How to relate compressive strengths of multi-directional laminates to fundamental unidirectional material strength?

近年来，纤维增强聚合物（FRP）已表现出优异的面内拉伸性能，并由于其显著的重量减轻而用于航空航天，汽车和能源应用。然而，面内压缩性能平均比拉伸性能低40%。FRP的抗压性能还没有得到很好的理解，由于确定材料的真实抗压强度的挑战。复合材料的基本压缩试验结果不一致，因为纤维不稳定会导致结构失效。为了使FRP材料在更大范围内得到应用，需要对复合材料的压缩性能进行进一步的研究。该研究项目得到EPSRC的支持，并有助于NextCOMP的下一代纤维增强复合材料的目标，以开发能够承受更高压缩承载能力的新型复合材料。复合材料压缩性能的发展可以导致复合材料在压缩应用中的进一步工业利用。本博士项目的目的是提高复合材料的压缩性能，通过对天然复合材料结构的回顾，启发设计和制造具有新颖结构的先进复合材料的新技术。- 必须审查和改进实验程序，以获得比报告更高的FRP材料压缩破坏应变。开发有限元分析（FEA）模型以验证实验结果。模型结果将用于预测使用不同结构的FRP材料的压缩性能。研究新的复合材料结构，以提高复合材料结构的面内压缩性能。设计、制造、测试和分析复杂的分层结构，从而提高复合材料的压缩性能。该项目的主要目标可以概括如下：-审查堆叠顺序的影响，以确定可以支持纵向加载纤维压缩的新技术。-评估目前的压缩试验方法，以确定合适的实验程序的压缩破坏内复合材料层压板。- 研究通过减少纤维错位来提高纤维压缩稳定性的方法。过度缠绕/过度编织结构，以延迟扭结带开始。使用拉挤杆结构嵌入当前的层压结构。- 监控单向材料稳定性及其通过使用混合复合材料的改进。研究结果为确定和改善单向FRP材料的抗压性能提供了理论依据。这将增加纤维增强塑料结构在进一步工程应用中的使用，特别是在航空航天和土木工程部门。所使用的传统材料运输成本昂贵，并可能对员工造成进一步的风险。玻璃钢结构将对现有结构进行再创新，以允许制造具有改进的耐腐蚀性能的便携式轻质结构。从天然复合材料结构和目前的抗压结构发展新的复合材料结构将导致识别技术，以提高FRP材料的压缩性能。

Over recent years, fibre-reinforced polymers (FRP) have demonstrated excellent in-plane tensile properties and are used in aerospace, automotive, and energy applications due to their significant weight reduction. However, in-plane compressive properties are 40% lower on average than that of tensile properties. The compressive performance of FRP hasn't been well understood due to the challenges of identifying the materials' true compressive strengths. Fundamental compressive tests of composites show inconsistency of results as fibre instability can lead to structural failure. Further research on the compressive performance of composites is required to utilize FRP materials in further applications. This research project is supported by EPSRC and contributes to the objectives of NextCOMP for the next generation of fibre-reinforced composites to develop novel composite materials that can endure higher compressive load-carrying capability. The development of composite compressive properties can lead to further industrial utilization of composites in compressive applications. A review of naturally occurring composite structures will be used to inspire new techniques to design and manufacture advanced composites with novel architecture.The aim of this PhD project is to improve the compressive performance of composite materials. - Experimental procedures must be reviewed and improved to obtain a higher compressive failure strain of FRP materials than those reported.- Development of finite element analysis (FEA) models to validate experimental results. The model results would be used to predict the compressive performance of FRP materials using different architectures.- Validate new architectures of composite materials to improve the in-plane compressive performance of composite structures.- Design, manufacture, test, and analyse complex hierarchical architecture that results in improved compressive properties of composite materials.The key objectives for this project can be summarised as follows: - Review the effects of stacking sequence to identify new techniques that can support longitudinally loaded fibres in compression.- Assess current compressive test methods to identify suitable experimental procedures for compressive failure within composite laminates. - Investigate methods for fibre stability in compression through the reduction of fibre misalignment.- Overwound / overbraid architectures to delay kink band initiation.- Use of pultruded rod architecture to embed into current laminate architecture. - Monitor uni-directional material stability and its improvement with the use of hybrid composites. The research would support the purpose of identifying and improving the compressive performance of uni-directional FRP materials. This would increase the use of FRP structures in further engineering applications, in particular the aerospace and civil engineering sector. The traditional materials used are expensive to transport and can cause further risks to employees. FRP structures would re-innovate the current structures to allow for the manufacturing of portable lightweight structures with improved corrosion resistance properties. The development of novel composite architectures from natural composite architectures and current compressive enduring structures will lead to identifying techniques to improve the compressive properties of FRP materials.