Experimental Study of Open-Cell Cellular Structures with Elastic Filler Material

Open-cell cellular structures have a high potential for use in automotive, railway, ship and aerospace industry as crash energy absorbers. This paper focuses on the influence of the second phase filler material as a way to further increase the capability of cellular material energy absorption. The behaviour of ductile (aluminium alloy) and brittle (polymer) cellular structures with regular topology with and without the pore filler (silicon rubber) under quasi-static and dynamic compressive loading conditions has been experimentally studied and evaluated. The base material properties of the aluminium alloy and the polymer were obtained with separate experimental testing. The use of second phase filler material resulted in significant changes in cellular material behaviour. It was observed that the pore filler material increases the capability of energy absorption and furthermore improves and stabilises the response of a brittle cellular structures. This paper was presented during the Advanced Computational Engineering and Experimenting ACE-X 2007 Conference, Portugal, July 12–13, 2007.     

Kelvin结构开孔泡沫材料的弹性性能研究

采用一修正的十四面体结构模型(Kelvin结构模型)对开孔泡沫金属的弹性性能进行研究,对低密度开孔泡沫材料表现出不可压的特性进行了分析。该模型考虑作用在泡沫筋条上的弯矩、剪力和轴向力,以及轴向力的平衡。修正模型的数值计算结果与实验结果及其他模型的结果进行了对比,结果表明修正模型计算的杨氏模量比原有模型的略有提高,筋条截面为星形的修正模型计算的结果与实验比较符合。在密度等同的条件下,筋条截面惯性矩越大的开孔泡沫材料,其弹性模量也越大,而泊松比则越小。Kelvin结构的开孔泡沫材料的泊松比随相对密度的减小而趋于0.5。     

A Continuum Model for Fluid Foams

A continuum theory of fluid foams regarded as a continuum of hexagonal micro cells with fluid walls is derived and some qualitative aspects of the equilibrium problem are discussed.     

Theory of Elastic Dielectrics Revisited

I develop a variational principle introduced in [2] for electromagnetic elastic bodies and discuss its consequences. Formulae for stress tensors and configurational stresses are derived by energy minimization.     

A Linear Theory of Porous Elastic Solids

The theory of porous elastic solids with large vacuous interstices, considered by Giovine like materials with ellipsoidal structure, includes, as a particular case, the nonlinear theory of Nunziato and Cowin of elastic materials with small spherical voids finely dispersed in the matrix.In this paper we propose appropriate constitutive relations and then specialize the basic balance equations of Giovine to the linear theory. Also, generalizing the developments of Cowin and Nunziato, we formulate boundary-initial-value problems and examine classical applications as responses to homogeneous deformations and small-amplitude acoustic waves.     

A Theory of Chiral Cosserat Elastic Plates

The mechanical behaviour of chiral materials is of interest for the investigation of carbon nanotubes, honeycomb structures, auxetic materials and bones. This paper is concerned with a theory of chiral Cosserat elastic plates. In this theory, in contrast with the case of achiral plates, the stretching and flexure cannot be treated independently of each other. First, we derive the basic equations which characterize the deformation of chiral plates. Then we establish a uniqueness result in the dynamical theory. In the equilibrium theory we establish conditions under which the Neumann problem admits solutions. Finally, the deformation of an infinite plate with a circular hole is studied. It is shown that, in contrast with the theory of Cosserat achiral plates a uniform pressure acting on the boundary of the hole produces a microrotation of the material particles.     

高精度舰艇航向姿态信息标校方法和测量模型研究

提出了一种基于全站仪(TPS)的高精度航向与姿态信息的标校方法和测量模型。通过对模型误差传递的理论分析,证明该模型的精度足以满足对INS等高精度导航设备动态标校的要求。试验结果验证了这一结论。     

A Theoretical Model with Experimental Verification to Predict Hydrodynamics of Foams

An experimentally validated theoretical model, based on hydraulic resistance network and scale analysis at the pore level, is developed to predict the pressure drop for flow through foams. The complex microstructure of the foams is modeled as a matrix of interconnected solid ligaments forming simple cubic arrays of cylinders. New correlations for permeability and form drag (inertia) coefficient are presented as functions of the mean pore and ligament diameter as well as the foam porosity. The present model makes it possible to conduct parametric studies. Results obtained from the proposed model are successfully compared with our experimental data as well those found in the literature to observe good agreement.     

Helical Birods: An Elastic Model of Helically Wound Double-Stranded Rods

We consider a geometrically accurate model for a helically wound rope constructed from two intertwined elastic rods. The line of contact has an arbitrary smooth shape which is obtained under the action of an arbitrary set of applied forces and moments. We discuss the general form the theory should take along with an insight into the necessary geometric or constitutive laws which must be detailed in order for the system to be complete. This includes a number of contact laws for the interaction of the two rods, in order to fit various relevant physical scenarios. This discussion also extends to the boundary and how this composite system can be acted upon by a single moment and force pair. A second strand of inquiry concerns the linear response of an initially helical rope to an arbitrary set of forces and moments. In particular we show that if the rope has the dimensions assumed of a rod in the Kirchhoff rod theory then it can be accurately treated as an isotropic inextensible elastic rod. An important consideration in this demonstration is the possible effect of varying the geometric boundary constraints; it is shown the effect of this choice becomes negligible in this limit in which the rope has dimensions similar to those of a Kirchhoff rod. Finally we derive the bending and twisting coefficients of this effective rod.     

