Locomotive wheel failure from gauge widening/condemning: Finite element modeling and identification of underlying mechanism

Gauge change in straight plate, locomotive, railway wheels is studied using finite element analysis. The study accounts for residual stresses generated during wheel manufacturing and fitment of the wheel on locomotive axle. A validated thermal model accounting for heat loss to rail, brake blocks and ambient air is considered for accurate prediction of wheel temperatures for a given train running and braking history. Results are obtained for low- and high-friction, composite brake blocks used by Indian Railways for two limiting braking scenarios: (i) synchronized braking where braking effort is uniformly distributed on all brake blocks and (ii) independent braking where braking effort to decelerate a train is provided solely by locomotive brake blocks. Results show that bending at hub–disc interface predominantly governs the gauge change. While compressive hoop stresses in the tread region, occurring from rim heating during braking, cause gauge reduction, tensile hoop stresses in the tread region, occurring during wheel cool down cause an increase in wheel gauge. Importantly, while gauge condemning is a transient phenomenon occurring only during braking, gauge widening is “permanent” as it exists even after the wheels cool to room temperature. Allowable reduction of wheel gauge of 0.5 mm, currently used by Indian Railways, is found to be highly restrictive. In fact, in service wheel failure based on this criterion is observed in all braking scenarios considered.     

Combined tension and bending testing of tapered composite laminates

A simple beam element used at Bell Helicopter was incorporated in the Computational Mechanics Testbed (COMET) finite element code at the Langley Research Center (LaRC) to analyze the responce of tappered laminates typical of flexbeams in composite rotor hubs. This beam element incorporated the influence of membrane loads on the flexural response of the tapered laminate configurations modeled and tested in a combined axial tension and bending (ATB) hydraulic load frame designed and built at LaRC. The moments generated from the finite element model were used in a tapered laminated plate theory analysis to estimate axial stresses on the surface of the tapered laminates due to combined bending and tension loads. Surfaces strains were calculated and compared to surface strains measured using strain gages mounted along the laminate length. The strain distributions correlated reasonably well with the analysis. The analysis was then used to examine the surface strain distribution in a non-linear tapered laminate where a similarly good correlation was obtained. Results indicate that simple finite element beam models may be used to identify tapered laminate configurations best suited for simulating the response of a composite flexbeam in a full scale rotor hub.The U.S. Government right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

Nonlocal nonlinear bending and free vibration analysis of a rotating laminated nano cantilever beam

In this article, we present the nonlocal, nonlinear finite element formulations for the case of nonuniform rotating laminated nano cantilever beams using the Timoshenko beam theory. The surface stress effects are also taken into consideration. Nonlocal stress resultants are obtained by employing Eringen’s nonlocal differential model. Geometric nonlinearity is taken into account by using the Green Lagrange strain tensor. Numerical solutions of nonlinear bending and free vibration are presented. Parametric studies have been carried out to understand the effect of nonlocal parameter and surface stresses on bending and vibration behavior of cantilever beams. Also, the effects of angular velocity and hub radius on the vibration behavior of the cantilever beam are studied.     

Stress distribution and performance of threaded bolts in gasketed flange joints

The performance of the flange joint depends on the relaxation of load in bolts. This in turn affects the gasket stress and control of leakage. A finite element model of flange joint with threaded bolt-nut fastener having zero helix angle is developed and analyzed for stress distribution in the threaded bolt. The stress concentration factor at the thread root region is observed to be non-uniform along the circumference due to the bending behavior of the bolt in the flange joint. The maximum stress is observed in the first engaged thread. The variation in bolt load due to internal fluid, thermal and external loads are also investigated for both single and twin-gaskets (two concentric half-sized single gaskets). The gasket material and gasket configuration are observed to be potential factors causing variation in the distribution of load in the flange joint. In a flange joint subjected to external bending load, the maximum stress concentration in the bolt is observed to be in the first thread, instead of the first engaged thread. Under external bending load, the flange joint loses its structural integrity before the traces of leakage occur in the joint.     

