Effect Of Residual Stress Research Articles

Laser shock peening regulating residual stress for fatigue life extension of 30CrMnSiNi2A high-strength steel

The improvement of material fatigue life has been a continuous pursuit in engineering. Laser shock peening (LSP) is an excellent processing method that can effectively enhance the service life of engineering materials. In this paper, the 30CrMnSiNi2A high-strength steel was treated with LSP to improve the fatigue life, respectively. The material's roughness has improved as a result of LSP treatment, and additional treatments have a more noticeable improvement than the energy density’s increase. The change in residual stress, however, presented a distinct pattern. There was not much difference between the laser treatment of once at 7.89 GW/cm2 and three times at 6.57 GW/cm2 in terms of compressive residual stress. The maximum hardness of the material surface was up to 589.8 HV under the combined effects of work hardening and compressive residual stress. In the fatigue life test of different loading stresses, the fatigue life of the treated samples was more than doubled compared with the untreated samples. The greatest life improvement occurred in high load fatigue testing. Combined with the analysis of fracture morphology, it could be found that the transfer of crack source from the surface to the interior caused by the gradient compressive residual stress is the reason for the increase in life.

Investigation of fracture parameters for a surface-cracked multi-pass T-joint considering welding residual stress

A numerical simulation procedure was carried out to evaluate the fracture parameters for a surface-cracked thick-plate T-joint considering welding residual stress (WRS) effect. Welding calculation was performed to simulate the welded joint then the results were verified against the experiment taken from the literature. The effect of the location of the final weld pass on WRS distribution was also analyzed numerically. Stress analyses were conducted using an intact T-joint model under different mechanical loading patterns, to determine the location of the hot spot stress and thereafter the location of the surface crack. Subsequently, the fracture parameters were thoroughly addressed under different conditions including external loading only and a combination of external loading and WRS. The effect of weld angle on the behavior of fracture parameters was also discussed. The numerical calculations succeeded in explaining the fundamental fracture characteristics of a multi-pass T-joint with a surface crack.

Crystallographic orientation-dependent corrosion behavior of aluminum under residual stress

The role of residual stress in the crystallographic orientation-dependent corrosion behavior of Al at the pit initiation and propagation stages was investigated. A clear correlation between step dissolution of Al, the crystallographic orientation of Al, and residual stress was experimentally and theoretically demonstrated. Al atoms exhibit sequential dissolution behaviors, resulting in step configuration of the surface. Residual stress can slightly restrain or promote pit nucleation at the pit initiation stage, depending on its sign. However, on the step surface, residual stress is a primary factor that can decrease and increase the dissolution rates of atoms up to 10% during the pit propagation stage, regardless of the crystallographic orientation. Neighboring coordination numbers and distance between atoms were measured to elucidate the effects of crystallographic orientation and residual stress on the corrosion behavior of Al. Results of the work function and density of states calculations were adequately consistent with each other and supported the experimentally determined pit density and depth behaviors.

Effect of Residual Stress on the Continuous Cooling Transformation of High‐Strength Low‐Alloy Hot‐Rolled Strip

The external stress will change the transformation process and microstructure of the material, and the residual stress generated during the processing of the material will also affect the transformation. Herein, the effect of residual stress is simulated by applying uniaxial elastic loads during the continuous cooling of high‐strength low‐alloy hot‐rolled strip. The transformation process and microstructure of the samples under different stress conditions are investigated. The results show that residual stress can accelerate the transformation process, and the tensile stress is greater than the compressive stress. The degree of lattice mismatch in stressed samples is larger than that in unstressed samples, leading to dislocation proliferation. It is found that there is a phenomenon of residual stress‐induced grain growth according to the statistics of grain size of different samples. Due to the higher dislocation density and smaller curvature of the parent phase interface under compressive stress, the compressive stress samples have a higher nucleation rate, resulting in smaller grain size than the tensile stress samples. In addition, the transformation texture also changes under residual stress.

Quantifying effect of overload-induced residual stress behind crack tip on fatigue crack growth

Separating and quantifying effect of overload-induced residual stress (RS) behind and ahead of crack tip on fatigue behavior are inevitable for random fatigue life prediction. In this study, fatigue crack growth measurements under constant stress intensity and different stress ratios for the same overload are performed together with analyzing crack compliance curves. The results show crack closure-depended RS contribution behind crack tip to fatigue retardation results from the variation of crack opening stress intensity which can be directly obtained in fatigue test. Crack closure influence is determined by both effective RS behind crack tip and contact length of crack wake.

