Stick-slip and wear phenomena at the contact interface between an elastic beam and a rigid substrate

In this paper, the static behavior of an elastic beam resting on a rigid substrate is investigated. The structure lies on a rigid substrate and exchanges with it tangential forces, in correspondence with a finite number of contact points. These actions entail extension of the beam in the longitudinal direction together with a negligible bending, owing to the small eccentricity between the beam’s axis line and the rigid substrate. The beam obeys a linear elastic law, while, at the interface, different nonlinear constitutive models are considered to account for stick-slip phenomena due to friction, as well as wear due to abrasion. It is assumed that the contact points are a-priori known, thus entailing that the structural system can be treated as naturally discrete. The static problem is accordingly shown to be governed by a system of nonlinear ordinary differential equations in time, which rules, in incremental form, the equilibrium at the contact points in the longitudinal direction. A numerical solution for the equilibrium equations is carried out, under different imposed time histories of the longitudinal displacement assigned at the boundary. Numerical results are presented to compare and discuss the in-time evolution of the contact interactions between the beam and the substrate.

An Iterative Method for Estimating Nonlinear Elastic Constants of Tumor in Soft Tissue from Approximate Displacement Measurements

Objectives. Various elastography techniques have been proffered based on linear or nonlinear constitutive models with the aim of detecting and classifying pathologies in soft tissues accurately and noninvasively. Biological soft tissues demonstrate behaviors which conform to nonlinear constitutive models, in particular the hyperelastic ones. In this paper, we represent the results of our steps towards implementing ultrasound elastography to extract hyperelastic constants of a tumor inside soft tissue. Methods. Hyperelastic parameters of the unknown tissue have been estimated by applying the iterative method founded on the relation between stress, strain, and the parameters of a hyperelastic model after (a) simulating the medium’s response to a sinusoidal load and extracting the tissue displacement fields in some instants and (b) estimating the tissue displacement fields from the recorded/simulated ultrasound radio frequency signals and images using the cross correlation-based technique. Results. Our results indicate that hyperelastic parameters of an unidentified tissue could be precisely estimated even in the conditions where there is no prior knowledge of the tissue, or the displacement fields have been approximately calculated using the data recorded by a clinical ultrasound system. Conclusions. The accurate estimation of nonlinear elastic constants yields to the correct cognizance of pathologies in soft tissues.

Discussion of Nonlinear Constitutive Models for Aluminium Alloy Material Engine Piston

The engine piston is the critical component of the automobile, which always show high nonlinear behaviours under the thermal and mechanical cycling load. By contracting known metal material’s common constitutive theory、analyzing its composition method of continuous function and considering the special requirements of engine piston runs in the high temperature environment, the thesis could find a practical constitutive model which is applicable for aluminum alloy material used on engine piston. Through ways of analyzing and contracting, the constitutive model proposed by Sehitoglu proved to be applicable.

Nonlinear Seismic Response Analysis of Half through CFST Arch Bridge under 3-D Earthquake Waves

A finite-element model for CFST members using a 3D composite beam fiber element is presented which accounts for the nonlinear constitutive models of steel and concrete separately. The model is proved to be valid by comparing the computational results of some test specimens with their experimental data. Using this model, a CFST arch bridge’s seismic response was calculated. The result indicated that the magnitude of displacements and moments at arch crown increases up to 10 percent caused by CFST hysteretic behavior which should be seriously considered during seismic design. Some measures and suggestions bring forward to guide the design and construction of this type of bridge.