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Experimental and numerical study on formability of friction stir welded TWB sheets based on hemispherical dome stretch tests 总被引:1,自引:0,他引:1
Wonoh Lee Kyung-Hwan Chung Daeyong Kim Junehyung Kim Chongmin Kim Kazutaka Okamoto R.H. Wagoner Kwansoo Chung 《International Journal of Plasticity》2009,25(9):1626
In order to investigate formability performance and also to obtain guidelines for the stamping process design of friction stir welded TWB (tailor welded blank) sheets, the hemispherical dome stretching test was experimentally performed and the results of the base and friction stir welded samples were compared. Also, in order to better understand the experimental results, numerical analysis was performed. In this work, five automotive sheets, 6111-T4, 5083-H18, 5083-O aluminum alloy, dual-phase steel (DP590) and AZ31 magnesium alloy sheets were considered by (friction stir) welding the same materials. To represent mechanical properties for the numerical analysis, the non-quadratic orthotropic yield function, Yld2000-2d, was utilized for the aluminum alloy and DP590 sheets, while the Cazacu anisotropic/asymmetric yield function was applied for the AZ31 sheet considering different hardening behavior in tension and compression. 相似文献
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《Acta Mechanica Solida Sinica》2011,(Z1):34-38
The effects of welding current and time on the joints quality of the resistance spot welded of DP600 by evaluating the welding nugget sizes and mechanical properties were investigated experimentally. The experiment results show that different welding current and time lead to different welding nugget sizes. There exists a critical welding parameter which can make the welding nugget size attain optimum. The welding nugget size is a critical control parameter of the mechanical properties of the spot welded joint. 相似文献
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In this study, the forced vibration of a curved pipe conveying fluid resting on a nonlinear elastic foundation is considered. The governing equations for the pipe system are formed with the consideration of viscoelastic material, nonlinearity of foundation, external excitation, and extensibility of centre line. Equations governing the in-plane vibration are solved first by the Galerkin method to obtain the static in-plane equilibrium configuration. The out-of-plane vibration is simplified into a constant coefficient gyroscopic system. Subsequently, the method of multiple scales (MMS) is developed to investigate external first and second primary resonances of the out-of-plane vibration in the presence of three-to-one internal resonance between the first two modes. Modulation equations are formed to obtain the steady state solutions. A parametric study is carried out for the first primary resonance. The effects of damping, nonlinear stiffness of the foundation, internal resonance detuning parameter, and the magnitude of the external excitation are investigated through frequency response curves and force response curves. The characteristics of the single mode response and the relationship between single and two mode steady state solutions are revealed for the second primary resonance. The stability analysis is carried out for these plots. Finally, the approximately analytical results are confirmed by the numerical integrations. 相似文献
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《International Journal of Solids and Structures》2003,40(16):4167-4180
A computational procedure is presented for evaluating the sensitivity coefficients of the thermomechanical response of welded structures. Uncoupled thermomechanical analysis, with transient thermal analysis and quasi-static mechanical analysis, is performed. A rate independent, small deformation thermo-elasto-plastic material model with temperature-dependent material properties is adopted in the study. The temperature field is assumed to be independent of the stresses and strains. The heat transfer equations emanating from a finite element semi-discretization are integrated using an implicit backward difference scheme to generate the time history of the temperatures. The mechanical response during welding is then calculated by solving a generalized plane strain problem. First- and second-order sensitivity coefficients of the thermal and mechanical response quantities (derivatives with respect to various thermomechanical parameters) are evaluated using a direct differentiation approach in conjunction with an automatic differentiation software facility. Numerical results are presented for a double fillet conventional welding of a stiffener and a base plate made of stainless steel AL-6XN material. Time histories of the response and sensitivity coefficients, and their spatial distributions at selected times are presented. 相似文献
