Changes In Residual Stress Research Articles

Numerical Study on the Influence of Polyimide Thickness and Curing Temperature on Wafer Bow in Wafer Level Packaging

In wafer level packaging, polyimide and electroplated copper are dielectric and conducting materials respectively in the so-called redistribution layers. During the wafer fabrication process large amount of stress is generated in those layers due to curing shrinkage of the polyimide and the coefficient of thermal expansion mismatch of both materials to silicon which can lead to severe wafer bow after a high temperature curing. In different applications polyimide can be used either only as passivation layer over electroplated copper, or polyimide is applied before the redistribution layer and then a second polyimide layer is applied as passivation. In the current study the effect of different polyimide integrations is investigated. In-situ wafer bow measurements and finite element method studies were conducted with samples, with and without polyimide below redistribution layer, exposed to different curing temperatures to understand the change in wafer bow and copper residual stress. It is observed that wafers with polyimide before redistribution layer show higher stress relaxation in copper with decreasing curing temperature, resulting therefore in a lower wafer bow. A good agreement is achieved between the experimentally measured and the simulated wafer bow.

Improving Wear Resistance and Corrosive Resistance of Cemented Carbide for Mud Pulser Rotor by Deep Cryogenic Treatment.

Cemented carbide used in the rotor of a mud pulser is subjected to the scouring action of solid particles and corrosive mud media for a long time, which causes abrasive wear and electrochemical corrosion. To improve the wear and corrosive resistance of cemented carbide, samples with different cobalt content (WC-5Co, WC-8Co, and WC-10Co) receive deep cryogenic treatment (DCT) at -196 °C for 2.5 h. An optical metalloscope (OM) and X-ray diffractometer (XRD) are used to observe the phase changes of cemented carbides, and the XRD is also used to observe the change in residual stress on the cemented carbide's surface. A scanning electron microscope (SEM) is used to characterize the wear and electrochemical corrosion surface microstructure of cemented carbides (untreated and DCT). The results show that the DCT promotes the precipitation of the η phase, and the diffraction peak of ε-Co tends to intensify. Compared with the untreated, the wear rates of WC-5Co, WC-8Co, and WC-10Co can be reduced by 14.71%, 37.25%, and 41.01% by DCT, respectively. The wear form of the cemented carbides is mainly the extrusion deformation of Co and WC shedding. The precipitation of the η phase and the increase in WC residual compressive stress by DCT are the main reasons for the improvement of wear resistance. The electrochemical corrosion characteristic is the dissolution of the Co phase. DCT causes the corrosion potential of cemented carbide to shift forward and the corrosion current density to decrease. The enhancement of the corrosion resistance of cemented carbide caused by DCT is due to the Co phase transition, η phase precipitation, and the increase in the compressive stress of cemented carbide.

Laser shock-induced gradient twinning microstructure in AZ31B alloy

Magnesium alloys are highly promising in biodegradable materials for medical applications. However, their applications are limited by weaknesses in mechanical strength and corrosion resistance. In recent years, advancements in a novel laser method, Laser Shock Peening (LSP), have been explored. Researchers suggest that LSP can induce surface compressive stresses and induce changes in residual stress and grain size gradients, thereby enhancing the material's fatigue resistance, corrosion resistance, and resistance to stress corrosion cracking. However, there is ongoing debate about whether LSP treatment can, in effect, create a gradient microstructure. In this study, we focused on the AZ31B alloy, notable for its dense hexagonal close-packed (HCP) crystal structure. This material is particularly interesting because, due to its low stacking fault energy, it is more prone to twinning deformation than to dislocation slip when it undergoes plastic deformation. To analyze the changes wrought by LSP, we employed optical microscopy (OM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) for examining the microstructures both before and after LSP treatment. Our findings revealed that LSP treatment refined the grain size, leading to a gradient distribution. In addition, we observed a direct correlation between the volume fraction of twinning and grain size. In contrast, the geometrically necessary dislocation (GND) density exhibited an inverse relationship. By measuring hardness and residual stress in the region affected by LSP, we determined that LSP could introduce a layer of plastic deformation up to a depth of 800–1000 μm. We also established a link between the gradient microstructure and hardness and provided a thorough discussion on the types of twinning and the mechanisms behind the induction of gradient microstructure on the surface.

