Elastic modulus

About: Elastic modulus is a research topic. Over the lifetime, 33153 publications have been published within this topic receiving 810247 citations.

Nanoindentation of Cu2O Nanocubes

Abstract: Nanoindentation tests were performed directly on solid and hollow cuprous oxide (Cu2O) nanocubes. The hardness and elastic modulus of solid Cu2O nanocubes were measured and compared with the values of bulk Cu2O. It is found that the hollow cube top wall acts as a membrane that bends under an indentation load. The Cu2O nanocubes are more ductile rather than brittle. Deformation behavior and fracture mechanics are discussed in conjunction with the structure of the Cu2O nanocube.

Elastic contact to a coated half-space - Effective elastic modulus and real penetration

Abstract: A new approach to the contact to coated elastic materials is presented. A relatively simple numerical algorithm based on an exact integral formulation of the elastic contact of an axisymmetric indenter to a coated substrate is detailed. It provides contact force and penetration as a function of the contact radius. Computations were carried out for substrate to layer moduli ratios ranging from 10−2 to 102 and various indenter shapes. Computed equivalent moduli showed good agreement with the Gao model for mismatch ratios ranging from 0.5 to 2. Beyond this range, substantial effects of inhomogeneous strain distribution are evidenced. An empirical function is proposed to fit the equivalent modulus. More importantly, if the indenter is not flat-ended, the simple relation between contact radius and penetration valid for homogeneous substrates breaks down. If neglected, this phenomenon leads to significant errors in the evaluation of the contact radius in depth-sensing indentation on coated substrates with large elastic modulus mismatch.

Stress wave emission and cavitation bubble dynamics by nanosecond optical breakdown in a tissue phantom

Abstract: Stress wave emission and cavitation bubble dynamics after optical breakdown in water and a tissue phantom with Nd : YAG laser pulses of 6 ns duration were investigated both experimentally and numerically to obtain a better understanding of the physical mechanisms involved in plasma-mediated laser surgery. Experimental tools were high-speed photography with 50000 frames s -1 , and acoustic measurements. The tissue phantom consisted of a transparent polyacrylamide (PAA) gel, the elastic properties of which can be controlled by modifying the water content. Breakdown in water produced a purely compressive stress wave. By contrast, in stiff PAA samples and for sufficiently large pulse energies, the compression wave was followed by an intense tensile wave, similar to the behaviour previously observed in cornea. The elastic/plastic response of the medium led to a significant decrease of the maximum size of the cavitation bubble and to a shortening of its oscillation period which was found to be related to the generation of the tensile stress wave upon breakdown. For increasing elastic modulus of the PAA, both the amplitudes of the bubble oscillation and of the stress wave emitted during bubble collapse decreased until the bubble oscillation was so strongly damped that no collapse stress wave was emitted. Numerical simulations were performed using a spherical model of bubble dynamics which includes the compressibility and elastic/plastic behaviour of the medium, viscosity, density and surface tension. The calculations revealed that consideration of the elastic/plastic behaviour of the medium surrounding the bubble is essential to describe the experimentally observed bipolar shape of the stress wave emitted upon optical breakdown. Water is a poor tissue model because the shape of the emitted stress waves and the bubble dynamics differ strongly for both materials. The mechanical properties of PAA were also found to be quite different from those of tissues. Experimental and numerical results provided evidence that the dynamic mechanical properties relevant for optical breakdown in PAA and tissue differ by as much as two orders of magnitude from the static values. The discovery of a tensile stress wave after optical breakdown in tissue-like media is of great importance for the assessment of collateral damage in laser surgery because biological tissues are much more susceptible to tensile stress than to compressive stress.

The significance of the elastic modulus of wood cell walls obtained from nanoindentation measurements

Abstract: Nanoindentation is a powerful method for the study of hardness and elasticity at small scale. When applied to the measurement of the longitudinal elastic modulus of wood cell walls, where the longitudinal modulus is approximately 10 times the transverse modulus, nanoindentation yields values considerably below results obtained from single-fibre tensile tests and model calculations, respectively. In a nanoindentation experiment on a wood cell wall using a Berkovich-type indenter, the cell wall is loaded at an angle of approximately 25° due to the inclination of the faces of the indenter pyramid. In the zone deformed by the indenter, the resulting three-dimensional stress state is governed not only by the longitudinal (Young's) modulus, but also affected by the much lower transverse modulus, which leads to an underestimation of the longitudinal modulus. It is concluded that nanoindentation using current isotropic theory is therefore not suitable for the direct measurement of the longitudinal elastic modulus of wood cell walls.