The Effects of Compressive Residual Stress on Properties of Kyanite-Coated Zirconia Toughened Alumina Ceramics.

In this study, the prestressed coating reinforcement method was employed to create kyanite-coated zirconia toughened alumina (ZTA) prestressed ceramics. Due to the mismatch of the coefficient of thermal expansion (CTE) between the coating and substrate, compressive residual stress was introduced in the coating. The effects of compressive residual stress on the mechanical properties of ZTA have been demonstrated. Results show that the flexural strength of the kyanite-coated ZTA ceramics improved by 40% at room temperature compared to ZTA ceramics. In addition, the temperature dependence of mechanical properties has also been discussed. And the results show that the reinforcement gradually diminished with increasing temperature and eventually disappeared at 1000 °C. The modulus of elasticity of the material also exhibits a decreasing trend. Furthermore, the introduction of the prestressing coating enhanced the thermal shock resistance, but the strengthening effect diminished as the temperature increased and completely disappeared at 800 °C.

Comparison of the continuum damage and fracture mechanics in fatigue assessment of components containing residual stresses

In the present study, the fatigue crack growth life of standard and smooth notched specimens containing residual stresses are evaluated based on the continuum damage and fracture mechanics approaches. It is indicated that fatigue crack growth lives assessed by the continuum damage model are closer to the experimental results, with a difference of <10% in the specimens containing residual stresses. The total stress intensity factor range is used to consider the effects of residual stresses in the estimation of fatigue crack growth life based on the fracture mechanics. It is found that in existing residual stresses, the stress intensity factor K is not a proper parameter to evaluate crack tip zone. Fatigue crack initiation life is experimentally obtained based on assessing variations of the slope of unloading curve in the force-displacement diagram of fatigue experiments. The cycle including a change in the slope is considered as fatigue crack initiation event. Isotropic and kinematic hardening parameters of ASTM A516 pressure vessel steel are considered in finite element analyses. Tensile residual stresses are introduced into the notched specimens by employing four-point-bending with a magnitude of around 90% of the yield stress of the material. The results indicate that at least 65% of the fatigue life of the specimens is decreased due to the presence of tensile residual stresses. Tensile residual stresses are measured using the hole-drilling technique.

Investigation of acoustoelastic surface acoustic waves in prestressed media

Dispersion of broadband surface acoustic waves (SAWs) is often used for the nondestructive evaluation of near-surface elastic properties of materials. The accurate forward model of SAW propagation is essential for inversion. In this paper, we present a combining semi-analytical finite element (SAFE) and perfectly matched layer method for accurately predicting the phase velocity dispersion, attenuation and polarization modes of SAWs in any prestressed anisotropic layered half-space. Equations of motion are formulated based on the Biot's theory of small deformations influenced by initial stress, so it does not matter whether the residual stress results from hyperelastic transformations. The simulated results are firstly validated by the solutions from the exact three-dimensional elasticity theory-based method. The SAFE method is then used to discuss the effect of material anisotropy and residual stress on the SAWs. Finally, the method is applied to two practical examples. The differences and similarities of two common types of acoustoelastic theories are also discussed.

Effects of Residual Stress Induced by Laser Shock Peening on Fatigue Crack Propagation Behavior in Directed Energy Deposition Stainless Steel

To investigate the effect of laser shock peening (LSP) on the fatigue crack propagation behavior of 316L stainless steel fabricated by directed energy deposition (DED), three‐dimensional finite element models of DED and compact tensile specimens before and after LSP are developed. The residual stress fields induced by DED and LSP are simulated, as well as the effects of different residual stresses on the stress intensity factor and effective stress ratio based on the contour integral method are also analyzed. The microstructure of the LSP region is observed by scanning electron microscope. When the crack length increases from 12 to 22.5 mm, the average effective stress ratio of the DED specimen is 0.133, and the average effective stress ratio of the DED specimen after LSP decreases to 0.110, which decreases by 17.3%. The fatigue lives of the DED specimen before and after LSP are 62.7% and 105.2% of that of the hot‐rolled plate. After LSP treatment, the fatigue life of the DED specimen is increased by about 1.68 times. The fracture morphology in the transient fracture zone changes from ductile and brittle mixed fracture to ductile fracture.

