1,050 research outputs found
The influence of laser welding configuration on the properties of dissimilar stainless steel welds
No full textLaser beam welding of dissimilar ferritic/martensitic stainless steels was performed in constrained butt joint configuration with the objective of identifying the influence of the melting ratio between the two base metals on the ultimate shear strength of the welds. Based on a full factorial design, experiments demonstrated that varying the incidence angle up to 45° and offsetting the focal position with respect to the materials’ interface within the limits imposed by the laser spot diameter are a reliable method to control the melting ratio and maintaining the expected resistance length at the material interface. The weld configuration parameters were correlated by means of the analysis of variance (ANOVA) method with shear resistance length and the melting ratio: the incidence of surface cracks can be significantly reduced increasing the ferritic steel area, involved in the formation of seam, over 60 % of the whole melt zone. Push-out tests performed on the specimens revealed that such a configuration has beneficial aspects on the ultimate shear strength of the seam meaning that the prevailing effect is the decreased brittleness of the weld by decreasing its carbon content under 0.5 % in weight
Experimental characterization of the inner surface in micro-drilling of spray holes: A comparison between ultrashort pulsed laser and EDM
No full textIn this research, the inner surface characteristics of micro-drilled holes of fuel injector nozzles were analyzed by Shear Force Microscopy (SHFM). The surface texture was characterized by maximum peak-to-valley distance and periodicity whose dimensions were related to the adopted energy. 180 μm diameter holes were drilled using ultrashort pulsed laser process using pulse energies within the range of 10-50 μJ. Laser ablated surfaces in the tested energy range offer a smooth texture with a peculiar periodic structure with a variation in height between 60 and 90 nm and almost constant periodicity. The Scanning Electron Microscopy (SEM) photograph of the Laser Induced Periodic Surface Structure (LIPSS) showed the co-existence of Low Spatial Frequency LIPSS (LSFL) and High Spatial Frequency LIPSS (HSFL). A comparative analysis was carried out between the highest laser pulse energy in the tested range energy laser drilling which enables the shortest machining time and micro-Electrical Discharge Machining (μ-EDM). On the contrary, results showed that surfaces obtained by electro-erosion are characterized by a random distribution of craters with a total excursion up to 1.5 μm with a periodicity of 10 μm. The mean-squared surface roughness (Rq) derived from the scanned maps ranges between 220 and 560 nm for μ-EDM, and between 50 and 100 nm for fs-pulses laser drilling
Experimental characterization of the inner surface in micro-drilling of spray holes: A comparison between ultrashort pulsed laser and EDM
No full textIn this research, the inner surface characteristics of micro-drilled holes of fuel injector nozzles were analyzed by Shear Force Microscopy (SHFM). The surface texture was characterized by maximum peak-to-valley distance and periodicity whose dimensions were related to the adopted energy. 180 mu m diameter holes were drilled using ultrashort pulsed laser process using pulse energies within the range of 10-50 mu J. Laser ablated surfaces in the tested energy range offer a smooth texture with a peculiar periodic structure with a variation in height between 60 and 90 nm and almost constant periodicity. The Scanning Electron Microscopy (SEM) photograph of the Laser Induced Periodic Surface Structure (LIPSS) showed the co-existence of Low Spatial Frequency LIPSS (LSFL) and High Spatial Frequency LIPSS (HSFL). A comparative analysis was carried out between the highest laser pulse energy in the tested range energy laser drilling which enables the shortest machining time and micro-Electrical Discharge Machining (mu-EDM). On the contrary, results showed that surfaces obtained by electro-erosion are characterized by a random distribution of craters with a total excursion up to 1.5 mu m with a periodicity of 10 mu m. The mean-squared surface roughness (R-q) derived from the scanned maps ranges between 220 and 560 nm for mu-EDM, and between 50 and 100 nm for fs-pulses laser drilling
A study on the control of melting ratio to increase mechanical properties of laser welded joints between AISI 440C and AISI 430F
No full textLaser beam welding of dissimilar AISI 440C and AISI 430F stainless steels was investigated in a circular constrained configuration. The beam incidence angle and the offset of the focusing position respect to the contact point between the two materials were used as main control parameters to vary the melting ratio inside the seam. The objective of the study is twofold: to avoid surface microcracks related to the high percentage of carbon of the martensitic steel and to enhance the shear strength of the weld by making it less brittle. To reach this scope the effects of incidence angle and offset on weld bead geometry and melting ratio were studied by means of metallographic analyses, microstructure and microhardness characterization. As last step, the weld mechanical strength was tested by tensile-shear stress test on the whole seam. Experiments demonstrated that varying incidence angle and offsetting the focal position is a reliable method to modify the melting ratio and maintaining the expected resistance length at the material interface, as well. It was found that increasing the percentage of ferritic steel into the joint has beneficial effects on the weld quality and on the shear resistance. The critical carbon content determining the mechanical properties in the fusion zone can be calculated by taking into account the melting ratio
