Coupled Temperature Displacement Research Articles

Investigation on performance of prestressed hollow core slabs exposed to elevated temperatures

PurposeThis study focused on identifying critical factors governing the fire response of prestressed hollow-core slabs. The hollow-core slabs used as flooring units can be subjected to elevated temperatures during a fire. The fire response of prestressed hollow-core slabs is required to develop slabs with greater fire endurance. The present study aims to determine the extent to which the hollow-core slab can sustain load during a fire without undergoing progressive collapse under extreme fire and heating scenarios.Design/methodology/approachA finite element model was generated to predict the fire response of prestressed hollow core slabs under elevated temperatures. The accuracy of the model was predicted by examining thermal and structural responses through coupled temperature displacement analysis. A sensitivity analysis was performed to study the effects of concrete properties on prediction of system response. A parametric study was conducted by varying the thickness of the slab, fire and heating scenarios.FindingsThermal conductivity and specific heat of concrete were determined as sensitive parameters. The thickness of the slab was identified as a critical factor at a higher load level. Asymmetric heating of the slab resulted in higher fire resistance compared with symmetric heating.Originality/valueThis is the first study focused on studying the effect of modeling uncertainties on the system response by sensitivity analysis under elevated temperatures. The developed model with a parametric study helps in identifying critical factors for design purposes.

Finite Element Modeling, Thermal–Mechanical Coupling Analysis, and Demonstration of Multibusbar Half-Cell Double-Glass Overlapping Photovoltaic Module During Lamination

The gap-free interconnect using structural round ribbons in overlapping photovoltaic modules is an effective measure to improve module efficiency. Cells in the overlapping module are interconnected by round ribbons with local flattened parts rather than conductive adhesive. The structure of overlapping modules has a crucial effect on the thermal–mechanical stress of crystalline silicon cells during the laminating process of modules. Excessive stress will produce microcracks in the cells, which will adversely affect the long-term reliability of the modules. In this article, the coupled temperature–displacement is used to simulate the stress evolution of the double-glass multibusbar overlapping modules during lamination and comparative experiments were carried out. The results show that in the overlapping area, the cell near the solder band will be subjected to more concentrated stress than other regions, resulting in local bending of the cell. Large stress concentration may induce the generation and propagation of microcracks. The cell stress is sensitive to the dosage of encapsulating agent and the thickness of the flattened ribbon. Increasing the amount of encapsulating agent and reducing the thickness of the flattened section will help to relieve stress concentration. Finally, we demonstrate the overlapping process with modules interconnected by 0.12-mm flattened round ribbons and encapsulated by 0.65-mm ethylene vinyl acetate. The overlapping modules pass 200 thermal cycles and 3600-Pa mechanical load without cracks.

Modeling residual stresses in hard turning with self-propelled rotary tools

Finite element (FE) models have been developed to predict average surface residual stresses during hard turning of AISI 4340 steel with self-propelled rotary tools (SPRT). Three dimensional chip formation analysis have been carried out using coupled temperature displacement analysis. In the next step, the workpiece is unloaded and allowed to cool till the attainment of room temperature using convective heat transfer model. The residual stresses in the cutting direction obtained using the FE models are validated using experimentally measured ones using X-ray diffraction technique. A good agreement has been found between the predicted and experimental values and the average errors are around 11–12%. In addition, residual stresses obtained with the fixed tool are also evaluated and compared with SPRT. The effects of cutting speed and feed rate on residual stresses using SPRT have also been analyzed and discussed.

Methodology for prediction of sub-surface residual stress in micro end milling of Ti-6Al-4V alloy

To meet the growing demands of sophisticated component service life and miniaturization, the study of surface integrity such as residual stress after the machining becomes more essential. Compressive residual stress improves wear resistance of topological pairs and inhibits the fatigue crack propagation. To obtain a better understanding of state of residual stress at surface and sub-surface level, continuum-mechanics based Finite Element (FE) modeling is established. Dynamic explicit time incrementation scheme with coupled temperature displacement transient analysis is performed. Critical uncut chip thickness and consequences of tool edge radius, feed per tooth, and axial depth on cutting forces are investigated through FEM modeling. Besides the FEM modeling, the theoretical elastoplastic orthogonal cutting model with coupling of thermal and mechanical field variables is also demonstrated. In present research, Ti-6Al-4 V was chosen as the workpiece material because of its wide range of applications in biomedical, electronics, optics and aerospace industry due to their superior mechanical, chemical and high-temperature properties. X-ray diffraction (XRD) technique was used to measure the residual stress developed during micro-end milling process. Simulated results were validated with the experimental observations. To assess the residual stress at sub-surface level, electro polishing is done to remove the surface layer. It was found that both experimental and simulated results follow a similar trend and gave a good agreement between them.

