The effectiveness of stress relief features in austenitic drillcollar connections

Standards designs for stress relief features and unmodified joints in non-magnetic (austenitic) drillcollar connections are investigated using finite element stress analysis. An NC-61 connection containing API pin and box stress relief grooves and box boreback features are compared. In addition to the recognized problem of fatigue failure from critically loaded threads, instances of stress corrosion cracking in pin bores have focused attention on this region and the effect which the presence of a pin stress relief groove has on the stresses there. The results of the analyses confirm the failure sites noted in service, and predict that the pin stress relief groove gives considerable benefit in terms of reducing the pin last engaged thread peak stress (fluctuations in which can cause fatigue), but causes an unexpected increase in the maximum pin bore axial stress (which can drive stress corrosion cracking).     

Failure analysis of a final drive transmission in off-road vehicles

This paper presents a case study in failure analysis of a final drive transmission in an off-road vehicle. The failure involved a satellite gear mounting shaft that departed from the differential assembly as a result of fracturing of a retaining pin. An investigation of the mechanical condition of various transmission components, consisting primarily of visual (macroscopic) inspection, geometrical investigation and analysis of mechanical loads, led to the assignment of two principal causes of failure. Firstly, it was established that the retaining pins installed in the assembly were shorter than required, allowing them to shift in their guide holes and assume a single-shear position. Secondly, in this position they were loaded to failure in shear by abnormally high frictional forces acting at the shaft/satellite interface. These loads were attributed to severe usage and handling of the vehicle. The scope of this case study is broadened to include a review of failure incidents, that followed in additional transmissions containing short retaining pins. An account of actions taken to address the problem from a maintenance and reliability viewpoint is also included, as are further recommendations made to the operator.     

Full Length Symmetric Versus Partial Length Un-symmetric Pin Loading Failure and Analysis for Clevis Attachments

In this paper, testing failure of the clevis–pin attachments for full length symmetric versus partial length un-symmetric configuration is considered. Theoretically and analytically it can be shown that due to higher stress levels in the partial length un-symmetric pin clevis configuration failure occurs sooner than in a full length symmetric pin clevis configuration. However, here by placement of the two different configurations at opposite ends of one axial tensile test setup the theory was put in test. The test results also indicated that the partial length clevis–pin attachment fails sooner than the full length clevis–pin attachment. Experimental procedures are described here in this paper. Both theoretical and finite element analyses are performed to validate the failure.     

Stress and failure analysis of the crankshaft of diesel engine

In this work the failure analysis of the crankshaft of diesel engine was performed. Visual examination of the crankshaft fracture showed that beach marks, typical for fatigue failure were observed. Additional observations of the crack initiation zone indicated that crack origin was not covered by material defects or corrosion products. Performed hardness test of the fractured crank pin showed that large HRC values were observed in central part of the pin only. On the corner of cylindrical pin surface where the crack origin was located the hardness of material was much smaller. In order to explain the reason of premature crankshaft damage, the finite element method was utilized. The results of nonlinear static analysis showed that during work of the engine with maximum power the high stress area was located in crack initiation zone. Based on results of performed investigations it was concluded that the main reason of premature fatigue failure was high-cycle fatigue of the material in external zone of the crank pin where the small structural radius was designed. In final part of the work the recommendations for increase of the fatigue life of analyzed crankshaft were formulated.     

预氧化Cf/SiC陶瓷基复合材料及其构件的抗疲劳特性研究

采用在线销钉集成技术实现了二维C_f/SiC复杂构件的近尺寸成型,并考察预氧化C_f/SiC销钉集成构件的高周疲劳寿命及破坏模式。实验结果表明:C_f/SiC构件在不同激振加速度条件下均表现为由销钉断裂所引起的整体分层破坏,层板连接处为C_f/SiC构件的振动疲劳薄弱部位。通过ANSYS振动应力分析和微观组织分析可以推论出,疲劳试验时,裂纹容易沿着层板间的基体扩展,在基体开裂失效后,全部应力施加于销钉处,最终在疲劳应力作用下销钉发生断裂,导致构件整体分层破坏。     

