三维纺织复合材料多尺度耦合的湿热老化研究

The proposed research project is to investigate hygrothermal aging for 3D polymer matrix textile composites (3D-PMTC) using a coupled multi-scale and coupled chemo-physical-mechanical method. As the first step, a theoretical framework will be established, which incorporates the effects of moisture absorption, chemical reaction, physical state changing and the consequential mechanical property degradation of polymer matrix. Based upon this framework, unit cell FE models and mathematical homogenization will be pursued at micro-scale (individual fiber srrounded in matrix) and at meso-scale (periodic braided tow architecture) respectively to investigate the mechanisms and evolutions of hydrothermal aging in these two scales. The further objective is to deliver a macro-scale theoretical hygrothermal aging model applicable to the analyses of engineering structures, such as beams and plates. As a part of the proposed project, a series of hygrothermal experiments are to be designed and conducted on polymer matrix, unidirectional composites and 3D-PMTCs, respectively. The mechanical properties and chemical and physical properties will be characterized and measured under various hygrothermal conditions and exposure durations. The microscopy will be taken on the surface and failure surface of specimen to observe signs of micro-scale damages. The aim of experiments is to reveal the relations between the mechanical degradations of 3D-PMTC (includs its constituents, e.g. polymer matrix,interface and fiber tow) to measurable chemical and physical coefficients. Another objective is come up with a practical scheme based on which accelerated ageing tests can be carried out for 3D-PMTCs. The main innovative elements in the proposed project are as follows. 1. Coupled multi-scale modelling and coupled chemo-physical-mechanical and hygrothermal aging study for 3D-PMTCs is proposed for the first time; 2. The theoretical approach considering the interaction between micro- meso-scale damages and moisture related processes, e.g. moisture absorption and swelling, has not been found in literature; 3. By introducing variables characterizing chemical and physical states in the damage mechanics, as well as aging mechanisms, a damage model is more comprehensive than any existing ones can be obtained; 4. By taking due consideration of the hygrothermal gradients from the boundary of the structure, appropriate formulation of unit cells under hygrothermal loading will be a novel development.

拟针对高分子基三维纺织复合材料(3D-PMTC)的湿热老化问题，逐级耦合地建立3D-PMTC的基体相、微观纤维束单丝尺度、细观周期编织结构尺度、宏观板梁工程部件尺度的吸湿模型和包含湿热化学、物理机制的损伤力学模型，并将上述各尺度模型嵌入FE软件中。对3D-PMTC（包括基体和同材料体系的单向复合材料）进行湿热老化试验研究，观测其化学物理特征参数、微观形貌与力学性能的老化演变，探寻有效的老化表征方法。从理论、数值和试验方面全面研究3D-PMTC各尺度上湿热老化的机理和发展规律，验证理论模型。初步提出3D-PMTC实验室加速湿热老化的评估方法。主要创新有:1.多尺度耦合的3D-PMTC老化研究是首次；2.微细观损伤与吸湿、溶胀等过程的相互影响尚少有模型研究；3.复合材料损伤力学中同时引入化学和物理状态参数，比现有模型更全面；4.将梯度的(湿热)边界条件引入胞元模型是对胞元方法的发展。

按照申请书的计划开展了研究，取得了如下主要成果：.1..系统研究了纯树脂（NE）和单向复合材料（UD）的湿热老化性能，它们对应了三维纺织复合材料（3D-TC）中富树脂区和纤维束相的老化规律。研究包括：制备了一种NE和玻、碳增强UD试验件，进行了室内、外自然条件和实验室加速条件下的吸脱湿（循环）试验和物理、力学性能老化试验，积累了基础数据；在纤维微观尺度建立了UD的等效湿扩散模型、两阶段吸湿模型和湿热老化模型，模型考虑了纤维/基体界面相的影响，给出了通过对比试验确定界面湿热参数的方法；初步提出了一种NE和UD基于环境当量的力学性能老化预测模型，通过自然老化与实验室老化对比试验，标定了模型参数。.2..以第1部分研究为基础，在纤维束细观编织结构尺度上研究了三维机织（3D-WC）和三维编织（3D-BC）两种3D-TC的湿热老化性能。研究包括:制备了玻纤和碳纤增强的这两种3D-TC的试验件，进行了实验室加速条件下的吸湿和力学性能老化试验；建立了针对3D-BC和3D-TC两种编织工艺的复合材料的细观理论和有限元湿热老化模型，依据同体系NE、UD的实验数据以及细观编织参数，推测出3D-TC宏观的湿热老化行为。.3. 在结构构件级别初步研究了3D-WC的湿扩散性能。制备了一种玻纤增强3D-WC加筋板，并对此进行了实验室加速湿热试验，测得了吸湿增重曲线；建立了针3D-WC复合材料薄壁结构的二维湿扩散模型，用上述试验检验了模型的准确性。.4. 研究了盐度对 NE、碳、玻增强UD湿扩散性能的影响。包括：在几种温度下进行了这几种材料不同盐度溶液中的水浴试验，测量了盐度对饱和吸湿量及饱和吸湿时间的影响。.研究工作的主要创新点：建立在组分材料系统试验基础上的多尺度耦合的3D-PMTC 老化研究是首次。