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1.
本文讨论对于各向异性硬化材料,裂纹定常扩展过程中,Ⅲ型裂纹的有限元分析的结果.利用数值计算结果,确定了(1)理想弹塑性;(2)各向同性硬化;(3)各向异性硬化三种情况下的局部渐近解的待定系数.得到了Ⅲ型定常扩展裂纹的全场解.指出,对于考虑各向异性硬化的材料,开口位移的近尖端断裂准则与裂纹尖端应变准则所描写的裂纹扩展阻力是不同的.它受到各向异性硬化参数M与硬化指数N的强烈影响.  相似文献   

2.
王海波  周伟  阎昱  李强  何东 《力学学报》2018,50(5):1051-1062
屈服准则对板料成形过程的理论解析、工艺优化和有限元模拟有着重要的影响. 通过提高屈服准则的各向异性表征能力, 可以确保成形过程的可靠性及实际预测的准确性. 本文基于非关联流动法则, 给出了Gotoh屈服准则一套全新的参数求解方法. 在结合常用屈服准则并考虑流动规律的基础上, 分别以5754O铝合金、DP980先进高强钢和SAPH440结构钢作为研究对象, 进行了不同加载路径下各向异性变形行为的预测. 根据Gotoh屈服准则推导的屈服函数、塑性势函数以及基于关联流动的理论函数计算出屈服应力和各向异性指数$r$值随加载角度的分布趋势, 进而针对平面应力状态的屈服轨迹展开分析, 验证了不同屈服准则和流动规律对各向异性屈服行为的预测精度. 理论与实验数据对比结果表明: 不同屈服准则针对同种板料在流动规律一致的情形下其表征各向异性的能力有显著差异; 相同屈服准则基于不同流动规律其表征能力也具有明显差别. 基于非关联流动的屈服准则能极大地提高精度, 各向异性表征能力显著加强. 相关结果能够为各向异性屈服准则在塑性成形领域的实际应用方案提供重要参考.   相似文献   

3.
屈服准则对板料成形过程的理论解析、工艺优化和有限元模拟有着重要的影响.通过提高屈服准则的各向异性表征能力,可以确保成形过程的可靠性及实际预测的准确性.本文基于非关联流动法则,给出了Gotoh屈服准则一套全新的参数求解方法.在结合常用屈服准则并考虑流动规律的基础上,分别以5754O铝合金、DP980先进高强钢和SAPH440结构钢作为研究对象,进行了不同加载路径下各向异性变形行为的预测.根据Gotoh屈服准则推导的屈服函数、塑性势函数以及基于关联流动的理论函数计算出屈服应力和各向异性指数r值随加载角度的分布趋势,进而针对平面应力状态的屈服轨迹展开分析,验证了不同屈服准则和流动规律对各向异性屈服行为的预测精度.理论与实验数据对比结果表明:不同屈服准则针对同种板料在流动规律一致的情形下其表征各向异性的能力有显著差异;相同屈服准则基于不同流动规律其表征能力也具有明显差别.基于非关联流动的屈服准则能极大地提高精度,各向异性表征能力显著加强.相关结果能够为各向异性屈服准则在塑性成形领域的实际应用方案提供重要参考.  相似文献   

4.
尺寸效应是微成形研究中的热点和难点之一。目前采用经典塑性理论仍不能对金属薄板液压胀形中尺寸效应对应力变化现象的影响进行较好的解释。为了深入分析该问题,结合应变梯度塑性理论,建立了第Ⅱ类尺寸效应影响下金属薄板液压胀形本构模型。基于该模型,分析了板料厚度变化以及胀形凹模直径变化对液压胀形过程流动应力变化的影响。研究结果表明应用该本构模型能较好地解释金属薄板液压胀形中尺寸效应对应力变化的影响,验证了该本构模型的正确性。  相似文献   

5.
采用大变形刚粘塑性有限元法模拟超塑性恒压轴对称充模胀形过程、分析了模具几何参数及材料参数对胀形过程中材料的流变行为、胀形制许厚度分布和成形时间的影响规律。给出了质点的流动轨迹、不同时刻制件的剖面形状及应力、应变分布;基于修正的Gurson粘塑性势推导了内部空洞体积分数累积增大模型并据此进行了变形-损伤耦合计算.  相似文献   

6.
采用大变形刚粘塑性有限元法模拟超塑性恒压轴对称充模胀形过程,分析了模具几何参数及材料参数对胀形过程中材料的流变行为、胀形制件厚度分布和成形时间的影响规律,给出了质点的流动轨迹,不同时刻制件的剖面形状及应力、应变分布;基于修正的Gurson粘塑性势推导了内部空洞体积分数累积增大模型并据此进行了变形-损伤耦合计算。  相似文献   

7.
基于弹塑性力学和损伤理论,建立了一个与应力球张量有关的具损伤正交各向异性材料的混合硬化屈服准则,该准则无量纲化后与各向同性材料的Mises准则同构,在此基础上,建立了正交各向异性材料的增量型和全量型弹塑性损伤本构方程,并以具确定弱区域正交各向异性矩形薄板为例,根据屈曲时的能量准则和全量理论,以等效塑性应变为内变量,对其弹塑性屈曲问题进行了分析,讨论了几何参数和弱区域对正交各向异性薄板弹塑性屈曲临界应力的影响.  相似文献   

