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To obtain the optimal mechanical properties, several processes including spray forming technology, two passes hot extrusion and substantial heating treatments were operated on an Al-Zn-Mg-Cu-Zr alloy. The characterization methods used in this study include tensile tests, X-ray diffraction, differential scanning calorimetry and microstructure observations by optical microscope, scanning and transmission electron microscopy. The typical characteristics were the refined grain, homogeneous precipitates and porosity in the as-deposited pre-forms. The ultimate tensile strength, yield strength, hardness and elongation improved significantly after two passes hot extrusion. A good combination of ultimate tensile strength at 704 MPa and elongation at 9.7% were achieved under peak-aged treatment. The best ultimate tensile strength was obtained at 732 MPa after re-aging and regression. It was main dimple fracture in the extruded and aging treated specimens while brittle fracture for the as-deposited. The secondary phases were main MgZn2 and Al3Zr dispersoids throughout all the states. The contributions of grain boundaries, dislocations, solid-solution and precipitates on the yield strength were analyzed using a quantitative equation.

Hot compression tests in the temperature range of 340–450 °C and strain rate range of 0.001–1 s−1 of spray-formed 7055 aluminum alloy were carried out to study its hot deformation behavior. Three phenomenological models including Johnson–Cook, modified Fields–Backofen and Arrhenius-type were introduced to predict the flow stresses during the compression process. And then, a comparative predictability of the phenomenological models was estimated in terms of the relative errors, correlation coefficient (R), and average absolute relative error (AARE). The results indicate that Johnson–Cook model and modified Fields–Backofen model cannot well predict the hot deformation behavior due to the large deviation in the process of line regression fitting. Arrhenius-type model obtains the best fit through combining the effect of strain rate and temperature.

The relationship among microstructures, mechanical properties and corrosion behaviors of spray formed 7055 aluminium alloy has been investigated upon peak-aging (T6), double-aging (DA) and retrogression and re-aging (RRA). The research is estimated by hardness test, tensile test, immersion test, detailed microstructure observation and potentiodynamic polarization under different aging treatments. Results demonstrate that the corrosion resistance rank of aging treatments is as follow: DA > RRA > T6. The continuous grains boundary precipitations (GBPs) and coarse Al7Cu2Fe particles increase the corrosion susceptibility. The appearance of the pit cavity attributes to coarse grains and the considerable potential difference between the matrix and GBPs or precipitate-free zones (PFZs) during intergranular corrosion (IGC) process. The wedging stress from hydrogen cracks and the accumulation of the corrosion products help induce the exfoliation corrosion (EXCO). Anodic dissolution and hydrogen embrittlement cause stress corrosion cracking (SCC) of the alloy under different aging treatments. The strengthening mechanism attributes to the distribution of matrix phases (MPs), η′ phase and Al3Zr particles.

The hot deformation behavior of spray formed ultra-high strength aluminum alloy was investigated by isothermal compression tests at 613–723 K and 0.001–1.0 s−1. The flow stresses were predicted by using phenomenological model (strain-compensated Arrhenius equation), physical-based model (diffusion model) and artificial neuron network. The predictive ability has been weighed through statistical analysis including relative errors, correlation coefficients and box charts. It has shown the artificial neural network contains the best capability to predict the flow stress over the applied phenomenological and physical-based model. The strain-compensated Arrhenius can track the flow stress well in all processing conditions. Moreover, the diffusion model can well describe the metallurgical mechanisms during deformation by the microstructure observation.

Misalignment between the shaft and the bearing of a journal bearing set may be inevitable and can negatively impact journal bearing performance metrics in many industrial applications. This work proposes a convex profile design of the journal surface to help counteract the negative effects caused by such a misalignment. A transient mass-conserving hydrodynamic Reynolds equation model with the Patir–Cheng flow factors and the Greenwood–Tripp pressure–gap relationship is developed to conduct the design and analysis. The results reveal that under transient impulse loading, a properly designed journal profile can help enhance the minimum film thickness, reduce mean and peak bearing frictions, and increase bearing durability by reducing the asperity-related wear load. The mechanism for the minimum film thickness improvement due to the profile design is traced to the more even distribution of the hydrodynamic pressure toward the axial center of the bearing. The reason for the reductions of the friction and wear load is identified to be the decreased asperity contact by changing the lubrication regime from mixed lubrication to nearly hydrodynamic lubrication. Parametric studies and a case study are reported to highlight the key points of the profile design and recommendations for profile height selection are made according to misalignment parameters.