Effect of residual stress and phase constituents on corrosion-cavitation erosion behavior of 304 stainless steel by iso-material manufacturing of laser surface melting

Different from additive manufacturing and subtractive manufacturing, iso-material manufacturing (also named isovolumetric manufacturing) is applied to 304 stainless steel (304SS) by laser surface melting (LSM) at four energy density (51 J/mm2, 44 J/mm2, 39 J/mm2, 37 J/mm2), aiming at improving the resistance to corrosion and cavitation erosion without any addition of precious metals. The experimental results show that the microstructure presents the transformation from plane crystal → columnar crystal → equiaxed crystal from interface to top surface. All the samples exhibit austenite+martensite+Cr23C6, and the martensite content is increased from 9.3% to 40.8% with the energy density decreasing after iso-material manufacturing. In addition, low angle grain boundary is increased, and nano-mechanical properties also show an increasing trend. The decreasing of energy density also enhances the residual tensile stress of the melting layer. The sample obtained at energy density of 51 J/mm2 displays the highest corrosion resistance in 3.5 wt% NaCl solution, which can be attributed to its low galvanic corrosion degree and small residual tensile stress. The sample obtained at energy density of 39 J/mm2 exhibits the highest cavitation erosion resistance (Re) and its passivation film displays better self-repairing and re-passivation ability as indicated by synergistic cavitation erosion-corrosion behavior. The high cavitation erosion resistance can be attributed to the proper compromise of the constituent phases and higher self-repairing of the passivation film for the melting layer. Moreover, the 304 stainless steel prepared in this study exhibits a high or comparable corrosion and cavitation erosion resistance in comparison with the samples prepared by other fabrication method reported previously.

Simulation of residual stress and micro-plastic deformation induced by laser shock imprinting on TC4 titanium alloy aero-engine blade

In laser shock processing (LSP) of aero-engine blades, overlap marks due to spot overlapping cause irregular surface morphology that becomes a source of cracks under fatigue behaviors. This reduces the beneficial effect of compressive residual stress induced by LSP and undermines fatigue performance of blades. In this paper, laser shock imprinting (LSI) is proposed to improve fatigue performance of aero-engine blades. In this process, a layer of contact film with micro-grooves is placed between the absorption layer and the workpiece (blade) of the LSP. By using the double action of laser shock wave and micro-grooves in contact film, blade surface morphology is transformed towards the direction conducive to improve its fatigue performance. Using ABAQUS software, Johnson-Cook model and Fabbro model were considered to study the plastic rheological behavior of blade surface material induced by LSI. Effect of process parameters namely, peak pressure, impact number and spot overlapping ratio on residual stress and micro-plastic deformation of blade surface were studied. Simulation results showed that under the action of laser shock wave, blade surface material flowed into micro-grooves in contact film via extrusion plastic deformation. This resulted in micro-bulge morphology having geometrically specific arrangement on blade surface, which achieved accurate control of micro-plastic deformation on blade surface. Increase in peak pressure and impact number increase the surface micro-bulges height. However, increase in peak pressure lowers the stress difference between bulging edge and non-bulge zones. It was found that 33% spot overlapping impact resulted in more uniform surface micro-bulge morphology on blade surface.

Imperfection Sensitivity of Plastic Shear Buckling Behavior in Corrugated Web Stainless Steel beams

AbstractThe shear behavior of corrugated web beams can be highly sensitive to the presence of initial imperfections. The designer has, in general, no prior information about the mechanical and geometric imperfections of welded elements. As a solution, in a FEM‐based design, the eigen buckling deformations with an equivalent maximum magnitude are included as an equivalent initial imperfection in a nonlinear analysis to account for the simultaneous effects of geometric imperfections and residual stresses. Previous researchers investigated the effects of initial imperfections in the form of different eigenmodes found via linear buckling analysis. They concluded that the shear strength rises with mode number, with the first mode providing the most crucial condition. However, it is shown in this paper that such a methodology is not applicable to stainless steel corrugated web beams in the medium slenderness ratio range when shear yielding precedes shear buckling. It is observed that, unlike in elastic buckling, in plastic buckling the first buckling mode does not result in the minimum strength. The results show that in FEM‐based design, using the first mode instead of the critical mode as the shape of the initial imperfection can result in a maximum of 19% and 31% overestimation of the ultimate shear capacity for the imperfection amplitudes of tw and hw/200, respectively.