Multi-Objective Optimization of Low-Alloy Hot-Rolled Strip Cooling Process Based on Gray Correlation Analysis

The residual stress in low-alloy hot-rolled strips seriously affects the use and processing of products. Reducing residual stress is important for improving the product quality of hot-rolled strips. In this paper, the changes in grain size and residual stress of hot-rolled strips under different cooling processes were investigated via thermal simulation experiments and electron backscatter diffraction. It was found that the optimum cooling process solution for single-objective optimization of grain size was a final rolling temperature of 875 °C, a laminar cooling speed of 50 °C/s, and a coiling temperature of 550 °C. When single-objective optimization of residual stress was carried out, the optimal cooling process scheme was 900 °C for final rolling temperature, 20 °C/s for laminar cooling speed, and 625 °C for coiling temperature. The significance of the effect of cooling processes on grain size and residual stress was analyzed based on the extreme deviation of the effect of each cooling process on grain size and residual stress in orthogonal experiments. The results show that the coiling temperature was the most influential factor on grain size and residual stress among the cooling process parameters. The difference was that grain size increased with increasing coiling temperature, and residual stress decreased with increasing coiling temperature. Using both grain size and residual stress as evaluation indicators, a multi-objective optimization of the cooling process for hot-rolled strips was carried out via the gray correlation analysis method. The optimized solution was 875 °C final rolling temperature, 30 °C/s laminar cooling speed, and 625 °C coiling temperature. At this time, the grain size was 4.8 μm, and the KAM (Kernel Average Misorientation) was 0.40°. The grain size under the actual production process scheme was 4.4 μm with a KAM of 0.78°. Compared to the actual production process solution, the multi-objective optimization solution showed little change in grain size, with only a 9% increase and a 49% reduction in KAM. The optimization scheme in this paper could significantly reduce the level of residual stresses while ensuring the fine grain size of hot-rolled strips, thus improving the overall quality of hot-rolled strips.

Effect of Different Microstructures on Surface Residual Stress of Induction-Hardened Bearing Steel

JIS SUJ2 steel is most widely used in bearing steel. The advantages are good hardenability, excellent fatigue, wear resistance and comprehensive mechanical properties. The wear resistance and fatigue resistance of this steel are attracting more attention, and the residual stress state and its distribution on the surface of the heat affected zone are critical factors affecting the fatigue life and wear resistance of the parts. In this study, SUJ2 is used as a material by which to study the surface residual stress and retained austenite distribution of induction-hardened steel. Quenching and tempering treatments were used to obtain different microstructures and an induction method was used to re-quench the case region. After the heat treatment, the residual stress and retained austenite volume on the surface were analyzed by X-ray diffraction and analyses of the microstructure and the hardness were also conducted. The results show that the microstructure after heat treatment contains unsolved carbides, tempered martensite and retained austenite. In the induction-hardened area, the residual stress is all compressive, and the values are more than −750 MPa. In conclusion, the microstructures of the specimens before induction hardening have a significant impact on the effective case depth for the same output power condition and the surface residual stress changes from a tensile to a compressive state. In the induction-hardened area, the maximum of the residual compressive stress was increased as the austenitized temperature of quenching increased.

Structural, infrared optical and mechanical properties of the magnesium fluoride films

In this research, the magnesium fluoride (MgF2) films are deposited by electron beam evaporation at different substrate temperatures. The structural, infrared optical properties, mechanical properties and application of the films are investigated. The films prepared at higher temperatures have better crystallinity. As indicated by SEM and AFM, large grains are formed on the film surface at higher temperatures. Preparing thin films at higher temperatures should effectively improve the microstructure with packing density, resulting in higher refractive index and lower moisture absorption. The infrared optical constants of the films are characterized by Gaussian oscillators, and the relationship between the optical absorption and the substrate temperature is revealed. The film deposited at 300 °C exhibits excellent hardness, which is above 9 GPa. The change of residual stress is mainly determined by thermal stress. By depositing MgF2 films on sapphire substrates, the transmittance of the sapphire is greatly improved in the range of 3 μm–5 μm. Besides, the MgF2 films are found to be excellent antireflective coatings for infrared optical elements.

