The sounding side of materials and products. A sensory interaction revaluated in the user-experience

The new trends in the world of materials and products, growingly focused on a new eco-friendliness and interaction with nature – yet still distinguished by a strong anthropocentrism – lead to the development of materials, systems, technology, and smart, interlinked, expressive, communicative, alive, and hybrid products. A world in which it is almost difficult for designers to find their bearings: how can one interact with such materials and products What is their reaction to touch and smell? What are their distinguishing visual traits? What are their sounds? There is a vast number of tools to analyse and assess such aspects: this article will focus on the “sound” element of materials and products, and using one tool in particular, the SounBe, used to qualitatively assess the acoustics of materials and artefacts

The role of the mobility law of dislocations in the plastic response of shock loaded pure metals

This article examines the role that the choice of a dislocation mobility law has in the study of plastic relaxation at shock fronts. Five different mobility laws, two of them phenomenological fits to data, and three more based on physical models of dislocation inertia, are tested by employing dynamic discrete dislocation plasticity (D3P) simulations of a shock loaded aluminium thin foil. It is found that inertial laws invariably entail very short acceleration times for dislocations changing their kinematic state. As long as the mobility laws describe the same regime of terminal speeds, all mobility laws predict the same degree of plastic relaxation at the shock front. This is used to show that the main factor affecting plastic relaxation at the shock front is in fact the speed of dislocations.The author acknowledges support by the EPSRC under the EPSRC Doctoral Prize Fellowship scheme. The author is indebted to D Dini, A P Sutton and D S Balint for their comments and useful discussions. The author reports no competing interests. This work did not involve any collection of human or animal data. This work does not have any experimental data

A stochastic study of the collective effect of random distributions of dislocations

The effect that random populations of dislocations have on a material is examined through stochastic integration of a random cloud of dislocations lying at some distance away from a material point. The problem is studied in one, two, and three dimensions. In 1D, the cloud consists of individual edge dislocations placed along the real line; in 2D, of edge dislocations and edge dipoles on the plane; in 3D, of dislocation loops. In all cases, the dislocation cloud is randomly distributed in space, associated to which several relevant physical parameters, including the material's slip geometry, the dislocation's sign, and its relative orientation, are also stochastically treated. A fully disordered population, i.e., one where the dislocation's signatures and orientations are entirely random, is first studied. It is shown that such disordered systems entail a strong indeterminacy in the collective stress fields, which here is solved by enforcing mass conservation locally. In 2D, this is achieved by modelling a cloud of edge dipoles instead of individual dislocations; in 3D, this is naturally guaranteed by the modelling of closed dislocation loops. The long-range fields of the dipoles in 2D and of the loops in 3D is modelled via their multipolar force expansions, which greatly simplifies the analytical treatment of the problem. The cloud's effect is then studied by performing the stochastic integration of the multipolar fields via Campbell's theorem. The local order, but not the magnitude of the dislocation density, is shown to be critical in contributing to the plastic relaxation of the material: fully disordered systems are shown to self-attenuate, leading to plastic neutrality; ordered and partially ordered systems, achieved when dislocation signatures are aligned, display a direct relationship between the dislocation density and the average stress shielding the material. We establish and generalise the conditions that a system of dislocations must fulfil to display Taylor's equation and the Hall-Petch relation, and offer adequate scaling laws related to this

On the transient dynamic antiplane contact problem in the presence of dry friction and slip

This article models the elastodynamic transient contact between two elastically similar half planes under antiplane loading and in the presence of friction. Contact is maintained along the positive real line under the presence of a certain remote contact pressure. An antiplane shear load is applied, which entails interfacial shear traction that opposes the frictional force entailed by the contact pressure. In order to balance the surface tractions, the surface must be allowed to slip. We derive the closed form solution of the interfacial traction due to a general antiplanar displacement distribution using a variant of the Wiener-Hopf technique. We also find closed-form expressions for the interfacial shear traction due to this remote antiplane load. In combination with the frictional force, this leads to an integral equation the solution to which is the distribution of relative slip. We quantify both this and the magnitude of the interfacial shear tractions under diverse loading, showing that transient loading leads to partial reverse slip of the contact surfaces. We show that the reverse slip tends to vanish over time, and that it is ameliorated if the friction coefficient is reduced

How strong is the temperature increase due to a moving dislocation?

