Tensile deformation behavior of TRIP-aided bainitic ferrite steel in the post-necking strain region
Tensile deformation behavior of TRIP-aided bainitic ferrite steel in the post-necking strain region
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DOI：
10.1080/27660400.2021.1922207
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发表时间：
2021-01
期刊：
影响因子：
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通讯作者：
T. Matsuno;Tomohiko Hojo;I. Watanabe;A. Shiro;T. Shobu;K. Kajiwara
中科院分区：
文献类型：
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作者：
T. Matsuno;Tomohiko Hojo;I. Watanabe;A. Shiro;T. Shobu;K. Kajiwara
相变诱导塑性（TRIP）钢表现出强度和延性的显著平衡。然而，由于它们的应力三轴依赖性，它们的后颈硬化行为是不可靠的，这是冲压成形和汽车碰撞模拟所需要的。因此，我们分析了拉伸加载TRIP钢颈后应变区的应力-三轴硬化，以准确评估应力应变分布。因此，在小圆棒试件上进行拉伸试验，以评估断裂前的真实应力与截面折减比曲线。此外，利用同步x射线衍射测量了每个样品内部的应力分布。利用这些测量结果，通过一系列有限元模拟确定了TRIP钢的硬化规律，其中简化的现象应变和应力三轴硬化与后颈缩应变区域的测量结果吻合得很好。结果表明，在均匀延伸极限应变下，TRIP钢的硬化速率突然降低。包括应力-三轴硬化在内的有限元模拟成功地再现了这种硬化行为，并且包括应力-三轴硬化及其饱和度在内的有限元模拟的值与XRD测量值最接近。该模拟结果与在远离颈部中心的拉伸方向上得到的测量结果也吻合得很好。颈部残留奥氏体的显微组织分析支持了这一结果。有限元模拟结果表明，TRIP效应及其失活共同加速了拉伸载荷作用下试件颈部的局部变形。图形抽象
ABSTRACT Transformation induced plasticity (TRIP) steels present a remarkable balance of strength and ductility. However, their post-necking hardening behavior, which is required for press-forming and automobile crash simulation, is unreliable because of their stress-triaxiality dependency. Therefore, we analyzed the stress-triaxiality hardening in the post-necking strain regions of tensile loaded TRIP steel to accurately evaluate the stress and strain distribution. Tensile tests were accordingly conducted on small, round-bar specimens to evaluate the true stress vs. cross-sectional reduction ratio curves up to fracture. Additionally, the stress distribution inside each specimen was measured using synchrotron X-ray diffraction. Using these measurements, the hardening law for the TRIP steel was identified through a series of finite element (FE) simulations, in which a simplified phenomenological strain and stress-triaxiality hardening were found to agree well with the measurements in the post-necking strain region. As a result, the hardening rate of the TRIP steel showed a sudden decrease at the uniform elongation limit strain. The FE simulations including stress-triaxiality hardening successfully reproduced this hardening behavior up to the fracture, and the FE simulation including stress-triaxiality hardening and its saturation presented values closest to the XRD measurements. This simulation also agreed well with the measurements obtained in the tensile direction away from the neck center. A microstructural analysis of the retained austenite at the neck supported this result. The FE simulations revealed that a combination of the TRIP effect and its deactivation accelerates the localized deformation at the specimen neck under tensile loading. GRAPHICAL ABSTRACT