Inhomogeneous Residual Stress Research Articles

On the Features of Inhomogeneous Residual Stress Identification Using the Digital Speckle Interferometry and the Hole-Drilling Method

On the Features of Inhomogeneous Residual Stress Identification Using the Digital Speckle Interferometry and the Hole-Drilling Method

Tensile mechanical behavior and failure mechanism of 2.5D woven fabric reinforced aluminum matrix composites involving residual stress

The tensile behavior of two and a half-dimensional (2.5D) woven fabric reinforced Al matrix composites involving residual stress was investigated experimentally and numerically. The residual stress and subsequent tensile behavior of the composites were predicted by multiscale finite element modeling. And the correctness of numerical simulation is verified by residual stress, tensile curve, surface strain diagram and fracture morphology. The results show that the inhomogeneous residual stress leads to the damage of the matrix and interface in the interweaving area of yarns. During the tensile process, the surface strain exhibits an obvious periodic distribution characteristic, which is related to the arrangement of yarns. With the increase of tensile strain, local matrix and interface damage accumulate and expand leading to the weft yarn cracking, matrix failure and interface debonding successively. The abrupt fracture of the composite can be attributed to the axial fracture of warp yarn, which exhibits obvious fiber fracture and pull-out characteristic.

A Theoretical Analysis for Arbitrary Residual Stress of Thin Film/Substrate System With Nonnegligible Film Thickness

Abstract Stoney formula is widely used in advanced devices to estimate the residual stress of thin film/substrate system by measuring surface curvature. Many hypotheses including that thin film thickness is ignored are required, thus bringing significant error in characterizing the inhomogeneous residual stress distribution. In this article, arbitrary residual stresses on thin film/substrate structures with nonnegligible film thickness are modeled and characterized. We introduce nonuniform misfit strain and establish the governing equations including mismatched strain, displacements, and interfacial stresses based on the basic elastic theory. The parameterization method and the method of constant variation are used in the process of equation decoupling. The expressions between displacements, surface curvatures, and misfit strain are determined through decoupling calculations. By substituting misfit strain, residual stresses are expressed by parametric equation related to surface curvature. It further indicates that there is a “non-local” part between the film stress and curvature at the same point. Compared to neglecting the film thickness, the proposed method eliminate relative errors up to 58.3%, which is of great significance for stress measurement of thin films and substrates.

On the features of inhomogeneous residual stress identification using the digital speckle interferometry and the hole-drilling method

A phenomenological approach to the actual problem of determining the inhomogeneous residual stress-strain state in the components of high-tech engineering systems at the stages of their design and operation is presented. The approach is based on physical and mechanical methods of measuring displacements. Current physical models describe the physical regularities of the residual states attributed to changes in the structure by the interaction of defects and dislocations in the field of micro- and meso-stresses. At the same time, there are the problems of the transition to the macrolevel, the construction of multilevel models, and the conversion of these models in engineering practice. In the framework of phenomenological approaches, in the general case, the solution of this problem requires the solution of three-dimensional inverse problems of thermoelasticity. A well-known mechanical method for determining a uniform field of residual elastic stresses recommended by ASTM E837 is described. The method proposed earlier by one of the authors for determining an inhomogeneous (in the plane) field of residual elastic stresses is discussed. A method of the three-dimensional inhomogeneous residual elastic stress-strain state determination based on the experimental determination of the displacement vector components by the method of step-by-step point hole-drilling and data of digital speckle interferometry and digital image correlation is developed. The constitutive relations for the components of the displacement vector are written in the form of Volterra integral operators. The basic operator functions are the functions of four variables, i.e., the coordinates of the cylindrical system (r, θ, z) associated with the hole, and the hole depth h. A method for verification of the basic functions is presented. The problem is reduced to the determination of three displacement functions of three variables: hole radius r, h, and z. Numerical simulation of basic functions is carried out. The obtained results are consistent with the known experimental data and calculated values of the deformation on the surface depending on the depth of the hole according to the ASTM E837 Standard.

