Papers by Keyword: Thermal Strain

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Authors: Uwe Reisgen, Christoph Geffers, Rahul Sharma, Jana von der Heydt
Abstract: Temperature-induced strain with, at the same time, reduced formability is, among other things, responsible for crack development in the range of high temperatures. For a more detailed examination of these so-called hot cracks, experimental measurements of the strain during the welding process have been carried out using neutron diffraction. The measurement of strain is important since it exerts decisive influence on the development of cracks.
Authors: M. Shibata, Yoshito Takemoto, Ichiro Shimizu
Abstract: Aluminium alloy composites reinforced with aluminium borate whiskers (ABw), developed recently by SHIKOKU KASEI KOUGYOU Co. Ltd., Japan, were fabricated using squeeze casting. The large mismatch in the coefficients of thermal expansion (CTE) between the reinforcement material and the matrix can generate significant stress and strain in composites during thermal cycling or during fabrication of the composites when using squeeze casting. When a transmission electron microscope is used to irradiate a very small area of a thin film of the material with a convergent electron beam of several nm in diameter, High Order Laue Zone patterns (HOLZ patterns) are obtained. These HOLZ patterns can reveal fine strain fields in the reinforcement materials that are used in composites fabricated using squeeze casting. Each (001) plane in the ABw was rotated towards the [020] direction by up to 0.5 ゚. With a unit of nearly 400 nm × 400 nm, each (100) plane was rotated towards the [020] direction in a corkscrew pattern. In addition the strain and the stress generated during the fabrication of the composites were estimated by using the finite element methods taking into account the anisotropies in both the CTE and the elastic modulus of the reinforcement material.
Authors: Je Se Choi, Yool Kwon Oh
Abstract: In the present study, AC7A aluminum alloy casting mold which consist of 8 pieces is introduced as an analysis model. Also, numerical work using a finite element method was applied to investigate the thermal strain that included the temperature distribution, stress and strain during the cooling process in AC7A casting mold. In addition, the numerical work was carried out that analysis results of the AC7A casting mold were compared with those of mild steel casting mold to prove the improvement and good quality. The numerical results such as temperature distributions, stress and strain are presented to help to make the effective and the best tire mold. In addition, the introduced technique of numerical work using a finite element method is very useful and especially needs to improve the precision of tire mold such as sectional type or puzzle type.
Authors: Dal Woo Jung, Il Bum Kwon, Nak Sam Choi
Abstract: A temperature-compensating fiber Bragg grating(FBG) sensor having two different FBGs in one fiber line was applied to the real time measurement of mechanical normal strain in structures. Measurement of mechanical strains of the aluminum beam surface by the double FBG sensor was performed under various thermal conditions, which was compared with results of electrical resistance strain gage. The FBG sensor fabricated in this study could detect accurately values of mechanical strains without containing any thermal strain component.
Authors: Chul Kim, Jong Heun Lee, J.H. Kim, Hoon Sang Choi
Abstract: The optimal stacking sequence and wall thickness of the composite strut tubes were determined to minimize thermal strains during orbital operation using generic algorithms and finite element analyses. From the results of previous thermal analyses of composite struts with various stacking sequences, the axial deformation is a matter of prime importance. For this reason, the optimization focuses to minimize the axial strains. The balanced and symmetric stacking sequences are used to minimize the radial and the twisting deformations. The genetic algorithm is known to be very effective for the discrete optimization such as stacking sequences of composite materials. As a result, the thermal deformations of the strut with an optimal stacking sequence are almost zero. The optimal strut tube consists of 6 plies and the weight of a composite strut is 22.4% that of aluminum strut. Finite element analyses showed that the optimal design of composite strut tubes withstood combined launch loads without buckling and failure. To validate the analyses, four composite struts were fabricated and their thermal strains were measured under the temperature increase of 100°C. The thermal and vibration experiments showed excellent correlations with analytical results.
Authors: Felaniaina Rakotovao, Zhao Jun Tao, Jean Luc Grosseau-Poussard, Benoit Panicaud, Gilles Bonnet, Patrick Girault, Mathieu Guerain
Abstract: The presence of residual stresses in thermal oxide layers has been recognized for a long time. In the present work, the mechanical fields for chromia oxide are determined either by XRD or Raman spectroscopy. In addition, the microstructure of the chromia films is investigated ant its influence on the evolution of the stress release processes is analyzed.
Authors: Zhao Jun Tao, Felaniaina Rakotovao, Jean Luc Grosseau-Poussard, Benoit Panicaud
Abstract: The presence of residual stresses in thermal oxide layers has been recognized for a long time. In the present work, the mechanical fields for chromium oxide are investigated. An extended model is established to take into account the effects of temperature and thermal cycling for the calculation of oxide stress. Numerical results are given in order to predict the influence of different parameters, especially the dependence of some material parameters with temperature. This enables to make comparison with experimental results.
Authors: Wen Mei Han, Tian He Kang, Chun Xia Xue
Abstract: Experimental studies on thermal strain of aerial laminated glasses by virtue of Moire Interferometry were done. The experimental results were as follows: in the U patterns of moire interference fringe, with temperature increasing, the fringes became denser and the thermal strain was augmented. In the V patterns of moire interference fringe, the sequence of the fringe patterns increased is intermediate film layer, external shielding layer and main bearing layer, respectively. The U and V fringe patterns results analyzed by digital image process system indicate that, with temperature increasing, the strain εx decreased. Because the difference of coefficients of thermal expansion of three materials is very large, the thermal strain is generated significantly, and the interlayer thermal shear strain exists in the end and intermediate position of the free boundary of the laminated glass.
Authors: W. Woo, Zhi Li Feng, X.L. Wang, K. An, W.B. Bailey, S.A. David, C.R. Hubbard, Hahn Choo
Abstract: Localized heating was imposed on a 6061-T6 aluminum alloy plate to cause thermal strains, and simultaneously interplanar spacing changes were measured using in-situ time-resolved neutron diffraction techniques. Two different methods were used: 1) direct real-time measurements of the transient behavior and 2) a series of measurements based on the quasi-steady state (QSS) principle. A comparison of the two results shows that the QSS method can represent the transient behavior under the current experimental conditions.
Authors: Chun Run Li, Zhi Peng Zhang, Yi Ming Zhang, Zong Tao Fang
Abstract: This paper takes the Q345 steel as an example, adopting finite element simulative analysis to study the influence of solid-state transformation on welding residual stress. By setting the value of the thermal strain in different temperature, the change in volume caused by the phase changes is equivalent to the thermal strain. Simulation includes two cases which are consideration of phase transformations and not consideration. The results showed that the distribution trend of the longitudinal stress of the weld zone is substantially the same in the two simulations. In the case of not consider the simulation of phase change, there is a lot of stress in the weld zone and the heat affected zone and the maximum value could be 427 MPa. In regard to transverse stress, phase change not only affects the value of the stress, but also changes the direction of the stress of the weld middle portion. Welding residual stress is also measured by X-ray. Phase change simulation and experimental results are in good agreement, it can be concluded that phase change in the welding process will result in a significant impact on the distribution of the residual stress, which could not be ignored in the finite element simulation of welding process.
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