泡沫塑料杨氏模量所满足的微分方程和一些的近似解的讨论

本文通过复合材料力学中的微分法和微观力学分析直接导出了泡沫塑料杨氏模量和泊松比所满足的微分方程组，并通过对方程组的讨论得到了泡沫塑料杨氏模量预测的近似公式。这些公式形式简单，与实验符合较好，便于工程应用。     

高孔隙度泡沫塑料的一种近似非线性本构关系

根据高孔隙度泡沫塑料杨氏模量满足平方律关系的理论和实验结果，并通过对泡沫塑料泊松比的合理近似，在假设基体材料服从幂律本构关系的基础上，研究了高孔隙度泡沫塑料的非线性本构行为，得到了用于非线性本构关系的应变势函数，给出了描述高孔隙度泡沫塑料非线性力学行为的一种有效，合理的本构关系的形式。此外，由此得到的泡沫塑料屈服应力与前人按照量纲分析方法得到的低密度闭孔泡沫塑料的结果相一致。     

空心陶瓷微珠对环氧泡沫塑料力学性能的影响

制备了空心陶瓷微珠填充的环氧树脂泡沫塑料;测试了材料的拉伸、压缩力学性能,计算得到材料的杨氏模量与泊松比,研究了各参数随空心陶瓷微珠体积含量的变化趋势。结果表明:随着空心陶瓷微珠含量的增加,材料的抗拉强度、拉伸断裂应变、抗压强度、泊松比呈下降趋势,杨氏模量呈上升趋势;微珠与基体之间的粘接力较小。     

玻璃纤维对硬质聚氨酯泡沫塑料增强机理的探讨

研究了硬质聚氨酯泡沫塑料的微观结构形态，通过实验探讨了玻璃纤维对聚氨酯泡沫塑料的增强作用，并分析了增强泡沫塑料的压缩破坏机理。     

具有球形胞体结构的泡沫塑料弹性常数的确定

通过微分法导出了泡沫塑料剪切模量和体积模量所满足的微分方程组，并利用泡沫塑料各向同性弹性常数间满足的关系求解；得到了泡沫塑料剪切模量与体积模量的关系，确定了剪切模量与材料孔隙比的关系；并且将本文结果同其他已有模型了对比。     

聚氨酯泡沫塑料胞体结构特性的确定

通过扫描电镜和显微镜观察相结合的手段，确定 了聚氨酯泡沫塑料胞体结构特性，其中包括不同密度的聚氨酯泡沫塑料的胞体结构形态，胞体尺寸及其分布情况，胞体的椭球度及泡沫塑料的孔隙度等重要的材料几何参数。这些参数的确定不仅为提高泡沫兼的质量和改进本文提供了必要的实验数据，也为研究聚氨酯泡沫兼的力学性能提供了重要的物理参数。在扫描电镜和显微镜观察结果的基础上，本文提出了一种确定泡沫塑料密度的方法，结果与实测     

阻尼材料模量与损耗因子的双边梁测量反演误差机理与控制EI北大核心CSCD

通过引入中间变量,得到了双边自由阻尼梁阻尼层杨氏模量和损耗因子的简化反演公式,并在此基础上进行误差分析,给出了高阶误差预测公式。研究表明,影响反演精度的重要参数为复合梁与基底梁的刚度比;刚度比越大,反演精度越高;当刚度比接近于1时,共振频率比和质量比的误差放大倍数急剧增加,导致反演误差变大;通过增大阻尼层与基底层的厚度比和模量比,可以增大刚度比,进而提高反演精度。仿真分析验证了该结论的正确性。     

增强聚氨酯泡沫塑料力学行为的研究

给出两种增强泡沫塑料静、动态压缩实验的一些新结果, 研究了它们变形及破坏的规律性。通过对加载后泡沫塑料试件进行的扫描电镜分析得到了这两种增强泡沫塑料变形和失效的机制, 并讨论了增强机理。      

