Crack initiation, propagation, and arrest in sintering powder aggregates
Crack initiation, propagation, and arrest in sintering powder aggregates
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DOI：
10.1111/jace.17170
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发表时间：
2020-06-07
影响因子：
3.9
通讯作者：
Cordero, Zachary C.
中科院分区：
文献类型：
--
作者：
Carazzone, Joseph R.;Martin, Christophe L.;Cordero, Zachary C.
烧结过程中的裂纹是粉末加工中的常见问题，通常是由于限制烧结材料在一个或多个方向上收缩而引起的。不同的因素影响烧结诱发裂纹，包括温度制度、堆积密度和试件几何形状。在这里，我们使用离散元方法，直接观察在单轴约束下烧成的边缘缺口板材的应力分布和烧结体开裂行为。这种几何形状便于与传统的断裂力学参数进行比较，便于分析烧结矿的开裂行为。我们发现，烧结过程中自应力引起的裂纹类似于完全致密材料中蠕变裂纹的扩展。通过从适当的本构方程推导出约束致密化速率，我们发现烧结体的有效泊松比对横向加载轴的线性收缩有加速作用。模拟了不同的缺口几何形状和初始相对密度，揭示了有利于致密化和最大限度减少裂纹扩展的条件，暗示了在实际烧结过程中避免裂纹的设计方法。我们结合远场应力和裂纹长度来计算净截面应力，发现它表征了缺口之间的应力分布，并与烧结裂纹扩展速率相关，显示了它在定量描述烧结裂纹方面的潜力。
Cracking during sintering is a common problem in powder processing and is usually caused by constraint that prevents the sintering material from shrinking in one or more directions. Different factors influence sintering-induced cracking, including temperature schedule, packing density, and specimen geometry. Here we use the discrete element method to directly observe the stress distribution and sinter-cracking behavior in edge notched panels sintered under a uniaxial restraint. This geometry allows an easy comparison with traditional fracture mechanics parameters, facilitating analysis of sinter-cracking behavior. We find that cracking caused by self-stress during sintering resembles the growth of creep cracks in fully dense materials. By deriving the constrained densification rate from the appropriate constitutive equations, we discover that linear shrinkage transverse to the loading axis is accelerated by a contribution from the effective Poisson's ratio of a sintering solid. Simulation of different notch geometries and initial relative densities reveals conditions that favor densification and minimize crack growth, alluding to design methods for avoiding cracking in actual sintering processes. We combine the far-field stress and crack length to compute the net section stress, finding that it characterizes the stress profile between the notches and correlates with the sinter-crack growth rate, demonstrating its potential to quantitatively describe sinter-cracking.