Plastic Deformation and Ductile Fracture of Ti-6Al-4V under Various Loading Conditions
Plastic Deformation and Ductile Fracture of Ti-6Al-4V under Various Loading Conditions
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发表时间：
2012
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通讯作者：
J. T. Hammer
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作者：
J. T. Hammer
研究了Ti-6Al-4V板材在多种加载条件下的塑性变形和韧性断裂。本研究的目的是生成实验数据，可用于开发和校准的本构和故障模型的动态事件的数值模拟。塑性变形在不同的应变速率，取向，温度和股票进行了研究。还研究了韧性断裂的应力状态依赖性。在应变率为1.0 × 10 s ~ 8000 s的范围内进行了单轴拉伸、压缩和纯剪切实验。样品由几种厚度为2.29 mm、3.56 mm、6.35 mm和12.7 mm的片材和板材制成。压缩和拉伸试验进行了几个不同方向的标本取向。这些数据显示了拉伸、压缩和剪切的显著应变率敏感性。两种板在拉伸和压缩时均表现出各向异性的塑性变形行为。每个板的响应对于屈服应力、流动应力、硬化、失效和各向异性效应是显著不同的。韧性断裂测试是在各种应力状态下进行的，这是通过对经受各种载荷条件的各种样品几何形状进行机械测试来实现的。对薄平板试样、宽平板试样和具有不同缺口半径的轴对称试样进行了拉伸试验。薄壁管试样承受轴向-扭转复合载荷，以获得附加应力状态。结果表明，应力三轴度单独是无法正确捕捉材料的破坏特征。采用数字图像相关法测量试样表面应变。并行LS-DYNA模拟用于确定应力状态和断裂应变。在应力三轴度和矿脉参数应力空间中创建Ti-6Al-4V的断裂轨迹，从而更准确地描述材料断裂。介绍了一种利用三维数字图像相关技术测量温度高达800 ℃的全场应变的实验技术。该测试装置被设计成一种直接、可重复和准确的方法，用于测量高温下的应变。设计障碍包括空气的热梯度、散斑图案粘附、观察窗图像失真、相机校准和相机传感器的红外光污染。为了验证，使用该技术测量了Ti-6Al-4V在高达800 ° C下的热膨胀系数，并与已发表的值进行了比较。对Ti-6Al-4V进行拉伸、压缩和扭转（剪切）试验。实验测得的热膨胀系数值与手册值相关性良好。该系统在这里进行的每一项测试中都表现良好，并且比标准方法提供了更多的数据。
Plastic deformation and ductile fracture of Ti-6Al-4V plate stock is investigated under multiple loading conditions. The objective of this study is to generate experimental data that can be used for the development and calibration of constitutive and failure models for numerical simulations of dynamic events. Plastic deformation is investigated at various strain rates, orientations, temperatures, and stocks. The stress state dependence of ductile fracture is also investigated. Uniaxial tension, compression, and pure shear experiments are conducted at strain rates ranging from 1.0 × 10s to 8000s. Specimens are fabricated from several sheet and plate stocks with thicknesses of 2.29mm, 3.56mm, 6.35mm, and 12.7mm. Compression and tension tests are conducted with specimens oriented in several different directions. These data show significant strain rate sensitivity in tension, compression and shear. Both plates exhibit anisotropic plastic deformation behavior in tension and compression. The response of each of the plates are significantly different for yield stress, flow stress, hardening, failure, and anisotropic effects. Ductile fracture testing is conducted at various stress states, which are achieved with mechanical tests on various sample geometries subjected to various loading conditions. Tension tests are conducted on thin flat specimens, wide flat specimens and axisymmetric specimens with varying notch radii. Thin walled tube specimens are subjected to combined axial-torsional loading for additional states of stress. The ii results show that the stress triaxiality alone is unable to properly capture the failure characteristics of material. Digital image correlation is used to measure surface strains of the specimens. Parallel LS-DYNA simulations are used to determine the stress states and fracture strains. A fracture locus for Ti-6Al-4V is created in the stress triaxiality and Lode parameter stress space giving a more accurate description of the material fracture. An experimental technique is introduced to measure full field strains using three dimensional digital image correlation at temperatures up to 800◦C. This test setup has been designed to be a straight forward, repeatable, and accurate method for measuring strains at high temperatures. Design hurdles included thermal gradients of air, speckle pattern adhesion, viewing window image distortion, camera calibration, and infrared light pollution of the camera sensor. For validation, the coefficient of thermal expansion for Ti-6Al-4V up to 800◦C is measured using the technique and compared to published values. Tests on Ti-6Al-4V were conducted in tension, compression, and torsion (shear). Experimentally measured coefficient of thermal expansion values correlate well with handbook values. The system performs well for each of the tests conducted here and gives substantially more data than standard methods.