阻尼材料模量与损耗因子的双边梁测量反演误差机理与控制

通过引入中间变量,得到了双边自由阻尼梁阻尼层杨氏模量和损耗因子的简化反演公式,并在此基础上进行误差分析,给出了高阶误差预测公式。研究表明,影响反演精度的重要参数为复合梁与基底梁的刚度比;刚度比越大,反演精度越高;当刚度比接近于1时,共振频率比和质量比的误差放大倍数急剧增加,导致反演误差变大;通过增大阻尼层与基底层的厚度比和模量比,可以增大刚度比,进而提高反演精度。仿真分析验证了该结论的正确性。     

扫描探针显微技术测量血管内皮细胞的弹性

血管内皮细胞的功能与许多疾病间存在关联,但现在对其功能好坏的定量描述仍十分少见。该文以内皮细胞的弹性作为衡量其功能的一个标准。通过理论建立压痕测量杨氏模量的计算方法,并利用扫描探针显微镜从实验上得到了正常及过氧化氢处理过的人脐静脉内皮细胞的杨氏模量。发现过氧化氢处理后细胞的杨氏模量升高,表明通过杨氏模量来表征细胞活性是可行的。     

研究单壁碳纳米管杨氏模量的一种能量方法

本文利用能量方法研究了单壁碳纳米管(single-walled carbon nanotubes, SWCNT)的杨氏模量.文中,首先采用分子力学理论得出了受轴向载荷作用下单壁碳纳米管的总势能;然后通过总势能与相应薄圆柱壳的应变能比较,推导出了单壁碳纳米管杨氏模量的计算公式.另外,从一系列碳纳米管杨氏模量的计算发现,本文研究结果与现有研究结果比较一致.     

环氧树脂复合泡沫材料的压缩力学性能

对空心玻璃微珠填充环氧树脂复合泡沫材料进行了准静态压缩实验, 研究了材料的宏观压缩力学性能, 并提出了弹性模量和屈服强度的预测公式。此外, 对压缩试件的断口进行了宏、细观观察, 研究了材料的压缩破坏机理。结果表明, 复合泡沫材料在压缩过程中, 具有普通泡沫材料的应力-应变曲线的典型特征, 在应变为2 %左右时材料发生屈服, 在应变大于30 %后发生破坏。此外, 材料的杨氏模量和强度均随密度的减小而下降, 预测公式给出的结果与实验值基本一致。压缩试件断口的宏、细观观察表明, 复合泡沫材料主要的破坏形式为剪切引起的弹塑性破坏。      

Chirality dependence of carbon single-walled nanotube material properties: axial Young's modulus

The potential use of individual carbon nanotubes as nano devices warrants detailed investigation of their mechanical behavior based on structural and geometrical configurations. The objective of this paper is to unravel the structural and chirality dependence of the axial Young's modulus of a carbon single-walled nanotube by analytical and numerical approaches. In this work, we employ the general homogenization composite shell model developed based on the asymptotic homogenization technique for analytical modeling of single-walled nanotubes. We derive the working formulae for the effective elastic properties of carbon single-walled nanotube of any chirality and predict the structural and chiral dependence of the effective axial Young's modulus of the nanotube. Also, a finite element analysis on the chirality dependence of the axial Young's modulus of the carbon nanotube is reported. The outcomes of our analyses are compared with available experimental and simulation results.     

Elastic and electric properties of closed-cell aluminum foams: Cross-property connection

Foamed aluminum (AlMg1Si0.6) in the porosity range 0.45–0.85 produced by the powder metallurgy method is analyzed with regard to its elastic and electric properties. Various predictive models for the electrical conductivity and Young's modulus of closed-cell metal foam are assessed based on the experimental measurements. It is shown that the differential scheme provides the best predictions of the electrical conductivity in the porosity range 0.7–0.85, while Mori–Tanaka's scheme gives the best results for the Young's modulus. Comparing the two sets of the experimental data, cross-property coefficient that connects changes in the Young's modulus and electrical conductivity of a material due to pores was determined. A non-trivial finding is that the best prediction of the cross-property coefficient is obtained in the framework of non-interaction approximation.     

