装药缺陷对固体火箭发动机内弹道性能的影响

采用仿真计算分析方法研究了管状推进剂装药缺陷的宽度、深度以及包覆层脱粘等因素对固体火箭发动机内弹道性能的影响规律。结果表明,随着固体推进剂装药裂纹深度与宽度比的增加,燃烧室内压强和裂纹出口气流速度也增加。管状药柱包覆层前端轴向脱粘可使燃面-肉厚曲线的斜率增加,装药的压强指数增大,最终可能造成燃烧室压力过高而解体爆炸。     

再制造喷涂层界面结合性能脉冲红外热像评估技术

针对再制造工程中常见的喷涂层界面结合性能评价问题,采用脉冲红外热像技术对3Cr13合金涂层的界面脱粘缺陷进行检测评估。以信噪比(SNR)为评价标准,对比了两种不同热图序列处理方法在预处理和后处理阶段的效果。结果表明:在预处理阶段,基于表面热信号的多项式拟合算法(PF)将原始热图的信噪比由5.34提升到9.61,其效果优于基于单张图像中值滤波算法(MF);而在后处理阶段,基于单张图像的主成分分析法(PCA)对缺陷特征的表征比基于表面热信号的脉冲相位法(PPT)更加准确,第三主成分重建热图的信噪比达到17.99。综合而言,基于单张图像的热图序列处理方法在再制造喷涂层界面结合性能评价中具有更好的效果。     

炭纤维/ 环氧复合材料单面修补中心裂纹铝合金板的静态和疲劳特性

利用真空袋压工艺, 采用单向炭纤维复合材料补片对中心裂纹铝合金板进行了单面胶接修补。测试了复合材料修补板的静态拉伸强度及修补板在拉拉疲劳过程中的裂纹扩展、界面脱粘和剩余拉伸强度等疲劳性能。结果表明, 复合材料补片胶接修补能有效地提高裂纹板的破坏强度和刚度, 降低裂纹板的疲劳裂纹扩展速率, 提高其疲劳寿命。裂纹板经单向炭纤维/ 环氧复合材料补片修补后, 其破坏强度从311. 48 MPa 提高到364. 74 MPa ,疲劳寿命从32217 次提高到77546 次。疲劳导致修补结构的粘接界面脱粘, 脱粘区域近似椭圆形; 脱粘面积随疲劳周次的增加而增加, 且增加的幅度与疲劳周次相关。      

含脱粘损伤的复合材料加筋板压缩破坏渐进损伤数值分析

本文提出了基于连续损伤力学的复合材料层合加筋壁板渐进损伤分析模型。该模型采用界面单元模拟筋条和壁板之间的连接界面,连接界面和复合材料层板分别采用Quads准则和Hashin准则作为失效判据,基于内嵌连续损伤状态变量的材料刚度退化方案,采用非线性有限元方法,研究了复合材料加筋壁板在压缩载荷下的破坏过程,分析了结构相应失效模式的细观失效机理。数值分析结果与实验数据吻合较好,证明该方法的合理性和有效性,并详细探讨了界面单元关键参数和层板铺设角度对加筋壁板结构力学响应的影响规律,得到了一些富有价值的结论。     

Analysis of the Notched Coating Adhesion Test

An analysis of the notched coating adhesion (NCA) test is presented. This simple adhesion test method is appropriate for measuring the interfacial fracture toughness of some classes of coatings and open-faced adhesive bonds. The NCA specimen consists of a single substrate coated with a thin layer of adhesive. The coating is notched to sever the coating and induce sharp interfacial debonds, and the specimen is then loaded in tension. The substrate strain at which coating debonding occurs is recorded and used to determine the critical strain energy release rate. Yielding of the substrate is permitted, and does not significantly affect the calculation of the strain energy release rate. Analytical and finite element analysis are used to quantify the available strain energy release rate for both steady state and laterally-constrained cases. The available strain energy release rate is shown to be quite insensitive to the initial debond length. The specimen geometry results in a mode mix which causes the adhesive to debond along the interface.     

