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On the application of laser shock peening for retardation of surface fatigue cracks in laser beam-welded AA6056
摘要： The present study aims to investigate the extent to which the fatigue behaviour of laser beam-welded AA6056-T6 butt joints with an already existing crack can be improved through the application of laser shock peening. Ultrasonic testing was utilized for in situ (nondestructive) measurement of fatigue crack growth during the fatigue test. This procedure allowed the preparation of welded specimens with surface fatigue cracks with a depth of approximately 1.2 mm. The precracked specimens showed a 20% reduction in the fatigue limit compared with specimens without cracks in the as-welded condition. Through the application of laser shock peening on the surfaces of the precracked specimens, it was possible to recover the fatigue life to the level of the specimens tested in the as-welded condition. The results of this study show that laser shock peening is a very promising technique to recover the fatigue life of welded joints with surface cracks, which can be detected by nondestructive testing.
关键词： fatigue crack,aluminium alloys,laser beam welding,ultrasonic crack tip diffraction,residual stress,laser shock peening
更新于2025-09-23 15:19:57
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Fatigue Life of Materials Strengthened by Laser Shock Processing
摘要： The influence of the thickness of 03Х22Н6М2 stainless steel samples strengthened by laser shock processing on their fatigue life is investigated by finite-element modeling. This technology is found to increase the fatigue life of thin (2 mm) samples more than threefold.
关键词： finite-element modeling,fatigue life,residual stress,laser shock processing
更新于2025-09-23 15:19:57
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Bionic Repair of Thermal Fatigue Cracks in Ductile Iron by Laser Melting with Different Laser Parameters
摘要： Nodular iron brake discs typically fail due to serious thermal fatigue cracking, and the presence of graphite complicates the repair of crack defects in ductile iron. This study presents a novel method for remanufacturing ductile iron brake discs based on coupled bionics to repair thermal fatigue cracks discontinuously using bio-inspired crack blocking units fabricated by laser remelting at various laser energy inputs. Then, the ultimate tensile force and thermal fatigue crack resistance of the obtained units were tested. The microhardness, microstructure, and phases of the units were characterized using a digital microhardness meter, optical microscopy, scanning electron microscopy, and X-ray di?raction. It was found that the units without defects positively impacted both the thermal fatigue resistance and tensile strength. The unit fabricated at a laser energy of 165.6+19?15 J/mm2 had su?cient depth to fully close the crack, and exhibited superior anti-cracking and tensile properties. When the unit distance is 3 mm, the sample has excellent thermal fatigue resistance. In addition, the anti-crack mechanism of the units was analysed.
关键词： bionic crack blocked unit,repair discontinuously,thermal fatigue crack,ductile iron,laser remelting
更新于2025-09-23 15:19:57
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Fatigue behavior improvements of laser-induction hybrid welded S690QL steel plates
摘要： In this paper, the improvements of fatigue performances of S690QL steel welded by laser-induction hybrid welding (LIHW) method were performed, mainly through the infrared imaging device to obtain the weld thermal cycle, fatigue machine to test the fatigue strength and scanning electron microscope to observe the fracture morphology. In fatigue tests, tension-tension fatigue loading and stress ratio R = 0.1 was selected. The LIHW fitted S-N curves were derived. It was found that the cracks with symmetrical grooves were initiated at the weld center (WC), while the single-laser welding (SLW) fatigue samples were fractured at the WC. However, the LIHW samples were finally fractured near heat-affected zone (HAZ). The fracture morphology of fatigue samples with stress amplitude of 108 MPa and 144 MPa were further selected to analysis. Due to different degree of defects or stress concentration, and different welding heat input absorption ability and cooling rate, in sudden fracture region, SLW fatigue samples mainly contained the brittle transient failure mode, LIHW fatigue samples mainly showed a ductile failure mode. It can thus be concluded that the LIHW method could improve the fatigue performance of S690QL steel joints.