8.
剪胀性是包括岩土材料在内的摩擦性颗粒材料的重要特征之一, 其形成机制与颗粒体系内部拓扑结构的演化有关. 基于颗粒体系细观数据, 可对颗粒体系内部的拓扑结构特征及演化进行分析, 进而建立拓扑演化与宏观剪胀变形之间的联系. 采用离散单元法, 根据密实、中密和松散摩擦性颗粒材料双轴试验的宏微观数据, 从拓扑参量演化及接触网络拓扑变化所引起的3类细观结构几何特征等方面研究了颗粒材料宏观剪胀变形的拓扑机制. 研究表明: 密实和中密颗粒体系双轴试验过程存在应变软化和剪胀现象, 与细观结构的拓扑演化与几何各向异性相关, 而松散颗粒体系剪胀效应不明显; 将接触网络剖分成多边形力环结构并根据拓扑演化定义新生、消失和不变3类细观结构, 在加载过程中不同拓扑属性细观结构所占比例及各向异性存在较大差异, 且较大尺寸的力环可承担较大的几何各向异性; 新生力环结构在双轴加载过程中能够表现出更加明显的剪胀特性, 颗粒体系整体的剪胀变形受到新生结构拓扑变化及恒定结构几何变化的综合影响.   相似文献   

9.
K0固结黏土在自然界广泛分布, 其通常同时具有超固结性与天然结构性, 而K0超固结性又与K0正常固结性质存在很大差异. 为了有效的描述K0超固结性质, 在结构性模型基础上, 做了如下三点改进, 使得原模型拓展为同时考虑K0超固结特性与天然结构性影响的本构模型. (1)引入相对应力比来描述屈服面, 并引入初始各向异性转轴参量ξ来表达初始各向异性对屈服面在p-q空间的位置影响. (2)基于给定的屈服面方程, 推导得到变相应力比参量, 并将变相应力比引入到统一硬化参数中, 利用统一硬化参数可以有效描述初始各向异性固结黏土在剪切加载下的剪缩与剪胀, 应变硬化及软化现象. (3)引入反映结构性胶结强度性质的胶结参量pe, 并给出pe随塑性偏应变的衰减演化方程, 利用胶结参量可描述结构性黏土的剪胀特性. 预测与试验结果对比表明, 所提的K0超固结结构性模型可有效描述K0超固结黏土的刚度提高效应, 黏土的包辛格效应, 结构性黏土胶结强度的损失现象以及结构性黏土的应变软化现象. 证明了所提模型的适用性以及合理性.   相似文献   

10.
采用刚粘塑性有限元法模拟了超塑性恒压充模胀形过程,分析了应变速率敏感性指数m、厚向异性系数R、初始板厚、界面摩擦等因素对应力、应变和应变速率等力学量场的影响;通过对铝合金LY12CZ板料的相应实验对模拟结果进行了验证  相似文献   

11.
In this paper, the influences of various material parameters, the hardening exponent (n), the rate sensitivity (m). the thickness anisotropy parameter (R) and the index M in the Hosford and Hill yield function, on the hydrostatic bulging of a circular clamped sheet of ductile metal materials are analysed by introducting a rigid-viscoplastic finite element method. By numerical studies, an empirical relationship within the average limit thickness strain – 3 * and the material parameters (n andm) is obtained. Besides, it has been found that the influences of surface shapes of the yield function on the average limit thickness strain can be reflected by the Barlat'sP value which represents the effects ofR andM values.This work is supported by the National Natural Science Foundation and Natural Science Foundation of the Youth of China.  相似文献   

12.
The paper presents a study of the Marciniak and Kuczynski (MK for short) model for the prediction of limit strains of orthotropic sheet metal under in-plane proportional biaxial stretching. In two particular cases analytical results can be obtained if the groove of the MK model is oriented along one of the in-plane symmetry axes. The first case is the plane strain loading mode. Necessary and sufficient conditions are derived for the MK-predicted plane strain limit strain to match exactly the experimentally measured limit strain. An example of material, the AA5182-O aluminum alloy, that does not satisfy these conditions is discussed. It is shown then that if a power-law strain rate sensitivity is included in the hardening law then the MK-model can match exactly any target plane strain limit strain. The second case is the non-hardening case for positive strain ratios. This case allows for an insight into the way the MK-predicted limit strains depend upon the yield function. Based on the theory developed for the plane strain case, material heterogeneity as a possible cause for unstable plastic flow is further discussed. It is shown that such heterogeneities can be modeled by perturbing the rate of deformation with an eigenstrain. This allows for an extension of the MK-model to sheets of uniform thickness.  相似文献   

13.
The distribution of stress, displacement and plastic strain in a rotating elastic–plastic solid disk of variable thickness in a power function form is investigated. The analysis is based on Tresca's yield condition, its associated flow rule and linear strain hardening material behavior. An analytical solution is obtained and numerical results are presented for different values of the geometric parameters. The validity of the solution is demonstrated by comparing the results with those for a uniform thickness disk available in the literature.  相似文献   

