Static and fatigue load performance of a gfrp honeycomb bridge deck

This paper investigates the performance of a glass fiber-reinforced polymer (GFRP) bridge deck under static and fatigue load cycles. The bridge deck has a sandwich panel configuration, consisting of two stiff face shells separated by a light-weight honeycomb core. The deck was manufactured using a hand lay-up technique. In this study, a full-size panel that had the same design as an actual bridge deck was tested. The experimental data are analyzed and compared to the results of finite element analysis. The data obtained have indicated that the failure of the system is governed by the delamination of the face shells from the honeycomb core, and the failure behavior is pseudo-ductile even though the material itself is brittle. Hence, the design of such a deck panel should be based on the shear strength of the face–core interface. However, the shear strength can depend significantly on the workmanship in the fabrication process. For design, if the interface shear strength can be reliably identified, the maximum shear stress should be no greater than 15% of the shear strength to avoid fatigue damage under the service load condition.     

含半椭圆表面裂纹圆柱壳体的三维热弹性动态断裂

研究了含轴向半椭圆表面裂纹的圆柱壳体在热应力与冲击载荷作用下的动态断裂情况,并应用所研制的三维动态断裂有限元程序进行了大规模的数值计算,确定了圆柱壳体的三维温度分布及热-力耦合下的动态应力强度因子,所得结果在一定程度上揭示了热-力作用下圆柱壳体的边界表面、裂纹面、物质惯性和弹性波的相互作用在结构动态断裂中的重要性。     

Failure Analysis of a Cracked Gasoline Engine Cylinder Head

This article presents a failure analysis on a gasoline engine cylinder head made of aluminum alloy, which has been used in passenger cars. During an endurance test, a crack initiated from the interior wall of a hole in the center of the cylinder head and then propagated through the thickness of the cylinder head. The metallurgical examinations are conducted in the crack origin zone. The results show that there are many casting pores due to poor quality of casting in the failed cylinder head which has certainly played a crucial role in initiating the crack. Finite element analysis of the cylinder head is performed to identify the stress components. Modeling of a bolt for the hole shows that the plastic stresses are occurred. Moreover, the lower strength of the material due to high assembly stress caused the failure in the cylinder head.     

Empirical,analytical and numerical approaches to failure analysis of a frictional power transmission composite roller

The current study investigated the impact of different parameters on the failure of a frictional power transmission mechanism composed of a steel tyre and a two-layer composite rotating roller. Empirical, analytical and finite element methods were employed to study the mechanism. As for the empirical approach, a few rollers were made with different materials for the outer layer of the composite driver roller in order to examine the probable causes of the failure. In addition, thermography was conducted to find the increase in the temperature due to the working conditions. Analytical formulations were also employed so, as to understand the correlation between stress distribution and deformation regime in the contacting parts. Moreover, through relating the analytical to the empirical data, a homogenous representative cylinder was defined as equivalent to the composite cylinder. In order to reveal the details of stress and deformation distribution inside the roller parts, numerical analysis was performed employing finite element method. The results of such modeling helped us understand the relationship between the tuneable parameters and output results. Furthermore, by relating FEM results to the empirical data, probable causes of the failures were explained. According to the interpretation of the results and the data obtained via the introduced approaches, a few suggestions were presented as applicable in designing proper two-layer composite rollers.     

Cone bit bearing seal failure analysis based on the finite element analysis

Failure analysis of cone bit bearing seals is important in reducing production cost and preventing in-service component failure. However, a generally accepted criterion for their failure has not yet been established because of complexities in both their material properties and the environment. In this study, a two-dimensional axisymmetric finite element analysis (FEA) numerical model was established. FEA software was developed based on the Mooney–Rivlin constitutive model of the rubber material, and the penalty function contact algorithm. The distributions of stress, strain and contact pressure were analyzed to establish their effect on failure. The locations and causes of the failure and preventive measures were determined by comparison with an actual failure case. It was found that stress concentration and uneven pressure distribution occur at the seal. Rubber rings are highly and unequally compressed. Metal ring structure mainly determines sealing performance. To reduce the occurrence of failure, the structure must be improved by: designing an appropriate angle-tapered metal ring end face structure instead of a plane to change the trend in pressure distribution, increasing the contact area of the metal ring end face to reduce contact pressure and make the contact pressure distribution more uniform to reduce sealing surface wear, reducing the radial thickness to reduce the compression of the rubber ring, and improving back support structures to reduce the stress concentration. Results from the study can prevent and minimize risk for future failures to increase bit life and reduce drilling costs.     

