Thermo-mechanical Material Model Research Articles

Performance of Shape Memory Alloy Lead Rubber Bearing (SMA-LRB) Isolated Building Under Blast-Induced Ground Motion Considering Parametric Uncertainty

Blast-induced ground motions (BIGM) can cause significant damage to the structure, leading to loss of life and economy. Previous studies proposed the use of base isolation system to prevent such adverse effects of blast loading on the structures. This study explores the effect of parametric uncertainty on the performance of shape memory alloy-assisted lead rubber bearing (SMA-LRB) isolator for the vibration control of building, under the BIGM. Nonlinear time-history analyses are performed to estimation responses, and compared them with the LRB isolated building. The building is modeled as a linear system, and nonlinear force–displacement behavior of LRB and SMA has been modeled via Bouc–Wen model and thermo-mechanical material model. To identify the critical design parameters and study the effect of parameter uncertainty, sensitivity analysis and Monte Carlo (MC) simulation are performed. Study results reveal that, compared to LRB, SMA-LRB reduces the peak floor acceleration by 20% with an added benefit of 35% and 67% reduction in peak and residual isolator displacement. Parametric uncertainty causes noticeable increase in mean responses of LRB isolated system than deterministic case, which get diminishes for SMA-LRB isolation system. This increase in the mean value of peak floor acceleration, peak, and residual isolator displacement are 64%, 68%, and 60% less for SMA-LRB than LRB isolated building. Further, compare to the LRB, SMA-LRB reduces standard deviation by 77% for the peak floor acceleration and peak isolator displacement, and 85% for the isolator residual displacement. Thus, conjunction of SMA with the LRB isolator enhances the performance and provides robust control effect under parameter uncertainty.

Energy related thermomechanical material model validation in complex tensile testing with self heating

AbstractThe objective of this work is the application of viscoplastic material models in a consistent thermomechanical framework to make use of infrared thermography as one source of a phenomenological model validation. The thermomechanical foundation led to the understanding, that each mechanical deformation can be analysed as a thermodynamical process. The usual balance equations applied in a mechanical process are completed by the first and second law of thermodynamics. In this setup, the classical stress‐strain characteristics is accompanied by the temperature evolution and the evolution of derived quantities such as the energy resp. energy‐rate transformation ratio (ETR). These three characteristics combined can improve the assessing procedure of the investigated deformation load path qualitatively as well as quantitatively. The initial boundary value problem of the coupled displacement and temperature fields is experimentally well supported by a high‐resolution infrared camera. A reduced thermal boundary value control simplifies the experimental measures to be realised. It is shown in the analysis, that the attained surface temperature accuracy is well‐suited for the identification of model parameters related to dissipative deformation phenomena. The common split into different fractions of free energy allows a detailed evaluation in terms of hardening related stored energy and other derived state entities. The potential of the instantaneous rate of energy storage is with respect to the comparability of different modelling approaches explained and is illustrated by experimental results. As a further consequence, a more complex tensile testing regime is proposed to validate the applied material model for metals.

Improvement of warpage prediction through integrative simulation approach for thermoplastic material

In the injection-molded parts, prediction of accurate warpage at initial level becomes mandatory to avoid iterative work of mold modifications. Simulation teams of many organizations are using existing commercial programs for process simulations. Material models in existing simulation technologies are having certain limitations and assumptions, which can regularly result in up to 50% variation of warpage results as compared to the actual physical warpage measurement. The commonly used Moldflow simulation model, for example, ignores temperature-dependent mechanical properties and the stress relaxation spectrum for viscoelastic materials. These assumptions affect the accuracy of the warpage prediction results significantly. To decrease these kinds of variations, BASF extended its Ultrasim® tool which is based on integrative simulation technology. Recently, a newly developed thermomechanical material model with temperature-dependent nonlinear mechanical properties and stress relaxation behavior was added in the Ultrasim. This model has been used in this work to consider the complete transient description of the warpage, which starts at packing phase of the part inside the mold, followed by actual cooling and ejection. In this article, unreinforced semicrystalline polybutylene terephthalate polymer material (Ultradur® B4520) is considered for warpage correlational study. The accuracy of the warpage prediction is compared between the integrative simulation approach, existing warpage simulation method, and the actual experimental inspection results. The result exhibits that the accuracy of the integrative simulation (Ultrasim)-based warpage simulation is relatively better than existing simulation technologies and closer to the actual measurement.

