Fatigue & Fracture of Engineering Materials & Structures, 2010
A B S T R A C T Numerical studies played a major role in the current understanding of plasticity ... more A B S T R A C T Numerical studies played a major role in the current understanding of plasticity induced crack closure (PICC), however it is well known that the numerical models simplify the reality by considering discrete crack propagations, relatively high fatigue crack growth rates, sharp cracks and that propagation occurs at a well-defined load. The objective of this paper is to find if despite these limitations, the numerical predictions of PICC are close to the experimental results. Experimental work was developed to obtain crack opening values in 1-mm-thick middle-tension (M(T)) specimens of AA6016-T4 aluminium alloy. The opening level was determined from remote compliance data captured by a pin microgauge placed at the centre of the specimen. A numerical model was developed and optimized replicating the experimental test in terms of sample geometry, loading parameters, material behaviour and crack opening measurement technique. The adoption, in the numerical analysis, of a remote measurement technique for determining PICC was found to be robust and adequate for mesh refinement studies. A good agreement was found between experimental and numerical results.
Fatigue & Fracture of Engineering Materials and Structures, 2008
In most of the previous three-dimensional (3D) numerical studies of plasticity induced crack clos... more In most of the previous three-dimensional (3D) numerical studies of plasticity induced crack closure (PICC), ideal shapes have been assumed for the cracks. The aim of present paper is to study the effect of crack shape on PICC. With this objective a 3D numerical model was developed to predict PICC in middle-tension (MT) specimens with different thicknesses and crack shapes. The radial size of crack tip elements and the stabilization of closure level were studied to ensure the quality of numerical predictions. Simultaneously, an independent numerical model was developed to predict crack shape evolution, stable crack shapes and corresponding K distributions. Crack closure was found to produce a significant tunnelling effect, with maximum values of K and K max at the surface. The curved crack presented significant plastic deformation near the free surface which has a high impact on the computation time, compared to the straight crack. The modification of K and K max with crack shape produced a variation of 38% in opening values at the interior positions, but relatively small variations at the surface. Considering the great influence of crack shape on PICC, it is fundamental to model realistic crack shapes.
The formability of similar and dissimilar tailor welded blanks (TWBs), obtained by friction stir ... more The formability of similar and dissimilar tailor welded blanks (TWBs), obtained by friction stir welding of 1 mm thick plates of AA 5182-H111 and AA 6016-T4 aluminium alloys, was analysed by deep drawing cylindrical cups. The metallurgical and mechanical characterization in tension of the welds was already published elsewhere [Leitao C, Leal RM, Rodrigues DM, Loureiro A, Vilaça P. Tensile behaviour of similar and dissimilar AA5182-H111 and AA6016-T4 thin friction stir welds. Mater Design 2009;30:101-8]. In order to understand the formability behaviour of the TWBs, the base materials anisotropy was studied by performing tensile tests at several angles with the rolling direction. Two different types of round TWBs, with 180 and 200 mm diameter, were used in the deep drawing tests. From current study it was possible to conclude that the formability of the TWBs is strongly influenced by the type of mismatch in mechanical properties, between the welds and the base materials, and also, by the initial size of the blanks. Rupture of the cups only occurred under the presence of weld defects, which confirms the good plastic behaviour of the friction stir welds both in overmatch and undermatch conditions.
The tensile behaviour of similar and dissimilar friction stir welds in 1 mm thick sheets of two a... more The tensile behaviour of similar and dissimilar friction stir welds in 1 mm thick sheets of two aluminium alloys (AA5182-H111 and AA6016-T4) is analysed in this paper. The heterogeneity in properties across the welds was studied by performing microhardness tests and microstructural analysis. The tensile tests were performed in samples extracted longitudinal and transverse to the weld direction. It was found that the tensile behaviour of the welds depends mainly on the grain size in the TMAZ, for the AA5182-H111 alloy, and on precipitate distribution, for the AA6016-T4 alloy. In all types of welds, the HAZ preserves the same properties of the base materials. The global mechanical behaviour of the AA5182-H111 similar welds is very similar to that of the base material. However, for the AA6016-T4 similar welds and for the AA6016-T4-AA5182-H111 dissimilar welds a 10-20% strength reduction relative to the base materials and important losses in ductility were reported.
