Thin compact tension specimens made of direct quenched ultra-high strength steel were tested unde... more Thin compact tension specimens made of direct quenched ultra-high strength steel were tested under constant rate uniaxial tensile load. The length of the crack was monitored using optical microscopes on both sides of the specimens during the fatigue pre-cracking (using a chevron V-notch). Deformations during the crack lengthening were recorded by a full-field measurement technique using a set of digital cameras to check the effect of side grooves on reduction of surface deformation. The Specimen without side grooves showed a high level of plasticity, thickness reduction, and crack growth along a deviating path. In addition, the fracture surface showed excessive failure along the inclined plane. The presence of side grooves, however, led to the decrease of the maximum applied force at final fracture while the force prior to crack tearing was almost the same as the specimen without side grooves. Grooves significantly reduced the inclination of the fracture plane and plastic deformation due to removal of low stress triaxiality on the surface. They led to the fracture along a straight path and approximately even surface which makes them beneficial especially when compliance method is used in plane stress fracture tests.
The load capacity equations for structural hollow section joints given in design guidance documen... more The load capacity equations for structural hollow section joints given in design guidance documents are frequently based on the yield line theory. These predictions are then confirmed or adjusted based on experimental findings. The calculated capacities are valid only for a certain failure pattern. For welded rectangular hollow sections (RHS) X- and T-joints, the failure can take place in the brace member, in the chord member or partly in both members. In this study the last mechanism is taken as general failure mode which covers other mechanisms. Theoretical load carrying capacity for this new mechanism is presented and it is compared with some experimental test results. The derived mechanism is applied to define optimal joint geometries for X- and T-joints.
The effect of the geometry and material properties on the fracture strength of welded X-joints fa... more The effect of the geometry and material properties on the fracture strength of welded X-joints fabricated from structural hollow section (SHS) profiles has been studied experimentally and by using nonlinear finite element analysis (FEA). The current paper focuses on four joints tested at −40°C. This was one part of an extensive series of laboratory experiments performed at temperatures +20°C… −60°C. At sub-zero temperatures the primary fracture mode was mainly ductile followed by final brittle failure. The radius and material properties in the corner area of a SHS are dependent on the fabrication method of the SHS. In cold-formed sections the corner radius is typically large and the yield strength is greater than the nominal yield strength of the base material. This bigger corner radius can provide different stiffness and load carrying capacity as compared to joints fabricated from hot-formed sections. Numerical simulation and experimental tests focused on the importance of this corner effect and the separate role geometry, yield strength, and fracture toughness on the total fracture strength of the joint.
European Journal of Mechanics A-solids, Aug 1, 2021
Abstract Studies conducted in recent years have shown that the ultimate load-bearing and deformat... more Abstract Studies conducted in recent years have shown that the ultimate load-bearing and deformation capacity of weldments manufactured from ultra-high-strength steel is often impacted by the heat-affected zone. Thus, to assess the strength properties of these welds, in addition to the base material properties and weld metal, the heat-affected zone's mechanical properties must be analyzed. In this study, a discretization and material parameter characterization are conducted for friction-welded joints in direct-quenched armor steel. The discretization is based on the microstructural analysis and hardness measurements conducted for the weld. After data analysis and considering the practical aspects, such as computational factors and other resources, a model with six different material parameter regions for the heat-affected zone was chosen. For all regions, the quasi-static part of the Johnson–Cook constitutive model was used. Three of the most distant zones measured from the weld interface were subcritically heated during the friction welding. The material parameters for these zones were identified using thermal simulations, tensile experiments, and numerical optimization, whereas the material parameters for the three remaining zones were identified using tensile experiments combined with numerical models and optimization routines. The generated model was successfully used in the fracture assessment of four friction-welded specimens with different degrees of metallurgical constraint. The effect of the subcritically-heated zones on the model's accuracy was studied. Neglecting the subcritical zone within the models caused an overestimation of the joint's tensile strength. Also, three alternative numerical models with different discretization's were generated and used in the fracture assessment. The validity of the generated models was tested by applying the HAZ model to models of tensile test specimens with different degrees of metallurgical constraint. The three alternative models could not correctly assess the fracture. In addition, the different models produced differing stress-strain curves.