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基于纳米压痕技术,对转子钢焊接接头不同区域(母材、焊缝和热影响区)开展了压入位移控制的单向压痕实验和压入载荷控制的循环压痕实验研究.首先,通过压入位移控制的单向压痕实验,采用多次测试取平均值的方式获得了焊接接头各个区域的弹性模量和硬度分布特征,同时对各区域弹性模量中值点的载荷-压入深度曲线进行了分析;其次,对各个区域进行压入载荷控制的循环压痕实验,比较其压入深度随循环周次的演化特征.结果表明,焊接接头不同区域力学性能差异较大,热影响区的弹性模量、硬度、抗拉强度和抗循环变形能力最高,焊缝次之,母材最弱;三个区域在循环压痕载荷下的接触载荷-压入深度滞回环曲线均表现出类似棘轮变形的演化特征,且母材演化速度高于焊缝,高于热影响区.研究结果对汽轮机焊接转子的焊接工艺的优化、寿命预测和可靠性设计具有重要的借鉴意义. 相似文献
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The effect of thermomechanically induced phase transformation on the driving force for crack growth in polycrystalline shape memory alloys is analyzed in an infinite center-cracked plate subjected to a thermal actuation cycle under mechanical load in plain strain. Finite element calculations are carried out to determine the mechanical fields near the static crack and the crack-tip energy release rate using the virtual crack closure technique. A substantial increase of the energy release rate – an order of magnitude for some material systems – is observed during the thermal cycle due to the stress redistribution induced by large scale phase transformation. Thus, phase transformation occurring due to thermal variations under mechanical load may result in crack growth if the crack-tip energy release rate reaches a material specific critical value. 相似文献
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大多数结构用铝合金通常要经过热处理或加工硬化以得到更高的力学性能.这种合金焊接后,焊接热会使焊缝附近局部区域(称为热影响区HAZ)强度降低.这一特点使得焊接铝合金梁构件极限承载力的研究与焊接钢梁构件相比变得更为复杂.由于我国目前还没有关于铝合金结构的设计规范,为此本文对两种典型的纵向焊接工字型截面铝合金梁构件进行了试验研究,并在参考国外规范的基础上,提出了适用于静力设计的纵向焊接铝合金梁设计公式的建议.通过对试验构件进行数值分析,验证了有限元分析焊接梁的可靠性.在此基础上进行了大量的数值分析,并将试验结果及有限元计算结果与公式计算结果进行了比较,可以看出建议公式计算结果富有较大安全度,从而验证了其适用性,为我国《铝合金结构设计规范》的编制提供了依据和参考. 相似文献
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Dipl.-Ing. U. Projahn Dipl.-Ing. H. Rieger Prof. Dr.-Ing. H. Beer 《Heat and Mass Transfer》1981,15(4):223-232
To investigate the thermal response of composed anisotropic structures, a numerical study has been carried out. By the use of a numerical mapping technique it was possible to handle complex multi-body geometries very efficiently. Due to the transformation method the restriction of the well known finite difference method to simple solution regions is removed. For the iterative solution of the corresponding finite difference equations the Strongly Implicit Procedure (SIP) has been employed. Based on the solution methodology, several numerical examples revealing the effects of anisotropy in thermal conductivity and composite structures are presented. 相似文献
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为研究空腔厚度对现场发泡夹心墙平面内、平面外抗震性能的影响,对20 片现场发泡夹心墙和2 片实心墙进行平面内、平面外受力的数值试验和模型试验,并验证数值试验的正确性和有效性. 对不同空腔厚度的现场发泡夹心墙进行平面内、平面外受力的数值试验研究. 结果表明平面内受力时,对相对位移差的影响最明显,平面外受力时,对承载力的影响最明显. 总体上看,对平面内的影响要大于对平面外的影响. 墙体的协调变形能力随空腔厚度的增加而明显降低,因此建议在高烈度区现场发泡夹心墙的空腔厚度不宜大于100 mm. 相似文献
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This paper investigates the in-plane and out-of-plane dynamics of a curved pipe conveying fluid. Considering the extensibility, von Karman nonlinearity, and pulsating flow, the governing equations are derived by the Newtonian method. First, according to the modified inextensible theory, only the out-of-plane vibration is investigated based on a Galerkin method for discretizing the partial differential equations. The instability regions of combination parametric resonance and principal parametric resonance are determined by using the method of multiple scales (MMS). Parametric studies are also performed. Then the differential quadrature method (DQM) is adopted to discretize the complete pipe model and the nonlinear dynamic equations are carried out numerically with a fourth-order Runge–Kutta technique. The nonlinear dynamic responses are presented to validate the out-of-plane instability analysis and to demonstrate the influence of von Karman geometric nonlinearity. Further, some numerical results obtained in this work are compared with previous experimental results, showing the validity of the theoretical model developed in this paper. 相似文献
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Very high cycle fatigue (VHCF) behaviors of bridge steel (Q345) welded joints were investigated using an ultrasonic fatigue test system at room temperature with a stress ratio R = ?1. The results show that the fatigue strength of welded joints is dropped by an average of 60% comparing to the base metal and the fatigue failure still occurred beyond 107 cycles. The fatigue fracture of welded joints in the low cycle regime generally occurred at the solder while at the heat-affected zone (HAZ) in the very high cycle regime. The fatigue fracture surface was analyzed with scanning electron microscopy (SEM), showing welding defects such as pore, micro-crack and inclusion were the main factors on decreasing the fatigue properties of welded joints. The effect of welding defects on the fatigue behaviors of welded joints was discussed in terms of experimental results and finite element simulations. 相似文献