Science and Technology of Welding and Joining, 2011
The aim of this investigation was to study the influence of shoulder cavity and welding parameter... more The aim of this investigation was to study the influence of shoulder cavity and welding parameters on torque, defect formation, microstructure and mechanical properties of friction stir welds in very thin sheets of deoxidised copper. Three types of tools were used: a flat shoulder tool and two tools with conical shoulder cavities of 3 and 6u respectively. The welding parameters analysed were tool rotation and traverse speeds. It was observed that the torque, the microstructure and hardness and the formation of defects in the welds are influenced mainly by tool rotation speed and, to a lesser extent, by the traverse speed and shoulder cavity. The tensile properties of welds carried out at high rotation speeds are little affected by the shoulder cavity.
The influence of the mismatch between material properties and constraint on the plastic deformati... more The influence of the mismatch between material properties and constraint on the plastic deformation behaviour of the heat affected zone of welds in high strength steels is investigated in this study, using finite element simulations. An elastoplastic implicit three-dimensional finite element code (EPIM3D) was used in the analysis. The paper presents the mechanical model of the code and the methodology used for the numerical simulation of the tensile test of welded joints. Numerical results of the tensile test of welded samples with different hypothetical widths for the Heat Affected Zone and various material mismatch levels are shown. The analysis concerns the overall strength and ductility of the joint and in relation to the plastic behaviour of the heat affected zone. The influence of the yield stress, tensile strength and constraint on the stress and plastic strain distribution in the soft heat affected zone is also discussed. #
The present work performs a numerical analysis of the plasticity induced crack closure under vari... more The present work performs a numerical analysis of the plasticity induced crack closure under variable amplitude loading, namely under single tensile overloads and High-Low block loading sequences. The optimisation of the numerical procedure was previously performed under constant amplitude loading for the same material. The physical model was analysed using MARC, a commercial finite element package. The numerical analysis was performed considering constant DK baseline level and stress ratio conditions. The crack opening values were based on the last contact in the first node behind the crack tip. The numerical results are compared with experimental measurements. Crack closure numerical results are consistent with experimental observations under peak overloads and High-Low load blocks, indicating that crack growth retardation under variable amplitude loading sequences is closely linked to the plasticity induced crack closure phenomenon. Moreover, the obtained crack profiles predict the formation of an enlarged hump of residual stretched material ahead of the load variation location. The numerical analysis produced reasonable closure levels when compared to experimental results when the partial closure phenomenon is taken into account in the closure measurements.
In present work friction stir welds produced in 1 mm thick plates of AA 6016-T4 aluminium alloy, ... more In present work friction stir welds produced in 1 mm thick plates of AA 6016-T4 aluminium alloy, with two different tools, were analysed and compared concerning the microstructure and mechanical properties. For each tool, the welding parameters were optimized in order to achieve non-defective welds. Assuming a relation between the welding parameters and the energy input per unit of length of the weld [Seidel TU, Reynolds AP. Visualization of the material flow in AA2195 friction stir welds using a marker insert technique. Metall Mater Trans A 2001;32A:2879-84; Sato YS, Urata M, Kokawa H. Parameters controlling microstructure and hardness during friction stir welding of precipitation-hardenable aluminum alloy 6063. Metall Mater Trans A 2002;33(3):625-35; Lim S, Kim S, Lee CG, Kim S-J. Tensile behavior of friction-stri-welded Al 6061-T651. Metall Mater Trans A 2004;35(9):2829-35; Yang B, Yan J, Sutton MA, Reynolds AP. Banded microstructure in AA2024-T351 and AA2524-T351 aluminum friction stir welds: Part I. Metallurgical studies. Mater Sci Eng A 2004;364(1-2):55-65; Peel MJ, Steuwer A, Withers PJ, Dickerson T, Shi Q, Shercliff H. Dissimilar friction stir welds in AA5083-AA6082. Part I: process parameter effects on thermal history and weld properties. Metall Mater Trans A 2006;37:2183-193; Gerlich A, Su P, Yamamoto M, North TH. Effect of welding parameters on the strain rate and microstructure of friction stir spot welded 2024 aluminum alloy. J Mater Sci 2007;42(14):5589-601; Lombard H, Hattingh DG, Steuwer A, James MN. Optimising FSW process parameters to minimise defects and maximise fatigue life in 5083-H321 aluminum alloy. Eng Fract Mech 2008;75(3-4):341-54]
In new car production, an innovative method to produce strong and light panels consists in applyi... more In new car production, an innovative method to produce strong and light panels consists in applying Tailor Welded Blanks (TWBs) in the body-in-white base structure. Since the fusion welding processes can induce significant changes in the material properties of the base materials, an important question is whether the weld bead has a significant influence on the overall behaviour of the welded blanks. In this work, some preliminary conclusions on this subject were achieved based on results of the numerical simulation of simple mechanical tests: tensile, shear and simple bending. The numerical simulations were performed with a fully implicit finite element program (DD3IMP). The results obtained show that for a slight mismatch of properties between the weld and the base materials, no important influence of the weld in the TWBs behaviour is noticed. However, a significant strength reduction can be observed for strong undermatch conditions (lower mechanical properties in the weld) even when the weld bead is very narrow.