A number of different theoretical approaches are commonly used to define the critical plane of ax... more A number of different theoretical approaches are commonly used to define the critical plane of axially loaded plate structures. The critical plane is the cross-section where yielding and failure occur in quasi-static axial loading. Conventional approaches such as maximum shear stress or octahedral shear stress yield criterion seem to work well in terms of load carrying capacity but they do not correctly predict the failure path in practice. A new approach based on removal of the stress parallel to the critical plane is presented in this work. This method was applied to define the effect of the incline of the butt weld on the axial loading capacity of the plate structure. The base material in this study is ultra-high strength steel, where softening in the weld has specific effects on the behaviour and capacity of the joint. The presented theoretical approach showed good agreement with experimental results and FE-calculations. The inclined angle of the weld should be 60 degrees in order to obtain any benefits as regards the capacity of the structure. In addition to butt welds, the results can be generalized to other types of joints, which increases the importance of knowledge of the critical plane considerably.
Recently, the capacity of welded joints made of direct-quenched ultra-high-strength steel (with n... more Recently, the capacity of welded joints made of direct-quenched ultra-high-strength steel (with nominal yield strength of 960 MPa) has been increasingly investigated. However, less attention has been paid to joints subjected to shear loading. In this research, work the punching shear capacity of a plated structure was studied. The effects of cold forming and welding were also included in the study. The capacities based on analytical calculations were compared with experimental results and values obtained by FEA. The results matched each other quite well. The experimental results proved that if the heat input is moderate the welding alone has only a small effect on the punching shear capacity. However, the heat input together with cold forming seems to decrease the load carrying capacity more significantly.
International Review of Mechanical Engineering-IREME, Jul 31, 2015
Many different approaches have been proposed for modeling of fatigue crack nucleation and microst... more Many different approaches have been proposed for modeling of fatigue crack nucleation and microstructurally short fatigue crack propagation in polycrystalline metals. The mechanisms governing dislocations and slip at micro- and nanoscale have to be taken into account to be able to modify the microstructure of metals and develop materials with improved fatigue resistance. This paper reviews modeling approaches that take the microstructure into the consideration specifically from the fatigue crack nucleation point of view. Key concepts are explained, challenges described, and uncertainties discussed, followed by a comprehensive list of articles on the subject published mainly in the past decade.
The data available in this article presents the microstructural information achieved via scanning... more The data available in this article presents the microstructural information achieved via scanning electron microscopy and electron backscatter diffraction to evaluate the microstructure of maraging stainless steel 13Cr10Ni1.7Mo2Al0.4Mn0.4Si, in its as-built and heat-treated conditions, fabricated by laser powder bed fusion. In addition, the statistical analysis of the defects is included to indicate the quality of the additively manufactured metal. Furthermore, true stress-logarithmic strain diagrams of the material with different types of post-processing are available, indicating the strain hardening behavior of the material. These diagrams were achieved via quasi-static tensile tests performed in conjunction with the digital image correlation technique. Finally, the sample designs, additive manufacturing parameters, and the heat treatment procedure carried out on the material are also available in this paper to guide future research and ensure the repeatability of the data in this data article and its linked research paper. The research paper investigates the effects of processing and post-processing parameters on the microstructure, surface quality, residual stress, and mechanical properties of 13Cr10Ni1.7Mo2Al0.4Mn0.4Si (conventionally known as CX developed by EOS GmbH) processed by laser powder bed fusion [1].
This study investigates four different joints under fluctuating tension cycles in the low-cycle f... more This study investigates four different joints under fluctuating tension cycles in the low-cycle fatigue (LCF) regime. The selected material was S960 ultra-high-strength steel, manufactured via the direct-quenching manufacturing route. Based on typical engineering solutions, the following joints were chosen to be investigated in the experimental tests: metal active gas and laser welded butt joints, fillet-welded load-carrying cruciform joints, and non-load-carrying double-sided transverse attachment joints. To evaluate the improvement gained by the post-weld treatment, both as-welded condition and high-frequency mechanical impact treated joints from all joint types were tested. In addition to the experimental tests, some of the joints were analyzed using finite element (FE) models, with the aim of comparing the accuracy of the different fatigue assessment methods and the effect of the toe radius on the computational fatigue lives. The results obtained from the experimental tests and ...
