拉挤成型纤维增强复合材料在横向荷载作用下的破坏机理及设计方法

Pultruded fiber reinforced polymer (PFRP) composites have advanced mechanical properties in the pultrusion/fiber direction. However, the properties in transverse direction are adversely affected by the pultrusion process. Researchers have reported premature failures of PFRP sections when subjected to transverse loading. Due to these premature failures, the advanced mechanical properties in the pultrusion direction of PFRP sections can hardly be utilized. This issue has largely constrained the application of PFRP sections in structural engineering. Unfortunately, there has been a lack of research addressing this issue. This research project aims to investigate the premature failure mechanism of PFRP section when subjected to transverse loading and propose corresponding design method. Firstly, the material testing and transverse loading testing will be conducted on PFRP sections. This is to understand the premature failure mechanism and identify the key parameters which determine such a failure mode. Then the numerical simulation will be carried out by finite element analysis. The finite element model will be firstly verified using the experimental results. Then parametric analysis will be used to understand how the key parameters will affect the premature failure mechanism. Finally, theoretical model will be setup based on the experimental data and numerical simulation results. With the description of the failure mechanism using the theoretical modelling, a design method will be proposed for PFRP sections under transverse loading. This research project will contribute to the understanding of the basic research problem of PFRP sections under transverse loading. The solutions to avoid the premature failures will be discussed, so that this premature failure issue will be solved in structural applications of PFRP sections. Eventually, the insights developed from this project will benefit the PFRP manufacturing industry and associated composite market.

拉挤成型纤维增强复合材料（简称PFRP型材）在拉挤方向/纵向上具有优越的力学性能，然而由于成型工艺的特殊性，其横向受力性能较差。国内外学者广泛报道了PFRP型材受横向荷载作用时出现提前破坏，使其拉挤方向上的优越性能无法发挥，制约了其结构工程应用。本项目专门研究PFRP型材横向受力的破坏机理和设计方法。首先通过材性实验和横向加载实验，揭示PFRP型材横向受力破坏机理，明确影响该破坏模式的关键几何和物理参数。然后进行有限元数值模拟，在重现实验结果的同时进行参数分析，其目的在于明确关键参数对PFRP型材横向受力性能的影响规律。最后结合实验数据和数值模拟结果，建立描述PFRP型材横向受力破坏的理论模型，并据此提出相关的设计方法。该项目的意义在于从根本上理解PFRP型材横向受力性能，并探讨解决其横向受力提前破坏这一关键问题，从而使PFRP型材突破这一结构应用中的技术瓶颈，推动PFRP型材产业发展。

拉挤成型纤维增强复合材料轻质高强、抗疲劳耐腐蚀，可用于建筑结构承重构件使用。但是由于生产工艺所限，拉挤型材在横向荷载作用下容易发生破坏，成为限制其工程应用的瓶颈问题。本项目围绕拉挤型材横向受力相关科学问题，开展了拉挤型材槽型截面的横向加载实验，采用了多种样品长度、不同截面尺寸、两种加载位置，发现了槽型截面横向受力条件下两种不同的破坏模式，包括翼缘-腹板连接处的剪切破坏和腹板屈曲破坏。试件的破坏模式受腹板长细比、加载方式、试件长度和承压板长度的影响。试件的刚度受承压板长度和破坏模式的影响，试件的腹板长细比和试件长度对试件的刚度几乎没有影响。试件的极限承载力明显受腹板长细比、加载方式、试件长度和承压板长度影响。本研究提出了拉挤型材槽型截面在横向集中荷载作用下的破坏机理，并依据破坏机理提出了预测拉挤GFRP型材槽型截面在横向集中荷载作用下极限承载力的预测公式。对于在翼缘-腹板连接处发生剪切破坏的试件，其极限承载力和材料的层间剪切强度、有效长度和剪切应力在翼缘-腹板连接处的分布有关。对于在腹板处发生屈曲破坏的试件，其极限承载力被假设成一个考虑长细比的抗压柱计算。柱的截面积考虑了型材腹板中间高度破坏位置的有效面积。通过公式得到的极限承载力的预测值和实验值吻合较好。研究成果有助于指导拉挤型材结构的设计，同时为寻找避免在实际应用中出现这种提前破坏的方法提供实验和理论的支持。本项目还开展了拉挤型材耐久性方面的研究工作，采用分子动力学模拟方法，分析了复合材料在潮湿、高温、盐雾等环境下力学性能的退化以及在持续荷载作用下的蠕变行为。研究发现复材在严酷的外界环境条件下其力学性能随时间退化，主要源于树脂基体和纤维-基体界面受到环境影响，同时也证明了复合材料的长期蠕变行为在结构设计中不可忽视。这部分复合材料耐久性多尺度模拟工作，有效地补充了文献中的实验结果，揭示了宏观现象的微观机理，同时也对复材结构设计方法提供了理论支撑。