- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Influence of laser weld shape on mechanical and fatigue behaviour of single lap laser welded joints
摘要： Traditional manufacturing processes, like arc welding and resistance spot welding, are still the main welding processes to join structural components used across the on/o?-road vehicle industry. Due to the abundance of data, experiences and insights over the decades of usage, lot of fatigue design data has been generated for different joint geometries produced using these methods. The laser welding process has excellent capabilities to join thin sheet metal structures with minimum heat input resulting into lower deformation and improved productivity that offers significant benefit as compared to the arc and resistance welding processes. However, due to the agility of designing joint configurations and limited availability of understanding regarding the fatigue behaviour of laser welded joints, the need arises for the fatigue design data. Most of the research presents the use of straight linear shape laser welds and limited knowledge exist regarding the influence of shape of laser welds on mechanical and fatigue performance of the laser welded joints. The laser welded joints produce small notch like radius at the root of laser weld which could act as a stress raiser causing early crack initiation. For this work, C-shape laser weld has been selected as the geometric shape in comparison to the straight linear shape of laser weld produced on a series of single lap joints. Detailed fatigue experimental investigation has been carried out for linear and C-shape laser welded joints tested in 3 different orientations with respect to the applied cyclic load and several different R-ratio’s and the results are compared. The metallurgical studies have been carried out to understand the failure mode and micro-hardness variations across the weld and heat affected zone. Further, the residual stress profiles have been compared for the C-shape laser weld with the linear welds using detailed X - Ray Diffraction based residual stress measurement.
关键词： Laser Weld,Ultra-high strength steel,C Shape,Crack propagation,High strength low alloy steel,Crack initiation
更新于2025-09-23 15:21:01
-
Study on the thermal initiation of shelled PBXN-109 under laser irradiation
摘要： In order to investigate the thermal initiation mechanism of a warhead under laser irradiation, small scale experiments have been carried out with shelled PBXN-109 to obtain the initiation time and critical metal temperature. It was found that, as the laser power increases, the initiation time decreases exponentially; while the critical metal temperature increases linearly due to the effect of thermal conduct resistance. Based on theoretical analysis, a prediction model was built with a good accuracy for engineering application. In order to establish the relationship between the small-scale and the full-scale experiments, the scaling law of the thermal response process was approximated with that of the thermal conduct process, which was deduced through equation analysis to avoid the difficulty brought by the exponential nonlinearity from the equation of the thermal decomposition of the explosive.
关键词： laser,PBXN-109,metal,initiation,scaling law
更新于2025-09-23 15:19:57
-
The effect of manufacturing defects on the fatigue life of selective laser melted Ti-6Al-4V structures
摘要： The manufacturing defects introduced by selective laser melting typically lead to lower fatigue strength and a larger variation in fatigue life compared to conventionally manufactured structures. X-ray micro computed tomography (μCT) is used to characterize the porosity and lack of fusion defects in terms of population, morphology, dimension and location. The defect size and location are combined with the NASA/FLACGRO (NASGRO) fatigue crack growth model to predict the likely fatigue life, in which an effective initial crack length is defined using the cyclic plastic zone and the defect radius. An eXtended defect zone (XDZ) describing the propensity for local plasticity during fatigue around a defect has been shown through numerical analysis to be a good indicator of the ranking of the threat to fatigue caused by differently located manufacturing defects. This indicates that the effect of a defect, initial radius, r0, is likely to be pronounced when its center is within 2r0 of the surface and maximal when it lies just beneath the surface.
关键词： Additive manufacturing,High cycle fatigue (HCF),Fatigue crack initiation and growth,Digital printing,Defect tolerance method
更新于2025-09-23 15:19:57
-
Investigation on solidification cracks in pulsed laser spot welding of an AZ31 magnesium alloy
摘要： A direction-dependent model of solidification crack initiation and propagation is established to analyze the influence of the melt pool shape on the distribution of solidification cracks in pulsed laser spot welding. The formation direction of the initial crack is related to the variation of the solidification parameters. When the aspect ratio of the spot welds with a default Rectangular pulse is greater than 0.3 and less than 0.8, an initial crack is formed in the 45° direction of the mushy zone, and then the crack propagates along the grain boundary. That is, the solidification cracks are distributed in the direction of 45° on both sides of the surface center of the welding cross-section. When the aspect ratio of the spot welds is less than 0.3 or greater than 0.8, an initial crack is formed in the 90° direction of the mushy zone, and then the solidification crack is vertically distributed at the center of the welding cross-section. The Step-Down-10ms-0.3P pulse can significantly reduce the solidification rate of the melt pool interface, preventing the formation of initial cracks in the sensitive directions of the spot welds with an aspect ratio less than 0.8, thereby eliminating solidification cracks.
