几种应变定义在有限变形下的适用性研究

按材料不可压缩假定 ,研究了 4种应变定义在有限变形情况下对变形的描述规律 ,指出在对有限变形过程进行描述时 ,对数应变定义最合适 ,其次是小变形定义和阿尔曼西应变定义 ,而格林应变定义不合适     

杆件受压时有限变形幂次强化计算方案

在测定铅的有限变形应力应变曲线基础上，采用幂次强化本构方程进行模拟，分别对2种不同方案进行了有限元计算分析。从计算精度和叠代收敛速度两方面考虑，定出了幂次强化本构方程的最佳回归参数并给出了合理的方案。     

12×4J轮辐斜冲模翻边变形分析

利用斜冲模对12×4J轮辐进行翻边时,将变形区看做是平面应力状态,探讨了翻边高度、初始孔径及斜冲模角对翻边变形区径向应变和轴向应变的影响,对12×4J轮辐翻边不同斜冲模角下的冲压力变化规律进行了计算.结果表明,影响变薄的因素除斜冲角以外,还与其周向应变有关.厚向应变和径向应变随斜冲角增大而增大,但翻边力却正好相反,综合考虑,斜冲角取α=30°～35°比较理想.     

KdV方程的对数型有限差分格式

给出了KdV方程的对数型有限差分格式,利用精确解给出初边值条件;利用Matlab软件编程求出数值解,并与指数型差分格式的数值解进行比较.结果表明,对数型有限差分格式具有精度高且可以长时间稳定计算的优点.     

KdV方程的对数型有限差分格式

给出了KdV方程的对数型有限差分格式,利用精确解给出初边值条件;利用Matlab软件编程求出数值解,并与指数型差分格式的数值解进行比较.结果表明,对数型有限差分格式具有精度高且可以长时间稳定计算的优点.     

KdV方程的对数型有限差分格式

给出了KdV方程的对数型有限差分格式,利用精确解给出初边值条件;利用Matlab软件编程求出数值解,并与指数型差分格式的数值解进行比较.结果表明,对数型有限差分格式具有精度高且可以长时间稳定计算的优点.     

利用图像分析系统对变形椭圆标志体进行自动二维应变分析

利用一个配备计算机程序的图像分析系统,来自动采集椭圆标志体的有关数据并计算其应变.在图像分析中可计算出各个二元化标志体的最佳拟合椭圆,它们的轴比和长轴方位可用来计算应变.当图像面积为512×480个像元,而该标志体的面积大于360个像元并且位于256×240个像元的中心部位时,本系统所获取的数据精度,轴比在±11％之内,长轴方位在±3°以内.对变形鲕状灰岩中275个鲕粒所作的应变分析表明,采用图像分析获取的数据计算出应变椭圆.其结果与手工方法相比.轴比高出约3％,长轴方位差值为2.6°.利用该图像分析方法可在短时间内自动准确地完成有限应变分析.     

DYJ型带式榨汁机榨辊轴的循环强度研究

带式榨汁机榨辊轴所受载荷是循环变化的,若采用一次变形下的应力应变强度设计计算,则实际弹塑性变形过程产生的重要影响将被忽略;而应采用循环变形下的弹塑性分析方法研究其应力应变强度问题,通过针对榨辊轴弹塑性变形进行分析与试验研究,提出循环变形下的弹塑性应变和强度计算步骤;并作出广义最大应变与广义载荷之间的关系表和关系曲线,供工程技术人员在设计计算时查找应用。     

金属有限变形两种构形下本构模型研究

分别拟合出有限变形时物质描述和空间描述下的本构方程 ,在此基础上给出了基于物质描述和空间描述的有限元算法 .空间描述的有限元算法计算值同试验值符合得很好 ,说明用空间描述法能较好地描述金属大变形压缩的有限变形问题 .     

TC18钛合金铸锭组织特征及热变形行为

文章主要介绍了TC18钛合金大型铸锭的组织特征,利用热模拟试验机对铸态组织开展了热压缩试验,研究了不同温度和应变速率下的热变形行为,分析了应力应变曲线,计算了表观变形激活能、应变速率敏感性指数和应变硬化指数等表征指标。结果表明:TC18钛合金铸锭头部和中部低倍组织相比,中部铸态组织出现了大晶粒区域;TC18钛合金铸态组织的表观变形热激活能平均值为189.81kJ·mol~(-1)。当应变为0.6时,应变速率敏感性指数在应变速率1s~(-1)时,随变形温度的增加,m值先增加后降低。     

挤压对灵武长枣应力应变影响的有限元分析

为了分析灵武长枣在采摘过程中内部应力应变对挤压的响应规律,为采摘机器人的设计提供理论依据,本文利用万能力学试验机在15、20、25、30、35 mm/min五种不同挤压速率下对灵武长枣整果进行了横向和纵向压缩,对力-变形曲线进行拟合,求得长枣在压缩破裂时的刚度及破裂力,并对15和35 mm/min两种横向挤压速率进行了有限元模拟,建立了有限元模型。结果表明:灵武长枣在受到挤压时,其力学性能具有各向异性,横向的抗压能力更强。横向压缩时,整果破裂负载为214.34~266.53 N,弹性模量为14.90~17.05 MPa,相对变形量为20.70%~22.67%;纵向压缩时,整果破裂负载为132.52~185.40 N,弹性模量为4.59~6.07 MPa,相对变形量为13.72%~17.25%。受力点的应力应变在果肉中是最大的,并沿赤道向果核周围延伸,且逐渐减小。压缩速率为15 mm/min的有限元模型的模拟值与其实验值的偏差为14.98%,35 mm/min的偏差为11.06%。运用有限元法对灵武长枣挤压模拟是可行的。     

