Surface Plastic Strain Research Articles

Damage healing mechanisms in polycrystalline copper under unconstraint ultrasonic vibration treatment

The fatigue performance and microstructure of polycrystalline copper treated by one (UUV1), two (UUV2), three (UUV3) passes of unconstraint ultrasonic vibration (UUV) treatment were investigated in this paper. The surface roughness, fatigue life, microstructure, and plastic strain energy before and after UUV treatment were compared. The results revealed that the surface integrity of the sample for UUV treatment higher than that of the original sample, and the microscope observation found that the grain orientation, the dislocation density, the low angle grain boundaries, the plastic strain energy of the damaged sample restored to the original state to a great extent after UUV treatment. The fatigue crack initiation life increased by 3 times after UUV3 treatment.

The Use of Strain-Induced Martensitic Transformation Phenomena to Estimate the Surface Plastic Strain Produced by Grit Blasting on Overaged 18Ni Maraging Steel

The Use of Strain-Induced Martensitic Transformation Phenomena to Estimate the Surface Plastic Strain Produced by Grit Blasting on Overaged 18Ni Maraging Steel

Characterization of the topography generated by low plasticity burnishing using advanced techniques

This work investigates the surface topography of AISI 304 austenitic stainless steel after low plasticity burnishing through the evaluation of the average surface roughness (Ra), surface texture direction, areal power spectral density (APSD), scale-sensitive fractal analysis and continuous wavelet transform (CWT). The reason for adopting these approaches resides in the fact that traditional amplitude profile parameters neglect dynamic aspects of the process and geometric features of the burnished surface. The direction, periodicity and anisotropy of the surface texture were influenced by number of passes and burnishing speed and, in general, less severe plastic strain conditions tended to produce surfaces with strongly anisotropic characteristics, preferred direction of motifs, with power spectrum indicating a well-defined spatial frequency of peaks, lower fractal complexity and uniform profile distribution. The increase in surface strain severity produced surfaces with more diffuse directional characteristics, which tended to present surface isotropy, higher spatial frequency dispersion of the peaks and higher fractal complexity. Furthermore, the transition from an anisotropic to an isotropic surface can occur without changes in the average surface roughness. The continuous wavelet transforms analysis indicated a dynamic variation on the surface plastic strain when burnishing. The intermediary burnishing speed induced a strong disturbance with loss of periodicity of the roughness profile, resulting in a remarkable influence on the roughness profile in small scales. The increase in number of passes elevated the plastic strain severity, affecting the surface macrogeometric profile. The isotropic surface promoted a less severe stress concentration, reducing the tensile stresses and retarding crack nucleation, thus increasing the fatigue considerably.

A microstructure-based mechanical model of deformation-induced surface roughening in polycrystalline α-titanium at the mesoscale

The article presents a microstructure-based mechanical model of hexagonal close-packed (hcp) α-titanium representative of the mesoscale and analyzes the contribution of a pyramidal slip to plastic deformation. We discuss the size of a representative volume element (RVE) enabling mesoscale phenomena to be correctly reproduced, focusing on deformation-induced surface roughening (DISR) and plastic strain localization. It is shown that the ignorance of a pyramidal slip in simulations leads to overestimated stress values in an hcp material. A polycrystalline model is capable of reproducing the mesoscale phenomena until plastic strain begins to localize at the length scale comparable to the model size.

Quantifying surface deformation around micrometer-scale indents by digital image correlation

Indentation tests provide a facile route to gathering strength and stiffness information from small-scale samples, but typically have not been used to systematically assess distributions of surface plastic strain. The objective of the present work is to quantify in-plane plastic strain around micrometer-scale indents via digital image correlation (DIC). We demonstrate the method by comparing pre- and post-indentation surface images, acquired with a scanning electron microscope (SEM). Applying this method to metal composites synthesized by liquid- and solid-metal dealloying, we find that the maximum surface strains around indents do not change with the indentation depth, that strain concentrates preferentially in regions with largest composite constituent dimensions, and that the constituents are not co-deforming. We conclude that the method we have demonstrated is suitable for characterizing the relative propensity of materials to undergo uniform or localized plastic flow.

Unraveling the Origin of Tribomagnetization in Ferromagnetic Materials.

