A numerical study on the influence of strain rate in finite-discrete element simulation of the perforation behaviour of woven composites

Predicting the perforation limit of composite laminates is an important design aspect and is a complex task due to the multi-mode failure mechanism and complex material constitutive behaviour required. This requires high-fidelity numerical models for a better understanding of the physics of the perforation event. This work presents a numerical study on the perforation behaviour of a satin-weave S2-glass/epoxy composite subjected to low-velocity impact. A novel strain-rate-dependent finite-discrete element model (FDEM) is presented and validated by comparison with experimental data for impacts at several energies higher and lower than their perforation limit. The strain rate sensitivity was included in the model by developing a novel user-defined material model, which had a rate-dependent bilinear traction separation cohesive behaviour, implemented using a VUSDFLD subroutine in Abaqus/Explicit. The capability of the model in predicting the perforation limit of the composite was investigated by developing rate-sensitive and insensitive models. The results showed that taking the strain rate into account leads to more accurate predictions of the perforation limit and damage morphology of the laminate subjected to impacts at different energies. The experimental penetration threshold of 89 J was estimated as 79 J by the strain-rate-sensitive models, which was more accurate compared to 52 J predicted by the strain-rate-insensitive model. Additionally, the coupling between interlaminar and intralaminar failure modes in the models led to a more accurate prediction of the delamination area when considering the rate sensitivity

Experimental and numerical study of the influence of pre-existing impact damage on the low-velocity impact response of CFRP panels

This paper presents an experimental and numerical investigation on the influence of preexisting impact damage on the low-velocity impact response of Carbon Fiber Reinforced Polymer (CFRP). A continuum damage mechanics-based material model was developed by defining a userdefined material model in Abaqus/Explicit. The model employed the action plane strength of Puck for the damage initiation criterion together with a strain-based progressive damage model. Initial finite element simulations at the single-element level demonstrated the validity and capability of the damage model. More complex models were used to simulate tensile specimens, coupon specimens, and skin panels subjected to low-velocity impacts, being validated against experimental data at each stage. The effect of non-central impact location showed higher impact peak forces and bigger damage areas for impacts closer to panel boundaries. The presence of pre-existing damage close to the impact region leading to interfering delamination areas produced severe changes in the mechanical response, lowering the impact resistance on the panel for the second impact, while for noninterfering impacts, the results of the second impact were similar to the impact of a pristine specimen

Mesoscopic BCS pairing in the repulsive 1d-Hubbard model

We study mesoscopic pairing in the one dimensional repulsive Hubbard model and its interplay with the BCS model in the canonical ensemble. The key tool is comparing the Bethe ansatz equations of the two models in the limit of small Coulomb repulsion. For the ordinary Hubbard interaction the BCS Bethe equations with infinite pairing coupling are recovered; a finite pairing is obtained by considering a further density-dependent phase-correlation in the hopping amplitude of the Hubbard model. We find that spin degrees of freedom in the Hubbard ground state are arranged in a state of the BCS type, where the Cooper-pairs form an un-condensed liquid on a ``lattice'' of single particle energies provided by the Hubbard charge degrees of freedom; the condensation in the BCS ground state corresponds to Hubbard excitations constituted by a sea of spin singlets.Comment: 15 pages, 6 figures. To be published on Physical Review

La comunicación de la emergencia climática en las redes sociales de los activistas ambientales : el caso de Greta Thunberg, Leonardo DiCaprio y Arturo Islas Allende

El cambio climático y la emergencia climática son temas que se discuten a nivel mundial en pos de hallar soluciones para frenar la problemática. Teniendo en cuenta la capacidad de comunicación de los activistas ambientales para educar y movilizar a la comunidad en cuestiones medioambientales, el presente estudio tiene el objetivo conocer cómo éstos comunican la problemática de ambos fenómenos en las redes sociales. El estudio se ha realizado a partir de tres casos: Greta Thunberg, Leonardo DiCaprio y Arturo Islas Allende. Para ello, se aplicó el análisis de contenido en redes sociales basado en las siguientes categorías de análisis: los recursos de comunicación, el propósito del mensaje y el contenido (el problema, las causas, las consecuencias y las soluciones). Finalmente, se analizó un total de 1.934 posts durante un periodo de 7 meses entre 2019 y 2020. Los resultados evidenciaron que los temas más tratados por los activistas ambientales no coinciden con los acontecimientos que se han producido a nivel internacional, como es el caso de los incendios en Australia provocados a finales de 2019. Greta Thunberg apuesta por la divulgación de protestas en contra de los cambios en el clima, Leonardo DiCaprio destaca diferentes consecuencias del cambio y de la emergencia climáticos y Arturo Islas Allende mantiene un discurso equilibrado tratando las causas, las consecuencias y las soluciones de los dos fenómenos.Climate change and the climate emergency are issues discussed at the global level in order to find solutions to curb the problem. Taking into account the communication capacity of environmental activists to educate and mobilize the community on environmental issues, this study aims to know how they communicate the problems of both phenomena in the social networks. The study was done from three cases: Greta Thunberg, Leonardo DiCaprio and Arturo Islas Allende. For this, content analysis on social networks was applied based on the following categories: the communication resources, purpose of the message and content (the problem, causes, consequences and solutions). Finally, a total of 1,934 posts were analyzed during a period of 7 months between 2019 and 2020. The results showed that the issues most addressed by environmental activists do not coincide with the events have taken place at the international level, as is the case of the fires in Australia generated at the end of 2019. Greta Thunberg bets on the dissemination of information about protests against climate change. Leonardo DiCaprio highlights different consequences of climate change and emergency and Arturo Islas Allende maintains a balanced discourse addressing causes, consequences and solutions of the two phenomena

