Surface Residual Stress Fields Research Articles

Simulation Analysis with Randomly Distributed Multiple Projectiles and Experimental Study of Shot Peening

Shot peening technology is used to improve the fatigue strength of materials and parts, and is one of the most effective surface engineering techniques to prolong fatigue life. In this paper, according to the finite element simulation analysis of shot peening, a randomly distributed multiple-shot finite element model was established. The superimposed effects of multiple projectile impact craters in shot peening are fully considered. The effects of shot velocity, shot peening angle and shot coverage on the residual stress field and surface roughness were studied. The alloy steel 20MnTiB, widely used in the automotive industry, was used as the raw material to process the specimens. The shot peening tests of different process parameters were carried out. The test results verified the correctness and accuracy of the random distribution model of multiple-shot. The shot-peening simulation model proposed in this paper allows a more accurate analysis of the effect of shot-peening parameters on the surface residual stress field and helps to quickly set the correct shot-peening process parameters. This paper further investigates the effect of shot peening parameters on fatigue life, providing a basis for the rational development of shot peening solutions.

Influence of tartaric‐sulfuric acid anodic film on four‐point bending fatigue behavior of AA 7050‐T7451 samples

AbstractTartaric–sulfuric acid (TSA) anodizing is an electrochemical process used for generating an anodic layer on the surface of aluminum alloys for aerospace applications. It must provide corrosion resistance and ensure no detrimental effect on the required fatigue properties for structural applications. This work aimed at analyzing the properties of the anodic layer and evaluating its influence on the fatigue behavior of the AA 7050‐T7451. The film properties were analyzed using optical and scanning electron microscopies. The surface residual stress (SRS) field in the as‐machined and anodized conditions was evaluated by the X‐ray diffraction technique.The results showed that TSA induces an appreciable reduction in the fatigue life, especially at lower values of stress amplitude, due to the presence of defects at the interface between the substrate and the anodic film. No correlation was observed between the presence of the anodic layer and the development of a tensile SRS field.

Investigation on surface “residual stress hole” of thin plate subjected to two sided laser shock processing

Two sided laser shock processing (TSLSP) is a novel surface processing technology, which is often used in surface modification of thin-section parts. In this paper, the phenomenon of residual stress hole (RSH) on the surface of 304 stainless steel thin plate subjected to TSLSP was researched by numerical simulation and experiment method. The influence of boundary reflection on surface residual stress field was investigated in detail. Based on the developed model validated by experiment, the effect of some key parameters such as spot diameter, spatial pressure distribution, peak pressure on RSH were further studied. The investigations show that the RSH does not occur when the very thin plate subjected to TSLSP. The RSH phenomenon mainly results from the convergence of surface stress wave emitted from the boundary of laser spot. When the size of treated plate is small, the effect of surface stress wave reflected by the plate boundary on the RSH cannot be neglected. Under the same conditions of TSLSP, the RSH easily occurs on the surface of the related thick-sectional sample. The peak value of RSH does not significantly vary with the increase of spot diameter, but the width of RSH broadens. The spatial pressures distribution of shock wave affects the RSH phenomenon. With the enhance of the applied pressure of shock wave, the RSH phenomenon becomes more obvious.

Bivariate Fourier-series-based prediction of surface residual stress fields using stresses of partial points

Surface residual stresses are critical parameters for evaluating the surface quality and can have an influence on many mechanical properties of solids. These stresses inevitably arise in almost all engineering components during manufacturing. However, most experimental and finite element approaches cannot obtain a complete surface residual stress field in a mechanical part. In this study, we propose a predictive method to determine surface stress fields, depending on residual stresses being self-equilibrating. The effectiveness of the approach is verified using a numerical surface of a beam example with ideal measurements and a casting–milling surface with experimental data. Using the proposed method, surface residual stress fields can be obtained from the stresses of a limited number of points including boundary points to solve the governing equations via a Fourier series bivariate polynomial as an Airy stress function with the Tikhonov regularization method. Our method does not require simulations of the residual stress generation process. This method is suitable for complex engineering parts where the manufacturing process is difficult to recreate in detail. The predicted stress field can be imported into a finite element solver as initial stresses to promote the design, manufacturing, and assessment of mechanical components.

