Applied Mechanics and Materials Vols. 809-810

Abstract: A nodular cast iron (NCI) has been surface melted using the high power direct diode laser (HPDDL) with a quasi-rectangular laser beam spot and the uniform distribution of power. The effect of a heat input and a shielding gas on the quality of surface melted layers (SMLs) has been investigated. The microstructure of the SMLs has been assessed by optical microscopy, scanning electron microscopy and X-ray diffraction (XRD). Comparative erosion tests between the SMLs and as-received NCI have been performed following the ASTM G 76 standard test method. The HPDD laser surface melting of the NCI enables to produce non-porous layers having a hardness up to 1000 HV. It has been determined that the hardness of SMLs depends on the amount of cementite and residual austenite in the fusion zone. The SMLs produced in an argon atmosphere contain higher volume fraction of austenite, than those produced in nitrogen, and consequently have the lower hardness. With increasing heat input the hardness increases, as the result of more complete dissolution of graphite and the higher amount of cementite. The SMLs exhibited significantly higher erosion resistance than the as-received NCI for erodent impact angle of 30°, and slightly lower at 90°.

Abstract: The majority of commercially available 3D printers utilize an additive manufacturing (AM) technique known as molten polymer deposition, whereby a solid thermoplastic filament is forced through a computer-driven extrusion nozzle. Even if it sounds simple at a first look, there are a series of factors that significantly influence the mechanical strength of parts manufactured by using the 3D printing method. The present work tries to investigate by using the finite element method and experimental research how the building orientation is influencing the mechanical strength of samples made from ABS M30 material using a Desktop 3D Printer machine that has been originally designed and produced at the Technical University of Cluj-Napoca (TUC-N).

Abstract: 4330V is a high strength, high toughness, heat treatable low alloy steel for application in the oil, gas and aerospace industries. It is typically used for large diameter drilling parts where high toughness and strength are required. The research describes the effect of preheat temperature, interpass temperature, heat input, and post weld heat treatment on strength, hardness, toughness, and changes to microstructure in the weld joint. Welding with the lower heat input and no post weld heat treatment resulted in optimal mechanical properties in the weld metal. Austempering at 400 °C resulted in optimal mechanical properties in the HAZ. Increasing preheat and interpass temperature from 340 °C to 420 °C did not improve Charpy V-notch values or ultimate tensile strength in the weld metal or heat affected zones. The higher temperature increased the width of the heat affected zone. Austempering at 400 °C reduced HAZ hardness to a level comparable to the base metal. Both tempering and austempering at 400 °C for 10 hours reduced toughness in the weld metal.

Abstract: Simulation software based on a finite element method have significantly changed the possibilities of determining welding strains and stresses at early stages of product design and welding technology development. But the numerical simulation of welding processes is one of the more complicated issues in analyses carried out using the Finite Element Method. A welding process thermal cycle directly affects the thermal and mechanical behaviour of a structure during the process. High temperature and subsequent cooling of welded elements generate undesirable strains and stresses in the structure. Knowledge about the material behaviour subjected to the welding thermal cycle is most important to understand process phenomena and proper steering of the process. The study presented involved the SYSWELD software-based analysis of MIG welded butt joints made of 1.0 mm thickness, 5xxx series aluminium alloy sheets. The analysis of strains and the distribution of stresses were carried out for several different cases of fixing and releasing of welded elements.

Abstract: Composite materials with metallic matrix are increasingly require more than traditional materials metallic, being lighter, more reliable and with their superior properties like: rigidity, tensile strength, flexural strength, fatigue strength, modulus of elasticity, hardness, etc. Due to these advantages, above mentioned, this process has largely penetrated industrial environment. Despite these advantages, there are restrictions on their combination through traditional fusion welding methods so that was passed at the solid-state welding processes, respectively at Friction Stir Welding (FSW). Our researches presents in this brief review: some general ideas about composite materials with metallic matrix and Friction Stir Welding process, appearance and benefits, basic information about the process and composite materials welded by this process, shows the current state of the research with respect to behaviour macrostructure, microstructure, microhardness, tensile properties and defects of the welded joint between composite materials with metallic matrix.

