Brief Review and Reconsideration of Fatigue Crack Closure Effect in Materials

The state-of-the-art of fatigue crack closure effect, involving the mechanisms, measurements, models, evaluation methods, influencing factors and existing problems is briefly reviewed. Attention is concentrated on a new consideration of closure effect and a re-definition of the effective driving force for the propagation of a fatigue crack. A theoretical basis for measuring the closure effect is established. The proposed closure concept takes into account the role of the tower portion of loading cycle below the opening load. The conventional closure concept is proven to be correct only for some extreme cases which are practically non-existent for engineering materials. A miniature strain gauge technique is developed to measure the crack closure. Stress-ratio-change tests at threshold level clearly indicate the shortcomings of the conventional closure concept, and the validity of the newly-proposed closure concept. The application of the proposed concept can give rise to a new method for the determination of the effective fatigue threshold of materials. If the fatigue threshold is measured at a sufficiently negative stress ratio (R<R(cr)) the tensile portion of the cyclic loading just reflects the effective fatigue threshold of the material.

Nature：大规模研究揭示生命所必需的基因

在哺乳动物基因组中。大约三分之一的基因是生命所必需的。在一项新的研究中，来自美国贝勒医学院等多个机构的研究人员描述了这些基因的大规模发现。以及它将如何影响对哺乳动物发育和人类疾病的理解。相关研究结果在线发表在Nature期刊上，论文标题为“High—throughput discovery of novel developmental phenotypes”。