Search

Abstract The prediction of wheel squeal vibration and noise under the presence of friction modifiers is investigated using an efficient analytical model. The enhanced modelling is used to determine instantaneous rolling contact traction-creep curves from quasistatically measured ones using a two disk testrig under dry and friction modified conditions. The analytical solution is then compared with both numerical and experimental measurements of squeal vibrations and sound pressure level amplitude over a range of angle of attacks. Squeal is shown to occur in both the dry and friction modified conditions at about the same steady state amplitude. The robustness of the model is further verified under a much lower speed and the amplitudes, occurrence and non-occurrence of squeal is well predicted within measurement error. The model is shown to provide efficient quantified insight into why squeal noise may and may not occur under oil-based friction modification. Subsequently the model is used to determine an optimised region of the measured quasistatic traction-creep curve within which friction modification can eliminate wheel squeal. [ABSTRACT FROM AUTHOR]

The prediction of vibration amplitude and sound pressure level of wheel squeal noise is investigated using a concise mathematical model that is verified with measurements from both a rolling contact two disk test rig and a field case study. The model is used to perform an energy-based analysis to determine a closed form solution to the steady state limit cycle amplitude of creep and vibration oscillations during squealing. The analytical solution compares well with a numerical solution using an experimentally tuned creep curve with full nonlinear shape. The predicted squeal sound level trend also compares well with that recorded at various crabbing velocities (proportional to angle of attack) for the test rig at different rolling speeds. In addition, further verification is performed against many field recordings of wheel squeal on a sharp curve of 300 m. A comparison with a simplified modified result from Rudd [1] is also provided and highlights the accuracy and advantages of the present efficient model. The analytical solution provides insight into why the sound pressure level of squeal noise increases with crabbing velocity (or angle of attack) as well as how the amplitude is affected by the critical squeal parameters including a detailed investigation of modal damping. Finally, the efficient model is used to perform a parametric investigation into means of achieving a 6 dB decrease in squeal noise. The results highlight the primary importance of crabbing velocity (and angle of attack) as well as the creep curve parameters that may be controlled using third body control (ie friction modifiers). The results concur with experimental and field observations and provide important theoretical insight into the useful mechanisms of mitigating wheel squeal and quantifying their relative merits. [ABSTRACT FROM AUTHOR]

• Closed form prediction of flutter occurrence in a generalised structure with damping. • Closed form prediction of flutter amplitude with damping, bilinear lift law and offset angle of attack. • Quantified prediction of the effect of structural and aerodynamic damping. • Identification of a type of dynamic divergence as a necessary condition for flutter. • Identification and quantification of viscous and stiffness mode coupling in flutter. • Efficient analytical predictions of necessary criteria for the occurrence of chaotic flutter. Flutter prediction of its occurrence, limit cycle amplitude and chaotic behaviour is investigated using a general binary (two degree of freedom) coupled modal model to provide new closed form analytical predictions and insight into the aeroelastic phenomenon. The generalised unsteady flutter model, based on flutter derivatives (for any cross-section) and an approximate continuous bilinear lift curve, is used in a mass decoupled form to formulate and develop analytical criteria for the onset and amplitude of flutter under damping and offset angle of attack. This is based on modal coupling through stiffness and damping terms, to clearly identify and clarify two forms of flutter based on stiffness and viscous mode coupling. Closed form analytical criteria for flutter onset are developed including a new necessary dynamic divergence criterion (analogous to spragging in brake squeal) based on flutter derivatives for any structure. The model is first validated with the well-known classical numerical and experimental airfoil results of Theodorsen and analytical results of Pines, which are also shown to correspond to stiffness mode coupling. In addition, the new modelling enables the detection and corresponding conditions of viscous mode coupling flutter which does not require closely spaced modes. The occurrence and conditions of both stiffness and viscous mode coupling flutter is verified numerically with results highlighting important structural parameters i.e. damping factors which could cause flutter outside classical conditions. In particular, the conditions for viscous mode coupling are newly identified and found to occur at flow velocities substantially lower (up to approximately 10%) than classical stiffness mode coupling values. Dynamic divergence is shown to be the lower bound for the critical flutter speed under a range of conditons. The viscous mode coupling is shown to occur under high levels of torsional damping (20 times the nominal 1% of critical), for the airfoil case, compared to vertical damping, but does not require the modal frequencies to be close. The efficient analytical prediction for flutter amplitude is then numerically verified for Theodorsen's airfoil. The results show that flutter amplitude is primarily dependent upon flow velocity and stall conditions without structural nonlinearity. Finally, a further nonlinear investigation of flutter identifies useful analytical criteria for the occurrence of chaotic flutter which is confirmed numerically. These results, based on a bilinear lift coefficient model, highlight that the occurrence of chaotic flutter can be due to simplified aerodynamics alone i.e. without nonlinear structural stiffness. The closed form analyses provide critical insight into; the occurrence and underlying mechanisms of flutter based on stiffness and viscous mode coupling, dynamic divergence as well as the nonlinear amplitudes and behaviour under an offset angle of attack and stall conditions. [ABSTRACT FROM AUTHOR]

Field application of friction modifiers on the top of rail has been shown to effectively curb squeal and reduce lateral forces, but performance can be variable, according to other relevant research. Up to now, most investigations of friction modifiers were conducted in the field, where it is difficult to control or measure important parameters such as angle of attack, rolling speed, adhesion ratio etc. In the present investigation, the effect of different friction modifiers on the occurrence of squeal was investigated on a rolling contact two disk test rig. In particular, friction-creep curves and squeal sound pressure levels were measured under different rolling speeds and friction modifiers. The results show friction modifiers can eliminate or reduce the negative slope of friction-creep curves, but squeal noise still exists. Theoretical modelling of instantaneous creep behaviours reveals a possible reason why wheel squeal still exists after the application of friction modifiers. [ABSTRACT FROM AUTHOR]

The article offers the author's insights regarding a typical day working in the Journal Usage Statistics Portal (JUSP). The author mentions several activities conducted by the team during an ordinary working day which include finding a missing usage data for subscribing sites, restatement of a journal usage data, and helping publishers to achieve compliance. He featured several members of the group including Ross MacIntyre, Jo Lambert, and Dave Chaplin.

