Fem Analysis of Residual Stresses in Welded Aluminum and Polyamide 6

Thermoplastic composites are growing in popularity in the aerospace and automotive industries; they enable weldable and recyclable structures. Resistance welded hybrid thermoplastic and metal joints are attractive for rapid assembly, but the thermal mismatch between metals and polymers introduces residual stresses, which can drive edge debonding and compromise durability. This study presents fabricated single-lap PC/CF–Al7075 coupons with measured mid-span bow resulting from welding, evaluated bond quality by step-heating thermography, and an evaluated framework for residual stress prediction using Ansys complemented by a bimetal analytical check. Three thermal cycles were examined with different temperature gradients (200, 220, 240 °C): the measured bow was 16.5 mm and remained constant, whereas analytical calculation increased with ΔT similarly to the FEM prediction. The current FEM under predicted the bow (Mean Absolute Percentage Error is 21%), showing stress contours that decay with distance from the bond and revealing pronounced peaks in both σxx and σzz components at weld edges, consistent with shear-lag theory. FEM returned edge-peaked peel rising from 43 to −64 MPa and σxx was up to 12% more compressive than analytical calculation; an effective CF/PC CTE of 1.5 × 10−6 K−1 reconciled curvature with test better than catalogue values. The temperature insensitive bow is attributed to polycarbonate flow/viscoelastic relaxation above Tg and hot relaxation in aluminum, with effects not represented in the elastic models. Edge peel and shear govern initiation risk.

In the present work, the prediction of residual stresses and distortion due to GTA welding process, a Finite Element (FE)Method has been developed and applied. Stainless steel plate of 3mm thickness is taken for the analysis. The prediction of residual stresses and distortion is performed by thermal and mechanical analysis that is sequentially coupled. The thermal analysis and mechanical analysis of the plate subjected to heat source movement have been studied consecutively. The FE analysis is performed in ANSYS software. In transient thermal analysis, Gaussian distribution model has been used for heat input of the arc. During modeling, the physical and mechanical properties that depend on temperature are considered. The heat transfer losses through all the three mechanisms are incorporated. For validating the FE simulated analysis, an experiment is conducted. The predicted thermal histories are very close agreement with measured thermocouple readings. After validation of thermal analysis results, the transient thermal histories are used as input for further mechanical analysis to simulate. The large displacement theory is used to conduct mechanical analysis. The effect of constraints on distortion and residual stresses are numerically studied. The predicted stresses and distortion results of different cases are discussed and presented.

The complicated steel wheel and rail interaction on curve causes side wear on rail head. Thus, the cost of maintenance for the track on curve is significantly higher than that for track on a tangent. The objective of this research is to develop 3D printing technology for repairing the side wear. In this paper, the study examines induced residual thermal stresses on a rail during the cooling down process after 3D printing procedure using the coupled finite volume and finite element method for thermal and mechanical analysis respectively. The interface of the railhead and additive materials should conserve high stresses to prevent any crack initiation. Otherwise, the additive layer would likely shear off the rail due to crack propagation at the rail/additive interface. In the numerical analysis, a cut of 75-lb ASCE (American Society of Civil Engineers) worn rail is used as a specimen, for which a three-dimensional model is developed. The applied residual stresses, as a result of temperature gradient and thermal expansion coefficient mismatch between additive and rail materials, are investigated. At the beginning, the worn rail is at room temperature while the additive part is at a high initial temperature. Then, additive materials start to flow thermal energy into the worn rail and the ambient. The thermal distribution results from thermal analysis are then employed as thermal loads in the mechanical analysis to determine the von-Mises stress distribution as the decisive component. Then, the effect of preheating on residual stress distribution is studied. In this way, the thermo-mechanical analysis is repeated with an increase in railhead’s initial temperature. In thermal analysis, the temperature contours at different time steps for both the non-preheated and preheated cases indicate that preheating presents remarkably lower temperature gradient between rail and additive part and also represents a more gradual cooling down process to allow enough time for thermal expansion mismatch alignment. In mechanical analysis, the transversal von-Mises stress distribution at rail/additive interface is developed for all cases for comparison purposes. It is shown that preheating is a key factor to significantly reduce residual stresses by about 40% at all points along transversal direction of interface.

