Thermo-mechanical analysis of reinforced concrete slab using different fire models

Suljevic, Samir,Medic, Senad,Hrasnica, Mustafa Techno-Press 2020 Coupled systems mechanics Vol.9 No.2

Coupled thermo-mechanical analysis of reinforced concrete slab at elevated temperatures from a fire accounting for nonlinear thermal parameters is carried out. The main focus of the paper is put on a one-way continuous reinforced concrete slab exposed to fire from the single (bottom) side as the most typical working condition under fire loading. Although contemporary techniques alongside the fire protection measures are in constant development, in most cases it is not possible to avoid the material deterioration particularly nearby the exposed surface from a fire. Thereby the structural fire resistance of reinforced concrete slabs is mostly influenced by a relative distance between reinforcement and the exposed surface. A parametric study with variable concrete cover ranging from 15 mm to 35 mm is performed. As the first part of a one-way coupled thermo-mechanical analysis, transient nonlinear heat transfer analysis is performed by applying the net heat flux on the exposed surface. The solution of proposed heat analysis is obtained at certain time steps of interest by α-method using the explicit Euler time-integration scheme. Spatial discretization is done by the finite element method using a 1D 2-noded truss element with the temperature nodal values as unknowns. The obtained results in terms of temperature field inside the element are compared with available numerical and experimental results. A high level of agreement can be observed, implying the proposed model capable of describing the temperature field during a fire. Accompanying thermal analysis, mechanical analysis is performed in two ways. Firstly, using the guidelines given in Eurocode 2 - Part 1-2 resulting in the fire resistance rating for the aforementioned concrete cover values. The second way is a fully numerical coupled analysis carried out in general-purpose finite element software DIANA FEA. Both approaches indicate structural fire behavior similar to those observed in large-scale fire tests.

Thermo-Mechanical Coupling Analysis of the Actuating Mechanism in a High Speed Press

Jin Cheng,Zhendong Zhou,Yixiong Feng,Zhenyu Liu,Yangyan Zhang 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.5

In order to ensure the manufacturing precision of an ultra-precision high speed press, an integrated thermo-mechanical coupling model of its actuating mechanism is proposed, which includes the mechanical models of the slider and crankshaft, the thermal models for calculating the heat generation powers at different bearings as well as the heat transfer and heat dissipation in the actuating mechanism. The validity of the proposed thermo-mechanical coupling model is verified by a thermal equilibrium experiment when the press operates under the full load of 3000kN at 300 rpm. A sensitivity analysis is conducted to investigate the simulation errors resulting from the variation of the ambient temperature, the results of which demonstrate that the average ambient temperature should be applied for improving simulation accuracy. Then the thermal stiffness of the actuating mechanism and the thermo-mechanical coupling characteristics of different parts are analyzed by the proposed model with the average ambient temperature applied. The influences of the thermally induced loads on the thermal stiffness are discussed in detail. It is concluded that the temperature rise of the actuating mechanism in the stamping process of a high speed press should be fully considered in the design phase for ensuring its manufacturing precision.

화재 열 유동을 고려한 구조물의 열응력해석

박홍락,강준원,이진우 한국전산구조공학회 2016 한국전산구조공학회논문집 Vol.29 No.4

이 연구는 화재에 노출된 구조물의 역학적 거동을 평가하기 위한 기반연구로서 화재 유동해석과 열응력해석의 통합 프레 임워크를 확립하고 이를 강재와 콘크리트로 이루어진 대표체적에 적용한 결과를 제시하였다. 먼저 Fire Dynamics Simulator(FDS)를 이용해 임의의 화재곡선으로 모델링되는 화원으로부터 구조물 표면까지 유동해석을 실시하였다. 이를 통 해 구조물 표면에서 시간에 따른 온도 분포를 계산하였고, 이 결과를 비선형 열응력해석에 경계조건으로 적용하였다. 이후의 과정은 화재의 성장 또는 감소에 따라 구조물 표면온도의 변화를 반영하는 열전달해석과 구조해석으로 이루어진다. 제시한 통합 프레임워크에 의해 화재 구조해석을 수행한 결과, 강재와 콘크리트의 대표체적 모두 동일한 하중이 작용할 때 상온 조 건에서는 탄성 거동을 보였지만 화재로 인한 온도 조건을 고려할 경우 소성 거동을 보였다. 이는 구조물이 화재에 노출되는 경우 설계하중보다 작은 하중에서도 한계상태에 이를 수 있다는 것을 의미하며, 따라서 원전구조물이나 교량과 같은 중요 사회기반구조물의 설계 시 구조물의 화재거동 평가가 고려되어야 한다고 할 수 있다. In this study, a numerical analysis framework for investigating the nonlinear behavior of structures under fire conditions is presented. In particular, analysis procedure combining fire-driven flow simulation and thermo-mechanical analysis is discussed to investigate the mechanical behavior of fire-exposed representative volume structures made of steel and concrete, respectively. First of all, fire-driven flow analysis is conducted using Fire Dynamics Simulator(FDS) in a rectangular parallelepiped domain containing the structure. The FDS simulation yields the time history of temperature on the surface of the structure under fire conditions. Second, mechanical responses of the fire-exposed structure with respect to prescribed uniformly distributed loads are calculated by a coupled thermo-mechanical analysis using the time-varying surface temperature as boundary conditions. Material nonlinearities of steel and concrete have been considered in the thermo-mechanical analysis. A series of numerical results are presented to demonstrate the feasibility of the multiphysics structural fire analysis for investigating the structural behavior under fire conditions.

