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

该奖项支持基础研究，研究如何提高半结晶聚合物的强度和韧性，以设计轻质和抗撕裂包装。半结晶聚合物因其容易获得和低价格而广泛用于包装工业。屈服和应变硬化是这种聚合物的两个关键特性。我们假设，结合具有不同屈服强度和应变硬化水平的联合收割机材料的层压膜将具有上级强度和韧性。该研究将对包装行业产生直接影响，从而使用已商业化的材料开发高性能包装解决方案。该研究还将减少这些包装系统中的材料量，从而减少其对环境的影响。此外，其他应用领域包括生物材料，通常是分层的，通常是应变硬化的，以及金属塑料复合材料。研究生培训和推广到本科生和大学预科生将与研究相结合。多层塑料作为包装材料无处不在，但他们的大应变行为知之甚少。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。该文献对严重应变硬化的影响几乎没有或根本没有提供任何见解，这种硬化只出现在大应变下。我们假设将屈服层与应变硬化层结合将（1）增加层压膜的强度和极限应变，以及（2）改善层压膜的缺陷容限和断裂韧性。该研究将包括基础和补充计算和实验研究，以测试这些假设。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了一个新的本构模型。在实验方面，我们将使用从弹性体到高度屈服的商业塑料。实验和计算将紧密结合在一起：初始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.