Properly designed micro-scale surface textures can have positive impact on adhesion reduction and lubrication enhancement, which can lead to lower friction and improved performance of a contact interface. The present study aims to utilize this function of textures to reduce the adhesion between a drill and a workpiece. In this study, rectangular surface textures were generated on the margins of drill bits using a diode-pumped Nd:YVO4 picosecond laser with a wavelength of 532 nm. Two designs were created in which the textures covered approximately 10 and 20 % of the margin surface area. Textured drills were tested by drilling a series of holes in a titanium plate while recording cutting forces, and the results were compared with the performance of baseline samples. Thermographic heat profiles and visual inspections of the drills were taken at increments of 5 and 10–15 holes, respectively. The comparison demonstrated an encouraging improvement in drill bit life as judged by the number of holes drilled before failure. Textured drills were found to reduce adhesion of titanium chips on the drill margins. This work has demonstrated the potential of texturing to significantly improve the lifetime of drill bits and similar cutting tools.

Friction is the reason for the process of rolling to actually take place, and it plays an important role in determining the rolling mechanics and deformation distributions of the strip. At the interface between the roll and strip, friction has a significant influence on the dimensional accuracy and strip surface quality. This paper presents the modelling of cold strip rolling taking into account the friction along the strip rolling and transverse directions. A 3D rigid plastic finite element method considering slightly compressible material, and an influence function method were employed, respectively, to analyse the cold strip rolling, and simulation results show that the friction in both directions has a significant effect on the rolling mechanics, strip shape and profile. Variation of the transverse friction affects the strip edge drop, but the friction variation along the rolling direction may affect the central and edge buckles of the strip. The calculated rolling forces are in good agreement with the measured values.

Steady-state mixed hydrodynamic lubrication of rigid journal bearing is investigated by using a finite difference form of the Patir–Cheng average Reynolds equation under the Reynolds boundary condition. Two sets of discretization meshes, i.e., the rectangular and nonorthogonal herringbone meshes, are considered. A virtual-mesh approach is suggested to resolve the problem due to the singularities of pressure derivatives at the turning point of the herringbone mesh. The effectiveness of the new approach is examined by comparing the predicted load with that found in the literature for a smooth-surface case solved in the conventional rectangular mesh. The effects of the skewness angles of symmetric and asymmetric herringbone meshes on the predicted parameters, such as load, friction coefficient, attitude angle, and maximum pressure, are investigated for smooth, rough, and herringbone-grooved bearing surfaces. It is found that the new approach helps to improve the computational accuracy significantly, as demonstrated by comparing the results with and without the treatment of the pressure derivative discontinuity although the latter costs slightly less computational time.

When a conformal interface is under low velocity and heavy load conditions, solid contact (or dry contact) may occur even in a system with smooth surfaces. This paper presents two approaches for solving steady-state and transient mixed elastohydrodynamic lubrication problems of journal bearings with smooth surfaces under low rotating speed. The first approach uses the reduced Reynolds equation with a combined finite element–backward finite difference scheme and the second applies a zero film thickness equation to describe the mechanical behavior of mating surfaces at solid contact points. The major advantages of these two approaches are (1) no division of the solution domain into a lubricated area and a solid contact area is necessary and (2) the solid contact pressure, lubricant pressure, and eccentricity ratio can be solved simultaneously. Numerical examples are presented for the application of these approaches. For the steady-state cases under low velocity studied in this work, pressure distributions a...

A new mesh free approach is put forwards for the numerical simulation of bulk metal forming processes. The approach is based on the utilization of the reproducing kernel particle method in conjunction with the flow formulation for incompressible and slightly compressible rigid-plastic materials. Special emphasis is placed on the utilization of adaptive cell procedures that are capable of generating a new set of background cells at the end of each increment of deformation. Results show that the proposed methodology is capable of efficiently handling large plastic deformations without remeshing and providing results that are in close agreement with both finite element predictions and experimental measurements.

