Thermomechanical Phenomena Research Articles

3D numerical simulation of drilling residual stresses

Drilling can affect the integrity of the surface of a mechanical component and reduce its fatigue life. Thus, drilling parameters such as lubrication or drilling velocity must be optimized to ensure a satisfactory residual mechanical state of the hole surfaces. Unfortunately, experimental tests are time consuming and it is not easy to observe the cutting process because of the confinement of the drill zone. The literature does not exhibit any numerical simulation capable of simulating 3D thermomechanical phenomena in the drill zone for large depth holes. Therefore, residual stresses cannot be easily simulated by means of the sole drilling parameters. The aim of this article is to propose a new numerical approach to compute drilling residual stresses for large-depth holes. A first simulation is developed to simulate heat transfer by means of a 3D thermoviscoplastic simulation in a new Rigid-ALE framework allowing the use of large calculation time steps. Then, a time interpolation and a spatial projection are implemented to rebuild the Lagrangian thermal history of the machined component. Finally, a thermo-elastoplastic simulation is carried out to compute residual stresses in the final workpiece. In this paper, the method is applied to a 316L austenitic stainless steel in the case of an unlubricated hole. The computed residual stresses are compared to experimental measurements.

Mechanistic modelling of station blackout accidents for a generic 900 MW CANDU plant using the modified RELAP/SCDAPSIM/MOD3.6 code

CANDU (CANada Deuterium Uranium) reactors have many unique design features that play important roles during a severe accident, however analysis of such features using Light Water Reactor (LWR) specific computer codes is challenging. Severe accidents in CANDU involve complex thermo-mechanical deformation phenomena which differ from the phenomena present during LWR accidents. For example, during complete station blackout scenarios with a failure of all emergency measures, the pressure tubes may balloon or sag into contact with the surrounding calandria tubes (CTs) establishing a thermal conduction pathway for heat rejection to the large moderator water volume. As the moderator liquid evaporates or boils its level decreases until fuel channels become uncovered in the calandria vessel. The uncovered channels heat up quickly and the entire fuel channel assembly (fuel, pressure tube and calandria tube) will sag and possibly disassemble. During the disassembly process some channel components may fall to the bottom of the calandria while others may form a suspended debris bed supported by channels which are still submerged in moderator liquid. These phenomena impact event-timing, accident progression, hydrogen production and fission product release.In this work several mechanistic channel deformation models have been developed and integrated into RELAP/SCDAPSIM/MOD3.6 to provide a coupled treatment of the deformation phase for such postulated accidents. MOD3.6 is a new version of the RELAP/SCDAPSIM code being developed to support the analysis of Pressurized Heavy Water Reactors (PHWRs) under severe accident conditions. In this paper, the code system is used to simulate a postulated station blackout accident for a generic 900 MW CANDU plant. To reduce the uncertainty in the modeling of core disassembly and to overcome the memory constraints of the code, the simulation is broken into two phases with the first phase (i.e., from initiating event to the channel failure and depressurization) simulated using a full-plant RELAP5 model providing relatively high spatial fidelity of the entire heat transport system, and the second phase (i.e. continued from the end of the first phase until calandria vessel dryout) using alternative nodalization focusing on the calandria vessel and fuel channel components. The paper assesses the entire accident progression up to the point of calandria vessel dryout and performs sensitivity analysis on model parameters to assess their relative importance.

Analysis of cure induced deformation of CFRP U-shaped laminates

The thermochemical and the thermomechanical phenomena that happen during the cure process of a composite material laminate are responsible for the rise of residual stresses and, consequently, for the deformation at the end of the manufacturing process. In this work, the influence of some parameters, such as the laminate thickness, the stacking sequence and the mold radius, on the spring-in angle of a U-shaped laminate was studied exploring a full factorial plan through numerical simulations. Moreover, the influence of the laminate shape on the deformation was investigated. First of all, a numerical model appropriate for cure simulation was introduced and its suitability to simulate the deformation behavior was demonstrated. Using a simulation model instead of running experimental test was important for analyzing the parameters influence without reduce the full factorial plan to a fractional one and without wasting a lot of time and material. As a result, only the stacking sequence influenced the spring-in value, while the effect of the tool radius and laminate thickness was minimal. Finally, a comparison between U-shaped and L-shaped laminates evidenced that the spring-in value was independent of part shape, while this parameter affected the flange warpage.

