Thermo-mechanical Simulation Model Research Articles

Heat Transfer and Structural Characteristics of Dissimilar Joints Joining Ti-64 and NiTi via Laser Welding

This study investigates the thermal-stress characteristics of a bi-metallic Ti-6Al-4V-Nitinol butt joints manufactured via laser welding. Particularly, the thermal profile along the weld interface and the deformation profile of the finished welded workpiece. A decoupled transient thermomechanical simulation model was constructed to recreate the welding process. This decoupled thermomechanical simulation model consisted of two transient simulation models. A transient thermal simulation model and a transient structural simulation model, with the thermal history of the transient thermal model being fed into the transient structural model. Both the thermal and structural portions of the model utilized temperature-dependent thermal and structural properties of Ti-6Al-4V and Nitinol. The temperature profile of the transient thermal-stress model aligns with the experimental thermal profile within 5% error. The deformation profile also matches the experimental results within 5% error. This approach to modeling laser welding can stand as a guide to predict both thermal and deformation profiles generated during the laser welding process.

Thermal Stress Characteristics of Dissimilar Joints Joining Ti-64 and CCM via Linear Friction Welding

Linear Friction Welding (LFW) is a unique welding process which enables dissimilar materials to be welded without filler material. In this study, bi-metallic Ti-64-CCM joints were manufactured utilizing LFW and subsequently analyzed. A coupled thermal-deformation model was created to accurately model both thermal and deformation profiles along the weld interface. Ti-64 and CCM stock were machined in accordance with ASTM standards for tensile testing. Temperature distribution of the two material surfaces were measured using an IR camera. Tensile testing was then performed to analyze weldability and bonding strength. A transient decoupled thermomechanical simulation model was generated to simulate the LFW process. The simulation model produced results within 5% error of both experimental results. The tensile testing results indicate that successful bonding of Ti-64 to CCM is possible for an oscillation amplitude of 2 mm under large forging pressure. The results also show that parameter optimization is essential for successful LFW, as the decrease in percent error from test set 1 to test set 4 was 62.5%. From the tensile testing and thermal data collected, it was concluded that bonding of Ti-64 to CCM via LFW is possible but further research into the necessary process parameters is needed.

Thermo elasto-plastic contact analyzis for high temperature applications

This study presents the development of a thermo-mechanical simulation model for an elastic-plastic contact problem between a half cylinder and a plane plate. The set of equations was solved using direct coupling method by ANSYS mechanical. The results obtained from the present numerical model of the structural contact without heat transfer are compared with those of analytical, experimental and other numerical models. Then, the contact problem was solved using a coupled thermo-mechanical model. Computational results showed significant effects of thermal consideration in the elastic-plastic contact problem. Large deformations of structure due to high temperature are predicted using the thermo-mechanical model with elastic-plastic deformations. This model is useful to predict deformations on the structural components due to contact at high temperature situation.

On the transient thermomechanical contact simulation for two sliding bodies with rough surfaces and dry friction

A transient thermomechanical contact model for two sliding bodies with rough surfaces is presented. The underlying equations are solved for mechanical, thermal and thermoelastic submodels from which dimensionless influence functions for a loaded rectangular element on a halfspace are derived. They can be used to calculate displacements, stresses as well as temperature distributions for arbitrarily shaped and time dependent heat sources or stress distributions on the surface. All formulas are verified by comparison to solutions from the literature. The submodels are afterwards combined into one thermomechanical simulation model by coupling the heat flux to the frictional power while avoiding the use of a prescribed friction coefficient. The solution process is described in detail. Calculations for two nominally flat but periodic rough surfaces with 256 × 128 elements are performed for a range of sliding velocities and indentations. Simulation results are discussed in particular with regard to the obtained transient friction coefficient.

Thermomechanical performance of carbon fiber reinforced polymer synchronizer friction liners

To improve the ability of a thermomechanical simulation model for carbon fiber reinforced polymer lined synchronizers to predict synchronization performance and reliability, temperature dependent material data for the specific carbon fiber reinforced polymer lining is needed. The compressive modulus, coefficient of thermal expansion, specific heat and thermal conductivity are determined experimentally. The effect of each material property on the focal surface temperature is analyzed, and it is shown that the compressive modulus has the largest influence for all analyzed load cases. Physical tests show that surface hot spots begin to appear at a simulated focal surface temperature of 200[Formula: see text]C, while performance degradation occurs at a simulated focal surface temperature of 230[Formula: see text]C–250[Formula: see text]C.