3D-Modeling of Hard Turning using Self-Propelled Rotary Tools

This study proposed a three-dimensional finite element (FE) model to simulate hard turning using self-propelled rotary cutting tools (SPRT). A complete tool geometry of the round cutting insert is considered to assess the self-cooling effect of the SPRT while machining hardened steel. A portion of the workpiece is considered according to the cutting parameters and the general contact algorithm has been employed to simulate cutting. Chip formation phase is carried out by coupled temperature displacement analysis using actual boundary conditions according to the experimental setup. The model is able to predict various performance measures like cutting forces, tool and workpiece temperatures, chip morphology and stresses on the workpiece. The model predictions are compared with the published experimental results on hard turning and a close agreement has been found. In addition, models with different feed rates are developed and its effects on cutting forces, chip morphology, stress and temperature distributions have been discussed.

Evaluation of Self-Propelled Rotary Tool in the Machining of Hardened Steel Using Finite Element Models.

This paper presents a model for assessing the performance of self-propelled rotary tool during the processing of hardened steel. A finite element (FE) model has been proposed in this analysis to study the hard turning of AISI 51200 hardened steel using a self-propelled rotary cutting tool. The model is developed by utilizing the explicit coupled temperature displacement analysis in the presence of realistic boundary conditions. This model does not take into account any assumptions regarding the heat partitioning and the tool-workpiece contact area. The model can predict the cutting forces, chip flow, induced stresses, and the generated temperature on the cutting tool and the workpiece. The nodal temperatures and heat flux data from the chip formation analysis are used to achieve steady-state temperatures on the cutting tool in the heat transfer analysis. The model outcomes are compared with reported experimental data and a good agreement has been found.

Comparative Analysis and Optimization of FEM and RSM Based Regression Model with Experimental Results for the Dry Turning of SiCp- Al7075 Composite

The paper presents a finite element based methodology by converting full scale turning operation to a two-dimensional plain strain machining model. The method is used for predicting the output cutting parameters by using the Johnson cook elastic and fracture model to improve the prediction capabilities for industrial applications. For material modeling purposes, ABAQUS Explicit module is used by taking coupled temperature displacement elements. Different input cutting regimes, i.e., feed rate, depth of cut, and cutting speed, have been varied to evaluate the values of cutting force, cutting temperature and also the effect of tool particle interaction for the turning of SiC (100 μm, 10% wt.) reinforced Al7075 composite. Moreover, to view the effect of variation of material and dimensional property fracture energy has been varied. Further, the response surface model is developed by using full factorial design to generate the regression equations for the estimation of output variables within the selected input variables range. A number of 256 different simulations were executed, out of which 230 were used for the training purpose, and 26 for validation purposes. Results depict the prediction error of the regression model for validatory runs, which varies from 0.21 to 17.13% for Fc, Ft, and Tt, respectively. The finite element model is validated with experimental analysis by examining a set of 8 random runs. Prediction accuracy based on the above comparison varies from 83.33 to 93.68% for cutting force components and cutting temperature. It is also observed that the finite element model and the response surface model are having a good agreement with experimental results.