Some Results in Linear Theory of Thermomicrostretch Elastic Solids

The aim of this paper is to study the spatial and temporal behavior of thermoelastodynamic processes for microstretch continuum materials. The spatial behavior is described by establishing estimates of Saint–Venant type and Phragmén–Lindelöf type for bounded and unbounded bodies, respectively, with decay rate being dependent or independent of time, while the temporal behavior is studied by establishing the relations describing the asymptotic behavior of the Cesàro means of the different parts of the total energy.     

A Simple Nonlinear Thermodynamic Theory of Arbitrary Elastic Beams

A ‘classical’ theory of beams (i.e., a theory in which the basic kinetic variables are a stress resultant and a stress couple) undergoing elastic, thermodynamic processes is developed by first deriving exact beamlike (one-dimensional) equations of motion and a beamlike Second Law (Clausius–Duhem inequality) by descent from three-dimensions. Then what may be considered as the three basic assumptions of a classical theory are introduced: an assumed form of the First Law (conservation of energy), a relaxed form of the Second Law, and a general form of the constitutive relations. Throughout, detailed specification of geometry, kinematics, or constitution is minimized. It is shown how the kinematic Kirchhoff hypothesis may be avoided by first introducing a mixed-energy density and then imposing a logically more satisfying constitutive Kirchhoff hypothesis. Mathematics Subject Classifications (2000) 74A15, 74B20, 74K10     

基于均匀化理论的管板有效弹性常数的研究

根据多尺度均匀化理论建立了管板有效弹性常数研究的有限元计算模型，在弹性平面状态下，计算结果与ASME规范中采用的有效弹性常数进行了比较，其相对误差在0．2％，然后对管板中胀接管子的加强作用进行了研究，得到了管板有效弹性常数与胀接管子在孔间带效率为0．4时的变化曲线。计算结果表明，用均匀化方法计算管板的有效弹性常数是可行的。     

Model for Elastic Modulus of Multi-Constituent Particulate Composites

In this paper, a methodology has been developed to accurately predict the elastic properties of multi-constituent particulate composites by accounting for irreversible effects, such as energy loss that arises due to internal friction. The complex dependence on loading density and particle properties (i.e., size, shape, morphology, etc.) is investigated in terms of their effects on the effective elastic modulus of the composite. Confirmed by experimental data from the compression loading of individual Ni and Al particles dispersed in an epoxy matrix, it is believed that this approach captures the effects of internal friction, consequently providing a more accurate and comprehensive representation for predicting and understanding the material behavior of multi-constituent particulate reinforced composites. The present methodology provides a model to directly compare the elastic modulus from an uncomplicated test, such as dual-cantilever beam loading in dynamic mechanical analysis (DMA), to the modulus obtained by other more complex experimental methods such as quasi-static compression. The model illustrates an efficient method to incorporate input data from DMA to represent realistic elastic moduli, hence promising for the characterization and design of particulate composites.     

Simulation of Entry-Region Flow in Open-Cell Metal Foam and Experimental Validation

Open-cell metal foam is distinguished from traditional porous media by its very high porosities (often greater than 90 %), and its web-like open structure and good permeability. As such, the foam is a very attractive core for many engineered systems, e.g., heat exchangers, filtration devices, catalysts, and reactors. The flow field inside the foam is rather complex due to flow reversal and vigorous mixing. This complexity is increased by the possible presence of an entry region. The entrance region in metal foam is usually underestimated and ignored, just like its counterpart in traditional porous media. In this paper, the actual entry length is determined by simulation and direct experiment on commercial open-cell aluminum foam. It is shown to be dependent on flow velocity and to reach a constant value for higher velocities. The complex and intrinsically random architecture of the foam is idealized using a unit geometrical model, in order to numerically investigate the flow field and pressure drop inside the foam. The Navier–Stokes equations are solved directly, and velocity and pressure fields are obtained for various approach velocities using a commercial numerical package. The entry length is ascertained from the behavior of the velocity field close to the entrance. Comparisons to experimental data were also carried out. The commercial foam that was used in the experiment had 10 ppi and porosity of 91.2 %. Air was forced to flow inside the foam using an open-loop wind tunnel. Good qualitative agreement between the modeling and experimental results are obtained. The agreement lends confidence to the modeling approach and the determined entry length.     

On Shear and Torsion Factors in the Theory of Linearly Elastic Rods

Lower bounds for the factors entering the standard notions of shear and torsion stiffness for a linearly elastic rod are established in a new and simple way. The proofs are based on the following criterion to identify the stiffness parameters entering rod theory: the rod’s stored-energy density per unit length expressed in terms of force and moment resultants should equal the stored-energy density per unit length expressed in terms of stress components of a Saint-Venant cylinder subject to either flexure or torsion, according to the case. It is shown that the shear factor is always greater than one, whatever the cross section, a fact that is customarily stated without proof in textbooks of structure mechanics; and that the torsion factor is also greater than one, except when the cross section is a circle or a circular annulus, a fact that is usually proved making use of Saint-Venant’s solution in terms of displacement components.