Brittle intergranular fracture of a thread: The role of a carburizing treatment

Carburised mechanical components that have to sustain contact compressive loads or fatigue loads with limited tensile stresses, usually do not display brittle fracture in service. However, when high tensile stresses combined with high stress concentrations and a martensitic microstructure is present, such a damage mechanism may play an important role. In these cases, a careful control and optimization of the production processes is required. In the present investigation, the role of a carburizing treatment on the intergranular fracture behaviour of a pinion thread has been investigated. A simplified evaluation of the maximum tensile stress at the thread root after tightening is presented, and specific three-point bending and instrumented impact tests on Charpy-U carburised specimens were carried out, in order to highlight the role of hydrogen embrittlement and to provide guidelines for the optimization of the production process.     

Fretting fatigue of a shrink-fit pin subjected to rotating bending: Experiments and simulations

Fretting fatigue initiation was studied for a shrink-fit pin at rotating bending. Eight assemblies with four different grips were manufactured from soft normalized steel and tested at loads well below bending endurance. All pins displayed rust-red fretting oxides deep into the contact and black oxidised fretting scars with fretting fatigue cracks at the rim. The slip evolution was simulated in a three-dimensional FE model including assembly, bending and sufficiently many rotations to reach a steady-state. The extension of cyclic slip agreed with the black oxidised scar. Deeper into the contact a monotonic slip developed to the positions with rust-red oxides. Asymmetric slip and traction on the interface sides together with a slight twist of the pin in the hub and the slip development process, illustrated that a three-dimensional analysis was required for the interface. Both the stress amplitude and the Findley multi-axial criterion predicted fretting fatigue of the pin although the rotating bend stress was well below the endurance limit.     

Influence of the accumulated error in thread pitch on the stress–strain state and cyclic strength of threaded joints

Using the finite element method, the analysis of influence of errors in pitch during the thread production on the behavior of stress distribution in stud–nut joints is performed. The value of maximum local stresses in studs of a threaded joint is shown to substantially depend on errors in thread pitch of a stud and a nut. On the basis of the analyses of stresses and strains under cyclic loading, fatigue curves are plotted for the threaded joints having deviations in thread pitch. It is shown that, with a rational selection of the deviation in pitch, the cyclic strength of threaded joints can be considerably increased. The results of analysis agree satisfactorily with the data of fatigue tests of the M39 × 3 threaded joints.     

Process-dependent Thermal-Mechanical Behaviors of an Advanced Thin-Flip-Chip-on-Flex Interconnect Technology with Anisotropic Conductive Film Joints

User experiences for electronic devices with high portability and flexibility, good intuitive human interfaces and low cost have driven the development of semiconductor technology toward flexible electronics and display. In this study proposes, an advanced flexible interconnect technology is proposed for flexible electronics, in which an ultra-thin IC chip having a great number of micro-bumps is bonded onto a very thin flex substrate using an epoxy-based anisotropic conductive film (ACF) to form fine-pitch and reliable interconnects or joints (herein termed ACF-typed thin-flip-chip-on-flex (TFCOF) technology). The electrical and thermal -mechanical performances of the micro-joints are the key to the feasibility and effectiveness of the technology. Thus, the main goal of the study is to assess the process-induced thermal-mechanical behaviors of the interconnect technology during the bonding process. To undertake the process modeling, a process-dependent simulation methodology that integrates both thermal and nonlinear thermal-mechanical finite element (FE) analyses together with ANSYS^® birth-death modeling technique is proposed. The validity of the process modeling is confirmed through various temperature and warpage measurements. Subsequently, the contact behaviors of the ACF joints under four-point bending and static bending tests are characterized through FE modeling. The simulated contact stresses are further correlated with the measured electrical resistance data using four-point probe method, by which the minimum threshold contact stress for achieving a reliable contact electrical performance is determined.     

