Papers by Keyword: Surface Damage

Abstract: The objective of this research is to study the surface damage of train wheels and rail under applied loads. The simulation of this damage was predicted and calculated using finite element method (FEM), specially with the ABAQUS program. According to the EN13674-1 (R350HT) and EN13262 standard for train rail and wheel, respectively, the train wheel and rail were modeled to create a suitable mesh and to simulate stress and deformation. The distribution of stress and deformation were first analyzed when the interaction between wheel and rail occurred. In this research the simulated damage was further discussed in the context of both rolling and non-rolling wheels on the rail. The simulated results showed that the maximum stress was distributed beneath the surfaces of wheels and rails, leading to initiation and propagation of crack. The continuous crack beneath the surface led to the surface fatigue, resulting in material loss. The fatigue life of surface was also evaluated and calculated based on these predicted stresses. The effect of plastic deformation occurring on the surface due to rolling fatigue were further discussed in this work.

Abstract: In this paper, surface galling failure process and mechanism of drill pipe’s rotary shouldered thread connection (RSTC) was studied by means of full-scale make-up and break-out (M&B) testing. The results showed that surface galling damage mainly appearred at the positions of leading flank, bearing flank and make-up shoulder of RSTC. The galling damage of three different positions was a process of mutual independence and mutual promotion, and they might appear simultaneously, and also appear at different stage. The surface galling failure was mainly due to metal’s plastic deformation and peeling off under the effect of compressive stress caused by friction and compression effect among the contacting metal surface. During M&B testing, deformed and peeling metal accumulated continually and resulted in "cold welding" at local position. In the subsequent M&B process, "cold welding" metal was torn open and peeled off from metal matrix, and metal surface galling was getting serious gradually. M&B testing results showed that torque load and thread compound had decisive influence on surface galling damage, while the influence of RSTC’s surface wear, rearranging, torque fluctuations and tensile load was not obvious.

Abstract: Sigma formation in duplex stainless steels is known to be detrimental to the mechanical properties of the material and limits the alloys to low temperature applications. In this paper, the surface damage caused by grinding on different grit sizes or polishing, is assessed using EBSD. The surface finish is then related to the depth of sigma formation in the surface region with a quantification of how the surface finish effects the sigma nucleation and growth. Finally, the effect of surface finish and sigma formation on the oxidation characteristics of the material is considered.

Abstract: Quartz glass is a typical hard and brittle material. During the manufacturing process of quartz glass components, ultra-precision grinding is widely used due to its high throughput and good dimensional accuracies. However, grinding will unavoidably induce large surface and subsurface damage. In this study, the surface and subsurface damage characteristics of quartz glass substrates ground by diamond wheels with different grit sizes were investigated in terms of surface roughness, surface topography, subsurface microcrack characteristic, and subsurface damage depth. Discussion was also provided to explore corresponding reasons of surface and subsurface damage induced by diamond grinding wheels with different grit sizes of #1500 and #2000. The experiment results showed that the surface roughness, surface damage, and subsurface damage depth induced by #2000 quartz glass was ground by #1500 diamond grinding wheel, and in ductile mode when ground by #2000 diamond grinding wheel.

Abstract: Hammers are the key machine element of high-speed hammer mills which lead to the coal pulverisation process. Progressive material loss from the hammer occurs due to the mechanical interactions between the coal particles and the hammer surface. Coal pulveriser industries implement extensive efforts to combat against premature material loss from the hammer surface due to coal particle impact which may result in premature failure. This work investigates the erosion wear mechanism through computational simulation. A numerical model is developed using Abaqus^® to simulate the solid coal particle impacting onto the hammer (target).The Abaqus/Explicit^® dynamic simulation solver is used for this analysis. The interactions between the solid coal particles and the target are modelled using the Abaqus/Explicit^® element deletion method. The Johnson and Cook plasticity model is employed to analyse the flow stress behaviour of ductile materials during impact. The developed stress and plastic strain are analysed through simulation on the impact surface. This model is applied to different ductile alloys to determine the best erosion wear resistance hammer material for extending the operating life of hammers in the coal pulverisation process.

Abstract: Mechanical preparation of mono-and multicrystalline silicon wafers by sawing, lapping, or grinding damages the surface. Depending on the mechanical impact of the treatment different degrees of damage structures occur. It is necessary for further processing of wafers to have damage free and contactless methods to characterize structures such as changes of the lattice structure by phase transformations or plastic deformations, and microcracks below the surface. In this paper we present results of investigations on the sub-surface damage by two contactless optical methods: Scanning infrared reflection polarimetry with SIREX and Raman spectroscopy. The investigations were carried out on silicon wafers sawn with the multi-wire technique using diamond coated wires. The sub-surface damage mainly consists of microcracks of different length, which penetrate several micrometers into the bulk. The results were compared with confocal microscopy and scanning electron microscopy analyses of the same damage structures.

Abstract: To remove the surface damages induced during mechanical polishing (MP) of 4H-SiC, a variety of wet etching recipes and etching conditions were studied. By evaluating the epilayers grown on these etching-treated wafers, it has been found that triangular defects (TRDs) are the main defects originated from the MP-induced damages in these samples. High temperature molten KCl etching at 1100 °C with KOH additive is very effective to remove the damaged surface while keeping a relatively flat surface. Epilayer grown on the KCl+KOH etched wafer showed a TRD density <0.9 cm^-2.

Abstract: The use of ceramics bearings in total hip joint replacement (THR) has increased markedly in the last ten years thanks to the optimum wear behaviour of ceramic-on-ceramic bearings and of the high biological safety of ceramic wear debris. As the number of ceramic THR bearings is increasing, also the number of implants that experience off-normal working conditions, e.g. edge loading, third bodies in the joint, soft tissues laxity, dislocation/subluxation of the joint, increases. Under all such conditions the surface of the bearing can be damaged to variable extent, leading eventually to a limitation of the expected performances of the implant.

Abstract: Two Cu samples: oxygen-free copper (99.99 wt% Cu) and deoxidized low-phosphorous copper (99.9 wt% Cu) were processed by equal channel angular pressing (ECAP). After the ECAP processing using 4 passes, equiaxed grains (~300 nm grain size) and elongated grains were formed for both samples. Fatigue strength of ultrafine grained Cu was enhanced by the addition of trace impurities. The formation behavior of surface damage and the change in surface hardness during stressing were monitored. A close relationship was observed between the change in hardness and the formation behavior of damage. The effect of trace impurities on the fatigue damage was discussed from the viewpoints of the grain coarsening and the crack initiation/growth behaviors.

Abstract: In this study, a U-channel bending test with tension were used to evaluate the surface damage resistance of dual-phase (DP) steel against heat treated Mo-Cr cast iron, and a numerical simulation model of the U-channel bending were developed to analyze the interface contact pressure on formed part that is an important influencing factor of surface damage. Investigation results for two bare steel sheets DP780 and DP590 demonstrate that DP780 steel showed more severe surface damage on formed part, and that for the steel DP780 greater interface contact pressure is induced as a result of effect of larger plastic deformation.