Consolidation and Warpage Deformation Finite Element Analysis of Filament Wound Tubes

This paper presents a process model for simulating the manufacturing process of prepreg filament wound composite tubes developed based on the finite element analysis. The model relates the process variables, such as degree of cure, viscosity, material property and temperature etc., to the parameters characterizing (residual stresses, warpage deformation) the composite tube and the mandrel. From the simulating results, several important trends in both the data and model are observed (1) Low temperature will go with low reaction rate and the reaction starts under low temperature will later compared with high temperature; (2) The results using CHILE model after demolding will smaller than the one using linear elasticity which assumes a stress-free prior to cool-down. After the mandrel (mold) is removed, some residual stresses, especially hoop stress will be released. (3) Remarkable stress concentration appeared in the transition zone between the boss and cylinder. In order to prevent the structural failure due to interlaminar shear or delamination, both the outer surface of the cylinder and the inner of the boss should have the same ply orientation angle.     

Uncoiler Assembly of Main Shaft and Segment Flate Finite Element Analysis

At present,the main method of finite element on the uncoiling machine main shaft or segment flate analysis is simplified equivalent to a separate analysis of various conditions,but this method is compa...     

温度作用对带铺装层钢桥面板疲劳效应的影响研究

以润扬大桥悬索桥为考察对象,基于实测结果研究了铺装层温度变化对钢桥面板两类焊接细节疲劳效应的影响特征。由于润扬大桥悬索桥疲劳分析模型计算单元数多且耗时大,首先利用模型参数敏感度分析方法确定钢桥面板疲劳效应简化分析模型中的敏感参数,然后利用敏感系数矩阵迭代法计算各个敏感参数的最优取值。在此基础上建立了带铺装层钢桥面板的疲劳效应简化分析模型,并考察了不同温度作用下两类典型焊接细节的疲劳效应。分析结果表明:1)两类焊接细节的日等效应力幅与钢桥面板温度存在较强的线性相关性;2)钢桥面板疲劳效应的简化分析模型为顺桥向支承在横隔板上、横桥向支承在顶板纵肋上的局部受力结构体系;3)带铺装层钢桥面板的疲劳分析方法能够准确计算车辆荷载和温度共同作用下焊接细节的疲劳效应。     

高温压力管道三通接头的应力应变分析及仿真

高温压力管道的爆管事故通常需要实时监控高温管道的薄弱部位的应力应变状况.选取高温管道的典型薄弱部位"三通接头"作为分析对象,在理论分析建模的基础上,运用有限元AYASYS分析软件,对三通接头高温管道稳态运行时的热应力应变状况进行了分析计算,确定出其高温工作时的应力分布状况以及最大应力部位.并相应地给出了二维应变花结构的高温应变片安装方案.     

Failure analysis and appropriate design of drill pipe upset transition area

In recent years, the drill pipe failures often happen in the case of ultra deep well drilling and complex geological conditions drilling. One of the main failure types is the stress concentration at the upset transition area of the drill pipe. Based on the elastic–plastic mechanics, finite element theory, and application of numerical simulation analysis for the actual mechanical properties of three-dimensional simulation analysis of drill pipe in the well, the finite element analysis (FEA) model of 5″ API standard drill pipe is established. The mechanical characteristic of API standard drill pipe upset transition area is simulated, which can provide a reasonable reference for the optimization of the size of new types 5″ drill pipe upset transition as well as the practical application. Based on the simulation model, the factors affecting the stress distribution of the drill pipe upset transition area are obtained, and the new type of upset is developed.     

环氧沥青铺装对钢桥面板受力影响试验研究

某悬索桥钢箱梁采用正交异性钢桥面板,运行数年后钢桥面板构件连接部位出现了4种疲劳裂纹,为考察新换环氧沥青混凝土铺装对疲劳敏感部位受力影响,建立了有限元模型,开展了长达6年的现场试验,试验涵盖原铺装、铺装铲除、新铺装三种状态,测试了疲劳敏感部位的受力及构件变形规律,开展了考虑温度影响的疲劳寿命改善效果分析研究。结果表明:6年试验期内环氧沥青混凝土铺装与钢桥面板组合受力处于稳定状态,在低温环境下,疲劳敏感部位1~4应力改善效果分别为80%、14%、32%、46%;4个疲劳敏感部位应力与温度线性关联,线性速率分别为?4.00、0.64、1.89、1.91;将实测应力统一至年均温度后,新铺装对部位1疲劳寿命相对改善较大,约提高了2.95倍,对部位4疲劳寿命改善次之,约提高1.64倍,对于部位2、3疲劳寿命改善效果不明显,高温环境下部位2、3开裂可能性仍较大。     

Failure analysis of gas turbine buckets

The failure of a gas turbine first stage bucket was investigated by visual inspection and finite element analysis. The failure of a major bucket cooling passage was a critical cause of the separation of a bucket segment and caused microstructural deterioration of the neighboring regions by serious thermal load. Changes of microstructural morphologies of the damaged buckets under the thermal and mechanical stress were observed. After coating stripping, the bucket surface condition was evaluated through visual inspection and finite element analysis. The TMF (thermal-mechanical fatigue) cracking of surface coatings on the suction and pressure sides of the bucket was described.     