关键词： Molten pool shape,Solidification cracking prevention,Cracking distribution,Nd:YAG laser spot welds,Cracking initiation direction
更新于2025-09-23 15:19:57
-
Shock Initiation of the Triaminotrinitrobenzene‐Based Explosive JBO‐9021 Measured with a Photon Doppler Velocimeter
摘要： Triaminotrinitrobenzene (TATB) is an important insensitive high explosive because of its low shock sensitivity and high energy. The evolution of shock into the detonation of TATB requires academic attention and research. A multi-points laser interferometer termed a photon Doppler velocimeter and a rotating mirror streak camera were used to study the shock initiation of detonation in a pressed solid explosive formulation, JBO-9021, which contained 85 wt.% TATB, 10 wt.% HMX and 5 wt.% Kel-F binder. In conventional experiments, the test explosive was assembled by using several columniform explosives with different external diameters. A new device was designed to solve complex problems. This device comprised a wedge-shaped explosive sample and a transparent window, and by using this device, the particle-velocity histories of eight shock positions and the shockwave velocity could be obtained. A series of shock-initiation experiments on high explosive JBO-9021 was performed, and the explosive samples were initiated at different intensity input shocks by an explosive-driven attenuator. The photon Doppler velocimeter was used to detail the growth from an input shock to detonation, and the increase in particle velocity in unreacted JBO-9021 was also obtained in low-intensity shock-initiation experiments. The shock velocity was measured with a rotating mirror streak camera in one experiment. Hugoniot data for JBO-9021 in the form of a shock velocity versus a particle velocity and the initial shock pressure versus a distance-to-detonation relationship (Pop-plot) were obtained. Based on the experimental results, the shock-sensitivity characteristic of JBO-9021 was described.
关键词： Shock initiation,Hugoniot,TATB,Pop-plot,Photon Doppler velocimeter
更新于2025-09-23 15:19:57
-
Examining Storm Asymmetries in Hurricane Irma (2017) Using Polarimetric Radar Observations
摘要： Dual-polarization radar observations of Hurricane Irma (2017) provide new insight into the microphysical structure of a mature tropical cyclone that can be tied to the cyclone dynamics. The primary eyewall exhibited a radar signature of hydrometeor size sorting, which implied that large drops fell out near persistent upward motion in the front-right quadrant of the storm, while smaller drops were advected downstream. In the outer rainbands, convective initiation was also preferred in the front-right quadrant, whereas stratiform precipitation was predominant downwind. For both the primary eyewall and outer rainbands, the preferred quadrant for convective initiation was consistent with the expected kinematic asymmetry of a tropical cyclone in weak environmental wind shear but with moderate translation speed. The developing secondary eyewall exhibited a different asymmetry that indicated a stratiform-to-convective transition associated with heavy precipitation in the rear quadrants. This transition is consistent with hypothesized dynamical theories for secondary eyewall formation.
关键词： hydrometeor size sorting,stratiform precipitation,microphysical structure,Hurricane Irma,tropical cyclone,convective initiation,dual-polarization radar,secondary eyewall formation
更新于2025-09-23 15:19:57
-
Laser pulse initiation of RDX-Al and PETN-Al composites explosion
摘要： The explosive thresholds H cr of the composites cyclotrimethylenetrinitramine (RDX)-Al and pentaerythritol tetranitrate (PETN)-Al under the action of neodymium laser (wavelength 532 nm, pulse duration 14 ns) were experimentally determined for the first time as a function of the aluminum content. The experiments were performed using aluminum nanopowder with average diameter 100 nm. The gas-dynamic energy losses were prevented. The minimal thresholds achieved in the experimental conditions were determined that are H cr = 1 J/cm 2 for the composites RDX-Al at the mass fraction of Al 0.2% and H cr = 0 . 33 J/cm 2 for PETN-Al composites at aluminum mass fraction 0.1%.
