温湿场交变环境下外加载荷对CFRP结构与力学性能影响

发布时间：2019-06-29 10:06

【摘要】：碳纤维增强复合材料(CFRP)具有比重小、比强度高、比模量高、耐高温、抗疲劳及耐化学腐蚀性能好等优点而被广泛应用于航天器主次受力构件及部分功能件。航天器用复合材料在服役期间会受到温度、湿度及紫外线辐射等各种严苛环境因素的影响,其中湿热环境是导致复合材料性能发生退化的最为重要的因素之一。目前,碳纤维增强复合材料湿热性能的研究主要集中在单一的湿、热或湿热条件,而弯曲载荷加载和湿热循环环境作用对碳纤维增强复合材料性能的研究尚少,因此研究碳纤维增强复合材料在湿热老化环境下外加弯曲载荷对其力学性能的影响规律具有重要意义。本文为探究不同孔隙率碳纤维/环氧树脂层合板在高低温湿热老化环境及外加载荷作用下力学性能的演变,基于材料服役期间的吸湿状态和内应力状态,对T700CF/3234EP进行高低温交变加速湿热循环老化试验。通过控制模压压力,制备3种孔隙率分别为0.04、0.08和0.11的层合板,将3种孔隙率的层合板进行加载,加载载荷分别为层合板最大弯曲载荷的0、30%、40%和60%,然后将其置于高低温环境模拟试验箱中,分别研究不同循环周期复合材料层合板的结构与力学性能变化,并采用ABAQUS软件对其力学性能进行有限元模拟,最后预测了层合板在湿热循环、弯曲载荷单独与耦合作用下的使用寿命。试验结果表明:层合板的孔隙多分布于富树脂区和层与层之间的界面区域附近。相同的孔隙率层合板,随着湿热循环周期的增加,孔隙数量增加明显,同一孔隙的变化并不明显,非常接近的孔隙,孔隙之间会连通起来形成更大的孔隙。加载后的层合板恰好相反,随着外加载荷的增大,单个的孔隙明显增大,孔隙的数量增加并不明显。随着高低温湿热循环周期的增加,弯曲和拉伸强度均呈现下降趋势。孔隙率越大的层合板,弯曲和拉伸强度下降越大。湿热循环的破坏机制主要是使纤维与树脂的脱粘。相同冲击能量下,湿热老化后层合板的凹坑深度小于没有经过湿热老化的层合板。随着冲击能量的增大,凹坑深度增加,从7.5J增加到10J时,层合板的凹坑深度会出现突变。随着湿热周期的增加,孔隙率越大的层合板剩余压缩强度下降越大。加载40%和60%的层合板在4-6周期时,分别增加了1.5%和1.6%。加载越大的层合板固化度提高越大,进而巴氏硬度提高越大,玻璃化转变温度下降越明显,但层合板的化学结构基本没变。随着湿热老化周期的增加,孔隙率和弯曲载荷越大,弯曲和拉伸强度下降越大,层合板分层和纤维脱粘现象越明显,在4-6周期时,由于树脂的二次固化,加载40%和60%载荷的层合板的弯曲和拉伸强度变化趋于平缓。随着湿热周期的增加,孔隙率相同的层合板,弯曲载荷越大,相同的冲击能量冲击后,凹坑深度越小;而外加弯曲载荷一样时,孔隙率越大,相同的冲击能量冲击后,凹坑深度越大。用ABAQUS软件模拟得到的弯曲、拉伸及冲击力学性能的模拟值与试验值非常吻合,并通过对层合板每一层的弯曲、拉伸和冲击力学性能的模拟,发现层合板每一层的弯曲、拉伸和冲击力学性能变化规律都是对称分布的,并且中间两层的强度最小。寿命预测结果显示湿热环境和外加弯曲载荷都大大减少了层合板的使用寿命
[Abstract]:The carbon fiber reinforced composite (CFRP) has the advantages of small specific gravity, high specific strength, high specific modulus, high temperature resistance, fatigue resistance and chemical corrosion resistance. The composite material for spacecraft is affected by various severe environmental factors such as temperature, humidity and ultraviolet radiation during service, and the damp-heat environment is one of the most important factors leading to the degradation of the performance of the composite material. At present, the research on the heat and heat performance of the carbon fiber reinforced composite material is mainly concentrated on a single wet, hot or wet heat condition, and the research on the performance of the carbon fiber reinforced composite material is low due to the action of the bending load loading and the damp-heat circulation environment. Therefore, it is of great significance to study the influence of the applied bending load on the mechanical properties of the carbon fiber reinforced composite in the damp-heat aging environment. In order to investigate the evolution of mechanical properties of different porosity carbon fiber/ epoxy resin laminated plates under the influence of high and low temperature damp-heat aging environment and the applied load, the high and low temperature and high-temperature alternating-accelerated wet-heat cycle aging test was carried out on the T700CF/ 3234EP based on the moisture absorption state and the internal stress state during the service period of the material. by controlling the compression pressure, three kinds of laminated plates with the porosity of 0.04, 0.08 and 0.11 are prepared, the three kinds of porosity laminated plates are loaded, the loading load is 0,30%,40% and 60% of the maximum bending load of the laminated plates, and then the laminated plates are placed in a high and low temperature environment simulation test box, The structural and mechanical properties of the composite laminates with different