对弹体侵彻混凝土靶体阻力函数计算公式的探讨

基于动态球形空腔膨胀理论,探讨了混凝土材料的单轴抗压强度、弹性模量、泊松比、压力硬化系数对阻力函数的影响,并指出,混凝土靶体的弹性模量和单轴抗压强度对阻力函数影响较明显,而泊松比和压力硬化系数的影响可以忽略不计。在此基础上,该文忽略泊松比和压力硬化系数的影响,通过引入弹性模量与单轴抗压强度的关系式,分别建立了基于弹性-断裂-塑性和弹性-塑性两种靶体响应模型下,同时考虑单轴抗压强度和弹性模量影响的阻力函数理论公式,并建立了弹体侵彻靶体的加速度时程计算模型。通过与不同尺寸弹体侵彻实验数据对比,验证了该文提出阻力函数表达式的适用性及其在加速度时程以及较大尺寸弹体侵彻深度计算中的优 越性。     

双钢管构件由点接触到线接触的连续过渡

针对轴向压力作用下的双钢管构件,提出了内核与有限刚度套管之间线接触的力学计算模型。利用小挠度二阶平衡微分方程推导了内核与套管处于点接触、线接触时内核的挠度、弯矩、剪力、接触反力等物理量的计算公式。理论公式和应用算例表明,在内核与套管之间由点接触到线接触过渡时,这些物理量满足必要的连续性和协调性条件。本文提出的力学计算模型也能应用于模拟内核与刚性套管的线接触。     

Transverse elastic moduli of unidirectional fiber composites with fiber/matrix interfacial debonding

An elastic contact model is developed to predict the transverse Young's modulus, Poisson's ratio and shear modulus of unidirectional fiber composites with interfacial debonding. The elastic deformation formulae of the fiber under contact pressure are derived by the use of elasticity theory. These results are then used in the formulation of an analytic boundaryelement method for solving the interfacial debonding problem. The two extreme cases of perfect bonding and the fiber-like void are also studied. On the basis of this theory, the upper and lower bounds of the transverse moduli for unidirectional fiber composites with imperfect fiber/matrix interfaces are provided. Numerical calculations of parametric studies are conducted for four composites, and some basic characteristics of the transverse elastic moduli of unidirectional fiber composites with interfacial debonding are presented.     

Young's Modulus Measurement of Thin Films by Resonant Frequency Method Using Magnetostrictive Resonator

At present, there are many methods about Young's modulus measurement of thin films, but so far there is no recognized simple, non-destructive and cheaper standard measurement method. Considering thin films with various thicknesses were sputter deposited on the magnetostrictive resonator and monitoring the resonator's first-order longitudinal resonant frequency shift both before and after deposition induced by external magnetic field, an Young's modulus assessing method based on classical laminated plate theory is presented in this paper. Using the measured natural frequencies of Au, Cu, Cr, Al and SiC materials with various thicknesses in the literature, the Young's modulus of the five materials with various thicknesses are calculated by the method in this paper. In comparison with the Young's modulus calculated by the other methods, it is found that the calculated Young's modulus for various thicknesses are in good agreement with the Young's modulus values in the literature. Considering the simple and non-destructive characteristics of this method, which can effectively describe the effect of the thickness on the Young's modulus, it has the potential to become a standard assessing method of thin film Young's modulus.     

充砂振动柱动态特性预估

本文对充砂振动柱在基础激励下的动态特性进行了理论和实验研究。把砂作为一种具有均匀密度的连续体,假设砂的弹性模量是砂柱高度的幂函数和砂柱中只存在纵向波,建立了波动方程,导出了原点导纳和传递导纳的理论公式。这个公式亦适用于非常短的砂柱。同时采用阻抗方法推导了充砂振动柱的结构损耗因子表达式。实验值和预估值基本相符。