Thermomechanical Loading Conditions Research Articles

Numerical implementation of a crystal plasticity model with dislocation transport for high strain rate applications

This paper details a numerical implementation of a single crystal plasticity model with dislocation transport for high strain rate applications. Our primary motivation for developing the model is to study the influence of dislocation transport and conservation on the mesoscale response of metallic crystals under extreme thermo-mechanical loading conditions (e.g. shocks). To this end we have developed a single crystal plasticity theory (Luscher et al (2015)) that incorporates finite deformation kinematics, internal stress fields caused by the presence of geometrically necessary dislocation gradients, advection equations to model dislocation density transport and conservation, and constitutive equations appropriate for shock loading (equation of state, drag-limited dislocation velocity, etc). In the following, we outline a coupled finite element–finite volume framework for implementing the model physics, and demonstrate its capabilities in simulating the response of a [1 0 0] copper single crystal during a plate impact test. Additionally, we explore the effect of varying certain model parameters (e.g. mesh density, finite volume update scheme) on the simulation results. Our results demonstrate that the model performs as intended and establishes a baseline of understanding that can be leveraged as we extend the model to incorporate additional and/or refined physics and move toward a multi-dimensional implementation.

Thermomechanical postbuckling of thick FGM plates resting on elastic foundations with tangential edge constraints

This paper investigates the effects of tangential edge constraints and elastic foundations on the buckling and postbuckling behavior of thick FGM rectangular plates resting on elastic foundations and subjected to thermal and thermomechanical loading conditions. Material properties are assumed to be temperature dependent, and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of constituents. Governing equations are based on the higher order shear deformation plate theory incorporating the von Karman geometrical nonlinearity, initial geometrical imperfection, tangential edge constraints and Pasternak type elastic foundations. Approximate solutions are assumed to satisfy simply supported boundary conditions and Galerkin procedure is applied to derive expressions of buckling loads and load-deflection relations. In thermal postbuckling analysis, an iteration algorithm is employed to determine critical buckling temperatures and postbuckling temperature-deflection equilibrium paths. The separate and simultaneous effects of tangential edge restraints, elastic foundations and temperature dependence of material properties on the buckling and postbuckling responses of higher order shear deformable FGM plates are analyzed and discussed.

Free-Edge Interlaminar Stresses in Angle-Ply Laminates: A Family of Analytic Solutions

A family of analytic solutions for the prediction of interlaminar stresses in angle-ply laminates has been developed and is presented in a unified form and as a unique set of solutions. The uniqueness of the formulation is demonstrated for the class of thermomechanical states of deformation for which the solutions are valid. These are shown to be limited to the specific cases wherein only two in-plane stress components and one interlaminar stress components are nonzero. Interlaminar shear stress in the angle-ply laminate subjected to thermomechanical loading conditions of uniaxial extension, uniform temperature change, and anticlastic bending is shown to make up the family of solutions in the unified formulation. Further, these are shown to comprise the complete set of the solutions and the conditions which control the limitations of this family of solutions are articulated.

Mechanical response of fine grained Ti2AlC under extreme thermo-mechanical loading conditions

An experimental investigation was conducted to evaluate the compressive constitutive behavior and fracture initiation toughness of fine grained (∼4.2μm) Ti2AlC in dynamic and quasi-static loading at different temperatures. A Split Hopkinson Pressure Bar (SHPB) apparatus was used in conjunction with an induction coil heating system for dynamic experiments at elevated temperatures, while a universal mechanical testing machine equipped with an extensometer and furnace was used for quasi-static compressive testing. A series of experiments were conducted at different temperatures from 25°C to 1200°C and strain rates of 10−4s−1 and 500s−1. A single edge notched specimen was used to determine the fracture initiation toughness in dynamic and quasi-static loading from ambient temperature to 900°C. The SHPB apparatus was modified for this purpose and high speed photography was incorporated to determine fracture initiation time, and the load corresponding to this time was used to calculate the dynamic fracture toughness. The results of this study reveal that the peak compressive failure stress in dynamic conditions decreases with increasing temperature, from 1600MPa at room temperature to 850MPa at 1200°C. In the dynamic testing condition, the failure remains predominately brittle even at temperatures as high as 1200°C. Under static loading conditions, the peak compressive stresses were always lower than those in dynamic loading conditions, but they also decreased monotonically with increasing temperature. Also under static conditions, a significant drop in peak compressive failure stress and an increase in ductility was observed above the brittle-to-plastic transition temperature of around 900°C. The fracture experiments reveal that the strength and fracture toughness in dynamic conditions are higher than the corresponding quasi-static values by approximately 35% at room temperature and that they both decrease with increasing temperatures. It was found that high temperature and low strain rate promote plastic behavior of Ti2AlC.

