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Exploring the Correlation between Subsurface Residual Stresses and Manufacturing Parameters in Laser Powder Bed Fused Ti-6Al-4V
摘要： Subsurface residual stresses (RS) were investigated in Ti-6Al-4V cuboid samples by means of X-ray synchrotron diffraction. The samples were manufactured by laser powder bed fusion (LPBF) applying different processing parameters, not commonly considered in open literature, in order to assess their influence on RS state. While investigating the effect of process parameters used for the calculation of volumetric energy density (such as laser velocity, laser power and hatch distance), we observed that an increase of energy density led to a decrease of RS, although not to the same extent for every parameter variation. Additionally, the effect of support structure, sample roughness and LPBF machine effects potentially coming from Ar flow were studied. We observed no influence of support structure on subsurface RS while the orientation with respect to Ar flow showed to have an impact on RS. We conclude recommending monitoring such parameters to improve part reliability and reproducibility.
关键词： additive manufacturing,Ti-6Al-4V,residual stress,synchrotron X-ray diffraction
更新于2025-09-11 14:15:04
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Effect of Centrifugal Shot Peening on the Surface Properties of Laser-Cut C45 Steel Parts
摘要： This article presents the results of experimental studies of the impact of centrifugal shot peening parameters on the roughness, microstructure, and microhardness of the surface layer of laser-cut C45 steel parts. Residual stress distributions and the presence of iron oxides on the surface of these elements were also examined. Centrifugal shot peening tests were performed on an FV-580a vertical machining center while using a specially designed peening head. The parameters that were varied during centrifugal shot peening included tangential speed of the tool vg and feed rate vf. The use of centrifugal shot peening for finish machining of laser-cut C45 steel parts allowed for obtaining a four-fold reduction in the surface roughness parameters Ra and Rz. As a result of shot peening, the geometrical structure of the surface of the steel parts was modified and it acquired new beneficial features, such as large values of the rounding radii of the micropeaks and high material ratios (Rmrmax = 92%). At the same time, the surface layer was hardened (microhardness increased by 16%) and a compressive residual stress layer was produced on the surface of the workpieces. Additionally, as the shot impacted the processed surface, combustion products were “blasted” or “sheared” off it. Shot peening using the proposed technique can be successfully performed while using CNC machines.
关键词： laser cutting,residual stress,microhardness,centrifugal shot peening,microstructure,surface roughness
更新于2025-09-11 14:15:04
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Stresses and fatigue of laser welds
摘要： The paper deals with the specific properties of laser welds in fine-grained high-strength steels. The main topic, however, are residual stresses in laser welds, their impact on the mechanical properties and fatigue behaviour of such welds. As documented, fatigue cracks initiate mainly on micropores or other subsurface defects. From X-ray diffraction studies it follows that thermal expansion is primarily responsible for the longitudinal tensile stresses, whereas transverse compressive stresses are caused by phase transformations. The behaviour of transverse stresses also explains why fractures in laser welds occur completely outside the weld metal and the heat-affected zone.
关键词： welding,laser,residual stress,fatigue
更新于2025-09-11 14:15:04
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Thermo-Mechanical Analysis of Laser Additive Manufacturing for Metals
摘要： The aim of this study is to develop a finite element analysis technique to characterize the distributions of temperature and stress in the process of multilayer deposition of metallic powders by laser additive manufacturing (LAM). Simulation results indicate the residual normal stress in the laser moving direction is greater than that in other directions due to a larger temperature gradient, and it increases with number of deposited layers. Highly residual stresses are present in the LAM build and at the base nearby the interface between the build and base.
关键词： laser additive manufacturing,temperature gradient,finite element analysis,metal,residual stress
更新于2025-09-11 14:15:04
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Residual Stress Analysis Based on Acoustic and Optical Methods
摘要： Co-application of acoustoelasticity and optical interferometry to residual stress analysis is discussed. The underlying idea is to combine the advantages of both methods. Acoustoelasticity is capable of evaluating a residual stress absolutely but it is a single point measurement. Optical interferometry is able to measure deformation yielding two-dimensional, full-field data, but it is not suitable for absolute evaluation of residual stresses. By theoretically relating the deformation data to residual stresses, and calibrating it with absolute residual stress evaluated at a reference point, it is possible to measure residual stresses quantitatively, nondestructively and two-dimensionally. The feasibility of the idea has been tested with a butt-jointed dissimilar plate specimen. A steel plate 18.5 mm wide, 50 mm long and 3.37 mm thick is braze-jointed to a cemented carbide plate of the same dimension along the 18.5 mm-side. Acoustoelasticity evaluates the elastic modulus at reference points via acoustic velocity measurement. A tensile load is applied to the specimen at a constant pulling rate in a stress range substantially lower than the yield stress. Optical interferometry measures the resulting acceleration field. Based on the theory of harmonic oscillation, the acceleration field is correlated to compressive and tensile residual stresses qualitatively. The acoustic and optical results show reasonable agreement in the compressive and tensile residual stresses, indicating the feasibility of the idea.
关键词： electronic speckle-pattern interferometry,residual stress analysis,acoustoelasticity,scanning acoustic microscopy
更新于2025-09-10 09:29:36
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Residual Stress Image Inspections based on Bending Testing for Flexible Transparent Conducting Substrates by Single-direction Common-path Image Interferometry
摘要： This paper proposes a method for automatic inspection of residual stress images based on bending testing for flexible transparent conducting substrates. A flexible characteristics inspection system with single-direction common-path image interferometry is utilized to inspect residual stress images automatically during the bending testing operation. Accordingly, a 5×5 cm2 residual stress image of a 203-μm line pattern on a conducting indium tin oxide (ITO) film deposited on polyethylene terephthalate (PET) substrate with up to 11,000 bending cycles is inspected and analyzed. The relationship between the residual stresses and resistance characteristics of the 203-μm line pattern on the ITO-deposited-on-PET substrate based on bending testing is also analyzed. It was found that the change results of residual stress can predict the resistance characteristics of the ITO-deposited-on-PET substrate sufficiently. Therefore, the inspection results of residual stress images depicted on flexible electronics may help designers and manufacturers to develop products and ensure quality control, respectively, in a manufacturing process.
关键词： residual stress image,bending testing,image single-direction common-path interferometry,flexible characteristics inspection system,ITO-deposited-on-PET substrate
更新于2025-09-09 09:28:46
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Residual stress in underlying silicon at the fixed end of SiO <sub/>2</sub> microcantilevers?— A micro-Raman study
摘要： In this work, nature of the residual stress developed in the convex corners created in underlying Si at the fixed end of SiO2 microcantilevers (MCs) fabricated by wet chemical etching method was investigated using micro-Raman spectroscopy with visible excitation. It revealed the presence of tensile stress near the sharp edge of the convex corner and is attributed to the localized stress generated in the neighborhood of the discontinuities, acting as stress concentration region. Residual stress estimated by micro-Raman technique across the convex corner was also validated by FEM simulations. Micro-Raman also revealed the presence of tensile stress on the etched Si surface, which is explained on the basis of stress induced by native oxide shells covering the etched features.
关键词： SiO2 microcantilever,convex corner in Si,micro-Raman spectroscopy using visible excitation,residual stress
更新于2025-09-04 15:30:14