Recent Developments in the Dual Reciprocity Method Using Compactly Supported Radial Basis Functions
No full textRecent Developments in the Dual Reciprocity Method Using Compactly Supported Radial Basis Functions
No full textWater jet guided laser as an alternative to EDM for micro-drilling of fuel injector nozzles: A comparison of machined surfaces
No full textTo characterize the inner surface of the fuel injector nozzle holes drilled by EDM and water jet guided laser drilling (Laser Micro-Jet) a specifically conceived scanning probe microscopy technique with true non-contact operating mode was used. A difference in morphology of the drilled surfaces is evident from the acquired surface topography along the hole axis for the two compared drilling techniques. Results showed that the surface texture can be characterized by (i) maximum peak-to-valley distance and (ii) periodicity. Acquired maps confirm that electro-eroded surfaces are an envelope of craters randomly distributed with total excursion up to 1.7 μm with a crater size of 15 μm. While, the efficient melt expulsion and immediate cooling of water jet guided laser generates a peak to valley distance of 800 nm with a periodicity of 18 μm. Average Rq derived from the measured cylindrical surfaces was 450 nm and 150 nm for EDM and Laser Micro-Jet, respectively. Water jet guided laser drilling has proved to be a reliable alternative to EDM from the point of view of repeatability of the results and surface quality to facilitate the atomization of the fuel jet
Water jet guided laser as an alternative to EDM for micro-drilling of fuel injector nozzles: A comparison of machined surfaces
No full textTo characterize the inner surface of the fuel injector nozzle holes drilled by EDM and water jet guided laser drilling (Laser Micro-Jet) a specifically conceived scanning probe microscopy technique with true non-contact operating mode was used. A difference in morphology of the drilled surfaces is evident from the acquired surface topography along the hole axis for the two compared drilling techniques. Results showed that the surface texture can be characterized by (i) maximum peak-to-valley distance and (ii) periodicity. Acquired maps confirm that electro-eroded surfaces are an envelope of craters randomly distributed with total excursion up to 1.7 μm with a crater size of 15 μm. While, the efficient melt expulsion and immediate cooling of water jet guided laser generates a peak to valley distance of 800 nm with a periodicity of 18 μm. Average Rq derived from the measured cylindrical surfaces was 450 nm and 150 nm for EDM and Laser Micro-Jet, respectively. Water jet guided laser drilling has proved to be a reliable alternative to EDM from the point of view of repeatability of the results and surface quality to facilitate the atomization of the fuel jet
Clostridium paraputrificum Bacteremia in a Patient with Human Immunodeficiency Virus Infection: A Case Report and Literature Review
No full textNehal Hosin,1,* Batool M Abu-Ali,2,* Abdullatif S Al Rashed,1,* Sara M Al-Warthan,3,* Asim E Diab1,* 1Department of Microbiology, College of Medicine, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia; 2Department of Internal Medicine, Infectious Diseases Division, King Fahad Hospital, Hofuf, Saudi Arabia; 3Department of Internal Medicine, King Fahd Hospital of the University (Imam Abdulrahman Bin Faisal University), Al Khobar, Saudi Arabia*These authors contributed equally to this workCorrespondence: Abdullatif S Al Rashed, Department of Microbiology, College of Medicine, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia, Tel +966555969048, Email [email protected]: Clostridium paraputrificum (C. paraputrificum) is clinically important due to its association with underlying medical conditions. Infection with C. paraputrificum may worsen HIV prognosis, leading to acquired immunodeficiency syndrome. However, it is not frequently isolated and its susceptibility to antibiotics has not been well studied. Our report examines the case of a patient with human immunodeficiency virus (HIV) infection, who was diagnosed with Clostridium paraputrificum bacteremia. A 59-year-old male was admitted to hospital with a medical history of human immunodeficiency virus (HIV), hepatitis C virus (HCV), and neck pain. Following episodes of high fever, the patient received a full work up to test for sepsis. Blood culture revealed bacterial growth, and MALDI-TOF mass spectrometry confirmed the diagnosis of Clostridium paraputrificum bacteremia. The patient received treatment with meropenem and vancomycin antibiotics, which cleared the infection after 48 hours; however, inflammatory markers remained high. To date, a limited number of reported cases of C. paraputrificum exist; thus, this case report contributes valuable information to the literature to improve our understanding of its action and resistance profiles and aid future bacteremia management.Keywords: clostridia, gram-positive bacteria, anaerobe, pathogen, hepatitis C, hepatitis
Ultrashort pulsed laser drilling and surface structuring of microholes in stainless steels
No full textMicroholes for the production of gasoline direct injection nozzles were obtained by ultrashort pulsed laser machining in martensitic stainless steels. The inner surface analysis was carried out by a specifically conceived Scanning Probe Microscopy instrument and revealed the presence of periodic surface microstructures whose formation was studied as a function of process parameters (pulse energy, repetition rate, rotational speed, drilling strategy). Experiments demonstrated that geometrical features of the microstructures can be varied by a proper parameter selection and open the perspective for an optimized process enabling a reduction of coking accumulation during service life and a more effective atomization of the fuel jet
- …