Estimation of the structural integrity of a runway repaired by compliant polymer concretes under thermomechanical loading conditions

When repair materials are applied for runway maintenance, possible material failures due to the differences in material properties and excessive shrinkage of the repair material needs to be investigated. Moreover, the repair part is subjected to various mechanical loadings, which should be taken into account for determining the best repair material. In this study, we investigate a real-time in-situ health monitoring system, which is composed of two Fiber Bragg Grating (FBG) optic sensors, to monitor the strain variations that are induced by environmental conditions and material shrinkage. The repair process with compliant polymer concrete (72:20:08(T)) was carried out at the Gimpo international airport (Korea) during the summer season. To consider the effect of mechanical loading on stress distribution in the materials, several dynamic analyses are also carried out by using the finite element analysis method. Based on the results, the feasibility and reliability of the health monitoring system using FBG optic sensors are verified.

Simulating Microstructure Evolution of Ultrasonic Welding of Battery Tabs

Ultrasonic welding offers ability to weld thin layers of malleable metals at low temperature and low power consumption. During ultrasonic welding, intensive material interactions occur due to the severe plastic deformation (SPD) and frictional heat generation, which leads to the microstructural change. Different grain microstructures have been observed after different ultrasonic welding conditions. Theory of the microstructural evolution was for the first time hypothesized as three regimes, namely SPD, dynamic recrystallization (DRX) and grain growth according to the material thermomechanical loading conditions. A novel metallo-thermo-mechanically coupled model was developed to model the temperature-dependent mechanical deformation and microstructural evolution during the ultrasonic spot welding process. The numerical analysis was carried out with a three-dimensional (3D) finite element model using DEFORM 11.0. The material constitutive model considered cyclic plasticity, thermal softening and acoustic softening. Dynamic recrystallization and grain growth kinetics laws were applied to simulate the microstructural evolution under different welding time durations. The simulation results demonstrated that the essential characteristics of the deformation field and microstructure evolution during ultrasonic welding were well captured by the metallo-thermo-mechanically coupled model. The numerical framework developed in this study has been shown to be a powerful tool to optimize the ultrasonic welding process for its mechanical properties and microstructures.

Analysis of influence of fibre type and orientation on dynamic properties of polymer laminates for evaluation of their damping and self-heating

Abstract In the following study, the dynamic behaviour of polymer laminates reinforced by glass and carbon fibres with different orientations was considered for several excitation frequencies and elevated temperatures. The obtained dynamic moduli, loss factors and glass-transition temperatures were used for the evaluation of damping capabilities and the self-heating phenomenon. In order to evaluate the influence of a fibre type, additional studies for a pure matrix were carried out and used in the analysis as the reference. The obtained results show significant differences both in thermal and dynamic mechanical properties with respect to a fibre type and its orientation, which has a direct influence on the analysed self-heating and damping phenomena. The results of the present study could be used for the design of composite properties with respect to thermal degradation resulting from coupled thermomechanical loading conditions. Several hypotheses on the influence of a heating rate on estimation of the thermomechanical properties as well as structural degradation of composites in such conditions were presented with appropriate discussion and argumentation. The present study has a preliminary character. Furthermore, it is planned to perform such tests for specimens with a low cross-linking degree in order to analyse its influence on the resulting thermomechanical response of fibre-reinforced composite structures.

Mechanical integrity of a carbon nanotube/copper-based through-silicon via for 3D integrated circuits: a multi-scale modeling approach

Carbon nanotube (CNT)/copper (Cu) composite material is proposed to replace Cu-based through-silicon vias (TSVs) in micro-electronic packages. The proposed material is believed to offer extraordinary mechanical and electrical properties and the presence of CNTs in Cu is believed to overcome issues associated with miniaturization of Cu interconnects, such as electromigration. This study introduces a multi-scale modeling of the proposed TSV in order to evaluate its mechanical integrity under mechanical and thermo-mechanical loading conditions. Molecular dynamics (MD) simulation was used to determine CNT/Cu interface adhesion properties. A cohesive zone model (CZM) was found to be most appropriate to model the interface adhesion, and CZM parameters at the nanoscale were determined using MD simulation. CZM parameters were then used in the finite element analysis in order to understand the mechanical and thermo-mechanical behavior of composite TSV at micro-scale. From the results, CNT/Cu separation does not take place prior to plastic deformation of Cu in bending, and separation does not take place when standard thermal cycling is applied. Further investigation is recommended in order to alleviate the increased plastic deformation in Cu at the CNT/Cu interface in both loading conditions.

