A virtual testing strategy to determine effective yield criteria for porous pressure sensitive solids

The aim of this work is to determine an effective yield criteria for porous pressure sensitive solids by employing a virtual testing strategy. The focus is on the pressure sensitivity typically displayed by geomaterials, such as sandstone. Virtual testing strategy is based on computational homogenisation approach following a unified variational formulation, which provides bounds on the effective material properties for a given choice of the Representative Volume Element (RVE). In order to estimate the effective properties of porous solid, the constitutive behaviour of continuum matrix is assumed to follow the standard Drucker–Prager elasto-plastic model. The computationally generated effective yield criteria for porous solids are obtained for various RVE choices and compared against the recently proposed analytical estimates for Drucker–Prager type solids and the SR4 constitutive model for soft rocks. The developed virtual testing strategy is applied to estimate the effective properties of a realistic rock sample, thus illustrating a wide range of potential applications

Experimental investigations of the human oesophagus: anisotropic properties of the embalmed muscular layer under large deformation

The oesophagus is a primarily mechanical organ whose material characterisation would aid in the investigation of its pathophysiology, help in the field of tissue engineering, and improve surgical simulations and the design of medical devices. However, the layer-dependent, anisotropic properties of the organ have not been investigated using human tissue, particularly in regard to its viscoelastic and stress-softening behaviour. Restrictions caused by the COVID-19 pandemic meant that freshhuman tissue was not available for dissection. Therefore, in this study, the layer-specific material properties of the human oesophagus were investigated through ex vivo experimentation of the embalmed muscularis propria layer. For this, a series of uniaxial tension cyclic tests with increasing stretch levels were conducted at two different strain rates. The muscular layers from three different cadaveric specimens were tested in both the longitudinal and circumferential directions. The results displayed highly nonlinear and anisotropic behaviour, with both time- and history-dependent stress-softening. The longitudinal direction was found to be stiffer than the circumferential direction at both strain rates. Strain rate-dependent behaviour was apparent, with an increase in strain rate resulting in an increase in stiffness in both directions. Histological analysis was carried out via various staining methods; the results of which were discussed with regard to the experimentally observed stress-stretch response. Finally, the behaviour of the muscularis propria was simulated using a matrix-fibre model able to capture the various mechanical phenomena exhibited, the fibre orientation of which was driven by the histological findings of the study

Scaling/LER Study of Si GAA Nanowire FET using 3D Finite Element Monte Carlo Simulations

3D Finite Element (FE) Monte Carlo (MC) simulation toolbox incorporating 2D Schrödinger equation quantum corrections is employed to simulate ID-VG characteristics of a 22 nm gate length gate-all-around (GAA) Si nanowire (NW) FET demonstrating an excellent agreement against experimental data at both low and high drain biases. We then scale the Si GAA NW according to the ITRS specifications to a gate length of 10 nm predicting that the NW FET will deliver the required on-current of above 1mA/μm and a superior electrostatic integrity with a nearly ideal sub-threshold slope of 68 mV/dec and a DIBL of 39 mV/V. In addition, we use a calibrated 3D FE quantum corrected drift-diffusion (DD) toolbox to investigate the effects of NW line-edge roughness (LER) induced variability on the sub-threshold characteristics (threshold voltage (VT), OFF-current (IOFF), sub-threshold slope (SS) and drain-induced-barrier-lowering (DIBL)) for the 22 nm and 10 nm gate length GAA NW FETs at low and high drain biases. We simulate variability with two LER correlation lengths (CL=20 nm and 10 nm) and three root mean square values (RMS=0.6,0.7 and 0.85 nm)

3-D Finite Element Monte Carlo Simulations of Scaled Si SOI FinFET With Different Cross Sections

Si SOI FinFETs with gate lengths of 12.8 nm and 10.7 nm are modelled using 3D Finite Element Monte Carlo (MC) simulations with 2D Schroedinger equation quantum corrections. These non-planar transistors are studied for two cross-sections: rectangular-like and triangular-like, and for two channel orientations: h100i and h110i. The 10.7 nm gate length rectangular-like FinFET is also simulated using the 3D Non-Equilibrium Green’s Functions (NEGF) technique and the results are compared with MC simulations. The 12.8 nm and 10.7 nm gate length rectangular-like FinFETs give larger drive currents per perimeter by about 25−27% than the triangular-like shaped but are outperformed by the triangular-like ones when normalised by channel area. The devices with a <100> channel orientation deliver a larger drive current by about 11% than their counterparts with a h110i channel when scaled to 12.8 nm and to 10.7 nm gate lengths. ID–VG characteristics at low and high drain biases obtained from the 3D NEGF simulations show a remarkable agreement with the MC results and overestimate the drain current from a gate bias of 0.5 V only due to exclusion of the interface roughness and ionized impurity scatterings

Friction Reduction through Ultrasonic Vibration Part 1: Modelling Intermittent Contact

International audienceUltrasonic vibration is employed to modify the friction of a finger pad in way that induces haptic sensations. A combination of intermittent contact and squeeze film levitation has been previously proposed as the most probable mechanism. In this paper, in order to understand the underlying principles that govern friction modulation by intermittent contact, numerical models based on finite element (FE) analysis and also a spring-Coulombic slider are developed. The physical input parameters for the FE model are optimised by measuring the contact phase shift between a finger pad and a vibrating plate. The spring-slider model assists in the interpretation of the FE model and leads to the identification of a dimensionless group that allows the calculated coefficient of friction to be approximately superimposed onto an exponential function of the dimensionless group. Thus, it is possible to rationalise the computed relative reduction in friction being (i) dependent on the vibrational amplitude, frequency, and the intrinsic coefficient of friction of the device, and the reciprocal of the exploration velocity, and (ii) independent of the applied normal force, and the shear and extensional elastic moduli of the finger skin provided that intermittent contact is sufficiently well developed. Experimental validation of the modelling using real and artificial fingertips will be reported in part 2 of this work, which supports the current modelling