IMECH-IR  > 流固耦合系统力学重点实验室(2012-)
复杂热-力载荷下CFRP层合板的失效行为及破坏机理研究
英文题名Failure behaviors and mechanisms of CFRP Laminates subjected to combined thermal and mechanical loadings
赵伟娜1,2
导师黄晨光 ; 宋宏伟
2018-05-24
学位授予单位中国科学院大学
学位授予地点北京
学位专业工程力学
关键词Cfrp层合板 热-力性能 激光烧蚀 失效行为 多尺度模型
摘要

碳纤维增强树脂基复合材料(CFRP)具有高比刚度、高比强度及可设计性强等特点,在航空航天等工程领域中得到了广泛的关注与应用。在使役过程中,CFRP复合材料结构通常或偶尔承受复杂或极端的热力载荷作用,对其在高温环境下的热-力性能与烧蚀行为进行表征就显得尤为重要。CFRP复合材料在高温条件下会经历一系列复杂的物理-化学变化过程,如基体的软化、熔融、热解、气化;热解残碳的生成、发展和氧化;碳纤维的氧化、升华;热膨胀或热收缩引起的纤维/基体界面脱粘、基体裂纹扩展和层间开裂等。这些物理-化学过程对CFRP的热-力学性能产生了不可逆的影响,显著地降低了复合材料及其结构的承载能力。此外,CFRP的热物性能和力学性能不仅与温度相关,还与温升历程相关。上述复杂过程与因素使得热-力载荷下CFRP复合材料的失效行为与破坏机理表征具有相当的困难性。

本文针对复杂环境下CFRP层合板的高温热-力学性能和激光烧蚀行为开展了一系列工作。主要的研究工作包括以下几个方面:

1. 开展了常规加热环境下CFRP层合板热力失效行为实验研究,包括:常温拉伸/压缩实验、高温拉伸/压缩实验、热屈曲实验,并对热-力联合加载下的失效模式和破坏载荷进行对比分析。实验中分别考虑了加载方式、温度及温升速率等因素对CFRP层合板失效行为的影响规律。实验发现,高温环境下环氧树脂基体和碳纤维均会产生了不可逆的热损伤,主要的失效机理为热解、氧化、层内开裂和层间脱层。同时,开展了不同功率密度的激光辐照后CFRP层合板的剩余强度实验研究,并与常规均匀升温条件下的剩余强度进行了比较。两种实验条件下的温度和升温速率均有显著差别,其中温升速率相差了2个数量级,激光辐照引起的局部高温使得碳纤维发生了升华。

2. 建立了从细观到宏观的CFRP层合板热-力学性能多尺度分析模型。从细观分析模型出发,通过对碳纤维和树脂基体进行热重分析,获取了热解动力学参数,获得了各组分含量随温度和温升速率的变化规律。根据建立的多尺度分析模型,获得了高温条件下CFRP复合材料单层板宏观热物性能与力学性能。然后,将多尺度模型获得的热-力性能引入经典层合板理论,得到了高温环境下CFRP层合板的热-力学失效机理与破坏阈值。将本文的分析模型与实验结果进行了比较,并与前人的分析模型进行了对比,本文的分析模型能够表征不同升温速率对CFRP层合板热力破坏行为的影响。

3. 开展了不同环境下连续激光辐照CFRP层合板的烧蚀实验。外界环境主要包括:静态氮气环境、静态空气环境、空气侧吹环境以及超声速风洞环境。分析了激光功率与外界环境对CFRP层合板烧蚀行为的影响。获得了烧蚀过程中CFRP层合板的三维烧蚀形貌、损伤剖面型线、温度响应、烧蚀率等试验数据。研究发现,高速气流作用产生的剥蚀效应加剧了材料的烧蚀,改变了材料的烧蚀形貌;对比烧蚀形貌和烧蚀率发现,空气侧吹环境下的烧蚀结果远小于超声速风洞环境。因此,在研究CFRP层合板的激光烧蚀行为时,不能用目前研究者普遍使用的冷空气侧吹环境来代替超声速风洞环境。

4. 建立了包含多种烧蚀机制的激光辐照CFRP层合板烧蚀行为数值分析模型,分析了环境条件与激光参数等对烧蚀行为的影响。首先,结合不同环境下的热化学分析建立了CFRP复合材料热力烧蚀模型,实现了对CFRP层合板的烧蚀反应过程的解耦和定量化表征。然后,将多尺度热-力学分析模型与热力烧蚀分析模型相结合,对CFRP层合板的激光烧蚀行为进行了数值模拟。采用“生死单元法”实现了移动烧蚀边界与传热的耦合计算;利用表单元法对每个单元的热物性、烧蚀反应过程及相应的反应热进行实时更新;使用有限元软件ANSYS的APDL语言实现烧蚀计算程序的编制。通过与激光烧蚀实验相对比发现,本文建立的数值分析模型能够准确地预测连续激光辐照下CFRP层合板烧蚀行为与失效阈值。