Tribomagnetization, a natural phenomenon known for decades, has many engineering applications today. However, its intrinsic origin remains controversial and the mechanistic-based model has not yet been developed to predict the tribomagnetization behavior. In this work, the origin of tribomagnetization is investigated via both the experimental and modeling approaches. For the first time, the expansion of surface plastic deformation to the subsurface layer (i.e., dislocation strain gradient) is characterized in conjunction with the tribological behavior of the interface. By performing the reciprocating sliding experiment in a pin-on-block contact configuration, the tribomagnetization evolution in different wear regimes is followed, the geometrically necessary dislocations (GNDs) developed in the subsurface are measured, and the formation of characteristic magnetic domains is revealed. A tribomagnetization model is proposed on the basis of the sliding-induced plastic deformation mechanism with GNDs, bringing the missing link with classical tribology and ferromagnetism. The model reveals that the surface plastic strain and width of a wear scar are two crucial factors in determining the surface magnetic field changes. We believe that the tribomagnetization originates from the magnetic distortion accompanied by the progression of GNDs in the subsurface. Our hypothesis is supported by the good agreement between the model prediction and experimental observation.

Analytical modeling of ultrasonic surface burnishing process: Evaluation of through depth localized strain

During surface treatment process, microstructure change beneath the surface layers and relevant mechanical properties depend to amount of work hardening occurs through depth of the treated samples. In the present work, an analytical model of surface plastic strain based on contact mechanic theorem is proposed to analyze the ultrasonic burnishing parameters. The model comprises effect of factors such static force, feed rate, ball diameter and ball material as well as ultrasonic vibration parameters such as amplitude and frequency. To incorporate effect of feed rate, two important parameters such as linear coverage coefficient and overlapping ratio have been defined and contributed in the model. The through depth localized plastic strain has been verified by 3D finite element simulation model for different parameter combination. Since, in surface treatment process such as ultrasonic burnishing the surface hardness and microstructure is directly influenced by the plastic strain, a series of experiments have been carried out and through depth hardness profiles has been obtained. It was found from the results that the through depth plastic strain distribution is consistent well with that derived from FE simulation. According to the analytical model, surface plastic strain and relevant affected depth increases by increase of static force and vibration amplitude. Also, it decreases by increase of ball radius and feed rate. On the other hand, it was found that using tungsten carbide ball significantly enhances the surface plastic strain compared to the ball made of steel and silicon nitride. The analytical model of strain and relevant affected depth was completely in line with the variation of through depth hardness and relevant hardened depth.

Development of Compact Marchiniak Testing Apparatus for In-situ Microscopic Observation of Surface Roughening

Abstract In the fields of medicine, electronics and information, the demand for micro-scale parts has increased significantly. In the metal forming using foil materials, it is known that different deformation behavior from sheet material can be observed. To investigate the surface roughening and plastic strain distribution for metal foils under various biaxial tensile states, a compact Marciniak testing apparatus is newly developed. The developed apparatus is installed on an automatic XY stage of the laser confocal microscope and the deformed specimen can be observed in real time. To confirm the possibility of in-situ observation of surface roughening and plastic strain distribution, the tests such as measurement of strain paths, observation of fracture points and surface roughening is conducted for pure copper foils. As a result, the plastic strain distribution and local necking behavior of the copper foil under various biaxial tensile states including equi-biaxial and uniaxial tensile states can be observed. Moreover, in-situ observation of surface roughening behavior on three proportional loading paths could be conducted. Therefore, an effectivity of the developed apparatus for investigation of surface roughening and plastic strain distribution is found.

Study of the influence of residual stresses on the fatigue strength of samples made of titanium and nickel alloys

In this paper, we compare the results of measurements of residual stresses and study the influence of residual stresses on the fatigue strength of samples made of titanium and nickel alloys after various types of treatment: turning with the use of various lubricating-cooling tools, grinding, and surface plastic strain operation.

A Wear Damage Assessment of High Temperature Forging Tool

High temperature forging tools are highly damaged by wear shearing under cyclic loading which reduces the life of tools. In real conditions, depending upon the tool areas, the level of wear can change. The surfaces of tools can be treated by cobalt-based hardfacing using different welding processes. This study focuses on tribological damages of Stellite 21 deposited by MIG process. Wear tests are carried out at room and high temperature on a ring on disc tribometer under high normal load. Different testing conditions are examined. The surface plastic strain due to the friction shear stresses is demonstrated by different methods like SEM observations, micro-hardness measurements and XRD analyses. More particularly, it is shown that the initial (200) crystallographic preferred orientation due to the welding process is modified into (111) crystallographic preferred orientation due to shear stresses regardless the loading. Moreover, a relationship between the gradient of the plastic shear strain at the friction subsurface and the level of the micro-hardness measurement has been established. In regard of the results, when the shear strain exceeds a threshold, the micro-hardness measurement is stabilised. The ultimate value could be induced by the stacking fault energy that is considered as weak in Stellites.

