A statistical model of fatigue failure incorporating effects of specimen size and load amplitude on fatigue life

Among many contributing factors, the load range, number of load cycles and specimen geometry (including configuration and size) are three major variables for fatigue failure. Most existing statistical fatigue models deal with only one or two of these three variables. According to the statistical distribution of microcracks with respect to their size and spatial location, a weakest-link probabilistic model for fatigue failure is established to incorporate the combined effect of load range, number of load cycles and specimen size. The model reveals a compound parameter of load range and number of load cycles reminiscent of the empirical formulae of fatigue stress-life curve and its correlation with another compound parameter of cumulative failure probability and specimen size. Four sets of published fatigue test data are adopted to validate the model

EFFECTS OF ENVIRONMENTAL MEDIA ON HIGH CYCLE AND VERY-HIGH-CYCLE FATIGUE BEHAVIORS OF STRUCTURAL STEEL 40Cr

选用40Cr结构钢,分别在空气、水和3.5%NaCl水溶液中进行旋转弯曲疲劳实验,研究环境介质对该结构钢高周和超高周疲劳特性的影响.结果表明,40Cr钢在水环境中的疲劳强度比在空气中明显降低;在3.5%NaCl水溶液环境中的疲劳强度比在水中低.断面观察显示,在水和3.5%NaCl水溶液中,疲劳裂纹多源萌生;在稳态扩展阶段,裂纹沿晶界扩展并存在广泛分布的沿晶二次裂纹

Fatigue properties and S-N curve estimating of 316L stainless steel prepared by SLM

This paper investigates the fatigue properties of 316L stainless steel manufactured by selective laser melting technology (SLM) under hot-isostatic-pressing (HIP) heat-treatment. The fatigue tests of 316L specimens were carried out under pulse tensile cyclic loading to obtain the fatigue performance. To avoid falling into local optima and improve the convergence speed, the dynamic multiswarm particle swarm optimizer (DMS-PSO) algorithm was first introduced for parameter optimization of the three-parameter Weibull distribution model, and then the S-N curves based on the model were obtained. The S-N curves were highly consistent with the metallographic and fractographic phenomena. Besides, both the S-N curves and fractographic analysis show that the resistance of high-stress fatigue fracture is significantly improved by using HIP heat-treatment

随机缺陷下结构疲劳寿命及其尺寸效应的概率建模与评估

通常球墨铸铁和铝合金制成的工程部件的疲劳寿命由制造过程中产生的制造缺陷所决定。因此,本文基于制造缺陷的尺寸和位置,提出了考虑制造缺陷对疲劳寿命影响的概率模型。具体而言,就是将CT扫描获得的缺陷近似作为圆形裂纹进行裂纹扩展分析,并结合威布尔分布对试件的疲劳寿命建模。基于此,提出一个基于表面初始裂纹损伤机理的表面缺陷修正系数,并利用三组铸铁和铝合金的实验数据对模型进行验证和比较。此外,还探讨了等幅载荷作用下统计尺寸效应对疲劳寿命分布的影响。最后,分别对三种不同尺寸材料的疲劳寿命进行预测,预测的P-S-N图表明所提出模型进行预测的结果与概率分散带吻合一致,具有较好的预测效果

ESSENTIAL CHARACTERISTICS AND INFLUENTIAL FACTORS FOR VERY-HIGH-CYCLE FATIGUE BEHAVIOR OF METALLIC MATERIALS

合金材料在超高周疲劳下具有与低周和高周疲劳不同的裂纹萌生和扩展行为以及不同的S-N曲线特征.材料的强度、循环加载的频率、所处的环境等都显著影响超高周疲劳的特性.本文综述了合金材料超高周疲劳行为的基本特征和影响因素的研究进展

强度状态对合金材料超高周疲劳行为的影响

合金材料超高周疲劳的裂纹萌生和初始扩展呈现出与低周和高周疲劳不同的特有过程,且具有不同的S-N曲线特征。强度状态显著影响合金材料的超高周疲劳特性。本文综述了强度状态对合金材料超高周疲劳行为影响的研究进展

Fractography and Crack Initiation of Very-High-Cycle Fatigue for a High Carbon Low Alloy Steel

Very-High-Cycle Fatigue (VHCF) is the phenomenon of fatigue damage and failure of metallic materials or structures subjected to 108 cycles of fatigue loading and beyond. This paper attempts to investigate the VHCF behavior and mechanism of a high strength low alloy steel (main composition: C-1% and Cr-1.5%; quenched at 1108K and tempered at 453K). The fractography of fatigue failure was observed by optical microscopy and scanning electron microscopy. The observations reveal that, for the number of cycles to fatigue failure between 106 and 4108 cycles, fatigue cracks almost initiated in the interior of specimen and originated at non-metallic inclusions. An “optical dark area” (ODA) around initiation site is observed when fatigue initiation from interior. ODA size increases with the decrease of fatigue stress, and becomes more roundness. Fracture mechanics analysis gives the stress intensity factor of ODA, which is nearly equivalent to the corresponding fatigue threshold of the test material. The results indicate that the fatigue life of specimens with crack origin at the interior of specimen is longer than that with crack origin at specimen surface. The experimental results and the fatigue mechanism were further analyzed in terms of fracture mechanics and fracture physics, suggesting that the primary propagation of fatigue crack within the fish-eye local region is the main characteristics of VHCF

低合金钢超高周疲劳的基本特征与机理

本文研究了两种低合金钢超高周疲劳行为的基本特征和裂纹萌生机理。采用旋转弯曲实验机对腰鼓形试样进行频率为52.5Hz的疲劳实验。试样疲劳断裂周次从10~4到10~8,对应的S-N曲线为阶梯状趋势。断口特征观察表明超高周疲劳的裂纹往往萌生于试样的亚表面且裂纹源区域呈现"鱼眼"和"暗区"斑图。本文提出了一个新的参量来说明裂纹起源位置由试样表面向内部转移的机理,即裂纹源位置受控于夹杂物尺度,晶粒尺度和施加应力