常温和湿热环境下含脱层的复合材料连接件强度试验研究

通过试验测定了含脱层的复合材料连接件在常温干燥和高温湿热环境下的挤压强度数值,探讨了含脱层的连接件在不同环境下强度和刚度数值的变化。结果表明,脱层对连接件挤压强度影响不大,但对孔口局部失稳载荷影响较大;湿热环境使连接件的强度和刚度有较大程度的降低。     

碳纤维复合材料湿热老化加速关系

受环境因素作用,碳纤维增强聚合物基复合材料(Carbon fiber reinforced polymer composities,CFRP)湿热环境下发生性能退化是一个重要的工程问题,而如何通过实验室加速试验再现自然环境对复合材料的老化作用成为解决此问题的关键。基于时间-温度-湿度等效原理,将湿热环境下CFRP粘弹性能的改变作为材料的老化损伤度量,建立不同湿热环境之间当量折算关系,提出加速老化当量折算系数的确定方法。以典型军机结构用CFRP为例,实例计算了材料不同温度、湿度环境下的当量折算系数,根据地面停放环境谱当量折算得到加速试验谱,加速效果令人满意。最后,对比分析了温度与湿度对当量折算系数的影响,结果表明,温度变化对当量折算系数的影响要比湿度变化的影响显著。     

非连续湿热作用对T700/TR1219B复合材料宏细观性能的影响

为研究非连续湿热作用对碳纤维环氧树脂基复合材料性能的影响,对T700/TR1219B试样进行了吸湿-脱湿试验,测试了其拉神性能,并采用SEM观察试样侧面;通过原子力显微镜的峰值力纳米力学成像技术(PF-QNM)对树脂进行纳米压痕测试。结果表明:吸湿率从0变化到1.2%,T700/TR1219B复合材料的一次及二次吸湿行为均满足Fick定律;经吸湿-脱湿-再吸湿,试样的拉伸强度、弹性模量及树脂的硬度及弹性模量均呈现先上升后下降的变化趋势。     

BA9916-Ⅱ/CCF300复合材料加筋板吸湿特性

为研究BA9916-II/CCF300复合材料加筋板的吸湿特性,在70℃/85%RH湿热环境中开展了吸湿实验,提出了基于厚度划分的Fick吸湿模型M_t=∑ni=1v_i[G_iM_(∞i)+M_(0i)(1-G_i)],并采用质量扩散模块进行了吸湿行为的有限元仿真。结果表明:提出的基于厚度划分的Fick吸湿模型能较好地描述该型结构的吸湿行为,具有较高的分析精度;但由于复合材料加筋板在吸湿后期存在阶段吸湿现象,Fick吸湿模型在该结构吸湿行为后期的描述上存在一定偏差;有限元仿真得到的吸湿动力曲线和水浓度分布结果验证了基于厚度划分吸湿模型的合理性,更好地还原了真实的吸湿过程与水分分布情况。     

Study on Compressive Properties of Z-pinned Laminates in RTD and Hygrothermal Environment

Compressive tests of [0] 12 and [90] 12 unidirectional laminates and [45/0/-45/90] 2S quasi-isotropic laminates are accomplished in both room-temperature and dry (RTD) and hygrothermal environment. And simulation studies on the compressive strength of Z-pinned laminates of [0] 12 and [45/0/-45/90] 2S are conducted by using finite element analysis (FEA). A microstructural unit cell for FEA is created to simulate a representative laminates unit with one pin. Within the unit cell, the first directions of the elements’ material coordinate systems are changed to simulate the fibres’ deflecting around the pin. The hygrothermal effect is simulated by the material properties’ adjustments which are determined by the compressive tests of non-pined laminates. The experimental results indicate that the percentage of reduction in the compressive modulus of Z-pinned laminates caused by Z-pin becomes smaller with the percentage of 0° fibres decreasing in the laminates; the compressive strength of quasi-isotropic laminates reduces and the percentage of the reduction in the compressive strength declines with Z-pin volume content increasing, and the moisture absorption ratio of the Z-pinned specimens is greater than that of the non-pinned specimens, because the cracks around Z-pin increase the moisture absorption. In addition, the simulations show that the deflection of fibres around Z-pin is the main factor for the reduction in the compressive strength of Z-pinned unidirectional laminates, the dilution of fibre volume content caused by resin-rich pocket is the principal factor for the decline in the compressive strength of Z-pinned quasi-istropic laminates, and the compressive strength of Z-pinned specimens in hygrothermal environment reduces as the result of superimposition of some factors, including the changes in material properties caused by hygrothermal environment, the deflection of fibres and the resin-rich pocket caused by Z-pin.     