Study on the stress characteristic and fatigue life of the shredder pin

The hammer shredder is the key equipment for cyclic utilization of retired car bodies. The axes' pin is the main component of the shredder, but it is damaged easily. To improve the shredding efficiency and lengthen the changing life of the shredder pin, it is significant to study its stress characteristic and the fatigue life. In this article, the complex force conditions of the shredder pin at the normal working condition were studied briefly by mechanics analysis method. The stress characteristics and fatigue life of the pin were analyzed by the finite element transient analysis method. The maximum stress distribution law of the shredder pin was found and the fracture mechanism of the retired car bodies was revealed. Furthermore, the reliability of the simulation results was verified by the experiment. It was found that when the pin rotates around the main shaft counterclockwise, the maximum stress of the pin at 0° of the main shaft is higher than other positions. Additionally, along the axial direction, the maximum stress occurs at the cross section at a distance of 2/9 of the pin length from the pin head and at 0° of this section, which orientation is made when the pin is at 270° of the main shaft. Comparing four working modes, it was found that the working life of the shredder pin could be doubled by changing the sides of the pin and rotate it along its axes by 180°.     

RTTS封隔器中心管外螺纹接头断裂分析

采用宏观检验、化学成分分析、力学性能测试、金相检验、断口分析和有限元计算等手段对一φ60．4mm封隔器中心管外螺纹接头断裂的原因进行了分析。结果表明：封隔器中心管外螺纹接头断裂失效模式为外螺纹接头第一完整扣根部过载拉伸断裂,是在高压射孔作业时（以及射孔枪爆炸后形成低压的瞬间）中心管外螺纹根部应力值已达到或接近材料的屈服强度,进而出现的塑性屈服破坏。     

Optimum Design of a Ceramic Tensile Creep Specimen Using a Finite Element Method

An optimization procedure for designing a ceramic tensile creep specimen to minimize stress concentration is carried out using a finite element method. The effect of pin loading and the specimen geometry are considered in the stress distribution calculations. A growing contact zone between the pin and the specimen has been incorporated into the problem solution scheme as the load is increased to its full value. The optimization procedures are performed for the specimen, and all design variables including pinhole location and pinhole diameter, head width, neck radius, and gauge length are determined based on a set of constraints imposed on the problem. In addition, for the purpose of assessing the possibility of delayed failure outside the gage section, power-law creep in the tensile specimen is considered in the analysis. Using a particular grade of advanced ceramics as an example, it is found that if the specimen is not designed properly, significant creep deformation and stress redistribution may occur in the head of the specimen resulting in undesirable (delayed) head failure of the specimen during the creep test.     

A study on axial cracking failure of drill pipe body

Frequently happening drill pipe failure accidents in oil and gas wells not only affect drilling speed, but cause enormous economic losses and many safety issues. Most of these accidents are transverse cracking of drill pipe body and pin thread or axial cracking of box thread. Based on the axial cracking failures of drill pipe body in an ultra-deep well in China, this paper give a systematic analysis of axial cracking failure in consideration of service condition, material quality and stress corrosion mechanism. Measurement and inspection are performed on macroscopic and microscopic morphology of crack surface, corrosion products and circumferential residual stress. Then stress corrosion cracking experiments against hydrogen sulfide is conducted. Finally, the critical stress value for sulfide stress corrosion cracking of the drill pipe material is obtained, and the mechanisms of axial cracking failure and corresponding preventive measures are proposed.     

S135钻杆内螺纹接头胀扣失效分析

本文对某油井发生的Ф127mmS135钻杆内螺纹接头胀扣失效事故进行了调研，并对其胀扣失效原因进行分析。结果表明，钻杆接头的材质符合行业标准要求；钻杆内螺纹接头胀扣失效的原因是外螺纹接头密封台肩面倒角直径过小，井下钻柱扭矩过大。内螺纹接头密封台肩面承受的接触压力超过材料屈服强度，导致内螺纹接头密封台肩面下陷，外螺纹接头密封台肩面进入内螺纹接头镗孔段，致使内螺纹接头发生胀扣失效。     

Failure analysis of a large ball valve for pipe-lines

In this work the failure of a sub-sea ball valve, used in an oil-piping line, is analysed. The valve was of the same type and material already used for the construction of valves that were worked in service without any problem. The valve failed in the first pressure cycles during the preliminary laboratory tests, although the applied pressure was less than the design value. Metallographic and microstructural analysis of the fracture surfaces performed by means of optical and scanning electron microscope (SEM), residual stress and hardness measurement, tensile, toughness and Charpy tests, were executed in order to identify the causes of the failure. The results allowed assessing that the failure was due to two concomitant factors: a severe notch effect and an incorrect thermal treatment.     

