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Fatigue behaviour of a laser beam welded CoCrFeNiMn-type high entropy alloy
摘要： Laser beam welding was used to produce butt joints from the CoCrFeNiMn-type high entropy alloy. The alloy in the initial condition had an fcc single-phase coarse-grained structure. Laser welding resulted in the M7C3-type carbides precipitation in the fcc matrix. The carbide particles precipitation resulted in a considerable increase in microhardness from 150 HV 0.5 for the as-sintered condition to 205 HV 0.5 in the fusion zone. Laser beam welding had a negligible effect on both static mechanical properties and fatigue behaviour of the alloy. The endurance limit of either type of specimens (i.e. with and without welding seam) was 200 MPa. Fracture of all specimens with the laser beam welded seams occurred in the base material area during both tensile and fatigue testing. Weak effect of welding on static/fatigue behaviour of the alloy can be attributed to the higher hardness of the fusion zone, resulting in strain localization in the base material area. An increase in load resulted in activation of secondary slip systems and formation of deformation twins in fatigue specimens.
关键词： Fatigue,Tensile strength,Microstructure,Laser beam welding,High entropy alloy
更新于2025-09-16 10:30:52
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Effects of laser peening on the fatigue strength and defect tolerance of aluminum alloy
摘要： The effects of laser peening (LP) on the bending fatigue strength of the 7075-T651 aluminum alloy were investigated. Accordingly, the defect tolerance of the aluminum alloy subjected to LP is discussed on the basis of fracture mechanics. The results indicate that a deeper compressive residual stress was induced by LP compared with the case of shot peening (SP). The fatigue strengths increased when both peening types were used. Semicircular slits with depths less than 0.4 and 0.1 mm were rendered harmless on the basis of the applications of LP and SP, respectively. The apparent threshold stress intensity factor range ΔKth,ap increased by approximately five and two times owing to LP and SP, respectively. The increase of the ΔKth,ap was caused by the compressive residual stress induced by the peening. The Kitagawa-Takahashi diagram of the laser-peened specimens shows that the defect tolerance of the aluminum alloy was improved by LP.
关键词： fatigue strength,laser peening,residual stress,shot peening,defect tolerance,aluminum alloy
更新于2025-09-16 10:30:52
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Laser Dissimilar Joining of Al7075T6 with Glass-Fiber-Reinforced Polyamide Composite
摘要： Dissimilar joining between metal and composite sheets is usually carried out by mechanical or adhesive joining. Laser dissimilar joining between metal and composite sheets could be an alternative to these methods, as it is a cost-effective and versatile joining technique. Previously, textured metallic and composite parts have been held together and heated with a laser beam while pressure is applied to allow the melted polymer to flow into the cavities of the metal part. The main issue of this process relates to reaching the same joint strength repetitively with appropriate process parameters. In this work, both initial texturing and laser joining parameters are studied for Al 7075-T6 and glass-fiber-reinforced PA6 composite. A groove-based geometry was studied in terms of depth-to-width aspect ratio to find an optimal surface using a nanosecond fiber laser for texturing. Laser joining parameters were also studied with different combinations of surface temperature, heating strategy, pressure, and laser feed rate. The results are relatively good for grooves with aspect ratios from 0.94 to 4.15, with the widths of the grooves being the most critical factor. In terms of joining parameters, surface reference temperature was found to be the most influential parameter. Underheating does not allow correct material flow in textured cavities, while overheating also causes high dispersion in the resulting shear strength. When optimal parameters are applied using correct textures, shear strength values over 26 kN are reached, with a contact area of 35 × 45 mm2.
关键词： metal polymer joint,groove aspect ratio,laser structuring,laser direct joining,shear strength
更新于2025-09-16 10:30:52
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Effect of Er:YAG laser on debonding strength of laminate veneers
摘要： Objective: The purpose of this study was to evaluate the debonding strength of laminate veneers after using erbium?doped: yttrium aluminium garnet (Er:YAG) laser. Materials and Methods: A total of 60 bovine mandibular incisor teeth were divided into two groups (n = 30). Cylindrical specimens (0.7 mm × 5 mm) were fabricated from Empress II ceramic. Then, they were cemented to incisors using dual?cured resin cement (Variolink II). In the first group, no laser application was performed. The Er:YAG laser was applied on each laminate veneer at the test group for 9 s by using the scanning method. Shear force to remove the laminate veneers were applied with universal testing machine at a crosshead speed of 1 mm/min. Results: Results of this study exhibited significant differences between the control (27.28 ± 2.24 MPa) and test group (3.44 ± 0.69 MPa) (P < 0.05). Conclusion: This study shows that application of Er:YAG laser decreased the bond strength of laminate veneers.