A high efficient surface-based method for predicting part distortions in machining and shot peening

The distortion of machined part caused by the introduction of surface residual stresses in machining and shot peening is a major concern in the manufacture of large structural components. Prediction of those distortions is the key to understand the distortion mechanism and derive optimized machining strategies. In this paper, a high efficient surface based method was proposed to predict the part distortion in machining and shot peening. In this method, the surface residual stress field is mathematically analyzed and equivalent to a group of face and edge loads. The part distortion problem is equivalent to an elastic deformation problem and is solved by the FEM software. The knowledge of surface differential geometry is used so that the method could handle part with curved surfaces. Compared with the existing method, the refinement of mesh in the surface-affected layer is not needed, which not only greatly decreases the workload and difficulty of mesh generation but also significantly reduces the amount of computation. What is more, the method was found to be particular fit for large curved surface parts such as propellers and blades. Software system was developed further to implement the method. Two examples were given to show the advantages of the proposed method. Finally, the method was verified by comparing the simulated results with the experimental data with a marine propeller example.

Development of a hybrid model for the prediction of shape deviations in milling

The productivity in machining of high precision components is limited among others by the achievable geometric accuracy. Shape deviations arise due to several mechanisms of which residual stresses and a varying material removal due to thermal expansion have been incorporated in a proposed hybrid model. The model is based on two initially separated sub models which require a set of experimentally obtained input parameters. Both sub models utilize the finite element method. Sub model 1 calculates the mechanic response of the workpiece loaded with a near surface residual stress field (source stresses) resulting from the interaction of tool and workpiece. Sub model 2 calculates the thermal expansion of the workpiece utilising a three‐dimensional simulation of a moving surface heat source. The resulting inhomogeneous material removal is superimposed with the calculated shape deviations from sub model 1. This work focuses on distortion caused by machining induced residual stresses which are modelled as source stresses (sub model 1). These so called source stresses can be calculated directly from the bending and torsion of machined specimens and represent the distortion potential of the face milling process. The results demonstrate a pronounced correlation between the obtained source stresses and the width of cut ae. They further indicate that a separation of the effects resulting from the removal of material containing workpiece inherent residual stresses and from the newly generated residual stresses in the machined surface layer is required for the calculation of machining induced residual stresses.

Development and Validation of a Hybrid Model for the Prediction of Shape Deviations in dry Machining Processes

Dry cutting operations offer economic and ecologic advantages over conventional machining. When machining conditions are pushed towards the regime of high performance cutting, the applicability of dry cutting is limited among others by the achievable geometric accuracy. In order to comply with increasing demands in machining precision and the necessity to expand the utilisation of dry cutting, a novel hybrid model has been developed exemplary for a face milling process. It enables a predictive minimisation of size and shape deviations in machining. The model takes into account deviations due to thermal expansion during the cutting operation and due to machining induced residual stresses which are especially important in the manufacturing of thin-walled high precision components. It is therefore based on two initially separated finite element sub-models. Sub-model 1 calculates the mechanic response of the workpiece loaded with a near surface residual stress field (source stresses) resulting from plastic deformations generated during the chip formation process. Sub-model 2 calculates the local thermal expansion of the workpiece during a three-dimensional simulation of a moving heat source.In this paper the focus lies on shape deviations resulting from thermo-elastic effects (sub-model 2). It covers a face milling process of plates made from normalized 42CrMo4. Transient three dimensional temperature fields are calculated in a FEM model of a moving surface heat source. The temperature fields are used to calculate the mechanical response of the workpiece which is coupled with a kinematic simulation of the tool movement to obtain the resulting surface shape. The results are validated against measured shape deviations for varying machining parameters. In the long term, the model will be applied to evaluate and identify optimal machining strategies.

Influence of Final Hand Polishing Process on Surface Residual Stress Field of Japanese Sword

800x600 The short and long Japanese swords “WAKIZASHI” (back up sword of the main sword, “KATANA”) were made by one sword craftsman. The short and long swords “WAKIZASHI” were machined by rough grinding and final hand polishing, respectively. The microstructure, carbon content and hardness of short sword were measured experimentally on the cross section of sword blade. The 2θ-sin2ψ diagrams from Fe-211 plane using Cr-Kα radiation on the ground and polished blade were measured. An influence of final hand polishing process on the surface residual stress field of sword blade was examined. As a result, biaxial principal compressive residual stresses were generated and had constant stress gradients in depth on the ground and polished surfaces because the ψ-splitting was not observed and the measured 2θ vs. sin2ψ relations could be approximated as a parabolic curve. Large compressive residual stresses more than −1.0 GPa were distributed on the ground surface from “HASAKI” to “HAMON” of short sword. The surface compressive residual stress and its gradient were diminished gradually from “HAMON” to “MUNE” (the ridge of sword). On the other hand, compressive residual stresses more than −650MPa were distributed on the pol­ished surface from “HASAKI” to “HAMON” of long sword. The surface compressive residual stress and its gradient were also diminished gradually from “HAMON” to “MUNE”, and the residual stress gradient in the transverse direction were greatly degraded in comparison to the short sword. Additional compressive residual stress field induced by rough grinding was superimposed on the residual stress field after tempering process. The residual stress field near the blade surface after rough grinding was released partly by final hand polishing. Normal 0 21 false false false DE X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Century","serif";}