Towards developing a control of grinding processes using a combination of grinding power evaluation and Barkhausen noise analysis

After grinding of hardened workpieces, especially in case of safety-relevant components, usually non-destructive testing is carried out to detect thermo-mechanical damages in the surface layer. In-process detection methods allow a fast reaction to negative changes before producing a large amount of rejects and open the possibility to save additional time for post-process inspection. However, these are not industrially used yet, since boundary conditions and application limits are not defined so far. This study shows the potential of a grinding process control based on a soft sensor combining a thermal limit in a Pc′′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${P}_{c}^{{\\prime}{\\prime}}$$\\end{document}− Δt-diagram and magnetic Barkhausen noise analysis applied in-situ during grinding (BN). The specific grinding power Pc′′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${P}_{c}^{{\\prime}{\\prime}}$$\\end{document} in dependence of the contact time Δt allows to identify/avoid grinding burn starting from light tempering zones. Furthermore, the BN is well suited for the detection of detrimental residual stress changes (tensile) occurring even before tempering zones are generated. The developed process control based on this combination optimizes the process parameters to prevent negative thermo-mechanical surface changes while keeping the productivity of the process as high as possible. The applicability is demonstrated for external cylindrical and non-circular grinding processes. Due to the radius varying over the workpiece circumference, the latter ones require special demands on signal evaluation, resolution and control speed.

Industrial application of diamond-electrochemical honing method

The method of diamond-electrochemical honing (DEH) is a finishing method that provides the required characteristics of surface roughness, the distribution of residual surface stress diagrams, which ultimately ensures the formation of a high-strength electroplated coating. This article presents studies of changes in surface roughness, residual stresses and other parameters depending on the selected DEH modes for parts made of steels 30KhGSA, 30KhN2MFA, 35KhN2MFASH, 50A. The article presents the design of the instrument-khon; with the solution of the issue of the geometric characteristics of the cathode part, the insulating coating and the material of the hone tool guides. The regime support of the DEH was formed on the basis of studies, the results of which are given in the article. The selected kinematic-geometric indicators of the hone-tool — workpiece system make it possible to form the drives of the DEH equipment. The optimal composition of the DEH electrolyte was chosen with the creation of an electrolyte storage and supply system. The article contains the results of studies demonstrating the effect of DEH on the reliability and durability of parts subject to the use of this method. Data on the technical and economic efficiency of the created industrial site of the DEH are presented.

Changes in Residual Stresses in the Vicinity of a Continuity Defect in an Elastoviscoplastic Material under Repeated Loading

The results of calculations of the stress-strain states of an elastoplastic material containing a single cylindrical continuity defect and loaded with external pressure are presented. The hydrostatic pressure on the surface distant from the defect initially increases, remains constant for some time and then gradually decreases to zero. The process of comprehensive compression leaves, after unloading, a formed level and distribution of residual stresses in the vicinity of the continuity defect. The change in such stresses is calculated upon repeated loading and unloading. Intensity and nature of repeated loads are considered identical to the original ones. Calculations are carried out within the framework of the stated one-dimensional problem of the theory of large deformations. The material is assumed to be incompressible. The development of areas of viscoplastic flow in the active part of the process and their attenuation during unloading are taken into account. Changes in the geometric dimensions of the evolving defect are assessed.

Combining turning with slide burnishing to improve surface integrity and stress corrosion resistance

The surface characteristics play a pivotal role in stress corrosion cracking (SCC) resistance and fatigue life. Strengthening and modifying the material surface properties during manufacturing is a promising approach to improving the component service performance. Therefore, this study proposes a new surface finishing and strengthening mode that combines turning with slide burnishing (TSB) with a common turning tool. The core idea is that the cutting edge of the tool removes the material surface layer as a chip while the tool corner with a large radius performs a slide burnishing process on the manufactured surface. The machining-induced surface integrity in terms of residual stress, surface roughness, micro-hardness and microstructure changes was examined, and the SCC susceptibility was tested in a strong corrosion environment. The results showed that the surfaces processed by TSB suffered lower biaxial residual stresses, higher micro-hardness and deeper hardened layer when compared with the traditional turned surfaces. Besides, it was observed the TSB processed surfaces were less susceptible to SCC initiation which could be attributed to the lower residual stress introduced by TSB. Additionally, the multi-pass TSB treated surfaces showed significant low SCC susceptibility. Consequently, this work suggests that the surface integrity and the service performance like SCC resistance can be improved by TSB.