14.
15.
In the present work, a comprehensive parametric study for establishing contact mechanics of instrumented normal spherical indentation on homogeneous materials and materials with plastically graded surface layer (PGSL) was undertaken by dimensional analysis and finite element modeling. The spherical indentation response for homogeneous materials can be described only by two dimensionless parameters: strain hardening exponent and a unified parameter that can describe effects of both the normalized yield strength and the normalized indentation depth. The influences of these two parameters were investigated for a wide range of engineering materials, and the results may be used as an estimate of loading response and pile-up/sink-in behavior when the material properties are known. In the materials with PGSL, a linear gradient in yield strength, and no variation in elastic modulus and strain hardening exponent were explored. The indentation response of the materials with PGSL can be described only by three dimensionless parameters: the normalized indentation depth, the dimensionless strength gradient parameter, and the normalized PGSL thickness. The effects of these three parameters were studied systematically. The normalized pile-up/sink-in parameter is found to be an increasing function of the strength gradient parameter. The normalized pile-up/sink-in parameter increases (decreases) with increasing PGSL thickness for a fixed positive (negative) gradient case at large indentation depth. The results also indicate that the materials with positive PGSL can bear more loads and have significantly more resistance to contact crack formation.  相似文献   

16.
The rheological nature of paper or board is usually treated either as elasto-plastic or as viscoelastic depending on the studied paper making process or behavior in converting and end use. In this paper we study several stress–strain curve models and the determination of material parameters from an elasto-plastic point of view. Finally, a suitable approach for all stress–strain curves measured from 180 strips is constructed using a linear function for an elastic region and a nonlinear function for a strain hardening region. This model determines a proportional limit (elastic limit) and gives fairly elegant dependencies between material/fitting parameters and two important factors of mechanical properties of paper: dry solids content and anisotropy. In this paper the dependency of a plastic strain on dry solids content and anisotropy is estimated using the introduced stress–strain curve model. Correspondingly, the model can be used to estimate many other mechanical behaviors, for example, the tension differences arising from non-uniform moisture content of the paper web profile. However, the main target of this study is to produce competent parameters based on modeled stress–strain curves for further construction of a material model. This elasto-plastic material model will be utilized in out-of-plane deformation and fracture models.  相似文献   

17.
Superconducting radio frequency (SRF) niobium cavities are widely used in high-energy physics to accelerate particle beams in particle accelerators. The performance of SRF cavities is affected by the microstructure and purity of the niobium sheet, surface quality, geometry, etc. Following optimum strain paths in the forming of these cavities can significantly control these parameters. To select these strain paths, however, information about the mechanical behavior, microstructure, and formability of the niobium sheet is required. Due to the lack of information, first an extensive experimental study was carried out to characterize the formability of the niobium sheet, followed by examining the suitability of Hill’s anisotropic yield function to model its plastic behavior. Results from this study showed that, due to intrinsic behavior, it is necessary to evolve the anisotropic coefficients of Hill’s yield function in order to properly model the plastic behavior of the niobium sheet. The accuracy of the newly developed evolutionary yield function was verified by applying it to the modeling of the hydrostatic bulging of the niobium sheet.  相似文献   

18.
Advances using optical fibres as sensors may represent an important contribution for development of minimally invasive techniques in biomedical and biomechanical applications. Concerning spine injuries, intervertebral disc (IVD) degeneration is a major clinical issue since it represents gross structural disruption and it is irreversible. Measuring biomechanical parameters of the IVD should contribute for better understanding on its mechanical response to external applied forces. The purpose of this study was to explore the potential of a Fibre Bragg Grating (FBG) sensor to measure strain caused by bulging of the intervertebral disc under axial compression. Disc bulging is a consequence of IVD compression and a technique to register this behaviour is addressed in this study. Needle-mounted sensors were already used to measure IVD pressure in cadaveric material. In this study we also explored the possibility of using needles only for sensor guiding and positioning leaving sensor directly in contact with the IVD material. An ex vivo porcine dorsal functional spinal unit was instrumented with a FBG sensor and submitted to axial compression. Results suggest the sensor’s ability to measure strain response to load. Bulging of the annulus fibrosus as a consequence of axial compression was confirmed using the FBG sensor. Hysteresis and viscoelastic behaviour were observable suggesting that energy is dissipated by the deformation of the annulus and that unloading time was insufficient for disc recovery. Nevertheless the relatively low strain sensitivity of the sensor as well as signal artefacts caused by transverse loading may constitute a problem in the analysis and interpretation of strain data. The technique may not be suitable for measurement of physiologic bulging being more indicative of the radial force exerted by the annulus.  相似文献   

19.
本文对于Hill(1979)屈服准则在平面应力条件下进行了展开,给出了五种特定条件下的等效应力和等效应变速率表达式,对这些特例的凸条件检验表明,其中的四种可做为合理的屈服函数,将这些屈服函数应用于金属薄板在拉伸范围内的成形极限图的M—K理论预测,获得了较为理想的结果。  相似文献   

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