压缩机连杆断裂失效分析

某炼油厂焦化装置富气压缩机连杆发生断裂。采用化学成分分析、金相检验、力学性能测试和断口分析等方法对断裂连杆进行了分析。结果表明,在交变栽荷的作用下,连杆的小头孔内应力集中处产生微裂纹并成为裂纹源,然后发生裂纹扩展,最终导致连杆小头处发生疲劳断裂。     

发动机连杆螺栓断裂原因分析

某汽车发动机连杆螺栓在发动机台架耐久试验中发生断裂。通过宏观检验、化学成分分析、扫描电镜分析、金相检验、能谱分析等方法,对螺栓的断裂原因进行了分析。结果表明:该连杆螺栓断裂模式为多源疲劳断裂;裂纹内部存在大量的磷和锌元素,说明在搓丝工序时螺栓已经产生了微小裂纹;在后期的磷化处理中,磷化液渗入微小裂纹中;台架耐久试验过程中裂纹逐步疲劳扩展并导致螺栓断裂。     

船用柴油机曲轴连杆断裂原因

某船用柴油机运行约1 000 h后其曲轴连杆发生断裂。采用宏观观察、化学成分分析、力学性能测试、粗糙度检测、金相检验等方法,对该连杆的断裂原因进行分析。结果表明：该连杆的断裂性质为疲劳断裂,裂纹起源于过渡圆弧段,引起断裂的主要原因为过渡圆弧段处加工粗糙度较差,且局部曲率偏大,导致该处应力集中程度增大,从而引起疲劳裂纹的萌生和扩展,最终使连杆发生断裂。     

波音737-500飞机前缘襟翼操纵连杆断裂分析

对波音737-500型飞机2根前缘襟翼操纵连杆断裂进行了断裂性质、断裂原因分析,分析结果表明襟翼操纵连杆属于疲劳断裂,疲劳裂纹的产生与变截面及齿底应力集中有关.     

45钢连杆锻件断裂分析

采用化学成分分析、金相检验及生产现场检测等方法对某批模锻连杆在喷丸过程中出现断裂的原因进行了分析.结果表明,连杆的锻造温度偏高,在未经正火处理就直接进行调质处理,其中淬火保温时间不够,连杆心部仍保留原始的锻造组织,造成连杆边缘和心部的组织内外应力差异增大,导致在冷却过程中产生裂纹.由此说明连杆在喷丸前已存在裂纹.     

发动机连杆断裂原因分析

某发动机连杆在轿车行驶过程中发生断裂。采用化学成分分析、硬度测试、金相检验和断口分析等方法对连杆断裂的原因进行了分析。结果表明:连杆的断裂属高周疲劳断裂。雨水随空气进入燃烧室,压应力过载,导致连杆弯曲变形并最终发生疲劳断裂。     

基于数值仿真的连杆裂解加工缺陷分析

为提高发动机连杆裂解加工质量和优化裂解工艺,针对实际生产中经常出现的一系列裂解缺陷,采用数值仿真方法对连杆断裂剖分启裂时的塑性区应力场、塑性位移场进行了研究,从工艺和裂解材料的角度分析了爆口与掉渣现象,并通过位移场定量分析了断裂剖分中的椭圆度问题.研究与分析结果表明:连杆断裂剖分的塑性区应力分散集中造成启裂点不唯一,且分散分布是裂解过程中产生夹屑、台阶与裂纹分叉等缺陷的主要原因;针对不同种类的裂解缺陷提出了相应的预防或改进措施,从而降低裂解缺陷、优化裂解质量.     

汽车悬架稳定杆连杆支架的疲劳仿真分析及结构优化

针对某型车辆常规耐久性试验过程中稳定杆连杆支架出现断裂的问题,对稳定杆连杆支架进行疲劳寿命分析和结构优化.首先运用ANSYS软件建立稳定杆连杆支架的有限元模型;然后基于静态有限元疲劳分析方法对连杆支架进行强度分析计算,并依据强度分析结果对稳定杆连杆支架进行疲劳寿命预测分析;其次根据等强梁理论对稳定杆连杆支架进行结构优化,支架截面由原来的等截面改为变截面,并对优化后的结构进行疲劳寿命预测;最后通过疲劳台架试验和裂纹断口分析,验证仿真分析结果.通过台架试验和仿真结果的对比可以得出,稳定杆连杆支架优化前后其疲劳寿命预测准确,优化后结构疲劳寿命符合预期.     

