The efficiency of cork as a material dedicated to energy absorption under impact loading is studied in the present work. The viability of the application of micro-agglomerate cork (MAC) padding on a motorcycle helmet, is studied using finite element simulations of impact tests, considering the specifications of the European Standard ECE-R.22/05. Expanded polystyrene (EPS) is a widely used material, with excellent results in energy-absorption applications. However, after a first impact, the capability of EPS for energy absorption is significantly decreased, due to the almost total absence of elastic springback. However, cork is a material characterized by having both a good energy-absorption capability and high elastic return, due to its viscoelastic behavior, meaning that its capacity to keep absorbing energy is almost unchanged after the first impact. In this work, a three-dimensional numerical model of the helmet-head system is developed, including the outer shell, safety padding and the head, together with its interactions and constitutive models suitable for the analyzed materials. Results show that the developed models can adequately reproduce the behavior of EPS and MAC, in the context of a preliminary analysis. The referred helmet-headform is then submitted to impacts at different points, as specified by the European Standard. The results from helmeted impacts with EPS padding are compared against experimental values. The application of MAC in the protective padding of the helmet is studied and the results, concerning the acceleration of the gravity center of the head, Head Injury Criterion (HIC) values and kinetic energy are presented. Results obtained with EPS and MAC are compared and discussed. Concerning cork, although the maximum acceleration values of the headform and the HIC values were not verified to be within the established limits of the regulatory standard, the results are promising, launching a sound basis for a more thorough work on the application of cork as a new material for advanced applications as an energy-absorption system.

Este é um artigo publicado em acesso aberto (Open Access) sob a licença Creative Commons Attribution Non-Commercial, que permite uso, distribuição e reprodução em qualquer meio, sem restrições desde que sem fins comerciais e que o trabalho original seja corretamente citado.Recebido: 18 Jan., 2017 Aceito: 21 Jun., 2017 E-mails: dcasassola@id.uff.br (DCG), mcindra@vm.uff.br (MPCF)Resumo: O conhecimento das tensões residuais geradas nos processos de soldagem apresenta especial importância no desempenho das estruturas e componentes soldados, pois durante a vida em serviço eles estarão sujeitos a diferentes níveis de carregamentos, que associados aos campos de tensões residuais pré-existentes podem levar à ruptura inesperada. Neste contexto, o presente trabalho tem como objetivo estudar o nível das tensões residuais geradas em juntas soldadas, pelo processo arame tubular (FCAW -Flux Cored Arc Welding), de aço ASTM A 131 Grau A, usadas na construção naval, por difração de raios-X, usando a técnica do sen 2 ψ. Foi realizado um estudo comparativo das mudanças nos campos de tensões quando adotadas restrições para manter a geometria de projeto da junta, bem como uma análise numérica computacional pelo método de elementos finitos, com os resultados obtidos pelo método experimental. A maioria dos resultados das tensões residuais mostrou que houve similaridade qualitativa, na sua natureza, entre o modelo e os experimentos nas regiões da zona termicamente afetada e do metal de solda. As análises de microdureza Vickers e a caracterização microestrutural por microscopia óptica das juntas soldadas complementaram o presente estudo.Palavras-chave: Soldagem; Tensões residuais; Graus de restrição; Difração de raios-X; Método dos elementos finitos. Numerical and Experimental Study of Residual Stress in Welded Joints with and without ConstraintAbstract: The knowledge of the residual stresses generated on the welding processes implies special relevancy in welded structures and components, because during his service life they will be working at several loading conditions that associated to the pre-existing residual stresses fields they can lead to a catastrophic failure. In this context, the present work has the purpose to study the residual stresses field generated in joints welded by the FCAW (Flux Cored Arc Welding) process, of ASTM A 131 grade A steel, used in ship construction, by X-ray diffraction, using the sin 2 ψ technique. It was realized a comparative study of the changes in the stress fields when adopted restrictions in order to maintain the design of the joint, as such a numerical computational analysis by the finite element method, with the results of the experimental analysis. The majority of residual stresses results had demonstrated qualitative similarity in their nature between the model and the experimental work in the heat affected region and welded zone. The Vickers microhardness analysis and microstructural characterization by optical microscopy had complemented the present work. Key-words:Welding; Residual stresse...