引爆装置长期储存失效研究

为提升火工品的作用可靠性,探索储存环境对火工品性能的影响,依据有关标准对某引爆装置进行了长期储存试验。试验结果显示,该引爆装置在高温储存试验后出现了电阻超差现象。采用故障树分析法对失效模式与失效机理进行了分析。研究表明,长期的湿热环境引起了金属焊锡丝、桥丝、脚线界面应力的差异,使得虚焊焊点瑕疵放大,导致电阻超差,从而失效。     

Stress and strength analysis of pin joints in laminated anisotropic plates

Mechanical joints in composites can be tailored to achieve improved performance and better life by appropriately selecting the laminate parameters. In order to gain the best advantage of this possibility of tailoring the laminate, it is necessary to understand the influence of laminate parameters on the behaviour of joints in composites. Most of the earlier studies in this direction were based on simplified assumptions regarding load transfer at the pin-plate interface and such studies were only carried out on orthotropic and quasi-isotropic laminates. In the present study, a more rigorous analysis is carried out to study pin joints in laminates with anisotropic properties. Two types of laminates with (0/ + ₄/90)_s and (0/ ± ₂/90)_s layups made out of graphite epoxy T300/5208 material system are considered. The analysis mainly concentrates on clearance fit in which the pin is of smaller diameter compared to the hole. The main aspect of the analysis of pin joints is the changing contact between the pin and the plate with increasing load levels. The analysis is carried out by an iterative finite element technique and a computationally efficient routine is developed for this purpose. Numerical studies indicate that the location and magnitude of the peak stresses along the hole boundary are functions of fibre angle and the overall anisotropic properties. It is also shown that the conventional assumption of cosine distribution for the contact pressure between pin and the plate in the analysis lead to underestimation of bearing failure load and overestimation of shear and tensile failure loads in typical (0/90₅)_s cross-ply laminates.     

Analysis of a modified microbond test for the measurement of interfacial shear strength of an aqueous-based adhesive and a polyamide fibre

The microbond test was used to measure the interfacial shear strength (IFSS) between a polyamide fibre and a water-based polyurethane. Due to the low viscosity of the water based polyurethane, the droplet could not be formed using a conventional preparation method. A disc shaped microbond droplet forms when an aqueous-based colloidal polymer adhesive was deposited onto the pin hole in a mounting card with a vertical polyamide fibre in the middle after drying and curing at an elevated temperature. Since the droplets were formed with a disc shape, which differs from the conventional ellipsoid, a finite element analysis of the stress distribution at the interface for these contrastingly shaped droplets were calculated and compared. The stress analysis showed that the interfacial shear stress profiles were well matched for both providing confidence that the disc-shaped droplets could be used for interfacial analysis. The microbond test using a disc-shaped droplet was used to study the influences of silane treatment and plasma treatment on the interfacial shear strength between a polyamide fibre and an aqueous deposited polyurethane. The interfacial shear strength of the fibre after plasma treatment was 10.3 MPa, much higher than that of the control and the silanised fibres, 5.2 MPa and 5.4 MPa respectively. The results showed that the microbond test could be used to investigate the interfacial properties of the polyamide fibre and water-based polymer adhesive.     

Numerical predictions and experimental measurements of residual stresses in fatigue crack growth specimens

Controlling macro residual stress fields in a material while preserving a desired microstructure is often a challenging proposition. Processing techniques which induce or reduce residual stresses often also alter microstructural characteristics of the material through thermo-mechanical processes. A novel mechanical technique able to generate controlled residual stresses was developed. The method is based on a pin compression approach, and was used to produce well-controlled magnitudes and distributions of residual stresses in rectangular coupons and compact tension specimens typically used in fatigue crack growth testing. Residual stresses created through this method were first computationally modeled with finite element analysis, and then experimentally reproduced with various levels of pin compression. The magnitudes and distributions of residual stresses in experimental specimens were independently assessed with fracture mechanics methods and good correspondence was found between residual stresses produced using the pin compression and processing techniques. Fatigue crack growth data generated from specimens with low residual stresses, high residual stresses resulting from processing, and high residual stresses introduced through the new pin compression technique were compared and validated. The developed method is proposed to facilitate the acquisition and analysis of fatigue crack growth data generated in residual stresses, validate residual stress corrective models, and verify fatigue crack growth simulations and life predictions in the presence of residual stresses.     

