Subsurface Stress Distribution Research Articles

Effect of reinforcements on rolling contact fatigue behaviors of titanium matrix composite (TiB + TiC)/Ti–6Al–4V

Rolling contact fatigue (RCF) behaviors of titanium matrix composites (TiB+TiC)/Ti–6Al–4V are investigated, including the microstructural variables, the stress distribution and the RCF life. The effect of reinforcements on RCF is observed in detail. The microstructural information, especially pertaining to the reinforcements, is obtained through scanning electron microscope. The influence of reinforcements on stress distribution is studied via analyses of subsurface stress distributions based on an approximate numerical method, in which the reinforcement distributions are taken into account. The results reveal that the existence of reinforcements causes RCF life reduction due to the stress concentration in and around the reinforcements.

Rolling Contact Fatigue Life Assessment of Induction Hardened Raceway

In this paper the assessment of the rolling contact fatigue life of an induction hardened raceway is presented. For determination of the equivalent subsurface stress distribution field in the raceway, 3D numerical model of the contact between the through hardened roller made of 100Cr6 steel and the surface hardened raceway made of 42CrMo4 was employed. The calculation of the contact fatigue life of the raceway was then carried out in the stress-life regime. Additionally, alternative HCF parameters for the 42CrMo4 steel in compression were experimentally determined with pulsating compression tests. For the experimental validation of computationally determined fatigue life of the induction hardened raceways, test specimens for RCF bench were manufactured and their testing has started.

An Improved Approach for 3D Rolling Contact Fatigue Simulations with Microstructure Topology

Several 2D and 3D numerical models have been developed to investigate rolling contact fatigue (RCF) by employing a continuum damage mechanics approach coupled with an explicit representation of microstructure topology. However, the previous 3D models require significant computational effort compared to 2D models. This work presents a new approach wherein efficient computational strategies are implemented to accelerate the 3D RCF simulation. In order to reduce computational time, only the volume that is critically stressed during a rolling pass is modeled with an explicit representation of microstructure topology. Furthermore, discontinuities in the subsurface stress calculation in the previously developed models for line and circular contact loading are removed. Additionally, by incorporating a new integration algorithm for damage growth, the fatigue damage simulations under line contact are accelerated by a factor of nearly 13. The variation in fatigue lives and progression of simulated fatigue spalling under line contact obtained using the new model were similar to the previous model predictions and consistent with empirical observations. The model was then extended to incorporate elastic–plastic material behavior and used to investigate the effect of material plasticity on subsurface stress distribution and shear stress–strain behavior during repeated rolling Hertzian line contact. It is demonstrated that the computational improvements for reduced solution time and enhanced accuracy are indispensable in order to conduct investigations on the effects of advanced material behavior on RCF, such as plasticity.

Lifetime Determination of the Raceway of a Large Three-Row Roller Slewing Bearing

This paper deals with calculation procedure for lifetime determination of a large three-row roller slewing bearing. First, the contact force distribution between the rollers and the bearing raceway is determined both analytically and numerically. Then, the position and the magnitude of the maximum contact force are identified. In a separate numerical model finite element analyses are performed to determine the subsurface stress distribution as the result of contact between the raceway and different rollers. These stress fields serve as an input for the fatigue lifetime calculation, which is done in accordance with the stress-life approach (S-N). At the end the influence of roller geometry on the calculated fatigue life is presented.

Study on single-cell contact model of thick-walled cellular solid

An analytical method was proposed by combining the classical Hertz theory with the method of an equivalent curved beam to investigate the contact mechanics of a thick-walled cellular solid. This method extended the range of applicability of Hertz theory and was applied to investigate the influence of porosity on the contact pressure and local stress distribution compared with finite element and experimental methods. The results show that the increase of the porosity had little effect on the maximum contact pressure and contact half-width under the given load. However, it resulted in a marked increase of the total radial displacement and local stress due to the bending deformation of the cell wall. Therefore, the improvement of contact fatigue life of cellular solids mainly depends on porosity and the corresponding change of subsurface stress distribution due to the influence of bending stress rather than contact deformation. The analytical contact mechanics solution for the thick-walled cellular solid examined is also applicable to some engineering applications, such as hollow cylinder in rolling elements bearings.

Load capacity of a three-row roller slewing bearing raceway

A calculation model for fatigue lifetime determination of a three-row roller slewing bearing raceway is presented. First, the contact force distribution between the roller and the raceway is analytically determined from the basic bearing geometry and the external loads acting on the bearing assembly. Then a numerical model is employed to calculate subsurface stress distribution in the raceway as a result of the contact force between the roller and the raceway. Numerically calculated subsurface stress field serves as an input for the fatigue calculation of the raceway, which is done according to the stress-life approach. Two different types of rollers are investigated: plain cylindrical roller and a profiled roller. Finally, the influence of the roller geometry on the fatigue life is pointed out.

