Local Residual Stress Distribution Research Articles

Microstructure and residual stress gradient evolution mechanism of electronic copper strip for lead frame

The miniaturization of integrated circuits has led to a shift in lead frame fabrication methods from physical stamping to chemical etching. However, this process is highly sensitive to residual stress. We investigated the gradient distribution of residual stress, microstructure, and macroscopic texture in electronic copper foils using a layer-by-layer peeling method, and proposed a novel strategy for evaluating residual stress levels. Our findings reveal that the rolling-induced residual stress exhibits a gradient distribution along the thickness direction. Specifically, from the surface to the central layer, the stress transitions gradually from tensile to compressive, with the stress type primarily influenced by metal flow during rolling. Additionally, we observed gradient variations in the S and Cube texture. Tensile stress favors the formation of Cube-texture, while compressive stress promotes S-texture development. Notably, Cube-texture can lead to strain localization during rolling, directly impacting the local residual stress levels and distribution. Furthermore, quantitative analysis of dislocation density using peak profile methods revealed a consistent trend between {111} plane dislocation density and lateral residual stress. Further investigation highlighted that dislocations and precipitates associated with {111} planes in face-centered cubic metals significantly influence residual stress, with their combined effects determining the overall stress magnitude in relation to texture, dislocations, and precipitates.

Prediction strategy for the forming and stuffing of non-circular tube

The manufacturing of exhaust filter systems for cars typically comprises the forming of a tube and the later stuffing of the formed product with a ceramic monolith and an elastomer mat for filtration. It is shown, that for oval tubes the stuffing process leads to inhomogeneous deformation of the final product wherefore it must be considered when designing the tools for the forming step. The high number of iterations for the tool design can hence be reduced. Additionally, under certain conditions, the necessity of simulating the forming process is shown to no longer be given. The reason for this is that during the stuffing step, no plastic deformation is introduced in the tubes. Consequently, the forming history, including local strain and residual stress distributions, do not need to be explicitly considered. A simplified methodology is presented based on these findings, which can find the required cross-section geometry of the tube entering the stuffing process. The goal of the previous forming process therefore is to produce exactly that geometry, which can be done using conventional forming process planning approaches.

Residual stress effects on fatigue life prediction using hardness measurements for butt-welded joints made of high strength steels

The fatigue resistance of welded connections made of high strength steel (HSS) is one of the most important topics for the application of HSS in the construction sector. One of the most challenging issues is how to predict the fatigue life of welded structures with complex geometry based on the test results from relatively simple coupon specimens. However, there are generally pre-existing residual stresses in the welded coupon specimens during fatigue tests, and these residual stresses vary greatly in welded structures with complex geometry. This increases the difficulty in predicting the fatigue behaviour of welded structures based on results at coupon scale. Hence, it is important to establish a relationship between the residual stress independent material characteristics and fatigue life. The fatigue behaviour of complex welded structures can be predicted by this residual stress independent material characteristics calibrated at the coupon level and simulated local residual stress distribution. In this paper, the residual stress-free characteristics, hardness, is employed to predict the fatigue life of butt-welded joints. Besides, the residual stress of V-shaped butt welds on a plate made of high strength steels are analysed by modelling of the welding process based on subsequent thermal analysis and mechanical stress analysis by implementing kill/birth strategies. The results show that it contributes to a better prediction compared with experimental results after considering the residual stress effects.

Cooling rate calibration and mapping of ultra-short pulsed laser modifications in fused silica by Raman and Brillouin spectroscopy

This paper focuses on the preparation of a new extended set of calibrations of cooling rate (fictive temperature) in fused silica determined by inelastic light scattering and its subsequent use to characterize the local cooling rate distribution in ultra-short pulsed (USP) laser modification. In order to determine the thermal history (e.g. cooling rate and fictive temperature) of fused silica, high-resolution inelastic light-scattering experiments (Raman and Brillouin spectroscopy) were investigated. Calibrations were performed and compared to the existing literature to quantify structural changes due to a change of fictive temperature. Compared to existing calibrations, this paper provides an extension to lower and higher cooling rates. Using this new set of calibrations, we characterized a USP laser modification in fused silica and calculated the local fictive temperature distribution. An equation relating the fictive temperature (Tf ) to cooling rates is given. A maximum cooling rate of 3000 K min−1 in the glass transition region around 1200 °C was deduced from the Raman analysis. The Brillouin observations are sensitive to both the thermal history and the residual stress. By comparing the Raman and Brillouin observations, we extracted the local residual stress distribution with high spatial resolution. For the first time, combined Raman and Brillouin inelastic light scattering experiments show the local distribution of cooling rates and residual stresses (detailed behavior of the glass structure) in the interior and the surrounding of an USP laser modified zone.