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.

Establishment and experimental verification of a three-dimensional finite element model for residual stress in surface processing of Inconel 718 alloy by laser cladding

The local load and residual stress changes of conventional forged Inconel 718 alloy can be simulated in a two-dimensional (2D) cutting simulation model, but the type and distribution of global residual stress field of the alloy cannot be predicted during laser cladding layer cutting. To address the shortcomings of conventional 2D cutting simulation models for forging Inconel 718 alloy, this paper proposed a 3D closed-loop finite element model, and taking the dry-side milling process of Inconel 718 alloy laser cladding layer as an example, the generation mechanism and distribution of residual stress are predicted during the machining process. Further testing of surface, near-surface, and subsurface residual stresses was conducted to analyze the specific distribution of residual stresses in the workpiece. The results indicated that the uneven distribution of cutting stress and temperature on the workpiece had a significant non-stationary thermal-mechanical effect on the surface of the machined workpiece; the distribution of surface residual stress was uneven, with the significant tensile residual stress at the workpiece boundary. As the depth increases, the influence of mechanical effects dominated, and the compressive residual stress was generated on the subsurface of the workpiece. Residual stress testing was conducted on the surface/near-surface, and the experimental results were consistent with the simulation results of the closed-loop simulation model. In the subsurface, residual stress showed a similar trend of change. This study compensated for the shortcomings of conventional finite element simulation and provided the reference value for the application of three-dimensional finite element simulation in laser cladding materials.

Effect of ultrasonic rolling on crack propagation behavior of Ti6Al4V titanium alloy laser welded joints

This study investigated the effect of ultrasonic rolling on the fatigue resistance of Ti6Al4V titanium alloy laser welded joints, with an emphasis on crack growth rate. Multiple analyses were conducted on samples subjected to different numbers of rolling passes, including analysis of surface roughness, morphology, cross-section structure, hardness, fatigue fracture, and residual stress. Ultrasonic rolling was found to considerably enhance the life cycle of the sample. One, three, and five rolling passes resulted in fatigue life increases of 17.14%, 46.38%, and 66.61%, respectively, when compared with untreated samples. Treated samples exhibited rough and intricate crack propagation paths on fracture surfaces, along with numerous secondary cracks. Fatigue striation width decreased by 48.6%, 62.5%, and 69.4% for samples receiving one, three, and five rolling passes, respectively. These fatigue striations, which were narrower and more densely distributed, indicate that ultrasonic rolling effectively increases fatigue life. The ultrasonic rolling treatment enhanced fatigue performance and reduced the rate of crack propagation due to changes in surface compressive residual stress, microstructure, microhardness, and improved surface quality. Crack retardation primarily occurred in initial stage of crack propagation and stable propagation stages, whereas inhibitory effects weakened during the final fracture stage due to superposition and offset of the higher driving force with compressive residual stress. In summary, the study demonstrates that treatment via ultrasonic rolling is an effective method for improving fatigue life and fracture toughness in Ti6Al4V titanium alloy laser-welded joints.

Effect of machining processes on the quenching and tempering surface layer of ultra-high strength steel

The initial characteristics of the surface layer following the quenching and tempering treatment of ultra-high-strength steel play a significant role in determining the subsequent precision machining. This study focus on investigating the influence of machining processes on the quenching and tempering surface layer. The machining processes affect both the oxidation of the quenching and tempering treatment and the development of a distinct preferred grain orientation. Gradual diminishment of surface abrasions leads to the transformation of the needle-like oxidation pattern into a layered oxidation structure. The preferred orientation of the grains prevents the grains from shear sliding, thereby enhancing the Taylor effect. Formation mechanisms of the microhardness and residual stress of the quenching and tempering surface layer induced by machining processes were also discussed and completely revealed. The microhardness is mainly attributed to the dynamic Hall-Petch effect, while plastic strain, dislocation energy storage, and phase transformation contribute to the residual stress changes.