Effect of dislocation and residual stress on etching performance of 12 μm thick rolled copper foil during pre-stretching

With the rapid development of new electronic information industry in 5G era, the development of various electronic components towards high speed and multi-functionality, and higher requirements have been put forward on the precision of circuit boards, the quality and rate of signal transmission. The 12 μm thick rolled copper foil is the thinnest rolled copper foil that can be stably produced, which is essential for the manufacture of high-end Flexible Printed Circuit (FPC) boards. The different microstructure and stress states of 12 μm thick rolled copper foil was obtained through different degrees of pre-stretching. And then the effect of dislocation and residual stress on the etching performance of copper foil was systematically investigated. The results show that the etching rate of copper foil increases and then decreases with the increasing of pre-stretching strain. And the etching rate of copper foil increases rapidly when the pre-stretching strain increases from 0.67% to 0.83%. For the dislocation, the rolled copper foil has higher dislocation density, and the dislocation density gradually increases with the increasing of pre-stretching strain. For the residual stress, the rolled copper foil has higher residual compressive stress. The residual compressive stress decreases and then turns into residual tensile stress with the increasing of pre-stretching strain. The residual compressive stress and dislocation reduce the etching rate of copper foil, and the residual tensile stress increases the etching rate of copper foil within a certain range. The four stages of etching rate variation of copper foil during pre-stretching were clarified, and the calculating model of etching rate was constructed when the dislocation density or residual stress acts as a single factor or dual factors.

Prediction of the effect of shot peening residual stress on fretting fatigue behaviour

Fretting occurs at two contact bodies, which sustain oscillation loading. The fretting phenomenon decreases the fatigue lifetime dramatically. Shot peening is a commonly used surface treatment to enhance the resistance to damage because the residual stress is introduced to the surface of the material. Some studies showed that residual stress was helpful to improve fatigue lifetime. Under fretting fatigue condition, there are two main stages: crack initiation stage and the crack propagation stage. In this paper, the authors apply the Critical Plane (CP) method combined with the Theory of Critical Distance (TCD) to study the fretting fatigue crack initiation behaviour under the influence of shot peening residual stress, including the crack initiation position, orientation and the crack initiation lifetime. Meanwhile, the Linear Elastic Fracture Mechanics (LEFM) theory and the Extension Maximum Tangential Stress (EMTS) criterion are adopted to study crack propagation behaviour considering shot peening residual stress effect. The results show that the methods applied in this paper can make good predictions of fretting fatigue behaviour, including both initiation and propagation stages. Meanwhile, the influence of residual stress in these two stages are studied as well.

Numerical investigation of residual stresses in thin-walled additively manufactured structures from selective laser melting

Selective laser melting (SLM), a metal laser powder bed fusion additive manufacturing method, involves several cycles of very high temperature gradient heating and cooling during the solidification of each layer, which can cause the accumulation of detrimental residual stresses in the 3D printed structure. This work uses a thermo-mechanical computational modeling approach to investigate the formation of residual stresses in thin-walled structures and also investigates the effects of varying taper on the evolution of residual stress profiles of the build. Three material grades; namely, Titanium alloy (Ti64), Stainless steel (SS316L) and Inconel (IN718) have been used for this study. The results show that varying taper thickness up to a certain value has a considerable effect on residual stress evolutions in thin-wall structures, however, beyond a certain value of the taper level, the residual stresses are observed to converge. Also, it is observed that the tensile stresses at the edges of the wall are almost equal or exceed the yield stress of the materials. Among the three material grades considered, the magnitude of residual stress was higher in Ti64 and the stresses are dominant in the build direction. The simulation framework is also applied to analyze the effect of residual stresses on the mechanical properties of complex thin-wall structures such as TPMS (Triply Periodic Minimum Surfaces) lattice structure, using Schwarz Primitive (SP) as a case study. It is observed that the residual stresses lower the effective elastic properties of the lattice structures by 6% ∼ 10% for the three material grades but has no effect on the effective plastic behavior of the material.

Quantification and Analysis of Residual Stresses in Braking Pedal Produced via Laser-Powder Bed Fusion Additive Manufacturing Technology.

This study focuses on the experimental verification of residual stress (RS) in a 3D-printed braking pedal using the Powder Bed Fusion (PBF) method with SS316L material. The RS was measured at two representative locations using the hole drilling method (HDM) and the dividing method, which are semi-destructive and destructive methods of RS measurement, respectively. The finite element method (FEM) was used with Ansys Workbench 2020R2 and Simufact Additive 2021 software to determine the magnitude of RS. The results provide insights into how RS is incorporated into metal 3D-printed components and the available tools for predicting RS. This information is essential for experts to improve the accuracy and functionality of SLM parts when post-subtractive or additive manufacturing processes are used. Overall, this study contributes to the advancement of knowledge on the effects of RS on 3D-printed metal components, which can inform future research and development in this area.