The reproducing kernel particle method based on the irreducible flow formulation is utilised to perform the numerical simulation of bulk metal forming processes. Emphasis is given on analysing the influence of employing triangular or quadrilateral background cells on the predictions of material flow, forming load and distribution of strain. A new proposal to smooth the distribution of average stresses during stress computations in the background cells is also included. The effectiveness of the proposed method is discussed by comparing its numerical predictions with a benchmark test case, finite element calculations and experimental data. The benchmark test case is included with the objective of illustrating the influence of several theoretical and numerical subjects such as; order of the basis correction functions, dimension of the compact support and computation of the volume associated to each nodal point. Experimental data was acquired from metal forming controlled laboratory-based tests that were designed so that the proposed method could be tested on its ability to efficiently handle large plastic deformations. It is shown that adaptive arbitrary triangular background cells are capable of efficiently handling large plastic deformations without remeshing.

This paper draws from the fundamentals of the finite integral mesh free representation methods and of the rigid-plastic formulation for slightly compressible materials to the main aspects of computer implementation and modelling of bulk-metal forming processes. Fundamental research and development is based on the reproducing kernel particle method (RKPM) and the corrected smoothed particle hydrodynamics (CSPH) method. Special emphasis is placed on a wide range of theoretical and numerical subjects such as discretization procedures, numerical integration of the system matrices derived from the weak form, relief of volumetric locking, geometrical update of the deforming workpiece, and treatment of the frictional contact interface between the workpiece and tooling.

A new approach is put forwards for the numerical simulation of steady and non-steady state bulk metal forming processes. The approach is based on the utilization of the reproducing kernel particle method in conjunction with the flow formulation for slightly compressible rigid-plastic materials.The effectiveness of the proposed approach is discussed by comparing theoretical predictions with finite-element calculations and experimental data for three different bulk metal forming operations: flat rolling (under steady-state conditions), compression of rods and heading of cylindrical billets. The overall comparisons comprise a wide range of topics such as material flow, geometry, strain distribution and forming load/torque. It is shown that, the proposed approach is capable of efficiently handling large plastic deformations without the need of remeshing procedures and providing results that are in close agreement with both finite-element predictions and experimental measurements.

A new approach based on the utilization of the reproducing kernel particle method is put forwards for the numerical simulation of bulk metal forming processes. The approach is based on the utilization of the reproducing kernel particle method in conjunction with the flow formulation for slightly compressible rigid-plastic materials. The effectiveness of the proposed methodology is discussed by comparing theoretical predictions with finite element calculations and experimental data. The later were obtained by means of simple metal forming experiments that were performed under laboratory-controlled conditions using aluminium Al6060 (natural aged). The overall comparisons comprise a wide range of topics such as material flow, geometry, forming load, strain and stress distributions. As results show, the proposed approach is capable of efficiently handling large plastic deformations without the need of remeshing procedures and providing results that are in close agreement with both finite element predictions and experimental measurements.

A finite element model is presented for mixed lubrication of journal-bearing systems operating in adverse conditions. The asperity effects on contact and lubrication at large eccentricity ratios are modelled. The elastic deformation due to both hydrodynamic and contact pressure, and the cavitation of the lubricant film are considered in the model system. Two verification problems with both theoretical and experimental comparisons are given to show the effectiveness of this model. Finally, a new example is presented which discusses the influence of waviness depth, secondary roughness, external force and shaft speed on the mixed lubrication. Copyright © 2004 John Wiley & Sons, Ltd.

This paper presents a numerical approach for analysing three‐dimensional steady‐state rolling by means of the reproducing kernel particle method (RKPM). The approach is based on the flow formulation for slightly compressible materials and a detailed description of RKPM and its numerical implementation is presented with the objective of providing the necessary background. Special emphasis is placed on the construction of shape functions and their derivatives, enforcement of the essential boundary conditions and treatment of frictional effects along the contact interface between the workpiece and the roll. The effectiveness of the proposed approach is discussed by comparing the theoretical predictions with the finite element calculations and experimental data found in the literature.