Influence of process-induced microstructure on hardness of two Al–Si alloys

This paper analyses the influence of thermal-induced aging on the strength of cast A319 and A356 aluminum alloys. This phenomena is of primary importance especially in the automotive industry, where on one hand the alloys experience Thermo-Mechanical and Low Cycle Fatigue loading conditions and on the other hand their microstructure is induced both by the manufacturing process and the thermal histories. The alloys studied here were produced using an industrial Lost Foam Casting process which affects significantly the microstructure and the precipitation compared to standard Die Casting process. The paper compares mechanical properties of these peculiar alloys in terms of microhardness at the macroscopic level as a function of thermal overaging time and at the microscopic level in terms of properties of the different phases (intermetallics, eutectics) present in the microstructure. Important differences can be observed between these different phases and the results are consistent with similar studies from the literature on different aluminum alloys and processes.

Thermal Stress Analysis of an Embedded Crack in a Graded Orthotropic Coating-Substrate Structure

An analysis of a coupled plane thermoelastic problem for a graded orthotropic coating-substrate structure is performed under thermomechanical loading conditions. The crack direction is parallel to the free surface. Applying the superposition principle and Fourier integral transform, the heat conduction and plane elasticity equations lends themselves to the derivation of two sets of Cauchy-type singular integral equations. The thermal stress intensity factors are defined and evaluated. In the numerical results, the effects of the orthotropy parameters, thermoelastic non-homogeneity parameters, and dimensionless thermal resistance on the temperature distribution and the thermal stress intensity factors (TSIFs) are studied. The obtained results can be used to design graded orthotropic coating-substrate structures under thermomechanical loading.

Dynamic fracture and local failure mechanisms in heterogeneous RDX-Estane energetic aggregates

Local failure initiation mechanisms, such as the nucleation and propagation of multiple cracks, have been investigated in energetic aggregates with a viscoelastic estane binder and crystalline RDX grains that have been subjected to dynamic thermo-mechanical loading conditions. A dislocation density-based crystalline plasticity, finite viscoelasticity, dynamic fracture nucleation and propagation, and non-linear finite-element formulations were used to study crack nucleation and propagation due to dynamic, tensile mechanical strain-rate loading conditions in RDX-Estane energetic aggregates. The interrelated effects of grain boundary (GB) misorientations, porosity, grain morphology, dislocation densities, polymer binder relaxation, and crystal-binder interactions were coupled with adiabatic plasticity heating, thermal decomposition, and viscous dissipation heating to fundamentally understand and predict aggregate behavior and local failure initiation mechanisms. The predictions indicate that local failure occurs when cracks nucleate at the peripheries of internal porosity and subsequently propagate toward the viscoelastic estane binder where crack arrest occurs at the interface, which results in large inelastic deformations and temperature accumulations at the interfaces.

Assessing the performance characteristics and clinical forces in simulated shape memory bone staple surgical procedure: The significance of SMA material model

This work is focused on the detailed computer simulation of the key stages involved in a shape memory alloy (SMA) osteosynthesis bone stapling procedure. To this end, a recently developed three-dimensional constitutive SMA material model was characterized from test data of three simple uniaxial-isothermal-tension experiments for powder metallurgically processed nickel-rich NiTi (PM/NiTi-P) material. The calibrated model was subsequently used under the complex, thermomechanical loading conditions involved in the surgical procedure using the body-temperature-activated PM/NiTi-P bone staple. Our aim here is to assess the immediate and post-surgical performance characteristics of the stapling operation using the material model. From this study: (1) it was found that adequate compressive forces were developed by the PM/NiTi-P bone staple, with the tendency of this force to even increase under sustained thermal loading due to the intrinsic “inverse relaxation phenomena” in the SMA material, (2) the simulation results correlated well with those from experimental measurements, (3) the body-temperature-activated PM/NiTi-P staple was proved to be clinically viable, providing a stable clamping force needed for speedy coaptation of the fractured bones, and (4) these realistic assessments crucially depend on the use of suitable and comprehensive SMA material models.

