Effect Of Initial Residual Stresses Research Articles

Investigation of the influence of initial residual stress and toolpaths on milling deformation of titanium alloy

Titanium alloy structural components are widely used in the aerospace industry due to their excellent physical properties. However, their susceptibility to machining deformation during milling, attributed to the presence of initial residual stress, poses a significant challenge. Therefore, this paper proposes a finite element model for predicting milling deformation in Ti6Al4V titanium alloy structural parts, considering initial residual stress. The methodology involves establishing the initial residual stress field of titanium alloy components based on a mathematical model of annealing heat transfer and a theoretical study of thermal elasto-plastic constitutive relation, with experimental confirmation of model accuracy. Based on the initial residual stress, a finite element model was developed to predict the maximum deformation under different toolpaths. Finally, a comparative analysis with milling experiments validated the proposed models. The experimental results demonstrated a remarkable alignment with the finite element model, showcasing the correctness of the developed models. The maximum deviation in deformation observed was within the range of 0.003 mm–0.011 mm. This study is the first to comprehensively consider the effects of initial residual stress and toolpaths on titanium alloy milling deformation, and to experimentally verify the proposed model’s accuracy and practicality. It provides a new theoretical basis and technical guidelines for titanium alloy milling deformation.

An Investigation of the Contact Fatigue Characteristics of an RV Reducer Crankshaft, Considering the Hardness Gradients and Initial Residual Stress.

The crankshaft is one of the core components of a Rotate Vector (RV) reducer. The fatigue life of the RV reducer is severely hindered by fatigue failure on the eccentric cylindrical surface of the crankshaft. The hardness gradients and residual stress in the crankshaft, associated with machining operations, exert an enormous impact on the rolling contact fatigue (RCF). In this work, a finite element method (FEM)-based three-dimensional elasto-plastic contact model is established to calculate the stress-strain field by taking hardness gradients and initial residual stress into account. The RCF characteristics of an RV reducer crankshaft is investigated by applying modified Fatemi-Socie (FS) multiaxial fatigue criterion. The results indicate that initial residual stress plays an influential role in the fatigue damage by altering the distribution of the maximum normal stress near the contact surface. The modified FS fatigue criterion could better consider the effect of initial residual stress and the shear stress, which significantly improves the prediction accuracy of the contact fatigue life model. The contact fatigue performance could be considerably improved by designing appropriate shot peening parameters to obtain optimized residual stress distribution. Therefore, the technique presented may serve as an important guideline for the anti-fatigue design of an RV reducer crankshaft.

Variance-based sensitivity analysis for the influence of residual stress on machining deformation

Sensitivity analysis is widely used in engineering design to illustrate the effect of the variations of input variables on the output response of a system efficiently. The current study proposes a novel method of variance-based sensitivity analysis to evaluate the effects of initial residual stress (IRS) and surface residual stress (SRS) on the uncertainty of machining deformation. This analysis introduced the variance as the uncertainty evaluation index and the variance contribution to reflect the effects of residual stress on machining deformation. The variance contributions were divided into two components: (1) independent contributions due to the variations from the independent portion of a variable and (2) correlated contributions due to the variations from the portion of a variable correlated with other variables. Uncertainty characteristics (variance σ 2 ) of residual stress were extracted and an analytical model for the relationship between residual stress and the bending moment was established. An importance measure matrix consisted of variance contribution of each residual stress variable was constructed. Concerning correlated residual stress variables, the effects of variances and correlation coefficients of residual stress on the variance of machining deformation were studied. Experimental work on a sidewall structure showed that the variance contribution of IRS at the surface layer was 5.3 to 17.8 times greater than SRS. Furthermore, the sensitivity analysis for correlated residual stress variables indicated that decreasing the variances of IRS and SRS (especially IRS) and keeping the values of correlation coefficients between −0.5 to 0.5 are beneficial to reduce the uncertainty of machining deformation. • A variance-based sensitivity analysis method for machining deformation was proposed. • Variance contribution reflected the effects of RS on the machining deformation. • An analytical model between bending moment and RS was proposed. • Standard deviations and correlation coefficients of RS were studied.

Effect of Initial Residual Stress on Machining Deformation of a Casing Part

Initial residual stress of blank is the main cause for the workpiece machining deformation. Based on the simplified equivalent model and the finite element analysis method, the effects of initial residual stress in bidirectional, axial direction and tangential direction on the deformation of an aluminum alloy conical case were studied respectively. The deformations of case were judged by flatness and roundness error of the end face of the case. From the results, it can be seen that the influence of the initial axial residual stress on the roundness error of the end face is greater than that of the radial residual stress; among all the errors, the roundness error of the large end face is much larger than that of other errors. It is shown that the roundness error of the large end face and the initial axial residual stress of the workpiece are the most important issues to be controlled in actual machining process. This conclusion has certain guiding significance for practical application.