The sound pressure level of wheel squeal has been shown to increase with angle of attack and rolling speed in both field and laboratory tests. However, the exact causes behind the manner of increase are still unknown. To investigate this, a simplified analytical vibration model in the time domain is integrated with nonlinear rolling contact theory developed for wheel squeal. This model is used to simulate the vibration velocity of a test rig wheel at different rolling speeds and angles of attack. The simulated vibration velocities correlate well in the trend with the recorded sound pressure levels of wheel squeal in laboratory tests. Lateral creepage and force at various angles of attack and rolling speeds in the rolling contact are simulated. It is found that due to the interaction of wheel vibration, lateral force and creepage, the vibration velocity amplitude of the wheel increases with angle of attack and rolling speed. The generation mechanism of wheel squeal is explained from the view of energy input per cycle of vibration. Furthermore, the reasons why the sound pressure levels of wheel squeal increase with rolling speed and angle of attack are investigated, and these phenomena are explained theoretically based on energy input and the nonlinear creep behaviour. [ABSTRACT FROM AUTHOR]

Abstract: Curve squeal is the result of the lateral force in rolling contact of rail and wheels along curves. Recently, field measurements of wheel squeal occurrences at a site in Australia showed an increasing possibility for a squeal event to occur as the relative humidity increases. To verify these results, a new method to measure the lateral and normal force simultaneously was developed on a test rig, so as to determine the friction-creep curves. To investigate the effect of relative humidity on squeal and friction creep curves, the relative humidity inside the acoustic enclosure of test rig was adjusted under controlled conditions of 50%, 70% and 90%. The test rig results show that the lateral adhesion ratio decreases slightly with the increase of relative humidity and that squeal is more likely in high relative humidity. The modelling analysis shows that the critical creepage decreases with the increase of the relative humidity, which means negative damping occurs for lower angle of attack. [Copyright &y& Elsevier]

This work characterises wear debris/particles generated naturally in grease-lubricated spherical roller bearings (SRBs) used in urban rolling stock. Morphological examination revealed the most active wear in grease lubricated SRBs is predominantly associated with the rolling/sliding contact and adhesive mechanisms, resulting in chunk, laminar and spherical wear debris found most frequently. Morphological transitions in spherical and chunky wear debris associated with bearings' service life was seen for the first time in railway SRBs. Interestingly, the formation of chunky wear debris was not necessarily governed by rolling contact fatigue and crack propagation mechanisms seen in oil lubricated systems, but rather associated with the collapse of larger spherical wear debris. Additionally, the surface complexity observed on individual debris, associated with rolling-sliding wear is also discussed. The findings add to the sparse knowledge of wear debris formation and their contribution to grease degradation, particularly for railway SRBs. Furthermore, an estimate of the contamination level of the SRBs was obtained by carefully adapting the fluid lubricant standards. The combination of these results will allow for improved wear prediction and the optimisation of bearing maintenance practices. • Seven types of wear debris naturally generated in grease lubricated rolling stock SRBs was identified and studied. • Formation of wear debris in the railway SRBs is mostly associated with rolling/sliding contact mechanism. • Morphological evolution of spherical debris linked with service life was seen for the first time in grease lubricated SRBs. • Chunk wear debris found in grease lubricated SRBs were governed by collapse and/or fracture of large spherical wear debris. [ABSTRACT FROM AUTHOR]

The Journal Usage Statistics Portal (JUSP) service is expanding rapidly, and aims to encompass all NESLi2-participating publishers by the end of 2011, together with all UK higher-education institutions subscribing to deals from those publishers. A key part of the success of JUSP will be the implementation of the Standardized Usage Statistics Harvesting Initiative (SUSHI) protocol for automatic harvesting of usage statistics directly from publishers. This article outlines development of the service and describes how JUSP is working with Oxford University Press to deliver usage statistics to libraries. We also describe future developments at JUSP, including the creation of our own SUSHI server, and explain how new initiatives and enhancements are developed and rolled out in conjunction with our participating institutions. [ABSTRACT FROM AUTHOR]

Abstract: Millipede forming, a novel sheet metal forming method, has been proposed and developed recently to overcome fundamental limitations in conventional roll forming. For this new method, there are two main aspects: use of an optimal transitional surface and implementation of a method to feed the strip through the transition surface. Achieving the optimal transitional surface involves defining the change of surface shape between a flat strip and a final shaped product conceptualised to the strip''s mid-surface, regardless of the strip''s thickness. In this paper, one method of implementing a transition surface, Millipede forming, is introduced. A prototype has been built to demonstrate the working principle and can be used to produce some simple profiles, within a short forming length of 200mm. [Copyright &y& Elsevier]

Abstract: The occurrence of chaotic instabilities is investigated in the swing motion of a dragline bucket during operation cycles. A dragline is a large, powerful, rotating multibody system utilised in the mining industry for removal of overburden. A simplified representative model of the dragline is developed in the form of a fundamental non-linear rotating multibody system with energy dissipation. An analytical predictive criterion for the onset of chaotic instability is then obtained in terms of critical system parameters using Melnikov''s method. The model is shown to exhibit chaotic instability due to a harmonic slew torque for a range of amplitudes and frequencies. These chaotic instabilities could introduce irregularities into the motion of the dragline system, rendering the system difficult to control by the operator and/or would have undesirable effects on dragline productivity and fatigue lifetime. The sufficient analytical criterion for the onset of chaotic instability is shown to be a useful predictor of the phenomenon under steady and unsteady slewing conditions via comparisons with numerical results. [Copyright &y& Elsevier]

The multibody dynamics of a satellite in circular orbit, modeled as a central body with two hinge-connected deployable solar panel arrays, is investigated. Typically, the solar panel arrays are deployed in orbit using preloaded torsional springs at the hinges in a near symmetrical accordion manner, to minimize the shock loads at the hinges. There are five degrees of freedom of the interconnected rigid bodies, composed of coupled attitude motions (pitch, yaw and roll) of the central body plus relative rotations of the solar panel arrays. The dynamical equations of motion of the satellite system are derived using Kane''s equations. These are then used to investigate the dynamic behavior of the system during solar panel deployment via the 7–8th-order Runge–Kutta integration algorithms and results are compared with approximate analytical solutions. Chaotic attitude motions of the completely deployed satellite in circular orbit under the influence of the gravity-gradient torques are subsequently investigated analytically using Melnikov''s method and confirmed via numerical integration. The Hamiltonian equations in terms of Deprit''s variables are used to facilitate the analysis. [Copyright &y& Elsevier]