An Approach for Modeling Material Grain Structure in Investigations of Hertzian Subsurface Stresses and Rolling Contact Fatigue

The continuum theory of elasticity and/or homogeneously discretized finite element models have been commonly used to investigate and analyze subsurface stresses in Hertzian contacts. These approaches, however, do not effectively capture the influence of the random microstructure topology on subsurface stress distributions in Hertzian contacts. In this paper, a finite element model for analyzing subsurface stresses in an elastic half-space subjected to a general Hertzian contact load with explicit consideration of the material microstructure topology is presented. The random internal geometry of polycrystalline microstructures is modeled using a 3D Voronoi tessellation, where each Voronoi cell represents a distinct material grain. The grains are then meshed using finite elements, and an algorithm was developed to eliminate poorly shaped elements resulting from “near degeneracy” in the Voronoi tessellations. Hertzian point and line contacts loads are applied as distributed surface loads, and the model’s response is evaluated with commercial finite element software ABAQUS. Internal stress results obtained from the current model compare well with analytical solutions from theory of elasticity. The influence of the internal microstructure topology on the subsurface stresses is demonstrated by analyzing the model’s response to an over rolling element using a critical plane approach.

Improved Method of Roller Bearing Fatigue Life Prediction under Edge Loading Conditions

It has been deemed to be proper to use subsurface stress distributions in life predictions of roller bearings under edge loading conditions. But by using this method the decreased life caused by edge stresses is normalized in the process of relating them to the lives of other parts, and therefore life prediction accuracy is lessened. The life calculation method by relating elements is irrelevant in this case. For this measure, an improved method is proposed. It is mainly based on Lundberg and Palmgren's (L-P) theory but differs in calculating the lives where the peak stresses arise; both edges and the center in a full crown roller case, for example. In this method, the center raceway life is corrected by multiplying by the stress uniformity factor. The stress uniformity factor considers the scatter of the material strength, like size effect. It varies according to the uniformity of stress distribution. The results of this method correspond very well to the results of roller endurance testing. In addition, not using the stress uniformity factor results in a good correlation.

Rolling Contact Fatigue Performance of Vibro-Mechanical Textured Surfaces

The rolling contact fatigue (RCF) performance of vibro-mechanical textured surfaces in a point elastohydrodynamic lubrication (EHL) condition is investigated. Two dimple designs, small (100 μ m × 100 μ m) and large (240 μ m × 100 μ m), are compared with a nontextured sample. Experimental RCF tests show that the textured surfaces exhibit a significantly reduced number of cycles to failure compared with the nontextured sample for the high load, pure rolling conditions evaluated. In order to understand these results, numerical models are used to calculate the lubrication and contact pressure conditions and the subsurface stress distribution. The fatigue failure trends observed experimentally are compared with the simulation results with good agreement. It is determined that RCF performance is related to the presence and size of the generated dimple.

Evaluation of an Ultrasound-Aided Deep Rolling Process for Anti-Fatigue Applications

An ultrasound-aided deep rolling process (UADR) for anti-fatigue applications was developed and used for surface enhancement of titanium alloy specimens. The rotating bending fatigue test was performed for the UADR-treated and untreated fatigue specimens. Fractography of the fatigue-fractured specimens was investigated via scanning electronic microscopy (SEM). Surface and subsurface residual stress distributions after UADR treatment were measured by X-ray diffraction method. Surface morphology and roughness were observed and measured via SEM micrograph and a Talysurf roughness tester, respectively. The results showed that a deep layer of residual compressive stress developed and surface roughness was reduced after UADR treatment. Fatigue strength of the titanium alloy specimens was substantially improved. The fractographic examination of the fatigue-fractured specimens showed that the UADR-treated specimens developed finer fatigue striations than the untreated specimen.

Stress Analysis on Layered Materials in Point Elastohydrodynamic-Lubricated Contacts

For multilayered or coated substrates in elastohydrodynamic-lubricated (EHL) contacts, the subsurface stress distributions under a normal load combined with shear traction have been analyzed in this article through computer simulations. The Papkovich-Neuber potentials and Fourier transform are adopted to deduce the pressure–displacement, pressure–stress, and shear traction–stress response functions in frequency domain for the coated substrates, and to calculate distributions of pressure and subsurface stress. The results from the analysis of EHL contacts on coated substrates are compared with those from dry contact model in which shear traction is assumed to obey Coulomb’s law. Effects of the Young’s modulus of coatings, the properties of lubricants, and the magnitude of traction are discussed. Similar to the results in dry contacts, hard coatings in lubricated cases tend to increase the von Mises stress, whereas soft coatings decrease the stress. Shear traction makes the max von Mises stress increasing and moving closer to surface. However, the changes in subsurface stress due to shear traction are less obvious in lubricated contacts. Comparison between EHL and dry contact models reveals that lubrication can reduce the von Mises stress in the coating layer due to smaller shear traction. The analyses show that pressure, film thickness, and subsurface stress distributions are influenced by surface coatings, sliding velocity, rheological models, and pressure–viscosity behaviors.

