Process-induced morphologies and fatigue properties of PEEK: 3D characterization and correlation

PEEK 工艺引起的形貌和疲劳特性：3D 表征和相关性

• 批准号: 536525135
• 负责人: Professor Dr.-Ing. Hans-Georg Herrmann
• 金额: --
• 依托单位: Lehrstuhl für Leichtbausysteme
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/536525135?language=en
• 关键词: Process; induced; morphologies; fatigue; properties

Polyetheretherketone (PEEK) is a semi-crystalline thermoplastic whose importance as a structural and functional material in biomedical and lightweight applications is growing. The morphology in semi-crystalline thermoplastics has a significant influence on the fatigue behaviour. In the injection moulding process, the morphology can be influenced by the process parameters pressure and temperature. Shear-induced and thermally induced crystallisation take place competitively and form geometrically different structures. In PEEK, shear-induced uniaxial nematic structures (liquid crystals) are already formed in the melt. In contrast to thermally induced crystals, shear-induced crystals have strongly anisotropic properties. Due to the stiff behaviour in the chain direction in PEEK, this shear-induced anisotropy is probably pronounced. The current state of research indicates that under fatigue loading, the damage mechanism in other semi-crystalline polymers is based in the morphology. In addition, the ratio and the change in the ratio of elastic to dissipated energy determines the fatigue life. Therefore, the project aims to correlate the injection moulding-induced morphology with the fatigue behaviour of PEEK. The knowledge gained in this way contributes to the understanding of the morphology influence on the damage mechanisms and to the targeted influencing of the fatigue properties. Methods with destructive sample preparation are currently used to characterize crystal structures inside the sample. Due to the destruction of the sample, the damage development can only be examined to a limited extent. In contrast, high-frequency ultrasonic testing offers considerable added value and, based on promising preliminary investigations, is to be enabled for the three-dimensional characterisation of polymer morphology (flow lines and property gradients). During fatigue, the morphology is investigated by combining high-frequency ultrasonic testing with in situ lock-in thermography. The focus is on the correlation of the measurement signals with the polymer properties on the one hand and the correlation of the injection moulding-induced morphology with the fatigue behaviour on the other hand. The fusion of the expertise of the research partners enables the development of methods (linking measurement signals with process understanding) and the correlation of the process influence with the fatigue behaviour, through supporting non-destructive testing. Comprehensive fatigue tests are carried out in which the influence of the elastic and dissipative properties and the shear- or thermally induced morphology on the fatigue behaviour is investigated. These investigations enable the measurement methodology to characterise the local morphology and, at the same time, the non-destructive in-situ method adds value to fatigue testing. Finally, it will be investigated, if and how far the results are transferrable to Polypropylene.

聚醚醚酮（PEEK）是一种半结晶热塑性塑料，作为一种结构和功能材料在生物医学和轻量化应用中的重要性日益增加。半结晶热塑性塑料的形貌对其疲劳性能有显著影响。在注射成型过程中，工艺参数、压力和温度会影响其形貌。剪切诱导结晶和热诱导结晶相互竞争，形成几何上不同的结构。在PEEK中，剪切诱导的单轴向列结构（液晶）已经在熔体中形成。与热诱导晶体相比，剪切诱导晶体具有很强的各向异性。由于PEEK在链方向上的刚性行为，这种剪切诱导的各向异性可能是明显的。目前的研究表明，在疲劳载荷作用下，其他半晶聚合物的损伤机理是基于形貌的。此外，弹性与耗散能量的比值和变化决定了疲劳寿命。因此，该项目旨在将注塑诱导的形貌与PEEK的疲劳行为联系起来。通过这种方式获得的知识有助于理解形貌对损伤机制的影响，并有助于有针对性地影响疲劳性能。目前使用破坏性样品制备方法来表征样品内部的晶体结构。由于样品的破坏，只能在有限的范围内检查损伤的发展。相比之下，高频超声测试提供了相当大的附加价值，并且基于有希望的初步研究，可以用于聚合物形态的三维表征（流动线和性能梯度）。在疲劳过程中，采用高频超声检测和原位锁定热成像相结合的方法研究了其形貌。重点研究了测量信号与聚合物性能的相关性，以及注射成型形貌与疲劳行为的相关性。通过支持无损检测，研究伙伴的专业知识的融合使方法的开发（将测量信号与过程理解联系起来）和过程影响与疲劳行为的相关性成为可能。进行了综合疲劳试验，研究了弹性和耗散性能以及剪切或热致形貌对疲劳行为的影响。这些研究使测量方法能够表征局部形貌，同时，无损原位方法为疲劳测试增加了价值。最后，将调查结果是否以及在多大程度上可转移到聚丙烯。