Numerical and experimental analysis of residual stress and plastic strain distributions in machined stainless steel

In this study, a numerical approach has been developed to predict the near surface residual stresses and plastic strain resulting from turning in orthogonal cutting configuration. This approach is based on the Arbitrary Lagrangian–Eulerian (ALE) formulation using the commercial finite element code Abaqus–Explicit. The coefficients of the used material behavior law and friction model required for the simulation are identified experimentally in this study. The simulated results are validated by experiments carried out on AISI 316L stainless steel. Using this method, the effect of the depth of cut (Doc) and the cutting speed (Vc) on the surface properties has been established. The simulated residual stress gradient resulting from machining has been experimentally validated by X-ray diffraction measurements. The simulated plastic strain gradient has been validated by an experimental microhardness–strain relationship established in this study.

On the Relationship Between Deformation-Induced Surface Roughness and Plastic Strain in AA5052—Is it Really Linear?

Three different heat treatments of aluminum alloy AA5052 were subjected to various levels of uniaxial plastic strain. The resulting surfaces were then evaluated using both scanning laser confocal microscopy (SLCM) and stylus profilometry. Three regression approaches were used to assess the quality of a linear and a curvilinear fit for the roughness data as a function of true plastic strain. While there were differences among the regression results, the analyses revealed that a linear model was more statistically appropriate for the finest grain size. As the grain size increased, the surface morphology became more complex and a quadratic model became more suitable. Since the relative area fractions of grain boundary–localized roughness and slip-induced roughness are grain size dependent, the higher order fit between the roughness and plastic strain reflects substantial changes in the ratio of these areas. The differences between the SLCM and profilometry results were attributed to the natural filtering that occurs during contact profilometry. This filtering skewed the roughness data toward the largest surface displacements, thereby reducing the measurement fidelity to the point where the only possible outcome was the linear relationship.

The effect of internal hydrogen on surface slip localisation on polycrystalline AISI 316L stainless steel

A statistical analysis of the effect of internal hydrogen on the surface slip morphology of relatively high nickel content AISI 316L type austenitic stainless steel was carried out on high resolution data obtained by atomic force microscopy. Surface plastic strain localisation was studied for different hydrogen contents, two grain sizes, and two plastic strain levels. The height and spacing of approximately 8000 slip bands, observed on 12 specimens, are shown to follow log-normal distributions. Hydrogen increased the mean slip-band height and the mean slip-band spacing for the two macroscopic plastic strain levels considered, and for the two hydrogen concentrations in coarse-grained specimens. The hydrogen effect was also observed for fine-grained specimens, but only for the highest hydrogen concentration. In addition, the emerging dislocation velocity increased by a factor 3 for high hydrogen content.

Surface plastic strain in contact problems: Prediction by a simplified non-linear kinematic hardening model

A previously published model for plasticity assessment in rolling contact, based on a simplification of the non- linear kinematic and isotropic hardening model of Chaboche and Lemaitre, is discussed, and an update is introduced in order to improve its accuracy in the plastic strain prediction within the region just underneath the contact surface. The update is based on a correction of the yield limit and of the strain rate as a function of the load ratio of the tensile stress in the direction parallel to the contact surface. The effectiveness and the accuracy of the updated model in not too severe conditions are demonstrated through comparisons with results obtained by finite element model (FEM) analyses. An application of the model to some experimental results obtained on rail and railway wheel steels is also carried out, and quite good agreement is found in plastic strain prediction, although some discrepancies are found. The method appears to be a valid tool for practical application, especially for its ability of combining the effects of different phenomena and of simulating a number of cycles of the order of millions in a reasonable time.

Corrosion resistance of Cr-Ni-Mo steel intended for urological stents

This work presents the influence of the surface treatment and plastic strain of Cr-Ni-Mo stainless steel, intended for implants applied in urogenital surgery, on the steel's corrosion resistance. Tests were carried out in simulated urine at a temperature of 37 1C and pH = 66,4. In particular, pitting and crevice corrosion resistance tests were carried out. Furthermore, through the applied technique of stent implantation, the deformability of the passive layer was evaluated. The deformability tests of the passive layer were carried out with the use of a bend test followed by a corrosion test.

The effect of surface waves on the interaction of incident particles with a solid surface

The incidence of two particles onto a thin solid plate has been studied by means of computer simulation. The influence of the impact-excited waves on the particle-surface interaction is considered. The waves excited in the target plate produce a significant change in the surface response dynamics. The distribution of surface damage and plastic strain generated by the incident particles is analyzed, and it is established that this distribution is correlated with the surface wave structure.