Thin compact tension specimens made of direct quenched ultra-high strength steel were tested unde... more Thin compact tension specimens made of direct quenched ultra-high strength steel were tested under constant rate uniaxial tensile load. The length of the crack was monitored using optical microscopes on both sides of the specimens during the fatigue pre-cracking (using a chevron V-notch). Deformations during the crack lengthening were recorded by a full-field measurement technique using a set of digital cameras to check the effect of side grooves on reduction of surface deformation. The Specimen without side grooves showed a high level of plasticity, thickness reduction, and crack growth along a deviating path. In addition, the fracture surface showed excessive failure along the inclined plane. The presence of side grooves, however, led to the decrease of the maximum applied force at final fracture while the force prior to crack tearing was almost the same as the specimen without side grooves. Grooves significantly reduced the inclination of the fracture plane and plastic deformation due to removal of low stress triaxiality on the surface. They led to the fracture along a straight path and approximately even surface which makes them beneficial especially when compliance method is used in plane stress fracture tests.
The load capacity equations for structural hollow section joints given in design guidance documen... more The load capacity equations for structural hollow section joints given in design guidance documents are frequently based on the yield line theory. These predictions are then confirmed or adjusted based on experimental findings. The calculated capacities are valid only for a certain failure pattern. For welded rectangular hollow sections (RHS) X- and T-joints, the failure can take place in the brace member, in the chord member or partly in both members. In this study the last mechanism is taken as general failure mode which covers other mechanisms. Theoretical load carrying capacity for this new mechanism is presented and it is compared with some experimental test results. The derived mechanism is applied to define optimal joint geometries for X- and T-joints.
The effect of the geometry and material properties on the fracture strength of welded X-joints fa... more The effect of the geometry and material properties on the fracture strength of welded X-joints fabricated from structural hollow section (SHS) profiles has been studied experimentally and by using nonlinear finite element analysis (FEA). The current paper focuses on four joints tested at −40°C. This was one part of an extensive series of laboratory experiments performed at temperatures +20°C… −60°C. At sub-zero temperatures the primary fracture mode was mainly ductile followed by final brittle failure. The radius and material properties in the corner area of a SHS are dependent on the fabrication method of the SHS. In cold-formed sections the corner radius is typically large and the yield strength is greater than the nominal yield strength of the base material. This bigger corner radius can provide different stiffness and load carrying capacity as compared to joints fabricated from hot-formed sections. Numerical simulation and experimental tests focused on the importance of this corner effect and the separate role geometry, yield strength, and fracture toughness on the total fracture strength of the joint.
European Journal of Mechanics A-solids, Aug 1, 2021
Abstract Studies conducted in recent years have shown that the ultimate load-bearing and deformat... more Abstract Studies conducted in recent years have shown that the ultimate load-bearing and deformation capacity of weldments manufactured from ultra-high-strength steel is often impacted by the heat-affected zone. Thus, to assess the strength properties of these welds, in addition to the base material properties and weld metal, the heat-affected zone's mechanical properties must be analyzed. In this study, a discretization and material parameter characterization are conducted for friction-welded joints in direct-quenched armor steel. The discretization is based on the microstructural analysis and hardness measurements conducted for the weld. After data analysis and considering the practical aspects, such as computational factors and other resources, a model with six different material parameter regions for the heat-affected zone was chosen. For all regions, the quasi-static part of the Johnson–Cook constitutive model was used. Three of the most distant zones measured from the weld interface were subcritically heated during the friction welding. The material parameters for these zones were identified using thermal simulations, tensile experiments, and numerical optimization, whereas the material parameters for the three remaining zones were identified using tensile experiments combined with numerical models and optimization routines. The generated model was successfully used in the fracture assessment of four friction-welded specimens with different degrees of metallurgical constraint. The effect of the subcritically-heated zones on the model's accuracy was studied. Neglecting the subcritical zone within the models caused an overestimation of the joint's tensile strength. Also, three alternative numerical models with different discretization's were generated and used in the fracture assessment. The validity of the generated models was tested by applying the HAZ model to models of tensile test specimens with different degrees of metallurgical constraint. The three alternative models could not correctly assess the fracture. In addition, the different models produced differing stress-strain curves.
