附集中质量悬臂板基本频率的数值解及其应用

首先导出薄板在附加集中质量时的横向弯曲自由振动方程，应用差分法解出它在三边自由和一边固支的边界条件下的基本频率。进而给出它与悬臂矩形薄板基本频率间的相关关系，除实验验证该关系外，本文还探讨用加速度计测量板材弹性模量Ｅ的途径。     

三向编织玻璃/环氧复合材料刚度性能

通过实验研究了三向编织玻璃/环氧复合材料的刚度性能 , 并考虑编织角和试件宽度参数的影响 , 探讨了拉伸和压缩刚度性能的差异。实验结果表明 : 在同一纤维体积分数条件下 , 随着编织角的增大 , 试件的纵向弹性模量有所减小 , 泊松比 (在编织角约大于 35° 时) 也有所减小 ; 宽度为两倍和三倍单胞宽度的试件的刚度性能基本相同; 试件的纵向弹性模量和泊松比远大于横向弹性模量和泊松比; 拉伸和压缩时试件的弹性模量和泊松比基本接近 ; 在横向拉伸和压缩时试件的应力2应变曲线具有明显的非线性特征。实验结果为编织复合材料结构设计提供了数据参考。      

三向编织复合材料弹性性能研究

基于均匀应变假设和界面连续性条件,并考虑到编织向纤维束波动周期在特定区域沿着自身横向的渐变,建立了一种分析三向编织复合材料弹性性能的理论预测方法.对比理论分析和实验研究结果,验证了理论预测方法的正确性.参数研究表明:在同一纤维体积分数条件下,随着编织角的增大,纵向弹性模量逐渐减小而横向弹性模量逐渐增大,面内剪切弹性模量和泊松比先增大后减小(分别在约50°和35°时达到最大值);随着轴向纤维束与编织向纤维束大小之比的增大,纵向弹性模量逐渐增大,而横向弹性模量、面内剪切弹性模量和泊松比逐渐减小.     

纸浆模塑材料在不同加载条件下的力学特性

实验测量了纸浆模塑材料在不同加载条件下拉伸时的强度极限、弹性模量和泊松比等力学性能,同时给出了纸浆模塑材料的应力-应变曲线,为纸浆模塑缓冲包装结构的有限元分析和设计提供了基础数据.实验结果表明:当加载速率提高时,试件强度极限和弹性模量随之增加;当温度升高时,纸浆模塑材料的强度极限和弹性模量随之逐渐升高;当湿度升高时,纸浆模塑的强度极限和弹性模量随之降低.纸浆模塑材料单向拉伸时横向变形很小,且对温、湿度等环境因素影响敏感,泊松比的测量比较困难.数字图像相关测量方法具有灵敏度高、非接触、直接测量物体表面全场变形的特点,采用该测量方法解决了材料泊松比的测量问题.实验测得纸浆模塑材料泊松比为0.097.     

灰底白板纸与白卡纸的弹性常数对比

目的 为了更加精确地测量灰底白板纸和白卡纸的泊松比和弹性模量。方法 将数字图像相关方法与单向拉伸实验相结合。通过对灰底白板纸和白卡纸试样拉伸变形前后的图像进行分析, 测量其泊松比; 通过对灰底白板纸和白卡纸的力-位移曲线进行分析, 测量其弹性模量。结果 测得了定量为300, 400 g/m2的灰底白板纸的泊松比分别为0.281和0.245, 其弹性模量分别为154.47, 226.06 MPa;300, 400 g/m2的白卡纸的泊松比分别为 0.312 和 0.276, 其弹性模量分别为 209.09, 297.79 MPa。结论同种类别的纸张中, 定量越高, 其弹性模量越大, 而泊松比越小; 在定量相同的情况下, 白卡纸的泊松比和弹性模量都比灰底白板纸的大。     