Local deformation and macro distortion of TC4 titanium alloy during laser shock processing

Experimental investigation has been carried out to understand the local deformation, macro distortion, and residual stress distribution of TC4 titanium alloy thin plate with different thickness during laser peening processing. The results show that the geometry distortions generate different profile directions depending on the laser shock processing condition. The deformation coefficient λ based on laser power density and sheet thickness is used to predict the macro deformation mode. When λ < 0.212, no macro distortion is produced; when 0.212 < λ < 0.58, volume is transferred along the top surface, the geometric distortion direction is away the laser beam, compressive residual stress is induced on the surface, and convex deformation is produced; when 0.65 < λ, volume is transferred along the bottom surface, the macro distortion direction is toward the laser beam, tensile residual stress is induced on the surface, and concave deformation is produced; the threshold of concave and convex deformation is about 0.62. The deformation coefficient λ and the threshold of concave and convex deformation can be adopted to predict and control the geometry distortion of TC4 titanium alloy thin plate during laser shock processing.

A nondestructive raman spectra stress 2D analysis for the pressure sensor sensitive silicon membrane

The residual stresses introduced by the bonding process has become a key effect for the MEMS product yield improvements. Many in-situ stress measurements have to destruct the devices. Raman spectroscopy is a nondestructive inelastic scattering measuring. Interpreting the silicon Raman frequency shifting can describe the stress location and intensity quantitatively in the lattice. The confocal microscopic observation can realize micrometer scale resolution. However, the limited visual field cannot provide the device stress distribution overview. In the meantime, the microscope loading platform displacement (only 100 μm) will introduce severe random errors (4 ± 1 μm) in the overlapping movements. Since the local stress intensity could be converted into a RGB gray pixel. Through the image mosaic algorithms, the measured local residual stress distribution maps (750 μm × 160 μm) could be stitched to an enlarged stress distribution map (750 μm × 340 μm). This methodology could not only expand the stress inspection overview(60 ± 2%), but also examine and eliminate the displacement random errors. The analysis results showed that the residual stresses were about 70 ± 5% of the simulation value. The uniform difference between the measured and simulated values indicated a trustable stress analysis.

Effects of Interface Bonding on the Residual Stresses in Cold-Sprayed Al-6061: A Numerical Investigation

A contact model that accounts for interfacial cohesion and thermal conduction is developed to investigate the influence of bonding on the final residual stresses build-up in cold spray. The residual stress evolution in the cold-sprayed Al-6061 coating on an Al-6061 substrate is investigated via three-dimensional single-particle and multi-particle impact simulations. It is shown that the interface bonding mainly affects the local residual stress distribution near the interfaces. The residual stresses are largely due to the kinetic peening and bonding effects. The thermal cooling has negligible influence. In general, this work finds that peening introduces compressive stress, while bonding causes relaxation. The balance between the peening and the bonding effects, which depends strongly on the local bonding environment, determines the final residual stress in the system. This work suggests that the interface bonding should be considered as one of the essential factors in numerical modeling of the residual stresses evolution in cold spray.

Critical Conditions of Cold Cracking in High Strength Steel Weld Based on the Local Stress Distribution and Hydrogen Accumulation

In this study, the occurrence of cold cracking in high strength steel welds were investigated in terms of residual stress and hydrogen diffusion behavior. The y-groove weld cracking test of TS780MPa grade steel plate was conducted with intentionally introducing hydrogen into the shielding gas during the gas-metal arc welding (GMAW). Since local stress is one of the most important factors for the cold cracking, residual stress distribution in the weld joint was measured by the neutron diffraction using TAKUMI in J-PARC. The root region, which is usually the crack initiation site in the y-groove cold cracking test, was under a multi-axial stress state and showed highest tensile residual stress in the transverse direction. It was considered that hydrogen diffusion and accumulation could be enhanced in the high stressed root region, resulting in cold cracking. Therefore, hydrogen diffusion behavior and stress distribution in the y-groove weld joint was investigated by a coupled thermo elastic plastic and hydrogen diffusion analyses. Hydrogen accumulation occurred in the root region where showed highest hydrostatic stress. The point where showed the hydrogen accumulation was well corresponded to the crack initiation site. It was indicated that local hydrogen concentration after welding was another important key factor for the cold cracking. From these investigations, it was essential to take the combination of local hydrogen concentration and residual stress distribution near the root region into account for the highly precise estimation of cold cracking.