Influence of Inhomogeneous Residual Stresses Arising from the Contact of the Cut on the Dispersion of Axisymmetric Longitudinal Waves in Two-Layer Hollow Cylinder

Influence of Inhomogeneous Residual Stresses Arising from the Contact of the Cut on the Dispersion of Axisymmetric Longitudinal Waves in Two-Layer Hollow Cylinder

Two laser beam modulation of microstructure and residual stress field in cold sprayed Al alloy for recovering fatigue performance

The cold spray (CS) process has been demonstrated to be an attractive additive manufacturing technology for the development of freeforms and coatings from temperature-sensitive materials. However, owing to the lower bonding strength and inhomogeneous residual stress field distribution, the fatigue performance of CS deposition cannot satisfy the requirements of numerous engineering conditions. This study proposes a novel and promising approach to recover the fatigue performance of CS-repaired Al alloy components using two laser beam modulations. In the treatment, a millisecond laser is used during the CS process to heat the impact location in situ, by which the bonding mode is transformed from mechanical bonding to metallurgical bonding, and massive Al2O3 reinforcements of nano/micro size are formed in the coating. Thus, the bonding strength is significantly improved. Next, another nanosecond laser is used as a post-treatment to act on the area except the repaired region of the sample, which optimised the residual stress distribution around the repaired zone by the mechanical effects of the laser-induced ultra-high shock waves. Through the combination of these two lasers, the fatigue performance of CS-repaired Al alloy samples is successfully restored to its original condition. This study demonstrates that this compound process of CS technology and laser processing presents a wide range of possibilities for further development of advanced repair technology.

Phase-field modeling of fatigue crack growth during tooth flank fracture in case-hardened spur gears

Tooth flank fracture (TFF) is a fatigue failure mode in gears in which the crack is initiated in a larger depth below the surface within the tooth volume. The crack propagates load-dependently and is not visually observable until final rupture of the tooth. The present publication focuses on numerical fatigue crack simulation of TFF in case-hardened spur gears. Herein, an existing phase-field model for fatigue fracture is revisited and extended to account for the simultaneous subsurface crack initiation and growth in high cycle fatigue during TFF. For this purpose, a gear tooth finite element model is implemented and parameterized using experimental data. Inhomogeneous material properties and residual stresses resulting from the manufacturing process are explicitly considered. The main interest of the study lies in the ability of the phase-field model to reproduce experimentally observable behavior during TFF such as subsurface crack initiation and the emerging subsurface crack path.

Analysis of the causes of undesirable curvature of the workpiece during longitudinal rolling using numerical simulation

Undesirable additional deformation was observed during the experimental cold rolling of steel. A simulation was performed in Deform software to clarify the causes. The influence of the unequal coefficient of friction, geometric inaccuracies of the rolls and the conveyor, and the situation when the rolls did not have the same diameter or rotated at different speeds were investigated. Simulations with different roll speeds corresponded best to reality. The simulation of the undesired curvature of the workpiece at different speeds of rotation of the rolls and 30% reduction was subsequently performed as an elastoplastic problem in order to determine the amount of springback and residual stress. Furthermore, the press straightening of the workpiece was simulated. Inhomogeneous and accidental deformation and residual stresses must be taken into account, especially when researching the effect of cold rolling on the mechanical properties and structure of the material.

Research on welding-induced inhomogeneous stress in thick plate EH40 butt joint considering phase transformation

In this work, the inhomogeneous residual stress distribution and evolution of thick plate in single-pass full penetration laser welding are systematically investigated using phase transformation model. The material constitutive model considering solid-state phase transformation according to the actual weld microstructure is proposed to predict the inhomogeneous stress distribution of the welded joint. The inhomogeneous stress distributions along the longitudinal, transverse and thickness direction surfaces of the welded joint are systematically analyzed and deeply discussed, respectively. The results show that there is an obvious inhomogeneous distribution of the temperature field between the start-welding, middle section and end-welding position of the weld. It is obviously observed that the top and bottom surfaces of welded joint produce remarkably high stress areas and high stress gradients. The maximum longitudinal and transverse stress gradient values in the top surface are up to 1240.1 MPa and 1175.7 MPa, respectively. It is found that martensitic transformation is the main reason for the inhomogeneous stress distribution including high stress areas and high stress gradients in thick plate welded joint. The current research is beneficial to reduce the detrimental effects of welding-induced inhomogeneous residual stress on thick plate welded joints.