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We study the coupled thermo-mechanical problem that is obtained by combining generalized standard materials with Fourier’s law for heat conduction. The analysis is conducted in the framework of non-smooth mechanics in order to account for possible constraints on the state variables. This allows models of damage and phase-transformation to be included in the analysis. In view of performing numerical simulations, an incremental thermo-mechanical problem and corresponding variational principles are introduced. Conditions for existence of solutions to the incremental problem are discussed and compared with the isothermal case. The numerical implementation of the proposed approach is studied in detail. In particular, it is shown that the incremental thermo-mechanical problem can be recast as a concave maximization problem and ultimately amounts to solve a sequence of linear thermal problems and purely mechanical (i.e. at a prescribed temperature field) problems. Therefore, using the proposed approach, thermo-mechanical coupling can be implemented with low additional complexity compared to the isothermal case, while still relying on a sound mathematical framework. As an application, thermo-mechanical coupling in shape memory alloys is studied. The influence of the loading strain-rate on the phase transformation and on the overall stress–strain response is investigated, as well as the influence of the thermal boundary conditions. The numerical results obtained by the proposed approach are compared with numerical and experimental results from the literature. 相似文献
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This paper investigates the complex interfacial kinematics and governing mechanisms during high speed impact conditions. A robust numerical modelling technique using Eulerian simulations are used to explain the material response of the interface subjected to a high strain rate collision during a magnetic pulse welding. The capability of this model is demonstrated using the predictions of interfacial kinematics and revealing the governing mechanical behaviours. Numerical predictions of wave formation resulted with the upward or downward jetting and complex interfacial mixing governed by wake and vortex instabilities corroborate the experimental observations. Moreover, the prediction of the material ejection during the simulation explains the experimentally observed deposited particles outside the welded region. Formations of internal cavities along the interface is also closely resemble the resulted confined heating at the vicinity of the interface appeared from those wake and vortex instabilities. These results are key features of this simulation that also explains the potential mechanisms in the defects formation at the interface. These results indicate that the Eulerian computation not only has the advantage of predicting the governing mechanisms, but also it offers a non-destructive approach to identify the interfacial defects in an impact welded joint. 相似文献
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In this paper we examine the stress-elongation response of a bar undergoing a thermoelastic phase transition. Attention is focussed on how this response is affected by the heat generated during the transformation. The analysis is based on a continuum model consisting of a two-well Helmholtz free-energy function, a kinetic relation and a nucleation criterion. The governing mathematical problem is related to one that describes a moving heat source, except that here, the strength and speed of the source are not knowna priori and the energy field equation involves coupling between thermal and mechanical effects. A finite difference solution of this moving boundary-value problem is carried out. The heat generated by the transformation is found to have a significant effect on the mechanical response whenever the prescribed elongation-rate is moderately large. 相似文献
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An Investigation of Random Fatigue Strength of K-Type Tubular Joints and Crack Propagation Behaviors
IntroductionAsaspecialformofstructures,tubularjoints (multi_ductpipes)weldedbycircularcylindricalshells (circulartubes)havebeenwidelyusedinengineering .Oneoftheprimaryfactorsthatareresponsibleformanyseriousaccidentsistheinsufficientfatiguestrengthofthejo… 相似文献
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Functionally gradient materials (FGM) are new engineering materials without fully understanding. One important aspect in mechanical analysis of FGM is to determine a gradient distribution that finally results in maximum thermal stress relaxation. In this paper, numerical analysis by finite element method and experimental analysis by Moire interference method were carried out to study the stress distribution in FGM. Much attention was paid on the edge effect stresses in the coating/substrate structures, and their dependence on the different gradient distribution of the new kind of composite materials. 相似文献