关键词： Transient failure mode,Single-laser welding,Cracks,Laser-induction hybrid welding,Fatigue strength
更新于2025-09-23 15:19:57
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Fatigue properties and damage mechanisms of components manufactured by laser additive welding of H13 on S355 steel
摘要： Laser additive manufacturing is an advanced, very perspective technology with potentially wide industrial applications, one of them being an improvement of durability of forms and dies. The aim is to improve surface properties like wear resistance using special layers of powder sintered or remelted by laser beam. Other possible applications are repairs of worn dies or shape changes. At present, dies are manufactured by machining with following bulk heat treatment, which is an expensive process. Another problem is to find suppliers with big size furnaces and limited capacity often results in long time dates and terms. Concerning repairs of dies, they are usually performed manually, using arc or plasma welding with numerous difficulties and disadvantages in comparison with promising and advanced laser overlaying. The paper contains results of a comprehensive evaluation of several types of hard overlayed powder of H13 tool steel on a S355 structural steel using laser beam. Properties like macro- and microstructure, mechanical properties like hardness and its course in the layers, high-cycle fatigue resistance in bending and fatigue damage mechanisms were investigated with the emphasis on fatigue crack initiation process evaluated using scanning electron microscopy. The results indicated that surface additive laser welded layers of a high quality can be reached. On the other hand, some drop of fatigue resistance and endurance limit was observed, affected by surface defects – small welding imperfections
关键词： Laser additive manufacturing,H13 and S355 steels,fatigue
更新于2025-09-23 15:19:57
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Dielectric and Ferroelectric Properties of P(VDF-TrFE) Films with Different Polar Solvents
摘要： We investigated the structural, dielectric, and ferroelectric properties of poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] films that were grown using dimethylformamide (DMF) and tetrahydrofuran (THF) polar solvents. The DMF solvent has a large dipole moment with a long bond length and evaporates slowly while the THF solvent has a small dipole moment with a short bond length and evaporates rapidly. Because of these differences, a thin film with a rough surface occurs when using DMF while a thick film with a smooth surface is formed when using THF. Compared to DMF solvent, the ferroelectric polarization is not well saturated and the dielectric constant is quite low for the THF solvent, which is possibly due to the residual paraelectric defects in the P(VDF-TrFE) films. For both solvents, the polarization switching can be explained by using the Kolmogorov-Avrami-Ishibashi (KAI) model with similar switching times. Both solvents enable the P(VDF-TrFE) films to have good retention and fatigue resistance for ferroelectric polarization.
关键词： Polar solvents,P(VDF-TrFE),Fatigue resistance,Ferroelectric switching,Retention
更新于2025-09-19 17:15:36
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A study on differences in human perception between a real and an AR scene viewed in an OST-HMD
摘要： With the recent growth in the development of augmented reality (AR) technologies, it is becoming important to study human perception of AR scenes. In order to detect whether users will suffer more from visual and operator fatigue when watching virtual objects through optical see-through head-mounted displays (OST-HMDs), compared with watching real objects in the real world, we propose a comparative experiment including a virtual magic cube task and a real magic cube task. The scores of the subjective questionnaires (SQ) and the values of the critical flicker frequency (CFF) were obtained from 18 participants. In our study, we use several electrooculogram (EOG) and heart rate variability (HRV) measures as objective indicators of visual and operator fatigue. Statistical analyses were performed to deal with the subjective and objective indicators in the two tasks. Our results suggest that participants were very likely to suffer more from visual and operator fatigue when watching virtual objects presented by the OST-HMD. In addition, the present study provides hints that HRV and EOG measures could be used to explore how visual and operator fatigue are induced by AR content. Finally, three novel HRV measures are proposed to be used as potential indicators of operator fatigue.
