Calculation of mechanical behaviors of shape memory alloy under multi-axial loading conditions

In this paper, for the calculation of the deformation behaviors of shape-memory alloy under multi-axial loading conditions with temperature changes, a two-dimensional mechanical model of polycrystalline shape memory alloy is constructed on the bases of the crystal plasticity and the deformation mechanism of shape memory alloy. In such a model, the orientation of crystal grain in the polycrystal and the loading direction can be considered. The deformation behaviors under some complex loading conditions are calculated with the model, and the results show that they are in good qualitative agreement with the experimental results.     

A metallographic examination of rollers subjected to wear under rolling-sliding conditions

Wear rate versus maximum contact pressure p₀ curves were obtained at 3%, 6% and 9% creep for rollers of a fracture tough rail steel (0.40 C-1.46 Mn) that were tested in a twin-disc wear and lubrication machine. Subsurface cracks were observed to form below and above the mild-severe wear transition; these increased in depth and profusion with increasing creep and increasing p₀. Cracks close to the surface are almost parallel with it and eventually break through to form flake-like particles of wear debris. Undeformed inclusions or inclusions with a low index of deformation are considered to be crack initiators, and Al₂O₃ particles were mainly associated with the cracks although more malleable MnS was also found. Tangential contact forces obtained from positive creep and an adequate coefficient of friction are necessary for crack formation. Microhardness tests disclosed that the wear rate appears to correlate with hardness at the extreme surface.     

A multivariate surface roughness modeling and optimization under conditions of uncertainty

Correlated responses can be written in terms of principal component scores, but the uncertainty in the original responses will be transferred and will influence the behavior of the regression function. This paper presents a model building strategy that consider the multivariate uncertainty as weighting matrix for the principal components. The main objective is to increase the value of R² predicted to improve model’s explanation and optimization results. A case study of AISI 52100 hardened steel turning with Wiper tools was performed in a Central Composite Design with three-factors (cutting speed, feed rate and depth of cut) for a set of five correlated metrics (R_a, R_y, R_z, R_q and R_t). Results indicate that different modeling methods conduct approximately to the same predicted responses, nevertheless the response surface to Weighted Principal Component – case b – (WPC1^b) presented the highest predictability.     

Postbuckling of shear-deformable flat and curved panels under combined loading conditions

The static postbuckling of flat and doubly-curved shallow panels under the combined action of a system of uniaxial/biaxial compressive edge loads and a lateral pressure field is investigated, and the effects of transverse shear, initial geometric imperfections and tangential edge constraints upon load carrying capacity of curved panels are emphasized. Comparisons of the classical and shear deformable theories are made and issues related to the sensitivity to the snap-through behaviour are discussed. A variety of loading systems and panel geometries are considered in the numerical illustrations and pertinent conclusions related to the postbuckling response are outlined.     

Friction and wear behaviour of AISI 5140 steel under rectangular wave loading conditions

Abstract

The tribological characteristics and wear mechanisms of AISI 5140 steel at ambient temperature were investigated using a home built ball on disc tribometer under constant normal loading and rectangular wave loading respectively. The worn surface and wear debris collected from the disc were studied using scanning electron microscope. Results show that the friction coefficients under the constant normal force correspond to the traditional theory. The coefficients all exhibited increased normal loads, whereas under the rectangular wave condition, the highest coefficient appeared when the peak value of the periodically alternative load was 90?N. The different underlying wear mechanism under different loading conditions was explored. It was found that abrasive wear was the main mechanism in the constant loading, whereas severe plastic deformation and adhesive wear were the main wear mechanism in the rectangular wave loading cases. This phenomenon can be attributed to the role of debris in the ‘lubrication’ process under the rectangular wave loading conditions.     

Relation between scuffing resistance and the increase in surface hardness during tests under conditions of rolling/sliding

The effect on scuffing resistance of a change in the condition of the rubbing surfaces, especially surface hardness, was investigated using a two-disc machine. Scuffing resistance increased with increasing surface hardness during testing. The increase of surface hardness by work hardening is more beneficial in preventing scuffing than is a change in carbon content or heat treatment. Work-hardened disc surfaces allow surface film formation as a result of plastic deformation. Materials with large Meyer indices and high surface hardness are less prone to scuffing.     

集装箱装卸运输振动冲击环境条件分析

分析了集装箱在装卸和运输过程中的振动冲击值,结合振动冲击等环境条件对货物的影响,提出了安全防护措施,为货物集装箱安全运输提供了理论依据.     

Effect of surface topography on mixed lubrication film formation during start up under rolling/sliding conditions

The start up operation of mixed lubricated contacts represents one of the transient conditions that bring the risk of the surface damage because of asperities interactions. This paper focuses on the effects of both artificially produced and real roughness features on mixed lubrication film formation during start up of non-conformal contacts operated under rolling/sliding conditions. Chromatic interferograms captured during start up enabled the detailed changes in lubrication film caused by surface features to be observed. The observation of the effects of surface dents artificially produced on the ball surface helped to better understand the behaviour of real surface topography. It was found that the presence of shallow surface features can help to separate mixed lubricated rubbing surfaces more efficiently than it could be suggested from the results obtained with smooth surfaces. Lubricant emitted from surface features appears to spread more easily within the mixed lubricated contact because of local decrease of pressure in the vicinity of real surface features. Conversely, high pressure within smooth contacts restricts the migration of lubricant emitted from surface pits much more. It can be suggested from the results obtained that the properly designed topography of the rubbing surfaces can help to reduce the asperities interactions under transient operational conditions.     

