Effect of Fiber-Matrix Interface on the Mechanical Response of a Woven Carbon Fiber/PEEK Composite Material.

This work studies the relationship between the interface shear strength (IFSS) and the mechanical response of a carbon fiber-reinforced composite with a polyether-ether-ketone (PEEK) thermoplastic matrix. Two types of laminates were studied: the first kind was manufactured with as-received fiber fabrics, while specimens belonging to the second one were fabricated with thermally treated fibers where the original sizing agent was removed. IFSS values were measured with the push-in test, showing that treated fibers exhibit a 25% higher critical shear stress. Microscopic inspection of the laminates revealed that untreated specimens were prone to debonding, generating a much higher crack density. This difference was detected by the C-Scan technique and triggered in the response of both laminates under tensile tests at ±45∘ fiber orientation, where maximum stress and strain at break values of desized specimens showed an increase of 37% and 190%, respectively. Results confirmed that the original fiber sizing weakened the fiber-matrix interface. Lastly, the tensile response of the composite is analyzed in light of interface quality.

Optimization of Processing Conditions and Mechanical Properties for PEEK/PEI Multilayered Blends.

The goal of producing polyetheretherketone/polyetherimide (PEEK/PEI) blends is to combine the outstanding properties that both polymers present separately. Despite being miscible polymers, it is possible to achieve PEEK/PEI multilayered blends in which PEEK crystallinity is not significantly inhibited, as opposed to conventional extruding processes that lead to homogeneous mixtures with total polymer chain interpenetration. This study investigated a 50/50 (volume fraction) PEEK/PEI multilayered polymer blend in which manufacturing parameters were tailored to simultaneously achieve PEEK-PEI adhesion while keeping PEEK crystallinity in order to optimize the mechanical properties of this heterogeneous polymer blend. The interface adhesion was characterized with the use of three-point bending tests, which proved that a processing temperature below the melting point of PEEK produced weak PEEK-PEI interfaces. Results from differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and X-ray diffraction analysis (XRD) showed that under a 350 °C consolidation temperature, there is a partial mixing of PEEK and PEI layers in the interface that provides good adhesion. The thickness of the mixed homogeneous region at this temperature exhibits reduced sensitivity to processing time, which ensures that both polymers essentially remain separate phases. This also entails that multilayered blends with good mechanical properties can be reliably produced with short manufacturing cycles. The combination of mechanical performance and potential joining capability supports their use in a wide range of applications in the automotive, marine, and aerospace industries.

Analysis of the Elastoplastic Response in the Torsion Test Applied to a Cylindrical Sample.

This work presents an experimental and numerical analysis of the mechanical behavior of a fixed-end SAE 1045 steel cylindrical specimen during the torsion test. To this end, an iterative numerical-experimental methodology is firstly proposed to assess the material response in the tensile test using a large strain elastoplasticity-based model solved in the context of the finite element method. Then, a 3D numerical simulation of the deformation process of the torsion test is tackled with this previously characterized model that proves to be able to predict the development of a high and localized triaxial stress and strain fields caused by the presence of high levels of angular deformation. Finally, the obtained numerical results are analytically studied with the cylindrical components of the Green-Lagrange strain tensor and experimentally validated with the measurements of shear strains via Digital Image Correlation (DIC) and the corresponding torque - twist angle curve.

Abuso sexual infantil en tiempos de COVID-19

Introducción: La crisis del COVID-19 representa un fenómeno sanitario mundial que afecta a diversos aspectos de la salud de las personas. Los niños y adolescentes representan a la población más afectada; debido al aumento del maltrato infantil y del abuso sexual, lo cual puede comprender el bienestar y desarrollo integral de la población infantil y adolescente. Objetivo: Examinar la situación actual del abuso sexual infantil durante la pandemia e identificar los factores de riesgo asociado a esta problemática. Métodos: Se realizó una revisión bibliográfica de estudios publicados entre 2010 y 2021 en las bases de datos Pubmed/medline, Science Direct, SciElo, Scopus, Dialnet. Se utilizaron las palabras clave: abuso sexual infantil, maltrato infantil, COVID-19, Pandemia. Análisis y síntesis de la información: Se registró un incremento del abuso sexual y maltrato infantil durante la pandemia por los efectos específicos de la COVID-19. Se identificaron factores de riesgo como los problemas económicos, aislamiento social y acceso a internet. Conclusiones: La pandemia por causa de la COVID-19 propició un aumento de las vulneraciones en los niños y adolescentes. Por estas razones se deben tomar medidas preventivas para disminuir cualquier tipo de agresión física, psicológica y sexual hacia la población infantil.

Introduction: The COVID-19 crisis represents a global health phenomenon that affects various aspects of people's health. Children and adolescents represent the most affected population due to the increase in child maltreatment and sexual abuse, which may include the well-being and integral development of the child and adolescent population. Objective: To examine the current situation of child sexual abuse during the pandemic and identify the risk factors associated with this problem. Methods: A literature review of studies published between 2010 and 2021 in the databases Pubmed/medline, Science Direct, SciELO, Scopus, Dialnet was conducted. The keywords used were: child sexual abuse, child maltreatment, COVID-19, Pandemic. Analysis and synthesis of information: There was an increase in sexual abuse and child maltreatment during the pandemic due to the specific effects of COVID-19. Risk factors such as economic problems, social isolation and internet access were identified. Conclusions: The COVID-19 pandemic led to an increase in violations among children and adolescents. For these reasons, preventive measures must be taken to reduce any type of physical, psychological and sexual aggression towards the child population.