基于Ogden公式的充压伸缩式水封非线性计算研究

考虑橡胶类止水材料性能对水封设计的重要作用,论文采用Mooney-Rivlin公式和Ogden公式对橡胶类止水材料的单向拉伸、单轴压缩和纯剪实验数据进行曲线拟合与研究.结合工程实例将该两种公式的拟合参数应用于充压伸缩式水封自由外伸量的非线性有限元计算中,并将计算结果与该水封自由外伸量模型实验进行对比研究.结果表明:Og...     

不同本构模型对橡胶制品有限元法适应性研究

为确定不同本构模型对橡胶制品进行非线性有限元分析的适应性,采用HyperMesh 和ABAQUS软件建立了橡胶标准试件和防尘罩制品的非线性有限元模型. 根据标准试件单轴拉伸试验数据,利用ABAQUS软件拟合了Mooney--Rivlin, Ogden 及Yeoh 3 种本构模型的特征参数,并给出了试件和制品轴向拉伸和压缩工况有限元分析结果. 实测试验与有限元分析结果对比发现:在应变不大于100% 时,两参数的Mooney--Rivlin本构模型计算误差较小;在应变大于100% 时, 用Yeoh 和Ogden 本构模型计算误差较小. 该结论对大变形橡胶元件的非线性特性理论分析具有实际意义.     

一种修正的低温流体空化流动计算模型

为了更准确地预测低温流体的空化流动特性, 基于Kubota空化模型, 对蒸发和凝结源项进行修正, 建立了一种考虑热力学效应的空化模型. 分别采用原始和修正的Kubota空化模型, 计算了绕对称回转体液氮的空化流动, 通过与实验结果的比较对修正的空化模型进行了评价. 结果表明, 与原Kubota空化模型比较, 修正的空化模型由于考虑了热力学效应, 计算获得的蒸发量减小, 凝结量增大, 空穴长度减小, 空穴界面形态呈模糊状态.计算结果与实验结果更加一致, 说明修正的空化模型能准确的描述低温流体空化过程的质量传输过程, 能够更准确模拟低温流体中的空化流动特性.      

点接触边界润滑吸附膜计算模型

根据2个假设提出1种边界润滑的计算模型,通过吸附热理论对公式进行修正,利用自行设计的球-盘摩擦磨损试验装置,在汉硬脂酸的石油醚溶液中进行试验,所用45#钢盘的表面粗糙度分别为0.2μm和0.4μm,对理论计算数据和实验数据进行对比,并分析温度和速度等参数对摩擦系数的影响.结果表明,计算结果和实验数据的变化趋势吻合,摩擦系数随着温度增加而增大,随速度增加略有减小.     

110甲基乙烯基硅橡胶材料参数的确定

应用INSTRON5544对110甲基乙烯基硅橡胶材料进行了单轴大变形压缩的力学特性测试。本文根据已有的Mooney-Rivilin模型和Yeoh模型的本构关系,采用泰勒级数展开的办法获得了基于小变形的本构关系表达式。利用本文所得本构关系,将实验数据进行了非线性拟合处理,得到了相应的Mooney-Rivilin模型和Yeoh模型的材料参数。拟合所得的名义应力-应变曲线与实测的名义应力-应变曲线吻合较好。利用非线性拟合所得的Mooney-Rivilin模型和Yeoh模型的材料参数,应用ABAQUS软件进行有限元分析计算。通过有限元的分析计算,验证了Mooney-Rivilin模型和Yeoh模型材料参数的正确性与可行性。     

基于非平衡多相模型的含铝炸药爆速研究

通过对爆轰反应区中铝粉压力、温度弛豫时间的计算,发现爆轰产物压力是平衡的,温度是不平衡 的。对传统CJ模型进行了改进,考虑爆轰产物的多相性和产物温度间的非平衡性,提出了一种新的计算含 铝炸药爆速的模型。采用该模型对几种含铝炸药的爆速进行了计算,并与已有的实验数据进行了对比,计算 结果优于传统CJ模型,与实验的误差在2%以内。     

