Exploring ultimate mechanical characteristics of polymers, from molecular to fracture mechanics

探索聚合物的最终机械特性，从分子力学到断裂力学

• 批准号: 2210184
• 负责人: Shi-Qing Wang
• 金额: $ 48万
• 依托单位: University of Akron
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-07-01 至 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2210184&HistoricalAwards=false
• 关键词: Exploring; ultimate; mechanical; characteristics; polymers

NON-TECHNICAL SUMMARYMechanical failure of polymers in all forms (including the familiar plastics) due to fracture limits the range of applications and increases the costs of polymeric products. This project will attempt to clarify the nature of polymer fracture in order to identify means to increase the threshold for failure. This could lead to reduction of the annual consumption (several hundred billion pounds) of petroleum-based plastics toward the goal of building a more sustainable economy by lowering the pressure for landfills. The project will explore and show the benefits of elucidating a connection between the resistance to fracture and the material strength that can be improved through chemical and physical means. Specifically, fracture behavior of polymeric materials will be examined in a different than conventional way to better illustrate the cause for fracture. The contrast between existing knowledge and new perspectives would be incorporated in a textbook on all aspects of polymer mechanics that the PI plans to work on. The project will also help to fill the knowledge gap in this area by training a new generation of scientists and engineers who can generate new solutions to existing and future challenges facing the properties and applications of polymeric materials. TECHNICAL SUMMARYThe planned project will investigate the fracture behavior of polymeric materials through establishment of a stress criterion based on birefringence measurements. The overall objective is to identify more effective means to increase the toughness of polymers. This cannot be achieved without proper explanation of why toughness is a material parameter and what dictates its magnitude. The PI plans to explore an intimate connection between material mechanical strength and toughness. For polymers in all forms, i.e., plastic, elastomeric and thermosetting, their brittle fracture behavior will be investigated from an angle that focuses on the stress state at the crack tip. The investigations will take into account the following effects. Enhancement of chain network through pre-melt stretching increases ductility of glassy amorphous polymers. Preservation of chain network during crystallization avoids brittle fracture in glassy semicrystalline polymers (e.g., crystalline polyethylene terephthalate). Structural changes to increase load-bearing strands per unit area result in stronger elastomers. The proposed research will gather more evidence relevant to a scenario where stress state at the crack tip explicitly dictates polymer fracture instead of Griffith-Irwin type energy balance argument. The entire project will attempt to answer why toughness is a material constant and what factors determine its magnitude for polymers in their various forms. For improvement of ductility and increased toughness of polymers an effective strategy will be explored through enhancement of structure of load-bearing chain network to increase the intrinsic mechanical strength.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.

非技术概要各种形式的聚合物（包括常见的塑料）由于断裂而导致的机械失效限制了应用范围并增加了聚合物产品的成本。 该项目将试图阐明聚合物断裂的性质，以确定提高失效阈值的方法。 这可能会减少石油基塑料的年消耗量（数千亿磅），从而通过降低垃圾填埋场的压力来实现建立更可持续的经济的目标。 该项目将探索并展示阐明抗断裂性与可通过化学和物理手段提高的材料强度之间联系的好处。 具体来说，将以不同于常规的方式检查聚合物材料的断裂行为，以更好地说明断裂的原因。 现有知识和新观点之间的对比将被纳入 PI 计划研究的关于聚合物力学各个方面的教科书中。 该项目还将通过培训新一代科学家和工程师来帮助填补该领域的知识空白，他们可以为聚合物材料的性能和应用面临的现有和未来挑战提供新的解决方案。 技术摘要计划的项目将通过建立基于双折射测量的应力标准来研究聚合物材料的断裂行为。 总体目标是找到更有效的方法来提高聚合物的韧性。 如果没有正确解释为什么韧性是一个材料参数以及什么决定了它的大小，这是不可能实现的。 PI 计划探索材料机械强度和韧性之间的密切联系。 对于所有形式的聚合物，即塑料、弹性体和热固性聚合物，将从关注裂纹尖端应力状态的角度研究它们的脆性断裂行为。 调查将考虑以下影响。 通过预熔融拉伸增强链网络可提高玻璃态无定形聚合物的延展性。 结晶过程中链网络的保留避免了玻璃状半结晶聚合物（例如结晶聚对苯二甲酸乙二醇酯）的脆性断裂。 通过结构改变来增加单位面积的承载股线，从而产生更坚固的弹性体。 拟议的研究将收集更多与裂纹尖端的应力状态明确决定聚合物断裂而不是格里菲斯-欧文类型的能量平衡论证相关的证据。 整个项目将试图回答为什么韧性是一个材料常数，以及哪些因素决定了各种形式聚合物的韧性大小。为了提高聚合物的延展性和韧性，将探索通过增强承载链网络结构以提高内在机械强度的有效策略。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。