Numerical simulation of lubrication of journal bearing often uses a rectangular discretisation mesh. Steady-state mixed hydro-dynamic lubrication of rigid plain journal bearing is investigated by using finite difference form of Patir-Cheng average Reynolds equation under Reynolds boundary condition. Two kinds of non-orthogonal discretisation meshes, i.e., helix mesh and symmetric herringbone mesh are considered respectively. Three difference schemes, i.e.: 1) central finite difference; 2) second order upwinding; 3) a new central finite difference considering the film thickness at the projected positions from the nodes of neighbouring rows; are used to difference the shear induced flow term (i.e., Couette term). The effectiveness of the three schemes is discussed using the skewed discretisation mesh by comparing theoretical predictions of load with that found in the literature for smooth lubrication using the rectangular discretisation mesh. The effect of the skewed angle of mesh on the predicted parameters such as load, friction coefficient, attitude angle and maximum pressure is investigated for both smooth and rough surfaces. It is found that generally these schemes may provide a reasonable satisfactory solution. However, when symmetric herringbone mesh is used, a larger relative deviation is found as the skewed angle is larger and the eccentricity ratio is smaller.

Steady-state smooth surface hydrodynamic lubrications of a pocketed pad bearing, an angularly grooved thrust bearing, and a plain journal bearing are simulated with the mass-conservation model proposed by Payvar and Salant. Three different finite difference schemes, i.e., the harmonic mean scheme, arithmetic mean scheme, and middle point scheme, of the interfacial diffusion coefficients for the Poiseuille terms are investigated by using a uniform and nonuniform set of meshes. The research suggests that for the problems with continuous film thickness and pressure distributions, the results obtained with these numerical schemes generally well agree with those found in the literatures. However, if the film thickness is discontinuous while the pressure is continuous, there may be an obvious deviation. Compared with both the analytical solution and other two schemes, the harmonic mean scheme may overestimate or underestimate the pressure. In order to overcome this problem artificial nodes should be inserted along the wall of the bearings where discontinuous film thickness appears. Moreover, the computation efficiency of the three solvers, i.e., the direct solver, the line-by-line the tridiagonal matrix algorithm (TDMA) solver, and the global successive over-relaxation (SOR) solver, are investigated. The results indicate that the direct solver has the best computational efficiency for a small-scale lubrication problem (around 40 thousand nodes). TDMA solver is more robust and requires the least storage, but the SOR solver may work faster than TDMA solver for thrust bearing lubrication problems. Numerical simulations of a group of grooved thrust bearings were conducted for the cases of different outer and inner radii, groove depth and width, velocity, viscosity, and reference film thickness. A curve fitting formula has been obtained from the numerical results to express the correlation of load, maximum pressure, and friction of an angularly grooved thrust bearing in lubrication.

A compliance operator is often utilized to evaluate the elastic displacement of surfaces in the simulation of transient and steady-state elastohydrodynamic lubrication of conformal-contact systems. The values of the compliance operator represent the elastic responses of all nodes when only one node is under a unit load. The accuracy of compliance operator values, computational cost, and storage size are important issues. Our study of steady-state conformal-contact elastohydrodynamic lubrication analyses suggests a method of selective-fine-mesh with selective-storage, as well as a special technique of the combined selective-fine-mesh with selective-storage mapping. These two techniques enable an efficient elasticity procedure for the simulation of steady-state and transient conformal-contact elastohydrodynamic lubrication systems by means of the finite element method.

Topography development is an important component of surface engineering. Surfaces with controlled micro geometry may help enhance the lubrication. The development and application of textured surfaces in bearing design requires deterministic analyses of the micro feature effect on lubrication. However, limited numerical tools are available on deterministic mixed lubrication solutions for conformal-contact systems with real engineering surfaces due to the difficulty that conformal geometry involves a much larger area of surface interaction as compared to point contact geometry. Generally, a huge amount of storage and computer time can be involved if a micro-scale fine mesh capable for asperity description is used for an overall conformal lubrication analysis. Although an absolute solution is difficult, the authors intend to try conditional solutions without losing generality. Reported in this presentation is a new deterministic model for the mixed lubrication of surfaces in conformal contact. Numerical schemes to accelerate computations are developed and tested, the model application to journal bearing lubrication is explored, and sample calculations are conducted.