脱胶缺陷尺寸对复合材料加筋板屈曲及后屈曲特性的影响

为确定脱胶缺陷对复合材料加筋板屈曲及后屈曲特性的影响,对含不同脱胶缺陷工型筋条的复合材料加筋板进行了压缩试验研究。结果表明,30 mm和50 mm的缺陷对试验件承载能力影响很小,当缺陷尺寸增至80 mm时,试验件后屈曲承载能力明显下降。借助超声检测技术对缺陷的扩展行为进行了监测,结果表明,当压缩载荷达到破坏载荷的85.3%时,预制缺陷的对角位置处出现扩展迹象。通过影像云纹法获得两半波和三半波失稳模态的形成过程。对失稳模态的监测结果还表明,随缺陷长度增加,该型加筋板的失稳模态从三半波向两半波转换。在试验基础上,利用ABAQUS软件建立有限元（FE）模型,依次进行了屈曲及后屈曲过程的数值模拟。屈曲分析用于获得试验件的失稳载荷及模态,在后屈曲分析中将失稳波形以几何扰动的形式引入FE模型,最终计算结果与试验结果基本吻合,表明该模型可以用于复合材料加筋板屈曲及后屈曲性能的预测。     

UHTCC/RC复合梁剪切性能试验研究

超高韧性水泥基复合材料(UHTCC)以其多重细密稳态开裂模式在宏观上展现出拉应变硬化特征,具有优异的裂缝控制能力,可用作修补材料。采用UHTCC替代部分受拉区混凝土对有腹筋UHTCC/RC复合梁进行了剪切性能研究。试验变量为UHTCC层厚度。结果表明:不同UHTCC层厚度的UHTCC/RC复合梁,其抗剪承载力均明显高于RC对比梁;即便配置较密集的箍筋,仍然无法阻止界面剥离,但可以避免界面剥离产生的荷载抖降;UHTCC能够限制和分散上层混凝土中的裂缝。最后,给出了UHTCC/RC复合梁在实际应用中的建议。     

A Stress Singularity Approach for the Prediction of Fatigue Crack Initiation in Adhesive Bonds. Part 1: Theory

Since crack initiation in adhesive bonds tends to occur near the interface corners where the stress fields are singular, we define a fatigue initiation criterion using stress singularity parameter, Q (a generalized stress intensity factor) and the singular eigenvalue, λ.

Hattori et al., successfully used a generalized stress intensity factor to characterize the static strength of bimaterial interfaces. We show that this criterion is only appropriate for situations in which the adhesive contact angle is no larger than 90° and the modulus ratio (adhesive to adherend) is smaller than 0.1. Fortunately, these conditions are often met in real joints, permitting the use of a single eigenvalue approach. We then extend this criterion to the case of fatigue arising from mechanical, thermal, or hygroscopic cycling.

In preparation for Part 2 (experimental), the special case of an epoxy wedge on a flat aluminum substrate is considered. The singularity is analyzed both analytically and numerically. The scale of the region dominated by the singularity is found to be of the order of 100 μm. The size of the plastically yielded zone near the apex is found to decrease extremely rapidly as the stress intensity factor goes down, thereby increasing the applicability of the method at the low stress levels often encountered in fatigue.     

固体火箭发动机壳体脱黏缺陷的热波检测

基于热波技术,对固体火箭发动机复合材料壳体/绝热层脱黏缺陷进行检测研究,采用去除背景和分水岭方法对热图进行降噪、增强和分割处理,利用表面热斑区域的面积对缺陷尺寸进行估算,根据热图序列的时间特征计算缺陷的深度,并与声-超声检测结果进行比较.结果表明,热波技术检测速度快,20 s可对缺陷准确定位,检测结果直观;5 mm深的3个缺陷最佳检测时间均为7 s;缺陷深度通过材料参数和缺陷尺寸进行计算,且缺陷越大,误差越小;与声-超声技术相比,热波检测更适合进行定量分析.     

A Stress Singularity Approach for the Prediction of Fatigue Crack Initiation in Adhesive Bonds. Part 2: Experimental

Using the epoxy-aluminum wedge specimens defined and analyzed in Part 1, we measure the number of cycles required to initiate an interfacial fatigue crack near the apex, where the stress field is predicted to be singular. The eigenvalue, λ, and the generalized stress intensity factor, Q, are varied via the wedge angle, and via the beam deflection, respectively. Crack initiation is detected using a strain gage bonded near the tip of the wedge.

Following the methodology developed in Part 1, the fatigue data are then used to construct a fatigue initiation criterion characteristic of the bimaterial interface. This criterion is a 3-D surface, with the ordinate representing the generalized stress intensity factor and the two horizontal axes representing the number of cycles to initiation and the eigenvalue, respectively. Three key assumptions of the model are found to be satisfied in the specimens tested herein: (1) geometric imperfections at the apex are smaller than the singular region, (2) the plastic zones near the apex are also smaller than the singular region, and (3) the locus of initiation is near interfacial.

Finally, a thermomechanical analysis indicates that the residual thermal stresses generated during the fabrication process make a significant contribution to the critical stress intensity factor. With high T_g adhesives and under unfavorable conditions (high modulus, high CTE, poor adhesion), we predict that the residual stresses alone could be sufficient to cause debond initiation.