A simplified and fast method to predict plain and notch fatigue of shot peened high-strength aluminium alloys under reverse bending

A simplified and fast method to predict plain and notch fatigue resistance of shot peened Al-7075-T651 is presented. For this purpose, different shot peening treatments were carried out on plain and notched samples. Reverse bending SN curves were determined for both notched and unnotched conditions. Initial and stabilized residual stresses were measured by X-ray diffraction on plain samples. An evolution to stabilised values of the surface stresses, depending on the applied loads, was observed. Residual stresses measured on plain samples were used for predicting, by means of finite element modelling, respectively the residual stress distributions in the notched samples and the residual stress relaxation in the vicinity of the notch due to the application of different fatigue loads. The results of the numerical analysis were used to validate a simplified analytical approach developed for computing residual stress relaxation and surface residual stress field both in plain and notched samples. The predicted residual stress distribution was finally incorporated into a multiaxial fatigue criterion. Specifically, the critical distances theory was used to predict the fatigue resistance of notched samples in the presence of a compressive residual stress field.

3D Finite Element Simulation of Hard Turning

A 3D model is established in this paper to simulate cutting process of PCBN tool cylindrical cutting hardened steel GCr15 using ABAQUS/Explicit. The model effectively overcomes serious element distortions and cell singularity in high strain domain caused by material large deformation by adopting shear failure criteria and element deletion criteria. In this study cutting force, cutting temperature, surface residual stress field as well as side flow are forecasted of hard cutting process with chamfering tool preparation. It shows that satisfactory results could be obtained by FEM. The simulation results provide theoretical basis for studying hard cutting mechanism and selecting the best cutting condition in practical.

Relationship between Surface Residual Stress Fields and Hydrothermal Environment on Low Temperature Aging of 3Y-TZP

Phase stability of 3 mol% yttria stabilized polycrystalline zirconia ceramics (3Y-TZP) was evaluated by aging test in water vapor environment and Raman spectroscopic technique. In our previous study, it has been confirmed that phase stability was improved by controlling sintering temperature. In this study, we pointed our attention and evaluated the influence of surface conditions related to machining and to heat treatment, thus monitoring the changes in phase transformation fraction and residual stress on the material surface. From the results of aging test, an increase in monoclinic fraction was observed for grinded surfaces as compared with polished surfaces. Samples subjected to heat treatment after machining showed improved phase stability. A Vickers indentation print was also introduced on a 3Y-TZP surface, and the relationship between surface condition and low temperature aging was evaluated in the neighborhood of the print. We found that the residual stress fields induced in phase-transformed areas were enhanced during low temperature aging, and that phase stability was improved by heat treatment.

Stress Dependence of Sapphire Cathodoluminescence from Optically Active Oxygen Defects as a Function of Crystallographic Orientation

The cathodoluminescence (CL) spectrum of the synthetic sapphire single crystal has been studied with respect to the different crystallographic planes of the crystal in order to describe the tensorial stress dependence of the band related to oxygen defects. Experiments provide the link between CL spectral shift and stress, which is referred to as the piezo-spectroscopic (PS) relationship. Using the biaxial stress field developed at the tip of cracks generated from the corners of a Vickers indentation, we clearly detected stress dependence for the cumulative band arising from the F+-center transition of optically active oxygen vacancies. The matrix of PS coefficients along different crystallographic axes of single-crystal sapphire could be precisely determined. The shallow nature of the electron probe may enable the characterization of surface stress fields with a spatial resolution that may not be easily available by conventional laser probes. The PS calibration results collected on oxygen-defect bands allow the direct determination of unknown surface residual stress fields stored in sapphire substrates for electronics applications.

Improvements in Residual Stress Measurement by the Incremental Centre Hole Drilling Technique

This paper presents results which advance and improve the usefulness, accuracy and efficiency of incremental centre hole drilling as a method of measuring near surface residual stress fields. Particular emphasis is placed on providing optimal values for the number of drilling step increments to be used and their corresponding size. Guidelines on the optimal values for the number and size of steps to use during measurements are presented for various ratios of hole radius to strain gauge rosette radius in the form of tabulated data. These guidelines are subsequently incorporated into a new data analysis program which permits very near surface residual stress fields to be accurately determined in real components. The benefits of the new approach are highlighted by reporting the results of measurements made on three industrial components, each of which has been subjected to a well-known engineering process. These components are a shot-peened spring-steel, a friction stir welded aluminium alloy, and a titanium alloy subjected to three different machining processes. The results reveal that the improvements to the incremental centre hole drilling technique can provide measured residual stresses from depths ranging from about 10 \(\mu \)m to 1 mm.