Contact fatigue and wear behaviour of bismaleimide polymer subjected to fretting loading under various temperature conditions

Cracking and wear induced by fretting is a critical problem for industrial composite structures. Thermosetting bismaleimide resin is a promising material due to its good mechanical and thermal properties. The effect of temperature regarding fretting cracking and fretting wear is presently investigated. The temperature effect on crack initiation and propagation is quantified combining experiments and modelling. The fretting wear is explained using a friction energy wear approach. A bilinear evolution of wear volume versus the dissipated energy is identified and related to a protective third body layer. These various damage evolutions are compared to the viscoelastic properties of the polymer.     

Functional needs, machining conditions, and economics of surface finishing

Two applications of surface finish technology to industrial problems are discussed. The first problem involves the deterioration of tools used to turn large numbers of parts. Preliminary observations indicated that waviness of the tool cutting surface impeded chip flow over the tool and reduced usable life. Changing the tool finishing conditions reduced waviness considerably and increased tool life between sharpenings from 8000 to 53 000 parts. The second case involves the degradation of flat steel tracks for rolling needle bearings in a moulding machine. Waviness of both the newly ground and refinished surfaces led to their rapid deterioration In addition, the hardness of the steel was also considered to be too low for this application. By improving the finishing process, the life of a set of guides was improved from typically 1500 hours to 5000 hours. For this case, the financial implications of the results are also discussed.     

Measurement of friction force and effects of oil fortifier in engine journal bearings under dynamic loading conditions

Commercial base oil and oil fortifier added to this oil are used to investigate the frictional behavior of the engine journal bearings using the theoretical Reynolds equation and experimental test rig. In the theoretical part of the study, the Reynolds equation that states the pressure distribution and friction force with finite width was solved by using the finite difference method. In the experimental part of the study, a new design test rig was conducted to measure the friction force, the lubricant film thickness of the engine journal bearing using base oil under dynamical loaded conditions. The effect of oil fortifier was detected measuring the friction force every three minutes in each 360 crank angle during 15 minutes of experiment. As the theoretical friction results showed similar variation with the experimental measurements of engine bearings, adding oil fortifier to the base oil presented a substantial reduction of friction force during the testing period.     

Plastic yielding of I-beams under shear, and shear and axial loading

Plane strain and plane stress slip-line field solutions previously published by the authors for cantilevers of rectangular cross-section are utilized to estimate the plastic collapse loads of corresponding I-sectioned beams. Uniform I-beams, tapered and haunched beams, and beams with rectangular holes and castellated beams are studied. Previous works in each case are reviewed and for uniform-section cantilevers with end shear loading, the results are compared with the theoretical results of others and with the experimental results of Green and Hundy.     

Toughness and fracture mechanisms of glass fiber/aluminum hybrid laminates under tensile loading

Tensile properties and fracture toughness of monolithic aluminum (Al), glass fiber reinforced plastics (GFRPs) and glass fiber/aluminum hybrid laminates (GFMLs) were examined in relation to the fracture processes of plain coupon and single-edge-notched specimens. Elastic modulus and ultimate tensile strength of GFMLs showed characteristic dependences on the kind of Al, fiber orientation and the Al/fiber layer composition ratio. Fracture toughnesses K_C and G_C of A-GFML-UD were comparable to those of GFRP-UD and were much superior to monolithic Al. However, GFML with a transverse crack parallel to the fiber layer deteriorated largely in toughness. Microscopic observation of the fracture zone in the vicinity of the crack tip revealed various modes of micro-cracks in the respective layers as well as fiber fractures and delamination between fiber/Al layers. Such damage advances in GFMLs dependent on the orientation of the fiber layer and the Al/fiber composition ratio strongly influenced the strength and toughness of GFMLs.     

A review on the progress towards improvement in surface integrity of Inconel 718 under high pressure and flood cooling conditions

Self-conditioning performance of polishing pad is an important characteristic to influence processing efficiency and service life in chemical mechanical polishing (CMP). The slurry can react with the pad surface, which affects its self-conditioning performance in fixed abrasive polishing process. Wear ratio of wafer material removal rate (MRR) and pad wear rate is introduced to evaluate self-conditioning performance of fixed abrasive pad (FAP). To clear the effect of chemical additive on FAP self-conditioning, wear ratio, FAP surface topography, friction coefficient, and acoustic emission signal of polishing process were investigated in fixed abrasive polishing of quartz glass with ferric nitrate, ethylenediamine (EDA), and triethanolamine (TEA) slurry, respectively. Results indicate that TEA slurry can provide excellent self-conditioning of FAP in fixed abrasive polishing of quartz glass. MRR and wear ratio maintain high levels during the whole polishing process. Friction coefficient and acoustic emission signal are more stable than that of the other two chemical additives. An appropriate amount of TEA, which is beneficial to enhance MRR and extends service life of FAP, is added in the polishing slurry to improve FAP self-conditioning in fixed abrasive polishing process.     