Material characterization of cyanate ester material for structures with high dimensional stability requirements

The degradation temperature, cure kinetics, viscosity, shrinkage, thermal expansion, and the modulus of RS-36-1 (modified epoxy), RS-3C and RS-3 (cyanate esters) are measured to evaluate the dimensional stability of these materials. L-shape carbon fibre-reinforced laminates with these polymer matrices are manufactured using Out-of-Autoclave (OoA) Vacuum Bag Only (VBO) processing and the spring-in angle is measured. Upon heating, cyanate ester resins experience expansion followed by shrinkage, which brings the overall shrinkage close to zero. Their coefficient of thermal expansion is found to be lower in comparison to the epoxy material, showing the lowest amount of spring-in. Finite Element simulation using COMPRO CCA is performed and the results are compared to the measurements performed on L-shape laminates. The methodology described herein shows phenomenological insight on the cyanate ester materials and the possibility to predict the effect of residual stresses during processing of composite parts, demonstrating high dimensional stability of cyanate esters.

Effect of compressive residual stress and press fitting on residual life assessment of deep-rolled EA4T steel railway axles

Deep rolling surface strengthening is an effective way to introduce compressive residual stress (CRS) along the railway axle, which can improve the fatigue resistance of the material. The CRS field was rebuilt adopting the proportional-integral (PI) iteration method and the unit pressure method (UPM) to study the fatigue cracking behavior of deep-rolled EA4T railway axles. The remaining life prediction model and the stress intensity factor (SIF) solution method were then validated using simulations and testing with small-sized specimens. The remaining life of the EA4T railway axle was then calculated by applying a realistic vertical load spectrum. The results showed that CRS prevented crack propagation, enhanced the critical propagation size of railway axle cracks, and prolonged the remaining life of the axle. Additionally, the remaining life of the axle may not support the following maintenance period if a crack with an extendable size emerges at the unloading groove of the railway axle. This work provides a theoretical basis for the optimization of the non-destructive testing (NDT) interval of deep-rolled EA4T railway axles.

Residual stress associated with crystalline phase transformation of 3–6 mol% yttria-stabilized zirconia ceramics induced by mechanical surface treatments

Monolithic dental prostheses made of 3–6 mol% yttria-stabilized zirconia (3–6YSZ) have gained popularity owing to their improved material properties and semi-automated fabrication processes. In this study, we aimed to evaluate the influence of mechanical surface treatments, such as polishing, grinding, and sandblasting, on the residual stress of 3–6YSZ used for monolithic prostheses in association with crystalline phase transformation. Plate specimens were prepared from five dental zirconia blocks: Aadva Zirconia ST (3YSZ), Aadva Zirconia NT (6YSZ), Katana HT (4YSZ), Katana STML (5YSZ), and Katana UTML (6YSZ). The specimens were either polished using 1, 3, or 9 μm diamond suspensions, ground using 15, 35, or 55 μm diamond discs, or sandblasted at 0.2, 0.3, or 0.4 MPa. The residual stress, crystalline phase, and hardness were analyzed using the cosα method, X-ray diffraction (XRD), and Vickers hardness test, respectively. Additionally, we analyzed the residual stress on the surfaces of monolithic zirconia crowns (MZCs) made of 4YSZ, 5YSZ, and 6YSZ, which were processed using clinically relevant procedures, including manual grinding, followed by polishing using a dental electric motor on the external surface, and sandblasting on the internal surface. Residual stress analysis demonstrated that grinding and sandblasting, particularly the latter, resulted in the generation of compressive residual stress on the surfaces of the plate specimens. XRD revealed that the ground and sandblasted specimens contained a larger amount of the rhombohedral phase than that of the polished specimens, which may be a cause of the residual stress. Sandblasting significantly increased the Vickers hardness compared to polishing, which may possibly be due to the generation of compressive residual stress. In the case of MZCs, compressive residual stress was detected not only on the sandblasted surface, but also on the polished surface. The difference in the residual stress between the plate and crown specimens may be related to the force applied during the automated and manual grinding and polishing procedures. Further studies are required to elucidate the effects of the compressive residual stress on the clinical performance of MZCs.

Introduction study on the influence of residual stress on contact stiffness of joint surface

The effects of residual stress on material properties can be divided into two main categories: its influence on material strength, such as fatigue, and its influence on harmful deformation, such as dimension deviation during or after processing. To investigate the effects of residual stress on the mechanical properties of material components, we select a simple structure that underwent loading and unloading cycles. In our finite element numerical simulation, we establish both a macroscopic solid model and an asperity model. Three different models are chosen, and load-displacement curves are obtained. The effects of residual stress on the stiffness of the contact surface are analyzed. Our results show that residual stress has a significant impact on the stiffness of the joint surface, from macroscopic to microscopic perspectives. Specifically, stiffness increases with residual stress when it is tensile stress.