Castor oil-based polyurethane/S2 glass/aramid hybrid composites manufactured by vacuum infusion

This study evaluates the hybridization effect of S2-glass/aramid on polyurethane (PU) composites produced by vacuum infusion. Different laminates were produced with similar thickness (around 2.5 mm), using, as reinforcement, only aramid fabrics (five layers, named as K5 ) or only S2-glass fabrics (eight layers, named as G8 ). Furthermore, hybridization was obtained by manufacturing symmetrical hybrid inter-ply laminates, with four S2-glass layers and two of aramid, (G2K)S and (KG2 )S. The mechanical response of the laminates was evaluated in tensile, interlaminar shear strength, dynamical mechanical analysis and quasi-static indentation tests, and related to their morphological characteristics. The main results show that the pure glass composites presented less voids, but a higher density as well as higher tensile stiffness and strength. The aramid laminates showed a high capability for absorbing impact energy (ca. 30% higher than the pure glass laminates), and the hybrid laminates had intermediate properties. More importantly, this work shows the possibility of using a polyurethane matrix for vacuum infusion processing, effective even for aramid/S2-glass hybrid composites with thermoset polyurethane resin. This study is therefore promising for impact absorption in applications such as protective armor. The studied hybrid laminate may display a suitable set of properties and greater energy absorption capability and penetration resistance for impact applications

TRAMPLE: the transmembrane protein labelling environment

TRAMPLE () is a web application server dedicated to the detection and the annotation of transmembrane protein sequences. TRAMPLE includes different state-of-the-art algorithms for the prediction of signal peptides, transmembrane segments (both beta-strands and alpha-helices), secondary structure and fast fold recognition. TRAMPLE also includes a complete content management system to manage the results of the predictions. Each user of the server has his/her own workplace, where the data can be stored, organized, accessed and annotated with documents through a simple web-based interface. In this manner, TRAMPLE significantly improves usability with respect to other more traditional web servers

Multiscale modelling approach for simulating low velocity impact tests of aramid-epoxy composite with nanofillers

The addition of nanofillers to composites has attracted great attention since it adds multifunctional potential. However, the presence of nanofillers inside a composite may cause a more complex response in many situations, e.g. damage accumulation processes, and this response poses extra challenges in the development of reliable numerical approaches. In this work, a three-step multiscale modelling strategy was used to investigate the mechanical properties and damage accumulation of plain-weave aramid-epoxy composites with hybrid nanofillers (carbon nanotubes and graphene nanoplatelets). First, the mean-field method was employed in a microscale model to provide the elastic modulus of the matrix with nanofillers inside. The mechanical properties of such a matrix were then used to predict the global mechanical properties of aramid-epoxy composite using mesoscale models. Finally, those predictions were added as input to a homogeneous material model used to replicate a more complex loading condition (low-velocity tests), for which the direct use of the mesoscale approach is not feasible. In the latter, the mechanical properties of aramid-epoxy composite with nanofillers have been modelled using MAT_162 in LS-DYNA. The agreement between the experiments and simulations with regards to the loading curves and damage phenomena can thus validate the presented approach. In addition, the effect of nanofillers on the mechanical properties and damage evolution of the woven composites in low-velocity impact has been discussed. Finally, the present work can be helpful to improve the awareness in the design of innovative materials by means of predictive modelling approaches

Role of Portion Size in the Context of a Healthy, Balanced Diet: A Case Study of European Countries

Over the past decades, a generalised increase in food portion sizes has probably contributed to the growing global obesity epidemic. Increasing awareness of appropriate portion sizes could contribute to reversing this trend through better control of calorie intake. In this study, a comparison of standard portion sizes in European countries for various food categories shows a wide variability of their importance for food, nutrient, and energy consumption according to government and institutional websites. On the other hand, the overall averages appear to be largely in line with the values indicated by the Italian Society of Human Nutrition, which is the most comprehensive and detailed document among those evaluated. The exceptions are milk and yoghurt, for which the reference portions in Europe are generally higher, and vegetables and legumes, for which portions are smaller than those reported in the Italian document. Moreover, the portion sizes of staple foods (e.g., pasta and potatoes) vary according to different food traditions. It is reasonable to consider that the creation of harmonised standard reference portions common to the European countries, based on international guidelines and scientific evidence, would significantly contribute to consumers' nutritional education and ability to make informed choices for a healthy diet