An analysis of longitudinal residual stresses in EN AW-5083 alloy strips as a function of cold-rolling process parameters

Abstract Various process nonhomogeneities in the cold rolling lead to an uneven distribution of deformation across the strip cross-section, resulting in the induction of residual stresses. This study investigates the longitudinal residual stresses in cold-rolled EN AW-5083 aluminum alloy strips using the finite element method (FEM) to achieve reliable predictions. The impacts of process parameters, including the reduction ratio, coefficient of contact friction, and front and back tensions, were analyzed. Changes in residual stresses, depending on the process parameters, were determined by the distribution of linear and shear strains, as well as the strain hardening conditions at the exit part of the deformation zone. An increase in the reduction ratio from 20 to 50%, as well as an increase in the friction coefficient from 0.1 to 0.2, resulted in decreased stress values. The residual stresses on the strip surface, determined by the experimental deflection method, were consistent with the results obtained by FEM simulation. Under the impact of back and/or front tensions, there is a reduction in longitudinal residual stresses, with the front tension exerting the greatest influence. The research results show that the FEM is a reliable tool for predicting residual stresses in cold-rolled strips.

Investigation of residual stress formation mechanism with water jet strengthening of CoCrFeNiAlx high-entropy alloy

This study investigates the strengthening mechanism of water jet (WJ) on the high-entropy alloy CoCrFeNiAlx (x = 0, 0.6, 1). Finite element simulation analysis was conducted to examine the changes in residual stress, surface roughness, and stress triaxiality of high-entropy alloys under different jet velocities and Al contents. Subsequently, an experimental validation of surface roughness was performed using the Al1 high-entropy alloy. The results reveal that the residual compressive stress and maximum residual compressive stress on the high-entropy alloy's surface increase with the jet velocity, irrespective of the Al content. However, the depth of the maximum residual compressive stress decreases as the Al content increases. At a jet velocity of 280 mm/s, the residual compressive stress on the surface of the Al1 high-entropy alloy surpasses that of the Al0.6 high-entropy alloy. Specifically, the residual compressive stress on the surface of the Al1 high-entropy alloy is approximately 265 MPa, which is significantly higher than the value of 9 MPa for the Al0.6 high-entropy alloy. When the jet velocity reaches 300 mm/s, the surface residual compressive stress of the high-entropy alloys shows a positive correlation with the Al content. The residual compressive stress on the surface of the Al1 high-entropy alloy is about 1.89 times and 1.23 times that of the Al0 and Al0.6 high-entropy alloys, respectively. As the jet velocity continues to increase to 320 mm/s, the maximum residual compressive stress of the high-entropy alloys follows the order: Al0.6 > Al0 > Al1. The maximum residual compressive stress of the Al0.6 high-entropy alloy measures approximately 477 MPa, which is approximately 82 MPa higher than that of the Al0 high-entropy alloy. Subsequently, at a jet velocity of 340 mm/s, the Al0.6 high-entropy alloy exhibits the highest maximum residual compressive stress, reaching a value of 650 MPa.Additionally, a negative correlation between surface roughness and jet velocity is observed. Moreover, an increase in Al content within the high-entropy alloys significantly reduces surface roughness under the same jet velocity impact.

Surface smoothing of additively manufactured Ti-6Al-4V alloy by combination of grit blasting and large-area electron beam irradiation

AbstractAdditively manufactured (AMed) titanium products are typically produced by electron beam melting (EBM), since oxidation of titanium alloy surface can be suppressed in vacuum environment. The surface roughness of AMed titanium products becomes more than 200 µm Rz, and the very rough surface would lead to reduction in fatigue strength. Therefore, a post surface finishing process is required. Abrasive blasting is one of the common surface smoothing processes of AMed metal products. Large surface roughness can be decreased, and compressive residual stress can be introduced to the surface. However, there is a limitation to reduction of surface roughness to several µm Rz. On the other hand, it was recently found that AMed metal surface produced by powder bed fusion with laser beam could be smoothed by large-area electron beam (LEB) irradiation. However, it is difficult to smooth surface with large initial surface roughness, and a tensile residual stress may be generated on the surface. In this study, surface smoothing and change in residual stress of AMed titanium alloy (Ti-6Al-4 V) were proposed by combination of grit blasting and LEB irradiation. Surface roughness of AMed Ti-6Al-4 V alloy significantly decreases from 265 to about 2.0 µm Rz by combination of grit blasting and LEB irradiation. Reduction rate of surface roughness by LEB irradiation linearly increases with decreasing mean width of blasted surface. Influence of the mean width on smoothing effect by LEB irradiation can be explained by thermo-fluid analysis. Moreover, tensile residual stress caused by LEB irradiation can be reduced when LEB is irradiated to blasted surface.