金属铍的压缩变形行为

利用材料试验机及Hopkinson杆装置系统开展热等静压金属铍在不同温度下的静动态压缩力学行为研究,获得了温度、应变率对金属铍屈服强度和加工硬化行为的影响规律。结果表明:金属铍在压缩应力状态下呈现出良好的塑性,同时其力学性能具有显著的应变率敏感性与热软化效应,屈服强度和流动应力随应变率提高呈明显增大趋势,随着温度升高逐渐降低。同时,室温下其加工硬化行为随着应变增大表现为分段硬化特征,随温度升高则趋于理想塑性。最后,采用修正的Johnson-Cook本构模型对实验结果进行了拟合,模型计算结果与实验结果吻合较好。     

加速度计相关误差模型辨识

本文讨论陀螺加速度计输出误差与陀螺加速度计各回路状态变量间的相关误差模型的辨识方法。陀螺加速度计各回路的状态变量包括:伺服回路引出的浮子的倾角,磁悬浮回路引出的浮子的轴向位移与径向位移信号、陀螺摆壳体组件内的热敏电阻引出的浮子的环境温度信号、以及陀螺马达的激磁电压等。文章首先介绍了辨识陀螺加速度计输出残差与各回路状态变量的相关误差模型ARMAX(n,m,p)的辅助变量法与相关估计法,然后进行了仿真实验,最后应用实际测量得到的陀螺加速度计输出与状态变量数据,给出了实验结果。实验结果表明,本文介绍的相关误差模型辨识方法是可行的。     

碳纳米管增强氟橡胶高温力学行为及本构关系研究

改性氟橡胶因其优异的耐油耐高温及良好的物理性能,广泛应用于汽车、航空航天和国防等领域。本文通过对不同温度(120 ℃~220 ℃)下碳纳米管增强氟橡胶的单轴拉伸试验结果进行分析,得到改性氟橡胶力学行为随温度变化的特点。通过本构模型评估和材料参数拟合,推导出适用于改性氟橡胶的温度相关修正本构方程。最终对比了特定温度下单轴拉伸的试验结果与模型预测结果,证明了温度相关的修正Yeoh模型可以较好地描述试验温度内碳纳米管增强氟橡胶的力学性能,为高温下改性氟橡胶的工程应用提供理论基础。     

帘线/橡胶复合材料各向异性黏-超弹性本构模型

帘线/橡胶复合材料广泛应用于轮胎等重要工程领域,为了描述其在服役条件下的大变形、非线性、各向异性和高应变率等材料力学行为,基于纤维增强复合材料连续介质力学理论,提出了一种考虑应变率效应的帘线/橡胶复合材料各向异性黏-超弹性本构模型. 该模型中单位体积的应变能被解耦为便于参数识别的基体等容变形能、帘线拉伸变形能、剪切应变能和黏性应变能四部分. 给出了模型参数的确定方法,并通过拟合文献中单轴拉伸、偏轴拉伸实验数据,得到了模型参数. 利用该模型预测了不同加载和变形条件下的力学行为,并将预测结果与实验结果对比分析. 结果表明, 考虑黏性模型和不考虑黏性模型对不同应变率变形条件下的预测结果相差很大,且考虑黏性模型的预测结果与实验结果吻合很好. 因此,与不考虑黏性模型相比,所提出的各向异性黏-超弹性本构模型能更好地表征帘线/橡胶复合材料在大变形、高应变率条件下的力学特性.      