Determination of structural stress for fatigue analysis of welded aluminium components subjected to bending

The results of extrapolation procedures for the determination of structural stresses are often questionable due to the fact that the stresses at extrapolation points obtained with finite element analyses can be strongly dependent on the mesh size of finite element model and loading mode. Also, existing design S–N curves are derived mostly on the basis of fatigue testing of joints loaded axially. In the present paper the influence of the finite element mesh size on the structural stress value determined by a linear extrapolation method is analysed. Also, the paper examines the possibility of using existing design S–N curves for cases of bending induced by a force on the welded stiffener. Fatigue test results from aluminium welded components with longitudinal or round pad stiffeners subjected to bending loads have been assessed using a structural stress range approach, and compared with the structural stress design S–N curve FAT 40 (IIW) and the structural stress design S–N curve FAT 44 (Eurocode 9). It is concluded that the more precise estimation of fatigue life of aluminium components subjected to bending can be achieved with structural stress design S–N curve proposed by Eurocode 9. The conclusions also include recommendations for regarding component finite element modelling for the determination of structural stresses in case of bending.     

Acoustic Modal Testing of Bicycle Rims

The stiffness, strength, and safety of a bicycle wheel depend critically on the stiffness of its rim. However, the complicated cross-sections of modern bicycle rims make estimation of the stiffness by geometric methods very difficult. We have measured the radial bending stiffness and lateral-torsional stiffness of bicycle rims by experimental modal analysis using a smartphone microphone. Our acoustic method is fast, cheap, and non-destructive, and estimates the radial bending stiffness, \(EI_{11}\), to within 8% and the torsional stiffness, GJ, to within 11% as compared with a direct mechanical test. The acoustic method also provides a direct measurement of the coupled lateral-torsional effective stiffness, which is necessary for calculating many useful properties of bicycle wheels such as stiffness, buckling tension, and the influence of spoke tensioning. For a complete bicycle wheel, the lateral stiffness can be determined by a superposition of equivalent springs for each mode in series, where each mode stiffness contains a rim stiffness and spoke stiffness combined in parallel. We give example calculations on two realistic bicycle wheels using our experimentally derived rim properties to show how stiff spokes can compensate for a flexible rim, while a very stiff rim doesn’t necessarily result in a stiff wheel.     

A mixed variational principle for finite element analysis

A mixed variational principle is developed and utilized in a finite element formulation. The procedure is mixed in the sense that it is based upon a combination of modified potential and complementary energy principles. Compatibility and equilibrium are satisfied throughout the domain a priori, leaving only the boundary conditions to be satisfied by the variational principle. This leads to a finite element model capable of relaxing troublesome interelement continuity requirements. The nodal concept is also abandoned and, instead, generalized parameters serve as the degrees-of-freedom. This allows for easier construction of higher order elements with the displacements and stresses treated in the same manner. To illustrate these concepts, plane stress and plate bending analyses are presented.     

A TORSIONAL SPRING-LIKE BEAM ELEMENT FOR THE DYNAMIC ANALYSIS OF FLEXIBLE MULTIBODY SYSTEMS

A new finite element beam formulation for modelling flexible multibody systems undergoing large rigid-body motion and large deflections is developed. In this formulation, the motion of the ‘nodes’ is referred to a global inertial reference frame. Only Cartesian position co-ordinates are used as degrees of freedom. The beam element is divided into two subelements. The first element is a truss element which gives the axial response. The second element is a torsional spring-like bending element which gives the transverse bending response. D'Alembert principle is directly used to derive the system's equations of motion by invoking the equilibrium, at the nodes, of inertia forces, structural (internal) forces and externally applied forces. Structural forces on a node are calculated from the state of deformation of the elements surrounding that node. Each element has a convected frame which translates and rotates with it. This frame is used to determine the flexible deformations of the element and to extract those deformations from the total element motion. The equations of motion are solved along with constraint equations using a direct iterative integration scheme. Two numerical examples which were presented in earlier literature are solved to demonstrate the features and accuracy of the new method.     