关键词： Laser initiation,Pentaerythritol tetranitrate,Cyclotrimethylenetrinitramine,Aluminum,Ultrafine particles,RDX
更新于2025-09-19 17:13:59
-
Laser-assisted 3D bioprinting of exocrine pancreas spheroid models for cancer initiation study
摘要： Pancreatic ductal adenocarcinoma (PDAC) is the most common malignancy of the pancreas. It has shown a poor prognosis and a rising incidence in the developed world. Other pathologies associated with this tissue include pancreatitis, a risk condition for pancreatic cancer. The onset of both pancreatitis and pancreatic cancer follows a common pattern: exocrine pancreatic acinar cells undergo a transdifferentiation to duct cells that triggers a 3D restructuration of the pancreatic tissue. However, the exact mechanism underlying this process remains partially undefined. Further understanding the cellular events leading to PDAC could open new avenues in the development of novel therapeutic approaches. Since current 2D cell culture models fail to mimic the tridimensional complexity of the pancreatic tissue, new in vitro models are urgently needed. Here, we generated 3D pancreatic cell spheroid arrays using laser-assisted bioprinting (LAB) and characterized their phenotypic evolution over time through image analysis and phenotypic characterization. We show that these bioprinted spheroids, composed of both acinar and ductal cells, can replicate the initial stages of PDAC development. This bioprinted miniaturized spheroid-based array model should prove useful for the study of the internal and external factors that contribute to the formation of precursor PDAC lesions and to cancer progression, and may therefore shed light on future PDAC therapy strategies.
关键词： pancreatic cancer,Laser-assisted bioprinting,early lesions,in vitro cancer model,cancer initiation
更新于2025-09-19 17:13:59
-
A new approach to correlate the defect population with the fatigue life of selective laser melted Ti-6Al-4V alloy
摘要： Microstructural features and defects arising from selective laser melting (SLM) determine the in-service performance of additively manufactured near-net-shape components. Here the grain type, shape, size and distribution were characterized using electron backscattered diffraction (EBSD). High-resolution synchrotron radiation X-ray computed tomography was used to quantify the population, morphology and dimensions of porosity and lack of fusion defects. For SLM Ti-6Al-4V alloy, the larger-sized defects in comparison with α′ grains are more important for crack initiation, typically leading to poor fatigue resistance and a pronounced variation in fatigue life. The fatigue strength was then evaluated in terms of the defect population using a combination of the statistics of extremes and the Murakami model. Finally, an extended Kitagawa-Takahashi fatigue diagram was established within the framework of defect-tolerant design, which includes a classical safe-life region and the defect-determined lifetime in the finite life region.
关键词： Defect tolerance assessment,Chapetti model,Fatigue crack initiation and propagation,Kitagawa-Takahashi diagram,Additive manufacturing
更新于2025-09-19 17:13:59
-
Influence of aluminum nanoparticles and binders on the laser initiation of cyclotrimethylenetrinitramine
摘要： Aluminum nanoparticles were added into cyclotrimethylenetrinitramine (RDX) to enhance the laser absorption and lower the initiation energy of pulse laser. Polyvinyl acetate (PVA), polyvinyl butyral (PVB), and fluororubber (F2314) were added into RDX as binders to prepare the RDX-based composite explosives with desirable mechanical behavior. The influence of aluminum nanoparticles and binders on the light absorption, thermal behavior, laser initiation energy and the electron temperature in aluminum plasma were investigated using reflectance spectroscopy, differential scanning calorimetry, laser initiation and laser-induced breakdown spectroscopy. Results showed that the addition of aluminum nanoparticles could prominently lower the laser initiation energy of the RDX-based explosives. The RDX doped with 2.0% aluminum nanoparticles could be reliably initiated with 1.5 J/cm2 laser energy (1064 nm, 8 ns). The laser initiation energy increased to 1.7, 2.4 and 2.9 J/cm2 with the additions of 0.5%, 1.0% and 2.0% F2314 binders, respectively. When the addition of PVA and PVB increased to 2.0%, the RDX-based explosives couldn’t be initiated by pulse laser. When the pulse laser radiated on the surface of the RDX-based composite explosives, the aluminum nanoparticles absorbed the laser energy and were heated to high temperature to initiate the explosives. The addition of binders can provide desirable mechanical behavior, but the laser initiation energy increased because the heat transmission from aluminum nanoparticles to RDX was hindered.
关键词： Laser initiation,Laser-induced breakdown spectroscopy,Binder,Aluminum nanoparticle
更新于2025-09-19 17:13:59