Thermo-mechanical System Research Articles

Thermomechanical Analysis System for Building Structures under Fire Based on MSCPATRAN Platform

In order to analyze the behavior of building structures in a real fire, a numerical method is proposed, which employs fire zone model to simulate the fire growing and the temperature distributions in a firing room. Two computer programs are developed to predict the thermomechanical response of the structures, one for thermal response analysis, and another for structural analysis. The structural analysis program contains a fiber beam element and a layered shell element. These elements, validated against data from experimental tests, can be used to predict the response of beam/column and slabs in fire conditions. Based on these programs, a system for analyzing the behavior of structures under fire is developed on MSC/PATRAN platform. The behavior of building structures under fire can be simulated with this system and the results can be used as the reference for the fire safety analysis and assessment of general building structures under fire.

Microstructure development in hot deformed AA6082

Age hardenable aluminium alloys are suitable for hot deformation at temperatures between 300 and 600°C, depending on the alloy and on the process. During thermo mechanical processes, dynamic and/or static restoration mechanisms take place. In this work, hot compression tests of hot rolled AA6082 and of a hot extruded AA6082 were carried out by means of a Gleeble® 1500 thermo-mechanical system, between 450 and 550°C and at 0.1–10s−1 of strain rate followed by fast cooling. The materials were thermo-mechanically processed before hot deformation to transform the complex initial microstructure into a fully recrystallized microstructure. Some compression tests of non recrystallized samples were carried out for comparison. All the samples were examined using electron backscatter diffraction (EBSD), followed by a determination of grain size and subgrain size distributions as well as of the local misorientation distribution. The as received samples showed a duplex microstructure consisting of elongated grains oriented in the rolling and extrusion directions, and some small recrystallized grains. The main restoration mechanism for all the materials is shown to be dynamic recovery, and the Zener–Hollomon parameter, as well as the flow stress was correlated to the subgrain size. The hot rolled material flow behaviour was sensitive to the initial microstructure, and geometric dynamic recrystallization was found.

Effect of Solute Depleted Area on the Distribution of MnS in Fe-3%Si

Hot deformation was applied on Fe-3%Si by the Gleeble-1500 thermo-mechanical system, and the effect of solute depleted area around the primary MnS particles precipitated prior to hot deformation on the distribution of strain-induced MnS particles was investigated. The obtained results showed that the depleted area around primary MnS particles affects significantly the distribution of strain-induced MnS particles, and the involved parameters were discussed.

Thermal characterization of microheaters from the dynamic response

Thermal characterization of surface-micromachined microheaters is carried out from their dynamic response to electrothermal excitations. An electrical equivalent circuit model is developed for the thermo-mechanical system. The mechanical parameters are extracted from the frequency response obtained using a laser Doppler vibrometer. The resonant frequencies of the microheaters are measured and compared with FEM simulations. The thermal time constants are obtained from the electrical equivalent model by fitting the model response to the measured frequency response. Microheaters with an active area of 140 µm × 140 µm have been realized on two different layers (poly-1 and poly-2) with two different air gaps (2 µm and 2.75 µm). The effective time constants, combining thermal and mechanical responses, are in the range of 0.13–0.22 ms for heaters on the poly-1 layer and 1.9 µs–0.15 ms for microheaters on the poly-2 layer. The thermal time constants of the microheaters are in the range of a few microseconds, thus making them suitable for sensor applications that need a faster thermal response.

Enhancement of Tire Durability by Considering Air Flow Field

Abstract Rolling tire performance is frequently affected by multiple physics. For instance, dry handling is influenced by the tire temperature as a consequence of the heat generation by material viscosity and the heat transfer to ambient air. The general phenomenon is complex and even interactive in that the elasticity parameter affecting tire deformation is a function of the temperature and that the temperature depends considerably on the air flow on tire surface. This paper refers to connecting the different physics of outside air flow and thermomechanical system of tire. Especially, the heat transfer across tire surface is focused from the viewpoint of thermofluid dynamics. Macroscopic flow turbulence to accelerate the heat transfer is studied in a case study of the run-flat tire, where high temperature due to very large deformation is of a key issue. Numerical simulation is conducted in parallel to experimental works in assessing heat flow and temperature on the surface. It is shown that the proposed geometry of rib sidewall reduces the tire temperature and improves the tire life remarkably.

