Direct comparisons are made between the crystallographic texture and residual stress distribution within two otherwise identical Inconel cubes produced by Selective Laser Melting (SLM) and Electron ...Beam Melting (EBM) additive manufacturing processes. In both respects, significant differences were observed; the SLM process produced a sample with high residual stress and cubic texture, while the EBM process generated negligible residual stress and a fibre texture. In the case of the SLM sample, the paper continues on to examine two different approaches to modelling the residual stress field; 1. a simplistic version based on an assumed radially symmetric isotropic eigenstrain, and 2. a layer-by-layer combined thermo-mechanical approach based on finite element modelling. Both models were able to capture the important overall features of the residual stress distribution, however the layer-by-layer approach showed more fidelity in the finer details.
•Residual stress and crystallographic texture from two 3D printing processes for inconel-718 samples are compared (SLM vs EBM).•Significant residual stresses up to yield are observed from SLM while EBM produced no detectable residual stress.•SLM and EBM produced very different texture; ‘Goss’ texture in the SLM sample, fibre texture in the EBM sample.•Two residual stress modelling approaches were compared; 1. An empirical model, and 2. A mechanistic layer-by-layer approach.•Both models captured the overall distribution of stress; the layer-by-layer showed more fidelity to small details.
•Residual stress mapping provides an efficient alternative to welding process simulations.•Upper bound distributions of experimental data secure conservatism in integrity assessments.•Internal ...equilibrium in the FE model play important role in residual stress mapping.
Residual stress is a factor which potentially affects the integrity of welded components. We have developed a methodology of assessment to establish the state of residual stress in a butt-welded plate by using a limited set of experimental measurements obtained using neutron diffraction. The unique longitudinal and transverse residual stress components, as a result of the welding process, are measured across the weld in three depths through the thickness. The measured residual stresses are then used to estimate a stress distribution for each stress component. The estimated stress distribution is then mapped to a finite element model of the weld plate, before adopting an iterative solution to reconstruct the residual stress fields. In addition, a traditional welding simulation is performed using the same weld plate details to predict and compare the residual stress distributions. It is shown that accurate residual stress field reconstruction is possible in and around the area of measurement using the limited measurement data from the neutron diffraction technique. In the estimated stress profiles, an upper-bound distribution is implemented in the weld and Heat Affected Zone (HAZ). This increases the efficiency and reduces the complexity of modelling. In the meantime, conservatism in the estimated stress is secured.
•A random multi-shots peening model considering the initial hardness gradient and residual stress conditions of a carburized rollers is developed.•The influence of shot peening coverage on detail ...evolution of surface morphology and residual stress is investigated.•The ratio between the layer thickness of compressive residual stress and the critical depth of maximum compressive stress generally lies in the regime of 3.6–4.3 after shot peening.
Shot peening is becoming a widely used surface strengthening technique for various key mechanical components for its enhanced influence on the fatigue performance. This technique allows to strengthen the mechanical properties of material via introduce a certain depth of compressive stress layer and change the surface topography. The relation of the shot peening processing parameters, the surface integrity including residual stress and the surface roughness remains a large unmet practical need. In this paper, the residual stress and surface topography obtained by various shot peening treatments were experimentally and theoretically examined. A random multi-shots peening model of a carburized roller, accounting for the initial hardness gradient and residual stress was developed. The measured residual stress and surface roughness present good agreements with the predicted results. Both the experimental and simulated results reveal that the axial and tangential residual stress components tend to be consistent after shot peening. In addition, the influence of peening coverage on detailed evolution of surface topography and residual stress is investigated. It is found that the ratio between the layer thickness of compressive stress and the critical depth of maximum stress generally lies in the regime of 3.6–4.3 after shot peening. As the coverage increases from 100% to 400%, surface roughness parameters Sa, Sq, S5z, Sku decrease, while the maximum magnitude of compressive stress fluctuates in the range of 1105∼1230 MPa. This work could act as an advisory reference for shot peening engineering practices.
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Residual stress is one of the main factors affecting the mechanical properties of materials, such as their strength, plasticity and surface integrity. For instance, tensile stress conditions can ...adversely affect material performance or component life, while compressive stress conditions can improve material fatigue strength. During the processing of integrated aviation structures, machining deformation caused by residual stress has become one of the most prominent manufacturing problems. Therefore, it is very important to measure and evaluate the stress for real applications. This paper reviews the research of residual stress measurement methods over the past five years by classifying them according to the measurement methods appearing in each stage. The existing problems and difficulties of each measurement technology are summarized, and future trends are forecasted. This paper provides a reference for further in-depth study of residual stress measurement technologies.
Background
There are various experimental measurement techniques used to measure residual stress and this work describes one such method, the slotting method, and its application to measure near ...surface residual stresses.
Objective
This work examines its application to macro-scale specimens.
Methods
A series of numerical experiments were performed to understand the size required to assume that the specimen is infinitely large, namely the thickness, width, and height. To assess measurement repeatability, 12 slotting measurements were performed in a shot peened aluminum plate.