Failure analysis of rolls with grooves

The failure analysis of rolls with grooves on a 3-high-roughing mill stand for hot rolling is presented. A detailed analysis of all the elements which influenced failure was carried out, namely, the cause of all failures was determined and all fracture surfaces are described; the rolling forces were determined by analytical and experimental methods; numerical analysis of the local stresses due to rolling forces was performed with the finite element method; stress time history of the individual local stress and stress spectrum were obtained from service loads; properties of the roll material (strength, hardness, toughness and ductility) were determined by experimental testing. Based on the results of investigation, the main causes of the failures are presented.     

Rubber covered rolls—the thermoviscoelastic problem. A finite element solution

The coupled thermomechanical behaviour of a layer of thermorheologically simple material bonded to a uniformly rotating rigid cylinder and indented by another rigid cylinder is studied by the finite element method. The various approximations necessary to reduce the problem to one of tractable size and the computational methods used are discussed in some detail. The complete thermal, deformation and stress fields may be computed. Some results, computed for a grid using ‘rectangular’ elements, presented graphically include the temperature distribution, the stress distribution near the bond surface, the contact pressure distribution and the asymmetric surface deformation of the rubberlike layer.     

An investigation of the repetitive failure in an aircraft engine cylinder head

Cylinder head (CH) failures in aircraft piston engine may have serious or fatal consequences to the safety of the crew and the aircraft. Moreover, when failure becomes undoubtedly repetitive and critical resulting in loss of aircraft, destruction of properties, and first and foremost loss of human lives, the cause of the failure requires to be investigated using a scientific approach. Therefore, the aim of this study is to investigate and identify the root cause of a repetitive premature failure in an aircraft engine CH.The piston engine of the training aircraft Utva-75 has malfunctioned during the flight due to the cracking of its aluminum cast CH. It has been the second engine failure of this type of aircraft due to the cracking in the CH in a very short span of time. From the visual examination of the mating fracture surfaces, it has been possible to observe typical beach and ratchet marks indicating the occurrence of fatigue failure. The crack has initiated from multiple origins located on the inner flange fillet on the exhaust side of the CH. Further examinations by using scanning electron microscopy as well as energy dispersive spectroscopy and metallography have shown that the fatigue had promoted from pre-existing material defect due to a high concentration of shrinkage pores at the initiation crack site and can be most likely associated with the manufacturing process of casting. The stress analysis of the cylinder assembly, carried out by means of finite element analysis, has also confirmed that the crack origin was located at the most stressed area of the cylinder assembly i.e. on the inner flange fillet of the exhaust side of the CH.This case study, together with the other recently reported, has definitely confirmed the repetitive and therefore systematic problems with the CH of air cooled, horizontally opposed, aircraft piston engines.     

Transient heat conduction analysis in a piecewise homogeneous domain by a coupled boundary and finite element method

A coupled finite element–boundary element analysis method for the solution of transient two‐dimensional heat conduction equations involving dissimilar materials and geometric discontinuities is developed. Along the interfaces between different material regions of the domain, temperature continuity and energy balance are enforced directly. Also, a special algorithm is implemented in the boundary element method (BEM) to treat the existence of corners of arbitrary angles along the boundary of the domain. Unknown interface fluxes are expressed in terms of unknown interface temperatures by using the boundary element method for each material region of the domain. Energy balance and temperature continuity are used for the solution of unknown interface temperatures leading to a complete set of boundary conditions in each region, thus allowing the solution of the remaining unknown boundary quantities. The concepts developed for the BEM formulation of a domain with dissimilar regions is employed in the finite element–boundary element coupling procedure. Along the common boundaries of FEM–BEM regions, fluxes from specific BEM regions are expressed in terms of common boundary (interface) temperatures, then integrated and lumped at the nodal points of the common FEM–BEM boundary so that they are treated as boundary conditions in the analysis of finite element method (FEM) regions along the common FEM–BEM boundary. Copyright © 2002 John Wiley & Sons, Ltd.     