Residual stress field and thermal relaxation behavior of shot-peened TC4-DT titanium alloy

Shot peening is an effective surface treatment method, which can improve the fatigue properties of metallic materials. In the present paper, the residual compressive stress field induced in TC4-DT titanium alloy under different shot peening conditions and the thermal relaxation behaviors of shot-peened TC4-DT were discussed. The shot peening can cause residual compressive stress on the material surface compared to un-peened materials. The subsurface residual stress distributions of original and shot-peened specimens were measured by an X-ray diffraction method. The residual compressive stress profiles accord with the characteristic curve of residual stress field. The maximum residual compressive stress is located at subsurface layer. Surface roughness also increases with increasing shot peening intensity. There is relaxation of residual compressive stress during temperature. Thermal relaxation behavior of residual stress was studied at 150 and 300 °C with different ageing time. The residual stress relaxation is influenced by temperature and time during ageing. Thermal relaxation of residual stress is a thermal recovery process. The relaxation process of thermal residual stress is analyzed by applying the Zener–Wert–Avrami function.

Abrasive waterjet peening with elastic prestress: A parametric evaluation

Abrasive waterjet peening (AWJP) has emerged as a potentially viable method of surface treatment for metal orthopedic devices. In this study the influences of AWJP with elastic prestress on the surface and subsurface residual stress distributions and surface texture of spring steel (ASTM 228) as well as titanium (Ti6Al4V) and nickel (inconel 718) alloys were studied. A design of experiments (DOE) and an analysis of variance (ANOVA) were used to identify the parameters with primary contributions to the dependent variables. Surface residual stress resulting from AWJP ranged from 500 to 2500 MPa, and the depth of compressive residual stress ranged from nearly 80 to 600 μm. While the elastic prestress had no effect on the surface texture, it was a primary contributor to the magnitude of surface residual stress, which increased with an increase in the elastic prestress. According to the results of this study, AWJP with elastic prestress can serve as a viable method of surface treatment in situations that require an increase in surface roughness and a compressive residual stress.

Laser ultrasonic diagnostics of residual stress

Ultrasonic NDE is one of the most promising methods for non-destructive diagnostics of residual stresses. However the relative change of sound velocity, which is directly proportional to applied stress, is extremely small. An initial stress of 100 MPa produces the result of δV/V∼10 −4. Therefore measurements must be performed with high precision. The required accuracy can be achieved with laser-exited ultrasonic transients. Radiation from a Nd-YAG laser (pulse duration 7 ns, pulse energy 100 μJ) was absorbed by the surface of the sample. The exited ultrasonic transients resembled the form of laser pulses. A specially designed optoacoustic transducer was used both for the excitation and detecting of the ultrasonic pulses. The wide frequency band of the piezodetector made it possible to achieve the time-of-flight measurements with an accuracy of about 0.5 ns. This technique was used for measuring of plane residual stress in welds and for in-depth testing of subsurface residual stresses in metals. Plane stress distribution for welded metallic plates of different thicknesses (2–8 mm) and the subsurface stress distribution for titanium and nickel alloys were obtained. The results of conventional testing are in good agreement with the laser ultrasonic method.

In vitro rapid intraoral adjustment of porcelain prostheses using a high-speed dental handpiece

In vitro rapid intraoral adjustment of porcelain prostheses was conducted using a high-speed dental handpiece and diamond bur. The adjustment process was characterized by measurement of removal forces and energy, with scanning electron microscopic (SEM) observation of porcelain debris, surfaces and subsurface damage produced as a function of operational feed rate. Finite element analysis (FEA) was applied to evaluate subsurface stress distributions and degrees of subsurface damage. The results show that an increase in feed rate resulted in increases in both tangential and normal forces (analysis of variance (ANOVA), P < 0.01). When the feed rate approached the highest rate of 60 mm min −1 at a fixed depth of cut of 100 μm, the tangential force was nearly seven times that at the lowest feed rate of 15 mm min −1. Consequently, the specific removal energy increased significantly (ANOVA, P < 0.01), and the maximum depth of subsurface damage obtained was approximately 110 and 120 μm at the highest feed rate of 60 mm min −1 using SEM and FEA, respectively. The topographies of both the adjusted porcelain surfaces and the debris demonstrate microscopically that porcelain was removed via brittle fracture and plastic deformation. Clinicians must be cautious when pursuing rapid dental adjustments, because high operational energy, larger forces and severe surface and subsurface damage can be induced.