关键词： Debonding,shear bond strength,scanning method,erbium-doped:yttrium aluminium garnet laser,laminate veneers
更新于2025-09-16 10:30:52
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Modification of geopolymer with size controlled TiO2 nanoparticle for enhanced durability and catalytic dye degradation under UV light
摘要： Geopolymer- a silica alumina-based polymer has attracted generous amount of interest since the last decades as a promising alternative binder to ordinary Portland cement (OPC) in the construction sector. Proper utilization of industrial waste (Fly ash) and their functionality enhancement is explored in the present exertion by incorporating titanium oxide (TiO2) nanoparticle with different size in it. Along with the development of advanced building composite photocatalytic ability of the synthesized product was also assessed. Rutile phase TiO2 NPs were synthesized hydrothermally and annealed at different temperatures which result in differences in their overall size. Different materials characterization techniques have been carried out for confirmation of phase, functional bond, binding energy, and morphology respectively. Geopolymeric (GT) composites (GT30, GT50, and GT100) were prepared at ambient temperature using this size-variant TiO2 NPs in fly ash and alkali activator. Integration of TiO2 nanoparticles (5%) enhances mechanical properties where the optimized composite GT30 shows the maximum compressive (53.59MPa) and tensile strength (6.8MPa). Mercury Intrusion porosimetry (MIP) and atomic force microscope (AFM) studies indicate that TiO2 nanoparticles of 30 nm (T30 NPs) reduce porosity and roughness of the structure, thus lead to densified matrix and high durability performances. Additionally, GT30 mortar has low water absorption capacity as T30 NPs decrease the apparent volume of permeable voids in its matrix. Degradation of Methylene Blue (MB), a model contaminant was investigated under ultraviolet (UV) light illumination. T30 NPs (1mg) and GT30 (5mg) are found to degrade >95% dye solution within 90 mins towing to the high surface area of TiO2 NPs and free radical generation. Such outcomes are well fitted in the Langmuir–Hinshelwood first-order rate model. These results will pave the way to explore industrial waste; fly ash in geopolymer for the excellent durability and wastewater treatment through dye degradation under UV light illumination with the aid of TiO2 NPs.
关键词： Strength and durability,Geopolymer,Dye degradation.,TiO2 NPs
更新于2025-09-16 10:30:52
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The effects of Er:YAG, Nd:YAG, and Diode (940nm) Lasers irradiation on Microtensile bond strength of two steps self-etch adhesives
摘要： Nowadays, studies show the effective laser irradiation role on the adhesion of bonding agents to the dentin. Therefore, the present study was set to find an appropriate protocol for the use of Nd:YAG, Er:YAG, and Diode lasers during the application of two steps self-etch adhesives in direct dental restorations in order to achieve higher microtensile strength.
关键词： Diode laser,Er:YAG,Bond strength,Adhesive,Nd:YAG
更新于2025-09-16 10:30:52
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Effect of acid etching, Er, Cr: YSGG laser conditioning and combining on shear bond strength of orthodontic metal bracket
摘要： Aim The present study aims to evaluate the shear bond strength and the adhesive remnants index (ARI) of metal brackets. For this purpose, enamel etched with acid, Er; Cr: YSGG (2780 nm) laser, and a combination of them. Methods In this study, 60 human premolars were divided into three groups (acid, Er, Cr: YSGG (2780 nm) laser, and combined etching). Each group contains 20 teeth. For testing of shear bond strength (SBS), the force applied by a universal testing machine. All the samples were examined under a light stereomicroscope to determine the bond failure mode. Results The results revealed that the laser-acid group had the maximum mean shear bond strength while the acid group had the minimum shear bond strength. The values of mean shear bond strength obtained of 25.90, 16.94, and16.60 MPa for laser-acid, laser, and acid, respectively. Laser and acid groups were negligibly different from each other, while they were significantly different from the lasers–acid group (p < 0.05). Regardless of the preparation of the enamel, bond failure occurred predominantly in the enamel-adhesive site. Conclusions Er, Cr: YSGG (2780 nm) laser conditioning in combination with acid led to high shear bond strength, but the hazardous effect on tooth should be considered. The bond failure mode was almost similar among all three groups, where there was no adhesive left on the surface of the tooth.