零泊松比蜂窝芯等效弹性模量研究EI北大核心CSCD

采用柔性悬臂梁模型和欧拉梁模型分别对零泊松比蜂窝芯斜壁板大变形条件下的弯曲变形和蜂窝芯横壁板小变形条件下的变形进行分析,推导出了零泊松比蜂窝芯面内等效弹性模量理论计算公式,并将理论计算结果和有限元仿真及力学模型实验进行对比分析。结果表明:理论计算公式正确、有效;零泊松比蜂窝芯大变形方向等效弹性模量具有明显的非线性特征;等效弹性模量的计算应根据受力方向及应变大小选择相应的计算公式进行计算;壁板之间的夹角θ对等效弹性模量的影响很大,零泊松比蜂窝结构参数可设计性较强。     

单向复合材料板弹性常数的动(静)态测定方法

根据薄板弯曲振动理论和应用差分法,分析了单向增强复合悬臂板的动特性,确定了方板在四角受集中力时的静特性,提出测试单向复合材料弹性常数的动(静)态方法.与常用的测定方法相比,它具有测试简便、快速、精度高和重复性好等优点.      

非线性能量阱在悬臂薄板振动抑制中的应用研究

悬臂结构在航空航天领域应用广泛,由于结构受到激励作用而产生共振行为,因此结构的振动抑制问题显得尤为重要。非线性能量阱(Nonlinear Energy Sink,NES)以质轻、能量单向传递以及减振效率高等特点,为其引入到航空航天结构的减振设计中提供了条件。利用NES对悬臂矩形板进行减振研究。考虑Kirchhoff经典薄板模型,建立了薄板与NES耦合的动力学方程,通过模态截断研究了薄板一阶横向弯曲时结构的响应问题,分析了不同参数下NES的减振效果,发现NES对结构响应位置较为敏感,并且在位移响应最大位置处减振效果最大。以期为悬臂结构在工程应用中提供一些理论上的支持。     

基于Voronoi随机模型的各向异性闭孔泡沫的弹性性能研究

基于Voronoi各向异性随机模型,通过引入Voronoi随机系数、壁厚随机度以及相对密度,讨论闭孔泡沫胞体分布的随机性、相对密度以及胞体壁厚的不均匀性对泡沫的弹性性能的影响,并将结果与理论预测结果以及实验值进行对比分析。结果表明,泡沫胞体的形状一定时,相对密度对弹性模量各向异性比、泊松比的影响很小,壁厚随机度的增加对弹性模量起减小作用,但对泡沫的弹性模量各向异性比以及泊松比的影响都很小;当泡沫形状各向异性比一定时,随机系数的增加会引起弹性模量、弹性模量各向异性比以及泊松比的减小。     

气激状态下粘弹性阻尼薄板的有限元建模与分析

创建气激载荷作用下的黏弹性阻尼板的振动特性分析模型是黏弹性阻尼减振研究的一项重要内容。基于实验数据，以薄板为对象，提出一种简单易行的气动载荷作用下黏弹性悬臂薄板振动特性的有限元建模方法。首先，简要介绍该建模方法的一般流程。接着，采用自制的气激试验台对贴敷黏弹性阻尼材料前后的悬臂薄板振动特性进行测试，获得气激载荷作用下板的共振频率及共振响应。再则，从有限元建模的需要出发，用计算流体力学仿真软件Fluent获取试验中作用于薄板上的气动载荷。然后按照反推法及薄板阻尼处理前后的耗能规律得到有限元建模所需的黏弹性材料杨氏模量和损耗因子。最后，引入所确定的气动载荷和黏弹性材料相关参数，对黏弹性阻尼板的谐响应进行计算，将分析结果与实验比对证实了分析模型的合理性。     

The mechanical properties and test of a single ZnO nanorod inside scanning electron microscopy

The bending and tensile tests of the ZnO nanorods were carried out by controlling a force sensor and a nano-manipulator inside a scanning electron microscope (SEM). The force sensor was mounted on the nano-manipulator, was controlled with the nano-manipulate. The load response during the mechanical test for the ZnO nanorod was obtained by using the force sensor which is formed as a cantilever. The elastic modulus of the ZnO nanorods after the tensile and bending tests were calculated and compared. The elastic modulus of ZnO nanorods was depended on a size and an aspect ratio of the ZnO nanorods. The difference of the elastic modulus of ZnO nanorods was obtained with a difference of test methods performed along crystal facets direction of the ZnO nanorods. The average elastic modulus calculated after the tensile test was approximately 57.15 GPa. In case of the bending test, the average elastic modulus was approximately 29.37 GPa.     