Modeling of residual stress distribution in D2 steel via grinding dynamics using a second-order damping system

Abstract A second-order system is proposed to model residual stress distributions in D2 tool steel under various heat treatment procedures and grinding dynamics. The study was motivated to predict the magnitude of the residual stress, tensile peak location, and to establish the nonlinear superposition relationship in the residual stress distribution due to the number of grinding passes. The grinding dynamics was represented as a lumped system composed of a spring-mass-damper of the grinding machine and a damper-stiffness of the workpiece. A nested factorial experiment of 18 conditions with 3 levels of tempering, 2 levels of grinding conditions and 3 multipass grinding levels was used for the model development and validation. The parameters of each condition were then optimized by using auto-regressive system identification. The proposed model depicts changes of the complex experimental treatment conditions and estimates in a precise and parsimonious way the corresponding change in the subsurface residual stress distribution. With only one parameter involved, the model facilitates conceptual progress in the residual stress superposition; the prediction elucidates grinding dynamics and supports a theory of the heat treatment and grinding effects on the material characteristics.

Iterative inversion method for eddy current profiling of near-surface residual stress in surface-treated metals

Because of their frequency-dependent penetration depth, eddy current measurements are capable of mapping the near-surface depth profile of the electric conductivity. This technique can be used to nondestructively characterize the subsurface residual stress distribution in certain types of shot-peened metals, e.g., in nickel-base superalloys. In this paper, a highly convergent iterative inversion procedure is presented to predict the frequency-independent intrinsic electric conductivity depth profile from the frequency-dependent apparent eddy current conductivity (AECC) spectrum. The proposed technique exploits three specific features of the subsurface electric conductivity variation caused by near-surface residual stresses in shot-peened metals. First, compressive residual stresses are limited to a shallow surface region of depth much less than typical probe coil diameters. Second, the change in electric conductivity due to residual stresses is always very small, typically less than 1%. Third, the electric conductivity depth profile is continuous and fairly smooth. The accuracy of the proposed iterative inversion procedure is one order of magnitude better than that of the previously developed simpler method (J Appl Phys 2004;96:1257).

High Space-Resolutive Evaluation of Subsurface Stress Distribution by Strain Scanning Method with Analyzer Using High-Energy Synchrotron X-Rays

The surface aberration effect in the strain scanning method with a Ge analyzer was examined using high- energy X-rays from the undulator synchrotron source. The synchrotron X-rays from the undulator source had an enough intensity for the strain scanning method using a goniometer with the analyzer. The use of a Ge (111) analyzer showed remarkable reduction of the surface aberration effect. However, there still existed the surface aberration for the very-near surface region from the surface to the depth of 50µm. A correction method was proposed by taking into account of the effects of the divergence of the Ge analyzer, the mis-setting of the analyzer and the X-ray attenuation. The proposed correction method was very useful for eliminating the surface aberration effect. The correction method enables a high space-resolutive evaluation of the subsurface stress distribution. The method was successfully applied to the determination of the residual stress distribution of the shot-peened steel. A precise d0 value of the strain-free lattice spacing necessary was determined from the surface stress measured by the conventional sin2ψ method using Cr-Kα radiation.

A thermodynamic approach for predicting fretting fatigue life

This paper extends the application of the theory of continuum damage mechanics (CDM) to predict the occurrence of fretting fatigue failure. It is concerned with the application of thermodynamic theory of CDM for predicting crack formation in fretting. This is done by calculating subsurface shear stress distribution due to fretting loading conditions and obtaining corresponding principal plane location. For given fretting conditions such as the load, the coefficient of friction and the bulk material properties, the present model predicts the number of cycles to failure. The results are validated with published experimental data.

Simple analytical approximations for eddy current profiling of the near-surface residual stress in shot-peened metals

Because of their frequency-dependent penetration depth, eddy current measurements are capable of mapping the near-surface depth profile of the electrical conductivity. This technique can be used to nondestructively characterize the subsurface residual stress distribution in certain types of shot-peened metals, e.g., in nickel-base superalloys. For quantitative evaluation of the experimental results, analytical and computational techniques are needed to solve the direct and inverse problems, i.e., to predict the frequency-dependent apparent eddy current conductivity from the depth profile of the frequency-independent intrinsic electrical conductivity of the specimen and vice versa. Simple analytical approximations are presented for both the direct and inverse eddy current problems by exploiting two specific features of the subsurface electrical conductivity variation caused by near-surface residual stresses in shot-peened metals. First, compressive residual stresses are limited to a shallow surface region of depth, much less than typical probe coil diameters. Second, the change in electrical conductivity due to residual stresses is always very small, typically less than 1%. The proposed approximations are verified by numerical comparison to much more complicated numerical solutions.