铝型材构件多点变曲率拉弯制件回弹研究

目的 研究不同预拉伸量和补拉伸量对矩形变曲率构件回弹的影响,以提高柔性三维拉弯成形精度。方法 用有限元模拟了矩形变曲率铝型材三维拉弯成形过程,并用试验验证了有限元模拟的精度,设计了5组不同的预拉伸量参数和补拉伸量进行三维拉弯成形有限元模拟。结果 大曲率和小曲率段试验和有限元模拟的回弹误差小于2 mm,表明有限元模拟分析可以很好地对矩形变曲率构件进行模拟。得出的数据表明预拉伸量对于小曲率弧段回弹的影响比对大曲率弧段的影响更大,当预拉伸量增长到1.0%以后,回弹的下降幅度不再明显;随着补拉伸量的增大,变曲率拉弯制件两段的回弹均得到较好的抑制,当补拉伸量为1.4%时,制件靠近夹钳端出现了缩颈缺陷,产生了较大的质量缺陷。结论 研究证明适量增加预拉量和补拉量能有效减小柔性三维拉弯成形回弹。     

A global-local higher order theory including interlaminar stress continuity and C0 plate bending element for cross-ply laminated composite plates

A C⁰-type global-local higher order theory including interlaminar stress continuity is proposed for the cross-ply laminated composite and sandwich plates in this paper, which is able to a priori satisfy the continuity conditions of transverse shear stresses at interfaces. Moreover, total number of unknowns involved in the model is independent of number of layers. Compared to other higher-order theories satisfying the continuity conditions of transverse shear stresses at interfaces, merit of the proposed model is that the first derivatives of transverse displacement w have been taken out from the in-plane displacement fields, so that the C⁰ interpolation functions is only required during its finite element implementation. To verify the present model, a C⁰ three-node triangular element is used for bending analysis of laminated composite and sandwich plates. It ought to be shown that all variables involved in present model are discretized by only using linear interpolation functions within an element. Numerical results show that the C⁰ plate element based on the present theory may accurately calculate transverse shear stresses without any postprocessing, and the present results agree well with those obtained from the C¹-type higher order theory. Compared with the C¹ plate bending element, the present finite element is simple, convenient to use and accurate enough.     

A quadrilateral hybrid-Trefftz plate bending element for the inclusion of warping based on a three-dimensional plate formulation

A plate formulation, for the inclusion of warping and transverse shear deformations, is considered. From a complete thick and thin plate formulation, which was derived without ad hoc assumptions from the three-dimensional equations of elasticity for isotropic materials, the bending solution, involving powers of the thickness co-ordinate z, is used for constructing a quadrilateral finite plate bending element. The constructed element trial functions, for the displacements and stresses, satisfy, a priori, the three-dimensional Navier equations and equilibrium equations, respectively. For the coupling of the elements, independently assumed functions on the boundary are used. High accuracy for both displacements and stresses (including transverse shear stresses) can be achieved with rather coarse meshes for thick and thin plates.     

Failure analysis of oxygen hose of the lance equipment in LD shop of Tata steel

The hose of the oxygen lancing equipment in LD shop # 2 has failed at the weld–bellows interface by reverse bending fatigue. The bending stresses were resulted due to inclined fitting of the hose at the fixed flange end. No metallurgical abnormalities or weld defects or mechanical damages were responsible for the fatigue crack initiation. It is recommended that if inclined fitment of the hose is not a process requirement, the original design be restored to realize the expected life of the component. On the other hand, if inclined fitment cannot be avoided, additional support may be provided for the hose at the fixed flange end to avoid reverse bending at the weld–bellows interface. A detailed analysis of the failure is presented in this report.     

A Smart Flexible Solid State Photovoltaic Device with Interfacial Cooling Recovery Feature through Thermoreversible Polymer Gel Electrolyte

Quasi‐solid‐state dye‐sensitized solar cells (DSSCs) fabricated with lightweight flexible substrates have a great potential in wearable electronic devices for in situ powering. However, the poor lifespan of these DSSCs limits their practical application. Strong mechanical stresses involved in practical applications cause breakage of the electrode/electrolyte interface in the DSSCs greatly affecting their performance and lifetime. Here, a mechanically robust, low‐cost, long‐lasting, and environment‐friendly quasi‐solid‐state DSSC using a smart thermoreversible water‐based polymer gel electrolyte with self‐healing characteristics at a low temperature (below 0 °C) is demonstrated. When the performance of the flexible DSSC is hindered by strong mechanical stresses (i.e., from multiple bending/twisting/shrinking actions), a simple cooling treatment can regenerate the electrode/electrolyte interface and recover the performance close to the initial level. A performance recovery as high as 94% is proven possible even after 300 cycles of 90° bending. To the best of our knowledge, this is the first aqueous DSSC device with self‐healing behavior, using a smart thermoreversible polymer gel electrolyte, which provides a new perspective in flexible wearable solid‐state photovoltaic devices.     