Studying the Darcy-Stefan problem on phase transition in a saturated porous soil

The Cauchy problem for the Darcy-Stefan model, which describes the process of freezing (thawing) of a saturated porous soil with allowance for liquid-phase filtration, is considered. The model includes the Darcy law, the equation of liquid-phase incompressibility, the equation of absence of solid-phase motion, the equation of energy balance in the porous soil-saturating continuous medium system, and also the Stefan condition and the condition of continuity of the normal components of the velocity field at the interface boundary. The existence of generalized solutions of the problem satisfying an additional condition of entropy nondecreasing in a thermomechanical system (i.e., the second law of thermodynamics) is proved by the method of the kinetic equation.

Effects of Heating Rate and Temperature Holding Time on Mechanical Behaviors of Aluminum Alloy

In this paper, the mechanical properties of several aluminum alloys are obtained experimentally at different temperatures, from room temperature to about 4000C by using the Gleeble 1500 thermomechanical system. Besides, the thermal softening characteristics, effects of heating rate and temperature holding time are discussed in details. It is found that the strength of LF6, a kind of antirust aluminum alloy, is not sensitive to the heating rate (0.1-1000K/s) and temperature holding time (0-1h). However, the mechanical behaviors of other alloys depend on these factors very obviously. At last, these phenomena are discussed in the viewpoint of the microstructures and techniques of ageing strengthening of these alloys.

Nonlinear Analysis of Rubber-Based Polymeric Materials with Thermal Relaxation Models

ABSTRACT Using mathematical modeling and computer simulation, nonlinear dynamics of rubber-based polymers has been studied with due regard for the effect of thermal relaxation. Main results have been obtained for the case of elongational oscillations of a ring-shaped body subjected to periodic (“internal”)boundary conditions. Particular emphasis has been placed on high-frequency and short spatial variations of temperature and displacement, in which the role of nonlinearities in the dynamics of the material and their close connection with the effect of thermal relaxation time can be best appreciated. It is shown how the vanishing relaxation time can lead to an attenuation of nonlinear effects in the thermomechanical system.

On the response sensitivity of an optimally designed functionally graded layer

Sensitivity of the response of an optimally designed functionally graded (FG) thermomechanical system is investigated. The system is a transversely isotropic layer subjected to a thermal gradient. The layer is modeled as a biconstituent composite with a microstructure characterized by the design parameters: fiber volume fraction, shape, and orientation. Performance is quantified by a linear combination of the layer's curvature and strain energy density. Of particular interest is the comparison of variability of response to variations in the design parameters versus variability in such things as constituent material properties, and fiber misalignment. These are issues of significance for the manufacturing of functionally graded materials (FGMs). It is concluded that while not all FG systems show a significant sensitivity to texture (i.e. fiber shape and orientation) there do exist some systems for which response is markedly affected by texture even in comparison to significant variabilities in constituent material properties and fiber misalignment.

HIGHLY ACCELERATED SOLDER JOINT RELIABILITY TEST USING A THERMO-MECHANICAL DEFLECTION SYSTEM (TMDS)

A Thermo-Mechanical Deflection System (TMDS) test method has been developed for evaluating the fatigue performance of solder joints in printed circuit board (PCB) assemblies. The TMDS test imparts cyclic twisting deflections on an assembled PCB test vehicle which is tested under controlled iso-thermal conditions in a thermal chamber. Tests were conducted at various angles of twist and isothermal conditions at 100°C and 25°C. Failure analysis using SEM showed that the solder joint failure for the TMDS test is comparable to the failure mechanisms for ATC test failures for solder joints. Weibull failure distribution plots for TMDS and ATC tests were compared and a Scale Factor (SF) was used to correlate the test results.

Continuum mechanical modelling of the dissipative processes in the sediment-water layer below glaciers

The solid mass of the saturated viscous, heat-conducting sediment-water layer below temperate glaciers grows by abrading the underlying rockbed. We propose to model this layer as a saturated mixture continuum of fluid and solid. We formulate its balance laws in volume and jump local forms following, e.g. Germain and Muller (1986). The water balance accounts for its drainage into the rockbed and the melting of ice within the overlaid ice sheet. Dissipation due to the power expended by stresses, the Darcy interaction force and sliding friction governs this thermomechanical system. Our analysis establishes that, contrary to what is stated in the literature, the listed dissipative mechanisms are all relevant.

Simulation of microstructure and liquation cracking in 7017 aluminium alloy

Welding in a 7000 series aluminium alloy can lead to the development of a white zone microstructure and liquation cracking in the heat affected zone adjacent to the fusion boundary. A Gleeble 1500 thermomechanical system has been used to study the conditions associated with damage development. A range of simulations has been carried out covering thermal and thermomechanical conditions typically encountered during weld manufacture. Results show that both the white zone microstructure and liquation cracking can be simulated at a sufficient scale to permit full characterisation in laboratory testpieces. Data analysis has defined and mapped the stress and temperature conditions leading to crack initiation. This evaluation demonstrates that the susceptibility for cracking is minimised by increasing the cooling rate following weld manufacture.