cycle cycles were studied. The mechanical properties of the composite laminates were simulated by using the ABAQUS software, and the service life of the laminated plates under the heat and heat cycle and the bending load was predicted. The results show that the porosity of the laminated plate is distributed in the vicinity of the interface area between the rich resin area and the layer and the layer. In the same porosity laminated plate, with the increase of the heat-heat circulation period, the number of pores is increased, and the variation of the same pore is not obvious, and the pores are very close, and the pores are communicated with each other to form larger pores. The loaded laminated plate is just opposite, with the increase of the applied load, the single pore is obviously enlarged, and the number of the pores is not obvious. With the increase of the high and low temperature and hot-heat cycle, both the bending and the tensile strength show a downward trend. The larger the porosity, the greater the bending and tensile strength. The mechanism of the heat-and-heat circulation is the debonding of the fiber and the resin. Under the same impact energy, the depth of the pit of the laminated plate after the damp-heat aging is less than that of the laminated plate which is not subjected to heat and heat aging. As the impact energy increases, the depth of the pit increases, from 7.5J to 10J, the depth of the pit of the laminated plate will change. With the increase of the damp-heat period, the larger the residual compressive strength of the laminated plate with the larger the porosity. The loading of 40% and 60% of the laminate increased by 1.5% and 1.6% at 4-6 cycles, respectively. The higher the curing degree of the laminated plate with the larger the loading, the greater the hardness of the glass transition, the more obvious the glass transition temperature, but the chemical structure of the laminated plate is basically unchanged. With the increasing of damp-heat aging period, the greater the porosity and bending load, the greater the bending and tensile strength, the more obvious the delamination of the laminated plates and the debonding of the fibers, and, at the time of 4-6, due to the secondary curing of the resin, The bending and tensile strength of the laminated plates loaded with 40% and 60% of the load tended to be gentle. With the increase of the damp-heat period, the larger the porosity, the larger the bending load, the smaller the depth of the pit after the same impact energy, and the larger the porosity, the greater the depth of the pit after the same impact energy. The simulated values of the bending, tensile and impact mechanical properties obtained by the ABAQUS software are in good agreement with the experimental values, and the bending, tensile and impact mechanical properties of each layer of the laminated plate are simulated, and the bending of each layer of the laminated plate is found. The variation of tensile and impact mechanical properties is distributed symmetrically, and the strength of the middle two layers is the least. The life prediction results show that the damp-heat environment and the applied bending load greatly reduce the service life of the laminated plate.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB332

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