International Journal of Mechanical Sciences, 2004
In order to study the influence of the heat-affected zone softening on the fracture behaviour of ... more In order to study the influence of the heat-affected zone softening on the fracture behaviour of welds with cracks in the weld metal centre line, a large variety of weld geometries and undermatch conditions of the heat affected zone mechanical properties, relative to the weld metal and base material, were addressed in this study. With this aim, the opening stress distribution in notched welded specimens was analysed using the numerical simulation of the three-point bending test. The numerical results show a reduction in the stress levels ahead of the crack tip for welded specimens with severe heat-affected zone undermatch. The stress distribution is strongly influenced by the crack position relative to the weld material/heat-affected zone interface, independently of heat-affected zone width. r
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008
The aim of this investigation was to study the influence of tool geometry on material flow during... more The aim of this investigation was to study the influence of tool geometry on material flow during heterogeneous friction stir welding in 1 mm thick plates of AA 5182-H111 and AA 6016-T4 aluminium alloys. Two types of tool shoulders were used: a shoulder with a conical cavity and a scrolled shoulder. Pin-driven flow was predominant in welds produced with the conical cavity shoulder, which are characterized by an onion ring structure. The interaction between pin-driven and shoulder-driven flow is restricted to the crown of the weld, at the trailing side of the tool, and extends throughout the weld thickness, at the leading side. Although no onion ring structure was formed in welds done with the scrolled shoulder, extensive mixing of the base materials occurred in a plasticized layer flowing through the thickness around the rotating pin. Shoulder-driven flow is intense and continuous around the tool.
Influence of Material Parameters on Plasticity Induced Crack Closure
Key Engineering Materials, 2009
ABSTRACT Plasticity Induced Crack Closure (PICC) is an important fatigue phenomenon affecting cra... more ABSTRACT Plasticity Induced Crack Closure (PICC) is an important fatigue phenomenon affecting crack growth under cyclic loading, which makes important to consider it in the design of components. In this paper a parametric study that correlates elastic-plastic material parameters with plasticity induced crack closure (PICC) is presented. Yield stress and hardening coefficient were selected as the material parameters of interest and a sensitivity analysis was developed. The influence of the different parameters on PICC is explained based on the analysis of crack tip micromechanisms for plastic deformation.
In this paper we present a methodology for trimming 3D solid finite element meshes using a non-un... more In this paper we present a methodology for trimming 3D solid finite element meshes using a non-uniform rational B-spline (NURBS) surfaces representation. The algorithms applied in the identification of the spatial position of the finite element (FE) nodes and elements relative to the trimming surface are described, as well as, the explanation of the correction methods adopted to geometrically rearrange the trimmed elements. Three different strategies are proposed to adjust, with greater or lesser accuracy, the trimmed FE mesh to the trimming surface. The first consists only of an element elimination strategy, while the other two are based on a nodal stretching strategy, aiming for more accurate adjustment of the finite elements boundary to the trimming surface. Finally, to highlight the capabilities of the developed program, a mesh generation example is given by trimming a mesh with the shape of a blank automotive panel. ᭧
Taguchi Analysis of the Effect of Process Parameters in Friction Stir Welding
Materials Science Forum, 2010
Abstract The task of obtaining suitable welding parameters for the friction stir welding process ... more Abstract The task of obtaining suitable welding parameters for the friction stir welding process is often a difficult one, due to the lack of published data and the fact that the exact mechanism by which the process operates has not yet been fully determined. Therefore, ...