Representative volume element-based simulation of multiple solid particles erosion of a compressor blade considering temperature effect

Solid particle erosion is one of the main failure mechanisms of a compressor blade. Thus, characterization of this damage mode is very important in life assessment of the compressor. Since experimental study of solid particle erosion needs special methods and equipment, it is necessary to develop erosion computer models. This study presents a coupled temperature–displacement finite element model to investigate damage of a compressor blade due to multiple solid particles erosion. To decrease the computational cost, a representative volume element technique is introduced to simulate simultaneous impact of multiple particles. Blade has been made of Ti-6Al-4V, a ductile titanium-based alloy, which is impacted by alumina particles. Erosion finite element modeling is assumed as a micro-scale impact problem and Johnson–Cook constitutive equations are used to describe Ti-6Al-4V erosive behavior. In regard to a wide variation range in thermal conditions all over the compressor, it is divided into three parts (first stages, middle stages, and last stages) in which each part has an average temperature. Effective parameters on erosive behavior of the blade alloy, such as impact angle, particles velocity, and particles size are studied in these three temperatures. Results show that middle stages are the most critical sites of the compressor in terms of erosion damage. An exponential relation is observed between erosion rate and particles velocity. The dependency of erosion rate on size of particles at high temperatures is indispensable.

A strain-gradient isotropic elastoplastic damage model with J3 dependence

A “plastic-strain-gradient” version of an isotropic elastoplastic damage model that depends on the third invariant J3 of the stress deviator is developed. The model is based on the “non-local” equivalent plastic strain ep defined by Peerlings et al. (2001) and Engelen et al. (2003) and introduces a “material length” ℓ to the constitutive equations. It is shown that the non-local equivalent plastic strain ep at a material point P can be identified with the average value of the local von Mises equivalent plastic strain ε¯p over a sphere centered at P and of radius approximately equal to 3 ℓ. A methodology for the numerical integration of the constitutive equations is presented. The algorithm is appropriate for rate-independent as well as rate-dependent (viscoplastic) models. The model is implemented in the ABAQUS general-purpose finite element program and both quasi-static and dynamic problems are solved. Two possible ABAQUS implementations are discussed. First,“user elements” are developed, which can be used for the solution of both quasi-static and dynamic problems. Reduced 1-point Gauss integration is discussed in 8-node hexahedral elements and the “physical stabilization” method of Puso (2000) is used to remove the resulting numerical singularities (hourglass control). Second, the implementation of the model via “user material” subroutines is discussed. Quasi-static problems can be solved with ABAQUS/Standard using a *COUPLED TEMPERATURE-DISPLACEMENT, STEADY STATE analysis together with user subroutine UMAT, in which temperature is identified with the non-local equivalent plastic strain ep; the solution of dynamic problems requires use of ABAQUS/Explicit together with a *DYNAMIC TEMPERATURE-DISPLACEMENT analysis option and user subroutines VUMAT and DFLUX. Several example problems are solved.

Study of TiC particle distribution in Al-MMCs using finite element modeling

In order to enhance the efficiency of cutting process before resorting to costly and time consuming experimental trials, it is necessary to model and simulate the machining process by using Finite Element (FE) analysis. However, modeling of composite machining is difficult owing to its distinctive structure and composition which is anisotropic and heterogeneous. Limited studies have been done using microscopic model without considering the effect of particle distribution on chip morphology and coupled temperature displacement analysis during machining simulation of MMCs. Therefore, in the current research work an FE model of machining MMCs is built for analyzing the effect of particle distribution in matrix, tool and geometry cutting parameters on machining process. In FE analysis, the main phases of an Al-TiC MMC workpiece, namely the particle phase and the matrix phase are modeled. Parameters such as morphology of chip, cutting force, and temperature and stress distribution have significant influence on cutting performance and are successfully analyzed by 2D FE models developed. Two different strategies (model A and B) are utilized to arrange the particles in the matrix. Model B with angular distribution of particles shows better performance than the linear distribution of particles in model A. The Performance of model B at different machining conditions is successfully performed and achieves closer to experimental results. Further, heat transfer properties are incorporated in the FE code to perform the cryogenic machining simulation. The authenticity of the developed model is ensured as the simulation results closely agree with the experimental results. The developed FE model affords an insight on effect of particle distribution, cutting parameters and cryogenic technology on machining of MMC. The details presented in the current work are likely to form a scientific basis to simulate machining of MMCs to address the present-day requirements of manufacturing industries.