• Brake squeal is analytically predicted under 'falling friction', spragging and mode coupling. • The mitigation of brake squeal is efficiently predicted and quantified. • Provides clearer insight into spragging and brake pad centre of pressure on mode coupled squeal. The occurrence, growth, limit cycle amplitude and mitigation of brake squeal noise are investigated using a predictive analytical coupled modal model. The model is developed to analytically determine the effect of the combined mechanisms of falling friction, spragging and mode coupling in brake squeal for the first time. In addition, the handling of the brake pad mechanics and sliding friction is newly contributed. The modelling leads to closed form analytical criteria for brake squeal that suggests that spragging is required for mode coupled squeal, in contrast with the falling friction mechanism. In particular, spragging is shown to be an important necessary condition for two types of mode coupled squeal; stiffness and viscous, determined by negative damping from the complex stiffness and coupled modal damping, respectively. The efficient analytical predictions are then verified using previous numerical and experimental investigations of brake squeal including the effect of damping. The results concur and quantify practical observations and show that squeal amplitude is primarily dependent upon sliding velocity and independent of growth rate with a minimal difference in squeal amplitudes due to the different mechanisms. The efficient closed form solution is then used to predict the amplitude of the limit cycle brake squeal noise and to investigate a wide range of parameters to mitigate its occurrence. The closed form modelling and solutions provide important insight; into the occurrence and mitigation of the underlying mechanisms of brake squeal (including falling friction, spragging, stiffness and viscous mode coupling), and on the brake pressure dependent modes and the brake pad angle of attack. [ABSTRACT FROM AUTHOR]

Wheel squeal vibration and noise amplitude under the effects of mode coupling and rising and falling creep behavior is investigated and predicted using an efficient analytical model. Based on previous research, a simplified modal dynamics model for wheel squeal noise amplitude is enhanced to include two coupled modes. Closed form analytical solutions for the vibration and squeal noise amplitude are determined under combined squeal mechanisms of full sliding falling friction and mode coupling. The analytical predictions are then compared with numerical time domain simulations of squeal vibrations with nonlinear creep and sound pressure level amplitude over a range of angle of attacks and contact angles for the inner and outer wheels in a curve. As an example, the effect of rail dynamics on squeal amplitude is quantified by comparing results with and without the mode coupling and the conditions and occurrences of stiffness and viscous mode coupling (where the stability is determined by the coupled structural complex stiffness, due to the closeness of the uncoupled modes, and damping, respectively) are clearly identified and quantified. The viscous mode coupling from the rail is shown to significantly reduce and/or eliminate conventional wheel squeal, for the inner and outer wheels, at higher contact angles defined by the friction coefficient. It can otherwise amplify (up to approximately 5 dB) or cause squeal, under high rail damping for the leading outer wheel. Conversely, it is shown that under only a small range of contact angles and closely matched uncoupled modes, stiffness mode coupling causes very high amplitude squeal beyond the scope of the simplified creep model. Rail mass and damping only models are shown to represent the occurrences of stiffness and viscous mode coupling, respectively, where the optimum amplitudes are dependent upon the complex stiffness and rail damping, respectively. The scope of the efficient analytical model is quantified and shown to be limited by excessive non-proportional damping and very high squeal amplitudes associated with reverse full sliding. The analytical model is shown to provide insight into the effects of mode coupling dynamics on wheel squeal noise amplitude and possibly help explain the enigma that squeal occurs seemingly unreliably in the field. [ABSTRACT FROM AUTHOR]

Friction modifiers have been shown to be effective in reducing wheel squeal noise but not reliable in eliminating the phenomenon. To investigate this, wheel squeal noise under water-based friction modifiers is predicted using a mathematical model taking into account assumed instantaneous traction-creep behaviour. The instantaneous lateral creep curves are determined from quasistatic measurements under water-based friction modified conditions and used to obtain analytical predictions of wheel squeal noise levels that are verified numerically and experimentally based on a two disk testrig. Similar levels of squeal are obtained in both dry and water-based friction modified conditions at higher speeds despite the measured lateral creep curve not showing 'falling friction'. For low speed, the water-based friction modification is shown to be successful in eliminating squeal except for very high angles of attack where noise levels are still greatly reduced. Subsequently, the efficient modelling is used to identify what modifications to the creep curve provide the best squeal noise reduction and elimination capabilities. • Squeal noise trends under water-based friction modifiers are analytically predicted and verified experimentally. • Squeal noise was not eliminated by friction modifiers in some cases at higher speeds and angles of attack. • Generalised optimal friction modified creep curves are predicted and verified numerically to control wheel squeal noise. • Squeal noise can be substantially reduced while still maintaining moderate friction levels by increasing the critical creep. [ABSTRACT FROM AUTHOR]

With an increasing demand to reduce the body weight of motor vehicles, advanced high strength steel (AHSS) is widely applied in the automobile industry. However, high residual stresses and redundant deformation caused by the cold roll forming process are still outstanding problems. Under such circumstances, Chain-die forming technology is developed. Through enlargement of the effective roll radius, the deformation length is significantly stretched, leading to a significant reduction in residual stresses and redundant strain. In this study, Chain-die formed AHSS U-channel products are investigated experimentally and numerically. The influences of a number of features such as material strength, sheet metal thickness, vertical forming gap, and effective virtual roll radius are discussed regarding average flange angle and the variation of flange angle along the longitudinal direction. The results show that the average flange angle decreases with the increase of material strength, vertical forming gap, and effective virtual roll radius. Furthermore, among all four controllable variables, effective virtual roll radius has the most significant impact on the variation of the flange angle along the longitudinal direction. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is an emerging flexible manufacturing technique. However, it is currently facing the challenge of popularization in industry since the poor geometric precision of the finished parts cannot meet the engineering standard. Aiming at enhancing product geometric precision, online path planning algorithms had been proposed by researchers. However, the existing algorithms had been applied successfully in manufacturing products with very simple geometries only and had limited capabilities of being generalized to complex products, which prevented the widespread application of ISF. To solve this long-lasting problem, more powerful and generic path planning algorithm needs to be proposed for the ISF process. In this study, an adaptive MPC-based path planning algorithm was developed for the ISF process, aiming at enhancing the geometric accuracies of products with more complex geometric features. The algorithm was formulated based on the state-space modelling of the process, the learning-based parameter identification approach, and quadratic programming optimization. The performance and the generality of the present adaptive MPC algorithm were experimentally validated in manufacturing parts with several complex geometric features that were typical in industrial parts using closed-loop ISF processes. In the first test, the present adaptive MPC algorithm showed a significant performance improvement of 56% in the reduction of maximum error on the base compared to the non-adaptive MPC. In the other two tests, the present algorithm also received satisfactory performances. Compared to the non-adaptive algorithm, the test results indicated that the present adaptive algorithm had a better performance and a higher generality. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is a promising manufacturing technology in which complex 3D shapes can be formed with one simple tool. Compared to conventional forming processes, for complex shapes, it is more flexible and economical with higher formability and shorter lead time. Therefore, ISF is ideally suitable to rapid prototype and small-batch production, especially in the aerospace and biomedical sectors. Over the last decade, although the process has been experimentally studied extensively, the associated deformation mechanics is still unclear and intensive investigation is needed. The purpose of this study is to provide further knowledge of the deformation mechanics of the sheet and clarify the deformation mechanism in a typical cone-forming process through finite element (FE) simulation approach. In particular, comprehensive FE models with fine solid elements are utilised, which allow the investigation of deformation modes including stretching, bending and shearing. The FE model is firstly validated with experimental results in terms of forming forces, and then, the evolution history of all the strain components along with the effective strain is presented. The contribution of each strain component to the effective plastic strain during the cone-forming process is discussed. Moreover, the characteristic of each strain component is investigated in detail. It is confirmed from the FE simulation that the deformation modes in the ISF process are a combination of shearing, bending and stretching, although the quantitative contributions in each direction are varied. The effect of step-down size on material plastic deformation as well as formability is also investigated. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is a new promising manufacturing technology with high potential to shape complex three-dimensional parts by using a relative small tool. However, ISF is presently limited due to non-uniform thickness distribution of formed parts, especially excessive thinning on severely sloped regions. This typically leads to fracture and hence limits process formability. This paper aims to tackle this issue by developing appropriate tool path strategies for multi-pass deformation design in ISF. More specifically, two more complex shapes are designed to validate the proposed multi-pass deformation design methodology by finite element simulations and experiments. The interactions of different tool path strategies on material thinning of the final part are evaluated in terms of process formability and thickness strain distribution given the same multi-pass design. Furthermore, the movement of material points is traced to explain the material flow mechanism in multi-pass forming compared to single-pass forming. It is concluded that both deformation passes (intermediate shapes) and tool path generation strategies would influence the thickness strain distribution as well as process formability. Appropriate tool paths should be devised to further reduce material thinning and improve the process formability by taking the geometrical features of the designed part into account. Additionally, the proposed multi-pass deformation design enables sufficient material to flow into the deformed region from the outside region so as to allow a compressive deformation state to develop and steeper shapes to be formed. [ABSTRACT FROM AUTHOR]