A number of different theoretical approaches are commonly used to define the critical plane of ax... more A number of different theoretical approaches are commonly used to define the critical plane of axially loaded plate structures. The critical plane is the cross-section where yielding and failure occur in quasi-static axial loading. Conventional approaches such as maximum shear stress or octahedral shear stress yield criterion seem to work well in terms of load carrying capacity but they do not correctly predict the failure path in practice. A new approach based on removal of the stress parallel to the critical plane is presented in this work. This method was applied to define the effect of the incline of the butt weld on the axial loading capacity of the plate structure. The base material in this study is ultra-high strength steel, where softening in the weld has specific effects on the behaviour and capacity of the joint. The presented theoretical approach showed good agreement with experimental results and FE-calculations. The inclined angle of the weld should be 60 degrees in order to obtain any benefits as regards the capacity of the structure. In addition to butt welds, the results can be generalized to other types of joints, which increases the importance of knowledge of the critical plane considerably.
Recently, the capacity of welded joints made of direct-quenched ultra-high-strength steel (with n... more Recently, the capacity of welded joints made of direct-quenched ultra-high-strength steel (with nominal yield strength of 960 MPa) has been increasingly investigated. However, less attention has been paid to joints subjected to shear loading. In this research, work the punching shear capacity of a plated structure was studied. The effects of cold forming and welding were also included in the study. The capacities based on analytical calculations were compared with experimental results and values obtained by FEA. The results matched each other quite well. The experimental results proved that if the heat input is moderate the welding alone has only a small effect on the punching shear capacity. However, the heat input together with cold forming seems to decrease the load carrying capacity more significantly.
International Review of Mechanical Engineering-IREME, Jul 31, 2015
Many different approaches have been proposed for modeling of fatigue crack nucleation and microst... more Many different approaches have been proposed for modeling of fatigue crack nucleation and microstructurally short fatigue crack propagation in polycrystalline metals. The mechanisms governing dislocations and slip at micro- and nanoscale have to be taken into account to be able to modify the microstructure of metals and develop materials with improved fatigue resistance. This paper reviews modeling approaches that take the microstructure into the consideration specifically from the fatigue crack nucleation point of view. Key concepts are explained, challenges described, and uncertainties discussed, followed by a comprehensive list of articles on the subject published mainly in the past decade.
The data available in this article presents the microstructural information achieved via scanning... more The data available in this article presents the microstructural information achieved via scanning electron microscopy and electron backscatter diffraction to evaluate the microstructure of maraging stainless steel 13Cr10Ni1.7Mo2Al0.4Mn0.4Si, in its as-built and heat-treated conditions, fabricated by laser powder bed fusion. In addition, the statistical analysis of the defects is included to indicate the quality of the additively manufactured metal. Furthermore, true stress-logarithmic strain diagrams of the material with different types of post-processing are available, indicating the strain hardening behavior of the material. These diagrams were achieved via quasi-static tensile tests performed in conjunction with the digital image correlation technique. Finally, the sample designs, additive manufacturing parameters, and the heat treatment procedure carried out on the material are also available in this paper to guide future research and ensure the repeatability of the data in this data article and its linked research paper. The research paper investigates the effects of processing and post-processing parameters on the microstructure, surface quality, residual stress, and mechanical properties of 13Cr10Ni1.7Mo2Al0.4Mn0.4Si (conventionally known as CX developed by EOS GmbH) processed by laser powder bed fusion [1].
This study investigates four different joints under fluctuating tension cycles in the low-cycle f... more This study investigates four different joints under fluctuating tension cycles in the low-cycle fatigue (LCF) regime. The selected material was S960 ultra-high-strength steel, manufactured via the direct-quenching manufacturing route. Based on typical engineering solutions, the following joints were chosen to be investigated in the experimental tests: metal active gas and laser welded butt joints, fillet-welded load-carrying cruciform joints, and non-load-carrying double-sided transverse attachment joints. To evaluate the improvement gained by the post-weld treatment, both as-welded condition and high-frequency mechanical impact treated joints from all joint types were tested. In addition to the experimental tests, some of the joints were analyzed using finite element (FE) models, with the aim of comparing the accuracy of the different fatigue assessment methods and the effect of the toe radius on the computational fatigue lives. The results obtained from the experimental tests and ...
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