热循环作用下单向炭纤维/环氧树脂复合材料的热应力

利用二维有限元模型对单向T700炭纤维/3234环氧树脂复合材料内部热应力分布进行了数值模拟,同时测试了T700/3234复合材料经不同次数真空热循环后的拉伸强度。研究结果表明,随热循环次数增加,基体应力单调下降,界面应力先下降后上升,25次热循环后变化趋于平缓。界面区域内热应力最大,且产生明显的应力集中。部分界面出现脱粘是复合材料在热循环作用下产生损伤的主要原因。     

径棒法编织C/C复合材料高温拉伸性能研究

采用化学气相沉积、沥青浸渍-高压碳化混合致密工艺向径棒法编织的预制体内引入基体碳,实现高密度(≥1.94g/cm3)炭/炭复合材料制备。利用快速通电加热测试技术,模拟C/C复合材料的高温工作环境,研究不同温度下材料的环向拉伸性能。结果表明:在2 300℃时,材料拉伸强度最大(80.3 MPa),断裂应变随着温度的升高而增加。采用扫描电镜对试样及断口形貌进行观察,发现测试温度、机加损伤及试样过渡区应力集中影响材料断裂特征。温度为1 800℃、2 300℃时材料在过渡区断裂;温度为2 800℃时,材料在标距区发生破坏,纤维与基体界面结合强度低,纤维拔出多,表现出假塑性断裂特征。     

有界面脱粘时颗粒增强金属基复合材料的弹塑性性能分析

基于Mori-Tanaka理论和Eshelby等效夹杂理论,假定基体和增强相界面结合完好,推导出在力的边界条件下两相复合材料各组成相的应力、应变以及复合材料的体平均应变和应力,并考虑了基体和增强颗粒热膨胀系数引起的热应变以及各相塑性应变的影响.在此基础上,假定基体和复合材料均为各向同性材料,颗粒仅产生弹性变形,基体产生弹塑性变形且满足Mises屈服准则和等向强化准则,由颗粒所受的拉应力控制界面的脱粘,脱粘概率由Weibull分布函数来描述,脱粘后的颗粒等效为孔洞,采用割线模量法讨论了球形颗粒增强金属基复合材料有界面脱粘时的弹塑性性能,理论预测与实验结果吻合较好.     

NiTi形状记忆合金丝的约束回复应力输出特性及本构模型

为促进工程结构领域对形状记忆合金(SMA)这一智能驱动材料的应用,研究了预应变大小和热循环次数对Ti-50.8(质量分数,%)Ni SMA丝的约束回复应力-温度曲线、最大约束回复应力、逆相变特征温度、相变温度区间和相变滞后温度区间等约束回复应力输出特性的影响,并在试验数据集合的基础上建立以温度和完全热循环次数为输入、约束回复应力为输出的BP神经网络(即按照误差逆向传播训练的神经网络算法)迟滞模型。结果表明:最大约束回复应力和马氏体逆向变特征温度随预应变的增加而增加;6%预应变的NiTi SMA丝在第一次热循环中约束回复应力最大,逆向变特征温度值最高。经过五次热循环后,NiTi SMA丝的约束回复应力-温度曲线逐渐稳定。该神经网络迟滞模型的数值计算结果与试验数据较为吻合,平均绝对误差不超过5%,且简单实用、精确度高,具有一定的工程指导意义。     

Al2O3sf·SiCp/Al复合材料的压缩变形力学行为及机制

对Al2O3sf·SiCp/Al复合材料进行高温及半固态区间压缩变形,观察其微观组织和组成,研究了在高温及半固态温度下的压缩变形力学行为和变形机制.Al2O3sf·SiCp/Al复合材料的流动应力随着压缩温度的提高而下降,随着增强体的体积分数、基体材料强度和应变速率的提高而上升.高温压缩使材料屈服后,由于动态回复抵消了材料的加工硬化,其流动应力值基本上保持不变.在半固态温度区间压缩而液相体积分数较低时,其流动应力的变化规律与高温压缩时相似;液相体积分数较高时,流动应力在材料屈服以后,液相的流出使流动应力下降;液相被挤出到侧表面后,流动应力呈上升趋势.复合材料在半固态区间压缩时具有应变速率敏感性.     