Effects of elevated temperature exposure on the residual stress state and microstructure of PVD Cr coatings on SiC investigated via in situ X-ray diffraction and transmission electron microscopy

Pure Cr coatings are being considered as corrosion-resistant layers for SiC-SiCf composite fuel cladding in light water reactors. The residual stress state and interdiffusion behavior of Cr coatings deposited on SiC substrates using bipolar high-power impulse magnetron sputtering (B-HiPIMS) and direct current impulse magnetron sputtering (DCMS) were studied using in situ X-ray diffraction experiments at 300 °C, 700 °C, and 1200 °C. After elevated temperature exposure, evolution of the coating microstructure and coating/substrate interdiffusion was characterized by transmission electron microscopy. The compressive residual stress of the dense B-HiPIMS coating at room temperature was gradually relieved at 300 °C, while the stress transitioned to a tensile state at 700 °C. Grain growth of the Cr coating and a Cr–SiC interdiffusion layer consisting of newly formed Cr–C and Cr–Si phases were observed in the B-HiPIMS coating after exposure at 700 °C. The phases in the interdiffusion layer were identified to be Cr7C3, Cr3Si, and Cr5Si3Cx experimentally and by thermodynamic predictions. For the DCMS coating, however, changes in residual stress and microstructure at the elevated temperatures were limited by the inherent porosity and inhomogeneous structure of the as-deposited coating. At 1200 °C, both coating types interacted rapidly with the underlying SiC substrate in the early stages of the experiment. The results from this study suggest that the characteristics of the Cr coatings do not significantly change at the reactor operating temperature of 300 °C, while changes in microstructure and stress state are expected in off-normal conditions of 700 °C and 1200 °C. The results from this study suggest the B-HiPIMS coating is best-suited as a protective coating for SiC fuel cladding.

Determination of Machining Parameters for a Specific Adjustment of the Residual Stress Profile by Induction Hardening*

Abstract Within the research work of the Transregional Collaborative Research Center TRR 136, process signatures were determined for processes that generate essentially thermal loading of the component surface layer. These process signatures represent correlations between material modifications (e. g. changes of residual stress, microstructure, hardness profile, etc.) and characteristic values of the material loading. The underlying idea is that the material does not know any processes but only loads caused by processes. In particular, the same loads lead to the same material modifications regardless of the kind of process. A decisive advantage of this concept over conventional approaches is the possibility of calculating the necessary internal material loads backwards on the basis of concrete specifications for the material modifications. If there are additional correlations between internal material loads and process quantities as well as between process quantities and machining parameters, the necessary machining parameters can be determined, too. In this paper, this procedure will be introduced using the example of one-sided induction hardening of cuboidal components made of 42CrMo4. The determination of the process signature by experimental and numerical investigations is described and work for experimental verifications are presented.

A modified formula for cyclic compression crack growth model considering compressive load effect

Fatigue crack growth under cyclic compression has been confirmed by experiments and widely exists in engineering applications, with the expression of stress intensity factor often serving as milestones. A typical difficulty in calculating the stress intensity factor under cyclic compression is the effect of compressive load on fatigue crack growth. Compressive load effect, resulting in the change of plastic zone and residual stress near crack tip, is a long-term challenge for predicting fatigue crack growth life. We modify the expression of effective stress intensity factor to predict fatigue crack growth life based on the distribution of residual stress, and analyze the effect of load characteristics. It considers the characteristic of material and load, and calculates the driving force of crack growth by integrating the residual stress in plastic zone. In the study of fatigue crack growth experiments under cyclic compression, the modified formula is proved to improve, by comparative analysis, the predictive ability on the whole range of experiment data. Consequently, the modified formula is conducive to calculate the fatigue crack growth.