How microscopic stress and strain analysis can improve the understanding of the interplay between material properties and variable amplitude fatigue
How microscopic stress and strain analysis can improve the understanding of the interplay between material properties and variable amplitude fatigue
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微观应力和应变分析如何提高对材料特性与变幅疲劳之间相互作用的理解
DOI：
10.1016/j.prostr.2016.06.398
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
Boller C.
中科院分区：
文献类型：
--
作者：
Thielen M;Marx M;Motz C;Sheikh-Amiri M;Boller C.
轻质结构是许多工程系统中最需要的技术之一。为了保证整个系统的安全性，必须改进模型来描述和预测其在负载下的行为。疲劳，即材料在循环载荷下的损伤，是导致例如汽车和航空航天部件失效的主要现象。在使用过程中的循环荷载通常不会以恒定的振幅发生，而是存在不同荷载水平的复杂模式。这些模式中的高负载变化导致偏离线性巴黎行为。强烈的减速是由于单个增加的拉伸载荷而发生的，这被称为过载效应。然而，这种影响并不影响所有材料相同，有材料，显示出强过载敏感性和其他材料上的过载只有很小的影响。其原因可以从超载效应的潜在机制的相互作用中看出：塑性诱导裂纹闭合和压缩残余应力。虽然这两种效应都导致裂纹尖端屏蔽和应力强度降低，但裂纹闭合延迟了裂纹尖端的张开，从而降低了有效Δ K范围，而压缩残余应力与裂纹尖端应力叠加，从而降低了Kmax。灵敏度差异的可能原因可能是静态和动态情况下应变硬化的差异以及应力符号的变化（包辛格效应）。由于裂纹扩展是由局部应力和应变驱动的，因此必须在微观尺度上进行测量以检查它们之间的差异。我们可以表明，通过结合现代测量技术-磁巴克豪森噪声和扫描电子显微镜中的数字图像相关性-我们能够定量地成像、分离和评估过载效应的机制。经过校准的磁性巴克豪森噪声显微镜允许我们测量残余应力，空间分辨率为10 µm。从数字图像相关的结果，我们可以评估裂纹尖端的驱动力，即裂纹的张开行为，在应力强度K和应变能释放率通过J积分的变化。使用一个简单的模型，基于这些结果，我们还能够预测由于过载效应的裂纹扩展行为。这些结果将用于扩展裂纹扩展模型，同时考虑材料特性与上述机制的相互作用。这应该能够实现基于物理的、改进的寿命预测和针对某些负载模式的材料选择。
Lightweight construction isone of the most demanded technologies in many engineering systems. In order to guarantee the safety of the whole system, it is mandatory to improve models that describe and predict its behavior under load. Fatigue, the damaging of materials under cyclic loading, is the main phenomenon leading to failure in e.g. automobile and aerospace components. Cyclic loading during service does usually not happen with constants amplitudes, rather there are complex patterns of different load levels. High load variations in these patterns lead to deviations from the linear Paris behavior. Strong decelerations occur as consequence of a single increased tensile load, which is known as the overload effect. Nevertheless, this effect does not affect all materials the same, there are materials that show a strong overload sensitivity and others on which overloads only have a minor influence. Reasons for this can be seen in the interplay of the underlying mechanisms of the overload effect: plasticity induced crack closure and compressive residual stresses. While both effects lead to crack tip shielding and a reduction of stress intensity, crack closure delays the opening of the crack tip and thereby reduces the effective ΔKrange, whereas compressive residual stresses superimpose with crack tip stresses and thereby reduceKmax. Possible reasons for differences in the sensitivity can be differences in the strain hardening, both in the static and in the dynamic case, as well as in changes of the sign of stresses (Bauschinger effect). Since crack propagation is driven by local stresses and strains, measurements to examine differences in them have to be performed on a microscopic scale.We could show that by the combination of modern measurement techniques – magnetic Barkhausen noise and digital image correlation in scanning electron microscope – we were able to image, separate and evaluate the mechanisms of the overload effect quantitatively. The calibrated magnetic Barkhausen noise microscope allows us measurements of residual stresses with a spatial resolution of 10 µm. From the digital image correlation results we could evaluate the crack tip driving forces namely the crack opening behavior, changes in the stress intensityKand in the strain energy release rate via theJ-integral. Using a simple model based on these results, we were furthermore able to predict the crack growth behavior due to the overload effect. These results will be used to extend crack growth models, while taking the interaction of materials´ properties with the mentioned mechanisms into account. This should enable a physically based, improved lifetime prediction and material selection for certain load patterns.
平面应变裂纹闭合和循环硬化
DOI：
--
发表时间：
2002
期刊：
影响因子：
--
作者：
S. Pommier
通讯作者：
S. Pommier
利用巴克豪森噪声和数字图像相关研究局部残余应力对疲劳裂纹扩展的影响
影响因子：
1.1
作者：
Thielen M;Marx M;Sheikh-Amiri M.Boller C. Motz C.
通讯作者：
Sheikh-Amiri M.Boller C. Motz C.