Two-dimensional finite element analysis investigation of the heat partition ratio of a friction brake

A two-dimensional coupled temperature–displacement finite element model is developed for a pad-disc brake system based on a restricted rotational pad boundary condition. The evolution of pressure, heat flux, and temperature along the contact interface during braking applications is analysed with the finite element model. Results indicate that different rotational pad boundary conditions significantly impact the interface pressure distribution, which in turn affects interface temperature and heat flux distributions, and suggest that a particular pad rotation condition is most appropriate for accurately modelling friction braking processes. The importance of the thermal contact conductance in the analysis of heat transfer in friction braking is established, and it is confirmed that the heat partition ratio is not uniformly distributed along the interface under normal and high interface thermal conductance conditions.

Effect of thermal and mechanical parameter’s damage numerical simulation cycling effects on defects in hot metal forming processes

Damage mechanisms in hot metal forming processes are accelerated by mechanical stresses arising during Thermal and mechanical properties variations, because it consists of the materials with different thermal and mechanical loadings and swelling coefficients. In this work, 3D finite element models (FEM) are developed to simulate the effect of Temperature and the stresses on the model development, using a general purpose FE software ABAQUS. Explicit dynamic analysis with coupled Temperature displacement procedure is used for a model. The purpose of this research was to study the thermomechanical damage mechanics in hot forming processes. The important process variables and the main characteristics of various hot forming processes will also be discussed.

Coupled Temperature Displacement Model to Predict Residual Stresses in Milling Process

Materials when subjected to plastic deformations, stresses are induced in the material. The stresses that are induced in the material due to machining is very high due to extreme plastic deformation. The nature and magnitude of the stresses plays a vital role in the functional performance of the components. The stresses can be tensile or compressive. Sometimes the stress are beneficial sometimes it is not. The present work is to develop a 2D coupled temperature displacement analysis to predict the surface residual stresses that are induced due to milling operation. In this work the material considered is AISI 1045 steel and the tool that is used is HSS tool. The finite element model is used to predict the residual stresses and it is compared with the experimental results. The predict results are in agreement with the experimental results. The residual stresses where experimentally determined using X-Ray diffraction method. Finite element method helps us to remove costly experiments and the process is rather quick. Apart from the residual stresses, force, temperature, Von Mises stress can also be obtained from the developed model.

Experimentally validated structural vibration frequencies’ prediction from frictional temperature signatures using numerical simulation: A case of laced cantilever beam-like structures

This article pertains to the prediction of structural vibration frequencies from frictional temperature evolution through numerical simulation. To achieve this, a finite element analysis was carried on AISI 304 steel cantilever beam-like structures coupled with a lacing wire using the commercial software ABAQUS/CAE. The coupled temperature–displacement transient analysis simulated the frictional thermal generation. Furthermore, an experimental analysis was carried out with infrared cameras capturing the interfacial thermal images while the beams were subjected to forced excitation, thus validating the finite element analysis results. The analysed vibration frequencies using a MATLAB fast Fourier transform algorithm confirmed the validity of its prediction from the frictional temperature time domain waveform. This finding has a great significance to the mechanical and aerospace engineering communities for the effective structural health monitoring of dynamic structures online using infrared thermography, thus reducing the downtime and maintenance cost, leading to increased efficiency.

Finite Element Analysis of the Effect of Cutting Speed on the Orthogonal Turning of A359/SiC<sub>p</sub> MMC

The application of Metal Matrix Composite (MMC) has been increasing due to its superior strength and wear characteristics but the major challenge is its poor machinability due to the presence of reinforcement in the matrix which is a hindrance during machining. The material behaviour during machining varies with respect to input variables. In this paper the effect of cutting speed during the orthogonal turning of A359/SiCp MMC with TiAlN tool insert is analysed by developing a 2D Finite Element (FE) model in Abaqus FEA code. The FE model is based on plane strain formulation and the element type used is coupled temperature displacement. The matrix material is modeled using Johnson–Cook (J-C) thermal elastic–plastic constitutive equation and chip separation is simulated using Johnson–Cook’s model for progressive damage and fracture with parting line. Particle material is considered to be perfectly elastic until brittle fracture. The tool is considered to be rigid. The FE model analyses the tool interaction with the MMC and its subsequent effects on cutting forces for different cutting speeds and feed rates. The chip formation and stress distribution are also studied. The FE results are validated with the experimental results at cutting speeds ranging from 72 – 188 m/min and feed rates ranging from 0.111 – 0.446 mm/rev at constant depth of cut of 0.5mm.