炭黑填充天然橡胶Mullins效应的仿真与计算分析

通过有限元分析软件Abaqus、Matlab数据拟合工具及单轴拉伸试验,研究了Yeoh本构模型、Ogden本构模型及伪弹性理论模型对炭黑填充天然橡胶的Mullins效应仿真效果及规律。结果表明,(1)对单轴拉伸主加载曲线的拟合,Ogden模型精度更高,而Yeoh模型随着炭黑含量的增加在小变形处的拟合效果变差;(2)提出了伪弹性参数与伸长比之间的关系,找到了一种快速计算伪弹性参数的方法,且精度良好,极大地提高了计算效率。     

A combined isotropic-kinematic hardening model for the simulation of warm forming and subsequent loading at room temperature

A coupled isotropic-kinematic hardening material model was developed based on phenomenological observations of performed two stage experiments on a medium carbon steel – SAE 1144, where the first deformation is performed at elevated temperatures and the second deformation at room temperature. Above all, deformations with orthogonal loading at various temperatures were investigated in order to determine the influence of the loading direction as well as of the temperature. Bergström’s theory of work hardening as well as the nonlinear kinematic hardening of an Armstrong–Frederick type were used as a basis for the model development. In the proposed model a relationship between material coefficients of the classical Bergström model and temperature was investigated. The aim of the new material model was to introduce the least possible amount of new parameters as well as to facilitate the mathematical determination of parameters during the fitting of the model with experimental data. The developed model was implemented in an in-house FE-Code in order to simulate the material behavior due to the dynamic strain aging and the hardening behavior after the dynamic strain aging process. Representative simulation results were compared with the experimental data in order to validate the efficiency and the application range of the model.     

常规螺杆泵定子有限元分析

螺杆泵定子橡胶不仅是易损构件，而且它与转子的配合状况对螺杆泵的工作性能影响显著。目前，还没有能够直接对实际工况下的定子橡胶的变形和受力状态进行测试的有效手段，因此对螺杆泵定子进行有限元分析自然是有益的尝试。重点研究定子橡胶衬垫内轮廓线的变形规律，而应力和应变分布情况仅作为辅助性的分析；对螺杆泵工况的考虑方面，重点研究均匀内压作用的情况，再考虑工作压差以及定子与转子的装配等所引起定子橡胶的变形和受力的变化。利用有限元分析软件Abaqus，对螺杆泵定子进行研究，得出了螺杆泵定子在不同工况下的受力状态和变形规律以及定子材料参数对变形规律的影响。利用此规律可对螺杆泵进行优化设计，提高其工作效率。     

Probabilistic and stochastic aspects of rubber hyperelasticity

The main aim of this work is to compare various models of rubber elasticity, i.e. neo-Hookean, Mooney-Rivlin, Yeoh, Gent, Arruda-Boyce as well as the Extended Tube model in terms of their application to the probabilistic analysis. Some discussions concerning failure analysis of the rubbers according to these models is provided also. Constitutive relations following these theories are tested for the case of uniaxial tension of the incompressible material, where deformation of a rubber specimen is treated as Gaussian random variable having a priori given expectation and standard deviations varying in some interval with bounds driven by various experimentation techniques. Probabilistic analysis is provided here in two alternative ways—via traditional Monte-Carlo technique as well as using higher order stochastic perturbation method implemented both in the symbolic computer algebra software. An application of non-Gaussian distributions relevant to the considered deformation, like lognormal one for instance has been also considered. This analysis includes computational determination of the first four basic probabilistic characteristics, i.e. expectation, coefficient of variation, skewness and kurtosis, and is provided to verify the resulting probabilistic distribution of the induced stress and its entropy. Some conclusions are drawn for the generalization of this method to other stress softening materials.     

A micromechanical model of hardening, rate sensitivity and thermal softening in BCC single crystals

The present paper is concerned with the development of a micromechanical model of the hardening, rate-sensitivity and thermal softening of bcc crystals. In formulating the model, we specifically consider the following unit processes: double-kink formation and thermally activated motion of kinks; the close-range interactions between primary and forest dislocations, leading to the formation of jogs; the percolation motion of dislocations through a random array of forest dislocations introducing short-range obstacles of different strengths; dislocation multiplication due to breeding by double cross-slip; and dislocation pair annihilation. The model is found to capture salient features of the behavior of Ta crystals such as: the dependence of the initial yield point on temperature and strain rate; the presence of a marked stage I of easy glide, specially at low temperatures and high strain rates; the sharp onset of stage II hardening and its tendency to shift towards lower strains, and eventually disappear, as the temperature increases or the strain rate decreases; the parabolic stage II hardening at low strain rates or high temperatures; the stage II softening at high strain rates or low temperatures; the trend towards saturation at high strains; the temperature and strain-rate dependence of the saturation stress; and the orientation dependence of the hardening rate.     