关键词： EOG,augmented reality,visual fatigue,ECG,optical see-through HMD,human perception
更新于2025-09-19 17:15:36
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Superior and Anti-fatigue Electro-strain in Bi <sub/>0.5</sub> Na <sub/>0.5</sub> TiO <sub/>3</sub> -based Polycrystalline Relaxor Ferroelectrics
摘要： For eco-friendly bismuth sodium titanate (Bi0.5Na0.5TiO3)-based materials, ultrahigh poling strain (Spol) is always accompanied with a sizable remnant strain (Srem), which severely restricts the cycling reliability of their superior electro-strain. Composition engineering is an effective way of eliminating Srem, but Spol will be sacrificed as well, leading to the overall inferior electro-strain. Here, by composition engineering and subtle criticality confinement, a giant recoverable electro-strain (S>0.7%, realizing the Srem modulation without Spol sacrifice) with reduced hysteresis is reported in BNT-based relaxor ferroelectrics, which can be kept at a high level (<2% variation) even after 105 fatigue cycles. As disclosed by the detailed electric field-dependent multi-scales analyses, the electro-strain behaviors are tightly associated with the agglomeration and deagglomeration process of polar clusters. More efficient release of mechanical mismatch stress among interacting polar entities is suggested to facilitate the deagglomeration process of polar clusters, ensuring a faster restoration of the electric field-induced ferroelectric state when the electric field is removed, which is responsible for the reduced hysteresis and the excellent fatigue performance. These results indicate the significance of 'subtle criticality confinement', and the insight for the design of polycrystalline ceramics with giant and anti-fatigue electro-strain may be useful to develop the new generation of eco-friendly actuators.
关键词： Lead-free Bi0.5Na0.5TiO3,Subtle criticality,Relaxor ferroelectrics,Giant and anti-fatigue electro-strain
更新于2025-09-19 17:15:36
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Large Piezoelectric Stability and Low Polarization Fatigue in 6Pb(Sc1/2Nb1/2)O3-70Pb(Mg1/3Nb2/3)O3-24PbTiO3 Crystals
摘要： The electrical properties and polarization fatigue of [001]-oriented 6Pb(Sc1/2Nb1/2)O3-70Pb(Mg1/3Nb2/3)O3-24PbTiO3 (6PSN-70PMN-24PT) crystals were investigated. Compared with binary Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) crystals, the ternary 6PSN-70PMN-24PT crystal showed a higher rhombohedral–tetragonal transition temperature (TR-T = 120°C) and a larger coercive field (Ec = 4 kV/cm). It was found that the piezoelectric constant (d33 ≈ 1200 pC/N) and electromechanical coupling coefficient (kt ≈ 61%) were weakly dependent on the thermal annealing temperature (Ta), maintaining over 90% of the original value at Ta < 120°C, indicating excellent piezoelectric thermal stability. Electric fatigue measurements showed that the ternary 6PSN-70PMN-24PT crystal exhibited slight fatigue characteristics below 105 bipolar cycles, while the binary PMN-PT crystal exhibited sudden polarization degradation when the cycle numbers were above 102 cycles. The improved fatigue stability for 6PSN-70PMN-24PT crystals was attributed to the large coercive field. The physical mechanisms of the enhanced coercive field and high transition temperature were discussed based on repulsive energy and polar domains.
关键词： piezoelectric stability,6PSN-70PMN-24PT,Ferroelectric crystal,fatigue
更新于2025-09-19 17:15:36
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[IEEE 2019 Workshop on Recent Advances in Photonics (WRAP) - Guwahati, India (2019.12.13-2019.12.14)] 2019 Workshop on Recent Advances in Photonics (WRAP) - Shadowgraphic Imaging of Cavitation Bubble Dynamics in Pulsed Laser Ablation of a Solid in Liquid
摘要： Insulated-gate bipolar transistor (IGBT) power modules find widespread use in numerous power conversion applications where their reliability is of significant concern. Standard IGBT modules are fabricated for general-purpose applications while little has been designed for bespoke applications. However, conventional design of IGBTs can be improved by the multiobjective optimization technique. This paper proposes a novel design method to consider die-attachment solder failures induced by short power cycling and baseplate solder fatigue induced by the thermal cycling which are among major failure mechanisms of IGBTs. Thermal resistance is calculated analytically and the plastic work design is obtained with a high-fidelity finite-element model, which has been validated experimentally. The objective of minimizing the plastic work and constrain functions is formulated by the surrogate model. The nondominated sorting genetic algorithm-II is used to search for the Pareto-optimal solutions and the best design. The result of this combination generates an effective approach to optimize the physical structure of power electronic modules, taking account of historical environmental and operational conditions in the field.
关键词： fatigue,power cycling (PC),insulated-gate bipolar transistors (IGBTs),thermal cycling (TC),reliability,optimization methods,finite-element (FE) methods,Aging,multiobjective
更新于2025-09-19 17:13:59