Modelling the coupling between hydrogen diffusion and the mechanical behaviour of metals

It is well known that hydrogen can have a detrimental effect on the mechanical properties of metals. The aim here is to provide a fully coupled model of the HELP (Hydrogen Enhanced Local Plasticity) mechanism with hydrogen transport. Using the similarities between the heat and mass diffusion equations, a coupled temperature–displacement procedure has been adopted to allow the coupling between hydrogen diffusion and the mechanical behaviour of the material to be simulated. The diffusion equation takes into account the fact that hydrogen atoms reside in interstitial sites and in trapping sites such as dislocations. In the simulations presented here it is assumed that concentration of hydrogen at the dislocations is in equilibrium with the concentration in the matrix interstitial sites. The mechanical behaviour of the material is represented by an isotropic hardening law in which the flow stress decreases with increasing hydrogen content in the matrix which is evaluated by solving the fully coupled mechanical diffusion equations. We use the model to analyse the response of a plane strain component which contains deep and sharp doubled-edged notches. For highly constrained components of this type the hydrostatic component of stress scales with the local yield strength of the material. A high local hydrostatic stress would result in a high hydrogen concentration, but a high hydrogen concentration results in softening, i.e. a low yield strength, and therefore a low hydrostatic stress. These conflicting relationships result in a balance being achieved between hydrostatic stress, hydrogen concentration and yield strength, i.e. the response does not become unstable. Also there is a high degree of kinematic determinacy in the way which the component deforms, i.e. the strain pattern in the presence of hydrogen is very similar to that when there is no hydrogen. A consequence of these two effects is that softening of the constitutive response due to the presence of hydrogen, does not lead to localization of strain and a macroscopic brittle response. Softening must be combined with other degradation process for the material to embrittle.

Modeling machining of particle-reinforced aluminum-based metal matrix composites using cohesive zone elements

Finite element modeling for the machining of heterogeneous materials like particle-reinforced metal matrix composites has not been much successful as compared to homogeneous metals due to several issues. The most challenging issue is to deal with severe mesh distortion due to nonuniform deformation inside the workpiece. Other problems are related to the modeling of the interface between reinforcement particles and matrix and tool-reinforcement particle interaction. In this study, different strategies are adopted for finite element models (FEM) to cope with the above issues and comparative analyses have been performed. These 2D FE models are based on plane strain formulations and utilize a coupled temperature displacement method. The workpiece is modeled using reinforcement particle size and volume fraction inside the base matrix. The interface between the reinforcement particles and the matrix is modeled by using two approaches, with and without cohesive zone elements, and the chip separation is modeled with and without using a parting line. This allows models to simulate the local effects such as tool-reinforcement particle interaction and reinforcement particle debonding. In addition, the models can predict cutting forces, chip morphology, stresses, and temperature distributions. The effects of different methodologies on the model development, simulation runs, and predicted results have been discussed. The results are compared with experimental data, and it has been found that the utilization of cohesive zone elements (CZE) with the parting line approach seems to be the best one for the modeling of metal matrix composite (MMC) machining.

