Progressive Failure Analysis of Laminated Composite Plates With Two Serial Pinned Joints

This study presents experimental and numerical failure analyses for two serial pin loaded holes in unidirectional carbon fiber/epoxy resin composite laminates. The failure loads and failure modes of composite laminates are determined for different geometrical parameters and different stacking sequences. Three-dimensional ANSYS Parametric Design Language codes are developed in the ANSYS® finite element software. Hashin Failure Criteria and material degradation rules are used to determine failure loads and failure modes in the numerical analysis. Experimental and numerical results show that failure loads and failure modes were affected with geometrical parameters.     

Analysis of Defective Carbon-Epoxy by Means of Lock-in Thermography

Abstract

The attention of the present work is focused on the analysis of defects in carbonepoxy laminates. Different specimens are manufactured by varying the laminate orientation code, the weave type (preimpregnated or nonimpregnated), and the kind of defect. In particular, defects such as inclusions of spurious materials, delamination, and localized lack or excess of resin are artificially created to simulate the most probable kinds of damage occurring in carbon-epoxy products during manufacturing and/or in service. Nondestructive tests are performed by means of lock-in thermography.     

固定板断裂的失效分析

为了找出40CrMn钢固定板开裂的真正原因,利用扫描电镜、直读光谱仪、拉力机试验机、硬度计和金相显微镜研究了固定板的断口形貌、化学成分、力学性能和微观组织。结果表明:固定板的化学成分、显微组织、力学性能符合技术要求;裂纹起源于沉孔的倒圆角位置,裂纹源处无夹杂物,断口属于疲劳断裂。经过工艺追溯,沉孔倒圆角为R0.5,而图纸要求R4,倒圆角过小产生了高度的应力集中效应,导致出现早期断裂失效。再次生产的固定板沉孔圆角按照R4加工,未出现早期断裂。     

Multicontinuum Failure Analysis of Composite Structural Laminates

Damage in a composite typically begins at the constituent level and may, in fact, be limited to only one constituent in some situations. Accurate predictions of constituent damage at points in a laminate provide a genesis for progressively analyzing failure of a composite structure from start to finish. In this article we develop an efficient constituent-based failure analysis for composite structural laminates. Continuum-based (phase-averaged) constituent stress and strain fields are computed in a finite-element environment without a computational time penalty. Constituent stress-based failure criteria are developed and used to construct a progressive failure algorithm in which one constituent is allowed to fail while the other constituent remains intact, e.g., matrix cracking. The proposed failure algorithm was used to predict failure of a variety of laminates under uniaxial and biaxial loads. The results were shown to be superior to comparable single-continuum failure analyses and in good agreement with experimentally determined failure loads.     

复合板基层厚度对激光焊接头腐蚀性能的影响

目的通过探索基层金属厚度对复合板激光穿透焊接的影响规律,分析其影响度与焊接速度、激光功率的差别,为双金属复合材料激光穿透焊接提供更多的技术支撑。方法以焊接速度、激光功率和基层金属厚度为变量,设计了三因素三水平的正交实验,对X65/DSS2205层状双金属复合材料进行激光穿透焊接实验,对不同焊接条件下接头的显微组织进行观察分析,采用EDS面扫方法对焊缝复层区进行成分扫描,测量接头复层侧动电位极化曲线,并比较了基层金属厚度的影响度较焊接速度与激光功率的大小。结果双金属复合板激光穿透焊接接头显微组织在厚度方向存在明显的分层;基层金属厚度为1.2 mm时,复层贵金属元素保留量最大;随着基层金属厚度的减小,接头综合耐腐蚀性能提高;基层金属厚度对接头耐腐蚀性能的影响小于焊接速度和激光功率2个变量;焊接速度为2.5 m/min,激光功率为3500 W,基层金属厚度为0.8 mm时,接头耐腐蚀性能最优。结论基层金属厚度对于复合板激光穿透焊接接头的焊缝复层元素含量、以及接头复层一侧耐腐蚀性能都有较为明显的影响,但相比于焊接速度与激光功率,其影响度相对较小,因此在进行复合板激光穿透焊接时,在选定基层金属厚度后,仍要对焊接速度和激光功率进行优化工艺设计。     

Analysis of Defective Carbon-Epoxy by Means of Lock-in Thermography

The attention of the present work is focused on the analysis of defects in carbon-epoxy laminates. Different specimens are manufactured by varying the laminate orientation code, the weave type (preimpregnated or nonimpregnated), and the kind of defect. In particular, defects such as inclusions of spurious materials, delamination, and localized lack or excess of resin are artificially created to simulate the most probable kinds of damage occurring in carbon-epoxy products during manufacturing and/or in service. Nondestructive tests are performed by means of lock-in thermography.     

