CAREER: Linking Processing Practice to the Performance of Materials in Design

9702017米勒这个材料加工/材料力学项目的总体目标是在材料加工与其使用性能之间建立切实的联系。一般来说，该项目的教育和研究部分都将采用的方法是使用实验来了解材料行为和微观结构演变的各个方面。在这些观察的指导下，将开发和实施纳入加工影响的在职绩效模型。本项目的研究部分，金属成形实践对在役循环性能的影响的调查，是出于对小应变循环塑性的统一本构模型框架的需要，该模型框架明确地包括了大应变加工诱发的影响。众所周知，平板轧制通过轧制板材的厚度产生强烈的内部组织梯度。在本项目中，将通过在不同位置沿轧制铝板的厚度进行单轴和平面双轴试验，研究小应变非弹性循环变形与加工诱导的初始组织(以晶体织构和大应变位错结构的形式)的相关性。在这些实验中，将监测力学响应和微观结构的演变，并确定哪种大应变效应对随后的小应变循环行为影响最深。然后，这些信息将被合并到统一的小应变循环模型中，该模型明确地解释了先前的大应变金属成形事件。虽然两者都涉及非弹性应变，但在金属成形过程中产生的大变形与部件在其使用寿命期间可能遇到的小应变循环历史有很大的不同。这些差异在模型结构方面产生了不连续性。大应变模型更侧重于描述材料由于晶体织构演化等过程而缓慢演化的行为，而循环塑性模型必须捕捉快速演化现象，如与位错晶胞和晶格结构的形核和演化有关的现象。尽管成形过程中产生的内部结构不同于小应变循环结构，但结构的演变在成形/服务界面上是连续的。正是这种国家演变的连续性，为开发一个统一的模型框架带来了希望。最初的模型将建立在目前存在的晶体塑性框架上，而最终的建模工作将提出新的微机械公式。教育计划采用加工材料设计，其总体目标是衔接加工/在职设计接口，主要侧重于本科生和研究生课程的开发以及实验室的开发和实施。现有的材料加工课程将更多地强调加工对设计的影响。在本科生水平上，学生将通过实验研究成形和热处理实践对被加工材料的性能的影响以及在加工过程中微观结构如何演变。在研究生水平上，正在开发一门新的材料加工实验课程，通过研究变形诱导的各向异性、速率和温度相关性、不稳定性和超塑性等问题，将加工效应纳入设计的更深层次的总主题。还建议根据拟议的课程改革，发展为康奈尔大学机械工程材料处理课程服务的教学实验室。

9702017 Miller The overall objective of this project in materials processing / mechanics of materials is to establish tangible links between the processing of a material and its in- service performance. In general, the method which will be employed in both the educational and research components of the project is to use experiments to understand various aspects of material behavior and microstructural evolution. Guided by these observations, models for in-service performance which incorporate processing effects will be developed and implemented. The research component of this project, An Investigation of the Effects of Metal Forming Practice on In-Service Cyclic Performance, is motivated by the need for a unifying constitutive model framework for small strain cyclic plasticity which explicitly incorporates large strain processing-induced effects. It is well known that flat rolling produces strong internal structure gradients through the thickness of rolled plate material. In this project, the dependence of small strain inelastic cyclic deformation on processing induced initial structure (in the form of crystallographic texture and large strain dislocation structures) will be investigated by taking uniaxial and planar biaxial test specimens at various locations through the thickness of rolled aluminum plate. Both the mechanical response as well as the microstructural evolution will be monitored in these experiments and a determination made as to which of the large strain effects have the most profound influence on the subsequent small strain cyclic behavior. This information will then be incorporated into unifying small strain cyclic models which explicitly account for prior large strain metal forming episodes. While both involve inelastic strains, the large deformations incurred during a metal forming episode differ sharply from the small strain cyclic history which a component may encounter during its service life. These differences produce a discontinuity with respect to model structure. Large strain models place more of an emphasis on the characterization of slowly evolving material behavior due to processes such as crystallographic texture evolution while models for cyclic plasticity must capture quickly evolving phenomena such as that related to the nucleation and evolution of dislocation cells and lattice structures. Even though the internal structure produced during forming is distinct from small strain cyclic structure, the evolution of structure is continuous across the forming/service interface. It is this continuity of state evolution which offers hope for developing a unifying model framework. The initial model will build on a currently-existing crystal plasticity framework while the final modeling effort proposes an new micromechanical formulation. The educational plan, Designing with processed materials, shares the overall goal of bridging the processing / in- service design interface and focuses primarily on undergraduate and graduate curriculum development as well as laboratory development and implementation. A stronger emphasis on the effects of processing on design will be interjected into existing materials processing courses. On the undergraduate level, students will investigate experimentally what effects forming and thermal processing practice have on the properties of the processed material and how the microstructure evolves during processing On the graduate level, a new experimental course in materials processing is being developed taking the general theme of incorporating processing effects into design to a greater depth by investigating issues such as effects of deformation- induced anisotropy, rate and temperature dependence, instabiliti es, and superplasticity. Development of the instructional laboratory which serves the materials processing curriculum in Mechanical Engineering at Cornell consistent with the proposed curriculum changes is also proposed.