Ultrasonic nondestructive testing and regulation technology of residual stress

Residual stress regulation technology is a procedure to reduce residual stress by means of high-energy ultrasonic after stress testing. Based on acoustoelasticity theory, the relationship between ultrasonic propagation and stress in aluminum alloy is researched. With the principle of exciting ultrasonic critically refracted longitudinal wave obtained, the ultrasonic stress testing system is established. For in situ regulation of residual stress, the interactive relationship between high energy ultrasonic and residual stress field is studied. We reduced the residual stress and improved stress state of components through effective control of high-energy beam and incentive mode. Thus in situ relief and control of local residual stress distribution in mechanical components in service are realized. The technology can improve the whole strength, anti-fatigue and corrosion resistance of mechanical components and enhance their service life, safety and reliability, and now is widely used in the stress testing and relief of aluminum alloy welding components.

Anisotropic distribution of the micro residual stresses in lath martensite revealed by FIB ring-core milling technique

Lath martensite structures in medium-carbon steels incorporate a significant amount of residual stresses that are mostly induced by the martensitic transformation process. Although former studies could identify these stresses using diffraction techniques, it was not possible to correlate the micro-scale distribution of the stress fields with respect to the morphological and the crystallographic parameters of the martensitic structure. In this study, we employ the micro-scale focused ion beam (FIB) ring-core milling technique for the measurement of local residual strain and stress distributions in fully martensitic microstructures. The aim is to study the residual stresses occurring within individual lath martensite crystals, and within areas of lath martensite which incorporate a parent austenite grain boundary. The relaxation strains obtained by the micrometer-sized ring-core milling, which correspond to the residual stresses prior to milling, are shown to exhibit an anisotropic distribution for each martensite variant. High extension relaxation strains (i.e. compressive stresses) prevail in the direction of the transformation-induced crystal shape deformation direction. Contraction strains (i.e. tensile residual stresses) are measured normal to the extension strains. In an area containing a prior austenite grain boundary, the residual stresses appeared – altogether – lower than in single crystal martensite laths. The significant residual tensile stresses identified in the martensite structures may support the formation of martensite micro-cracks, either in the as-quenched state or during deformation.

Investigation of correlation between material properties, process parameters and residual stresses in roller levelling

When processing metal strips, roller levelling is the first process the sheet metal undergoes after decoiling. The process of roller levelling mainly aims on the flatness of the material. Additionally, the resulting residual stress distribution after levelling is of great importance since a strip might be flat but have a disadvantageous residual stress distribution for further processing. In this paper the correlations between the incoming strip condition, the roll intermeshes and the residual stresses are evaluated in order to achieve both, a constant flatness as well as a distinct residual stress distribution after levelling. The investigations are focusing on a seven-roll levelling machine with three individual load triangles. The first load triangle ensures a constant plastification of the incoming strip, the load triangle in the middle aims on the residual stress distribution and the last load triangle sets the flatness of the sheet material. Within a numerical model of this setup, a variation of the incoming material properties by means of yield stress and kinematic hardening is done. From the numerical model both global values such as the forces acting on the rolls as well as the local residual stress distribution are obtained. Accompanying experiments are conducted on a laboratory-scale roller levelling machine. Furthermore, the residual stresses across the sheet thickness after levelling are measured using diffraction analysis. The results indicate a distinct relationship between process parameters and the target values of flatness and residual stress distribution. Finally, a strategy for an online process control acting on both flatness and residual stress distribution is introduced based on these results.

Using Barkhausen Noise and Digital Image Correlation to Investigate the Influence of Local Residual Stresses on Fatigue-Crack Propagation