飞机操纵系统链条销轴断裂分析

某型飞机操纵系统链条销轴在使用中断裂。采用化学成分分析、外观检查、断口分析和表面质量检验等方法对断裂销轴进行了分析,又对有裂纹的销轴与断裂销轴进行了对比分析。结果表明：销轴表面存在原始缺陷,加上链条链板在长期使用中的磨损使得链板间隙增大,导致销轴承受剪切力的同时又承受弯曲载荷,最终导致销轴发生疲劳断裂。     

某带泡沫护帽的筒装导弹跌落仿真分析

目的验证某肩扛发射的筒装导弹在0.5 m跌落工况下聚氨酯泡沫护帽的缓冲效能。方法对筒弹进行0.5 m无损跌落试验,发现挡销块被剪切破坏,通过固定在弹体上的加速度传感器,得到弹体加速度数据;然后通过有限元仿真软件Ansys/LS-DYNA模拟筒装导弹的跌落过程,分别得到挡销块应力分布及弹体加速度数据。结果挡销块某区域应力超过其材料强度极限,从而发生单元失效,与试验现象一致;弹体在弹轴方向上的加速度最大值为200g,与试验值183g的误差为9.3%,表明建立的仿真模型合理有效。根据此模型对提出的2种改进优化方法的有效性进行了仿真验证。结论通过试验与仿真对比建立合理有效的有限元仿真,验证了更改挡销块材质及加厚护帽,均可满足在0.5 m跌落环境下的强度要求,为产品下一步的改进优化提供了有效建议,可提升产品的研制效率,节约试验成本。     

An equivalent uniaxial fatigue stress model for analyzing landing gear fuse pins

We study the biaxial stress state conditions in landing gear fuse pins in the fuse groove. This biaxial state comprises a combination of shear stresses which are usually the largest stresses in the fuse pin by design, and compressive stresses which keep the half-section of the fuse pin in equilibrium. Conventional fatigue analysis techniques use an equivalent uniaxial stress, based on the Mises stress of a pure-shear condition. The respective predicted fatigue damages are much higher than those obtained from fuse pin cyclic tests. A new equivalent uniaxial fatigue stress model is proposed that includes the additional compressive stress as a relief on the fatigue damage in the fuse groove, thereby explaining the observations from fuse pin tests. The model is used in conventional uniaxial strain-life fatigue software (Goodrich Aerospace’s Fatigue Life V2) to predict the fatigue damage on a landing gear fuse pin with a sample load spectrum. The results are then compared to the pure shear model, and to a biaxial finite element fatigue analysis. As compared to the equivalent Mises model, the proposed model provides less conservative estimation of the fuse pin fatigue life, the latter value being higher than that provided by the two-dimensional finite element calculation. __________ Translated from Problemy Prochnosti, No. 3, pp. 85–98, May–June, 2006.     

Investigations on fretting fatigue in aircraft engine compressor blade

An investigation of several cracked blade tangs in the military aircraft engine compressor was conducted to identify the root cause of the failure. These cracks were found during the scheduled maintenance with fluorescent penetration inspection. The engine compressor blade made of Ti–6Al–4V is attached to compressor rotor by means of inserting retaining pin through rotor and blade tang. By analyzing the fracture surface of the failed blade tang, it is found that the crack in the blade tang was initiated by fretting fatigue and propagated under low cycle fatigue. Stress analysis of the blade using a non-linear finite element method is coincident with the results of fractography. The clearance between retaining pin and tang hole caused small amplitude of sliding motion leading to fretting wear during engine operation. Consequently, the damaged area due to fretting wear acts as a stress raiser inside tang hole and contributes to accelerate fretting fatigue.     

盘形悬式瓷绝缘子钢脚结构的尺寸优化

对绝缘子各部分的应力求解能够清楚地了解到绝缘子的结构性能,优化它的各部分形状对于降低高压输电线路的工程造价具有重要的意义.根据盘形悬式瓷绝缘子轴对称结构的特点以及轴向拉伸载荷的性质,将其转换为二维问题,利用有限元分析软件ANSYS,对其进行静力分析,并在此基础上提取结果建立优化参数,以钢脚的体积作为目标函数对绝缘子进行尺寸优化设计.结果显示每一设计参数以及钢脚的体积都有适量的减小,通过计算得到每只钢脚节约的钢材使用量为25.12 g.因此,对绝缘子进行分析和优化具有很重要的意义,不仅验证了结构的合理性,同时也使得钢脚的体积减小,为企业节省了可观的原材料,取得很好的经济效益.