A viscoplastic constitutive model for nickel-base superalloy,part 2: modeling under anisothermal conditions

In Part 2 of this study, extensive deformation tests were carried out on the nickel-base polycrystalline superalloy IN738LC under isothermal and anisothermal conditions between 450 and 950 °C. Under the isothermal conditions, the material showed almost no rate/time-dependency below 700 °C, while it showed distinct rate/time-dependency above 800 °C. Regarding the cyclic deformation, slight cyclic hardening behavior was observed when the temperature was below 700 °C and the imposed strain rate was fast, whereas in the case of the temperature above 800 °C or under slower strain rate conditions, the cyclic hardening behavior was scarcely observed. Unique inelastic behavior was observed under in-phase and out-of-phase anisothermal conditions: with an increase in the number of cycles, the stress at higher temperatures became smaller and the stress at lower temperatures became larger in absolute value although the stress range was approximately constant during the cyclic loading. In other words, the mean stress continues to evolve cycle-by-cycle in the direction of the stress at lower temperatures. Based on the experimental results, it was assumed that evolution of the variable Y that had been incorporated into a kinematic hardening rule in Part 1 of this study is active under higher temperatures and is negligible under lower temperatures. The material constants used in the constitutive equations were determined with the isothermal data, and were expressed as functions of temperature empirically. The extended viscoplastic constitutive equations were applied to the anisothermal cyclic loading as well as the monotonic tension, stress relaxation, creep and cyclic loading under the isothermal conditions. It was demonstrated that the present viscoplastic constitutive model was successful in describing the inelastic behavior of the material adequately, including the anomalous inelastic behavior observed under the anisothermal conditions, owing to the consideration of the variable Y.     

Constitutive modeling of isotropic hyperelastic materials in an exponential framework using a self-contained approach

In this paper, an exponential framework for strain energy density functions of elastomers and soft biological tissues is proposed. Based on this framework and using a self-contained approach that is different from a guesswork or combination viewpoint, a set strain energy density functions in terms of the first and second strain invariants is rebuilt. Among the constructed options for strain energy density, a new exponential and mathematically justified model is examined. This model benefits from the existence of second strain invariant, simplicity, stability of parameters, and the state of being accurate. This model can capture strain softening, strain hardening and is able to differentiate between various deformation-state dependent responses of elastomers and soft tissues undergoing finite deformation. The model has two material parameters and the mathematical formulation is simple to render the possibility of numerical implementations. In order to investigate the appropriateness of the proposed model in comparison to other hyperelastic models, several experimental data for incompressible isotropic materials (elastomers) such as VHB 4905 (polyacrylate rubber), two various silicone rubbers, synthetic rubber neoprene, two different natural rubbers, b186 rubber (a carbon black-filled rubber), Yeoh vulcanizate rubber, and finally porcine liver tissue (a very soft biological tissue) are examined. The results demonstrate that the proposed model provides an acceptable prediction of the behavior of elastomers and soft tissues under large deformation for different applied loading states.     

温度对炭黑填充橡胶复合材料力学性能影响的实验研究

采用岛津万能试验机对天然与丁苯共混橡胶(NSBR)试件进行不同温度下多步松弛循环加卸载实验和单向拉伸加卸载循环实验，对比两者的宏观力学响应，并研究温度对炭黑填充复合材料力学性能的影响．结果表明：(1)随着温度的升高，未填充橡胶逐渐变“硬”，而炭黑填充橡胶是“先变软后变硬”．(2)随着温度的升高，橡胶的迟滞损耗呈线性减小．(3)比较单向拉伸和应力松弛平衡点的应力应变曲线，填充橡胶“先变软后变硬”的温度转折点不同，这是由于应力松弛过程基本消除了粘弹性效应．