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Nanoindentation tests were conducted at different indentation depths, ranging from 3000 to 30 nm, to study the characteristics of indentation size effects in epoxy. Taking the effects of tip imperfection/bluntness into account, nanoindentation tests performed with a three-sided Berkovich tip exhibited strong increases in the hardness with decreasing indentation depth. However, comparative testing with a spherical tip with a radius of 250 microns, showed no changes in the material properties with respect to the distance from the surface. Consequently, different deformation mechanisms must be present in the indentation tests with Berkovich and spherical tips, suggesting effects related to second order gradients of the displacement (such as strain or rotation gradients), which increase with a Berkovich tip but essentially stay constant with a spherical tip when indentation depth decreases. [ABSTRACT FROM AUTHOR]

Abstract: Nanoindentation tests were performed on polydimethylsiloxane to characterize its mechanical behavior at different indentation depths and loading times. Astonishing indentation size effects have been observed in these experiments where the universal hardness increases by about 15 times from indentation depths of 5000 down to 100 nm. The hardness was found to depend on the loading time at small indentations, while at larger indentation depths the hardness hardly changed with loading time. In an attempt to unveil the underlying deformation mechanisms, an in-depth experimental study is pursued in this article with detailed analysis of the experimental data. Applying different loading times, the indentation experiments were evaluated at indentation depths from 100 to 5000 nm with respect to (a) universal hardness, (b) ratio of remaining indentation depth after unloading to maximum indentation depth, (c) ratio between elastic and total indentation works, and (d) indentation stiffness at maximum applied force. All these characteristics are found to be significantly different compared to a reference material that does not exhibit indentation size effects. The corresponding experimental data has been analyzed with an existing indentation depth dependent hardness model for polymers that has been motivated by a Frank elasticity related theory incorporating rotation gradients. [Copyright &y& Elsevier]

Abstract: Based on the continuum Lennard-Jones model, the van der Waals interaction of two concentric and eccentric carbon nanocones with different or identical sizes are investigated in this paper. Also, on the basis of classical mathematical modeling techniques, a new semi-analytical solution is given to evaluate the van der Waals potential energy and interaction force distributions of two concentric carbon nanocones. Finally, a universal potential energy is presented for the carbon nanocones. [Copyright &y& Elsevier]

Abstract: Based on the three-dimensional anisotropic elasticity, the stress analysis of multi-layered filament-wound composite pipes subjected to cyclic internal pressure and temperature loading is conducted in this article. The time-dependent stress, strain and deformation distributions are numerically obtained by the use of the finite difference technique. The pressure and temperature are considered to be symmetrical about the axis of the cylinder and independent of the axial coordinate. Each layer of the pipes is made of a homogeneous, anisotropic and linearly elastic material and it is assumed that the material properties do not change with increasing the temperature. The shear extension coupling is also considered because of lay-up angles. Numerical results obtained from the present model are compared with other published results and good agreement has been achieved. [Copyright &y& Elsevier]