A simplified and versatile element model for elastomeric seismic isolation bearings

A novel approach for two-dimensional modeling of elastomeric bearings using three springs in parallel is presented. This simplified element model considers as follows: (1) an elastoplastic spring with a smooth transition between branches; (2) a linear elastic spring; and (3) a non-linear elastic spring, and is fully defined by only six parameters. The main advantages of the simplified model are twofold: (1) versatility, as a single model is capable of accurately reproducing the main characteristics of the hysteretic behavior of different types of rubber-based seismic isolators, including low damping rubber bearings (LDRBs), high damping rubber bearings (HDRBs), and lead-core rubber bearings (LRBs) and (2) simplicity, as it requires fewer parameters and it is easier to calibrate from experimental cyclic test results than most currently available models. Model parameters’ identification is illustrated using quasi-static cyclic and earthquake simulator tests of HDRBs and LRBs, demonstrating that the model shows a good agreement between the test-measured and model-predicted hysteretic behavior. Different objective functions are evaluated in the optimization procedure, and their effect on the identified parameters is studied and discussed. This practitioner-oriented model is particularly amenable for implementation in general-purpose structural analysis software. Its usage is strongly recommended as an initial-stage design tool to select the optimal isolation system for a specific project.

Tool wear and spring back analysis in orthogonal machining unidirectional CFRP with respect to tool geometry and fibre orientation

Machining abrasive carbon fibre reinforced polymers (CFRP) is characterised by extensive mechanical wear. In consequence, the cutting edge micro-geometry and thus the tool/material contact situation are continuously changing, which affects process forces and machining quality. As a conclusion, a fundamental understanding of the tool wear behaviour and its influencing factors is crucial in order to improve performance and lifetime of cutting tools. This paper focuses on a fundamental tool wear analysis of uncoated tungsten carbide cutting inserts with different combinations of fibre cutting angles and tool geometries. For this purpose, orthogonal machining experiments with unidirectional CFRP material are conducted, where the wear progression of the micro-geometry is investigated by means of five wear parameters lα, lγ, γ*, α*, and bc. For detecting the actual contact zone of the cutting edge and to measure the elastic spring back of the material, the flank face is marked via short pulsed laser processing. Furthermore, the process forces and the wear rate are measured. It is shown that the material loss due to wear clearly varies along the tool’s contact region and is highly dependent on the clearance angle and the fibre cutting angle Φ, while the influence of the tested rake angles is mostly negligible. Especially in machining Φ=30° and Φ=60°, a strong elastic spring back is identified, which is more intense for smaller clearance angles. For all tested configurations, the material’s elastic spring back increases in intensity as wear progresses which, in combination with the decreasing clearance angle, is the main reason for high thrust forces.

Designing a Low-Cost Mechatronic Device for Semi-Automatic Saffron Harvesting

This paper addresses the design of a novel mechatronic device for saffron harvesting. The main proposed challenge consists of proposing a new paradigm for semi-automatic harvesting of saffron flowers. The proposed novel solution is designed for being easily portable with user-friendly and cost-oriented features and with a fully electric battery-powered actuation. A preliminary concept design has been proposed as based on a specific novel cam mechanism in combination with an elastic spring for fulfilling the detachment of the flowers from their stems. Numerical calculations and simulations have been carried out to complete the full design of a proof-of-concept prototype. Preliminary experimental tests have been carried out to demonstrate the engineering feasibility and effectiveness of the proposed design solutions, whose concept has been submitted for patenting.

Generalised viscoelastic fibre at small strain

A straight elastic fibre is usually perceived as a one-dimensional structural component, and its similarity with a cylindrical rod makes its concept analogous, if not equivalent with the concept of an elastic spring. This analogy enables this communication to match the one-dimensional response of a relevant viscoelastic fibre with that of a viscoelastic spring and, hence, to describe its one-dimensional behaviour in the light of a new, generalised viscoelastic spring model. The model shares simultaneously properties of an elastic spring and an inelastic damper (dashpot) and this communication is interested on its applicability at small strain only. However, the form of its constitutive equation, which is based on the combined action of an internal energy function and a viscous flow potential, is non-linear as well as differential and, also, implicit in the stress. The model enables a posteriori determination of (i) the manner that the elastic and the inelastic parts of the fibre strain are assembled and form the observed total deformation, (ii) the part of stress that creates recoverable work and the part of stress wasted in energy dissipation, and (iii) the amount of work stored in the material as well as the amount of energy dissipation during the fibre deformation. A detailed analysis is presented for the case that small-strain, steady viscoelastic deformation takes place in a spatially homogeneous manner. This includes a complete relevant solution of the problem of interest and is accompanied by an adequate set of corresponding qualitative numerical results.

Negative Effective Mass in Plasmonic Systems

We report the negative effective mass (density) metamaterials based on the electro-mechanical coupling exploiting plasma oscillations of a free electron gas. The negative mass appears as a result of the vibration of a metallic particle with a frequency of ω, which is close the frequency of the plasma oscillations of the electron gas m 2 relative to the ionic lattice m 1 . The plasma oscillations are represented with the elastic spring k 2 = ω p 2 m 2 , where ω p is the plasma frequency. Thus, the metallic particle vibrated with the external frequency ω is described by the effective mass m e f f = m 1 + m 2 ω p 2 ω p 2 − ω 2 , which is negative when the frequency ω approaches ω p from above. The idea is exemplified with two conducting metals, namely Au and Li.