and the weld metal zone) and the welding process used (buried and metal polar gas arc welding) similar. However, the fatigue crack growth performance of welded joints is worse than that of the base metal. The observation of crack closure reveals the fact that the fatigue crack is fully open throughout the loading process due to the residual stress distribution in the middle of the welded joint being in tension. This observation also explains the reason why the stress ratio has little effect on the fatigue crack propagation properties of the welded joint and the reason why the fatigue crack propagation properties of the welded joint are worse than the base metal.