Results
The numerical experiments determined the specimen should have a thickness greater than or equal to 21.6 mm (0.85 in), a total specimen width (normal to the slot length) greater than or equal to 44.5 mm (1.75 in), and total height (parallel to the slot) greater than or equal to 38.1 mm (1.5 in) for the specimen to be assumed to be infinite. Slotting measurement repeatability was found to have a maximum repeatability standard deviation of 30 MPa at the surface that decays rapidly to 5 MPa at a depth of 0.3 mm from the surface. Comparison x-ray diffraction measurements were performed.
Conclusions
Infinite plate dimensions and slot length were determined as well as measurement repeatability. Slotting was shown to have significantly better repeatability than X-ray diffraction with layer removal for this application.
A prediction model for machining deformation considering machining-induced residual stress (MIRS) and initial residual stress (IRS) of the blank is proposed in the present study based on the ...equivalent stiffness numerical calculation and elastic mechanics. The deflections of six thin-walled parts (includes two thin-walled specimens designed in the present study and four cases in the literature
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) are predicted using the proposed model, and the corresponding finite element analysis (FEA) and experiments are implemented to verify the model. The machining deformation can be ultimately expressed by MIRS and IRS with the influence coefficients on the basis of the proposed model, and the effects of MIRS and IRS on the machining deformation are analyzed. It is shown that the predicted deformation by the proposed model has a good consistency with the FEA and experiment results. By comparison with the model only considering IRS in literature
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, the prediction accuracy visibly increases when both MIRS and IRS are considered. The contribution ratio of MIRS and IRS on the machining deformation is affected by the stress magnitude and depth, equivalent bending stiffness, and material removal rate. Also it can be easily gotten based on the proposed model.
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•RSP and precised grinding operations improve the surface quality after SSP.•RSP enhances non-indexed region and thickens the nanocrystalline structure.•Precised grinding has no ...adverse effect on the residual stress towards interior.•RSP has greater contribution on low-cycle fatigue performance compared SSP.•SSP played an impressive role on high cycle fatigue performance.
In this study, effects of conventional shot peening, severe shot peening, re-shot peening and precised grinding were performed to AISI 1050. By two-stage operations (SSP + RSP), residual stress depth and the magnitude on the surface were quite high. While deepest compressive stress was measured in A24 + G, maximum stress was observed in A24 + N14. Grinding and re-shot peening powerfully reduced the roughness. The increase in SP intensity improved the hardness considerably, besides the most effective hardness depth was observed after A36. N7 and N14 contributed effective results in the low cycle fatigue, whereas A24, A18, A18 + N14 and A36 in high cycle fatigue.
This investigation addresses the effect of surface nanostructure developed through ultrasonic shot peening (USSP) on corrosion behavior of 7075 aluminum alloy. USSP develops surface nanostructure, ...induces severe plastic deformation, refines grain size up to certain depth and imparts compressive residual stress in the surface region. The sample USSPed for 15 s (USSP 15) exhibited lower current density (0.564 μA/cm2) and higher corrosion potential (−0.695 V) as compared with that of the un-USSP specimen with 1.269 μA/cm2 and -0.839 V respectively. The enhancement in corrosion resistance of USSPed sample is due to rapid development of uniform, homogeneous and effective passive layer on the nano-structured surface coupled with refinement of the coarse precipitates. Also, there is optimum combination of surface roughness, compressive residual stress, and dislocation density in the surface region to produce highest corrosion resistance in the USSP 15 condition.
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•Ultrasonic shot peening successfully induces nanostructure layer in surface region.•Refinement of second phase reduced the galvanic coupling.•Nanostructure causes uniform, homogeneous and effective passive layer formation.•Increased surface roughness leads to deterioration in corrosion resistance.•Combination of several factors governs the corrosion behavior.
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•Surface gradient structure was prepared by LSP with different pulse energies.•Effect of pulse energy on corrosion fatigue behaviour was studied.•LSP generated refined lath, carbide ...fragment and nano-sized precipitation•Corrosion fatigue life was increased by 29.28 % using gradient laser pulse energies.•The CFCG rate equation considering both pH value and gradient CRS was developed.•Corrosion fatigue cracking modes were determined by surface gradient structure.
Surface gradient stress distribution was prepared on AISI 420 martensitic stainless steel (MSS) by massive laser shock peening treatment (MLSPT) with different pulse energies, and effects of MLSPT on residual stress and corrosion fatigue properties in NaCl solutions with different pH values were investigated by microstructural observation, residual stress measurement, corrosion fatigue test, and fractural morphology. Results showed that the coupling effect of MLSPT-induced surface microstructural evolution and gradient stress distribution effectively contributed to an extension in corrosion fatigue properties. Furthermore, the corrosion fatigue crack growth rate equation considering both gradient compressive residual stress and pH value was developed.
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