Burning underground will change the surface of microstructure of BHA, and accelerate corrosion and fatigue crack initiation and propagation;
③井下发生燃爆，会改变下部钻具表面的金相组织，加速了腐蚀和疲劳裂纹萌生、扩展；
The result shows: the local residual tensile stress and cyclic compressive loading thrust fatigue crack initiation and propagation in the size of compressive plastic zone.
结果表明，疲劳裂纹是在残余拉应力和循环压应力作用下萌生和扩展的，压塑性变形是裂纹萌生和扩展的必要条件。
The primary failure model is fatigue fracture that is always resulted by the crack initiation and propagation.
疲劳断裂是气门弹簧失效的主要模式，它是疲劳裂纹萌生及其扩展的结果。
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