Sandia Fracture Challenge: blind prediction and full calibration to enhance fracture predictability
Sandia Fracture Challenge: blind prediction and full calibration to enhance fracture predictability
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DOI：
10.1007/s10704-013-9923-3
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发表时间：
2014-01
影响因子：
2.5
通讯作者：
K. Pack;M. Luo;T. Wierzbicki
中科院分区：
文献类型：
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作者：
K. Pack;M. Luo;T. Wierzbicki
麻省理工学院的冲击和耐撞性实验室参加了桑迪亚断裂挑战赛，并使用非常有限的材料特性，包括狗骨试件的单轴拉伸试验，在具有三个孔(B、C和D)的紧凑拉伸试件的拉伸测试中预测了裂纹的萌生和扩展路径。采用最大剪应力和修正的Mohr-Coulomb断裂模型。预测的A-C-E裂纹路径与Sandia国家实验室进行的13次实验中的2次相吻合，准确地捕捉到了最大载荷以及第一次和第二次裂纹萌生时的载荷水平。然而，对应于两个裂纹萌生的裂纹尖端张开位移(Cods)分别被高估了12%和24%。挑战结束后，我们从Sandia收到了剩余的材料，并通过对具有两个对称圆槽的试件、一个有中心孔的试件和一个具有双曲率的蝴蝶试件进行了额外的断裂测试，包括拉伸测试，进行了全面的塑性和断裂校准。此外，还对一个蝴蝶试件进行了纯剪切试验。新确定的断裂参数再次预测了A-C-E裂纹路径，但力-COD响应几乎可以完美地再现。详细的校准程序和验证进行了讨论。此外，为了考察加工质量对结果的影响，在起始器缺口A以及B、C和D三个孔周围的第一层有限元中引入了预损伤值，加速了孔A与D(以及D与C之间)之间的剪切局部化，并将裂纹路径改为A-D-C-E。对预损伤值的参数研究表明，存在两条竞争的裂纹路径，相应的力-COD曲线受预损伤值的影响。讨论了网格尺寸和边界条件对计算结果的影响。
The Impact and Crashworthiness Lab at Massachusetts Institute of Technology participated in the Sandia Fracture Challenge and predicted the crack initiation and propagation path during a tensile test of a compact tension specimen with three holes (B, C, and D), using a very limited number of material properties, including uniaxial tensile tests of a dog-bone specimen. The maximum shear stress and modified Mohr–Coulomb fracture models were used. The predicted crack path of A–C–E coincided with two out of thirteen experiments performed by Sandia National Laboratories, and the maximum load, as well as the load level at the first and second crack initiation, was accurately captured. However, the crack-tip opening displacements (CODs) corresponding to the initiation of the two cracks were overestimated by 12 and 24 %, respectively. After the challenge ended, we received the leftover material from Sandia and did full plasticity and fracture calibration by conducting extra fracture tests, including tensile tests, on a specimen with two symmetric round notches, a specimen with a central hole, and a butterfly specimen with double curvature. In addition, pure shear tests were carried out on a butterfly specimen. Newly identified fracture parameters again predicted the A–C–E crack path, but the force–COD response could be reproduced almost perfectly. Detailed calibration procedures and validation are discussed. Furthermore, in order to investigate the influence of the machining quality on the results, a pre-damage value was introduced to the first layer of finite elements around the starter notch, A, and the three holes, B, C, and D. This accelerated shear localization between holes A and D (and between D and C as well) and changed the crack path to A–D–C–E. Parametric study on the pre-damage value showed that there exist two competing crack paths, and the corresponding force–COD curve is influenced by the pre-damage value. The effect of mesh size and boundary conditions are also discussed.