Thermomechanical analysis induced by interrupted cutting of Ti6Al4V under several cooling strategies

Cryogenic machining has mainly investigated in continuous cutting. Therefore, there is a lack of knowledge on the application of this technology to interrupted cutting, such as in milling. This study aims to investigate the thermomechanical phenomena in interrupted cutting of Ti6Al4V alloy under cryogenic, flood cooling and dry conditions. Due to the complexity of the thermomechanical analysis in milling, a special designed experimental setup has been developed through interrupted turning tests. This work highlights the influence of cryogenic flow rate and cutting time/non-cutting ratio on tool temperature. The obtained results can be extrapolated to milling operation.

Domain-Independent Thermoviscoelastic Modeling Framework: A Physical Approach on Thermoelasticity by Bond Graph

Controlling the thermomechanical behavior of a multiphysical system has always been a challenging issue, because the general behavior of the system in this case is a result of complex energetic transactions between the system’s existing physical subdomains. In this study, a novel thermoviscoelastic modeling framework is proposed in which the thermomechanical behavior of the system is generated from the interactive dynamics of its involving subdomains. To this aim, by means of the Bond graph approach, the dynamic behavior of each subdomain is first generated separately with respect to the interactions of its own energetic components. The dynamics of all involving subdomains are then coupled via generating reversible and irreversible interactions between the counterpart energetic components of different subdomains. The impacts of geometrical and material changes on the system dynamics are finally added to the model via the compatibility consideration of the energetic components of different subdomains. The proposed modeling framework provides an energetic structure with which the general dynamics of the system are obtained from the constructive dynamics of each of the subdomains. This special capability of the proposed modeling framework leads to an automatic capture of the thermomechanical phenomena inside the system. The obtained simulation results for a simple beam structure demonstrate the impacts of the internal dynamics on the observable behavior of the system and prove the applicability of the proposed approach to the modeling of a wide range of thermomechanical behaviors, including material softening, vibrational heating, dilation, relaxation, conduction, and damping.

Spring-in analysis of CFRP thin laminates: numerical and experimental results

During the cure process of CFRP laminates, some geometrical unconformities can arise, due to several thermomechanical and thermochemical phenomena that make residual stress rise. Among these unconformities, one of the most studied is the spring-in, that is the deviation of the flange-to-flange angle from the design value. In this work a numerical model suitable to determine the spring-in value was developed and verified. The proposed model considered both the thermo-chemical and thermo-mechanical phenomena that happen during the cure process. Then, the numerical model was used for calculating the spring-in angle of lots of different laminates in order to evaluate the influence of the thickness, the corner radius and the layup sequence on the laminate deformation. For evaluating the influence of the above mentioned parameter on the spring-in a full factorial plan was designed, and the FEM analysis allowed a saving of time, energy and material. It was found that only the layup sequence influenced the spring-in. Finally, a preliminary analysis stated the possibility to extend the proposed model also to other geometries, such as U-shaped laminates.

Consequence of Cutting Parameters on Residual Stresses of AISI 1018 Cold Rolled Steel

This paper deals with residual stresses induced by machining processes are a consequence of thermo-mechanical and micro structural phenomena developed during the machining process. In the present study a numerical model has been developed to predict residual stresses near the surface in AISI 1018 Cold Rolled steel. The influence of cutting parameters namely cutting speed, feed rate and depth of cut were investigated using the developed model and validated with the experimental results. A Finite Element Code ABAQUS is being used to simulate the residual stresses during dry turning of AISI 1018 steel. Explicit Dynamics Time Integration with adaptive meshing Finite Element Method is employed to simulate the 2D model. The Johnson-Cook material model is used for illustration the work material behaviour to simulate machining with an orthogonal cutting. X-Ray diffraction technique is being used for the determination of residual stresses induced in machined surface for different cutting conditions. This present study will be useful in understanding of phenomenal behavior of AISI 1018steel. The variation in cutting speed or feed rate strongly influences the residual stresses in the machined surface.

Residual Stresses during Hard Turning of AISI 52100 Steel: Numerical Modelling with Experimental Validation

Residual stresses induced by machining processes are a consequence of thermo-mechanical and microstructural phenomena generated during the machining operation. In this study, a numerical approach has been developed to predict the near surface residual stresses resulting from turning of AISI 52100 alloys steel and validated by experimental results. Effect of cutting parameters, namely cutting speed and depth of cut on induced residual stresses in machined surface was investigated by modelling using ABAQUS/CAE 14.0 software. Explicit Dynamics time integration with adaptive meshing finite element method is employed to simulate the 2D model. The Johnson-Cook material model is used to describe the work material behaviour to simulate high speed machining with an orthogonal cutting. And also for experimental analysis X-Ray diffraction method is considered. While study residual stresses at different cutting speed, feed rate, and depth of cut is studied. As a conclusion we can say that cutting speed and feed rate plays major role as compared to depth of cut. And as cutting speed or feed rate increases tensile residual stresses increases.