A comparison of the fracture resistance of three machinable ceramics after thermal and mechanical fatigue

The thermal analysis of a rotary engine mechanism requires taking into consideration the transfer of heat from the combustion gas to the engine parts, which include rotating parts and fixed parts, as well as the transfer of heat to the environment. During an engine mechanism rotation, the conditions of convective heat transfer are variable, and the surfaces of fixed parts exposed to combustion gas are continuously changing. In this case, the transient thermal analysis using the finite elements method is very complex because of the permanent modification of surfaces covered with combustion gas, as a consequence of mechanism rotation. Therefore, in the current paper, an equivalent model for steady-state thermal analysis is developed, so that the same results are obtained as in the long transient thermal analysis, but with significantly smaller requirements of time and computational resources. The transient thermal analysis performed for a large number of rotations, which provides the stationary thermal conditions of mechanism parts, is compared with the equivalent steady-state thermal analysis performed using the equivalent film coefficients and the equivalent convection temperatures. The distributions of fixed part temperature and heat flux obtained from the steady-state thermal analysis are compared to those obtained from the transient thermal analysis, and very good similarities are ascertained. In conclusion, the equivalent steady-state thermal analysis provides similar results, compared with the transient thermal analysis, but with significantly lower computational effort.

The transient thermal and residual stresses in the metal-to-ceramic brazed joints were analysed by using the finite element method (FEM). The thermal and residual stresses which were induced mainly by the difference in the thermal expansion coefficients between the brazed materials were successively calculated. The high tensile residual stress occurred in the brazed joint interface, which has the potential to cause internal cracks in the brazed joints. In order to reduce the tensile residual stress in the brazed joint, the mechanical loading cycle was adopted during the brazing thermal cycle. The calculation results revealed that the tensile residual stress in the brazed ceramics can be reduced by the mechanical loading cycle and that the magnitude of the applied load and the temperature at which the mechanical loading cycle started greatly influence the reduction amount of the tensile residual stress. For a comparison of the simulation results, the residual stress in the brazed joints was measured by using the X-ray diffraction method. The results calculated by the FEM analysis showed a similar tendency to the results measured by the X-ray diffraction method. In the case of brazed joints with 0.1 mm thick filler metal, the residual stress in the ceramic part after the mechanical loading cycle showed a lower tensile stress compared to that of brazed joints without the mechanical loading cycle. The larger the applied load, the smaller was the tensile residual stress occurring in the metal-to-ceramic brazed joint.

R IGOROUS validation of computational tools places stringent demands on the accuracy of measured experimental data. This is increasingly the case in fluid dynamics, in which computational approaches havematured to the point at which certain propertiesmay be predicted to the same level of accuracy that can be measured. In such a situation, a discrepancy between computation and experiment cannot simply be assumed to lie exclusively in either the computational or experimental result. Rather, a thorough evaluation of both the computational and experimental techniques is required. Such is the case for perfect-gas wind-tunnel measurements of surface heat transfer for a simple body in an attached laminar flow. A standard technique for measuring the heat-transfer rate to a surface is via thermocouple instrumentation. The thermocouples may be subjected to an unknown heat flux for some period of time, and temperature histories may be obtained. This surface temperature history can then be used as a boundary condition in a transient thermal analysis from which the heat-transfer rate may be inferred. This technique is often employed in wind-tunnel tests that seek to quantify the aerothermodynamic environment for a given geometry. In such applications, the thermocouple instrumentation is typically too sparse to determine a true multidimensional surface temperature distribution, which could then be used in a three-dimensional thermal analysis. Consequently, the thermocouple temperature histories are often used in conjunction with a one-dimensional heat-transfer analysis, which only considers conduction normal to the surface. For geometries with regions of tight curvature and/or substantial lateral gradients in heat-flux distribution, the validity of the onedimensional assumption comes into question. This Note investigates the modeling error induced by the combined factors of lateral heat-flux distribution and multidimensional curvature for a specific geometry that was recently tested in the Arnold Engineering Development Center’s Hypervelocity Wind Tunnel no. 9. A purely analytical approach is used that combines steady computational fluid dynamics simulation, transient threedimensional thermal analysis, and the standard transient onedimensional thermal analysis technique to quantify the modeling error introduced through the data-reduction process for each gauge. The remainder of the Note is organized as follows: Section II provides an overview of the experimental test series that provides the motivation for this work, Sec. III describes the analytical approach used to predict the external convective heat-transfer and the transient thermal analysis, Sec. IV presents results for the specific case of a scaled Orion Crew Module model at wind-tunnel conditions, and some general conclusions are discussed in Sec. V.

