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.
Wire crimping, a process commonly used in the automotive industry, is a solderless method for establishing electrical and mechanical connections between wire strands and terminals. The complexity of ...predicting the final shape of a crimped terminal and the imperative to minimize production costs indicate the use of advanced numerical methods. Such an approach requires a reliable phenomenological elasto-plastic constitutive model in which material behavior during the forming process is described. Copper alloy sheets, known for their ductility and strength, are commonly selected as terminal materials. Generally, sheet metals exhibit significant anisotropy in mechanical properties, and this phenomenon has not been sufficiently investigated experimentally for copper alloy sheets. Furthermore, the wire crimping process is conducted at higher velocities; therefore, the influence of the strain rate on the terminal material behavior has to be known. In this paper, the influence of the strain rate on the anisotropic elasto-plastic behavior of the copper alloy sheet CuFe2P is experimentally investigated. Tensile tests with strain rates of 0.0002 s−1, 0.2 s−1, 1 s−1, and 5.65 s−1 were conducted on sheet specimens with orientations of 0°, 45°, and 90° to the rolling direction. The influence of the strain rate on the orientation dependences of the stress–strain curve, elastic modulus, tensile strength, elongation, and Lankford coefficient was determined. Furthermore, the breaking angle at fracture and the inelastic heat fraction were determined for each considered specimen orientation. The considered experimental data were obtained by capturing the loading process using infrared thermography and digital image correlation techniques.
In this study, we performed a numerical simulation and experimental measurements on a steel circular patch welded structure to investigate the temperature and residual stress field distributions ...caused by the application of buried-arc welding technology. The temperature histories during the welding and subsequent cooling process were recorded for two locations, with the thermocouples mounted inside the plate close to the weld bead. On the upper surface of the welded model, the temperature-time changes during the cooling process were monitored using an infrared camera. The numerically calculated temperature values correlated well with the experimentally measured ones, while the maximum deviation of the measured and calculated temperatures was within 9%. Based on the numerical result analysis regarding circumferential and radial stresses after the completion of the welding process, it is concluded that both stresses are primarily tensile within the circular disk. Outside the disk, the circumferential stresses turn from tensile to compressive, while on the other hand the radial stresses disappear towards the ends of the plate.
In this study, a numerical simulation of a single pass welding of two thick-walled pipes with the buried-arc method was performed in order to determine the residual stresses caused by welding. The ...numerical simulation procedure in the thermal analysis was performed by the element birth and death method while the structural analysis was performed simultaneously, without the application of the element birth and death technique in order to reduce the duration of the numerical simulation. The simulation results were validated by experimental residual stress measurements on the outside surfaces of the welded model using the X-ray diffraction technique. A good agreement between the results of the numerical simulation and experimental measurements was confirmed.
In this study, numerical and experimental research of residual stresses was carried out on an I-profile structure model and welded by using the Metal-cored Arc Welding (MCAW) technique. The numerical ...research was carried out by sequential simulation, using the birth and death element in the thermal analysis, while the same was omitted in the mechanical analysis in order to speed up the calculation process. The measurement of residual stresses was conducted on the outer surfaces of the model at a depth of 0.015 mm below the surface. It was determined that the longitudinal stresses in the weld and its immediate surroundings are tensile, while towards the ends of the model, they change to compressive. Transversal residual stresses exist mainly around the weld itself, and the immediate surroundings and decrease towards the ends of the model. A high agreement between the numerical and experimental results was found.
The present study deals with the influence of residual stresses induced by the buried-arc welding on the crack behavior in two butt-welded 20 mm thick plates. The following steps were undertaken: the ...thermo-mechanical simulation of the welding process, the mapping of stress results from a finite element (FE) mesh used for the welding simulation to a new FE mesh with a crack, the stress balancing, and the stress intensity factor (SIF) calculation. The FE and weight function (WF) methods were used to investigate the SIFs at the deepest point of semi-elliptical surface cracks with different geometries, orientations, and positions in relation to the weld line. In the case of cracks perpendicular to the weld line, the FE and WF results showed a good agreement for smaller cracks, while deviation between the results increases with the size of the crack. Considering the SIF solutions for the cracks of arbitrary orientation, it was observed that for some cases, the SIF value for mode III of crack opening can be of significant influence.
In this work, the phase-field approach to fracture is extended to model fatigue failure in high- and low-cycle regime. The fracture energy degradation due to the repeated externally applied loads is ...introduced as a function of a local energy accumulation variable, which takes the structural loading history into account. To this end, a novel definition of the energy accumulation variable is proposed, allowing the fracture analysis at monotonic loading without the interference of the fatigue extension, thus making the framework generalised. Moreover, this definition includes the mean load influence of implicitly. The elastoplastic material model with the combined nonlinear isotropic and nonlinear kinematic hardening is introduced to account for cyclic plasticity. The ability of the proposed phenomenological approach to naturally recover main features of fatigue, including Paris law and Wöhler curve under different load ratios is presented through numerical examples and compared with experimental data from the author’s previous work. Physical interpretation of additional fatigue material parameter is explored through the parametric study.
Summary
The paper deals with the numerical simulation and experimental investigations of a buried‐arc welding process on a butt‐welded plate sample. In the numerical investigations, the finite ...element analysis is carried out by applying the element birth and death technique in the thermal analysis, while the mechanical analysis is performed simultaneously in one step to reduce simulation time. The temperature history at two locations is recorded with thermocouples, while residual stresses are measured by using the hole‐drilling stress relaxation method at four points. The heat input efficiency for the buried‐arc welding process is determined by using a parametric analysis. The numerically obtained temperatures and residual stresses correspond very well with the experimental measurements. Furthermore, by using buried‐arc welding, 73% of the weld filler material is saved and 59% of energy, whereas the CO2 emission to the atmosphere is reduced by 83% in comparison with conventional metal active gas welding for a model of the same dimensions.
Buried‐arc welding of thick plates is studied numerically and experimentally.
Numerical model for simulation of butt welding is proposed and validated.
Heat input efficiency factor is determined by employing parametric analysis.
Mesh sensitivity analysis is performed using submodeling technique.
Energy savings of 59% and CO2 emission reduction of 83% compared with conventional metal active gas (MAG) welding.
In this paper, a 3D phase-field model for brittle fracture is applied for analyzing the complex fracture patterns appearing during the Vickers indentation of fused silica. Although recent phase-field ...models for the fracture caused by the indentation loading have been verified by some simpler academic axis-symmetric examples, a proper validation of such models is still missing. In addition, heavy computational costs, and a complicated compression stress field under the indenter, which demands different energy decompositions, have been identified as the most important impediments for the successful application of the phase-field method for such problems. An adaptive strategy is utilized for reducing the computational costs, and some modifications are introduced, which enable an accurate simulation of the Vickers indentation fracture. Here, the fracture initiation ring outside the contact zone is detected by using different energy decompositions, and the dominant cone-crack formation under the Vickers indenter is observed. Different contact conditions are investigated. The proposed model is validated by experimental measurements, and a quantitative and qualitative comparison between experimental and numerical results is conducted.
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