Thermo-mechanical analysis of functionally graded wheel-mounted brake disk

Tohid Mahmoudi,Ali Parvizi,Esmaeil Poursaeidi,Abbas Rahi 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.10

Having higher speed for trains requires improvement in braking performances. The brake system is an important part of locomotivesafety system in which the mechanical energy is converted to the thermal energy and distributed through the disks and pads. As a result,the temperature at the disks surfaces increases sharply. This phenomenon is called the thermal shock that causes the negative effects onthe brake disk surface such as fast aging, early wear, thermal cracks and the brake fade. Using Functionally graded materials (FGMs)which are more resistant to the thermal shock is a new trend to deal with this issue. In this study, the effects of using FG materials in thewheel-mounted brake disk R920K for the ER24PC locomotive on its thermo-mechanical behavior are investigated. For this purpose, theuncoupled thermo-mechanical analysis is performed for the disk made of FG Al-A359/SiCp, aluminum and ductile cast iron materials. Comparing the results of brake disk made of ductile cast iron with those from experimental data, the accuracy of present FE model isverified. Concerning the stress analysis, it is shown that the safety factor for the disk made of FG material is higher than the other ones. Furthermore, the gradation index of FG material has the most important effect on the thermo-mechanical performance of FG disks.

Thermo-mechanical finite element simulation and validation of rubber curing process

Sittichai Limrungruengrat,Arisara Chaikittiratana,Sacharuck Pornpeerakeat,Tonkid Chantrasmi 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.6

Vulcanization, or curing, is a very important process in producing useful rubber products. The curing process takes place when heat is transferred to the rubber compounds inside a heated mold. The temperature distribution in the rubber significantly affects cure level distribution throughout the part. The problem of non-uniformity of cure level of the final product often occurs in a large rubber component, such as a tire or a rubber track, leading to poor quality and performance. The expansion of the rubber due to temperature increase and the rise of elastic modulus during the curing process lead to an increase in stress inside the mold, which can cause excessive mold deformation and the appropriate mold press force should be determined. This work’s aim was to develop a methodology for the analysis of the vulcanization process using a coupled thermo-mechanical finite element method to simulate a nonlinear heat transfer process coupled with curing kinetics and the evolution of thermal and mechanical properties. User subroutines UMATHT and UMAT were developed and implemented into the finite element package ABAQUS to evaluate the cure level distribution and stress developed inside the mold during curing. Experimental tests were carried out to study and evaluate the thermal, curing, and mechanical properties as dependent functions of temperature and cure level. A simple compression molding test was performed and the results were used to validate the simulated predictions. It is shown that the predictions of the temperature, cure level distribution in the rubber part and press force during curing process obtained from the developed finite element analysis are in the good agreement with the experimental data. Furthermore, the simulations with thermal and mechanical properties varying with temperature and cure level are closer to the measured data than one with constant properties.

Thermo-mechanical behavior of cast-in-place energy piles

Sung, Chihun,Park, Sangwoo,Lee, Seokjae,Oh, Kwanggeun,Choi, Hangseok Elsevier 2018 ENERGY Vol.161 No.-

<P><B>Abstract</B></P> <P>An energy pile induces heat exchange with the ground formation by circulating heat carrier fluid through a heat exchange pipe, which is encased in pile foundation. During heat exchange, temperature variation in energy pile generates thermally-induced stress due to the different thermo-mechanical behavior between the pile and surrounding ground, and the restriction of pile deformation. A series of full-scale field tests was performed to identify the thermo-mechanical behavior of a cast-in-place energy pile equipped with 5-pair-parallel U-type heat exchange pipe. During the field investigation, each cooling and heating test lasted for 30 days, including a 15-day operating period and 15-day resting period, and the thermal stress generated in the energy pile was monitored. The maximum thermal stress was evaluated to be 2.6 MPa in the cooling test, which is about 10% of the design compressive strength of concrete. In addition, a finite element (FE) numerical model was developed to simulate the thermo-mechanical behavior of the energy pile. In the numerical analysis, relevant boundary conditions and interface model were determined by comparing with the field measurement. Finally, a parametric study was performed to estimate the thermal stress and deformation of a cast-in-place energy pile for various ground conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A large-diameter cast-in-place concrete energy pile was constructed in a test bed. </LI> <LI> The maximum thermal stress was evaluated to be 2.6 MPa in the cooling test. </LI> <LI> This value is about 10% of the design compressive strength of concrete. </LI> <LI> A parametric study for the thermos-mechanical behavior of energy piles. </LI> </UL> </P>

