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Evolution of Mechanically Formed Bow Due to Surface Waviness and Residual Stress difference on Sapphire (0001) Substrate
摘要： Single crystalline sapphire is one of the most widely used wafers for modern high-technology electronic and optical devices owing to the well-established mass production, own physical properties with high thermal, mechanical, and chemical stability, and lattice constants suitable for growth of highly crystalline films. When single crystalline wafers are used as substrates, the curvature of the wafer surface usually called bow is inevitable. Since bow can degrade the quality of deposited film by defects generation or undesirable strain at the interface, to reduce the bow and surface roughness, procedures such as lapping, annealing, and polishing are followed after wafer slicing. Although single crystalline sapphire has sufficiently high hardness for the device applications, surface waviness after abrasion and residual stress within wafer can induce bow. In this study, we revealed the mechanism of bow evolution using high-resolution X-ray diffraction and Raman spectroscopy following each wafering steps. We found that bow in single crystalline sapphire wafer is mainly determined by the irregularly abraded surface after wafer slicing at earlier wafering process. This kind of bow is significantly reduced after lapping and annealing procedure. However, additional surface polishing can inflict stress on the surface and increase bow due to residual stress difference between the polishing surface and the opposite surface. While bow can be effectively reduced by further polishing on the opposite surface, the surface lattice remains still strained.
关键词： HR-XRD,Machining process,Residual stress,Sapphire,Bow,Raman spectroscopy
更新于2025-09-19 17:15:36
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Numerical and experimental investigation of the formation mechanism and the distribution of the welding residual stress induced by the hybrid laser arc welding of AH36 steel in a butt joint configuration
摘要： Formation mechanism of the welding residual stress (WRS) is a key part of welding research. However, there is a lack of meaningful numerical models of the WRS. In this work, a thermal-metallurgical-mechanical (TMM) model was developed using SYSWELD to investigate the distribution and the formation mechanism of WRS during the hybrid laser arc welding of AH36 steel. A series of simulations were conducted to explore the effects of various factors on the WRS. The numerical results matched well with the experimental data. The computational accuracy was improved by considering the typical “wine glass” weld profile and the dilution rate during simulation. The evolution of the WRS is strongly affected by the interaction of phase transformation and strain hardening. The austenite-martensite transformation has a great potential to reduce the WRS whereas the austenite-bainite transformation produces high levels of WRS. The phase transformation temperature has a great influence on WRS.
关键词： Hybrid laser arc welding,Welding residual stress,Phase transformation,Numerical modeling
更新于2025-09-19 17:13:59
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Local deformation and macro distortion of TC4 titanium alloy during laser shock processing
摘要： 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.
关键词： Thin plate,Residual stress,Geometry distortion,Laser shock peening
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE International Symposium on Applications of Ferroelectrics (ISAF) - Lausanne, Switzerland (2019.7.14-2019.7.19)] 2019 IEEE International Symposium on Applications of Ferroelectrics (ISAF) - Vibrating Piezoelectric Energy Conversion Efficiency of Sol-Gel PZT Films with Various Crystal Orientations on MEMS Buckled Diaphragm Structures
摘要： Vibrating energy conversion efficiency was investigated on piezoelectric transducers fabricated on MEMS buckled diaphragm structures from the viewpoint of crystal orientation of sol-gel derived lead-zirconate-titanate (PZT) films. The crystal orientation dominates in-plane stress and spontaneous polarization direction of the PZT films. The in-plane stress affects the static buckling of the diaphragm where a large convex buckling results in a high mechanical conversion efficiency from the flexural vibration to the in-plain vibration. The polarization direction affects the intrinsic piezoelectric conversion efficiency. The crystal orientation of the sol-gel PZT was controlled through pyrolysis temperature between 250?C and 350?C, resulting in a texture variation from (100)-oriented films to (111)-oriented ones. Highly (111)-oriented films showed large polarizations but small buckling deflections, while highly (100)-oriented films showed vice versa. Intermediately textured films with 40–45% (111)-orientation index showed the highest conversion efficiency.