Abstract: It is well known that CO and microparticles generated during GMAW welding processes can affect the welder's health and the environment quality and should be avoided. The main goal of the research was to quantitatively assess the concentrations of CO and microparticules resulting through melted wire - shielding gas - welding pool interaction, specific to fusion welding process, in particular MAG-M (Metal Active Gas with Corgon shielding gas)) process. The concentrations of microparticles and emission of CO developed by several combinations of filler metal and shielding gas, such as ordinary solid wire, basic flux-cored wire, rutile flux-cored wire, metal powder cored wire, low fume metal powder cored wire and Corgon 18, as shielding gas mixture, have been monitored and investigated in detail. The experimental data, achieved for different wire feed speed values, were collected by using special devices as Multilyzer NG and MicroDust Pro and further processed, plotted and comparatively analysed. The analysis revealed that the low fume rutile flux-cored wire significantly developed lower concentrations of microparticles and CO, in comparison with the other types of wires used in MAG-M welding process, and a better protection of the environment would be achieved. Important conclusions related to the influence of the wire type on the concentrations of CO and microparticles produced during MAG-M welding process have been drawn and some recommendations useful for the producers of welded structures are provided at the end of the paper.

Abstract: Exposure of welders to welding fumes and microparticles produced during electric welding can be dangerous and may cause serious maladies. It is important to understand the formation mechanism of microparticles generated during welding process on the one hand and the methods to diminish the risk on the welder’s health on the other hand. Experimental research results related to the assessment of microparticles size, generated during MAG welding process, are presented and discussed in detail in this paper. Rutile flux-cored and low fume metal powder cored wires with 1.2 mm diameter in combination with CO₂ shielding gas or M21 gas mixture (Corgon 18) have been used in the investigations. The experimental tests were performed in a special enclosure, equipped with Glass Fiber Filters and a Philips vacuum, with the aim to capture the microparticles developed by the MAG welding process. The microparticles collected during the experimental program have been analysed and measured by electron microscopy method with (SEM/ESEM - EDAX) Quanta 200 microscope. The study showed that low fume metal powder cored wires determined the achievement of smaller microparticles in comparison with rutile flux-cored wires. Finally, several conclusions emerged from the findings of this study are synthetically presented.

Abstract: Friction Stir Welding (FSW) is the latest innovative and most complex process which is widely applied to the welding of lightweight alloys, such as aluminum and magnesium alloys, and most recently, titanium alloys, copper alloys, steels and super-alloys. Friction stir welding is a highly complex process comprising several highly coupled physical phenomena. The experiments are often time consuming and costly. To overcome these problems, numerical analysis has frequently been used in the last ten years. In this paper is presented a brief review of scientific papers in recent years on numerical simulation of Friction Stir Welding of aluminum alloys. The main elements analyzed by FSW simulation, and briefly in this paper are: temperature and residual stress distribution; work tool geometry (size and shape of the pin); distribution of equivalent plastic deformation; main areas resulted after welding; distribution of microstructure (grain size); parameters and optimization of the FSW process.

Abstract: Considering the advances of lightweight materials, such as Aluminium, Magnesium and composite materials, as well as their growing use in various applications, the demand for dissimilar materials joining methods is increasing, as more modern hybrid structures in various industries are using these novel materials which need to be joined either between them or with traditional ones. The paper presents the results of a project aimed to develop a simple and efficient tool for the selection of suitable joining methods for a large variety of dissimilar materials, and capable to provide a summary of technical information, including process parameters and limitations, required equipment, joint structural performances, etc. for each selected method. The dissimilar joining selection tool DIJO-S was developed using Excel environment, which is very accessible to most of the users, user friendly and visually attractive by using the functions of Visual Basic. After processing the input data, the selection tool provides not just the summary of the suitable joining methods, but also detailed process fiches, which support the user for selecting the best feasible option.

Abstract: Our past research to estimate residual stress into steel welded parts was based on dependence between sound velocity and elastic modulus using longitudinal sound wave. To conduct the experiments was designed sample as a frame. The sample was loaded using adapted equipment and the results were used for FEA tools (SolidWorks SimulationXpress) to obtain the distribution of stresses and displacements. This approach allowed the location of points of interest to the investigation with ultrasound. During the experimentation we arrived to suspect the influence of marginal effect on analysis of residual stresses in steel welded parts using ultrasounds. New experiments were carried out by using part samples permitting to avoid the marginal effect.