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871.
飞机结构在飞行过程中同时承受气动载荷和振动载荷的联合作用,这两种载荷的耦合加载试验对于飞机结构成为一项重要的研究内容,所以有必要对此类试验的可行性及其耦合加载方式进行研究。此次试验以气囊加载静载/常规疲劳载荷状态下试件的振动响应测试为目的,设计符合试验要求的试件和整套试验装置。得到了气囊5种不同加载情况下试件振动响应变化情况,并对此试验结果进行了理论分析,得出以下结论:a)气囊模拟静载/常规疲劳载荷加载不会大幅改变结构本身振动特性,此耦合试验方法所模拟环境比较接近飞机结构真实载荷环境;b)加载气囊的个数、部位及加载力的不同对试件结构的振动响应有一定影响,应增加气囊蓄能器或在试验前进行分析以选择合理的加载点。 相似文献
872.
《International Journal of Solids and Structures》2014,51(25-26):4357-4372
The motivating key for this work was the absence of a phenomenological model that can reasonably predict a variety of non-proportional experimental data on the anisotropic Mullins effect for different types of rubber-like materials. Hence, in this paper, we propose a purely phenomenological direction dependent orthotropic model that can describe the anisotropic Mullins behaviour with permanent set and, has orthotropic invariants that have a clear physical interpretation. The formulation is based on an orthotropic principal axis theory recently developed for nonlinear elastic problems. A damage function and a direction dependent damage parameter are introduced in the formulation to facilitate the analysis of anisotropic stress softening in rubber-like materials. A direction dependent free energy function, written explicitly in terms of principal stretches, is postulated. The proposed theory is able to predict and compares well with experimental data available in the literature for different types of rubberlike materials. 相似文献
873.
The Poynting effect, in which a cylinder elongates or contracts axially under torsion, is an important nonlinear phenomenon in soft materials. In this paper, analytical solutions are obtained for homogeneous and bi-layered cylinders under torsion, axial and combined loadings, employing second-order elasticity and Lagrangian equilibrium equations. Explicit parameters for judging the sign of the Poynting effect are given. It is found that the effect in a soft composite may be significantly amplified over that in homogeneous materials and that it is strongly influenced by the interface position and by the material configuration in the composite. A coupled axial force–twist effect under combined loading, i.e., the twist of a torsionally loaded cylinder can be affected by the axial loading, is also found. Comparison of the predictions with the torque-tension-twist data for cardiac papillary muscles shows reasonable agreement. The solutions also provide the basis for a mechanistic method of determining third-order elastic constants. 相似文献
874.
We consider the problem of Nicolai on dynamic stability of an elastic cantilever rod loaded by an axial compressive force and tangential twisting torque in continuous formulation. The rod is assumed to be non-uniform, i.e. having variable cross-section with non-equal principal moments of inertia. New linear equations and boundary conditions are derived from nonlinear governing equations. These equations form the basis for analytical and numerical studies. The important new details of this formulation include the pre-twisting effect due to the torque and compressibility of the rod. General formulae for the influence of small geometrical imperfections to the stability region are derived and numerical examples are presented. 相似文献
875.
Micro-scale behavior of granular materials during cyclic loading 总被引:1,自引:0,他引:1
Md. Mahmud Sazzad 《Particuology》2014,(5):132-141
This study presents the micro-scale behavior of granular materials under biaxial cyclic loading for differ- ent confining pressures using the two-dimensional (2D) discrete element method (DEM). Initially, 8450 ovals were generated in a rectangular frame without any overlap. Four dense samples having confining pressures of 15, 25, 50, and 100 kPa were prepared from the initially generated sparse sample. Numeri- cal simulations were performed under biaxial cyclic loading using these isotropically compressed dense samples. The numerical results depict stress-strain-dilatancy behavior that was similar to that observed in experimental studies. The relationship between the stress ratio and dilatancy rate is almost indepen- dent of confining pressures during loading but significantly dependent on the confining pressures during unloading. The evolution of the coordination number, effective coordination number and slip coordina- tion number depends on both the confining pressures and cyclic loading. The cyclic loading significantly affects the microtopology of the granular assembly. The contact fabric and the fabric-related anisotropy are reported, as well. A strong correlation between the stress ratio and the fabric related to contact normals is observed during cyclic loading, irrespective of confining pressures. 相似文献
876.
877.
878.
GIULIO MAIER 《基于设计的结构力学与机械力学》2013,41(2):213-230
Limit design in three dimensions is discussed and formulated as a constrained minimax problem in kinematic and geometric variables. A finite element discretization is proposed which, combined with piecewise linearization of the yield surfaces, reduces the minimum weight design to a pair of dual problems in linear mixed zero one programming. The relevant duality theory is shown to be useful for the theoretical frame of the mechanical problem. Various ways of reducing the number of variables and constraints are pointed out, in order to make available algorithms economically applicable to practical situations. 相似文献
879.
Fiber-reinforced polymer (FRP) composites are increasingly becoming suitable and durable materials in the repair and replacement of traditional metallic materials. The built-in promise of performance assurance and retention of structural integrity in harsh and hostile environments of these materials certainly offers an alternative and attractive avenue for a wider range application to explore its potential to the zenith. The toughest challenge faced by material scientists is to assess and ascertain its behavioral log in a range of loading rates. The heterogeneity and responses of multiple distinct phases to varying loading conditions are most often complex and far away from comprehensive conclusion. Furthermore, composites with common structural polymer matrices quite often absorb moisture during service period. Then, FRPs become a much more complex system to comprehend its sensitivity to experimental variation. The present article emphasizes the need for understanding this perpetual problem of FRPs which might pose a threat to its prospects. 相似文献
880.
Peptide‐Directed Self‐Assembly of Functionalized Polymeric Nanoparticles. Part II: Effects of Nanoparticle Composition on Assembly Behavior and Multiple Drug Loading Ability 下载免费PDF全文