a b s t r a c tThe fracture and fatigue properties of porous materials are strongly influenced by stress concentrations around the pores. In addition, failure of structural components initiates at locations of high stress concentration which is often caused by holes, inclusions or other discontinuities. In view of this, the stress concentration around a spheroidal cavity embedded in an elastic medium is studied under dynamic loading conditions. While solutions abound for static loads, only limited solutions exist for dynamic loads. The stress field around a spheroidal cavity is determined by using a hybrid methodology that combines the finite element technique with a spherical wave function expansion method. The stress concentrations within the matrix are found to be dependent on the frequency of excitation, aspect ratio of the cavity and the Poisson's ratio of the matrix. The study reveals that dynamic stress concentrations can reach much higher values than those encountered under static loading.
Experiments were conducted on the pressure experienced on a surface underlying a textile layer when exposed to a blast wave environment. Injury to humans subjected to blast loading affects the soft organs of the body, and the effects of clothing on these loads is of interest. It was shown that considerable amplification of the pressure load can occur depending on the textile properties. Shadow photographs of the wave interaction with muslin, cotton, and satin textiles are presented in order to identify the physical processes. As the textile becomes more permeable the transmitted wave increases in strength relative to the reflected wave, gas passage through the specimen is greater, and textile movement is less. The effect of a slab of gelatin under the textile was investigated with a view to simulating the effect of animal tissue covering a hard surface such as a rib. Both single and multiple layers of seven widely different cloth types were also tested for their amplification properties. It was found that pressure amplification of up to four times that of an uncovered surface can be generated. Further investigation is necessary to establish the effects of textile structure on the loads.
Background and Objectives Nanostructured devices are finding ever increasing use in industrial applications which has prompted a need to further understand their mechanical properties. Research has shown that as the size of structures such as reinforcing particles and fibres is reduced to nanometers, their particular mechanical properties vary. This variation of the material behaviour has mainly been attributed to surface/interface energy around the free surface or interface of the nanostructures. Since such nanostructured materials exhibit characteristic length in nanometers, their elastic properties are affected by surface stresses that can displace atoms from the equilibrium positions which they normally occupy in bulk macroscopic assemblies. As such properties are not normally noticed in macroscale, as they are limited to only a few atomic layers, the free surface/interface effects are often neglected in the classical continuum mechanics. This paper investigates the effect of the surface/interface elasticity on the dynamic stress state in a matrix around the nano-particle reinforcements due to asymmetric dynamic loading. Methods In the surface/interface elasticity theory, an interface between a nano-particle reinforcement and matrix is considered a negligibly thin surface or a membrane glued to the underlying bulk materials without slipping. The elastic constants of the membrane are different from those of its adjoining materials, and its inertia can be neglected in the dynamic problem. This leads to a set of non-classical boundary conditions at the interface. Results: Different surface properties are investigated under varying frequencies of shear waves as well as different matrix and nano-reinforcement material properties. The stress concentrations values around the nano-particles are found to be significantly dependent on the frequency of excitation and surface properties. The effect is localized near the nano-particle matrix interface and disappears away from the interface into the matrix bulk. Conclusions: Dynamic stress field at the reinforcement-matrix interface is significantly affected by surface/interface elasticity as the reinforcing particle size reduces to nanometers. The increasing surface elastic constant μs can significantly reduce the stress concentration values at the nano-particle matrix interface.
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