A semi-analytical technique for bending analysis of cylindrical panels with general loading and boundary conditions

Cylindrical panels are structural elements widely used in engineering structures for high value of strength to weight ratio. Exact solutions of cylindrical panels are available only for a very limited number of cases. The main target of this paper is to utilize a semianalytical technique to study bending behavior of cylindrical panels with different boundary conditions under general distributed loading. The solution of the partial differential equations was reduced to an iterative sequential solution of a double set of ordinary differential equations using extended Kantorovich method. The competence and accuracy of the method is established by comparison with available results in the literature and finite element analyses which shows good agreement.     

Influence of ball burnishing on surface quality and tribological characteristics of polymers under dry sliding conditions

In this paper, the application of ball burnishing as a new surface treatment process for polymers is investigated. The polymers used were polyoxymethylene (POM) and polyurethane (PUR). The lowest surface roughness value achieved for POM was 0.44 μm (45% decrease) and for PUR was 0.46 μm (42% decrease). The lowest coefficient of friction value achieved was 0.22 (32.9% decrease) for POM and 0.24 (28.8% decrease) for PUR. The lowest specific wear rate value achieved was 0.31×10⁻⁶ mm³/N m (38.6% decrease) for POM and 0.41×10⁻⁶ mm³/N m (37.9% decrease) for PUR.     

Buckling analysis of FGM plates under uniform,linear and non-linear in-plane loading

The paper investigates the buckling responses of functionally graded material (FGM) plate subjected to uniform, linear, and non-linear in-plane loads. New nonlinear in-plane load models are proposed based on trigonometric and exponential function. Non-dimensional critical buckling loads are evaluated using non-polynomial based higher order shear deformation theory. Navier’s method, which assures minimum numerical error, is employed to get an accurate explicit solution. The equilibrium conditions are determined utilizing the principle of virtual displacements and material property are graded in the thickness direction using simple Voigt model or exponential law. The present formulation is accurate and efficient in analyzing the behavior of thin, thick and moderately thick FGM plate for buckling analysis. It is found that with the help of displacement-buckling load curve, critical buckling load can be derived and maximum displacement due to the instability of inplane load can be obtained. Also, the randomness in the values of transverse displacement due to inplane load increases as the extent of uniformity of the load on the plate is disturbed. Furthermore, the parametric varying studies are performed to analyse the effect of span-to-thickness ratio, volume fraction exponent, aspect ratio, the shape parameter for non-uniform inplane load, and non-dimensional load parameter on the non-dimensional deflections, stresses, and critical buckling load for FGM plates.

     

Effect of friction-induced hardening on the features of magnetic and eddy-current behavior of an annealed structural steel under cyclic loading conditions

The effect of friction processing on the mechanical properties in uniaxial tension, the magnetic properties, and the electromagnetic characteristics of an annealed Steel 3 (St3) grade structural steel has been studied. It is established that the coercive force, residual magnetic induction, initial magnetic permeability, and eddy-current characteristics can serve as parameters for monitoring the quality of steel hardened by friction processing. Features of friction-induced changes in the strength, magnetic properties, and electromagnetic characteristics of St3 grade steel loaded in the region of low-cycle fatigue are revealed. It is shown that magnetic and eddy-current techniques can be used for monitoring the state of a friction-hardened surface layer of steel samples in the course of their cyclic loading.     

Wear and surface analysis of 38 mm ceramic-on-metal total hip replacements under standard and severe wear testing conditions

The purpose of this study was to compare the wear of zirconia-toughened alumina (ZTA) and alumina femoral heads tested against as-cast CoCrMo alloy acetabular cups under both standard and severe wear conditions. A new severe test, which included medio-lateral displacement of the head and rim impact upon relocation, was developed. This resulted in an area of metal transfer and an area of increased wear on the superior-anterior segment of the head that were thought to be due to dislocation and rim impact respectively. While the wear of all ceramic heads was immeasurable using the gravimetric method, the wear rates for the metallic cups from each test were readily calculated. An average steady state wear rate of 0.023 +/- 0.005 mm3/10(6) cycles was found for the cups articulating against ZTA under standard wear conditions. A similar result had previously been obtained for the wear of cups articulated against alumina heads of the same size (within the same laboratory). Under severe wear conditions an increase in the metallic cup steady state wear rate was found with the ZTA and alumina tests giving 0.623 +/- 0.252 and 1.35 +/- 0.154 mm3/10(6) cycles respectively. Wear of the ceramic heads was detected using atomic force microscopy which showed, under severe wear conditions, a decrease in polishing marks and occasional grain removal. The surfaces of the ZTA heads tested under standard conditions were virtually unchanged from the unworn samples. Friction tests showed low friction factors for all components, pre and post wear.