Нелинейная модель вязкоупругопластичности типа Максвелла: моделирование влияния температуры на кривые деформирования, релаксации и ползучести

Исследуются область применимости, арсенал возможностей и способы идентификации и настройки нелинейного определяющего соотношения типа Максвелла для вязкоупругопластичных материалов с двумя произвольными материальными функциями и двумя параметрами (в случае одноосного изотермического нагружения). Оно нацелено на описание комплекса основных реологических эффектов, типичных для реономных материалов, обладающих наследственностью, высокой скоростной чувствительностью и разносопротивляемостью, для которых характерны установившаяся ползучесть, стадия течения при постоянном напряжении и возрастание податливости, скоростей диссипации, релаксации, ползучести и рэтчетинга и скоростной чувствительности с увеличением температуры. К ним относятся, в частности, многие полимеры, их расплавы и растворы, композиты, твердые топлива, асфальтобетоны, титановые и алюминиевые сплавы, углеродные и керамические материалы при высоких температурах и др. Для учета влияния температуры на механическое поведение материалов (при изотермических процессах) два материальных параметра модели (коэффициент вязкости и «модуль упругости») рассматриваются как функции температуры. Найдены ограничения на свойства этих функций, необходимые и достаточные для адекватного описания качественных характеристик влияния температуры на экспериментальные кривые ползучести, релаксации, деформирования с постоянными скоростями, ползучести при ступенчатом нагружении, на касательный модуль и предел текучести, скоростную чувствительность и скорость накопления пластической деформации, типичных для стабильных вязкоупругопластичных материалов в изотермических квазистатических испытаниях. Они получены в результате аналитического изучения свойств кривых релаксации, ползучести и деформирования, порождаемых определяющим соотношением типа Максвелла с произвольными материальными функциями, и их сопоставления с типичными свойствами экспериментальных кривых реономных материалов. Доказано, что коэффициент вязкости, «модуль упругости» и их отношение (время релаксации ассоциированной линейной модели Максвелла) должны быть убывающими функциями температуры, и это обеспечивает адекватное качественное описание десятка наблюдаемых базовых термомеханических эффектов, свидетельствующих о возрастании податливости материалов (в частности, убывании касательного модуля и предела текучести), скоростей релаксации, ползучести и рэтчетинга и скоростной чувствительности с ростом температуры.

Computer Methods for Determination of Deformations in Welded Closed Profiles

The work concerns the numerical prediction of deformations in welding of two rectangular profiles using TIG method. Numerical analysis of thermomechanical phenomena are carried out in the Abaqus FEA software using finite element method. Geometry of the joint is numerically recreated on the basis of the real welded joint of rectangular profiles. For this geometry a discretization of the system and numerical simulations of welding deformations are performed. The calculations are performed for the rectangular profiles made of steel X5CrNi18-10. Numerical analysis takes into account thermomechanical properties of welded elements changing with temperature. DFLUX subroutine is used in Abaqus software, allowing the modeling of moveable welding heat source. Mathematical Goldak‘s description of the heat source is assumed to described the distribution of movable heat source power. Results of numerical analysis of the temperature distribution in the welded joint are presented in this study. The estimation of the shape and size of melted zone is performed as well as the prediction of stress state and welding deformations. Numerically predicted deformations are compared with results of the measurement.

Numerical Analysis of Thermomechanical Phenomena in Laser Welded Pipe-to-Flat

Numerical prediction of deformations in laser-welded joints is important at the stage of construction design. The work concerns the modeling and numerical analysis of thermomechanical phenomena occurring in the laser welding process. Three dimensional discrete model of pipe-to-flat fillet weld is created in Abaqus FEA engineering software. Numerical analysis takes into account changing with temperature thermomechanical properties of welded plate made of austenitic steel. Additional numerical subroutine included into the solver takes into account a mathematical model of heat source power distribution. It is assumed that the heat source is moving in the polar system. The positioning of the source relative to the joined edge is taken into account in the analysis.