An efficient transient three-dimensional thermomechanical modeling of dynamic thermal stress building and releasing in a selective laser melting process

The heat-transfer and thermal stress distributions in one-pass submerged arc welding (SAW) were numerically determined using the finite element method (FEM) for a V-grooved rectangular steel plate in which the weld preparation was filled during welding. A two-dimensional non-linear heat-transfer analysis was performed for a transverse section of the plate. This was followed by a thermo-elasto-plastic transient thermal stress analysis, assuming plane strain to be constant for the same model section. The same stress model was used to simulate a mechanical stress relief (MSR) treatment of the plate. This has frequently been used in the fabrication of large pressure vessels instead of post-weld heat treatment (PWHT). In this way its effect in reducing the residual stress in the welded plate was investigated. MSR was simulated by enforcing a constant displacement loading in the welding direction. The solution of the thermal stress analysis showed that it was possible for the residual stress around the weld centre to be accurately estimated by accurate modelling of the dilution of the filler metal in the fused zone of the base metal. The conclusion derived from the MSR simulation was that it could quantitatively predict the effect of reducing the residual stress in the welded plate. Only limited experimental data were available. The mechanism of stress reduction was plastic straining in regions of high residual stress. The amount of stress reduction at the weld centre had a linear relationship to the magnitude of the external stress relieving load. The numerical results for the MSR simulation agreed fairly well with experimental ones obtained from the MSR test performed on a welded plate.

In this paper, we analyze the bridge legs in which the largest deformation can be observed by conducting simulation via ANSYS tools and determine the membrane layer structure, which consists of one 0.1μm thick VOX thermal sensing layer and 7 other layers with thickness ratio 0.1μmSi3N4/0.3μmSiO2/0.1μmSi3N4/0.05μmNiCr/0.1μmSi3N4/0.3μmSiO2/0.1μmSi3N4. The stable and transient thermal simulation analysis of the microbridge is performed. From the stable thermal analysis of temperature field profile, the highest and lowest temperatures and the temperature heterogeneity of the bridge deck are 300.526K, 300.468K and 0.058K respectively. The thermal time constant 6.0ms is acquired from the transient thermal analysis, which can reach the requirement of 60fps frame rate. Moreover the joule heating effect is then examined, which has influence on temperature rise of bridge deck with 3V voltage applied between two legs. The highest temperature of bridge deck is 300.354K which is lower than 300.526K caused by thermal radiation. At last, the force simulation analysis of microbridge is performed, which is based on the forementioned thermal analysis, the largest deformation is 46.45nm, the largest equivalent stress is 2.503GPa.

Studied the transient thermal transfer analysis method due to a kind of supersonic ellipsoidal dome, which is a conformal dome. Illuminated the principle of transient thermal transfer analysis. Accomplished the transient thermal analysis based on the model of ellipsoidal dome, and studied the influence about the different material and the different velocity. Considered three materials consist of MgF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , and ZnS, and meanwhile, the velocity was Mach2.5, and the time consists of 10s, 20s and 60s. The temperature initial loads were from FLUENT thermal simulation. The thermal conduction analysis and the thermal convection analysis were finished in software ANSYS, in which the entire transient thermal analysis consists of modeling, meshing element, calculating and getting the results. The different temperature distributions based on varied time were gotten about the different materials. The results from analysis showed the temperature distribution of the structure of ellipsoidal dome, which could help the following coupled thermal-structure analysis.

Experimental and numerical study of residual stresses in 550 MPa high strength steel welded angle sections

Simulation of residual stress in thick thermal barrier coating (TTBC) during thermal shock: A response surface-finite element modeling

The thermal cycle at the interface due to spraying has been investigated through the finite element method and experiments of the thermal cycle. The experiments of spraying Al2O3 and 80% Ni-20% Cr powders on steel showed that the thermal cycle in the experiment was not similar to the numerical result. The thermal cycle in the experiment is dependent on the transfer function of the measuring instrument. The results of experiments on microstructure and residual stress at the vicinity of the interface suggest that the thermal cycle in the experiment is the average value of the region which is decided from the mode of the interval time between deposited powders. The experimentally obtained electron diffraction pattern indicates that the thermal cycle at the interface is similar to the thermal cycle obtained by the finite element method.

Thermal barriers made up by a ceramic top coating and a metallic bond coating are subjected to thermal cycles in service. The thermal stresses vary during the cycles and the residual stresses change as a result of plastic flow and creep. The stress state in thermal barrier coatings during a thermal cycle has been examined with a finite element method using temperature dependent material data. The calculated results were verified by measurements of the residual stresses with the layer removal technique before and after cycling of specimens heated in furnace with air environment. According to the simulation of a thermal cycle to 700 ° C, using a finite element method, the bond coat is approximately stress free after 1 hour dwell time. Thus, the residual stresses after a thermal cycle is a result of thermal expansion mismatch and temperature drop.