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81.
On the basis of the experimental data, we show that the difference between the macroscopic and microscopic fatigue crack growth rates in the second section of the kinetic diagram of fatigue fracture is caused by the effect of crack closure within the limits of its existence. We establish the relationships between the macroscopic and microscopic fatigue crack growth rates and the structure of the material in the second section of the diagram for various values of the load ratio with regard for the effect of crack closure and propose a procedure of examination of the fracture processes in structural materials based on the analysis of microscopic and macroscopic fatigue crack growth rates. 相似文献
82.
Rotating-bending uniaxial fatigue tests and micro-fatigue crack initiation tests were carried out using a permanent mold cast
(PMC) and semi-solid die cast (SDC) with Al−7%Si−0.35%Mg composition in order to examine the relationship between solidification
structures and fatigue behaviors. The crack length was measured using a replication method. Fatigue strength was improved
in SDC, which was almost consistent with the predicted fatigue strength using the size of Si particle cluster. Resistance
to fatigue crack initiation and fatigue strength were improved in SDC owing to the finer Si cluster and to higher ultimate
tensile strength. Fatigue crack in PMC was preferentially initiated at pores. For SDC, the fatigue crack was initiated at
the Si particle/matrix interface, and then sucessively grew along eutectic cell boundaries. 相似文献
83.
The effect of ductile crack growth on the near tip stress field in two different specimen geometries has been investigated. For homogeneous specimens it is observed that the peak stress level increases with ductile crack growth. The effect is most pronounced up to about 1 mm of crack growth. For low and intermediate hardening there is a significant effect of specimen size on the stress level. In case of mismatch in yield stress, the simulations show that the increase in stress level in the material with the lower yield stress is of a similar magnitude as is the case for stationary cracks. In case of ductile crack growth deviation from the original crack plane occurs, the highest stresses are still found close to the interface, and not in front of the current crack tip. 相似文献
84.
85.
The effects of the uncertainties associated ith the apparent strain and gauge factor data, given by the manufacturer, in the evaluation of principal strains are examined. Principal strains are obtained by a reduction of the strains measured ith electrical resistance strain gauge rectangular or delta rosettes. The theoretical analysis points out the relevance of the effects caused. 相似文献
86.
A comparative study of numerical solutions to non-linear discrete crack modelling of concrete beams involving sharp snap-back 总被引:1,自引:0,他引:1
Numerical problems are often encountered in modelling crack propagation in concrete beams using non-linear finite element (FE) analysis, especially when sharp snap-back behaviour in load-displacement relations occurs. This paper firstly identifies 16 arc-length control based numerical strategies based on extensive literature review. They are then used to carefully model the structural behaviour of a four-point single notched shear beam using discrete crack modelling approach in which cracks are represented by interface elements with bilinear softening constitutive laws. Based on extensive FE analyses, detailed comparisons of the merits and demerits of these numerical algorithms are then made. The results indicate that the effectiveness and efficiency of different algorithms may vary considerably from one to another, with the local arc-length based procedures in conjunction with tangential stiffness strategy and reversible unloading model being the most robust. 相似文献
87.
研究了用固体润滑石墨、碳化硅、二硫化钼等填料改性的聚苯硫醚 (PPS)涂层的耐磨性能。实验结果表明 ,聚苯硫醚复合涂层具有优良的耐磨性 ;加入适量 ( 3 0 % )的石墨、碳化硅等固体润滑剂 (石墨 :碳化硅 =2∶3 ) ,可以有效提高涂层的耐磨性能 ,而二硫化钼和三氧化二铬的减摩效果更佳 相似文献
88.
混凝土结构的质量通病——裂缝 总被引:3,自引:1,他引:2
从材料、结构构造、施工工艺、地基变形、温湿度变形等方面论述了混凝土裂缝产生的原因 ,提出只有真正了解裂缝产生的原因 ,才能有针对性地采取有效措施 ,确保工程质量 相似文献
89.
90.
高层地下室底板混凝土施工的裂缝控制 总被引:1,自引:0,他引:1
以德益花园写字公寓楼地下室底板205m厚混凝土的施工工程为例,坚持预防为主的原则,采取了一系列温控技术措施,有效地防止或控制了温度裂缝(收缩裂缝)的产生,确保了混凝土的施工质量。 相似文献