Heterogeneous thermo-mechanical behavior and hot spot formation in RDX–estane energetic aggregates

Hot spot formation has been investigated in energetic aggregates with a viscoelastic binder and crystalline grains that has been subjected to dynamic thermo-mechanical loading conditions. A dislocation-density based crystalline plasticity, finite viscoelasticity, and specialized finite-element formulations were used to predict hot spot formation due to dynamic thermo-mechanical loading conditions in RDX–estane energetic aggregates. The interrelated effects of grain boundary (GB) misorientations, porosity, grain morphology, dislocation densities, polymer binder relaxation, and crystal–binder interactions were coupled with adiabatic plasticity heating, thermal decomposition, viscous dissipation heating, and thermal conduction to analyze aggregate behavior and hot spot formation. The predictions indicate that hot spot formation occurs when temperatures become unbounded in localized regions at the peripheries of RDX crystals where RDX–estane interfacial incompatibilities result in crystal sliding and localized plastic deformation at RDX crystal edges and interfaces.

Numerical modelling and experimental characterization of temperature-dependent viscoelastic effect on the ferroelastic behaviour of 1–3 piezocomposites

The objective of this work is to study the effect of viscoelastic matrix in 1–3 type piezocomposite subjected to thermo-mechanical (compressive) loading condition. Experiments are performed to understand the time-dependent (viscous) behaviour of 1–3 piezocomposites subjected to a uniaxial compressive stress applied along the fibre direction for various loading rate at an elevated ambient temperature. The measured electric displacement and longitudinal strain on piezocomposites subjected to mechanical loading, show a non-linear behaviour (ferroelastic switching). In order to predict the time-dependent behaviour, a thermodynamic based micro-mechanical model has been developed and incorporated into a 3D finite-element framework. The homogenized temperature-dependent effective properties of 1–3 piezocomposites are evaluated based on representative volume element (RVE) approach. The predicted thermo-electro-elastic effective properties are incorporated into the developed micromechanical model, and the simulated results are compared with the experimental observations. It is observed that the polymer matrix, and the elevated ambient temperature exhibit a strong influence on the time-dependent ferroelastic response of 1–3 piezocomposites.

Modeling and simulation of the thermo-mechanical response of NiTi-based Belleville springs

Nickel–titanium (NiTi) Belleville washers exhibit unique mechanical and functional features due to the reversible stress-induced and/or thermally induced phase transition mechanism of NiTi alloys. In this article, the thermo-mechanical response of such washers has been analyzed by finite element simulations as well as by a special semi-analytical model, which is based on a modified literature approach. The effects of the geometrical configuration of the washers as well as of different thermo-mechanical loading conditions, under stress-induced phase transformation regime, have been analyzed. The results highlighted a marked hysteretic response, in terms of force–deflection curve, due to the hysteresis in the stress–strain behavior of NiTi alloys. In addition, a marked influence of the geometry, as well as of the temperature, has been observed on the thermo-mechanical response of the washer.

On the modeling of the thermo-mechanical responses of four different classes of NiTi-based shape memory materials using a general multi-mechanism framework

The properties of a shape memory alloy (SMA) have been shown to be highly dependent on the chemical composition and thermo-mechanical processing applied to the material. These differences dictate the degree of superelasticity, pseudoplasticity, shape memory effect, and evolution under mechanical/thermal loading cycles, that is observed in the material. Understanding and utilizing these unique phenomena has become essential in many engineering applications. It is, therefore, important to provide two key ingredients in any SMA constitutive model; (i) a sufficiently comprehensive scope in the mathematical formulation to handle different classes of SMA materials; and (ii) a general model parameterization derived from fundamental tests that can be used for a specific SMA as intended for use in a given application. The present work is aimed at a detailed investigation of the interaction aspects between the above items (i) and (ii) in the context of using a recent three-dimensional, multimechanism-based SMA framework to model the experimentally measured responses of four different classes of SMA materials: (a) a commercial superelastic NiTi, (b) a powder metallurgically-processed NiTi-based SMA material, (c) a commercial Ni49.9Ti50.1 actuation material, and (d) a high-temperature Ni50.3Ti29.7Hf20 alloy. To facilitate the parameterization task, the model parameters are classified into two groups, i.e., (1) fixed parameters that are designed to capture the non-linear, hysteretic response under any thermo-mechanical loading condition, and (2) a set of functionally dependent material parameters which account for a number of refinements including asymmetry in tension and compression responses, temperature- and stress-state dependencies, etc. The results of the work showed that the complexity of the characterization is dependent on the SMA feature exploited by the specific application intended, which in turn dictates the amount and type of test data required to accurately predict a given application response.