FINITE ELEMENT MODELING OF THE ORTHOGONAL MACHINING OF PARTICLE REINFORCED ALUMINUM BASED METAL MATRIX COMPOSITES

2D finite element models (FEM) are developed to simulate orth- ogonal machining of particle reinforced aluminum based metal matrix composites (MMC). The models predict cutting forces, chip morphology, temperatures and stresses distributions. The simulations were carried out by developing a fully coupled temperature displacement model. In contrast to the equivalent homogeneous material (EHM) methodology, a heterogeneous model is developed based on reinforcement particle size and volume fraction. This allows models to simulate the local effects such as tool-reinforcement particle interaction, reinforcement particle debonding. The interface between the reinforcement particles and the matrix is modeled by using two approaches; with and without cohesive zone elements. Similarly the chip separation is modeled with and without using a parting line. The effect of different methodologies on the model development, simulation runs and predicted results have been discussed. The results are compared with experimental data and it has been found that the utilization of cohesive zone modeling (CZM) with the parting line approach seems to be the best one for the modeling of MMC machining. homogeneity and abrasive nature of reinforcement particles. Mostly MMC are fabricated with near net shape processes but some machining and finishing cuts are indispensable for final dimensions and surface finishes. Cutting tools such as high speed steel, cast cobalt alloys, cemented carbides and cermets cannot be used for machining of MMC due to high wear rate. Diamond cutting tools are found to be the best option for machining of MMC and they are being utilized in the last ten years for both particles and fibers based MMC (Looney 1992, Schwartz 1997, Muthukrishnan 2008). Fiber reinforced composites are anisotropic as fibers are not equi- axes, whereas particulate reinforced composites are isotropic like conventional metals. The later provide higher ductility and their isotropic nature make them a better choice as compared to fiber reinforced composites. Machinability of particulate reinforced composites depend on many factors like particulate type, its orientation, tool material, tool geometry and cutting conditions like cutting speed, feed etc. Numerous studies exist in the literature to analyze machining of MMC using experiments and mostly related to measure performance variables like tool wear, surface roughness, sub surface damage, cutting forces, cutting temperatures and chip morphology (Davim 2011). It has been found that parameters related to structure of composite greatly affect the machinability. These include reinforcement material, reinforcement type, volume fraction of the particles, base metal properties and overall arrangement of constituent phases. Polycrystalline diamond inserts (PCD) are commonly employed for their machining (Weinert 1993, Quigley 1994). Use of other ceramics materials like cubic boron nitride (CBN), alumina and silicon nitride are also reported but did not have a major success. Effects of cutting parameters (speed, feed and depth of cut) on machinability of MMC is almost similar to that found in machining of conventional metals with some differences due to abrasive nature of particles. The reinforced particles tend to expelled out from the base metal and slide in front of the cutting tool edge. This results in plowing through the newly generated machined surface and groove marks on it (El-Gallab 1998) (Manna 2003).

Deformation kinetics of pH‐sensitive hydrogels

AbstractPolymeric gels can undergo large deformation when subjected to external solutions of varying pH. It is imperative to understand the deformation process of pH‐sensitive hydrogels for the effective application of these attractive materials in the biomedical and microfluidic fields. In the modeling of these multi‐phase materials, finite element (FE) modeling is a useful tool for the development of future applications, and it allows developers to test a wide variety of material responses in a cost‐effective and efficient manner, reducing the need to conduct extensive laboratory experiments. Although a FE user‐defined material model is available for the equilibrium state, the transient response of pH‐sensitive gels has not been effectively modeled. Based on our recent work using the heat transfer analogy to tap into the readily available coupled temperature–displacement elements available in the commercial FE software ABAQUS for simulation of the transient swelling process of neutral hydrogels, the transient swelling process of a pH‐sensitive hydrogel is studied and a FE model is further developed to simulate the transient phenomena. Some benchmark examples are investigated to demonstrate the model's capabilities in the simulation of nonlinear deformation kinetics relevant to several applications of pH‐sensitive hydrogels. © 2013 Society of Chemical Industry

A Fundamental Study on the Heat Partition Ratio of Vehicle Disk Brakes

The interface tribolayer (ITL) in an automotive brake friction pair is a layer of material created from transfer films, wear particles, and surface transformations between the rotor and stator. Its presence in a brake friction interface has been proven, e.g., by the existence of a temperature “jump” across the friction interface. In this paper, two 1D static transient heat transfer models have been used to investigate the ITL behavior and obtain an equivalent thermal conductance value which will reduce computational requirements and software restrictions. The approach is developed into a more realistic 2D coupled temperature–displacement model using commercial finite element analysis (FEA) software (abaqus) that utilizes the contact pressure, real contact area, and the ITL equivalent thermal conductance to estimate the effective thermal conductance at the friction interface. Subsequently, the effective thermal conductance relationship is combined with the 2-D coupled temperature–displacement model to provide a new method of heat partition prediction in brake friction pairs where heat partition is neither uniform nor constant with time.