Plastic surface strain mapping of bent sheets by image correlation

A technique using a single CCD camera, a precision rotation/translation stage, a telecentric zoom lens, and digital image correlation software is described for measuring surface profiles and surface plastic strain distributions of a bent thin sheet. The measurement principles, based on both parallel and pinhole perspective projections, are outlined and the relevant mathematical equations for computing the profiles and displacement fields on a curved surface are presented. The typical optical setup as well as the experimental measurement and digital image correlation analysis procedure are described. The maximum errors in the in-plane and out-of-plane coordinates or displacements are about ±5 and ±25 μm, respectively, and the maximum errors in surface strain mapping are about 0.1% or less based on a series of evaluation tests on flat and curved sample surfaces over a physical field of view of 15.2 × 11.4 mm2. As an application example, the shape and surface plastic strain distribution example, the shape and surface plastic strain distributions around a bent apex of a flat 2 mm thick automotive aluminum AA5182-O sheet, which underwent a 90° bend with three bend ratios of 2t, 1t, and 0.6t, are determined using the proposed technique.

Characterization of plastic deformation in a disk bend test

A disk bend test technique has been developed to study deformation mechanisms as well as mechanical properties. In the disk bend test, a transmission electron microscopy (TEM) disk size specimen of 3 mm diameter ×0.25 mm thick is clamped around its rim in a circular holder and indented with a tungsten carbide ball of 1 mm diameter on its back face. AISI 316LN austenitic stainless steel and 9Cr–2WVTa ferritic/martensitic steel were selected as test materials. A model was developed to determine the average plastic strain and surface plastic strain in the disk bend test. The deformation regimes of the plastic strain versus deflection curves corresponded to those of the load versus deflection curves. The stress state of the disk bend deformation was analyzed for the two test materials and compared with those of other mechanical tests such as uniaxial tensile, compact tension, and ball indentation tests. Slip line features at the deformed surface and the corresponding TEM microstructures were examined for both tensile and disk bend specimens. Differences and similarities in deformation between the disk bend and the tensile tests are described.

The prediction of polyethylene wear rate and debris morphology produced by microscopic asperities on femoral heads.

Counterface damage in the form of scratches, caused by bone cement, bone or metallic particles, has been cited as a cause of increased wear of ultra-high molecular weight polyethylene (UHMWPE) acetabular cups. It is known that high levels of particulate wear debris lead to osteolysis. Surface damage was characterized in a series of explanted Charnley femoral heads. The heads had a mean scratch height of 1 microm with a mean aspect ratio (defined as height divided by half width) of 0.1. Wear discs were artificially scratched using these scratch geometries as a guide. In addition, the scratch geometries were incorporated into a finite element model of a stainless steel asperity repeatedly sliding over UHMWPE under conditions similar to those in an artificial hip joint. Wear tests showed a strong correlation between the average cross-sectional area of the scratch lip above the mean zero line and the measured wear factor. The finite element model predicted increases in the area of UHMWPE suffering plastic strain with increases in the cross-sectional area of the asperity above the mean line. Analysis of the wear debris showed the mode of the particle size was 0.01-0.5 microm for all cases. The morphology of the particles varied with aspect ratio of the asperity, with an increased percentage mass of submicrometer-sized debris with increased scratch lip aspect ratio. The finite element results predicted that the maximum surface strains would increase with increasing asperity aspect ratio. Examination of the worn UHMWPE pin surfaces showed an association between increased surface damage, probably due to high surface strains, and increased aspect ratio. The large areas of surface plastic strain predicted for asperities with high cross-sectional areas above the mean line offer an explanation for the positive correlation between wear rate and the average cross-sectional area of the scratch lip material. The higher surface strains predicted for the higher aspect ratios may explain the increased percentage mass of biologically active submicrometer-sized wear particles found for scratch lips with higher aspect ratios.

Machined surface plastic strain in orthogonal cutting by subsequent recrystallizations technique

The subsequent recrystallization technique, an experimental strain measurement method by use of recrystallization phenomena, has been successfully applied for machined surface plastic zones with equivalent plastic strain ϵ≥0.5, 0.12 and 0.02 of type 304 stainless steel. The depth of the zone with ϵ≥0.5 is very small, 10–50 μm, while zones with ϵ≥0.12 and 0.02 are 100–200 μm and 200–450 μm, respectively. The depths increase with increasing depth of cut and with decreasing rake angle. The relation between the depth of the zones and the cutting parameters are shown. The deformation state ahead of the quick-stop cut tip was also well visualized by the technique.