关键词： Piezoelectric,Sol-gel,Residual stress,Buckling,PZT,Polarization,Energy conversion,Diaphragm
更新于2025-09-19 17:13:59
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Fatigue Life Behavior of Laser Shock Peened Duplex Stainless Steel with Different Samples Geometry
摘要： Two different stress raiser geometries (fillet and notched) were treated by laser shock peening (LSP) in order to analyze the effect of sample geometry on fatigue behavior of 2205 duplex stainless steel (DSS). The LSP treatment was carried through Nd:YAG pulsed laser with 1064 nm wavelength, 10 Hz frequency, and 0.85 J/pulse. Experimental and MEF simulation results of residual stress distribution after LSP were assessed by hole drilling method and ABAQUS/EXPLICIT software, respectively. The fatigue tests (tensile-tensile axial stress) were realized with stress ratio of R = 0.1 and 20 Hz. A good comparison of residual stress simulation and experimental data was observed. The results reveal that the fatigue life is increased by LSP treatment in the notched samples, while it decreases in the fillet samples. This is related to the residual stress distribution after LSP that is generated in each geometry type. In addition, the fatigue crack growth direction is changed according to geometry type. Both the propagation direction of fatigue crack and the anisotropy of this steel results detrimental in fillet samples, decreasing the number of cycles to the fatigue crack initiation. It is demonstrated that the LSP effect on fatigue performance is influenced by the specimen geometry.
关键词： laser shock peening,residual stress,duplex stainless steel,fatigue life,sample geometry
更新于2025-09-19 17:13:59
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Crack closure mechanisms in residual stress fields generated by laser shock peening: A combined experimental-numerical approach
摘要： Laser shock peening (LSP) is successfully applied to retard fatigue cracks in metallic lightweight structures by introducing specific, in particular compressive, residual stress fields. In this work, experiments and a multi-step simulation strategy are used to explain the fatigue crack retarding and accelerating mechanisms within these LSP-induced residual stress fields. Crack face contact is identified as main mechanism to retard the fatigue crack as the stress distribution changes and the stress intensity factor range decreases. Crack face contact is experimentally detected by load vs. crack opening displacement (COD) curves and scanning electron microscopy (SEM) of the crack faces, as well as during numerical simulations. The convincing agreement between experiment and simulation, especially regarding the specific crack face contact areas, allowed the proper evaluation of the stress intensity factors depending on the crack length. It is found that crack closure is indeed one of the main reasons for the efficient application of LSP for fatigue crack retardation. Furthermore, the occurrence of crack closure does not indicate a zero value stress intensity factor in complex residual stress fields, as the areas of crack face contact depend strongly on the LSP-induced compressive residual stresses.
关键词： Stress intensity factor,Laser shock peening,Residual stress,Fatigue crack growth,Crack closure
更新于2025-09-16 10:30:52
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Controlled oxidation of Ni for stress-free hole transport layer of large-scale perovskite solar cells
摘要： The effect of the residual thermal stress of NiO films on the performance of an inverted type perovskite solar cell was studied. In this study, NiO films were grown on fluorine doped tin oxide (FTO) substrates of different surface roughness by thermally oxidizing Ni film and were tested as a hole transport layer for large-scale perovskite solar cells. Experimental and simulation results show that it is very important to suppress the appearance of the residual stress at the NiO–FTO interface during the oxidation of the Ni film for effective hole extraction. The Ni oxidation on the flat FTO film produced in-plane compressive stress in the NiO film due to the Ni film volume expansion. This led to the formation of defects including small blisters. These residual stress and defects increased leakage current through the NiO film, preventing holes from being selectively collected at the NiO-perovskite interface. However, when Ni was deposited and oxidized on the rough surface, the residual stress of the NiO film was negligible and its inherent high resistance was maintained. Stress-free NiO film is an excellent hole transport layer that stops the photogenerated electrons of the perovskite layer from moving to FTO. The improvements in the structural and electrical qualities of the NiO film by engineering the residual stress reduce the carrier recombination and increase the power conversion efficiency of the perovskite solar cells to 16.37%.