英文摘要

Due to superior characteristics such as light weight, high specific strength, high specific stiffness and excellent designability, carbon fibers reinforced plastic (CFRP) is being increasingly used in industrial sectors such as aeronautic and aerospace engineering. CFRP composites are usually or accidentally subjected to the combination of complicated or extreme thermal and mechanical loadings. In these cases, it is important to systematically investigate the high temperature thermal-mechanical behavior and ablation mechanism of CFRP composites. When a polymer-matrix CFRP composite is exposed to high temperature environment, complex chemical processes and physical processes may take place. The chemical processes involve viscous softening, fusing, pyrolysis and vaporization of the matrix, the generation, development and oxidation of pyrolytic carbon residue, oxidation and sublimation of carbon fibers. The physical processes involve thermal expansion and contraction, thermally-induced strains, fibers-matrix interfacial debonding, matrix cracking and delamination damage. As a result, the thermo-mechanical properties of CFRP are irreversibly affected by these physical and chemical processes, which significantly reduce the load-bearing capacity of CFRP composites and its structures. Moreover, the thermophysical and mechanical properties of CFRP are not only dominated by the temperature, but also affected by the heating history. The above complicated processes or factors make theoretical modeling of failure behavior and ablation mechanism of CFRP composite under complex thermal and mechanical loadings a very challenging work.

In this paper, the thermo-mechanical properties and laser ablation behaviors of CFRP laminates under complex environments are investigated. The main research includes the following aspects:

1. Experiments on the failure behavior of CFRP laminates under thermal/ mechanical loadings in conventional heating environment are performed. The experiments include tensile and compressive tests at room temperature, tensile and compressive tests at elevated temperatures, and thermal buckling tests. Then, the failure modes and failure strength of CFRP laminates subjected to combined thermal and mechanical loadings are analyzed. In these tests, the effects of different thermo-mechanical loadings, temperatures and heating rates on the failure behavior of CFRP laminates are discussed. Experimental results show that irreversible heat damages of epoxy resin matrix and carbon fibers are obtained under high temperature, and the failure behavior can be attributed to the pyrolysis, oxidization, intralamina cracks and interlamina delaminating. Meanwhile, the residual strength of CFRP laminates after laser irradiation with different laser power is tested, and test results are compared with those obtained from uniform heating conditions. Obvious difference in both the temperature and heating rate are found in these two experimental conditions, and the difference between two heating rates is over two orders of magnitude. The local high temperature caused by the laser irradiation results in the sublimation of carbon fibers.

2. A multi-level analysis model, which is capable of describing mesoscopic and macroscopic behaviors of CFRP laminates under thermo-mechanical loadings, is established. First, using the mesoscopic analysis model and thermal gravimetric analysis (TGA) results of carbon fibers and epoxy matrix, the kinetic pyrolysis parameters and the relationship of different components with temperature and heating rates are obtained. Based on the multi-level analysis model, the macroscopic thermophysical and mechanical property of single CFRP lamina can be readily achieved. Then, the aforementioned multi-level model is combined with the classic laminates theory to study the thermo-mechanical failure behavior and failure threshold of CFRP laminates under high temperatures. Compared with the experimental results and previous analysis model, the newly developed model is able to accurately describe the failure behavior of CFRP laminates under thermal and mechanical loadings with various heating rates.

3. Systematic experiments are carried out to obtain the ablation behavior of CFRP laminates irradiated by continuous laser power at complex environments, such as static nitrogen environment, static air environment, open airflow environment as well as the supersonic wind tunnel environment. The effects of laser power on the ablation of CFRP laminates are discussed, and the three-dimensional ablation morphologies, cross-sectional ablation lines, temperature histories, ablation ratio and ablation rate are obtained. Experimental results show that the surface tangential airflow causes denudation of materials, which further accelerates the ablation of the materials and changes ablation morphologies. Compared with the experimental results in supersonic wind tunnel environment, much smaller ablation rate and ablation affected area are observed in the open airflow environment. As a result, the commonly adopted experimental measure of open airflow is not suitable for the simulation the ablation behavior of CFRP laminates in a real supersonic airflow environment.

4. Analytical model considering multiple mechanisms is established to simulate the ablation behavior of CFRP laminates irradiated by high power laser, and the effects of different environments and laser parameters are investigated. First, using the thermochemical analysis results under different environments, the ablation processes of CFRP composites are decoupled and the reaction mechanisms are quantified. Then, taking advantage the thermochemical ablation model and multi-level analysis model, the ablation behavior of CFRP laminates is simulated. Death-and-birth elements are adopted in the numerical model to accommodate the regression of ablation boundary and heat conduction. To update the thermophysical properties, ablation reaction, and corresponding reaction heat of each element, the form element method is also used. Finally, based on the finite element software ANSYS and APDL programming platform, the ablations processes of CFRP laminates are simulated. Compared with experimental results, the numerical model is capable of describing and predicting the ablation behavior and ablation threshold of CFRP laminates irradiated by high power laser.

语种中文
文献类型学位论文
条目标识符http://dspace.imech.ac.cn/handle/311007/73151
专题流固耦合系统力学重点实验室(2012-)
作者单位1.中国科学院力学研究所流固耦合系统力学重点实验室
2.中国科学院大学工程科学学院
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赵伟娜. 复杂热-力载荷下CFRP层合板的失效行为及破坏机理研究[D]. 北京. 中国科学院大学,2018.
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