Four commercial greases with various thickeners and base oils were experimentally examined to compare their false brinelling wear resistance in a test rig simulating roller bearings during rail/sea transportation for the first time. Greases containing zinc dialkyl dithiophosphates (ZDDP) showed superior false brinelling reduction, evidenced by no visible wear mark in the raceways. The mechanism for false brinelling mitigation was shown to be from a ZDDP-induced tribofilm which decreases the friction and wear coefficient in the contact area. Surface chemical analysis showed that for grease lubricated fretting contacts, ZDDP-derived tribofilms can be generated in the presence of micro-sliding motions and energy dissipation at the contact interface at low frequency (i.e., 4–8 Hz), due to the mechanochemical reactions. For greases without ZDDP, false brinelling wear was reduced by 97% when using grease with a more abundant and less viscous oil, which bleeds readily from an open structured thickener. The results highlight the ability of ZDDP as an additive in grease to better protect roller bearings against false brinelling during rail/sea transportation. [ABSTRACT FROM AUTHOR]

Abstract: Rolling contact fatigue cracks in railway track called squats are studied in this paper. In the first part, the effects of an elastic foundation (sleepers and the ballast) on stress intensity factors obtained at a crack tip are studied. A simplified finite element model (FEM) and an extended finite element model (XFEM) were created to investigate these effects, the XFEM model being limited in geometrical size, but more able to model crack growth. Both FEM and XFEM confirmed that an elastic foundation leads to an additional bending stress which increases the crack growth rate significantly. Field results also authenticate that squat form cracks appear on timber sleepers more commonly than on concrete ones. These results indicate that considering these bending stresses in a FE model, is important to achieve a more realistic model of squat development. In the second part, a short crack of 250μm length is simulated to investigate how variations of traction ratio (TR), friction coefficient between the crack faces (FC) and the crack angle affect SIFs when the rail is mounted on an elastic foundation. Simulations show that a crack on a rail laid on elastic foundation (clips, sleepers and ballast) can lead to significantly higher SIFs in many conditions and consequently raises crack growth rate. This indicates that foundation stiffness is as important as water entrapment and friction coefficient between the crack faces. [Copyright &y& Elsevier]

Experiments are conducted for investigating the effect of normal pressure, sliding amplitude and oscillating sliding frequency on friction, wear coefficient and threshold energy for wear activation of 52100 high carbon bearing quality steel (ASTM A295) during a false brinelling test. The cylinder-on-cylinder set-up is used. The investigation showed that the friction coefficient decreases with increasing normal pressure and increases with increasing sliding amplitude; however, there is no influence of an increase in oscillating sliding frequency. Similarly, the wear coefficient decreases with increasing normal pressure and increases with increasing sliding amplitude; however, unlike the friction coefficient, it increases with an increase in oscillating sliding frequency. Different conditions do not have a significant influence on the threshold energy for wear activation. By incorporating a varying friction and wear coefficient with changing sliding parameters, the analytical prediction for false brinelling are improved by 10–50% over the constant parameter model. • The effect of varying conditions on friction, wear coefficient was investigated. • The effect of different parameters on threshold energy for wear activation was investigated. • The results were then used to improve and validate the false brinelling models developed previously. [ABSTRACT FROM AUTHOR]

Model predictive control (MPC) is an advanced control algorithm that has been successfully implemented in the on-line path optimization of computer-numerical-control (CNC) machines for performing single-pass incremental sheet forming (ISF) processes, aiming at precision enhancements of products. Multi-pass ISF technique is usually employed to manufacture parts with extremely large wall angles which cannot be achieved without failure using the single-pass ISF. However, existing studies show that the geometric precision of the products of multi-pass ISF is usually very poor, which has significantly hampered the widespread application of this technique in industry. In the present study, two control algorithms based on the MPC framework were proposed, targeting at achieving a more precise geometry of multi-pass ISF products. MPC-1 was an extension of the control algorithm for the single-pass ISF process reported in our previous work, and MPC-2 was developed for the first time. The developed MPCs were comparatively validated by a group of physical benchmark test. Compared to MPC-1, MPC-2 reduced the maximum geometric error in the wall, conjunction, and base zones on the same part by 26%, 51%, and 73%, respectively. The test results show that MPC-2 had a better performance in multi-pass ISF processes. [ABSTRACT FROM AUTHOR]

