Thermal analysis is one of the cardinal studies essential for arc welding processes. Thermal field and temperature distribution in arc welds affect the quality of welds as they govern the ...microstructural and thermo-mechanical properties. Therefore, thorough understanding of the thermal behaviour in arc welds is an absolute necessity. Significant efforts have been made in the past to determine the temperature field associated with arc welding. However, for accurate determination of the temperature field/distribution, it is necessary to understand the heat source which influences the temperature distribution in welds. Rosenthal reported the first concept of modelling the heat source, which was then improvised and new models have been instituted through the years. This review article summarizes a collective study made on the heat source and the resulting temperature distribution in arc welds. Numerous methods have been developed to conduct transient temperature distribution studies on arc welds. Analytical approaches with constant material properties, numerical approaches with variable material properties, infrared imaging systems, machine vision systems with soft computing, etc. have been developed to facilitate understanding of transient temperature in arc welds. We first summarize heat source studies followed by literatures on various techniques and methods devoted to transient temperature investigations. Eventually, latest methods used for thermal studies, such as image processing, machine learning and intelligent systems are summarized and discussed.
In this study, the effect of powder spreading direction was investigated on selectively laser-melted specimens. The results showed that the metallurgical properties of the specimens varied during ...fabrication with respect to their position on the build tray. The density, porosity, and tensile properties of the Co–Cr–W–Mo alloy were investigated on cuboid and tensile specimens fabricated at different locations. Two different significant positions on the tray were selected along the powder spreading direction. One set of specimens was located near the start line of powder spreading, and the other set was located near the end of the building tray. The main role in the consequences of powder layering was played by the distribution of powder particle sizes and the packing density of the layers. As a result, laser penetration, melt pool formation, and fusion characteristics varied. To confirm the occurrence of variations in sample density, an additional experiment was performed with a Ti–6Al–4V alloy. Furthermore, the powders were collected at two different fabricating locations and their size distribution for both materials was investigated.
In this paper, we will show the topological optimization of a load-carrying structural parts and the errors that can occur when the topological solution in the form of a triangulated mesh of the ...surface of the optimized part is reconstructed into a parametric CAD form. Such a reconstruction always introduces geometric errors in the resulting optimal structure of the structural element. A numerical example will be used to show how quickly stress concentrations are reproduced on surfaces where they should not be. The numerical results are also supported by experiment. In the conclusion, it is suggested how, with a specific topological model, the obtained stress concentrations at the edges of the structure can be reduced.
In the field of long-life fatigue, predicting fatigue lives and limits for mechanical components is crucial for ensuring reliability and safety. Fracture mechanics tools have enabled the estimation ...of fatigue lives for components with small cracks or defects. However, when dealing with defects larger than the microstructural characteristic size, estimating the fatigue resistance of a material requires determining the cyclic resistance curve for the defect-free matrix, which depends on knowledge of the material’s intrinsic fatigue limit. This study focuses on the experimental evidence regarding the intrinsic fatigue limit and its correlation with naturally nucleated non-propagating cracks. Fracture mechanics models for small crack propagation are introduced, and their disparities and limitations are analyzed. The concept of intrinsic fatigue limit is then introduced and applied to reanalyze a recent publication. Methods for estimating the intrinsic fatigue limit are explored and applied to experimental results reported in the literature. The need to clarify and accurately predict the intrinsic fatigue limit is highlighted in alloys where the processing generates defects larger than the microstructural size of the matrix, as often observed in materials and components produced using additive manufacturing.
The heterogeneity of welded joints’ microstructure affects their mechanical properties, which can vary significantly in relation to specific weld zones. Given the dimensional limitations of the ...available test volumes of such material zones, the determination of mechanical properties presents a certain challenge. The paper investigates X welded joint of S690QL1 grade high strength steel (HSS), welded with slightly overmatching filler metal. The experimental work is focused on tensile testing to obtain stress-strain properties, as well as fracture mechanics testing. Considering the aforementioned limitations of the material test volume, tensile testing is carried out with mini tensile specimens (MTS), determining stress-strain curves for each characteristic weld zone. Fracture mechanical testing is carried out to determine the fracture toughness using the characteristic parameters. The experimental investigation is carried out using the single edge notch bend (SENB) specimens located in several characteristic welded joint zones: base metal (BM), heat affected zone (HAZ), and weld metal (WM). Fractographic analysis provides deeper insight into crack behavior in relation to specific weld zones. The numerical simulations are carried out in order to describe the fracture behavior of SENB specimens. Damage initiation and evolution is simulated using the ductile damage material behavior. This paper demonstrates the possibility of experimental and numerical determination of fracture mechanics behavior of characteristic heterogeneous welded joint zones and their influence on crack path growth.
The local residual stresses (tensile) generated on the surface of a component during its manufacturing (machining, welding) cause deterioration of its service life. To eliminate the negative effect ...of the stresses, the surface is treated using different methods (shot peening, laser shock peening, heat treatment, water jet peening). The application of ultrasonic technology to modify the continuous jet has been intensively researched for treating advanced stages of erosion. In this work, the modifications in the mechanical properties (tensile strength, micro-hardness and residual stress measurements) of AISI 304 Tungsten inert gas welded joints were investigated after ultrasonic pulsating water jet treatment in the incubation stage of erosion. This revealed that the initial tensile residual stress in the welded joints was converted to compressive stress after the treatment. The micro-hardness of the joints after the treatment increased about 40% in the heat affected zone in the near-surface region. Also, the tensile properties increased by about 37.8% and 34.6% in yield strength and ultimate strength, respectively. The microstructural examination of the near-surface region showed the grain reformation mechanism.