关键词： perovskite solar cells,large scale processing,nickel oxidation,residual stress,surface roughness
更新于2025-09-16 10:30:52
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Residual stress in laser cladded heavy-haul rails investigated by neutron diffraction
摘要： Residual stress is one of the critical parameters affecting the fatigue behaviour of tribological components, which can be introduced by a thermo-mechanical process such as laser cladding. In this study, the residual stress distribution of laser cladded rails was evaluated using a neutron diffraction technique. The substrate rail for the laser cladding was hypereutectoid rail steel used in Australian heavy-haul railway track, and the cladding materials were 410L (a low carbon content stainless steel alloy) and Stellite 6 (a Co-based alloy). The cladding materials were selected based on their high wear, corrosion and fatigue resistance properties. This study measured the residual stress in full-scale laser cladded rails where the residual stresses were measured in the cladding layer, heat affected zone (HAZ) and substrate zone of the railhead. A new sample preparation strategy was developed to quantify the residual stresses in the full-scale rails with high spatial resolution. Higher compressive residual stress was found in the cladding layer, which may have resulted from the martensitic transformation occurred in that region. Tensile stresses occurred in the HAZ to a depth of 4 mm, which might be mainly caused by thermal contraction and volumetric change in the microstructure. The addition of a second cladding layer did not significantly affect the magnitude of the residual stresses, but the peak tensile residual stress shifted to a deeper location from the surface, which is beneficial in resisting wear. Post-cladding heat treatment significantly reduced the undesirable high residual stress from the cladding layer and HAZ.
关键词： Post-cladding heat treatment,Residual stress,Neutron diffraction,Laser cladding,Heavy-haul rail
更新于2025-09-16 10:30:52
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Method of Reducing Residual Stress Generated by Laser Cutting by Light Indentation of Sheet Metal Edge
摘要： The aim of the present research is to propose a new method for the reduction of the residual stress which was generated by laser cutting. Laser cutting has been expected to be used as an effective and potent method for cutting out blanks from rolled sheet metals because of its high flexibility of the cutting line and high productivity. However, residual stresses, which are inevitably generated by laser cutting, have been the greatest obstacle to the prevalence of laser cutting. One of the problems is the warping that occurs in the sheet metal subjected to bending processes following laser cutting. The authors present a new method for reducing residual stress generated by laser cutting. The method involves applying is to give light indentation on the sheet metal edge. The FEM analyses were carried out to study the feasibility of this method, to determine the method of applying indentation, and to optimize the conditions. Experiments were conducted for verification. As a result, the warp generated by the residual stress was significantly reduced to one-tenth of that without the new treatment, and the magnitude was satisfactorily small for industrial usage.
关键词： laser cutting,longitudinal camber,V bending,blank sheet metal,residual stress
更新于2025-09-16 10:30:52
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Coupled Thermal-Mechanical Analysis of CO<sub>2</sub> Laser Irradiation on Fused Silica
摘要： To grind fused silica in ductile mode, it was proposed to repair surface and subsurface micro cracks of fused silica by CO2 laser irradiation. However, excessive residual stress remains on the surface because the melt fused silica on the surface quenches in air. It causes the critical depth of cut for ductile grinding fused silica to be smaller than 0.2μm. To investigate the distribution of the residual stress and look for an optimal manner of irradiation to control residual tensile stress, a numerical model of was built for simulating the dynamic behavior of fused silica when irradiated by CO2 laser. Laser energy absorption, heat transmission, viscoelastic behavior of fused silica and thermally induced stress were considered in the numerical simulation. The results show how the residual stress is formed and distributed. We found that an appropriate control of the temperature field as a function of time and position in the laser process is the key to reduce the residual stress. Therefore, three kinds of processes were proposed to reduce residual tensile stress on the surface of fused silica introduced by laser irradiation. The residual stress distributions of these three processes were compared by numerical analysis to decide a better method of laser irradiation.
关键词： fused silica,laser irradiation,ductile grinding,viscoelastic,residual stress
更新于2025-09-16 10:30:52