With the increasing application of the advanced high strength steel material in the automobile industry, the thickness reduction of the bending area has attracted more and more attention since the product strength is highly influenced by the quality of the bending region. In this paper, three major factors, the thickness reduction, the variation of the local bending radius within the bending zone, and the tooling mark on the product's surface, are investigated through three different loading patterns for a free U-bending profile numerically and experimentally. The results demonstrate a thinning pattern consists of three peaks over the bending region for large bending ratio (R/t = 2.14) and only one peak for small bending ratio (R/t = 0.5). Corresponding valleys for the local radius are found to match the thinning pattern. Further, the use of finite element simulation can successfully predict the location and the severity of the wear on the product. From the experiment results, even if the metal blank only experienced one stroke, the tooling mark contains both adhesive and abrasive wear. A better understanding of the characteristics of the bending zone is achieved, and the findings can help in improving the design process for forming strategies. [ABSTRACT FROM AUTHOR]

Two-point incremental forming (TPIF) shows higher forming limits than single-point incremental forming (SPIF) especially for producing complex industrial functional components. However, unexpected failure still occurs occasionally under certain forming conditions in TPIF. In this paper, the applicability of six damage models for failure prediction in TPIF is evaluated. The procedure of damage parameter calibration and finite element modelling are presented. The predicted failure depth and location with these damage models are evaluated under different loading conditions. Furthermore, the stress and strain and damage evolution in TPIF are provided and discussed in detail. It is concluded that the failure location and depth can be predicted more accurately by the Ayada model than others in this work. It is noted that once double-sided contact occurs in TPIF, it reduces the variation of triaxiality through the thickness, altering the accumulation of damage. [ABSTRACT FROM AUTHOR]

This study presents a novel and non-destructive method for quantitatively analysing grease lubricated bearing wear by using X-ray microcomputed tomography (μCT). The efficacy of μCT to measure rolling contact wear via wear debris analysis was demonstrated, as was quantifying grease contamination and wear debris identification. Test rig experiments of grease lubricated spherical roller bearings, were performed to simulate rolling contact wear. Six grease samples were collected from two bearings at three different intervals to investigate wear progression. Results showed μCT measured wear volume increased exponentially with increasing bearing operation times. Grease cleanliness (particle counts per ml) worsened nonlinearly due to the exponential growth of wear debris over longer bearing operational times. Comparing the conventional ISO281 bearing assembly and operating condition assessment, a particle-count based method via μCT analysis provided a less subjective and dynamic assessment for quantifying grease contamination. Grease contamination was found to increase with longer operational timeframes due to the combination of wear debris growth and decreased lubrication film thickness. Finally, laminar, chunk and spherical wear particles, associated with rolling contact wear, were identified by the morphometric parameters measured by μCT. This study highlights the potential of μCT as a wear monitoring and grease quality assessment technique for railway bearing applications. • Microcomputed tomography is pioneered to measure wear in test rig bearings. • The proposed method is nondestructive and requires no sample manipulation. • The efficacy in wear measurement is proven through debris analysis in grease. • Quantitative analysis of 3D wear debris images provides wear mechanism assessment. • Grease contamination worsens with wear debris growth exponentially and lubricant film thinning. [ABSTRACT FROM AUTHOR]

A rolling contact two disk test rig is used to measure the lateral adhesion ratio under dry and wet conditions, and the results show that after the application of water the lateral adhesion ratio decreases. This effect is especially evident for low speed at large angle of attack, and the reduction rate is almost up to 50%. In contrast, the effect of water application on the lateral adhesion ratio at high speed is almost negligible. In this research, the effect of rolling speed on the lateral adhesion ratio under dry and wet conditions are also investigated. It is found that the lateral adhesion ratio decreases with rolling speed under dry conditions; while after the application of water, the measured results show an opposite trend. Furthermore, a model of wheel/rail contact mechanics is developed based on previous models and experimental measurements. Using this model, the simulated friction creep curves shift down with the increase of rolling speed. In comparison with previous mathematicla models, the correlations of this theoretical model with measured lateral adhesion ratios at various rolling speeds are much improved. Hereby, the authors would like to highlight the following innovations and contributions of this paper. ● The lateral adhesion ratios at various yaw angles and rolling speed are measured under dry and wet condition, and the effect of water application is investigated. ● The effect of rolling speed on lateral adhesion ratio under wet condition is investigated and illustrated, and the effects of low speed and high speed are compared. ● A theoretical model for wheel/rail contact in the lateral direction based on the contact theory of Kalker is developed and its correlation with experimental measurements is much improved. [ABSTRACT FROM AUTHOR]

The geometrical error of the formed part is one of the most significant limitations that restricts the widespread application of incremental sheet forming (ISF) in aerospace industry. The geometry of ISF parts is dependent upon the tool path, so its correction can improve the part precision. Previous research has utilized model predictive control approach to achieve this, but the method was restricted to simple convex shapes. In this study, the tool path and the formed shape were parameterized and the analytical models of geometry responses relative to tool perturbations were proposed. Then, a model predictive control algorithm was developed, aiming at reducing the geometrical errors of the parts with complex non-convex shapes in the ISF process. Experimental validation of the developed control algorithm was carried out by forming a complex shape by single-point incremental forming. The results show that the developed control algorithm greatly reduced the geometrical error in the closed-loop process. [ABSTRACT FROM AUTHOR]

Residual stresses in metallic components greatly affect the geometrical accuracy of advanced high-strength steels (AHSS) products used for automotive industry. Chain-die forming is a promising method to fabricate AHSS products which can minimize the residual stress induced. This paper aims to understand the residual stress in chain-die-formed dual-phase (DP) steels through analytical and numerical modelling together with experimental validation. Analytical and numerical models were firstly employed to predict the stress development and associated residual stresses induced by chain-die forming in consideration of an as-received residual stress field and a comprehensive material-hardening model. The residual stresses in different regions of formed parts were practically measured using the neutron diffraction method to verify the developed models. Same as the mesh size of the examining points of finite element analysis (FEA) models, the averaged over the same sampling size is measured to guarantee the accuracy. It seems to be consistent with the simulation and experimental results in consideration of both factors. However, compared with as-received residual stress, the kinematic factor has a more dominating impact on the final residual stress. The results presented should contribute to the prediction of geometric errors and minimize product defects caused by the residual stresses in chain-die forming or equivalent sheet metal-forming industry. [ABSTRACT FROM AUTHOR]