A thermo-mechanical material model for rubber curing and tire manufacturing simulation

In this contribution, the phase change of unvulcanized to vulcanized rubber is described by a thermo-mechanical material model within the finite element method (FEM) framework. Before the vulcanization process (curing), rubber exhibits an elasto-visco-plastic behaviour with significant irreversible deformations without a distinct yield surface. After exposing rubber to high temperature, the molecular chains build-up crosslinks among each other and its mechanical behaviour changes to stiffer viscoelastic material. The proposed model assumes, that both phases are present during the vulcanization process. The ratio changes from the uncured phase at the beginning to the cured phase according to the current state of cure. A constitutive curing formulation is introduced into the model, to capture the shape change during the vulcanization and to ensure, that the second law of thermodynamics is fulfilled. A multiplicative split of the deformation gradient is assumed to describe incompressible material. Thermal expansion due to the change of temperature is taken into account in the volumetric part, as well as shrinkage during the vulcanization process. In the isochoric part, the phase change from elasto-visco-plastic to viscoelastic material is described by micro-macro transition based on the micro-sphere model. The consistent formulation of the material model and its tangent are important for a successful implementation into a three-dimensional finite strain FEM framework. The capabilities of the model are shown by the simulation of an axisymmetric tire production process starting at the green tire inserted into the heating press up to a post-cure inflation step.

Modelling multiple cycles of static and dynamic recrystallisation using a fully implicit isotropic material model based on dislocation density

This paper presents the development and numerical implementation of a state variable based thermomechanical material model, intended for use within a fully implicit finite element formulation. Plastic hardening, thermal recovery and multiple cycles of recrystallisation can be tracked for single peak as well as multiple peak recrystallisation response. The numerical implementation of the state variable model extends on a $$J_{2}$$ isotropic hypo-elastoplastic modelling framework. The complete numerical implementation is presented as an Abaqus UMAT and linked subroutines. Implementation is discussed with detailed explanation of the derivation and use of various sensitivities, internal state variable management and multiple recrystallisation cycle contributions. A flow chart explaining the proposed numerical implementation is provided as well as verification on the convergence of the material subroutine. The material model is characterised using two high temperature data sets for cobalt and copper. The results of finite element analyses using the material parameter values characterised on the copper data set are also presented.

Thermomechanical modeling of fiber reinforced material including interphasial properties and its application to epoxy/glass composites

Purpose – The purpose of this paper is to investigate of interphasial effects, including temperature dependency, within fiber reinforced polymers on the overall composite behavior. Providing theoretical and numerical approaches in terms of a consistent thermomechanical finite element method framework are further goals of this research. Design/methodology/approach – Starting points for achieving the aims of this research are the partial differential equations describing the evolution of the displacements and temperature within a continuum mechanical setting. Based on the continuous formulation of a thermomechanical equilibrium, constitutive equations are derived, accounting for the modeling of fiber reinforced thermosets and thermoplastics, respectively. The numerical solutions of different initial boundary value problems are obtained by a consistent implementation of the proposed formulations into a finite element framework. Findings – The successful theoretical formulation and numerical modeling of the thermoinelastic matrix materials as well as the thermomechanical treatment of the composite interphase (IP) are demonstrated for an epoxy/glass system. The influence of the IP on the overall composite behavior is successfully investigated and concluded as a further aspect. Originality/value – A thermomechanical material model, suitable for finite thermoinelasticity of thermosets and thermoplastics is introduced and implemented into a novel kinematic framework in context of the inelastic deformation evolution. The gradually changing material properties between the matrix and the fiber of a composite are continuously formulated and numerically processed, in order to achieve an efficient and realistic approach to model fiber reinforced composites.

