Enhancement of Strength and Toughness of Layered Polymer Composites by Strain Hardening

该奖项支持基础研究，研究如何增强半结晶聚合物的强度和韧性，以设计轻质和抗撕裂的包装。半结晶聚合物因其易于获得和价格低廉而广泛应用于包装工业。屈服和应变硬化是这类聚合物的两个关键特性。我们假设，结合不同屈服强度和应变硬化水平的材料的层压膜将具有优越的强度和韧性。这项研究将对包装行业开发高性能包装解决方案产生直接影响，这些解决方案使用的材料已经在商业上使用。这项研究还将减少这些包装系统中的材料数量，从而减少它们对环境的影响。此外，其他应用领域还包括生物材料，这些材料通常是分层的，通常是应变硬化的，以及金属塑料复合材料。研究生的培训和对本科生和大学预科学生的拓展将与研究相结合。多层塑料是一种普遍存在的包装材料，但人们对其大应变特性了解甚少。这种知识的缺乏与许多关于复合材料的小变形力学和断裂力学的书籍形成鲜明对比。这些文献很少或没有深入了解严重应变硬化的影响，这只出现在大应变下。假设屈服层与应变硬化层的结合可以(1)提高层合膜的强度和极限应变，(2)提高层合膜的缺陷容忍度和断裂韧性。研究将包括基础和补充的计算和实验研究，以检验这些假设。在计算方面，我们将使用定制的非线性有限元框架，并为屈服和应变硬化塑料开发新的本构模型。在实验方面，我们将与商业塑料合作，从弹性塑料到高产量塑料。实验和计算将紧密结合：最初的实验将确定聚合物的真实应力-真实应变行为，然后将其输入模拟以进行预测，然后进行实验测试。

This award supports fundamental research to study how the strength and toughness of semi-crystalline polymers can be enhanced to design lightweight and tear-resistant packaging. Semi-crystalline polymers are widely used in the packaging industry for their easy availability and low price. Yielding and strain hardening are two key characteristics of such polymers. We hypothesize that laminated films that combine materials with differing levels of yield strength and strain hardening will have superior strength and toughness. The research would have direct impacts on the packaging industry in developing high-performance packaging solutions using materials that are already used commercially. The research would also reduce the amount of materials in these packaging systems and therefore their environmental impacts. In addition, other application areas include biological materials, which are often layered and often strain hardening, and metal-plastic composites. Graduate student training and outreach to undergraduate and pre-college students will be integrated with the research.Multilayered plastics are ubiquitous as packaging materials, yet their large strain behavior is very poorly understood. This lack of knowledge is in sharp contrast of numerous books on small-deformation mechanics and fracture mechanics of composites. That literature gives little or no insight on the effects of severe strain hardening, which appear only at large strain. We hypothesize that bonding yielding layers to strain hardening layers will (1) increase in strength and ultimate strain of laminate films, and (2) improve flaw tolerance and fracture toughness of the laminate films. The research will include fundamental and complementary computational and experimental studies to test these hypotheses. On the computational side we will use custom nonlinear finite element framework with a new constitutive model developed for yielding and strain hardening plastics. On the experimental side, we will work with commercial plastics that range from being elastomeric to highly yield-like. The experiments and computations will be tightly integrated: initial experiments will determine the true stress-true strain behavior of the polymers, which will then be fed to the simulations to make predictions, which will then be tested experimentally.