Reduction of distortions in large aluminium parts by controlling machining-induced residual stresses

Large aluminium monolithic parts used in the aeronautic industry frequently show significant geometric distortions after the machining process. These distortions are the consequence of the initial residual stresses of the raw material as well as machining-induced residual stresses. Therefore, to minimise distortions, it is fundamental to understand the effect of the different parameters of the manufacturing process and define the optimum manufacturing strategy. This work studies the effect of initial residual stresses of aluminium plates and the residual stresses generated by the machining process on the final geometric distortions of the part. First, 7175-T7351 aluminium bars (40 mm wide × 38 mm thick × 400 mm long) were face milled at two different cutting conditions reducing the thickness to 6 mm. The distortions were measured in a coordinate measuring machine. The results revealed that the machining strategy significantly influenced the distortions, as a difference of 65% on distortions was found between the two cutting conditions. In addition, an FEM model to predict distortions was developed. This model considers initial residual stresses (measured by the contour method) and residual stresses induced by the machining process (measured by the hole drilling technique). Once the FEM model was validated, the study was extended to more complex geometries. These new studies revealed that final distortions are sensitive to machining-induced residual stresses. Furthermore, this finding indicates that it is possible to define machining conditions which generate desirable residual stress profiles to minimise part distortion.

Numerical Study of Laser Shock Peening Effects on Alloy 600 Nozzles With Initial Residual Stresses

This paper investigates the effect of initial residual stress and prestrain on residual stresses due to laser shock peening for Alloy 600 using numerical simulation. For simulation, the strain rate dependent Johnson–Cook hardening model with a Mie–Grüneisen equation of state is used. Simulation results are compared with published experimental data, showing good agreement. It is found that the laser shock peening (LSP) process is more effective for higher initial tensile residual stress and for larger initial prestrain in terms of compressive stress at the near surface. However, the effective depth decreases with increasing initial tensile residual stress and initial prestrain.

A comprehensive experimental and numerical study on redistribution of residual stresses by shot peening

Shot peening is one of the most effective surface strengthening treatment technologies in which compressive residual stresses are induced beneath the specimen surface. Effects of various factors on the distribution of residual stress profile induced by shot peening have been investigated by many researchers. However, initial residual stresses are one of the important factors which affect the shot peening residual stress.This study is aimed to present comprehensive numerical and experimental study on the effect of initial residual stresses on the shot peened specimen. Initial residual stresses were induced using a four-point bending rig and grinding. Incremental center hole drilling (ICHD) technique was employed to measure residual stresses on bent, ground, shot peened, bent plus shot peened and ground plus shot peened specimens. Numerical analyses of these processes were performed to provide quantitative comparison of different combinations of residual stresses. The comparison with experimental results helped to have a better understanding on how shot peening residual stresses were redistributed. Furthermore, the surface hardness was measured for all specimens.

Effect of Initial Residual Stress and Machining-Induced Residual Stress on the Deformation of Aluminium Alloy Plate

During the machining of aerospace thin-walled components, a large amount material is removed, and machining-induced residual stress is induced in the boundary layer of the work piece, which results in deformation of the components. In this study, the effects of material initial residual stress and machining-induced residual stress on the deformation of aluminium alloy plate are studied. A theoretical model of the plate is analysed first, and the experiments of the milling deformation under different initial residual stress conditions are performed. The results show that the machining-induced residual stress is the primary factor of distortion. The coupling action of compressive initial residual stress and machining-induced residual stress increase the plate deformation, and the coupling action of tensile initial residual stress and machining-induced residual stress decrease the plate deformation. The finite element simulation results are compared with experimental results and found to be in good agreement.

Effects of simulation parameters on residual stresses for laser shock peening finite element analysis

By using finite element analysis, we proposed an applicable finite element method of laser shock peening (LSP) and discussed various parameters, such as solution time, stability limit, dynamic yield stress, peak pressure, pressure pulse duration, laser spot size, and multiple LSP. The effects of parameters related to the finite element simulation of the LSP process on the residual stresses of 35CD4 30HRC steel alloy are discussed. Parametric sensitivity analyses were performed to establish the optimum processing variables of the LSP process. In addition, we evaluated the effects of initial residual stress, such as welding-induced residual stress field.