Wheel squeal noise is a common problem that occurs in railway systems especially on curved tracks. These tonal noises are usually found at high frequency, typically over 1 kHz. The cause of the squeal noise remains unclear and could be different under varied conditions. Several mechanisms that could cause wheel squeal, including falling friction and mode coupling, have been proposed in literature. Most existing lab experimental investigations were focused on the squeal noise caused by falling friction with vertical contacts. As a result, the squeal noise generated by mode coupling could be missed due to the absence of a non-vertical contact angle. In this work, a two-wheel test rig has been designed with curved wheel profiles to achieve adjustable contact angles with lateral components. Experimental and numerical modal analysis of the two-disk system was conducted to determine the dynamic characteristics for exploration of mode coupling effects. Using a set of benchmark parameters predicted to be the cause of significant mode-coupled instability, squeal noise was found at frequencies higher than the existing falling friction experimental tests as reported in the literature. The frequency and amplitude measured in the experiments agreed with the predictions of the analytical mode coupling model. Further experiments varying control parameters, contact angle, angle of attack and direction of rotation were performed, confirming that the new squeal noise was caused by mode coupling. • The first experimental verification of mode coupling wheel squeal mechanism using two-disk testrig. • Experimental generated squeal noise level and frequency agreed well with the analytical model prediction. • Additional experiment with reversed rotation confirmed the identified squeal noise was caused by mode coupling. • Further parametric experiments varying contact angle and angle of attack were conducted, and the results were compared with the analytical model prediction and literature. [ABSTRACT FROM AUTHOR]

Abstract An adaptive finite element model was developed to predict false brinelling in a cylindrical bearing, during the transportation of new trains and then compared with experimental measurements. The model was developed, based on the Archard wear equation, using ABAQUS and developing an ABAQUS UMESHMOTION code. A false brinelling monitoring system was designed and installed to record the vibration and rotational motion of the bearing, during the train's road and sea transportations and were used as inputs for the FE model. A set of laboratory experiments were conducted to determine wear and friction coefficients and the threshold energy for the bearing that were used in the simulation process. To compare the FE results with a real case, a profilometry measurement of false brinelling marks in a damaged bearing was performed. According to the FE wear profile results, rotational displacement of the bearing is the most likely cause for false brinelling during transportation. Due to the wear energy being below the threshold, it was predicted that no false brinelling occurred due to lateral and axial vibrations at the roller. The existence of the partial slip area, in the contact, causes the development of W shape wear marks that was seen in the profilometry measurement of the damaged sample. Highlights • An adaptive finite element model was developed to predict false brinelling in a bearing. • A monitoring system was designed to record the vibration during the train's transportations. • Laboratory experiments were conducted to determine bearing material coefficients. • Profilometry measurement of false brinelling marks in a damaged bearing was performed. • Rotational displacement was the most likely cause for false brinelling. [ABSTRACT FROM AUTHOR]

Chain-die forming is a new sheet metal forming technology proposed which has the capability to fabricate advanced high-strength steel (AHSS) variable cross-section profiles. The existing research reveals that the control of longitudinal plastic strain and web-warping are two significant issues which determine the success of the fabrication of AHSS variable cross-section profiles. In this paper, both analytical and numerical methods are employed to analyse the longitudinal plastic strain and web-warping in Chain-die-formed AHSS sections with variable widths. By contrast to the existing analytical modelling in regards to flexible roll forming of irregular profiles, in this study, as Chain-die forming can be considered a continuous stamping process, the analytical models are purely established on the basis of geometric relationships between the pre-cut sheet and forming tools. In theory, no longitudinal plastic strain, id est maximum web-warping, could occur. No web-warping, id est maximum longitudinal plastic strain, could also arise. The real situation is included between such two extremes, and they are strongly dependent on some critical geometric parameters of the pre-cut sheet and forming tools. This is seen to be consistent with the simulation and experimental results. Subsequently, due to different forming mechanisms and loading processes, the severity and characteristics of the longitudinal plastic strain and web-warping of chain-die-formed AHSS sections with variable widths show distinct differences compared with those of flexible-rolled-formed profiles. Finally, Chain-die forming has been further proved to maximally reserve the material's elongation as the redundant deformation is almost avoided during the forming process. This study provides an effective mathematical expression to analyse and predict longitudinal plastic strain and web-warping of chain-die-formed AHSS variable cross-section profiles. It is expected to be useful to tooling designers to quickly assess the severity of a Chain-die forming process in the tooling design stage in order to shorten the tooling development time. [ABSTRACT FROM AUTHOR]

In Incremental Sheet Forming (ISF) of metal sheets, it is desirable to develop a quick method to predict the mechanical behaviour during forming, and ultimately, to optimise the process. The aim of this paper is to propose a Rapid Kinematic Method (RKM) for a quick update of the positions of the material points in two-point Incremental Sheet Forming (TPIF) of metal sheets. Based on this method, the strain and thickness distributions in the part can be determined and its tendency to fail assessed. The developed RKM is used to simulate single-stage and three-stage ISF of an ellipsoidal shape made of thin aluminium sheets, and the RKM predictions are compared with Finite Element Analysis simulations and experiments. The change in the deformation mechanism introduced by multi-staging has been carefully examined and a strategy for enhancing the sheet formability by structural means identified. The RKM presented here is applicable to parts of general shapes and the updated positions of the material points during ISF thus established can be used as an initial guess for a more rigorous model of mechanics. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is an emerging forming technology that promises high flexibility and formability. These properties make it suited for small-scale and customised production. However, the poor geometric accuracy of ISF limits the wide application of this flexible forming technology. This paper presents a two-directional toolpath correction approach to enhance ISF forming accuracy using a model predictive control (MPC) algorithm. A toolpath optimisation method for vertical toolpath correction has been validated in our previous work (Lu et al., Int J Adv Manuf Technol 72:1-14, 2015), and it helps to reduce errors in the base of the test shapes to a suitable level while its major limitation is that horizontal geometric errors are relatively large. This paper extends our previous work (Lu et al., Int J Adv Manuf Technol 72:1-14, 2015) by augmenting the vertical control module with a new control module for horizontal toolpath correction. The proposed control algorithm was experimentally validated in single-point incremental sheet forming (SPIF) using two forming case studies. In the first case study (a truncated pyramid), two control approaches with different assumptions for the horizontal springback distribution along the horizontal cross-sectional profile were tested and compared. Then, the developed MPC control algorithm was applied to form a more complex asymmetric shape. The results show that the developed strategy can reduce the forming errors in the wall and base of the formed shape compared to the existing works. The ISF process with MPC control leads to significant accuracy improvement in comparison with the typical ISF process that is without toolpath control. [ABSTRACT FROM AUTHOR]

