【作者】 谢小林；

【导师】 熊传溪； 王钧；

【作者基本信息】 武汉理工大学 ， 复合材料学， 2010， 博士

【摘要】 碳/环氧复合材料具有优异的力学性能、耐热性、耐腐蚀性、耐疲劳性,在航空航天、武器装备、国民经济等方面有较广泛的应用。由于碳纤维有良好的导电性,在较高碳纤维含量的碳/环氧复合材料中碳纤维之间相互接触,形成导电网络。当受到外力作用时,复合材料内部结构会发生变化,引起导电网络的变化,进而导致复合材料电阻产生变化。因此,可以利用碳纤维作为复合材料外力传感器,通过复合材料电阻变化来反映其内部结构的变化。本文选用在航空工业中广泛应用的G803/5224碳布增强环氧树脂预浸料为原料,按照[0/90]、[0/90/±45]、[±45]铺层方向,采用模压成型方法制备了碳纤维体积含量分别为56%、64%的碳/环氧复合材料；依据复合材料通道导电和隧道效应导电的模式,研究了温度变化对复合材料电阻的影响；研究分析了在拉伸、开孔拉伸、压缩、开孔压缩、弯曲、冲击条件下,复合材料的电阻随外力作用的变化规律,确定了复合材料损伤诊断依据；在综合分析冲击能量、冲击损伤(超声F扫描图)、剩余压缩强度、电阻变化等指标的基础上,提出了评价复合材料冲击损伤的新思路；编写了复合材料冲击损伤计算机诊断程序,构建了由复合材料、计算机、多通道数据采集器组成的复合材料冲击损伤自诊断系统,并通过试验得到了验证。(1)在-50℃-160℃温度范围,不同规格复合材料的电阻均逐渐下降,复合材料表现出负温度系数效应。其中,[±45]8复合材料电阻下降幅度最大,降幅为9.37%。在(-50～-20)℃、(-20～130)℃、(130～160)℃等不同温度区间,随着温度升高,复合材料电阻下降速率并不相同。其中,在(-20-130)℃区间,复合材料电阻下降速率最大。(2)在拉伸、开孔拉伸、压缩、开孔压缩、弯曲试验中,复合材料的破坏包括环氧树脂的普弹形变、强迫高弹形变、树脂裂纹、树脂破坏、复合材料分层、碳纤维断裂等形式,最终复合材料被破坏。在试验过程中,复合材料中的碳纤维接触状况、自由电子数目会发生变化,使得其中的导电通道、隧道导电效应产生变化从而引起电阻变化。(3)在拉伸和开孔拉伸试验中,当[0/90]、[0/90/±45]复合材料应变大于1.8%,[±45]复合材料应变大于1.27%时,则在复合材料内部会产生拉伸损伤；当复合材料试样的电阻增幅超过此时的电阻增幅时,则可诊断复合材料试样中存在损伤。在压缩试验中,当[0/90]7、[0/90]8复合材料试样的电阻增幅分别超过3.6%、2.6%时,则可诊断复合材料试样中存在轻微的压缩损伤；当[0/90]7、[0/90]8复合材料试样的电阻增幅分别超过10.2%、3.4%时,则可诊断在复合材料试样中存在较严重的压缩损伤。在弯曲试验中,当[0/90]7、[0/90]8复合材料试样的电阻增幅分别超过25.8%、31.3%时,则可诊断复合材料试样已经断裂；同时,不能依据复合材料电阻变化情况反映复合材料断裂之前的状况。(4)不同规格的复合材料冲击损伤的能量阈值和损伤容限的冲击能量阈值也各不相同。小于冲击损伤能量阈值的冲击,会使复合材料各电极点间电阻变小。大于冲击损伤能量阂值的冲击使冲击点周围的电极点电阻上升。在相同能量冲击下,不同电极点间电阻变化并不相同是因为冲击能量以冲击点为中心向四周呈放射状扩散,离冲击点越近,冲击作用越明显。大于损伤容限的冲击能量阈值的冲击不仅使复合材料电阻发生明显变化,而且复合材料会被冲击破坏。(5)在冲击试验中,复合材料上由4个电极点围成的长×宽为6cm×5cm区域中,只要3个电极点或不连续的2个电极点的电阻增幅都小于由复合材料损伤容限冲击能量阈值所引起的所有电极点电阻第二增幅时,冲击后的复合材料仍处“正常”状态；当电阻增幅大于第三增幅时,冲击后的复合材料处于“损伤”状态；当电阻增幅大于穿孔性损伤所引起的第三增幅时,冲击后的复合材料处于“严重损伤”状态。更多还原