Energetic, structural, thermal and fatigue analysis of heavy duty process pumps

Design of heavy duty process pumps usually based on the end user requirements. Operating conditions of pumps in the system dictate technical solution to reach high performance pump design. Pumps for special application like nuclear power plants, petroleum, petrochemical and natural gas industry should reach very high design criteria and have to fulfil requirements of different international standards for pumps. Usually energetic and cavitation characteristics are necessary issues of the development procedure. In this paper structural analysis that include thermo-mechanical loading and fatigue phenomena are also considered, because they are very important for estimation of long service life. Repeated thermomechanical loading and unloading which leads to fatigue of pumps are obtained using unsteady Computational Fluid Dynamics (CFD) with taking into account also thermodynamics equations. Complete numerical analysis is done for an example of centrifugal pump with the specific speed around nq=24. The results show energetic characteristics, thermal stresses and deformations and maximal number of operation cycles for safe and reliable operation.

Numerical Simulation of the Friction Stir Welding Process Using Coupled Eulerian Lagrangian Method

Friction Stir Welding (FSW) is a solid state joining process that relies on frictional heating and plastic deformation realized at the interaction between a non-consumable welding tool that rotates on the contact surfaces of the combined parts. The experiments are often time consuming and costly. To overcome these problems, numerical analysis has frequently been used in last years. Several simplified numerical models were designed to elucidate various aspects of the complex thermo-mechanical phenomena associated with FSW. This research investigates a thermo-mechanical finite element model based on Coupled Eulerian Lagrangian method to simulate the friction stir welding of the AA 6082-T6 alloy. Abaqus/cae software is used in order to simulate the welding stage of the Friction Stir Welding process. This paper presents the steps of the numerical simulation using the finite elements method, in order to evaluate the boundary conditions of the model and the geometry of the tools by using the Coupled Eulerian Lagrangian method.

(Invited) The Use of Broadband Electric Spectroscopy to Probe the Relaxations and Polarizations in Phase Seperated Polymer Electrolytes

There has been a recent surge in interest in the use of anion exchange membranes (AEMs) as the separator in many electrochemical conversion devices such as fuel cells, electrolyzers, redox flow cells, and for uses in electrochemical water purification processes. This is because electrocatalysis is generally more facile in alkaline conditions, and so these devices could potentially operate with non-precious metal catalysts and with catalysts capable of oxidizing or generating fuels beyond hydrogen. An AEM with high anionic conductivity would overcome many of the disadvantages of proton exchange membrane devices that need precious metal catalyst and work best with hydrogen. Improved AEMs are also required for water purification applications. Realization of AEM devices, therefore, would revolutionize electrochemical energy conversion, as inexpensive versatile devices could be made available. While much attention has been focused on generating new AEMs with stable cations and backbones, very little attention has been paid to the design of AEMs to maximize ionic conductivity and water transport. The work presented here represents the first detailed study of the thermomechanical, polarization, and dielectric phenomena related to morphology in a series of AEMs. In detail in this presentation, the micro-structure is studied by Small Angle X-ray Scattering (SAXS), the thermal stability and transitions are detected by High-Resolution Thermogravimetry (HR-TG) and by Modulated Differential Scanning Calorimetry (MDSC), respectively. The mechanical properties and transitions are investigated by Dynamic Mechanical Analysis (DMA). Broadband Electrical Spectroscopy (BES) is used to study the electric response and the conductivity mechanisms of the membranes in the frequency and temperature range of 0. 01—107 Hz and -105 — 100 °C, respectively. BES is a powerful technique, which allows us to fully understand the overall electric response and dielectric relaxations of the membranes, both in a completely dry state and after full hydration, thus allowing clarification of the role played by both ion solvation phenomena and water cluster structure on performance of these materials. The integration of the information acquired by the above techniques allows us to propose a reasonable mechanism for the long-range charge migration processes in polyvinylbenzyltrimethylamne bromide-block-polymethylbutylene [PVBTMA][Br]-b-PMB, it hydoxide analogue and the random polymers of the same chemistry crosslinked by UV and thermal methods. We have also extended this study to polyphenylene-b-[PVBTMA][OH] and the pentablock quaternary ammonium functioalized analogue of the sulfonated polymer, Nexar. In amny of these polymers we observe an order-disorder transition, Tδ, where dispersed cations aglomorate due to the interactions of their dipoles. As Tδ often occurs above 0°C this phenomenom is of nterset to the development of practical devices. This study has important consequences for the design of next generation revolutionary AEMs.

