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温度场的计算对淬火过程中热应力和热应变的分析有较大影响。对淬火后试件的残余应力和微观结构分析也有较大影响。本文以45钢圆柱试件为研究对象,采用文献(2)所得到的非线性表面换热系数 ,将Norsette法用于有限单元分析中,计算了淬火过程中的非经恶性循环温度场,有效地避免了在小时间步长下数值解出现震荡的问题,有限单元法数值解与实验结果吻合较好。 相似文献
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在金属淬火过程的数值模拟中,换热系数的正确求解是工件温度场、应力/应变场模拟结果与实际相符合的先决条件.据此研究和分析了换热系数反求法的数学模型,分别采用一维和三维有限元法对该数学模型求解.研究表明:与采用一维有限差分的求解法相比较,计算过程由一维有限元法增加到三维有限元法,与实际情况更为接近;用有限元方法求解的换热系数曲线连续且平滑,结果可靠,且编程量小;用求得的换热系数计算金属淬火试件的中心温度场变化曲线,计算结果与实测数据相吻合. 相似文献
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圆柱体激光相变硬化三维温度场数值计算 总被引:3,自引:0,他引:3
建立了圆柱体工件激光相变硬化过程的三维传热学模型,根据此模型,采用有限差分法对圆柱体工件在激光相变硬化过程中的三维非稳态温度场进行了数值模拟,预测了42CrMo钢圆柱体工件激光相变硬化区的宽度和深度,对42CrMo钢圆柱体工件进行了激光相变硬化实验,并实测了工件激光相变硬化区的宽度和深度,研究结果表明:采用数值计算的方法,可以准确地计算出圆柱体激光相变硬化过程的温度分布及微观组织分布;预测的激光相变硬化区宽度和深度与实验测量结果符合的较好。 相似文献
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Abstract Laser heating of SKD61 steel usually causes the formation of a melting layer on the steel surface, which is of poor thermal conductivity and diffusivity. The modified Ashby‐Easterling heat‐transfer equation was used to simulate the temperature distribution for laser surface hardening of SKD61 steel. The phase transformation temperatures of SKD61 in the quenched and as‐received conditions were compared with each other for different laser energy densities. When the laser was focused on the steel, the temperature of the SKD61 was raised. Due to the effect of superheating, the critical phase transformation temperature in laser hardening became higher than the austenized temperature (1010°C) in traditional quenching. However, the critical phase transformation temperature of SKD61 decreased with increasing laser energy density. 相似文献
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This paper deals with the stochastic finite element analysis of nonlinear structural dynamic problems, consisting of a linearly elastic square plate lying on a nonlinear foundation and loaded with a deterministic uniform transverse dynamic load. The plate can be either simply-supported or fixed-all-around. The stochasticity of the problem arises from the spatial randomness of the elastic modulus of the plate and/or from the spatial randomness of a coefficient controlling the degree of nonlinearity of the foundation. Monte Carlo simulation techniques along with a finite element formulation of the problem are used in order to analyze the system. It is concluded that the maximum deflection at the center of the square plate fits to the lognormal distribution. Various conclusions are also drawn on the influence of the stochasticity of the elastic modulus and/or the stochasticity of the nonlinear foundation and the degree of nonlinearity of the foundation on the value of the coefficient of variation of the maximum deflection at the center of the plate. 相似文献
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G. Z. KANG Y. LI Q. GAO Q. H. KAN J. ZHANG 《Fatigue & Fracture of Engineering Materials & Structures》2006,29(2):93-103
The cyclic deformation of three structural steels, SS316L stainless steel, 40Cr3MoV bainitic steel and 25CDV4.11 steel, were studied experimentally by uniaxial cyclic straining or stressing tests at room temperature. The cyclic softening/hardening behaviours of the steels were discussed first by cyclic straining tests; and then the effects of cyclic softening/hardening behaviours on the uniaxial ratchetting of the materials were investigated by asymmetrical cyclic stressing tests. It is concluded from the experimental results that the ratchetting greatly depends on the cyclic softening/hardening behaviours of the materials, as well as the loading history. Different ratchetting and failure behaviours are observed for the prescribed steels. It is also stated that the proposed unified visco‐plastic constitutive model can provide a fairly reasonable simulation of the uniaxial ratchetting of SS316L stainless steel and 25CDV4.11 steel; but cannot simulate the ratchetting of 40Cr3MoV bainitic steel since the dependence of cyclic softening behaviours on the applied inelastic strain amplitude cannot be reasonably described in the discussed constitutive model. Some significant conclusions are obtained, which are useful to construct constitutive model to describe the ratchetting of the materials with different cyclic softening/hardening behaviours. 相似文献
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In this paper, some key technologies of computing the quenching temperature field are given. According to the characteristics
of quenching process, a new method of computing phase-transformation latent heat is presented to ensure the computation accuracy
of temperature. The phase-transform latent heat is regarded as the internal heat source because it can result in the rise
of temperature in the process of cooling. A new method of self-control and adaptive time-step is presented in this paper.
This method can be used to compute the time-step according to maximum and minimum difference values of the temperature field
between the previous simulating step and the current simulating step. A finite element method (FEM) software for evaluating
the temperature and the phase-transformation is developed by using the methods presented in this paper, the lump parameters
method and fine mesh method. The experimental results or analytical values of two cases are used to check the accuracy of
FEM simulation. The comparisons show that the simulation results of FEM software are consistent with experimental results
or analytical values. 相似文献
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为降低成形过程的热应力,抑制成形过程裂缝的产生,减小成形过程试样和基板的翘曲变形,激光金属沉积成形往往需要进行基板预热,因此研究不同基板预热温度对激光金属沉积成形过程温度场的影响具有非常重要的意义.根据有限元分析中的“单元生死”技术,利用APDL编程建立了基板预热对激光金属沉积成形过程温度场影响的三维多道多层数值模拟模型,详细分析了基板未预热和分别预热到200,300,400,500,600 ℃时对沉积成形过程温度场和温度梯度的影响.通过中国科学院沈阳自动化研究所自行研制的激光金属沉积成形系统和基板预热系统,在与模拟过程相同的参数下,利用镍基合金粉末在基板未预热和分别预热到300,400,500,560 ℃时进行了成形试验,试验结果跟数值模拟结果吻合较好. 相似文献
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A Ramalingam B J Kalaiselvi S Sridharan P K Palanisamy V Masilamani 《Bulletin of Materials Science》1998,21(3):247-249
Surface modification of metals and alloys using lasers has acquired considerable importance because the changes achieved are
highly localized and superficial. In this process the mechanical and structural properties of the bulk are retained as such
because of the high temperature gradient and high rate of change of temperature that are unattainable by conventional methods.
The present report is on surface hardening of oil-hardened nonshrinking (OHNS) steel using Ruby laser in normal mode. It is
found that surface hardening increases thrice the size of base material and the microstructure of the laser-heated zone changes
from pearlite phase to martensite phase. 相似文献
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本文采用ANSYS对某汽车40Cr转向节的淬火冷却过程温度场进行了数值模拟、温度场的求解,并考虑了材料热物性参数随温度的变化,得到瞬态温度场,进而对照40Cr的CCT推导组织转变,利用临界冷却速度预测了某些位置的淬硬层深度,并通过金相组织分析和硬度测试进行了验证。模拟结果和实验结果基本吻合。实测淬硬层与预测淬硬层深度相比,其值偏大;实测硬度值与预测硬度值相比,其值偏小。 相似文献