Thermodynamic gradient-based poroplastic theory for concrete under high temperatures

Concrete materials subjected to long term exposures to high temperatures suffer severe degradations in its mechanical properties (cohesion, friction, strength and stiffness) and changes in their failure mechanisms. These degradations may lead to irreversible damage or sudden collapse of the related structures. From the predictive analysis stand point, accurate constitutive theories are required to simulate the variations of concrete mechanical failure behavior under high and durable temperature fields. In the realm of the smeared crack approach, non-local model strategies are required to objectively reproduce failure behaviors under coupled thermo-mechanical loading conditions, while realistic descriptions of the involved characteristic lengths are needed to objectively reproduce the variation from ductile to brittle failure modes depending on the acting confining pressure and temperature. In this work, a thermodynamically consistent gradient poroplastic model for concrete subjected to high temperatures is proposed. A particular and simple form of gradient-based poroplasticity is considered whereby the state variables are the only ones of non-local character. The degradations of these variables due to coupled thermo-mechanical effects are described in the framework of the thermodynamic approach. After describing the material formulation, numerical analyses are presented which demonstrate the predictive capabilities of the proposed constitutive theory for different stress paths and thermal conditions.

In situ determination of internal stresses in mixed ceramic cutting tools during friction testing using synchrotron radiation

In order to get a better understanding of wear mechanisms in cutting tool materials, the internal stress states caused by complex external thermo-mechanical loads during cutting processes should be investigated. This can be done using in situ X-ray diffraction with high energy synchrotron radiation. For this reason, in first model tests, the strain state in ceramic cutting tool materials (Al2O3–Ti(O,C)) for hard turning applications is determined during friction testing. An experimental set-up is presented which allows the measurement of lattice strain tensor components in the major phases of the mixed ceramic material under a two-dimensional loading condition during friction. Results show that during friction almost no lattice strains in lateral direction can be measured due to strain compensation. In contrast, in normal direction, lattice strains increase due to the addition of strains. Stress tensor components are calculated from lattice strains and show higher internal stress states for Ti(O,C) than for Al2O3 due to a higher Young’s modulus of Ti(O,C). The set-up represents a major step forward towards future in situ characterization of internal stress states in cutting tool materials exposed to complex thermo-mechanical loading conditions during cutting processes.

Material Modelling and Lifetime Prediction of Ni-Base Gas Turbine Blades under TMF Conditions

Under cyclic thermomechanical loading conditions, various damage mechanisms such as strain accumulation, creep cavitation, ageing, fatigue surface cracking etc. may take place in the material of a gas turbine blade. Depending on the loading conditions, all these effects can contribute to reduce the lifetime of the component. Subject of the present work is the development of a material model to describe the mechanical effects mentioned above, as well as the development of a lifetime model able to discriminate the different damage mechanisms.

A constitutive model for inelastic behavior of casting materials under thermo-mechanical loading

High-temperature components, for example turbochargers, are often subject to complex thermal and mechanical loading paths. Non-uniform temperature distribution and constraints by neighboring components result in complex timely varying stress and strain states during operation. The aim of this paper is to analyze inelastic behavior of a casting material Ni-resist D-5S in a wide stress, strain rate and temperature ranges. The material model including a constitutive equation for the inelastic strain rate tensor and a non-linear kinematic hardening rule is discussed. To calibrate the model, experimental databases from creep and low cycle fatigue tests are generated. They include creep curves for temperatures within the range 600–800 °C and stress levels from 10 to 150 MPa. The low cycle fatigue data collect a family of hysteresis loops for the strain rate of 10−3 1/s, the strain amplitude from 0.4% to 2% and temperature levels within the range 200–800 °C. For the verification of the model, simulations of the material behavior under uniaxial thermo-mechanical fatigue loading conditions are performed. The results for the stress response are compared with experimental data.