Numerical Modelling of Thermo-Mechanical Effects Developed in Resistance Spot Welding of E304 Steel with Copper Interlayer

Resistance spot welding is a technique applied to join two or more similar or dissimilar metals, by applying pressure and electric current to the spot-weld area. Based on the electrical resistance property of metals, a great amount of heat is generated and used to carry out materials joints, by creating a molten metal nucleus between the components to be welded. The influence of an interlayer material, positioned between the parent materials, on the strength of similar or dissimilar welded joints was studied by researchers worldwide. In most cases, by optimising the process parameters, an increase in the welded joint strength was achieved. In this paper, the resistance spot welding of 1mm thick E304 stainless steel sheets, both with and without a copper foil interlayer, was investigated, by applying, in all cases, the same process parameters. The tensile test of the joints showed a decrease in the strength of joints performed with interlayer metal. A method to control the deterioration level of the joint’ mechanical properties is the Finite Element Analysis which allows to optimise the process parameters so that the negative effects of the process on the joint quality to be limited. It was found that an increase in amperage is needed to compensate for the addition of the interlayer metal and to obtain an adequate melting in the spot-weld area. This modification causes an increase of the molten core diameter that will lead to improvement of the welded joint strength, while no significant influence on the internal stress level was noticed in the processing and numerical analysis of the output data

Tribological and Wear Properties of Multi-Layered Materials

The usage of fabrics as reinforcements in composites is spreading due to fabrics’ properties. The use of fabrics allows obtaining of sinuous surfaces, for instance, unlike the use of prepregs. Using fabrics as reinforcements it is also possible to obtain laminate-like materials having the same matrix in all their volume. In the case of pre-pregs usage always it is necessary to discuss about the bonding between individual plies. For this study eight materials were formed. The forming method consisted in placing the pre-polymer imbued fabric pieces into a mould to obtain plates of composites. Two types of fabric were used: one simple type of untwisted tows of carbon fibres and the second one simple type of alternated untwisted tows of carbon and aramide fibres. Both fabrics were prepared in order to ensure the matrix adherence. The polymer matrix is realised from epoxy system EPIPHEN RE 4020 / EPIPHEN DE 4020 filled with clay and talc in equal amounts of 5% (weight ratio). The use of clay and talc were meant to improve the thermal dimensional stability of final materials. Tribological properties of formed materials were studied using pin-on-disk method with steel disk and pins made of materials. Both orientation of reinforcement fibres relative to friction direction were taken into account. Results are encouraging further studies in order to identify the best solution of forming a multi-component material with more than one designable property

Numerical Model Developed for Thermo-Mecahnical Analysis in AlCrFeMnNiHf0.05–Armox 500 Steel Welded Joint

High entropy alloys are a new category of materials that contain at least four main chemical elements. One of the main advantages over the traditional alloys is the ability to maintain their properties at low or high temperatures. Researchers have investigated the possibility of welding these alloys so that they can be used in industrial applications. Good results have been obtained by welding butt joints of thin sheets, without the use of filler materials. In this paper it is investigated the possibility of welding overlap joints, with applications in the military field, of medium-thickness plates of AlCrFeMnNiHf0.05 high entropy alloy on an Armox 500 steel support plate, using filler materials available on the market. The research focuses on the numerical simulation of three welding processes commonly used in on-site repair operations, namely manual metal arc, metal inert gas, and tungsten inert gas

Vacuum inversion and securing of distal colonic pseudodiverticula with novel spiked O-rings

Diverticular disease is increasingly prevalent in Western societies and is associated with significant morbidity. OBJECTIVE: Two-stage endoscopic device development for inversion and secured ligation of colonic diverticula; first, human cadaver studies were performed to measure forces required for diverticular inversion; second, a novel set of devices (elastic spiked O-ring with delivery system) was tested in animals. DESIGN: Prospective, observational study of human cadavers and prospective, interventional study of a porcine model. SETTING: University hospital pathology laboratory and animal facility. INTERVENTION: Full-thickness inversion of the colonic wall with a pipelike delivery instrument to produce an inverted pseudodiverticulum that was secured with a spiked O-ring. MAIN OUTCOME MEASUREMENTS: The forces required for diverticular inversion, the secured closure of inverted pseudodiverticula, and the time until necrotic tissue falls off. RESULTS: A total of 248 of 248 of cadaveric sigmoid diverticula could be inverted by means of vacuum or forceps. The forces required for inversion ranged from 0.28 to 0.47 N (median, 0.37 N). Twenty-four spiked O-rings were delivered in 6 living pigs to produce 24 inverted pseudodiverticula. One animal died the day after the procedure of a pulmonary thromboembolism. In the remaining 5 pigs, all delivered spiked O-rings remained in place for 7 to 22 days. At necropsy, none of the inverted sites showed signs of perforation but rather full-thickness reparative scarring with ingrowth of connective tissue. LIMITATIONS: Animal model, stiff pipelike delivery instrument, variations in diverticular location, diameter, and size. CONCLUSIONS: Endoluminal inversion and securing of colonic diverticula induces tissue necrosis, diverticular sloughing, and full-thickness scarring

Static and vibration analysis of functionally graded beams using refined shear deformation theory

Static and vibration analysis of functionally graded beams using refined shear deformation theory is presented. The developed theory, which does not require shear correction factor, accounts for shear deformation effect and coupling coming from the material anisotropy. Governing equations of motion are derived from the Hamilton's principle. The resulting coupling is referred to as triply coupled axial-flexural response. A two-noded Hermite-cubic element with five degree-of-freedom per node is developed to solve the problem. Numerical results are obtained for functionally graded beams with simply-supported, cantilever-free and clamped-clamped boundary conditions to investigate effects of the power-law exponent and modulus ratio on the displacements, natural frequencies and corresponding mode shapes

Novel inhibitors of the calcineurin/NFATc hub - alternatives to CsA and FK506?

The drugs cyclosporine A (CsA) and tacrolimus (FK506) revolutionized organ transplantation. Both compounds are still widely used in the clinic as well as for basic research, even though they have dramatic side effects and modulate other pathways than calcineurin-NFATc, too. To answer the major open question - whether the adverse side effects are secondary to the actions of the drugs on the calcineurin-NFATc pathway - alternative inhibitors were developed. Ideal inhibitors should discriminate between the inhibition of (i) calcineurin and peptidyl-prolyl cis-trans isomerases (PPIases; the matchmaker proteins of CsA and FK506), (ii) calcineurin and the other Ser/Thr protein phosphatases, and (iii) NFATc and other transcription factors. In this review we summarize the current knowledge about novel inhibitors, synthesized or identified in the last decades, and focus on their mode of action, specificity, and biological effects

Sustainable Groundwater Management in the Arid Southwestern US: Coachella Valley, California

Sustainable groundwater management requires approaches to assess the influence of climate and management actions on the evolution of groundwater systems. Traditional approaches that apply continuity to assess groundwater sustainability fail to capture the spatial variability of aquifer responses. To address this gap, our study evaluates groundwater elevation data from the Coachella Valley, California, within a groundwater sustainability framework given the adoption of integrative management strategies in the valley. Our study details an innovative approach employing traditional statistical methods to improve understanding of aquifer responses. In this analysis, we evaluate trends at individual groundwater observation wells and regional groundwater behaviors using field significance. Regional elevation trends identified no significant trends during periods of intense groundwater replenishment, active since 1973, despite spatial variability in individual well trends. Our results illustrate the spatially limited effects of groundwater replenishment occur against a setting of long-term groundwater depletion, raising concerns over the definition of sustainable groundwater management in aquifer systems employing integrative management strategies