Residual stress evolution and tailoring of cold pilgered Ti-3Al-2.5V tube

Cold pilgering has been considered as one of the preferred fabrication technologies for high-strength titanium alloy tube. However, the complex multi-pass thermo-mechanical loading histories in whole cold pilgering, viz., multi-stroke rolling and annealing as well as surface strengthening treatment might significantly influence the inhomogeneous deformation and residual stress which closely related to the fatigue and other service performances of tube products. The objective of this manuscript was to clarify the residual stress evolution characteristics in cold pilgering of high-strength titanium alloy tube while to propose an efficient approach for the tailoring of the residual stress. The residual stress distribution features at different deformation zones during cold pilgering were numerically investigated base on the verified finite element model. On account of the coordination of inhomogeneous deformation along the tube wall, the cold pilgered tube exhibited residual tensile and compressive stress on outer and inner surface, respectively. The effects of key process parameters on the residual stress of the cold pilgered tube were explored as well as the relevant inhomogeneous deformation features were discussed, the results showed that the value of residual stress could be affected by the variation of the Q value and area reduction but independent with other parameters. By combining the experiment, it can be also concluded that the residual stress states of the cold pilgered tube were maintained with the variation of the process parameters of cold pilgering and annealing. Furthermore, aiming at the residual stress tailoring and service performances improvement of the tube, the magnetic abrasive finishing (MAF) was introduced while the measurement results indicated that large residual compressive stress could be generated on the outer and inner surface of the tube simultaneously.

Effects of microstructure and inherent stress on residual stress induced during powder bed fusion with roller burnishing

A hybrid metal-additive manufacturing (AM) process that combines laser-based powder bed fusion (PBF-LB) with interlayer burnishing is investigated using a comprehensive modeling framework to provide new insights into how the inhomogeneous microstructure and residual stress from the laser powder bed fusion process affect the induced residual stress field that evolves during interlayer burnishing. Researchers have recently studied changes in microstructure resulting from similar hybrid metal-additive processes, however, it was only hypothesized that the resulting microstructure has some influence on the induced residual stress. In addition, researchers have numerically investigated the influence of burnishing/rolling process parameters on induced stress but neglected the effects of microstructure, thereby making homogeneous, isotropic assumptions. Such practice inhibits the prediction of microstructure-driven anisotropy that can exist in the inhomogeneous fused layer. This paper parametrically examines the influence of microstructure modeling, inherent residual stress mapping, and environment temperature on the induced residual stress during the hybrid metal-additive process. The demonstrated modeling framework incorporates inherent residual stresses that emerge from the laser powder bed fusion process, as well as the predicted microstructure, in a subsequent burnishing simulation to elucidate their individual and combined influences on the burnishing-induced residual stress. Findings reveal that modeling an inhomogeneous PBF-LB microstructure introduces an anisotropic distribution of plastic strain and residual stress along the burnished surface; a periodicity in planar stress components along the treated surface coincides with the PBF-LB scan lines. Effects of inherent residual stress on the burnishing-induced residual stress is less significant, but nonetheless observable. Elevated temperatures not only reduce the magnitude of compressive residual stress induced but also result in less variation of residual stress component magnitudes predicted along scan lines and hatch spaces. The presented framework offers new insights into the decoupled influences of microstructure and PBF-LB residual stress on burnishing-induced stresses that are not distinguishable via experimental techniques. However, trends in averaged residual stress through the depth of the specimen, as well as surface hardness magnitudes after burnishing show good agreements, respectively, with X-ray diffraction and microindentation measurements documented in the literature.