小麦堆修正剑桥模型的参数研究

通过TSZ-6A应变控制式三轴仪对小麦堆(宁麦13号)进行三轴压缩试验,测定并计算出小麦堆修正剑桥模型的参数:临界状态应力比M、对数硬化模量λ、等向膨胀指数κ和弹性模量E。试验结果表明:小麦堆含水率为10.20%,12.46%,14.05%w.b.时,临界状态应力比M分别为0.924 9,1.013 1,0.978 5;对数硬化模量λ分别为0.067 7,0.061 3,0.073 3;等向膨胀指数κ分别为0.025 4,0.027 0,0.026 3。含水率对M、λ和κ无显著性影响,对试验数据进行分析,推导出弹性模量E与广义剪切力q和平均主应力p的关系式。     

Axial compressive deformation and damage of four-step 3-D circular braided composite tubes under various strain rates

This paper reports the axial compressive deformation and damage of three-dimensional (3-D) braided carbon/epoxy composite circular tubes under quasi-static and high strain rate loadings. Three kinds of 3-D circular braided composite tubes with different braiding angles of 25°, 35°, and 45° were tested under strain rates of 0.001/s, 330/s, 500/s, and 650/s. The stress–strain curves, deformation and damage of the braided tubes under axial compressions were obtained to analyze the compressive failure mechanisms and the influences of the braiding angles on the compressive behaviors. A finite element model based on the meso-structure of the braided preform and the braided composite was established to reveal the axial compressive deformation and damage mechanisms. The axial compressive behaviors were compared both in the finite element analyses (FEA) results and the tested data, and good agreements were found. From the FEA and experimental results, it was concluded that the compressions deformation, damage, and stress–strain curves are sensitive to the strain rate and the braided angles. The strain rate and braided angle are the key parameters for the design of the braided composite tubes with high compression strength.     

CONSTANT STRAIN RATE COMPRESSION OF BIOPOLYMER GELS

Usually, uniaxial compression of food materials is performed at constant speed, which causes an increase of the true strain rate during experiments. By using a method described previously (Jaros and Rohm 1994) highly elastic biopolymer gels were compressed at standard conditions and with decreasing crosshead speed in order to maintain constant strain rate conditions during test. In the case of gels showing failure at a Hencky deformation of > 0.5-0.6, significantly lower values for apparent fracture strain were found in constant strain rate compression. Differences in stress at apparent fracture showed good agreement with respect to this critical value. Implications and consequences on interrelation between sensory and instrumental measurements as well as on relationships between rheological and fracture properties are discussed.     

Dough characteristics of Irish wheat varieties I. Rheological properties and prediction of baking volume

Eight wheat varieties suitable for cultivation in Ireland were examined for the rheological properties and baking quality. Large deformation extensional rheology was used employing the Extensograph, the Kieffer extensibility rig, the Alveograph and biaxial extension by uniaxial compression. Similar discrimination between the wheat samples was achieved with both uniaxial extension methods used. Stress during uniaxial extension was higher at all strains measured than biaxial extension and the difference between uniaxial and biaxial stress increased with increasing strain. Also, differences existed in the strain hardening index between uniaxial and biaxial extension which depended on the sample tested. Significant correlations were established between loaf volume and the rheological properties determined in both uniaxial and biaxial extension. It was found that high loaf volumes can be achieved when biaxial and uniaxial extensibility is high and biaxial extensional viscosity is low. The importance of considering the standard error for validating the value of the correlation for prediction purposes was also demonstrated. When the standard error of the correlation was considered, the value of the correlation for prediction purposes was limited in practice. Nevertheless, the rheological tests provided useful information, and the results were valuable for screening flours for baking quality.     

有限压缩拉格朗日描述本构模型

对铅的有限变形压缩试验进行了分析,给出了基于拉格朗日描述的有限压缩本构模型,对设计侧向约束的复杂应力状态进行了理论探讨.无量纲压力的理论模拟值同试验结果一致,表明基于拉格朗日描述的本构模型可应用于复杂应力状态情形.     

金属材料拉伸和压缩过程的有限元模拟

编制8 节点等参单元弹塑性有限元程序,对拉伸和压缩过程中金属的变形规律进行了计算,得到应变场及外力等信息,并模拟出在拉伸和压缩过程中的颈缩及单鼓和双鼓现象.将计算所得到的总压力同实验作比较,两者结果一致     

鲜枣整果力学特性研究及其有限元分析

为预测鲜枣在收获、贮运过程中的机械损伤,对甘肃靖远产小口大枣进行整果压缩特性研究及仿真分析。通过压缩实验,获得了不同加载速率条件下（10～30 mm/min）整果在横向和纵向上的弹性模量、破裂负载和破裂相对变形量：横向分别为：8.23～9.70 MPa、227.52～305.97 N、16.07%～17.46%;纵向分别为：10.05～11.44 MPa、288.50～383.17 N、16.33%～20.12%。通过观察鲜枣破裂特征,建立鲜枣压缩力学有限元模型,比较鲜枣在横向和纵向受压的模拟值和实验值,最大差异为11.4%。结果表明：鲜枣的抗挤压能力具有各向异性（相同压力下,鲜枣横向放置时的变形量大于纵向放置;相同压缩位移下,纵向承载压力大于横向）。在验证了仿真数值可行的基础上,利用有限元法可分析鲜枣内部应力应变的分布情况。研究结果可为鲜枣的作业装备设计以及减少其机械损伤提供理论依据。