非连续增强LY12复合材料蠕变机制研究

研究了应力、温度和热处理对22vol%莫来石短纤维增强LY12复合材料性能的影响,实验采用铸态、退火态和T4处理复合材料,三种状态下复合材料的抗蠕变性能均高于基体材料LY12铝合金.文中提出一种复合材料的蠕变机制:在低应力阶段,复合材料的蠕变受位错的攀移过程所控制;在高应力阶段,复合材料的蠕变受增强体与基体的界面所控制.用TEM分析了材料的界面.     

真空热循环对碳/双马来酰亚胺复合材料低速冲击性能的影响

对T700/HT280复合材料进行真空热循环处理(-140～180℃,10~(-3) Pa),分别测试真空热循环处理前后复合材料的质损率、动态力学性能和低速冲击性能。采用宏观目视、超声C扫描和有限元分析对低速冲击损伤状况进行分析、表征和模拟。结果表明,随真空热循环次数的增加,由于发生析气效应,T700/HT280复合材料及基体树脂的质损率先急剧升高然后趋于平缓。经历真空热循环处理后T700/HT280复合材料出现了一定程度的后固化、热老化和局部界面脱粘。低冲击能时主要损伤模式为基体树脂受到压缩,高冲击能时主要损伤模式转化为基体开裂、复合材料分层。有限元模拟结果与实验结果吻合。随冲击能量的增大,复合材料吸收能增加。冲击能量为30～40 J条件下,吸收能可以有效地表征出真空热循环对复合材料的环境损伤效应。     

影响碳—铝复合材料耐蚀性的因素

本文研究了热暴露、热循环、表面粗糙度、基体合金以及纤维种类对碳-铝复合材料耐蚀性的影响。试验结果表明,无论是在蒸馏水中还是在3.5%NaCl盐水中热暴露都加剧了复合材料界面腐蚀使复合材料的耐蚀性变坏,热循环对复合材料的耐蚀性影响很少,粗糙表面对复合材料耐蚀性有有害的影响,C/Al复合材料比C/LD2复合材料更耐腐蚀,而Gr/Al复合材料比C/Al复合材料具有高的耐蚀性。     

钛酸钾晶须增强铝基复合材料的热循环尺寸稳定性

用挤压铸造工艺制备了钛酸钾晶须增强铝基复合材料,研究了其热膨胀系数和热循环尺寸稳定性。复合材料的热膨胀系数低于ZL109合金且随晶须含量的增加而降低。50℃~280℃热循环实验中,ZL109合金和复合材料中都观察到应变滞后现象。ZL109合金的热循环曲线具有最大的应变滞后和残余塑性应变,而30 vol%复合材料热循环前后几乎没有尺寸变化,具有很高的尺寸稳定性。最后,我们认为可以用热循环曲线来分析工作在变温环境下的结构材料的尺寸稳定性和失效。     

单向纤维增强陶瓷基复合材料单轴拉伸行为

采用细观力学方法对单向纤维增强陶瓷基复合材料的单轴拉伸应力-应变行为进行了研究。采用Budiansky-Hutchinson-Evans（BHE）剪滞模型分析了复合材料出现损伤时的细观应力场,结合临界基体应变能准则、应变能释放率准则以及Curtin统计模型三种单一失效模型分别描述陶瓷基复合材料基体开裂、界面脱粘以及纤维失效三种损伤机制,确定了基体裂纹间隔、界面脱粘长度和纤维失效体积分数。将剪滞模型与3种单一失效模型相结合,对各个损伤阶段的应力-应变曲线进行模拟,建立了准确的复合材料强韧性预测模型,并讨论了界面参数和纤维韦布尔模量对复合材料损伤以及应力-应变曲线的影响。与室温下陶瓷基复合材料单轴拉伸试验数据进行了对比,各个损伤阶段的应力-应变、失效强度及应变与试验数据吻合较好。     