THERMO-MECHANICAL ANALYSIS OF CYCLICALLY LOADED PARTICLE-REINFORCED ELASTOMER COMPONENTS: EXPERIMENT AND FINITE ELEMENT SIMULATION

ABSTRACT Elastomer components are often subjected to periodic loading conditions during service. Elastomer parts are used because of their large extensibility and significant damping characteristics, where the latter originate from inelastic material features. Combined with cyclic loading conditions, the inelastic properties of the material yield mechanical energy dissipation, its transformation to thermal energy, and heat buildup in the elastomer component. The experimental and numerical understanding of the thermo-mechanical coupling of elastomers is a prerequisite to predict the temperature rise in elastomer components. In this contribution, experimental and numerical investigations on cyclically loaded dumbbell-shaped elastomer components are addressed. A thermo-mechanical material model representing finite nonlinear viscoelasticity and a temperature- and deformation-dependent heat capacity is used within the finite element method to compute the heat buildup in the dumbbell-shaped elastomer components. The simulation results (surface temperature evolution) for three different loading frequencies are compared with experimental data.

Finite element simulations of microstructure evolution in stress-induced martensitic transformations

Microstructure evolution in single crystal and polycrystal shape memory alloys under uniaxial tension and compression is investigated using the finite element method. To determine stress-strain diagrams and evolution of martensitic microstructure during external loading, a micromechanics based thermo-mechanical material model is used. The results reveal the significant difference between the local and global material behavior when defects are present. It is shown that defects act as nucleation sites and result in transformation localization, which in turn causes a sudden drop in the stress-strain diagram followed by a stress plateau. Moreover, it is found that some regions undergo reverse transformation although the elastic moduli of the phases are equal and the loading is monotonic. Increase in athermal friction, which is the resistance to interface propagation, is found to delay the phase transformation and different magnitudes of hysteresis are obtained at different friction values. The model predicts the tension-compression asymmetry observed in shape memory alloys. The simulation results are in qualitative agreement with several experimental studies.

Tool thermal conditions for tailored material properties

Abstract With the press hardening technology it is possible to produce components with tailor- made material properties. The present work is based on a comprehensive thermo-mechanical material model for simulation of press hardening and similar processes. The model accounts for and predicts time dependent and time-independent phase transformations, mechanical and thermal properties as well as transformation plasticity during the complete cooling and deformation process from 900 °C to room temperature. The model predicts the microstructure evolution during the complete process as well as the final fractions. The thermal contact properties and the thermal properties in the tools have influence on the final material state. Solutions for tool heating and cooling for manufacturing of components with soft zones are studied. Based on the results from the press hardening simulations, thermal properties of special tool materials are taken into account in order to optimise the manufacturing thermal cycle.

Modelling and Characterization of Ultrasonic Consolidation Process of Aluminium Alloys

ABSTRACTUltrasonic consolidation process is a rapid manufacturing process used to join thin layers of metal at low temperatures and low energy consumption. In this work, finite element method has been used to simulate the ultrasonic consolidation of Aluminium alloys 6061 (AA-6061) and 3003 (AA-3003). A thermomechanical material model has been developed in the framework of continuum cyclic plasticity theory which takes into account both volume (acoustic softening) and surface (thermal softening due to friction) effects. A friction model based on experimental studies has been developed, which takes into account the dependence of coefficient of friction upon contact pressure, amount of slip, temperature and number of cycles. Using the developed material and friction model ultrasonic consolidation process has been simulated for various combinations of process parameters involved. Experimental observations are explained on the basis of the results obtained in the present study. The current research provides the opportunity to explain the differences of the behaviour of AA-6061 and AA-3003 during the ultrasonic consolidation process. Finally, trends of the experimentally measured fracture energies of the bonded specimen are compared to the predicted friction work at the weld interface resulted from the simulation at similar process condition. Similarity of the trends indicates the validity of the developed model in its predictive capability of the process.

Thermomechanical model and temperature measurements for shocked ammonium perchlorate single crystals

A consistent thermomechanical material model was developed for unreacted ammonium perchlorate (AP) single crystals for shock compression normal to the (210) and (001) crystal planes. Building on previous work, the mechanical response for both orientations was described using a single isotropic elastic-plastic model and an overstress model to describe rate-dependent yielding. Velocity interferometer measurements to 12 GPa were performed to extend the AP Hugoniot curve to higher stresses. The specific heat cv, the coefficient of thermal pressure (∂P/∂T)V, and the isothermal bulk modulus BT were determined from Hugoniot and isothermal compression curves, along with available data at atmospheric pressure. Time-resolved Raman spectroscopy experiments were carried out under stepwise loading to obtain temperatures in the shocked state. Calculated temperatures using our material model are in good agreement with the temperatures obtained from our experiments, thus providing validation for our modeling approach.