Coupled transient thermoelastic contact problems for axial cracks in hollow cylinders

A coupled transient thermoelastic behaviour of an axial-cracked hollow circular cylinder subjected to a sudden heating is investigated in this study. It is shown that surface heating may induce the compressive thermal stress near the inner surface of the cylinder which in turn may force the cracked surfaces to close together. Assuming that the existence of the crack does not alter the temperature distribution, we can divide this problem into two parts and solve it by the principle of superposition. First, the temperature and transient thermal stress distributions along the axisymmetric surface of the imaginary cylinder without crack are obtained by finite element implicit time integration method Secondly, the opposite sense of the stress distributions along the cracked surfaces, which is obtained previously, is treated as the traction boundary conditions; the contact length and contact pressure of the real cracked cylinder are obtained by modified elimination finite element scheme. Finally, we also obtained the normalized stress intensity factor for the crack tip of the cylinder. It is concluded that the effect due to thermoelastic coupling term on stress intensity factor becomes more important for higher coupling coefficient, and this coupling term also results in a small time lag in temperature, thermal stress and stress intensity factor.     

Failure Analysis of Primary Suspension Spring of Rail Road Vehicle

WAG-9-type electric rail vehicle, of Indian Railways’ fleet used for goods train hauling and maintained at Ajani, Nagpur Electric Loco Shed of central railway, has a history of frequent failure of middle axle primary inner suspension spring. The study of failures revealed that this specific component fails at a very high rate. The failure investigation starts the experimental spectroscopy analysis to find chemical composition for different failed specimens of springs, and it is observed that all parameters are within the recommended range. Also the stiffness of primary middle axle and end axle suspension springs has been checked on spring testing machine to measure deflection of spring, and it is as per recommended values. Further static stress analysis is carried out using analytical and finite element analysis for various phases of operation of rail vehicle like straight track, curved track and also for tractive effort. The static stress analysis has not revealed the cause of failure, and hence the dynamic analysis is performed. For dynamic analysis, dynamic model of suspension system is considered and analyzed using analytical method, finite element method and using MATLAB Simulink model. The vibration response of actual suspension system is also measured using FFT analyzer. It has been seen that the frequency of excitation and the natural frequency of the system are very close to each other which has resulted into suspension vibration amplitude of 6–8 mm. Fatigue analysis is carried out using finite element method to investigate the effect of dynamic loading on the failures of suspension spring. This analysis revealed that the middle axle inner suspension spring has finite life and due to which spring failure occurs earlier.     

Thermal shock and thermal fatigue study of ceramic materials on a newly developed ascending thermal shock test equipment

A test equipment was designed to study thermal shock and thermal fatigue of ceramic materials subjected to fast heating (ascending). The equipment was designed to generate thermal stress in a test specimen by heating one surface of it by an oxy-hydrogen flame while cooling the opposite surface. The sample cracked when thermal stress exceeded its mechanical strength. The in situ crack formation was detected by an acoustic emission system coupled to the set up. The hot zone temperature was measured by an infra red pyrometer. The equipment was also designed to run thermal fatigue test cycles in automatic mode between two selected temperatures. The temperature and thermal stress distribution in the test specimen were modelled using finite element software. The effect of temperature distribution of the top and bottom surfaces on thermal stresses was studied. It was observed that the thermal stress is very sensitive to the temperature distribution on the top surface and maximum near the periphery of the top surface. This was in agreement with the experimental results in which the cracks were originated from the periphery of top surface. It was also observed that the failure temperature was higher for thicker samples.     

Micromechanical multiplane finite element modeling of crack growth in fiber reinforced materials

The purpose of this study was to devise and verify a scheme of analysis which can be used to investigate the micromechanical failure mechanisms and determine an effective fracture toughness for a class of fiber reinforced materials. The material of primary interest in this study consists of a linearly elastic matrix material reinforced with rows of parallel, linearly elastic and straight fibers. Micromechanical multiplane finite element and experimental studies of the stress conditions near a crack front in a side cracked fiber reinforced epoxy tensile specimen were conducted. The 2-D multiplane method of analysis, recently developed at Syracuse University for approximate analysis of a class of 3-D problems, was the basis of the micromechanical finite element analytical technique developed in this study. Since failure of a member fabricated from a fiber reinforced material is generally proceeded by local failures, sequential finite element analyses were performed to model the progressive failure mechanism. Local failure modes considered in the analysis are yield in either the matrix material or fibers, crack extension in the matrix material, and failure of the matrix to fiber bond. The agreement between the multiplane analytical and laboratory test results show that the multiplane method provides a useful tool for micromechanical study of fiber reinforced composite materials.