As a flexible forming technology, Incremental Sheet Forming (ISF) is a promising alternative to traditional sheet forming processes in small-batch or customised production but suffers from low part accuracy in terms of its application in the industry. The ISF toolpath has direct influences on the geometric accuracy of the formed part since the part is formed by a simple tool following the toolpath. Based on the basic structure of a simple Model Predictive Control (MPC) algorithm designed for Single Point Incremental Forming (SPIF) in our previous work Lu et al. (2015) [1] that only dealt with the toolpath correction in the vertical direction, an enhanced MPC algorithm has been developed specially for Two Point Incremental Forming (TPIF) with a partial die in this work. The enhanced control algorithm is able to correct the toolpath in both the vertical and horizontal directions. In the newly-added horizontal control module, intensive profile points in the evenly distributed radial directions of the horizontal section were used to estimate the horizontal error distribution along the horizontal sectional profile during the forming process. The toolpath correction was performed through properly adjusting the toolpath in two directions based on the optimised toolpath parameters at each step. A case study for forming a non-axisymmetric shape was conducted to experimentally validate the developed toolpath correction strategy. Experiment results indicate that the two-directional toolpath correction approach contributes to part accuracy improvement in TPIF compared with the typical TPIF process that is without toolpath correction. [ABSTRACT FROM AUTHOR]

Chain-die forming is a promising manufacturing technology that is emerging as an alternative to roll forming and stamping in fabricating advanced high-strength steel (AHSS) products. The maximum edge longitudinal membrane strain (MELMS) and the springback are regarded as the crucial indicators for evaluating the quality of fabricated AHSS products. As Chain-die forming is a newly developed sheet metal fabricating method, the evaluations and predictions of the effects of the independent product parameters on MELMS and springback are of high interest. This paper selects three important quantitative product parameters (tensile strength, flange height, and thickness) to investigate experimentally the effects of different product parameters on the quality of Chain-die-formed U-profile AHSS products. Experimental verification on a new group of experimental samples using the established mathematical expressions is also performed successfully. This study shows that response surface methodology with Box-Behnken design can be efficiently applied for evaluating and predicting the MELMS and springback of Chain-die-formed AHSS products. It is found that the most influential parameter which determines the severity of the MELMS is the linear effect of flange height. This study also indicates that the springback is largely determined by the linear effect of tensile strength. The findings are expected to help designers and researchers to identify the formability range and predict the quality of Chain-die-formed AHSS products in advance of the quality control and fabrication stages. [ABSTRACT FROM AUTHOR]

Chain-die forming is a new sheet metal forming technology which has been developed as a supplement to roll forming in fabricating Advanced High-Strength Steel (AHSS) products. It has an advantage by reducing redundant plastic deformation during the forming process. The implementation is achieved through increasing the deformation length, via increasing the virtual roll radii. The rolls with large radii are assemblies of shaped die-blocks through chains and therefore it is called “Chain-die Forming”. In this paper, a simplified analytical model, purely based on the geometric relationships of forming parameters is established to estimate the longitudinal strain development in Chain-die forming. The analytical model is verified successfully by finite element analysis (FEA) and experimental work. The factors affecting the peak longitudinal strain are also investigated. The study is expected to be useful to tooling designers to quickly assess the severity of a Chain-die forming process in the tooling design stage in order to shorten the tooling development time. [ABSTRACT FROM AUTHOR]

The residual stresses in a roll formed product play a critical role in determining the product quality. They are generally very complex and frequently difficult to predict due to the complicated fabricating process and its parameters. Consequently, they attract many concerns from roll forming scholars and engineers. However, how to inspect the residual stresses in roll formed products efficiently and economically is still a challenge. This paper introduces a novel, highly efficient, operationally simple and accurate residual stresses measurement method for evaluating the residual stresses in roll formed products. It utilizes a modification of the current sectioning methods to firstly obtain the membrane and bending residual stresses components. Then a novel material removal approach, the tapered removal, is employed to determine the layering stresses component by measuring the curvature variations of the remaining sample through its thickness direction. A practical implementation of the method is performed through the residual stresses measurement of a typical roll formed square hollow section (SHS). The method is successfully verified by the neutron diffraction method. The new method is expected to become a routine measuring method to determine the residual stresses distribution in roll formed products, with potentially significant impact on the roll forming industry. [ABSTRACT FROM AUTHOR]

The locomotive traction motor electric dynamics and its impact on the rail and vehicle have not been investigated deeply in transient wheel–rail contact conditions. Such transient traction behaviour could be more significant to dynamic traction performance and track degradation (i.e. corrugation formation, fatigue, wear, etc.) than steady state behaviour. In order to study this, detailed numerical simulations are performed to investigate the locomotive multi-body dynamic response to a change in contact conditions with an AC and DC electrical traction motor respectively. In particular, creep response, locomotive vibration, and dynamic normal and tractional forces are determined using a developed full scale locomotive dynamics model. The model includes the detailed AC and DC motor dynamics. Further investigation has been undertaken to understand the wear caused during and after the change of friction conditions from dry to wet and wet to dry. The result shows the GT46Ace locomotive AC drive can achieve higher traction efficiency compared to the equivalent DC drive running under notch 8, especially in the wet condition. It is also demonstrated that the AC drive produces slightly lower wear on average than the DC drive after the transient. However, the transient dynamic oscillation of wear caused by the AC drive is significantly higher than the DC drive. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is a highly flexible sheet forming process, but it suffers from poor geometric accuracy. This paper presents a feedback control strategy using model predictive control (MPC) to obtain improved geometric accuracy in ISF. Based on the incremental deformation mechanism of ISF, a novel model for shape state prediction has been proposed. The step depth of the toolpath was optimised based on shape state feedback during the forming process. Two different cases were studied for experimental validation of the developed control strategy. Comparisons between formed parts in both controlled and uncontrolled ISF processes were implemented in terms of cross-sectional profiles, formed depth at the bottom area and global deviation distribution. Results show that the geometric accuracy in ISF with feedback control has been greatly improved at the bottom area of the formed parts compared with a standard ISF approach without control. Improved geometric accuracy has been achieved on the wall of the parts as well. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is a promising manufacturing process that features benefits of reduced forming forces, enhanced formability and greater process flexibility. It also has a great potential to achieve economic payoff for rapid prototyping applications and for small quantity production in various applications. However, limited research has been conducted from the sustainability point of view, particularly for energy consumption. More consumed energy will generate more heat and affect tool and product wear. Also, geometric accuracy is still one of the dominant limits for the further development and commercialization of the ISF technology. Therefore, the aim of this study is to investigate how different process parameters affect the consumed energy during the forming process and also find the optimal working condition for lower deformation energy with higher geometric accuracy. A Box-Behnken design of 27 tests for pyramid-forming processes have been performed for a multi-objective optimisation that considers four factors: step down, sheet thickness, tool diameter and wall angle at three levels. The deformation energy during the forming process was calculated based on the measured forming forces. It was found that the deformation energy heavily depends on the sheet thickness because of higher plastic energy required to deform the material. Increasing step-down size within a limited range or decreasing the wall angle is also an effective approach to reduce the deformation energy. Moreover, the effects of various process parameters on the global geometric accuracy have also been investigated. The geometric error has been empirically predicted by quadratic equations giving the influence of the most influential forming parameters. It was concluded that the geometric quality is largely determined by the quadratic effect of wall angle, the linear effect of sheet thickness and the interaction effect of thickness and step down. Finally, the optimal working conditions for both independent and simultaneous minimisation of deformation energy and geometric error during the pyramid-forming process are provided. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is a promising forming process which is able to deform a flat sheet into a complex 3D shape by using a generic moving tool. The flexibility, increased formability and the reduced forming force make the ISF process ideal for rapid prototype and small batch production. However, the effective production design and optimization in ISF require the efficient prediction of forming force, especially the tangential force which is the actual force component that does plastic work during the forming process. In this paper, in order to investigate the deformation mechanism in the ISF process, a comprehensive finite element (FE) model for the cone-forming process with fine solid elements is established which allows the quantitative study of the deformation behavior of stretching, bending and shearing during the process. Based on such analysis, an efficient model for tangential force prediction is deduced analytically in which all these three deformation modes are considered. In particular, the contribution from each deformation mode is related to the variation of forming parameters. Additionally, the proposed efficient model is comprehensively validated with both truncated cone and pyramid shapes by varying four forming parameters (i.e. step down, wall angle, tool radius and sheet thickness). In both cases, the predicted forces show good agreements with the experimental results. Furthermore, the proposed model is generalized to deal with more complex shapes (e.g. ellipsoidal cup). It is found that the trend of tangential force could be properly represented by the change of the curvature of the formed part. Considering the proposed model can be solved within only several minutes, it will guide the forming process and shorten the lead time. [ABSTRACT FROM AUTHOR]