柴油机连杆盖及连杆螺栓断裂分析

采用化学分析,金相检验及力学性能测定方法对汽车柴油机在运行中发生的连杆盖及上、下螺栓的早期断裂进行了分析。结果表明,连杆盖首先发生疲劳断裂,随后导致连杆螺栓的断裂,而这种断裂既与应力有关,又与零件的加工工艺有关。     

20CrMo连杆断裂失效分析

采用光学金相和电子探针分析仪等分析手段，对20CrMo嘉陵摩托车连杆的断裂进行了分析。结果表明：连杆在热处理过程中在其表面层形成了粗大的马氏体针状组织是造成断裂的主要原因，并在其显微断口上形成沿晶断口。     

Transient Elastic Impact Response of Slender Graphite Rods

Graphite rods are manufactured by extruding the mixture of calcined petroleum coke and coal tar pitch into the desired shape and baking the cooled specimens at about 800°C. Cracking can occur in rods during the manufacturing process. It is useful to be able to detect the presence of such cracks in the rods prior to their being machined and put into use as electrodes or cathodes or thermal insulator. In an effort to develop a nondestructive testing approach to evaluation of the rods, transient elastic impact was determined for slender rods. Theory for solid, slender rods provided an important starting point for this work. Subsequently, numerical models were developed and simulation was used to determine the response of rods containing cracks. Experiments on graphite rods with and without cracks were conducted and the internal condition determined from the recorded signals. The rods were then cut lengthwise to reveal the internal condition and verify the predicted results. In all cases the knowledge gained from simulation allowed for the presence of cracks to be detected.     

Experimental and Numerical Failure Analysis of Vertical Rods Used in Paper Molding Machine

A failure investigation has been conducted on the vertical rods which used in paper molding machines. The vertical rods are important elements for paper molding machines to support press forces. Each of the vertical rods that are analyzed was broken into two parts in service. The two failed vertical rod specimens were exposed to various tests such as visual inspection, chemical analysis, hardness measurement, metallographic examination with optical and scanning electron microscopes. A stress analysis was also carried out by the finite element technique for the determination of highly stressed regions on the vertical rods. The results indicated that due to high stress concentrations, the vertical rods failed by fatigue with cracks initiated at the surface close to the shoulder region which has sharp corner.     

An investigation of brittle fracture of composite insulator rods in an acid environment with either static or cyclic loading

The effect of static and cyclic loading conditions on the stress corrosion cracking of unidirectional glass reinforced polymer (GRP) rods used in composite high voltage insulator has been investigated. A series of stress corrosion experiments have been performed on unidirectional E-glass/modified polyester composite rods. The rods have been subjected to mechanical tensile static and cyclic stresses in the presence of a nitric acid solution. The stress corrosion fracture process in the rods was monitored using acoustic emission techniques. The experimental loading conditions simulated possible in-service loadis for composite suspension insulators. The results obtained in this study showed that the brittle fracture process can be generated in the rods when subjected to relatively low tensile stresses in the presence of a nitric acid solution. The morphology of the experimentally generated brittle fracture cracks in the rods closely resemble those from in-service failed composite suspension. It has also been shown in this research that low frequency, low amplitude vibrations in tensile loads can significantly accelerate the fracture process. It appears that the brittle fracture cracks in the rods generated under cyclic loads are less planar in nature in comparison with the cracks formed under static conditions. It has also been found that the acoustic emission generated during the stress corrosion fracture process in the rods is sensitive to the placement of the transducers. However, reasonably good correlation between the stress corrosion crack growth rates and acoustic emission has been attained.     

静电除尘器星形线材的组织与性能

研究了国产仿YUS110及进口SUS316L两类静电除尘器不锈钢星形线材的显微组织、静拉伸性能与疲劳特性.结果表明,两类线材的屈服强度相同,但进口线材的疲劳强度明显高于国产线材;进口线材的疲劳扩展辉纹较国产线材明显细密,且二次裂纹较多较深.分析认为这与两类星形线材的材质及其成形加工造成的形变强化效应有直接关系.     