Effect of rim and web interaction on crack propagation paths in gears by means of XFEM technique

The objective of this work is to investigate the correlation between rim and web thickness on the crack propagation path in thin‐rimmed gears, referring to bending failures. To this aim, numerical simulations have been performed, based on the 3D extended finite element method. Results related to gear models with different web and rim thickness have been interpreted in ISO Standard environment, relating the crack path to the so called gear blank factor C_R, useful in cases of mating gears consisting of rims and webs. Results show that the interaction between web and rim thickness may influence the crack propagation and the corresponding safe or catastrophic failure mode.     

Using three-dimensional finite element analysis for simulation of residual stresses in railway wheels

One of the most important issues in railway wheels is residual stresses. It is desirable to produce less residual stresses when possible and to decrease the remaining residual stresses in the wheels. The objective of this paper is to provide an estimation of the residual stresses in the rail wheel caused by the stress field from heat treatment process of a railway wheel. A three-dimensional nonlinear stress analysis model has been applied to estimate stress fields of the railway mono-block wheel in heat treatment process. After forging or casting, railway wheels are heat-treated to induce the desirable circumferential compressive residual stress in the upper rim. Finite element analysis model is presented applying the elastic–plastic finite element analysis for the rail wheel under variable thermal loads. Calculative analysis applying a finite element method (FEM) has been used to predict residual stresses. The quenching and annealing segments of the wheel manufacturing process are simulated using a decoupled heat transfer and stress analysis. Three-dimensional finite element analysis results obtained show good agreement with those achieved in field measurements.     

Simulations of stress distributions in crankshaft sections under fillet rolling and bending fatigue tests

The residual stresses due to fillet rolling and the bending stresses near the fillets of crankshaft sections under bending fatigue tests are important driving forces to determine the bending fatigue limits of crankshafts. In this paper, the residual stresses and the bending stresses near the fillet of a crankshaft section under fillet rolling and subsequent bending fatigue tests are investigated by a two-dimensional plane strain finite element analysis based on the anisotropic hardening rule of Choi and Pan [Choi KS, Pan J. A generalized anisotropic hardening rule based on the Mroz multi-yield-surface model for pressure insensitive and sensitive materials (in preparation)]. The evolution equation for the active yield surface during the unloading/reloading process is first presented based on the anisotropic hardening rule of Choi and Pan (in preparation) and the Mises yield function. The tangent modulus procedure of Peirce et al. [Peirce D, Shih CF, Needleman A. A tangent modulus method for rate dependent solids. Comput Struct 1984;18:875–87] for rate-sensitive materials is adopted to derive the constitutive relation. A user material subroutine based on the anisotropic hardening rule and the constitutive relation was written and implemented into ABAQUS. Computations were first conducted for a simple plane strain finite element model under uniaxial monotonic and cyclic loading conditions based on the anisotropic hardening rule, the isotropic and nonlinear kinematic hardening rules of ABAQUS. The results indicate that the plastic response of the material follows the intended input stress–strain data for the anisotropic hardening rule whereas the plastic response depends upon the input strain ranges of the stress–strain data for the nonlinear kinematic hardening rule. Then, a two-dimensional plane-strain finite element analysis of a crankshaft section under fillet rolling and subsequent bending was conducted based on the anisotropic hardening rule of Choi and Pan (in preparation) and the nonlinear kinematic hardening rule of ABAQUS. In general, the trends of the stress distributions based on the two hardening rules are quite similar after the release of roller and under bending. However, the compressive hoop stress based on the anisotropic hardening rule is larger than that based on the nonlinear kinematic hardening rule within the depth of 2 mm from the fillet surface under bending with consideration of the residual stresses of fillet rolling. The critical locations for fatigue crack initiation according to the stress distributions based on the anisotropic hardening rule appear to agree with the experimental observations in bending fatigue tests of crankshaft sections.