Mismatch Plasticity Via Pressure Cycling

9705558 Daehn这个集实验、模拟和分析于一体的程序旨在从根本上了解通过压力循环进行粉末固结的过程。FRG研究了循环加压引起的非均质粉末系统中的失配塑性，这种失配通过EShelby失配产生了等效效应，尽管速率适合于大规模生产。最近的实验表明，循环压力对固结密度的影响很大，对生坯压实强度的影响更大。前者允许加工具有高增强分数的粉末，而后者引入了对高增强绿色压坯进行二次加工的可能性，这两种方法对传统加工都非常具有挑战性。对实际粉末和理想化粉末进行了一系列二维和三维实验，并与分析和有限元模拟进行了比较。为了更广泛地应用于细观力学模拟，提出了一种适用于大应变有限元的稳健接触算法。对于实验和模拟的每一种组合，将压实密度和强度作为循环压力应用的函数进行比较。应该通过压力循环来更好地理解失配塑性，并开发一种稳健的数值方法来模拟涉及真实接触特性的微观力学问题。这些进展消除了当今理论和模拟中固有的可疑假设的必要性。对联邦德国的影响是在几个技术领域。该项目的结果将展示生产粉末加工零件的方法，无论是否进行二次加工，都可以获得更高的一致性和形状精度。将确定通过粉末冶金途径加工增强金属基复合材料的新技术。***

9705558 Daehn This integrated program of experimentation, simulation, and analysis is aimed at a fundamental understanding of powder consolidation by pressure cycling. The FRG investigates mismatch plasticity in heterogeneous powder systems induced by cyclic pressure application which induces an equivalent effect via Eshelby mismatch, albeit at rates suitable for mass production. Recent experiments demonstrate the dramatic impact of cyclic pressure on consolidation densities and the even greater impact on green compact strengths. The former allows processing of powders with high reinforcement fractions while the latter introduces the possibility of secondary processing of highly reinforced green compacts, both of which are very challenging with traditional processing. A series of 2-D and 3-D experiments using real and idealized powders are compared with analysis and finite element modeling (FEM). A robust contact algorithm for large-strain FEM is developed for application to a wide range of micro-mechanical simulation. For each combination of experiment and simulation, compact densities and strengths are compared as functions of cyclic pressure application. An improved understanding of mismatch plasticity via pressure cycling and a robust numerical method for simulating micromechanical problems involving real contact properties should be developed. These advances eliminate the need for questionable assumptions inherent in today's theories and simulations. %%% The impact to the FRG is in several technological areas. Results from the project will demonstrate methods for producing powder-processed parts with greater consistency and shape accuracy, with or without secondary processing. New techniques for processing reinforced metal matrix composites via powder metallurgical routes will be identified. ***