关键词： Er,Shear bond strength,Orthodontic bracket,Cr: YSGG laser,Acid etching
更新于2025-09-12 10:27:22
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Estimation of THz field strength by an electro-optic sampling technique using arbitrary long gating pulses
摘要： We demonstrate a simple approach to retrieve the original peak electric field (E-field) strength of high-intensity THz pulses using an electro-optic sampling (EOS) technique and the Poynting flux approach. The latter supposes assessment of THz pulse intensity by measurement of pulse energy, duration and spot size, but its applicability to a few-cycle THz pulse needs detailed consideration. We applied a deconvolution procedure to the raw EOS data to retrieve the THz field waveform. We describe a two-step procedure that allows us to assess the field strength of an extreme THz field. First, the EOS measurements of the THz field should be performed at low pulse energies to retrieve the THz waveform and estimate pulse duration and amplitudes of each particular oscillation. Next, the field strength of an extreme THz pulse can be assessed from the Poynting flux approach with correction to the abovementioned data obtained from the EOS measurements. We show good experimental coincidence between peak strength estimation from the EOS directly and from the combined approach at ‘low’ field strength. Hence, an extreme THz E-field strength can also be assessed from preliminary EOS measurements and full energy measurements based on the Poynting flux approach. We also show that the Poynting flux approach for extreme few-cycle THz pulses gives prominent, at least two-fold, underestimation without preliminary EOS measurements.
关键词： electro-optic sampling (EOS),intense terahertz pulse,electric field (E-field) strength
更新于2025-09-12 10:27:22
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Welding strength of dissimilar laser-welded NiTi and NiTiCu shape memory wires
摘要： NiTi shape memory alloys are widely used in various medical and aerospace products because of their outstanding properties, namely superelasticity and shape memory effect. Joining of dissimilar NiTi shape memory wires can be applied in the design of smart components made up of different functionalities or properties. However, preserving the shape memory effect of the welded regions is really challenging due to the influence of laser heat on the microstructure and consequently activation temperature of the welded samples. This paper investigates the mechanical properties of the welded NiTi to NiTiCu wires using tensile test and microhardness analysis. In fact, the experimental results allow to identify the optimum operational parameters for joining of dissimilar NiTi shape memory wires.
关键词： Laser Welding,Welding Strength,Dissimilar Joints,Shape Memory Alloys
更新于2025-09-12 10:27:22
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Assessment of microcracks and shear bond strength after debonding orthodontic ceramic brackets on enamel priorly etched by different Er,Cr:YSGG and Er:YAG laser settings without acid application: An in vitro study
摘要： Background data > Enamel microcrack formation has a high incidence after mechanical debonding of ceramic brackets. This may be due to high delivered shear bond strength values when enamel is priorly etched by phosphoric acid. It is still not well elucidated in the literature if laser etching affects enamel the same way. The aim of the research was to analyze different Er,Cr:YSGG and Er:YAG laser etching settings as an alternative to phosphoric acid, in an attempt to prevent enamel microcrack formation during laser etching and mechanical debonding, while reducing the shear bond strength to the minimal clinical acceptable value. Materials and methods > One hundred and thirty-three teeth were randomly divided into 7 experimental groups according to their etching modalities. Settings used for enamel etching were in Er,Cr:YSGG groups: Er,Cr:YSGG (1.5 Watt, W/20 Hertz, Hz); Er,Cr:YSGG (1.5 W/15 Hz) and Er,Cr:YSGG (2 W/20 Hz) and settings used for enamel etching in Er:YAG groups were: Er:YAG (60 millijoules , mJ), Er:YAG (80 mJ) and Er:YAG (100 mJ). Group C etched with 37% phosphoric acid served as control. Microscopic analysis was performed to assess presence of enamel microcracks. Shear bond strength was evaluated after thermocycling using Weibull survival analysis. Results > All groups showed a reduction in additional microcracks after debonding when compared to control, but only group Er:YAG (60 mJ) exhibited a statistically significant difference. Groups Er:YAG (80 mJ), control and Er:YAG (100 mJ) showed respectively the highest probability of survival at various stress levels followed by groups Er:YAG (60 mJ); Er,Cr:YSGG (1.5 W/15 Hz); Er,Cr:YSGG (2 W/20 Hz) and Er,Cr:YSGG (1.5 W/20 Hz) that presented a relatively considerable risk of failure, even at low stress levels.
关键词： Shear bond strength,Microcracks,Etching,Erbium laser
更新于2025-09-12 10:27:22