The aim of this work was to include a local variation in material properties to simulate the fracture behaviour in a multi-pass mis-matched X-weld joint. The base material was welded with an over and ...under-match strength material. The local variation was represented in a finite element model with five material groups in the weld and three layers in the heat-affected zone. The groups were assigned randomly to the elements within a region. A three-point single edge notch bending (SENB) fracture mechanics specimen was analysed for two different configurations where either the initial crack is in the over or under-matched material side to simulate experimentally obtained results. The used modelling approach shows comparable crack propagation and stiffness behaviour, as well as the expected, scatter and instabilities of measured fracture behaviour in inhomogeneous welds.
In this investigation, a T-joint numerical welding simulation of thick steel plates is performed to estimate transient temperature distributions, residual stress field and model deflections. A ...sequential simulation method is applied in the numerical simulation, where the thermal analysis is done by using the EBD technique to simulate the weld wire melting and metal filler addition while the mechanical analysis is performed in one step without EBD to shorten the calculation time. Thermocouples, non-destructive X-ray diffraction and semi-destructive hole-drilling methods are used to measure the temperature and residual stress distributions. In the thermal analysis, a simplified heat flux is used which causes a relatively large temperature discrepancy in the weld pool area between the numerical and experimental results. The calculated temperature histories outside the weld pool and its vicinity correlate very well with the experimental measurements with an acceptable discrepancy of approximately 4%. The residual stresses are firstly measured on the model surface without electropolishing and then two times after that, at depths of 0.005 and 0.015 mm. The results of residual stress obtained by numerical modelling and measurement with X-ray agree better when the electropolishing removing layer is set to 0.015 mm, due to a significantly smaller effect of surface conditions that originate from steel plate production.
Porosity in sintered materials negatively affects its fatigue properties. In investigating its influence, the application of numerical simulations reduces experimental testing, but they are ...computationally very expensive. In this work, the application of a relatively simple numerical phase-field (PF) model for fatigue fracture is proposed for estimation of the fatigue life of sintered steels by analysis of microcrack evolution. A model for brittle fracture and a new cycle skipping algorithm are used to reduce computational costs. A multiphase sintered steel, consisting of bainite and ferrite, is examined. Detailed finite element models of the microstructure are generated from high-resolution metallography images. Microstructural elastic material parameters are obtained using instrumented indentation, while fracture model parameters are estimated from experimental S-N curves. Numerical results obtained for monotonous and fatigue fracture are compared with data from experimental measurements. The proposed methodology is able to capture some important fracture phenomena in the considered material, such as the initiation of the first damage in the microstructure, the forming of larger cracks at the macroscopic level, and the total life in a high cycle fatigue regime. However, due to the adopted simplifications, the model is not suitable for predicting accurate and realistic crack patterns of microcracks.
Severe plastic deformation (SPD) is a popular group of techniques applied to achieve the nanostructuring of the metallic biomaterials and improvement of their mechanical characteristics. One of the ...most commonly used SPD methods is the high-pressure torsion (HPT) technique which enables the obtainment of the microstructure with small grains and high strength. In the present study, the influence of the plastic deformation and surface modification treatment on the tensile and corrosion properties of the Ti–13Nb–13Zr (wt%) alloy is investigated. In that purpose, the coarse-grained (CG) Ti–13Nb–13Zr (TNZ) alloy was subjected to the HPT processing by applying a pressure of 4.1 GPa with a rotational speed of 0.2 rpm and 5 revolutions at room temperature to obtain the ultrafine-grained (UFG) microstructure. The alloy microstructure before and after HPT processing was analysed using the scanning electron microscopy (SEM) and the X-ray diffraction (XRD). The homogeneity of the UFG TNZ alloy was determined by microhardness testing and microscopic observations. The nanotubular oxide layer on the surface of the TNZ alloy, both in CG and UFG condition, was formed by electrochemical anodization in 1 M H
3
PO
4
+ NaF electrolyte for 90 min. SEM analysis was used to characterise the morphology of the anodized surfaces, while energy dispersive spectroscopy was applied to determine the chemical composition of the nanostructured layers formed at the alloy surfaces. Mechanical properties of the TNZ alloy, before and after HPT processing and electrochemical anodization, were determined by tensile testing. After tensile testing, the fractographic analysis was conducted to identify the fracture mechanisms. The potentiodynamic polarization technique was used to determine the corrosion resistance of the alloy before and after plastic deformation and surface modification treatment. The obtained results showed that the alloy is reasonably homogeneous after the HPT processing. The XRD analyses reviled the presence of α′ and β phases in the CG TNZ alloy microstructure, while the additional ω phase was detected in the microstructure of the UFG TNZ alloy. The HPT obtained alloy exhibits higher hardness and improved tensile properties than the alloy in the as-received CG condition, while the electrochemical anodization leads to a decrease of its mechanical properties. Both CG and UFG alloys show excellent corrosion stability in Ringer’s solution. Moreover, electrochemical anodization leads to a decrease or an increase of the corrosion resistance of these materials, depending on the morphology of the formed nanotubular surface layers. The results indicate that the anodized CG TNZ alloy is characterized by a lower modulus of elasticity and better corrosion resistance properties than the anodized UFG TNZ alloy.
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