Fatigue & Fracture of Engineering Materials & Structures, 2010
A B S T R A C T Numerical studies played a major role in the current understanding of plasticity ... more A B S T R A C T Numerical studies played a major role in the current understanding of plasticity induced crack closure (PICC), however it is well known that the numerical models simplify the reality by considering discrete crack propagations, relatively high fatigue crack growth rates, sharp cracks and that propagation occurs at a well-defined load. The objective of this paper is to find if despite these limitations, the numerical predictions of PICC are close to the experimental results. Experimental work was developed to obtain crack opening values in 1-mm-thick middle-tension (M(T)) specimens of AA6016-T4 aluminium alloy. The opening level was determined from remote compliance data captured by a pin microgauge placed at the centre of the specimen. A numerical model was developed and optimized replicating the experimental test in terms of sample geometry, loading parameters, material behaviour and crack opening measurement technique. The adoption, in the numerical analysis, of a remote measurement technique for determining PICC was found to be robust and adequate for mesh refinement studies. A good agreement was found between experimental and numerical results.
Fatigue & Fracture of Engineering Materials and Structures, 2008
In most of the previous three-dimensional (3D) numerical studies of plasticity induced crack clos... more In most of the previous three-dimensional (3D) numerical studies of plasticity induced crack closure (PICC), ideal shapes have been assumed for the cracks. The aim of present paper is to study the effect of crack shape on PICC. With this objective a 3D numerical model was developed to predict PICC in middle-tension (MT) specimens with different thicknesses and crack shapes. The radial size of crack tip elements and the stabilization of closure level were studied to ensure the quality of numerical predictions. Simultaneously, an independent numerical model was developed to predict crack shape evolution, stable crack shapes and corresponding K distributions. Crack closure was found to produce a significant tunnelling effect, with maximum values of K and K max at the surface. The curved crack presented significant plastic deformation near the free surface which has a high impact on the computation time, compared to the straight crack. The modification of K and K max with crack shape produced a variation of 38% in opening values at the interior positions, but relatively small variations at the surface. Considering the great influence of crack shape on PICC, it is fundamental to model realistic crack shapes.
The formability of similar and dissimilar tailor welded blanks (TWBs), obtained by friction stir ... more The formability of similar and dissimilar tailor welded blanks (TWBs), obtained by friction stir welding of 1 mm thick plates of AA 5182-H111 and AA 6016-T4 aluminium alloys, was analysed by deep drawing cylindrical cups. The metallurgical and mechanical characterization in tension of the welds was already published elsewhere [Leitao C, Leal RM, Rodrigues DM, Loureiro A, Vilaça P. Tensile behaviour of similar and dissimilar AA5182-H111 and AA6016-T4 thin friction stir welds. Mater Design 2009;30:101-8]. In order to understand the formability behaviour of the TWBs, the base materials anisotropy was studied by performing tensile tests at several angles with the rolling direction. Two different types of round TWBs, with 180 and 200 mm diameter, were used in the deep drawing tests. From current study it was possible to conclude that the formability of the TWBs is strongly influenced by the type of mismatch in mechanical properties, between the welds and the base materials, and also, by the initial size of the blanks. Rupture of the cups only occurred under the presence of weld defects, which confirms the good plastic behaviour of the friction stir welds both in overmatch and undermatch conditions.
The tensile behaviour of similar and dissimilar friction stir welds in 1 mm thick sheets of two a... more The tensile behaviour of similar and dissimilar friction stir welds in 1 mm thick sheets of two aluminium alloys (AA5182-H111 and AA6016-T4) is analysed in this paper. The heterogeneity in properties across the welds was studied by performing microhardness tests and microstructural analysis. The tensile tests were performed in samples extracted longitudinal and transverse to the weld direction. It was found that the tensile behaviour of the welds depends mainly on the grain size in the TMAZ, for the AA5182-H111 alloy, and on precipitate distribution, for the AA6016-T4 alloy. In all types of welds, the HAZ preserves the same properties of the base materials. The global mechanical behaviour of the AA5182-H111 similar welds is very similar to that of the base material. However, for the AA6016-T4 similar welds and for the AA6016-T4-AA5182-H111 dissimilar welds a 10-20% strength reduction relative to the base materials and important losses in ductility were reported.