湿热环境下聚酰亚胺复合材料的拉脱性能研究

复合材料结构已被广泛应用于航空航天领域,为了研究复合材料在不同湿热环境下的力学性能,分别对低温干态（CTD）、室温干态（RTD）和高温湿态（ETW）三种环境下的某型聚酰亚胺复合材料层压板进行拉脱试验,并对RTD 试验过程进行仿真分析;通过试验获得两类典型铺层的拉脱强度与破坏模式,并利用有限元仿真预测失效载荷。结果表明：某型聚酰亚胺复合材料具有优异的热稳定性,CTD 环境下复合材料的拉脱强度较RTD 环境下的拉脱强度提升8.1%~9.0%,ETW 环境下某型聚酰亚胺复合材料的拉脱强度与RTD 环境下的拉脱强度相当;（30/60/10）铺层的拉脱强度略高于（50/40/10）铺层。     

湿热老化后碳纤维复合材料层间剪切强度实验方法对比研究

通过短梁法和双切口法研究湿热老化对T700/TDE-85复合材料层间剪切强度的影响,讨论两者吸湿规律随老化时间的变化关系,并对试件断口形貌进行分析。结果表明:两种试件吸湿规律均符合Fick第二定律,但两者平衡吸湿率和吸湿时间有所差别,双切口法试件的吸湿速率和平衡吸湿率均比短梁法试件高;双切口试件所测层间剪切强度受湿热老化影响比短梁明显,短梁试件每隔500 h层间剪切强度保持率为74.5%,61.0%,53.2%,50.6%,双切口每隔500 h层间剪切强度保持率为60.9%,38.3%,42.6%,33.0%;短梁试件失效模式随着湿热老化时间的增长变化比双切口更为复杂。     

3238树脂及其改性

 采用芳香二胺对3238韧性中温固化环氧树脂体系进行了改性。通过芳香二胺和环氧树脂预先反应,消除了芳香二胺对中温环氧树脂的固化及工艺的影响,改性前后差示扫描量热法（DSC）初始温度和峰顶温度的差别仅有3 ℃,最终固化程度的差别也仅有1%。通过芳香二胺刚性结构的引入,由于芳香二胺和环氧树脂的交联密度高于双氰胺环氧树脂体系,因此引入芳香二胺刚性结构提高了3238树脂的耐热性,干态玻璃化转变温度提高了29 ℃,且纯固化后树脂吸湿量降低了0~34%,湿态玻璃化转变温度提高了46 ℃。改性后树脂可能形成了高低交联密度区,产生了固化物交联状态的不均匀,在提高树脂体系耐热性能的同时,保持其原有的韧性,树脂浇注体的拉伸应力应变曲线呈明显的塑性变形,拉伸断裂伸长率达5~31%,复合材料的断裂韧性达1 133 J/m²。     

Effect of Stitching on Plain and Open-hole Strength of CFRP Laminates

 Experimental and analytical investigation is conducted to explore the effects of stitching on plain (without hole) and open-hole compressive and tensile strength of uniweave T300/QY9512 laminates under different environmental conditions (20 篊/dry and wet, 150 篊/dry and wet). Strength performance of stitched composite laminates is also studied using finite element analysis (FEA) model and compared with the experimental results to validate the model. It is found that under similar environmental conditions, the open-hole compressive strength of stitched laminate is decreased and open-hole tensile strength increased as compared to the unstitched laminates. Predicted tensile and compressive strengths are found to be in a good agreement with the test results and the relative error in all cases is less than 15%.     

湿热环境下胶接修理碳纤维/环氧树脂基层合板振动特性

通过理论推导和有限元仿真,研究四端固支的复合材料层合板胶接修理结构在湿热环境下的振动特性。基于Mindlin一阶剪切变形理论和Hamilton原理,考虑湿热应力,利用温度与湿度的等效性,推导受湿热环境影响的复合材料层合板本构方程,采用有限元法求解层合板的振动特征方程。利用有限元软件ABAQUS,建立胶接修理层合板模型,并与文献结果进行对比,讨论不同的湿热环境和附加补片个数对胶接修理层合板振动特性的影响。结果表明:湿热环境下,附加补片的引入都使得胶接修理层合板各阶固有频率降低,附加补片个数由一个变为两个时,一阶固有频率进一步下降;湿度增加对固有频率降低的影响大于温度增加对固有频率的影响;在温度、湿度同时升高的环境下,附加补片的引入会使层合板胶接修理结构更早地达到湿热屈曲的状态。