Abstract Fatigue-crack propagation is, by far, the most crucial failure mechanism of technical systems. The key to understanding microscopic processes that lead to failure lies in the knowledge of local stresses, the driving force of cracks. We present the mapping of stress and strain fields induced by a single overload on a fatigue crack and their influence on transient crack-growth retardation. In contrast to former work, in which synchrotron x-ray diffraction (XRD) was used, this investigation was performed by using a calibrated magnetic Barkhausen noise microscope in combination with digital image correlation based on in situ scanning electron microscope imaging. The underlying mechanisms, residual stress effects in front of the crack tip and plasticity-induced crack closure caused by the plastic wake, have been studied. Specifically, a crack in S960Q steel has been followed through the overload (OL) region while examining measurements at distinctive overload points: before OL, after OL, at maximum retardation, and at recovery. We observe a strong correlation of the local fatigue-crack-growth rate with the local residual stress distribution obtained from magnetic Barkhausen noise, which remains nearly unchanged after the crack has passed by. Digital image correlation results reveal the influence of these residual stresses on crack-tip opening reactions and strain fields under external loads. Although strain fields show a strong decrease because of the OL event, differences in crack opening stresses remain rather low at first, but prevail in the second part of the OL region. The applicability of new measurement methods and their results regarding the dominating retardation mechanism are discussed. These indicate that the residual stress effect on the strain fields can be associated to be more significant than plasticity-induced crack closure at maximum retardation with a change of mechanisms on reacceleration.

Effect of residual stress on magnetic properties of motor cores

The magnetic properties of electrical steel sheet deteriorates due to residual stress, which occurs during the manufacturing process. Therefore, it is important to know the relationship between the magnetic property and the residual stress in order to utilize electrical steel sheets effectively. This paper presents the effect of residual stress on the magnetic properties of motor cores in a rotating machine. First, the local residual stress distribution of the motor core is measured using an X-ray stress measurement system. Next, the magnetic properties of the motor cores for the different residual stress distributions are measured using a single sheet tester. Based on these results, the maximum permeability and magnetic power loss differed depending on the sample, each of which had a different residual stress. In addition, we attempt to measure the inductance of the motor core in order to easily evaluate the magnetic property. The difference in the inductance of each sample was obtained based on the excitation voltage and frequency measured using an LCR meter. It is very useful to evaluate the inductance in order to easily determinine the difference in the residual stress.

Residual Stress Analysis on Thick Film Systems by the Incremental Hole-Drilling Method – Simulation and Experimental Results

The residual stress state in thick film systems, as for example thermal spray coatings, is crucial for many of the component’s properties and for the evaluation of the integrity of the coating under thermal and/or mechanical loading. Therefore it is necessary to be able to determine the local residual stress distribution in the coating, at the interface and in the substrate. The incremental hole-drilling method is a widely used method for measuring residual stress depth profiles, which was already applied for thermally sprayed coatings. But so far no reliable hole-drilling evaluation method exists for layered materials having a stress gradient in depth. The objective was to investigate, how far existing evaluation methods of the incremental hole-drilling method that are only valid for residual stress analysis of homogenous material states can be applied to thick film systems with coating thicknesses between 50 μm and 1000 μm and to point out the application limits for these already existing methods. A systematic Finite Element (FE) study was carried out for coating systems with an axisymmetric residual stress state σ1 = σ2. It is shown that conventional evaluation methods developed for homogeneous, non-layered material states can be successfully applied for a stress evaluation in the substrate and the coating for small and for sufficiently large coating thicknesses, respectively, regardless of the type of evaluation algorithm used i.e. the differential or the integral method. The same accounts for material combinations that have a Young’s modulus ratio close to one, between 0.8 and 1.2. The studies indicated that outside the given ranges case specific calibration must be applied to calculate reliable results. Further, calibration data were determined case specifically for a selected model coating system. The accuracy of a residual stress determination using these case specific calibration data was examined and the sensitivity of the evaluation with respect to an accurate knowledge of the boundary conditions of the coating system i.e. the coating thickness and the Young modulus was studied systematically. Finally, the calibration data were applied on a thermally sprayed aluminium coating on a steel substrate analysis and the results for using the incremental hole drilling method were compared to results from X-ray stress analysis.

Evaluation of local residual stress distribution of stator core in a rotating machine

It is well known that magnetic properties deteriorate in constructed cores due to conditions of stress such as riveting and welding during the manufacturing process, or punching and shearing during the cutting of the electrical steel sheets. Therefore, it is important to know the relationship between the stress and magnetic properties of electrical steel in order to design electrical machinery. In this paper, the local residual stress distribution on the cross section of the stator core in a rotating machine is measured with an X-ray stress measurement device. As a result, the difference in the residual stress distribution of each component is obtained in the teeth and core back of the stator core. In addition, we estimated the deterioration of the magnetic properties in the teeth region. We demonstrate that the magnetic properties of the electrical steel sheet deteriorated due to the residual stress. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(3): 1–8, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21271