Science and Technology of Welding and Joining, 2011
The aim of this investigation was to study the influence of shoulder cavity and welding parameter... more The aim of this investigation was to study the influence of shoulder cavity and welding parameters on torque, defect formation, microstructure and mechanical properties of friction stir welds in very thin sheets of deoxidised copper. Three types of tools were used: a flat shoulder tool and two tools with conical shoulder cavities of 3 and 6u respectively. The welding parameters analysed were tool rotation and traverse speeds. It was observed that the torque, the microstructure and hardness and the formation of defects in the welds are influenced mainly by tool rotation speed and, to a lesser extent, by the traverse speed and shoulder cavity. The tensile properties of welds carried out at high rotation speeds are little affected by the shoulder cavity.
The influence of the mismatch between material properties and constraint on the plastic deformati... more The influence of the mismatch between material properties and constraint on the plastic deformation behaviour of the heat affected zone of welds in high strength steels is investigated in this study, using finite element simulations. An elastoplastic implicit three-dimensional finite element code (EPIM3D) was used in the analysis. The paper presents the mechanical model of the code and the methodology used for the numerical simulation of the tensile test of welded joints. Numerical results of the tensile test of welded samples with different hypothetical widths for the Heat Affected Zone and various material mismatch levels are shown. The analysis concerns the overall strength and ductility of the joint and in relation to the plastic behaviour of the heat affected zone. The influence of the yield stress, tensile strength and constraint on the stress and plastic strain distribution in the soft heat affected zone is also discussed. #
The present work performs a numerical analysis of the plasticity induced crack closure under vari... more The present work performs a numerical analysis of the plasticity induced crack closure under variable amplitude loading, namely under single tensile overloads and High-Low block loading sequences. The optimisation of the numerical procedure was previously performed under constant amplitude loading for the same material. The physical model was analysed using MARC, a commercial finite element package. The numerical analysis was performed considering constant DK baseline level and stress ratio conditions. The crack opening values were based on the last contact in the first node behind the crack tip. The numerical results are compared with experimental measurements. Crack closure numerical results are consistent with experimental observations under peak overloads and High-Low load blocks, indicating that crack growth retardation under variable amplitude loading sequences is closely linked to the plasticity induced crack closure phenomenon. Moreover, the obtained crack profiles predict the formation of an enlarged hump of residual stretched material ahead of the load variation location. The numerical analysis produced reasonable closure levels when compared to experimental results when the partial closure phenomenon is taken into account in the closure measurements.
In present work friction stir welds produced in 1 mm thick plates of AA 6016-T4 aluminium alloy, ... more In present work friction stir welds produced in 1 mm thick plates of AA 6016-T4 aluminium alloy, with two different tools, were analysed and compared concerning the microstructure and mechanical properties. For each tool, the welding parameters were optimized in order to achieve non-defective welds. Assuming a relation between the welding parameters and the energy input per unit of length of the weld [Seidel TU, Reynolds AP. Visualization of the material flow in AA2195 friction stir welds using a marker insert technique. Metall Mater Trans A 2001;32A:2879-84; Sato YS, Urata M, Kokawa H. Parameters controlling microstructure and hardness during friction stir welding of precipitation-hardenable aluminum alloy 6063. Metall Mater Trans A 2002;33(3):625-35; Lim S, Kim S, Lee CG, Kim S-J. Tensile behavior of friction-stri-welded Al 6061-T651. Metall Mater Trans A 2004;35(9):2829-35; Yang B, Yan J, Sutton MA, Reynolds AP. Banded microstructure in AA2024-T351 and AA2524-T351 aluminum friction stir welds: Part I. Metallurgical studies. Mater Sci Eng A 2004;364(1-2):55-65; Peel MJ, Steuwer A, Withers PJ, Dickerson T, Shi Q, Shercliff H. Dissimilar friction stir welds in AA5083-AA6082. Part I: process parameter effects on thermal history and weld properties. Metall Mater Trans A 2006;37:2183-193; Gerlich A, Su P, Yamamoto M, North TH. Effect of welding parameters on the strain rate and microstructure of friction stir spot welded 2024 aluminum alloy. J Mater Sci 2007;42(14):5589-601; Lombard H, Hattingh DG, Steuwer A, James MN. Optimising FSW process parameters to minimise defects and maximise fatigue life in 5083-H321 aluminum alloy. Eng Fract Mech 2008;75(3-4):341-54]
In new car production, an innovative method to produce strong and light panels consists in applyi... more In new car production, an innovative method to produce strong and light panels consists in applying Tailor Welded Blanks (TWBs) in the body-in-white base structure. Since the fusion welding processes can induce significant changes in the material properties of the base materials, an important question is whether the weld bead has a significant influence on the overall behaviour of the welded blanks. In this work, some preliminary conclusions on this subject were achieved based on results of the numerical simulation of simple mechanical tests: tensile, shear and simple bending. The numerical simulations were performed with a fully implicit finite element program (DD3IMP). The results obtained show that for a slight mismatch of properties between the weld and the base materials, no important influence of the weld in the TWBs behaviour is noticed. However, a significant strength reduction can be observed for strong undermatch conditions (lower mechanical properties in the weld) even when the weld bead is very narrow.
