Application of Two-Phase Regression to Geotechnical Data

2000 Mathematics Subject Classification: 62F10, 62J05, 62P30A method for estimating a transition parameter in two-phase regression is described. The two phases are fitted and simultaneously the transition point is estimated. Practical application of the method is demonstrated on the data for determining soil hydraulic properties.Partly supported by projects FOR 444, Deutsche Forschungsgemeinschaft, Germany, MM1301/2003, National Science Fund, Bulgaria, and PRO-ENBIS: GTC1-2001-43031

Anisotropic bounding surface plasticity with rotational hardening for unsaturated frictional materials

A constitutive model for inelastic mechanical behaviour of inherently anisotropic soils is presented. An existing single surface model with isotropic hardening for empty and saturated cohesionlessoils [1] and general bounding surface plasticity [2-3] form the basic framework to which rotational hardening is added. The concept of state parameter [4] is used to predict the response of soil to different densities, drainage and stress paths. Unsaturated behaviour is described using net stress and suction as independent stress variables and modifying the basic constitutive surface parameters and hardening rules to consider the role of suction

Sharp Bounds for Strains and Stresses in Uncertain Mechanical Models ⋆

Abstract. Many mechanical systems, involving interval uncertainties and modelled by finite element method, can be described by parameter dependent systems of linear interval equations and response quantities depending on the system solution. A newly developed hybrid interval approach for solving parametric interval linear systems is applied to a 2D engineering model with interval parameters and the results are compared to other interval methods. A new technique providing very sharp bounds for the response quantities, such as element strains and stresses, is developed. The sources for overestimation when dealing with interval computations are demonstrated on a numerical plain strain example.

A Coupled Hydro-Mechanical Analysis for Slope Instability Processes in San Leo (RN, Italy)

The calcarenite rock slab, on which the medieval town of San Leo is situated, is severely tectonized and crossed by a number of joint sets and faults. It is affected by lateral spreading instability processes associated with rock falls and topples. The underlying clayey substratum is involved in movements, like earth flows and slides. In the present work these phenomena are analysed within the framework of unsaturated soil mechanics. A coupled hydro-mechanical model employing viscoplasticity (BBM-VP) is adopted herein to numerically simulate the landslide processes in San Leo region. The model allows simulating the hardening and softening processes in the rock material due to hydraulic loading and unloading, and the shear strength change with degree of saturation. The results are then compared with those obtained for the same problem but employing different constitutive model for explaining the viscoplastic behaviour that is independent on suction and based on Drucker-Prager plasticity. The differences of the two conceptual model approaches are analysed

Microstructure and mechanical properties of stress-tailored piezoelectric AlN thin films for electro-acoustic devices

Nanoindentation measurements along with atomic force microscopy, X-ray diffraction, and residual stress analyses on the basis of Raman measurements have been performed to characterize stress-tailored AIN thin films grown using reactive RF magnetron sputtering. The intrinsic stress gradient caused by the growing in-plane grain size along film thickness was minimized by increasing the N-2 concentration in the Ar/N-2 gas mixture during the growth process. The increase of N-2 concentration did not degrade the device-relevant material properties such as crystallographic orientation, surface morphology. piezoelectric response, or indentation modulus. Due to comparable crystallographic film properties for all investigated samples it was concluded that mainly the AIN crystallites contribute to the mechanical film properties such as indentation modulus and hardness, while the film stress or grain boundaries had only a minor influence. Therefore, by tailoring the stress gradient in the AIN films, device performance, fabrication yield, and the design flexibility of electro-acoustic devices can be greatly improved