Development of the Hole-Drilling Method as Applied to the Study of Inhomogeneous Residual Stress Fields

Development of the Hole-Drilling Method as Applied to the Study of Inhomogeneous Residual Stress Fields

Static and dynamic characteristics of a compound sphere using Initial Stress Reference Independence

We study the influence of residual stress on the static and dynamic characteristics of a spherical structure. We consider a shrink-fitted compound sphere, where residual stress is developed due to the interference between outer and inner spherical layers. We calculate this residual stress and model the residually stressed material with suitable hyperelastic strain energy satisfying Initial Stress Reference Independence (ISRI). Under the action of inhomogeneous residual stress, the compound sphere behaves as an anisotropic, functionally graded composite sphere, which is reflected by the model. We apply this model to obtain stress distributions and inflation characteristics of the compound sphere. Our results demonstrate the hypothesis that residual stress moderates the stress concentration and reduces the stress gradient in biological/engineering structures. We obtain critical stretch and pressure for spherically symmetric deformations. An increase in interference/residual stress increases the critical stretch/pressure and improves the structural stability. We then apply an analytical approach to calculate the natural frequency of the compound sphere for small amplitude radial vibration. We observe that an increase in residual stress increases the natural frequency and widens the range of stable free vibration. We numerically investigate the free and forced vibration of the compound sphere. Forced vibration amplitude reduces as interference/residual stress increases, which is reflected in the frequency–amplitude plots. The frequency response shows a small hardening non-linearity. We investigate the subharmonic and superharmonic responses for small and large amplitude vibration.

DEVELOPMENT OF A HOLE DRILLING METHOD APPLIED TO STUDYING INHOMOGENEOUS RESIDUAL STRESSES FIELD

DEVELOPMENT OF A HOLE DRILLING METHOD APPLIED TO STUDYING INHOMOGENEOUS RESIDUAL STRESSES FIELD

Inhomogeneous thermal-mechanical analysis of 316L butt joint in laser welding

Inhomogeneous thermal-mechanical distributions in laser welding of austenite stainless steel 316L were analyzed, and the effect of shear behavior caused by residual stress on tensile strength was also discussed. A double cone combined heat source model was used to simulate the transient distribution of temperature field. The simulation results showed a good agreement with the experiment results in weld geometry, and the maximum prediction error was 5.84%. The temperature gradient at front wall of weld pool was apparently higher than that at back wall. Time- and space-dependent mechanical behaviors such as strain, stress and deformation were analyzed. It was indicated that stresses along longitudinal and transverse directions were related with temperature gradient, while the deformation fluctuation was dependent upon the high temperature gradient at the front wall of weld pool. The tensile test samples obtained at start-end and middle positions showed fracture interface lines with curve and rectilinear shapes, respectively. The reason is that a shear behavior, which could reduce the weld tensile strength, is caused by the coupling compressive stress and tensile stress in the joint with inhomogeneous residual stress. The shear behavior could be intensified with the increased inhomogeneity in weld residual stress.

Anisotropic Swelling Governed by Orientation-Dependent Interfacial Na Diffusion in Single-Crystalline Sb

The anisotropic volume expansion of anode materials produces locally inhomogeneous residual stresses, which frequently induce fracture of the anode materials and reduce battery capacity and cycle life. Much of our understanding of the anisotropic swelling behavior of anode materials is based on electron microscopy and macroscopic structural analysis techniques, which are insufficient to elucidate the atomistic origin of the anisotropic swelling behavior. In this study, we perform in situ sodiation experiments with single-crystalline Sb anodes followed by atomic simulations to determine the diffusion kinetics governing the sodiation of Sb and its associated swelling behavior. In situ sodiation experiments demonstrate that the rate of diffusion of Na into single-crystalline Sb anodes differs by more than a factor of 2 depending on the orientation of the Sb crystal, causing the crystal to swell anisotropically. This observed anisotropic diffusion is explained here by determining the orientation-dependent dif...

