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Reproducibility of metal fatigue

机译：金属疲劳的再现性

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The discipline of fatigue and fracture was the setting more than three years ago, for. a case of scientific fraud in the National Aerospace Laboratories (NAL). This communication attempts to explain why what happened constitutes a scientific fraud and why what followed represents a cover-up. The science behind the fraud is briefly explained. The objective is to place before the scientific community a well-documented case study. In doing so, we invite criticism and cross-examination in the knowledge that only open and honest discussion holds the promise of better prospects for Indian science and technology. When metals are subject to repetitive (cyclic) loading, they eventually fail. Fatigue occurs at stress levels that may be only a fraction of ultimate strength. Cyclic loading leads to the formation and growth of fatigue cracks. Such cracks start growing at a rate, da/dN, lower than 10~(-7) mm/cycle and steadily accelerate by over five orders of magnitude to eventually cause catastrophic failure, da/dN over the interval 10~(-5) < da/dN < 10~(-3) mm/cycle can be approximated by the expression da/dN = C{[S_(max) - max(S_(min), S_(op))] sqrt(#pi#a)}~m, where C and m are material constants (m approx 4 for many materials, including the alloys referred to in this communication), S_(max) is maximum stress. S_(min) is minimum stress and Sop is crack closure (or opening) stress. S_(max) and S_(min) determine the magnitude of the load cycle. The phenomenon of crack closure determines what portion of this load cycle effectively drives the crack. The crack cannot grow if it is fully closed, i.e. S_(max) <= S_(op). Closure is absent if S_(op) <= S_(min). This makes fatigue crack closure an important phenomenon.
机译：疲劳和断裂的纪律是三年前制定的。美国国家航空航天实验室（NAL）发生的科学欺诈案件。这段交流试图解释为什么发生的事情构成了科学欺诈，为什么随后发生的事情却掩盖了事实。简要解释了欺诈背后的科学。目的是在科学界提出一个有据可查的案例研究。这样，我们邀请批评和盘问，因为只有公开和诚实的讨论才能为印度科学技术带来更美好的前景。当金属承受重复（循环）载荷时，它们最终会失效。疲劳强度可能仅是极限强度的一小部分。循环载荷导致疲劳裂纹的形成和增长。这种裂纹以小于10〜（-7）mm /周期的da / dN速率开始增长，并稳定地加速超过五个数量级，最终在10〜（-5）间隔内导致灾难性的破坏，da / dN。

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