International Journal of Mechanical Sciences, 2004
In order to study the influence of the heat-affected zone softening on the fracture behaviour of ... more In order to study the influence of the heat-affected zone softening on the fracture behaviour of welds with cracks in the weld metal centre line, a large variety of weld geometries and undermatch conditions of the heat affected zone mechanical properties, relative to the weld metal and base material, were addressed in this study. With this aim, the opening stress distribution in notched welded specimens was analysed using the numerical simulation of the three-point bending test. The numerical results show a reduction in the stress levels ahead of the crack tip for welded specimens with severe heat-affected zone undermatch. The stress distribution is strongly influenced by the crack position relative to the weld material/heat-affected zone interface, independently of heat-affected zone width. r
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008
The aim of this investigation was to study the influence of tool geometry on material flow during... more The aim of this investigation was to study the influence of tool geometry on material flow during heterogeneous friction stir welding in 1 mm thick plates of AA 5182-H111 and AA 6016-T4 aluminium alloys. Two types of tool shoulders were used: a shoulder with a conical cavity and a scrolled shoulder. Pin-driven flow was predominant in welds produced with the conical cavity shoulder, which are characterized by an onion ring structure. The interaction between pin-driven and shoulder-driven flow is restricted to the crown of the weld, at the trailing side of the tool, and extends throughout the weld thickness, at the leading side. Although no onion ring structure was formed in welds done with the scrolled shoulder, extensive mixing of the base materials occurred in a plasticized layer flowing through the thickness around the rotating pin. Shoulder-driven flow is intense and continuous around the tool.
Influence of Material Parameters on Plasticity Induced Crack Closure
Key Engineering Materials, 2009
ABSTRACT Plasticity Induced Crack Closure (PICC) is an important fatigue phenomenon affecting cra... more ABSTRACT Plasticity Induced Crack Closure (PICC) is an important fatigue phenomenon affecting crack growth under cyclic loading, which makes important to consider it in the design of components. In this paper a parametric study that correlates elastic-plastic material parameters with plasticity induced crack closure (PICC) is presented. Yield stress and hardening coefficient were selected as the material parameters of interest and a sensitivity analysis was developed. The influence of the different parameters on PICC is explained based on the analysis of crack tip micromechanisms for plastic deformation.
In this paper we present a methodology for trimming 3D solid finite element meshes using a non-un... more In this paper we present a methodology for trimming 3D solid finite element meshes using a non-uniform rational B-spline (NURBS) surfaces representation. The algorithms applied in the identification of the spatial position of the finite element (FE) nodes and elements relative to the trimming surface are described, as well as, the explanation of the correction methods adopted to geometrically rearrange the trimmed elements. Three different strategies are proposed to adjust, with greater or lesser accuracy, the trimmed FE mesh to the trimming surface. The first consists only of an element elimination strategy, while the other two are based on a nodal stretching strategy, aiming for more accurate adjustment of the finite elements boundary to the trimming surface. Finally, to highlight the capabilities of the developed program, a mesh generation example is given by trimming a mesh with the shape of a blank automotive panel. ᭧
Taguchi Analysis of the Effect of Process Parameters in Friction Stir Welding
Materials Science Forum, 2010
Abstract The task of obtaining suitable welding parameters for the friction stir welding process ... more Abstract The task of obtaining suitable welding parameters for the friction stir welding process is often a difficult one, due to the lack of published data and the fact that the exact mechanism by which the process operates has not yet been fully determined. Therefore, ...
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