铝合金板材磁脉冲辅助U形弯曲过程回弹数值模拟分析

目的揭示铝合金板材磁脉冲辅助弯曲成形对回弹的影响机理。方法基于两种磁脉冲辅助成形方案,采用数值模拟软件LS-DYNA,建立磁脉冲辅助U形弯曲的有限元模型。结果与准静态成形相比,磁脉冲辅助U形弯曲成形能减小板料圆角区的残余应力,方案Ⅰ板料圆角区等效塑性应变大于方案Ⅱ板料圆角区的等效塑性应变;电磁体积力能有效减小回弹,且放电能量越大,回弹角越小;磁脉冲辅助U形弯曲成形能减小板料的弹性应变能。结论相同放电电压下,方案Ⅰ的回弹控制效果好于方案Ⅱ的回弹控制效果。磁脉冲辅助U形弯曲减小回弹的主要原因是板料圆角区残余应力的减小和弹性应变能的降低。     

The small length scale effect for a non-local cantilever beam: a paradox solved

Non-local continuum mechanics allows one to account for the small length scale effect that becomes significant when dealing with microstructures or nanostructures. This paper presents some simplified non-local elastic beam models, for the bending analyses of small scale rods. Integral-type or gradient non-local models abandon the classical assumption of locality, and admit that stress depends not only on the strain value at that point but also on the strain values of all points on the body. There is a paradox still unresolved at this stage: some bending solutions of integral-based non-local elastic beams have been found to be identical to the classical (local) solution, i.e.?the small scale effect is not present at all. One example is the Euler-Bernoulli cantilever nanobeam model with a point load which has application in microelectromechanical systems and nanoelectromechanical systems as an actuator. In this paper, it will be shown that this paradox may be overcome with a gradient elastic model as well as an integral non-local elastic model that is based on combining the local and the non-local curvatures in the constitutive elastic relation. The latter model comprises the classical gradient model and Eringen's integral model, and its application produces small length scale terms in the non-local elastic cantilever beam solution.     

Anisotropic orthodontic force from the hollow super-elastic Ti-Ni alloy wire by transforming the wire cross-section

The purpose of this research was to devise a method for transforming the cross-section of the hollow super-elastic Ti-Ni alloy round wire and to examine the changes in its bending properties for clinical orthodontic application. The specimen wires were pressed with the use of heated pliers to transform the cross-sectional shape. As a result, transformation of the wire cross-section with super-elasticity was possible. As a verified by cantilever test and three-point bending test of the transformed specimens, a two-dimensional orthodontic force, which was different in each bending direction, was obtained. The hollow wire showed considerably high load level in the long axis along with markedly low load level in the short axis, which was mainly caused by the change in the moment of inertia by transforming the cross-section. It was revealed that, by transforming the wire cross-section of the hollow super-elastic Ti-Ni alloy round wires, anisotropic orthodontic force in bending properties could be obtained with super-elasticity.     

Experimental study on the dynamic behavior of TiNi cantilever beams with rectangular cross-section under transversal impact

The experimental investigation of TiNi alloy cantilever in the PE state and R-SME state, respectively, was conducted under transversal impact by using a modified Hopkinson bar apparatus. For comparison, the impact response of A3 steel cantilevers with the same geometry was also studied. The results show that at an early stage the elastic flexible waves dominate the wave response of the beam. After about 1 ms the dynamic structural response will be the main response. Under impact the “phase transformation hinge (TH)”, which differs from the conventional plastic hinge (PH), may form and undertake the main deformation and energy absorption in a cantilever. The impact position has a great influence on the location, time and number of the formation of TH, hence the response mode of a cantilever. After impact there is no residual deformation for a PE cantilever, there is a small residual deformation for an R-SME cantilever due to the R transition and large residual deformation for steel cantilevers due to the plasticity. The energy absorption efficiency of cantilevers for different materials and impact conditions are discussed.     