This article calculates the temperature increase resulting from the motion of a dislocation. The temperature rise is ascribed to two separate effects, both of which are calculated: the dissipative effect resulting from the energy lost by the dislocation as it overcomes the intrinsic lattice resistance to its motion; and the thermomechanical effect arising from the constrained changes in volume the dilatational field of a moving dislocation may entail. The dissipative effect is studied in an uncoupled continuum solid, whilst the thermomechanical effect is studied in a fully coupled thermo-elastodynamic continuum. Explicit solutions are provided, as well as asymptotic estimates of the temperature field in the immediacy of the dislocation core.Research funded with the support of Trinity College Cambridg

Exact solution of the spin-isospin proton-neutron pairing Hamiltonian

The exact solution of proton-neutron isoscalar-isovector (T=0,1) pairing Hamiltonian with non-degenerate single-particle orbits and equal pairing strengths (g_{T=1}= g_{T=0}) is presented for the first time. The Hamiltonian is a particular case of a family of integrable SO(8) Richardson-Gaudin (RG) models. The exact solution of the T=0,1 pairing Hamiltonian is reduced to a problem of 4 sets of coupled non linear equations that determine the spectral parameters of the complete set of eigenstates. The microscopic structure of individual eigenstates is analyzed in terms of evolution of the spectral parameters in the complex plane for system of A=80 nucleons. The spectroscopic trends of the exact solutions are discussed in terms of generalized rotations in isospace.Comment: 4 pages, 2 figure

How Natural Are the “Natural” Materials? Proposal for a Quali-Quantitative Measurement Index of Naturalness in the Environmental Sustainability Context

The overall purpose of the paper is overcoming the misunderstanding of the “naturalness” attribute of materials. This is due to the always-increasing innovative materials considered “environmentally sustainable” and “natural” by producers, material libraries, and designers. The investigated research problem is: how to simply and effectively evaluate the degree of naturalness of a material, preventing a complete and complex LCA analysis? The basic design of the study was focused on (i) creating a multicriteria quali-quantitative method—Material Naturalness Index (MNI)— in order to assess materials’ naturalness scientifically, and (ii) test it by running the evaluation on 60 innovative materials. MNI was set considering the least number of parameters of the Material Life Cycle (i.e., resource kingdom, material resource, material processing, post-use processing). The 60 latest materials selected from the “natural” material family of six international material libraries were selected to test the index. The data analysis was based on the Theory of Attractive Quality, considering attractive, must-be, or reverse qualities. Major findings concerning the index utility were found as a result. MNI was demonstrated to support different actors with different aims: (i) designers, in independently evaluating naturalness of materials using real evidence and pursuing a critical point of view not influenced by marketing claims; (ii) producers, in facing the challenge of naturalness; (iii) material libraries, which are collocated between the two other actors, in proposing measurable information concerning naturalness. In conclusion, the study demonstrated how the key-concept of “naturalness” should be assumed as an attribute rather than as a material family

Generalised Kanzaki force field of extended defects in crystals, with applications to the modelling of edge dislocations

The Kanzaki forces and their associated multipolar moments are standard ways of representing point defects in an atomistically informed way in the continuum. In this article, the Kanzaki force approach is extended to other crystalline defects. The article shows how the resulting Kanzaki force fields are to be computed for any general extended defect by first computing the relaxed defect's structure and then defining an affine mapping between the said defect structure and the original perfect lattice. This methodology can be employed to compute the Kanzaki force field of any mass-conserving defect, including dislocations, grain and twin boundaries, or cracks. Particular focus is then placed on straight edge dislocation in face-centered cubic (fcc) and body-centered cubic (bcc) pure metals, which are studied along different crystallographic directions. The particular characteristics of these force fields are discussed, drawing a distinction between the slip Kanzaki force field associated with the Volterra disregistry that characterizes the dislocation, and the core Kanzaki force field associated with the specific topology of the dislocation's core. The resulting force fields can be employed to create elastic models of the dislocation that, unlike other regularization procedures, offer a geometrically true representation of the core and the elastic fields in its environs, capturing all three-dimensional effects associated with the core

Dynamics of Coherent States in Regular and Chaotic Regimes of the Non-integrable Dicke Model

The quantum dynamics of initial coherent states is studied in the Dicke model and correlated with the dynamics, regular or chaotic, of their classical limit. Analytical expressions for the survival probability, i.e. the probability of finding the system in its initial state at time $t$, are provided in the regular regions of the model. The results for regular regimes are compared with those of the chaotic ones. It is found that initial coherent states in regular regions have a much longer equilibration time than those located in chaotic regions. The properties of the distributions for the initial coherent states in the Hamiltonian eigenbasis are also studied. It is found that for regular states the components with no negligible contribution are organized in sequences of energy levels distributed according to Gaussian functions. In the case of chaotic coherent states, the energy components do not have a simple structure and the number of participating energy levels is larger than in the regular cases.Comment: Contribution to the proceedings of the Escuela Latinoamericana de F\'isica (ELAF) Marcos Moshinsky 2017. (9 pages, 4 figures