Fluorescence spectroscopic analysis of surface and subsurface residual stress fields in alumina hip joints

We aim to establish a confocal spectroscopic technique able to study the features of fluorescence spectra arising from native Cr3+ impurity in polycrystalline alumina (Al2O3) as a biomaterial and to use their emission lines as microscopic probes for the characterization of residual stress fields stored in artificial hip prostheses during their implantation in vivo. As an application of the technique, we report for the first time concerning the evolution of microscopic (residual) stress fields stored on the surface and in the subsurface of N=7 retrieved Al2O3 hip joints after exposure in the human body from a few months to 19 yr. The micrometric diameter of the laser beam waist impinging on the joint surface (typically about 1 microm in lateral resolution) enables us to estimate the patterns and magnitude of residual stress with high spatial resolution, at least comparable with the grain size of the material. In addition, a selected confocal configuration for the optical probe enables minimization of the probe size along the in-depth direction. According to a statistical collection of data on the microscopic level for retrieved femoral heads in toto, a residual stress field arising from loading history in vivo during the lifetime of the Al2O3 femoral head can be revealed. Finally, an interpretation is given of microscopic wear mechanisms in Al2O3 artificial hip joints consistent with the observed evolution of surface residual stress fields on elapsed time in vivo.

Mapping of Residual Stress Field Based on Residual-Stress-Free State by ESPI Analysis

We study the residual stress mapping of indented Cu by ESPI (electronic speckle pattern interferometry). Based on the identification of the residual stress-free state using electronic speckle pattern interferometry (ESPI), we modeled the relaxed stress in annealing, the thermal strdin/stress and the residual stress field in case of both single and film/substrate systems by using the thermo-elastic theory and the relationship between relaxed stresses and displacements. Thus we mapped the surface residual stress fields on the indented bulk Cu and the 0.5⊔ Au film by ESPI. In indented Cu, the normal and shear residual stress are distributed over -800 MPa to 700 MPa and -600 MPa to 600 MPa respectively around the indented point.

Determination of Residual-Stress-Free State and Mapping of Residual Stress Fields Using Speckle Interferometry and Thermal Relaxation

ABSTRACTWe used an electronic speckle pattern interferometer (ESPI) for nondestructive measurement in-situ displacement fields in microsystems. A four-step phase-shift technique and magnifier with long working distance were adopted to increase displacement resolution to ∼10−2 μm and spatial resolution to ∼2 μm. A thermal vacuum chamber was designed to induce thermal treatments, including annealing. From the identification of the residual-stress-free state, we quantitatively modeled thermal strains/stress fields, relaxation stresses during annealing, and residual stress fields. Thermoelasticity theory was applied to model the relationship between the relaxation stresses and the displacements measured by ESPI during the evolution of the residual-stress-free state. We assessed the surface residual stress fields of indented bulk Cu; a Fe-Ni lead frame of 100 μm width; and 0.5 μm Au film. In the indented Cu, the normal and shear residual stresses around the indented point range from –1.7 GPa to 700 MPa and –800 MPa to 600 MPa, respectively, and the residual stress in the bending area of the Fe-Ni lead frame was estimated at 148 MPa and verified using beam-bending theory. In the Au film, tensile residual stresses are uniformly distributed from 500 MPa to 800 MPa as verified by X-ray diffraction.

Mapping of Surface Residual Stress Field by Laser Interferometry Using Stress Relaxation Method

ABSTRACTBased on the identification of the residual stress-free state using electronic speckle pattern interferometry (ESPI), we modeled the relaxed stress in annealing, the thermal strain/stress and the residual stress field in case of both single and film/substrate systems by using the thermo-elastic theory and the relationship between relaxed stresses and displacements. Thus we mapped the surface residual stress fields on the indented bulk Cu and the 0.5μm Au film by ESPI. In indented Cu, the normal and shear residual stress are distributed over -800 MPa to 700 MPa and -600 MPa to 600 MPa respectively around the indented point and in deposited Au film on Si wafer, the tensile residual stress is uniformly distributed on the Au film from 500 MPa to 800 MPa. Also we measured the residual stress by the x-ray diffractometer (XRD) for the verification of above residual stress results by ESPI.