Effect of Initial Residual Stress on Stress Relaxation in Cold-Drawn Steel Rods

This work shows the effect of the initial residual stress state on the stress relaxation behavior of cold-drawn steel rods. The evolution of residual strains at several locations along the rod diameter was measured in-situ by neutron diffraction during a stress relaxation experiment. It was found that if residual stresses are significant, stress relaxation is not homogeneous in the cross-section of the rods. This also explains the higher stress losses found in the rods with high residual stresses.

Effect of residual stresses on interface crack growth by void expansion mechanism

Crack growth along an interface between two adjacent elastic–plastic materials in a layered solid is analysed, using special interface elements to represent the fracture process ahead of the crack-tip. These interface elements account for ductile failure by the nucleation and growth of voids to coalescence. In these elements the stress components normal to the interface and the shear stresses are given by equilibrium with the surrounding material, and the stress component tangential to the interface is determined by the requirement of compatibility with the surrounding material in the tangential direction. It is assumed that the layers are sufficiently thick, so that the plastic regions around the crack-tip are much smaller than the thickness of the nearest layers. The analyses focus on the effect of initial residual stresses in the layered material, or on T-stress components induced during loading. The results show that the value of the T-stress component in the softer material adjacent to the interface crack plays the dominant role, such that a negative value of this stress component gives a significant increase of the interface fracture toughness.

Influence of plasticity on interface toughness in a layered solid with residual stresses

For crack growth along an interface between two adjacent elastic–plastic materials in a layered solid, the resistance curve behaviour is analysed by approximating the behaviour in terms of a bi-material interface under small scale yielding conditions. Thus, it is assumed that the layers are thick enough so that the extent of the plastic regions around the crack tip are much smaller than the thickness of the nearest layers. The focus is on the effect of initial residual stresses in the layered material, or on T-stress components induced during loading. The fracture process is represented in terms of a cohesive zone model. It is found that the value of the T-stress component in the softer material adjacent to the interface crack plays a dominant role, such that a negative value of this T-stress gives a significant increase of the interface fracture toughness, while a positive value gives a reduction of the fracture toughness.

505 溶接過程における板材の変形に及ぼす初期残留応力の影響

505 溶接過程における板材の変形に及ぼす初期残留応力の影響

Cavity growth in ductile particles bridging a brittle matrix crack

The addition of a dispersed ductile phase in a brittle ceramic can result in an increased fracture toughness, mainly due to plastic dissipation during crack bridging. The large elastic-plastic deformations of a ductile particle intercepted by a brittle matrix crack are here analysed numerically with main focus on the effect of the growth of a single void in the particle centre, as has been observed experimentally. Particle-matrix debonding is incorporated in the numerical model, represented in terms of a cohesive zone formulation, and so is the effect of initial residual stresses induced by the thermal contraction mismatch during cooling from the processing temperature. The bridging behaviour is studied for different combinations of material parameters, and the void growth behaviour is related to previous results for cavitation instabilities in elastic-plastic solids.

NONLINEAR ANALYSIS OF THIN-WALLED FRAMES AND MEMBERS WITH ARBITRARY OPEN CROSS SECTIONS

An incremental equilibrium equation for a beam-cloumn with arbitrary open cross sections is derived in a stiffness matrix form by using a moving element coordinate system and an incremental variational principle. A segmentation method for the cross section is used to analyze the development of plastic zones in the cross section and the effect of initial residual stresses arbitrarily distributed in the cross section. Yielding of the material is judged as a bi-axial stress problem under normal and shear stresses by using the flow theory of plasticity associated with von Mises yield criterion. Validity and efficiency of the present method are shown by illustrative examples.

疲労き裂伝ぱに及ぼす初期残留応力の影響

The fatigue crack propagation behavior of S35C steel plates having initial residual stress was studied. Fatigue crack propagation tests under a constant stress intensity factor range, ΔK, were carried out, and the effect of initial residual stress on crack propagation was examined. The initial residual stress was given to the specimens by pure bending. A FEM elastoplastic analysis of fatigue crack growth was made, and the relation between the mechanical quantity calculated from the analysis and the crack propagation rate was discussed.The results obtained are summarized as follows:(1) The influence of initial residual stress on fatigue crack propagation depends on the loading stress and the stress ratio, and it is difficult to estimate the propagation rate from only the initial stress distribution.(2) For the materials having initial residual stress the fatigue crack propagation rate is not related to the stress intensity factor range, ΔK, but closely related to a strain range at the crack tip, Δεymax.