This paper presents the locomotive traction controller performance with respect to the track wear under different operation conditions. In particular, an investigation into the dynamic response of a locomotive under changing wheel–rail friction conditions is performed with an aim to determine the effect of controller setting on track wear. Simulation using a full-scale longitudinal–vertical locomotive dynamic model shows that the appropriately designed creep threshold, controller, settings can effectively maintain a high tractive effort while avoiding excessive rail damage due to wear, especially during acceleration under low speed. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) has been attractive during the last decades because of its greater flexibility, increased formability and reduced forming forces. However, traditional finite element simulation used for force prediction is significantly time consuming. This study aims to provide an efficient analytical model for tangential force prediction. In the present work, forces during the cone-forming process with different wall angles and step-down sizes are recorded experimentally. Different force trends are identified and discussed with reference to different deformation mechanisms. An efficient model is proposed based on the energy method to study the deformation zone in a cone-forming process. The effects of deformation modes from shear, bending and stretching are taken into account separately by two sub-models. The final predicted tangential forces are compared with the experimental results which show an average error of 6 and 11 % in respect to the variation of step-down size and wall angle in the explored limits, respectively. The proposed model would greatly improve the prediction efficiency of forming force and benefit both the design and forming process. [ABSTRACT FROM AUTHOR]

Highlights: [•] Two open-loop analytical models for multi-pass deformation design have been developed and tested given the predicted thickness strain of the final part as a main parameter using the assumption of shear deformation. [•] A comprehensive methodology for closed-loop multi-stage deformation pass design incorporating two developed models is proposed. [•] FEA and experimental tests have been performed to validate the comprehensive closed-loop design methodology with two analytical models. [•] The proposed closed-loop pass design methodology with M2 is proved to be an effective approach to designing multi-stage deformation passes in order to quantitatively control the material flow. [ABSTRACT FROM AUTHOR]

Highlights: [•] Field results are statistically analyzed and effects of different parameters on squat growth rate investigated. [•] A 3D finite element model is created and effects of some parameters are assessed. [•] Both FEM and statistical studies confirmed sleeper type and curve radius affect squat growth rate. [•] The correlation between field results and FEM validates results obtained from FEM. [ABSTRACT FROM AUTHOR]

• A hybrid constitutive model is developed to describe the stress-strain behaviors under ultrasonic vibration. • Finite element models are developed and verified for the ultrasonic-assisted ISF process. • The affecting mechanism of ultrasonic vibration on material deformation behavior is revealed. • Ultrasonic-actuated dynamic recovery is observed through microstructure examination. Ultrasonic vibration has been applied in the incremental sheet forming process and shows the potential to reduce the forming force and increase the formability, but the constitutive behavior and deformation behaviors of material under the high-frequency vibration are still not completely explained. In the present work, a hybrid constitutive model which combines the phenomenological, thermal activation and dislocation annihilation models is established and experimentally calibrated. Then, a finite element model is developed for the ultrasonic-assisted incremental sheet forming (UISF), in which the hybrid constitutive model and a user defined subroutine were incorporated to describe the ultrasonic effect and to simulate the high-frequency vibration, respectively. Compared with the experimental forming force, the FE analysis with the hybrid constitutive model shows good predictability with errors less than 10 %. Based on the simulation results, the improvement of formability was observed and the material deformation behavior during ultrasonic-assisted incremental sheet forming was analyzed in detail. Moreover, the material microstructural features were analyzed through Electron Back Scatter Diffraction (EBSD). The occurrence of relative larger grains and the increase of low angle grain boundaries (LAGBs) indicates the occurrence of ultrasonic-actuated dynamic recovery of the material. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the stress intensity factors (SIFs) around a 3D semi-elliptical squat on a rail surface are investigated. Elastic foundation and water trapped inside the crack are considered as key factors in crack propagation. It is found that the opening mode and shear modes show different behavior compared with former models. Also the lateral load can change the SIF pattern significantly. The superposition traction ratio and lateral load can increase the equivalent SIF up to 200%. This study confirms the pressurized water in a crack changes crack propagation direction making a squat. [Copyright &y& Elsevier]

Abstract: Tool wear manifests in change of roughness of roll surfaces and governs the surface quality of both coated and uncoated products. Decrease of friction and wear in the roll–strip interface will stabilize the performance of the cold roll forming (CRF) mill and ensure uniform process output. The scope of this paper includes an experimental study of adhesive wear of hardened tool steel blocks sliding against a mild steel wheel and field observation of tool wear in the CRF of zinc coated mild steel. Wear mechanisms are identified for the materials interacting during the CRF process. The results include an empirical value of tool wear coefficient for D2 steel sliding against unlubricated uncoated hot rolled AISI C1020 mild steel. [Copyright &y& Elsevier]