Understanding the Transition between Ductile and Brittle Fracture Modes in Sintering Materials

烧结是一种高温过程，用于将松散结合的粉末集合体转化为近净形状、致密的物体，并控制孔隙率。在许多烧结应用中，外部约束可能会阻止粉末集料在一个或多个方向上致密。在这些受限的烧结条件下，内应力会在烧结材料中产生，在极端情况下，这些应力可能会变得如此之大，以至于撕裂粉末集合体。这种被称为烧结矿破裂的破碎过程降低了产品质量，降低了产量，并且在制造过程中被证明是非常不受欢迎的。该奖项支持了解烧结矿破裂现象的基础研究。这项研究的目的是阐明这种裂纹产生的原因，以期确定在约束烧结过程中抑制断裂的处理策略。通过将材料性能、几何因素和工艺变量与烧结裂纹的扩展联系起来，这项研究将指导材料工程师制定工艺和制造参数，以防止灾难性的烧结裂纹。这一新的科学知识将在粉末加工行业中有重要的应用，潜在地使一系列制造业受益，特别是那些使用新的3D打印技术的行业，包括航空航天、汽车和能源部门。这项研究项目旨在了解烧结材料的延性到脆性的转变。3D打印将用于在烧结实验中独立地改变重要的几何特征，如起始裂纹的大小、试件厚度和未开裂韧带的初始长度。通过将这些3D打印试件的实验与离散元方法的烧结开裂模拟相结合，应力和应变的连续描述将与裂纹尖端发生的颗粒尺度现象联系在一起，以发展对烧结开裂和延性-脆性转变原因的多尺度、基于物理的理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Sintering is a high-temperature process used to transform loosely bound powder aggregates into near net-shaped, dense objects with controlled amounts of porosity. In many sintering applications, external constraints can prevent a powder aggregate from densifying in one or more directions. Under these constrained sintering conditions, internal stresses can develop in the sintering material, and in extreme cases, these stresses can grow so large that they tear the powder aggregate apart. This fracture process, referred to as sinter-cracking, degrades product quality, lowers yield, and proves highly undesirable in manufacturing processes. This award supports fundamental research to understand the sinter-cracking phenomenon. The goal of this research is to clarify why this cracking occurs, with a view toward identifying processing strategies for suppressing fracture during constrained sintering. By relating material properties, geometric factors, and process variables to the growth of sinter-cracks, this research will guide materials engineers towards processing and manufacturing parameters to prevent catastrophic sinter-cracking. This new scientific knowledge will have important applications in the powder processing industry, potentially benefiting a range of manufacturing sectors, particularly those making use of new 3D printing technologies, including the aerospace, automotive, and energy sectors.This research project aims to understand the ductile-to-brittle transition in sintered materials. 3D printing will be used to independently vary important geometric features during sintering experiments such as the size of the starter crack, the specimen thickness, and the initial length of the uncracked ligament. By coupling experiments on these 3D printed specimens with discrete element method simulations of sinter-cracking, continuum descriptions of stresses and strains will be linked with particle-scale phenomena occurring at the crack tip to develop a multi-scale, physics-based understanding of sinter-cracking and the causes of the ductile-brittle transition.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.