Crack-parallel stress effect on fracture energy of plastic hardening polycrystalline metal identified from gap test scaling
Crack-parallel stress effect on fracture energy of plastic hardening polycrystalline metal identified from gap test scaling
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DOI：
10.1016/j.jmps.2023.105222
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发表时间：
2023-02-22
影响因子：
5.3
通讯作者：
Bazant, Zdenek P.
中科院分区：
文献类型：
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作者：
Donmez, A. Abdullah;Nguyen, Hoang T.;Bazant, Zdenek P.
差距试验是2020年开发的一种新型断裂试验，其中缺口梁的端部支撑安装有间隙，该间隙仅在缺口旁边的弹塑性垫引入所需的恒定平行裂纹压缩σ（xx）（也称为T应力）后闭合。该测试使用尺寸效应方法来确定这种压缩如何改变材料断裂能G（f）和断裂过程区（FPZ）的特征尺寸c（f）。2020年，实验表明，中等σ（xx）使准脆性材料（混凝土）的G（f）增加一倍，而高σ（xx）使其G（f）几乎为零。Nguyen等人（2021）的初步研究表明，差距测试可以扩展到塑性硬化多晶金属。推导了小结构大范围屈服的具有中间渐近线的广义标度律，并通过有限的铝合金试验验证了其适用性。在这项研究中，几何比例的缺口三点弯曲断裂试样的铝的间隙试验进行了三个不同水平的西格玛（xx）。一个扩展的结构强度标度律，捕获从微米级FPZ通过毫米级屈服区（YZ）的大型结构，遵循线弹性断裂力学（LEFM）的过渡，然后应用到分析的影响西格玛（XX）。本文介绍了铝合金的差距试验。在试验中，对深度为.的四点弯曲缺口梁施加三种不同水平的σ（xx）。= 12，24，48和96 mm。使用塑性硬化金属的扩展尺寸效应定律，发现在平行裂纹应力σ（xx）接近屈服强度的-40%时，临界J积分值大约增加了四倍，这不仅是因为众所周知的宽度为毫米级的硬化YZ的扩大，也是由于微米级FPZ宽度的增加。这些结果既不能再现线裂纹模型，包括LEFM，内聚裂纹和相场模型，也不是由周向和各种非局部模型，忽略了在裂纹尖端的材料应力的张量性质。裂纹带模型，能够代表一个有限宽度的FPZ和YZ的大小取决于西格玛（xx）的演变，可以捕捉到的效果，平行裂纹应力提供了一个现实的三维张量损伤本构模型被使用。在这里，Bai-Wierzbicki的模型被示出为定性地捕获sigma（xx）对G（f）和J（GP）的影响。
The gap test is a new type of fracture test developed in 2020, in which the end supports of a notched beam are installed with gaps that close only after the elasto-plastic pads next to notch introduce a desired constant crack-parallel compression sigma(xx) (also called the T-stress). The test uses the size effect method to identify how such a compression alters the material fracture energy, G(f), and the characteristic size c(f) of the fracture process zone (FPZ). In 2020, experiments showed that a moderate sigma(xx) doubled the G(f) of a quasibrittle material (concrete) and a high sigma(xx) reduced its G(f) to almost zero. A preliminary study by Nguyen et al. (2021) showed that the gap test can be extended to plastic-hardening polycrystalline metals. A generalized scaling law with an intermediate asymptote for large-scale yielding in small structures was derived, and limited tests of aluminum alloy showed its applicability. In this study, geometrically scaled gap tests of notched three-point bend fracture specimens of aluminum are conducted at three different levels of sigma(xx). An extended structural strength scaling law that captures the transition from the micrometer-scale FPZ through millimeter-scale yielding zone (YZ) to large-scale structures which follow linear elastic fracture mechanics (LEFM) is derived and then applied to analyze the effect of sigma(xx). Presented here are the gap tests of aluminum alloy, in which three different levels of sigma(xx) are applied to scaled notched four-point-bend beams of depths.. = 12, 24, 48 and 96 mm. Using an extended size effect law for plastic-hardening metals, it is found that, at crack-parallel stress sigma(xx) approximate to -40% of the yield strength, the critical J-integral value gets roughly quadrupled, not only because of the well-known enlargement of the hardening YZ whose width is of millimeter scale, but also because of the increase of the FPZ width of micrometer scale. These results can be reproduced neither by line crack models, including the LEFM, cohesive crack and phase-field models, nor by peridynamic and various nonlocal models that ignore the tensorial nature of the material stress at the crack tip. The crack band models, being able to represent an FPZ of finite width and a YZ whose size evolves depending on sigma(xx), can capture the effect of crack-parallel stresses provided that a realistic 3D tensorial damage constitutive model is used. Here, Bai-Wierzbicki's model is shown to capture the sigma(xx) effect on the G(f) and J(GP) qualitatively.