Modelling grain growth in the framework of Rational Extended Thermodynamics

Grain growth is a significant phenomenon for the thermomechanical processing of metals. Since the mobility of the grain boundaries is thermally activated and energy stored in the grain boundaries is released during their motion, a mutual interaction with the process conditions occurs. To model such phenomena, a thermodynamic framework for the representation of thermomechanical coupling phenomena in metals including a microstructure description is required. For this purpose, Rational Extended Thermodynamics appears to be a useful tool. We apply an entropy principle to derive a thermodynamically consistent model for grain coarsening due to the growth and shrinkage of individual grains. Despite the rather different approaches applied, we obtain a grain growth model which is similar to existing ones and can be regarded as a thermodynamic extension of that by Hillert (1965) to more general systems. To demonstrate the applicability of the model, we compare our simulation results to grain growth experiments in pure copper by different authors, which we are able to reproduce very accurately. Finally, we study the implications of the energy release due to grain growth on the energy balance. The present unified approach combining a microstructure description and continuum mechanics is ready to be further used to develop more elaborate material models for complex thermo-chemo-mechanical coupling phenomena.

Some insights on the modelling of chip formation and its morphology during metal cutting operations

The present paper deals with the mechanisms of chip formation during cutting operations. It deals with some experiments characterising the chip morphologies and microstructure chip investigations under high loadings. In this contribution, mechanisms of chip segmentation are presented. The effect of cutting conditions on cutting forces is treated. Consequently, the chip segmentation phenomenon was correlated to cutting forces evolutions. Also, an investigation on chip strain localisation is carried out. Numerical simulations dealing with chip formation and considering thermomechanical phenomena are also presented. Some numerical results related to chip formation based on the theory of strain gradient plasticity are also discussed. Moreover, the effect of machining system stiffness on chip segmentation is analysed.

Description of the performances of a thermo-mechanical energy harvester using bimetallic beams

Many recent researches have been focused on the development of thermal energy harvesters using thermo-mechanical or thermo-electrical coupling phenomena associated to a first-order thermodynamic transition. In the case of the bimetallic strip heat engine, the exploitation of the thermo-mechanical instability of bimetallic membranes placed in a thermal gradient enables to convert heat into kinetic energy. This paper is a contribution to the modeling and the comprehension of these heat engines. By restraining the study to the simply-supported bimetallic beams and using a Ritz approximation of the beam shape, this paper aims to give an analytical solution to the first mode of the composite beams and then to evaluate the efficiency of the harvesters exploiting these kinds of instability.

Numerical Analysis of Deformations in Sheets Made of X5CRNI18-10 Steel Welded by a Hybrid Laser-arc Heat Source

The laser-arc hybrid welding is widely used in many industries through the combination of advantages found in welding technologies used in this single process. A significant issue is the determination of the influence of heat source power distribution on welding deformations generated at the interface of joined elements and adjacent zones. Numerical estimation of welding deformations is very important and allows for the proper selection of technological parameters as well as the prediction of welded joints quality. This work concerns numerical simulation of thermomechanical phenomena in hybrid welding of sheets made of X5CRNI18-10 steel using laser beam and electric arc heat sources. Three dimensional discrete model is created in Abaqus FEA in order to estimate welding deformations generated by temperature field in the joint. Additional numerical subroutine is created in Abaqus/Standard module in which the distribution of movable hybrid heat source is implemented. The shape and size of the fusion zone is determined on the basis of numerically obtained temperature field as well as welding deformations occurring in hybrid butt-welded joints.

Modeling, Dimension Reduction, and Nonlinear Vibrations of Thermomechanically Coupled Laminated Plates

A unified formulation of thermomechanical, geometrically nonlinear, laminated plates that integrates mechanical and thermal aspects is presented. It allows for constructing and comparing a variety of continuous models of different mechanical richness and with full thermoelastic coupling embedded, as well as for deriving minimal reduced order models suitable to provide useful information on fundamental thermomechanical phenomena occurring in the system nonlinear and complex dynamics. Comparative numerical investigations of free and forced vibrations can be carried out through both models of three, fully coupled, ordinary differential equations and simplified, partially coupled, models of two, or even one, ODEs, with the aim to unveil the actual importance of accounting for the various terms to reliably describe the most important thermomechanical effects on the system response.

A multi-physics and multi-time scale approach for modeling fluid–solid interaction and heat transfer

A novel non-conservative formulation for equations governing thermo-mechanical phenomena is developed to address multi-material and multi-physics issues. The first key point is that this formulation achieves a unifying equation for compressible viscous fluid flow and elastic solid deformation. The second is that the thermo-mechanical equations are both written with velocity and thermal flux variables to solve them simultaneously. With that formulation, interaction conditions at the fluid–structure interface become implicit and state equation is no longer necessary. Multi-time scale problems are solved, from the time scale of acoustic and thermoacoustic wave propagation, to longer time scale of fluid flow and thermal diffusion.