Numerical Simulation of Residual Stresses due to Multipass Welding in High Strength Steel Plates and Validation against Experimental Measurements

Multipass arc welding is commonly used for thick plates assemblies in shipbuilding. Sever thermal cycles induced by the process generate inhomogeneous plastic deformation and residual stresses. Metallurgical transformations contribute at each pass to the residual stress evolution. Since residual stresses can be detrimental to the performance of the welded product, their estimation is essential and numerical modelling is useful to predict them. Finite element analysis of multipass welding of a high strength steel is achieved with a special emphasis on mechanical and metallurgical effects on residual stress. A welding mock-up was specially designed for experimental measurements of in-depth residual stresses using contour method and deep hole drilling and to provide a simplified case for simulation. The computed results are discussed through a comparison with experimental measurements.

Experimental Analyses on Multiscale Structural and Mechanical Properties of ε-Si/GeSi/C-Si Materials

Strained silicon (ε-Si) is a promising material that could extend Moore’s law by enhancing electron mobility. A ε-Si material is usually composed of multiscale, multilayer heterostructures, where the strained-silicon film or strap is tens-of-nanometers thick, and its buffer layers are of the micrometer scale. The structural properties determine the electrical performance and reliability of ε-Si-based devices. Inhomogeneous residual stress is induced during the preparation, which induces ε-Si structure failure. In this work, biaxial strained-silicon films that contain graded and relaxed germanium-silicon buffer layers were prepared on monocrystalline silicon wafers through reduced-pressure chemical-vapor epitaxy. The layer components and thicknesses were measured using energy-dispersive spectroscopy and scanning-electron microscopy. Crystal and lattice characters were observed by using high-resolution transmission-electron microscopy and micro-Raman spectroscopy. The residual stress distribution along cross-sections of the ε-Si multilayer structures was examined by using micro-Raman mapping. The experimental results showed that, with a gradual increase in germanium concentration, the increasing residual stress was suppressed owing to dislocation networks and dislocation loops inside the buffer layers, which favored the practical application.

Effects of Residual Stress Distribution on Interfacial Adhesion of Magnetron Sputtered AlN and AlN/Al Nanostructured Coatings on a (100) Silicon Substrate.

The present study investigated the influence of nanoscale residual stress depth gradients on the nano-mechanical behavior and adhesion energy of aluminium nitride (AlN) and Al/AlN sputtered thin films on a (100) silicon substrate. By using a focused ion beam (FIB) incremental ring-core method, the residual stress depth gradient was assessed in the films in comparison with standard curvature residual stress measurements. The adhesion energy was then quantified by using a nanoindentation-based model. Results showed that the addition of an aluminum layer gave rise to additional tensile stress at the coating/substrate interface, which can be explained in terms of the differences of thermal expansion coefficients with the silicon substrate. Therefore, the coatings without the Al layer showed better adhesion because of a more homogeneous compressive residual stress in comparison with the coating having the Al layer, even though both groups of coatings were produced under the same bias voltage. Results are discussed, and some general suggestions are made on the correlation between coating/substrate property combinations and the adhesion energy of multilayer stacks. The results suggested that the Al bond layer and inhomogeneous residual stresses negatively affected the adhesion of AlN to a substrate such as silicon.

Residual Stresses in Explosively Welded Plates Made of Titanium Grade 12 and Steel with Interlayer

Distributions of residual stress components in explosively welded three-layer plate composed of titanium Grade 12, titanium Grade 1 and SA516 Grade 70 steel are investigated in this paper. The study applied the sectioning and the hole-drilling strain gage methods for residual stress measurement. The results have shown an inhomogeneous residual stress distribution, approximated by fourth-order polynomial along the thickness of a three-layer plate. Biaxial compressive residual stress state is observed in titanium Grade 12 and Grade 1 layers which change to tensile type in the vicinity of the interface between titanium Grade 1 and steel. Microstructure observation reveals the presence of the adiabatic shear bands in titanium Grade 12 layer at the interface with titanium Grade 1 interlayer. The observed distribution of residual stress components is justified by the occurrence of the shock wave phenomena.