挤出机推力轴承盘失效分析

挤出机推力轴承服役几个月推力盘便发生了断裂失效。采用宏观分析、化学成分分析、硬度测试、金相检验和断口扫描电镜分析等方法对断裂的推力盘进行了分析。结果表明：该轴承推力盘失效形式为起源于次表层的接触疲劳,装配和使用过程造成推力盘过载是导致其早期接触疲劳失效的主要原因。     

旋转复合材料板的动力学性能研究

研究了旋转复合材料板的动力学建模方法.基于经典层合板理论,建立了旋转复合材料的动力学方程,考虑了传统建模方法忽略的二次耦合变形量.采用有限单元法对板进行离散,利用Iagrange方法建立了动力学方程.将该模型计算结果与传统模型计算得到结果比较,发现在转速较低的情况下,两者比较吻合,随着转速的提高,结果出现明显差异.建立了转动复合材料板的频率方程,研究了板的参数对其动力学性能的影响,转动板的一阶频率随着中心刚体半径以及转速的增加而增加,随着铺层角的增大而减少;对于正规对称正交层合板,随着铺层数的增加,其角点的最大变滗形也随着增加.     

复合材料层合板机械连接处失效过程的数值模拟

考虑了损伤累积、刚度退化和破坏准则,研究了带孔洞复合材料层合板受面内载荷作用的失效过程.应力分析建立在三维有限元模型基础上,借助有限元商业软件ANSYS中的参数化设计语言APDL,考虑材料损伤累积和刚度退化,采用迭代算法,实现了层合板机械连接处的破坏过程模拟.为验证三维有限元模型的有效性,将模拟计算得到的孔边应力分布与文献中的结果进行了比较,两者十分吻合.进一步计算了层合板的位移一挠度曲线,并与实验结果进行了比较,验证了数值模拟的正确性.     

某型飞机作动筒关节轴承开裂分析

通过断口及成分分析方法对关节轴承失效进行了分析.结果表明,关节轴承失效属于应力腐蚀断裂.     

Failure Analysis of High Density Polyethylene Butt Weld Joint

This article discusses a detailed failure analysis conducted on high density polyethylene which acts as the liner of composite compresses natural gas cylinder. Leakage from the cylinder was observed after about 2000 cycles of hydrostatic pressure testing at 250 bars. Visual inspection revealed that the leakage occurred from the circumferential fusion joint between the cylinder and dome section. The cylinder and dome sections were produced from different techniques and joined together by using a heated tool butt welding process conducted by a local manufacturer. The joined components work as an integral part. The investigation was carried out using various techniques including mechanical, thermal and metallurgical examination. Fractography of the failed joint surface showed stepwise marks typical of a fatigue failure. Mechanical testing results showed that the strength of dome section was significantly lower than that of the cylinder section. Moreover, both the tensile and fatigue strength of joint was also almost half that of the cylinder. The fracture surface of the broken welded joint showed brittle failure. The melting points of both the cylinder and the dome sections were found almost same by differential scanning calorimeter but large difference was found between the melt point indexes of both sections. The results suggested that the failure was actually a stress cracking via a process of slow crack growth, which occurred due to use of a dome material having inferior properties and very high melt flow index. These properties inhibited proper fusion and resulted in a poor weld joint. Consequently, the weld joint of lower strength eventually failed in macroscopically brittle manner upon cyclic loading.     

Characterization and Failure Analysis of an Automotive Ball Joint

This case study describes the failure analysis of an automotive lower ball joint that fractured under normal driving conditions. Through spectroscopy, the material was determined to be SAE-AISI 5135H steel. The metallographic examination revealed a tempered martensitic structure, and hardness measurements radially across the surface of the cut ball stud suggested that the stud was through hardened. Scanning electron microscopy of the fracture surfaces indicated fatigue as the main failure mechanism. Finite element analysis was used to analyze the performance of the part under a normal loading condition. A detailed fatigue analysis to determine the effect of various loads on the life of the ball joint was completed using three methods: S-N curve approximation using hardness values, S-N approach using Basquin’s equation, and a linear elastic crack-growth model. The cause of failure was determined to be from surface cracks forming in the high stress concentration neck region where the ball and stud are joined. The presence of a small surface flaw in this region was shown to significantly reduce the fatigue life of the ball joint.     