A compliance operator, Eji , is often utilized to evaluate elastic deformation in the simulation of transient and steady state elastohydrodynamic lubrication of conformal-contact systems. The values of the compliance operator represent the elastic responses of all nodes when only one node is under a unit load. The accuracy of compliance operator values, computational cost, and storage size are important issues. Based on our previous study on steady-state conformal-contact elastohydrodynamic lubrication systems, an advanced method of selective-fine-mesh with selective storage is suggested, and a special technique of combined selective-fine-mesh with selective storage mapping is proposed. These two techniques enable an efficient elasticity procedure for the simulation of transient conformal-contact elastohydrodynamic lubrication systems.Copyright © 2008 by ASME

A compliance operator is often utilized to evaluate the elastic deformation during simulation of elastohydrodynamic lubrication of conformal-contact systems. The values of the compliance operator represent the elastic deformations of all nodes when only one node is under a unit external load. The accuracy of compliance operator values, computational cost, and storage size are important issues. It is found that values only in a small region surrounding the loading node should be used and those in other regions can be discarded. Moreover, the mesh refinement in thickness direction is found to be more important than that along the longitudinal and width directions. A simple formula is suggested as the relationship between the values of a compliance operator and refinement steps. These two approaches enable an efficient elasticity procedure for the simulation of conformal-contact Elastohydrodynamic lubrication systems.Copyright © 2007 by ASME

The effect of roughness is an important consideration in the lubrication analysis and surface geometric design of heavy-duty machine elements. Deterministic simulation techniques have been developed for the investigation of point-contact mixed-lubrication problems. Such approaches should also be extended to obtain deterministic mixed lubrication solutions for journal-bearing conformal-contact systems. However, journal-bearing mixed lubrication involves a much larger area of surface interaction as compared to that in point contact problems. It is difficult to use similar micro/nano scale meshes directly to journal bearings under the current computation capability. It is a great challenge to develop a new deterministic numerical model for the mixed lubrication of journal bearing systems with the consideration of the effect of surface geometry design. This paper presents a macro-micro scale finite-element local-enrichment model for the deterministic analysis of conformal-contact mixed lubrication, in which a coarse mesh is used to determine the elastic deformation of a journal bearing surface, whilst locally refined meshes are used for the analysis of the roughness effect. The results from investigating the performance of bearing surfaces with sinusoidal and dimple textures suggest that the minimum film thickness may be improved through an appropriate surface texture configuration.Copyright © 2006 by ASME

The effect of roughness should be taken into consideration in the lubrication and geometric design of heavy-duty machine elements. Deterministic simulation techniques have been developed for the investigation of point-contact mixed-lubrication problems. Such approaches should also been extended to deterministic mixed lubrication solutions for journal-bearing conformal-contact systems. However, journal-bearing mixed lubrication involves a much larger area of surface interaction as compared to point contact problems. It is difficult to use similar micro/nano scale meshes directly to journal bearings under the current computer capability. It is a great challenge to develop a new deterministic numerical technique for the mixed lubrication of journal bearing systems with the consideration of the effect of surface roughness design. This paper presents a special technique for deterministic analyses of journal-bearings in mixed lubrication conditions, in which the coarse mesh is used to determine the elastic deformation of the journal bearing, whilst locally refined meshes are used for the effect of roughness. Journal-bearing systems in heavy machinery are often subject to dynamic loading. Therefore, a transient refinement scheme is also introduced.Copyright © 2005 by ASME

A mesh-free approach is used for analysing the effect of the friction factor on three-dimensional steady state slab edging, which is based on the Reproducing Kernel Particle Method (RKPM, Liu et al., 1995) and the material flow formulation for slightly compressible materials (Osakada et al., 1982). In order to cope with the singularity at the corner of the roll entry, a simple technique with a very thin array of cells at the inlet region adjacent to the plastic deformation zone (Xiong et al., 2003) is used. The results show that the dog-bone shape becomes smaller with the increment of friction factor. The roll separating force and total rolling torque increase with the friction factor.