钨合金正挤压棒坯溶剂脱脂缺陷的形成与控制

粉末挤压成形技术是制备大长径比钨基高比重合金棒材最有效的方法之一,而脱脂过程直接影响着样件缺陷控制及合金力学性能的改善效果.探讨了Φ12 mm和Φ15 mm钨基合金正挤压棒坯溶剂脱脂缺陷的形成及其控制,采用可控恒温仪调控溶剂脱脂速率,利用数码相机和扫描电镜分别对棒坯表面形貌和微观结构进行观察.结果表明：钨基合金正挤压棒...     

Enhancing mechanical properties and avoiding cracks by simulation of quenching connecting rods

If the service load onto a part is heavy, e.g. for the connecting rods of high-power diesel engine, high mechanical properties are critically required. When quenched in oil, it cannot meet the requirements. While quenching it in aqueous polymer quenchant or water, the mechanical properties could be higher than that required but cracking would occasionally happen. In order to obtain the expected mechanical properties and avoid cracking by quenching and tempering, the heat transfer coefficients of quenchants were measured and calculated, and the quenching process of connecting rods was simulated by using finite element method so that its processing parameters were determined. The results show that the mechanical properties of the treated rods have been enhanced and cracks were avoided.     

基于神经网络的超声导波钢杆缺陷识别

利用基于BP神经网络的缺陷识别算法,从不同实验条件下获得的信号样本中抽取特征量,对钢杆中不同深度和位置的径向裂纹进行了识别。首先,采用频率为235kHz激励轴对称纵向模态导波对钢杆中的径向裂纹进行了检测。实验表明,在235kHz时获得的超声导波信号含较单一的L(0,2)模态,避免了用L(0,1)模态检测小尺寸缺陷时检测能力较弱的问题,又减少了用轴对称纵向高阶模态检测缺陷时模态较多不易分辨缺陷回波的现象。其次,利用算法对钢杆中的径向裂纹进行识别。结果表明,在已有实验样本数下,缺陷识别算法从整体上很好地识别不同深度和位置的裂纹,识别正确率稳定在87%。     

Cracking in cement paste induced by autogenous shrinkage

Detection and quantification of microcracks caused by restrained autogenous shrinkage in high-performance concrete is a difficult task. Available techniques either lack the required resolution or may produce additional cracks that are indistinguishable from the original ones. A recently developed technique allows identification of microcracks while avoiding artefacts induced by unwanted restraint, drying, or temperature variations during sample preparation. Small cylindrical samples of cement paste are cast with steel rods of different diameters in their centre. The rods restrain the autogenous shrinkage of the paste and may cause crack formation. The crack pattern is identified by impregnation with gallium and analyzed by optical and scanning electron microscopy. In this study, a non-linear numerical analysis of the samples was performed. Autogenous strain, elastic modulus, fracture energy, and creep as a function of hydration time were used as inputs in the analysis. The experimental results and the numerical analysis showed that samples with larger steel rods had the highest probability of developing microcracks. In addition, the pattern and the width of the observed microcracks showed good agreement with the simulation results.     

Cracking due to Cu and Ni segregation in a 17-4 PH stainless steel piston rod

The 17-4 PH stainless steel is employed to produce piston rods in industry due to the high strength and toughness, good workability and nice corrosion resistance. In the present failure analysis, obvious long cracks were observed along the longitudinal direction on the surface of the commercial 17-4 PH stainless steel piston rod after heat treatment. The cracks were carefully looked into by observing the crack tip and characterizing the microstructure along the cracks. The results showed that the cracks were mostly initiated from the surface of the rod and propagated along the phase boundary between martensite and δ ferrite. The EDXA showed that the segregation of Cu and Ni should be responsible for the cracking after heat treatment. In order to define when the crack was coming into being, oxidation film along the crack was considered as a clue. The scrutiny of the oxidation film on the crack edge illustrated that the crack should be formed right in the heat treatment of aging.     

Cervical Stent Failure Analysis

Harrington rods failed after a short period in service. Metallurgical analysis showed (1) notches were present on the rods, (2) small cracks present in the bent regions of the rod, and (3) the fractures occurred at clamped locations. All of these conditions can shorten the fatigue life by eliminating the crack initiation stage of fatigue and allowing corrosion fatigue to occur.