Modelling of multiscale nonlinear interaction of elastic waves with three-dimensional cracks

This paper presents a nonlinear elastic material model able to simulate the nonlinear effects generated by the interaction of acoustic/ultrasonic waves with damage precursors and micro-cracks in a variety of materials. Such a constitutive model is implemented in an in-house finite element code and exhibits a multiscale nature where the macroscopic behavior of damaged structures can be represented through a contribution of a number of mesoscopic elements, which are composed by a statistical collection of microscopic units. By means of the semi-analytical Landau formulation and Preisach-Mayergoyz space representation, this multiscale model allows the description of the structural response under continuous harmonic excitation of micro-damaged materials showing both anharmonic and dissipative hysteretic effects. In this manner, nonlinear effects observed experimentally, such as the generation of both even and odd harmonics, can be reproduced. In addition, by using Kelvin eigentensors and eigenelastic constants, the wave propagation problem in both isotropic and orthotropic solids was extended to the three-dimensional Cartesian space. The developed model has been verified for a number of different geometrical and material configurations. Particularly, the influence of a small region with classical and non-classical elasticity and the variations of the input amplitudes on the harmonics generation were analyzed

Curvature Tuning in Folded Strips Through Hyperstatic Applied Rotations

Folding a strip of paper generates extremely localized plastic strains. The relaxation of the residual stresses results in a ridge that joins two flat faces at an angle known as the dihedral angle. When constrained isostatically, the strip will be at its undeformed roof-like state. Instead, if confined hyperstatically, the flat faces will undergo bending. We demonstrate that the generated curvatures can change their sign with appropriate rotations applied at the ends. We use Euler's theory of the Elastica and a shooting method to match the applied rotations at the boundaries. We also consider a constitutive model for the discontinuous rotation that takes into account the initial dihedral angle and the rotational stiffness of the fold. We show that the curvatures on the left and the right of the fold change according to a law also confirmed by the Euler-Bernoulli beam theory for small displacements and rotations. For opposite applied rotations, the fold disappears in the limit of zero rotational stiffness; instead, for applied rotations of the same sign, there exists a theoretical non-zero critical rotational stiffness that neutralizes the fold. Below such critical value, the fold can mutate, for example, from a mountain to a valley fold

‘Original Sin’ in Latin America (2000-2015): Theory, Empirical Assessment and Alternatives.

 The matter of the ‘original sin’, the inability to borrow abroad in domestic currency, came to the centre of the academic discussion after the dramatic episodes in Asia, Russia and Latin America. According to this international framework, this paper is an empirical analysis of ‘original sin’ for six Latin American countries based on the index (OSIN3) developed by Haussmann and Panizza (2003). This paper finds that the situation for some countries have been improving reflecting a reduction of the index. This fact could be related to recent economic policies policies related to an ‘abstinence’ rather than ‘redemption’, an attitude seen as a response to the debt crisis. Finally, the paper focuses on possible policy alternatives that could be adopted to overcome the ‘original sin’ phenomenon, it includes North-South and South-South cooperation and a multilateral arrangement. However, such alternatives are limited to feasibility mainly due to the turbulent political and economic scenario in the region

Teaching heterodox macroeconomics

This contribution examines recent developments in post-Keynesian macroeconomics teaching through an analysis of five textbooks: Blecker and Setterfield (2019), Hein (2014; 2023), and Lavoie (2014; 2022). The focus is on Hein’s latest book, Macroeconomics after Kalecki and Keynes (2023), which aims to provide a comprehensive and teachable post-Keynesian macroeconomic model, by covering topics such as effective demand, policy coordination, distribution and growth, finance-dominated capitalism, and ecological constraints. The review discusses Hein’s textbook in a comparative way, highlighting points of strength and aspects that should be explored further, particularly (but not related to) the field of climate change and environmental constraints to growth. Overall, it is argued that Hein's book contributes to the literature on post-Keynesian economics and provides a valuable resource for undergraduate and graduate students in the field

Biofunctional Silk Kirigami With Engineered Properties.

The fabrication of multifunctional materials that interface with living environments is a problem of great interest. A variety of structural design concepts have been integrated with functional materials to form biodevices and surfaces for health monitoring. In particular, approaches based on kirigami-inspired cuts can engineer flexibility in materials through the creation of patterned defects. Here, the fabrication of a biodegradable and biofunctional "silk kirigami" material is demonstrated. Mechanically flexible, free-standing, optically transparent, large-area biomaterial sheets with precisely defined and computationally designed microscale cuts can be formed using a single-step photolithographic process. Using modeling techniques, it is shown how cuts can generate remarkable "self-shielding" leading to engineered elastic behavior and deformation. As composites with conducting polymers, flexible, intrinsically electroactive sheets can be formed. Importantly, the silk kirigami sheets are biocompatible, can serve as substrates for cell culture, and be proteolytically resorbed. The unique properties of silk kirigami suggest a host of applications as transient, "green", functional biointerfaces, and flexible bioelectronics