Thermal expansion behaviour of ultra-high modulus carbon fibre reinforced magnesium composite during thermal cycling

The thermally induced strain response of unidirectional P100S/AZ91D carbon fibre-reinforced magnesium composite was studied over five cycles in the ±100 °C temperature range. A temperature-dependent one-dimensional model was employed to predict the anticipated response to the cycling thermal environment. Strain hysteresis was observed during cycling and attributed to matrix yielding. First cycle residual plastic strains were modelled with reasonable agreement. Experimental results deviated from predictions during subsequent cycles with continued thermal ratcheting shifting the hysteresis loops to higher strains with increasing cycles. This was thought to be associated with interfacial debonding and frictional sliding at fibre/matrix interfaces. The effect of thermal treatment on composite expansion behaviour was investigated and the results discussed in terms of minimising thermally induced deformations during anticipated service conditions. Treatments were found to affect the first cycle behaviour, reducing in particular residual plastic strain generation. Matrix yield strength was exceeded over the thermal cycle due to a lack of sufficient hardening, and since interfacial conditions were unaltered, interfacial sliding and thermal ratcheting could not be eliminated. The potential for improvement of C/Mg composite thermal strain response was explored in the light of the current findings.     

Fatigue Hysteresis of Carbon Fiber-Reinforced Ceramic-Matrix Composites at Room and Elevated Temperatures

When the fiber-reinforced ceramic-matrix composites (CMCs) are first loading to fatigue peak stress, matrix multicracking and fiber/matrix interface debonding occur. Under fatigue loading, the stress–strain hysteresis loops appear as fiber slipping relative to matrix in the interface debonded region upon unloading/reloading. Due to interface wear at room temperature or interface oxidation at elevated temperature, the interface shear stress degredes with increase of the number of applied cycles, leading to the evolution of the shape, location and area of stress–strain hysteresis loops. The evolution characteristics of fatigue hysteresis loss energy in different types of fiber-reinforced CMCs, i.e., unidirectional, cross-ply, 2D and 2.5D woven, have been investigated. The relationships between the fatigue hysteresis loss energy, stress–strain hysteresis loops, interface frictional slip, interface shear stress and interface radial thermal residual stress, matrix stochastic cracking and fatigue peak stress of fiber-reinforced CMCs have been established.     

Comparative study on stress–strain hysteresis response of SAC solder joints under thermal cycles

The present study attempts to evaluate the stress-strain hysteresis responses of SAC solder joints in Resistor and FleXBGA144 packages subjected to thermal cyclic loading using several constitutive models. The total deformation of the solder material consists of elastic, rate-independent plastic and rate-dependent creep components. The constitutive models discussed in this study each weighted elastic, plastic and creep deformations differently. At low stresses SAC solder alloys were found to be creep resistant, where at higher stresses, the influence of different microstructures disappears as matrix-creep dominates in this region. Thus, the proper constitutive model requires all the three ingredients of the elastic, the creep, and the time-independent plastic data for different stress levels to effectively predict the hysteresis behavior of the SAC solder alloys. The hysteresis loops predicted by constitutive models were also found in close agreement with the loops generated by FEM for the SAC solder joint subjected to thermal cycling.     

真空热循环对空间级缩合型硅橡胶拉伸性能的影响

对空间级缩合型硅橡胶KH－X－B进行了真空热循环试验（123－403K，10^-5Pa），测试了热循环前后材料的质损率，拉伸性能，热膨胀性能，讨论了循环过程中的应变滞后效应和附加残余应变以及它们对材料的强化作用，结果表明，材料质损率随循环次数增加而提高后趋于平缓，室温及高温拉伸强度随循环次数的增加是先增强而后下降，循环过程中发生应变滞后现象，且第一次循环后产生附加残余应变，206次循环后残余应变消失，材料强化，400次循环后重新产生残余应变，材料强度下降。     