Local Residual Stress Distribution at the Tooth Root Surface of a Broached Steel Component

Broaching is an important technique for creating tooth structures in mechanical components. In the present work, the effects of the broaching process on the material state in the near surface region at the root of the tooth was analyzed. The studies were carried out on broached plates made from case hardening steel SAE 5120. The cutting speed and machining condition (cooling lubricant, dry machining) were varied. During broaching with a TiAlN coated tool the cutting forces were monitored. Subsequently, the local residual stresses at the root of the tooth were determined using X-ray diffraction. Further, surface roughness and micro hardness measurements as well as microstructure analysis complement the results. The results indicate that cutting forces have a high influence on the development of the residual stress state at the machined surface whereas no significant effect on changes in surface hardness and microstructure could be observed. Dry cutting with relatively high cutting speeds (≥ 30m/min) result in low cutting forces and hence in high tensile residual stresses in broaching direction.

Local Residual Stress Distributions Induced by Repeated Austenite-Martensite Transformation via Laser Surface Hardening of Steel AISI 4140

The effects of laser surface hardening of steel samples on the microstructure and residual stresses were determined for single as well as multiple laser pulses. Samples made of steel grade AISI 4140 were hardened by means of a high-power diode laser (HPDL) system using either single or multiple laser pulses resulting in single as well as repeated austenite-martensite transformations. The hardening was carried out in a specially designed process chamber allowing laser surface treatment in inert atmosphere in order to avoid oxide scale formation. The residual stress distributions in lateral and in depth direction were analysed by means of X-ray diffraction for samples hardened by up to 27 laser pulses. Residual stress analyses were carried out by means of the sin²y- method. The results indicate the extension of the hardened zone in lateral and in depth direction with an increase in the number of applied laser pulses. This evolution is connected with significant changes in the local residual stress distributions.

回転機固定子鉄心における局所的残留応力分布の評価

回転機固定子鉄心における局所的残留応力分布の評価

The influence of welding process parameters on residual stresses by means of coupled thermo-mechanical simulation

To achieve an accurate lifetime assessment based on welded joints, the value of the effective notch stress by means of local approaches has to be determined. Moreover, detailed knowledge of the local material properties at the complex thermo-mechanical welding process must be available. Hence, a special challenge in the knowledge of local conditions must be performed. The impact of the welding process, e.g., by change of the heat-affected-zone, conducts the local residual stress distribution as well as the restraining boundary condition. The significance of the specimen clamping condition was shown by strain gauge measurements. The need of a local thermo-mechanical coupled simulation model is given especially in the case of strain-based interacting weld seams. The size and shape of the heat-affected-zone was verified by metallographic investigations. Finally, a fatigue life calculation based on the structural stress approach was done.

3D-modelling of the local plastic deformation and residual stresses of PM diamond–metal matrix composites

Abstract A computational strategy is developed to model the effects and interactions of non-metallic inclusions with metal bases. As an industrial case study, the present paper characterises the local elasto-plastic deformation and residual stress distribution induced through the sintering process of the diamond–metal matrix hot-pressed tool, which is a special metal matrix composite (MMC) reinforced by diamond particles, with average diameters ranging from 10 μm to 0.5 mm, to increase the capability for cutting hard materials such as stones. The residual stress fields in the nearby region of a diamond particle via plastic deformation due to sintering process are examined to study the effects of the sintering temperatures and the compression pressure on the upper surface of the metal matrix during the sintering process. In the simulations, the metal matrix is modelled as an elastic–plastic material with combined isotropic–kinematic hardening. The diamond particle is modelled as isotropic and linear elastic. For simplicity, two geometries of the diamond particles are considered to study their effects on local plastic deformation and residual stress distributions. All simulations were performed using the ABAQUS finite element code. For the diamond particles embedded inside the metal matrix, 8-node axisymmetric quadrilateral, reduced integration ABAQUS solid element type CAX8 is used. For the diamond particles on the surface of the matrix, 4-node reduced integration ABAQUS solid element type C3D4 is used in the simulations. Simulating the sintering process and the cutting forces in service, it is demonstrated that the diamond retention capacity induced by the metal matrix (important for extending the life of a diamond tool) is mainly dependent on the sintering process. Optimum design of the diamond cutting tools can be achieved by selecting the appropriate sintering temperatures, the stress–strain behaviour of the metal matrix, the diamond particle shape and the compression pressure on the upper surface of the metal matrix during the sintering process.