【Abstract】 Carbon fiber/epoxy-matrix composite materials have been widely used in aerospace, automobile, weapons and equipment, and national economy for their excellent mechanical properties, temperature resistance, corrosion resistance, and fatigue resistance. Due to the optimal electrical conductivity of carbon fibers, the electrical conductivity network of carbon fibers can be formed in carbon fiber/epoxy-matrix composite materials with high volume content carbon fiber by contacting tightly each other. The internal structure of composite materials will be changed by external force, which can causes the changes in conductive network and further lead to the variation of resistance of composite materials. Therefore, carbon fiber can be used as the external sensor of composite materials, which can measure the variation of internal structure by diagnosing the change of electrical resistance composites.In this thesis, carbon/epoxy composite materials were prepared by molding compression with G803/5224 carbon fabric/epoxy prepreg, which were used widely in the aviation industry. The stacking angle of prepreg was [0/90], [0/90/±45],[±45], and carbon fiber volume content was 56%,64%, respectively. Based on channel conduction and tunnel effect conduction, the influence of temperature on the resistance of composites was studied. The resistance change of composites resulted from tension, opening tension,compression, open hole compression, bending, impact conditions was studied, and the basis for damage diagnosing of composites was determined. A new idea of evaluating impact damage in composites was proposed by comprehensive analysis of the effect of impact energy, impact damage (ultrasonic F-scan images), residual compressive strength, resistance change. Computer program of diagnosing damage in composites was compiled. The system of self-diagnosing impact damage in composites was established, which was composed of composite materials, computers, and multichannel data acquisition device, and it was validated by tests.(1) The resistance of different specifications of composites decreased, namely negative temperature coefficient effect can be found in composites when measured in the temperature from-50℃to 160℃. Among these composites, [±45] 8 composites showed a sharp drop with the degree of 9.37%. The resistance of composites declined with different degree in different temperature range of (-50--20)℃, (-20-130)℃, (130-160)℃. In the case of (-20-130)℃, the rate of descent was the maximum.(2) The destruction test of composite materials was measured including epoxy elastic deformation, forced high-elastic deformation of epoxy resin, resin cracks, resin damage, composites delamination, carbon fiber fracture, etc. in the cases of tension, opening tension, compression, open hole compression, and bending test. During the test, the resistance change of composites was caused by the change of conductive channel, the tunnel effect of composite materials, resulted from the contact conditions among carbon fibers and the number change of free electrons.(3) In the cases of tensile and opening tension test, there was tensile damage in composites,when the strain of [0/90]、[0/90/±45]、[±45]composites was more than 1.8%、1.8%、1.27%, respectively. When the increase rate of resistance in composites was more than the rate of resistance at this time, the tensile damage can be diagnosed in composites. In the cases of compression test, when the resistance increase rate of [0/90]7、[0/90]8 composites was more than 3.6%、2.6%,, respectively, the slight compress damage can be diagnosed in composites. When the rate of was more than 10.2%、3.4%, respectively, the serious compress damage can be diagnosed in composites. In the cases of bending test, when the increases rate of resistance of [0/90]7、[0/90]8 composites was more than 25.8%、31.3%, composites may have been broken. Damage in composites was hard to diagnose by resistance change before they were broken.(4) Impact energy threshold of damage and damage tolerance of different specifications of composites were different. When the value of impact damage energy was less than the threshold, there can make the resistance value of composites between electrode points smaller. When the value of impact damage energy was greater than the threshold, there can make the resistance value of composites between electrode points bigger. The resistance change rate of different electrode points in composites was different under the same impact damage energy. It can be mainly due to the spread of impact energy from the impact point to the surrounding radially, the distance was nearer, and the impact was more obvious. When the composites were impacted by a impact greater than the impact damage tolerance energy threshold, not only the resistance of the composites was significant change, but also the composite materials was destroyed.(5) In the case of impact test, composites can be regarded as "normal" state in the region rounded by 4 electrode points with the length of 6 cm and the width of 5 cm, as long as the resistance increase rate of three electrode points or 2 discrete electrode points was less than the second resistance increase rate of all electrode points of impacted composites arising from the impact damage tolerance energy threshold. When the resistance increase rate was more than the third resistance increase rate, composites can be regarded as "damage" state. When the resistance increase rate was more than the third resistance increase rate of impacted composites by perforation damage, composites can be regarded as "serious damage" state.更多还原