透声复合船体板结构的声学性能分析

建立了垂直入射时复合船体板结构中前行波和回行波声压幅值在层间的传递矩阵,计算了该类复合结构的透声系数,并对典型夹芯板结构进行了分析,指出对于阻抗匹配层要降低材料的损耗因子,而对于阻抗失配层要降低厚度,才能显著提高复合板结构的透声性能,有助于水声复合材料的设计以及声学试验的数值验证。     

层合板螺栓连接的渐进失效分析

以三维渐进损伤理论为基础,采用ANSYS的二次开发语言,建立了复合材料层合板螺栓连接模型,在拉伸栽荷下对含孔复合材料板进行数值失效模拟计算．分析各铺层的失效过程和失效形式特点,得到层合板的初始失效栽荷和最终失效栽荷,为复合材料含孔板强化结构的研究提供一定参考．     

Fem Analysis of Progressive Failure for Composite Hypar Shells

Strength of Materials - The finite element method is used to to study progressive failure aspects of laminar composite skewed hypar shells with straight edges employing the eight-node isoparametric...     

钻杆接头台肩根部刺漏失效分析

通过力学性能测试、化学成分分析、金相检验和断口分析等方法对某井发生的钻杆接头台肩根部刺漏失效原因进行了分析。结果表明：材料冲击功低于标准要求,接头台肩根部受到严重腐蚀,形成大而深的腐蚀坑,在交变应力作用下,裂纹萌生于腐蚀坑底部,并迅速扩展,最终导致钻杆接头发生早期腐蚀疲劳失效。     

超声波振动激励下焊点失效分析与改进

为了解决管脚焊点在超声波焊接后出现的失效问题，研究用数值仿真的方法来进行建模分析，并提出改进方法。根据超声波能量转化形式，简化焊接系统模型，提出适合仿真的加载方法和边界条件，并根据热-力耦拿尊真尊温度场结果分析模型的可行性。针对具体的手机电池产品，建立超声波焊接系统整体三维有限元模型，利用仿真结果分析失效原因，提出减振措施并做实验验证。     

空调连接接头失效分析及预防

空调制冷连接接头在销售后出现钎料开裂泄漏故障。对故障的样件进行了力学性能试验、材料组织成分检测、失效分析、耐冲击安全系数分析。结果表明,耐运转冲击应力安全系数经计算仅为0．417,设计的安全系数不够导致焊料在冲击疲劳载荷下裂漏,是造成事故主要原因。经对设计结构优化调整为2．66,经模拟空调冲击载荷,进行20万次试验验证,可以达到售后运转6年的质量要求。     

Failure of Composite Materials

Abstract:  An overview is given of the state of the art of theories and procedures for predicting and analysing failure in composite materials. Of the scores of failure theories available, only those representative of each of the following categories are discussed: limit or noninteractive, interactive, and failure mode-based theories. The validity and applicability of the various theories are evaluated from the point of view of convenience of application and agreement with experimental results. Both lamina and laminate failures are discussed. In the case of ultimate laminate failure, a progressive damage scheme coupled with a failure mode-discriminating criterion is discussed. Special attention is given to textile composites where new three-dimensional experimental results are reported and a new interlaminar failure theory is proposed.     

Failure Analysis and Robust Optimization of an Exhaust Manifold Diffuser Plate

Diffuser plates in exhaust system manifolds are designed to provide uniform flow pattern within the manifold for maximum utilization of the catalytic converter substrate during high-temperature applications. In this paper, failure analysis of a diffuser which survived only 20% duration of a manifold crack test and various design optimization studies of the diffuser plate using computer-aided engineering (CAE) analyses are presented. During the manifold crack test, the failure occurred at the inner and outer periphery of the diffuser. Metallurgical failure analysis coupled with CAE thermal fatigue analysis of the component concluded that thermal fatigue was the root cause of the failure. The new recommended robust design showed considerable improvement in the thermal durability of the diffuser plate assembly.