Study on the Thermal Expansion and Thermal Cycling of AlNp／Al Composites

The AIN particle reinforced aluminum matrix composites with 50% volume fraction were fabricated by squeeze-casting technology.The thermal expansion behavior and its response to thermal cycling were studied between 20℃ and 400℃.Compared with four theoretical models,the measured CTEs of the composite lie within the elastic bounds derived by Schapery′s analysis .Schapery′s model and Kerner′s model agree well with the CTEs of the composites at lower temperature and elevated temperature,respectively.Strain hysteresis was observed between heating and cooling curves during cycling.This was attributed primarily to the anelastic behavior of the matrix induced by matrix residual stresses.     

Modeling the Effect of Multiple Matrix Cracking Modes on Cyclic Hysteresis Loops of 2D Woven Ceramic-Matrix Composites

In this paper, the effect of multiple matrix cracking modes on cyclic loading/unloading hysteresis loops of 2D woven ceramic-matrix composites (CMCs) has been investigated. The interface slip between fibers and the matrix existed in matrix cracking mode 3 and mode 5, in which matrix cracking and interface debonding occurred in longitudinal yarns, are considered as the major reason for hysteresis loops of 2D woven CMCs. The effects of fiber volume content, peak stress, matrix crack spacing, interface properties, matrix cracking mode proportion and interface wear on interface slip and hysteresis loops have been analyzed. The cyclic loading/unloading hysteresis loops of 2D woven SiC/SiC composite corresponding to different peak stresses have been predicted using the present analysis. It was found that the damage parameter, i.e., the proportion of matrix cracking mode 3 in the entire cracking modes of the composite, increases with increasing peak stress.     

Thermal cycling studies of a cross-plied P100 graphite fibre-reinforced 6061 aluminium composite laminate

Response to thermal cycling of a 0/90 cross-plied P100 Gr-6061 aluminium composite laminate was studied between a minimum temperature (T _min) of 25 C and maximum temperatures (T _max) of 100 and 540 C. Strain hysteresis was observed between the heating and cooling half-cycles and was attributed to anelastic strains induced by matrix residual stresses. A residual plastic strain was also observed after the first cycle, and was seen to disappear after subsequent cycles. Alteration of the thermal residual stress state of the matrix via heat treatments was found to change significantly the magnitude of the plastic strain. These results were compared with those of studies on unidirectionally reinforced P100 Gr-6061 aluminium composites, and the differences were explained on the basis of the residual stresses resident in the matrix. Optical and electron microscopy were also utilized to observe thermal damage, which occurred predominantly along improperly bonded fibre-matrix interfaces.     

Modeling of residual stresses variation with thermal cycling in thermal barrier coatings

Thermal barrier coatings (TBCs) are commonly used as protective coatings for engine metal components to improve performance. Many investigations have shown that residual stresses in TBCs applications play an important role, but the residual stresses are mainly obtained by simulation method. As we know, there are a few analytical solutions of residual stress in TBCs system. In this paper, a new two-dimensional analytical solution has been obtained under the condition of non-linear coupled effects of temperature gradient, thermal fatigue, deposited residual stress, thermally grown oxide (TGO) thickening, elasto-plasticity deformation and creep deformation of TBC. Moreover, the influences of bending moment and curvature on stress variation in TBCs are considered during thermal cycling. The calculated results are in agreement with the prior experimental results.     

多相复合陶瓷刀具材料残余热应力的有限元模拟

以SiC和(W,Ti)C颗粒增强Al₂O₃多相复合陶瓷刀具材料为基础,运用有限元方法详细研究了材料内部残余热应力的大小与分布形态。计算结果发现,单元模型取法、弥散相颗粒大小、分布及其含量均对多相复合陶瓷刀具材料中的残余热应力有较大影响。基体内不仅存在拉应力区,而且存在不同程度和范围的压应力区,拉、压应力区的结构形式与弥散相颗粒的分布方式密切相关。研究表明,残余热应力的存在与材料的力学性能和微观结构有着密切的关系。