Assessment of non-polynomial shear deformation theories for thermo-mechanical analysis of laminated composite plates

Yadwinder S. Joshan,Neeraj Grover,B. N. Singh 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.27 No.6

In the present work, the recently developed non-polynomial shear deformation theories are assessed for thermo-mechanical response characteristics of laminated composite plates. The applicability and accuracy of these theories for static, buckling and free vibration responses were ascertained in the recent past by several authors. However, the assessment of these theories for thermo-mechanical analysis of the laminated composite structures is still to be ascertained. The response characteristics are investigated in linear and non-linear thermal gradient and also in the presence and absence of mechanical transverse loads. The laminated composite plates are modelled using recently developed six shear deformation theories involving different shear strain functions. The principle of virtual work is used to develop the governing system of equations. The Navier type closed form solution is adopted to yield the exact solution of the developed equation for simply supported cross ply laminated plates. The thermo-mechanical response characteristics due to these six different theories are obtained and compared with the existing results.

Thermo-mechanical Coupled Analysis of Laser-assisted Mechanical Micromilling of Difficult-to-machine Metal Alloys Used for Bio-implant

Ninggang Shen,Hongtao Ding 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.

This study is focused on a numerical modeling analysis of laser-assisted mechanical micromilling (LAMM) for difficult-to-machine biomedical implant alloys, such as Ti6Al4V and stainless steels. Multiple LAMM tests are performed on these materials with 100 μm diameter endmills at various laser powers. A 3D thermal model is used to quantitatively analyze the material temperature increase due to laser heating during the LAMM process. Finite element (FE) models are developed using ABAQUS to simulate the continuous chip formation, and strain gradient constitutive material models are implemented to model the size effect. The quasi steady-state workpiece temperature after multiple milling cycles is analyzed with a heat transfer analysis based on the chip formation analysis and thermal model simulations. The modeling results in temperature, force and cutting stress are discussed and compared with the experimental results.

3D quasi-transient thermo-mechanical analysis for vehicle brake disc

Biao Hu,Xingyan Zhang,Yang Liu,Junjie Yan,Xiaobing Liu,Xin Wang,Richard Sun 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.2

An alternative numerical method is developed to predict the thermo-mechanical behavior of brake disc during braking. Steady-state aerodynamic simulation for entire vehicle with variant speeds are conducted to analyze the convective heat transfer characteristic of the disc surface. Then the transient heat transfer boundary of the disc is obtained by interpolating the steady-state simulation results. Based on that, the transient thermo-mechanical coupled simulation for brake disc is performed via finite element method. With those work, the characteristics of transient temperature field and stress field of the brake disc are analyzed. Meanwhile, the characteristic of contact pressure distribution on friction interface is also obtained. The results show that during the braking process, for any node in the friction areas of the brake disc surface, its temperature rise curve fluctuates like a sawtooth. The temperature field has a significant effect on the stress field of the brake disc, both in distribution and variation. To verify the numerical method and validate the simulation results, a full-scale vehicle brake-thermalperformance test is carried out. By comparison, the simulation results show good agreement with the experimental results. The proposed numerical method enables an efficient and economical way to predict and evaluate the thermo-mechanical behavior of the brake disc in early phase of vehicle development.

A thermo-mechanical stress prediction model for contemporary planar sodium sulfur (NaS) cells

Jung, Keeyoung,Colker, Jeffrey P.,Cao, Yuzhe,Kim, Goun,Park, Yoon-Cheol,Kim, Chang-Soo Elsevier 2016 Journal of Power Sources Vol.324 No.-

<P><B>Abstract</B></P> <P>We introduce a comprehensive finite-element analysis (FEA) computational model to accurately predict the thermo-mechanical stresses at heterogeneous joints and components of large-size sodium sulfur (NaS) cells during thermal cycling. Quantification of the thermo-mechanical stress is important because the accumulation of stress during cell assembly and/or operation is one of the critical issues in developing practical planar NaS cells. The computational model is developed based on relevant experimental assembly and operation conditions to predict the detailed stress field of a state-of-the-art planar NaS cell. Prior to the freeze-and-thaw thermal cycle simulation, residual stresses generated from the actual high temperature cell assembly procedures are calculated and implemented into the subsequent model. The calculation results show that large stresses are developed on the outer surface of the insulating header and the solid electrolyte, where component fracture is frequently observed in the experimental cell fabrication process. The impacts of the coefficients of thermal expansion (CTE) of glass materials and the thicknesses of cell container on the stress accumulation are also evaluated to improve the cell manufacturing procedure and to guide the material choices for enhanced thermo-mechanical stability of large-size NaS cells.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A comprehensive FEA model is introduced to predict stress in contemporary planar NaS cell. </LI> <LI> Model includes relevant experimental procedures for planar NaS cell assembly and operation. </LI> <LI> Large stresses were developed on the outer surface of insulating header and solid electrolyte. </LI> <LI> Cell container thickness plays an important role in the stress accumulation of planar NaS cell. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>