Reduced order modelling for spatial-temporal temperature and property estimation in a multi-stage hot sheet metal forming process

A concise approach is proposed to determine a reduced order control design oriented dynamical model of a multi-stage hot sheet metal forming process starting from a high-dimensional coupled thermo-mechanical model. The obtained reduced order nonlinear parametric model serves as basis for the design of an Extended Kalman filter to estimate the spatial-temporal temperature distribution in the sheet metal blank during the forming process based on sparse local temperature measurements. To address modeling and approximation errors and to capture physical effects neglected during the approximation such as phase transformation from austenite to martensite a disturbance model is integrated into the Kalman filter to achieve joint state and disturbance estimation. The extension to spatial-temporal property estimation is introduced. The approach is evaluated for a hole-flanging process using a thermo-mechanical simulation model evaluated using LS-DYNA. Here, the number of states is reduced from approximately 17 000 to 30 while preserving the relevant dynamics and the computational time is 1000 times shorter. The performance of the combined temperature and disturbance estimation is validated in different simulation scenarios with three spatially fixed temperature measurements.

The Thermomechanical Finite Element Analysis of 3003-H14 Plates Joined by the GMAW Process

The gas metal arc welding (GMAW) process was used to weld 3003-H14 plates under restricted and unrestricted thermal expansion. Experimental and numerical analysis were conducted to determine the relation between weld thermal cycles and residual stresses. A customized data acquisition system with K-type thermocouples was used to measure the weld thermal cycles, while residual stresses were determined by the hole drilling method. Thermo-mechanical simulation models for the two restricted conditions were implemented from the experimental data obtained. A double ellipse heat distribution geometry was used to model the heat moving source by using the finite element method. Thermal rates and peak temperatures were approximated by the finite element model with 2% difference, with respect to the experimental weld thermal cycles. Longitudinal and transverse normal residual stresses determined by the finite element model showed a good comparison with experimental measurements. The larger residual stresses were in the transverse direction for both clamping conditions, which indicated that working loading paths along the lateral direction of the welded plate are more influenced by the post-welding residual stresses.

Determination of process forces during remote laser beam welding for the design of fastening features

Welding of sheet metal structures in the automotive industry involves inflexible and expensive clamping devices to properly position and fasten the parts. The approach of feature-based fixturing can reduce fixtures in the joining process. It is based on part-inherent fastening features that realize the fixture functions. The proper design of these features requires knowledge of forces that result from the joining process and thus need to be compensated. For this paper, process forces were investigated during remote laser beam welding. This was achieved by using a thermomechanical simulation model. The aspects described in this paper are model build-up and validation, application of the approach to a real structure, and affiliated parameter studies. The studies show that required clamping forces depend, among other things, on the clamping condition and on the weld strategy. Finally, the simulation model allows for the design of fastening features to reduce joining fixtures in the automotive body shop.

Modeling of the thermally induced residual stresses during laser transmission welding of thermoplastics

Laser transmission welding is one of the various welding techniques used to join thermoplastics. Low heat introduction into the welded parts and a high welding speed are the reasons why laser transmission welding established itself in the plastic processing industry. In all welding processes for thermoplastics, residual stresses occur due to the thermal expansion during heating and its resetting during subsequent cooling. These thermally induced residual stresses impair the mechanical properties of the welded components. To estimate the residual stresses and therefore to improve the process setup and understanding of the welding process, a thermo-mechanical simulation model for the laser transmission welding is developed at the IKV. In a linked simulation, the temperature distribution and mechanical stresses are calculated parallelly for each time step. The material, a polyamide 6.6, is modeled with elastic, elastoplastic, and linear viscoelastic behavior. After cooling, residual stresses of a realistic magnitude are calculated. However, as the yield point of the polyamide is exceeded in the welding process, the tensile/compression ratio in the welded component is only mapped correctly for the elastic-plastic material model.

Finite element analysis of in-situ distortion and bulging for an arbitrarily curved additive manufacturing directed energy deposition geometry

With the recent rise in the demand for additive manufacturing (AM), the need for reliable simulation tools to support experimental efforts grows steadily. Computational welding mechanics approaches can simulate the AM processes but are generally not validated for AM-specific effects originating from multiple heating and cooling cycles. To increase confidence in the outcomes and to use numerical simulation reliably, the result quality needs to be validated against experiments for in-situ and post-process cases. In this article, a validation is demonstrated for a structural thermomechanical simulation model on an arbitrarily curved Directed Energy Deposition (DED) part: at first, the validity of the heat input is ensured and subsequently, the model’s predictive quality for in-situ deformation and the bulging behaviour is investigated. For the in-situ deformations, 3D-Digital Image Correlation measurements are conducted that quantify periodic expansion and shrinkage as they occur. The results show a strong dependency of the local stiffness of the surrounding geometry. The numerical simulation model is set up in accordance with the experiment and can reproduce the measured 3-dimensional in-situ displacements. Furthermore, the deformations due to removal from the substrate are quantified via 3D-scanning, exhibiting considerable distortions due to stress relaxation. Finally, the prediction of the deformed shape is discussed in regards to bulging simulation: to improve the accuracy of the calculated final shape, a novel extension of the model relying on the modified stiffness of inactive upper layers is proposed and the experimentally observed bulging could be reproduced in the finite element model.