Experimental and theoretical studies in subsea pipeline buckling

Field failures of trenched and/or buried subsea pipelines due to in-service buckling have recently been admitted in literature. Herein presented are the results of a recently completed series of model tests involving full thermomechanical system representation. The problematical vertical buckling mode, applicable to trenched and/or buried subsea pipelines, is considered in terms of both isolated prop and contact undulation imperfection topologies. Experimental data is compared with that obtained from a suite of computer-based theoretical models. It is contended that highly satisfactory experimental/theoretical correlation is provided regarding definition of the crucial upheaval buckling state subject to adequate imperfection specification.

Model reduction and process control of thermomechanical behaviour of non‐linear material deformation

AbstractThis paper describes a design procedure for metal forming processes by using the controllable subspace of the full system. The velocity profile of the moving die is designed using the reduced order system. The metal forming processes are simulated using non‐linear finite element methods based on the rigid viscoplastic flow formulation. The balanced model reduction technique is applied to reduce the full state space model to a reduced order model that retains the controllable subspace of the thermomechanical system. The linear quadratic regulator theory with output tracking is used as an off‐line design tool to design the die velocity schedule. The process design is carried out to maintain the strain rate of the critical portion of the billet at a desired value. The procedure for designing the process parameters is demonstrated using two case studies.

Quality assessment of polyester chips and yarn by TMS‐2

AbstractPenetration in polyester chips of different manufacturers and yarn (undrawn and drawn) was studied between 323 and 423 K on a thermomechanical system (TMS‐2) using a penetration kit. It was observed that the penetration of the probe varied in the case of chips from manufacturer to manufacturer. The undrawn and drawn yarns from different batches and also within the same batch showed a clear variation in penetration curve, which may be attributed to the degree of crystallization. The same technique can be utilized for an assessment of the quality of yarn in continuous production and for differentiating the manufacturing process of polyester chips.

On crack propagation in a nonlinear coupled thermo-mechanical system

The crack propagation problem in a coupled thermo-mechanical system of nonlinear media have been considered and the related path-independent integrals are given. It is shown the dynamical crack extension force in a coupled thermo-mechanical system equals to this integral, thus it could consider such integrals as a nonlinear fracture criterion for coupled thermo-mechanical fracture dynamics.

On crack propagation in a coupled thermomechanical system of nonlinear media

In some engineering problems, thermo-mechanical coupling is important and may not be ignored. This paper deals with the crack propagation problem in a coupled thermo-mechanical system of nonlinear media. Various nonlinear media, including nonlinear elastic and elastic-plastic cases, have been considered and the related path-independent integrals are given. To explain the physical meaning of these integrals, a notched specimen has been considered, and the dynamical crack extension force in a coupled thermo-mechanical system is shown to be equal to this integral. Thus, we could consider such integrals as some nonlinear criteria for coupled thermo-mechanical fracture dynamics.

Crack temperature rise due to crack propagation in visco‐plastic materials

AbstractAn attempt is made to simulate the temperature field connected with a propagating crack in a visco‐plastic material. The authors apply modern continuum thermodynamics of strain‐rate sensitive work‐hardening materials to describe heat dissipation, convection, and conduction phenomena connected with the temperature development in the near‐crack region. The powerful finite element technique has been used to solve the coupled thermomechanical system of field equations being highly non‐linear. The results are in a better agreement with experiments than those obtained by the classic uncoupled methods.

Sul criterio dell'energia per la stabilitá di un sistema termomeccanico

The energy criterion for mechanical stability asserts that the stable configurations are those that minimize the potential energy. Recent studies have shown that the energy criterion can be extended to stability of thermomechanical systems under suitable environment conditions, provided that the «stored energy» is interpreted as the equilibrium free-energy at the environmental temperature θe. The aim of this paper is to provide a contribution to a general theory of thermomechanical stability. Essentially we have restated the theory for general materials introduced by Gurtin with a new framework in the light of recent theories of Noll and Coleman-Owen on simple materials and on thermodynamical potentials. We define a «thermomechanical system» which posseses two main features: i) state space has a «natural topology» depending on the thermodynamical behaviour of system; ii) internal energy E and entropy S are not supposed to exist but are expressely obtained with their smoothness properties.