Transverse shear modulus and strength of honeycomb cores

The transverse shear mechanical behavior and failure mechanism of aluminum alloy honeycomb cores are investigated by the single block shear test in this paper. The transverse shear deformation process of honeycomb cores may be approximately categorized into four stages, namely elastic deformation, plastic deformation, fracture of cell walls and debonding of honeycomb cores/facesheets. The elastic deformation of unit cell under transverse shear displacement is also investigated by the finite element method, and the result shows that the bending deformation of the cell walls is similar to that of the cantilever beam. In order to precisely predict the equivalent transverse shear modulus and strength, not only shear deformation but also bending deformation of cell walls should be considered. Therefore, in the present paper, the equivalent transverse shear modulus and strength are predicted by application of the cantilever beam theory and thin plate shear buckling theory in conjunction with simplifying assumption as to the displacement in the cores. It is concluded that the contribution of bending deformation of cell walls to equivalent transverse shear modulus and strength is obvious with the decreasing height of cell walls.     

Fracture analysis of surface- and through-cracked sheets and plates

The Neuber stress-concentration relation for notches in an elastic-plastic material subjected to shear loading was generalized for a crack in a finite plate subjected to tensile loading, similar to the way in which Kuhn modified the Hardrath-Ohman notch equation for a cracked plate. An equation was derived which related the linear elastic stress-intensity factor, the applied stress, and two material parameters. The equation was then used as a two-parameter fracture criterion for surface- and through-cracked specimens.Fracture data from the literature on surface- and through-cracked sheet and plate specimens of steel, titanium alloy, titanium weldment, and aluminum alloy tested at room and cryogenic temperature were analyzed according to the proposed equation. For surface cracks, wide ranges of crack-depth to crack-length ratio and crack-depth to specimen-thickness ratio were considered. For through cracks, wide ranges of crack length and specimen width were also considered. An empirical equation for the elastic magnification factors on stress intensity for a surface crack in a finite-thickness plate was also developed. The fracture stress predictions computed from the two-parameter fracture criterion for both surface- and through-cracked sheet and plate specimens are consistent with experimental failure stresses.     

TbDyFe磁致伸缩薄膜悬臂梁弯曲性能的研究

以TbDyFe磁致伸缩薄膜悬臂梁为研究对象,采用有限元分析方法(FEM)对薄膜厚度及薄膜与衬底材料的弹性模量比对悬臂梁最大挠度值的影响规律进行了研究.通过FEM计算发现:当薄膜厚度小于衬底厚度的十分之一时,最大挠度值随薄膜厚度线性增加,计算结果与文献的理论计算结果吻合很好;当薄膜厚度为衬底厚度的一半时,悬臂梁的自由端挠度值达到最大.磁性薄膜与衬底材料有效弹性膜量比值的增加可以显著地提高悬臂梁的挠度值,同时挠度最大值向薄膜/衬底厚度比减少的方向移动.     

Electromechanical coupling and output efficiency of piezoelectric bending actuators

Electromechanical coupling mechanisms in piezoelectric bending actuators are discussed in this paper based on the constitutive equations of cantilever bimorph and unimorph actuators. Three actuator characteristic parameters, (e.g., electromechanical coupling coefficient, maximum energy transmission coefficient, and maximum mechanical output energy) are discussed for cantilever bimorph and unimorph actuators. In the case of the bimorph actuator, if the effect of the bonding layer is negligible, these parameters are directly related to the transverse coupling factor lest. In the case of the unimorph actuator, these parameters also depend on the Young's modulus and the thickness of the elastic layer. Maximum values for these parameters can be obtained by choosing proper thickness ratio and Young's modulus ratio of elastic and piezoelectric layers. Calculation results on four unimorph actuators indicate that the use of stiffer elastic material is preferred to increase electromechanical coupling and output mechanical energy in unimorph actuators.     

复合材料层合夹芯板局部变形行为研究

在局部荷载作用下,带软夹芯层的夹芯板结构将产生一定的局部变形现象。本文采用双参数基础模型模拟软夹芯材料与受载层合面板间的相互作用,基于经典层合板理论,推导并给出了夹芯板结构局部变形问题的半解析分析方法,并通过算例讨论了边界条件、荷载作用方式、夹芯层厚度与弹性模量等因素对该类结构局部弯曲和局部屈曲行为的影响。