Process forces during remote laser beam welding and resistance spot welding – a comparative study

Welding of sheet metal in the automotive industry involves inflexible and expensive joining fixtures to properly position and fasten the parts that are to be joined. Feature-based fixturing is an approach to reduce fixtures in the assembly process. The approach relies on part-inherent fastening features that realize the functions of positioning and fastening. The proper design of these fastening features requires knowledge of forces that result from the joining process and thus need to be compensated. This paper describes the investigation of process forces during remote laser beam welding and during resistance spot welding. This is achieved by using a thermo-mechanical simulation model and experimental studies. The comparison shows significant differences in process forces that result from the two different processes. Finally, the results allow for the design of fastening features to reduce joining fixtures in the automotive body shop.

Ordinal-Optimization-Based Framework for Optimization of Cooling Conditions for Reducing Distortion in Hot-Rolled Asymmetric Sections

Modeling and simulation tools are used increasingly to model thermo-mechanical processing of materials. Often these simulations are computationally expensive, and use of formal optimization tools to enhance product or process performance, or both, is practically infeasible in view of the large search space (variables), leading to a large number of function evaluations. Ordinal optimization (OO) adopts a different strategy compared to traditional optimization algorithms. It uses the “order” in the performances among designs, rather than the “value” and provides set of “good enough” solutions with a guarantee, instead of a unique best solution. It has been successfully applied to optimization of such computationally intensive problems. OO can be easily integrated with other optimization algorithms. OO’s integration with genetic algorithms (GA) leads to a hybrid algorithm called “genetic ordinal optimization” (GOO). It has better stopping criteria, along with a high probability of finding truly “good enough” design compared to the traditional GA. Cooling of asymmetric sections, post hot rolling, leads to a large distortion because of thermal gradients and phase transformations. Lengthwise distortions pose operational difficulties and challenges for post-rolling operations, including straightening. Here, a possible scheme of a sequence of forced convection cooling stages is considered in place of the traditionally used free convection on the cooling bed. In this work OO, GOO, and GA are applied to optimize the sequence of forced cooling for minimal distortion. A simplified regression model for distortion, built using results of a detailed thermo-mechanical simulation model, is used in the optimization loop. Results obtained show reduction in the distortion by a significant amount as compared to the natural convection cooling on the cooling bed. Besides providing a possible solution, this work also shows the efficacy of OO and GOO for application to industrial problems.

Linear creep and recovery analysis of ketchup–processed cheese mixtures using mechanical simulation models as a function of temperature and concentration

Full mechanical characterization of ketchup (K), processed cheese (PC), and K–PC mixtures was established to obtain internal structure of these samples using creep and recovery analysis along with oscillatory measurements. To simulate the viscoelastic behavior of these samples as a function of PC concentration and temperature, Burger model was successfully used to describe the effect of these factors. The effect of temperature on creep properties of K–PC mixtures was clearly explained by the Arrhenius relationship. Exponential model described better than the power-law model with respect to effect of concentration ranges; but for description of temperature ranges, the opposite was true. Remarkable changes in the mechanical properties of K–PC mixtures were determined using the thermo-mechanical simulation model, revealing that the PC and temperature levels could remarkably change the internal structure and deformation properties of the K–PC mixtures. The final percentage recovery also changed remarkably with concentration and temperature.

Numerical simulation and experimental investigation of temperature and residual stresses in GTAW with a heat sink process of Monel 400 plates

A 3D thermo-mechanical simulation model was developed to predict distributions of temperature and residual stresses during the gas tungsten arc welding (GTAW) process with a heat sink for Monel 400 plates using finite element method. The model was validated against the experimental measurements of both temperature and released strain in the welded plates. Effects of heat input, pipe diameter and water flow rate in the heat sink welding process were investigated. The results showed that in the GTAW process with a heat sink, the high temperature region was only limited to the vicinity of heat source and the maximum temperature of the sample was much lower than that of conventional GTAW process. This resulted in a lower residual stresses and even compressive stresses near the weld zone.

Response Surface Modeling for Nonlinear Packaging Stresses

The present study focuses on the development of reliable response surface models (RSM’s) for the major packaging processes of a typical electronic package. The major objective is to optimize the product/process designs against the possible failure mode of vertical die cracks. First, the finite element mode (FEM)-based physics of failure models are developed and the reliability of the predicted stress levels was verified by experiments. In the development of reliable thermo-mechanical simulation models, both the process (time and temperature) dependent material nonlinearity and geometric nonlinearity are taken into account. Afterwards, RSM’s covering the whole specified geometric design spaces are constructed. Finally, these RSM’s are used to predict, evaluate, optimize, and eventually qualify the thermo-mechanical behavior of this electronic package against the actual design requirements prior to major physical prototyping and manufacturing investments.