Characterisation of creep behaviour using the power law model in copper alloy

This paper presents a numerical strategy for the characterisation of the creep behaviour model of the copper alloy, which is widely used in aircraft applications under creep conditions. The high possibility of the material failing, while operating under load at an elevated temperature, has led to the important study of the creep lifetime prediction analysis, by presenting the Norton’s rule based on the Power-law model to describe the secondary creep behaviour of the material. In order to demonstrate the nature of the creep formulation, the SOL 400 modules from MSC Nastran 2014 are implemented in order to conduct the uniaxial tensile test in 2000 N of applied load and 473 K of temperature condition. As a result, the exponential curve is formed from the relationship of the creep strain rate and stress, with a 5.1% error based on the value of the stress exponent, n, between the simulation and experimental results and this was still be acceptable because it was relatively small due to the formulation in the simulation. Consequently, a relation of the creep rate curve can then be plotted with respect to the load steps and the variation patterns due to the stress factor also being discussed. Therefore, the results show a good agreement, which indicates the capability of this model to give an accurate and precise estimation of the secondary creep behaviour of the materials

What triggers a microcrack in printed engineering parts produced by selective laser sintering on the first place?

The proximity of un-melted particles within Selective Laser Sintered (SLS) printed engineering parts made of Nylon-12 is found as a major triggering effect for cracking and ultimately failure. The numerical investigation, by means of the eXtended Finite Element Method (XFEM), was performed over samples with different arrangements of un-melted particles obtained experimentally. The onset and propagation of microcracks was simulated. This included inherently how the degree of particle melt (DPM) in SLS parts affects and controls both crack initiation and propagation. The results evidenced that a microcrack started invariably between the two closest un-melted particles in all numerical tests performed considering different arrangements of un-melted particles

Three-dimensional static and dynamic analysis of a composite cruciform structure subjected to biaxial loading: a discontinuum approach

A three-dimensional structural integrity analysis using the eXtended Finite Element Method (XFEM) is considered for simulating the crack behaviour of a chopped fibre-glass-reinforced polyester (CGRP) cruciform specimen subjected to a quasi-static tensile biaxial loading. This is the first time this problem is accomplished for computing the stress intensity factors (SIFs) produced in the biaxially loaded area of the cruciform specimen. A static crack analysis for the calculation of the mixed-mode SIFs is carried out. SIFs are calculated for infinite plates under biaxial loading as well as for the CGRP cruciform specimens in order to review the possible edge effects. A ratio relating the side of the central zone of the cruciform and the crack length is proposed. Additionally, the initiation and evolution of a three-dimensional crack are successfully simulated. Specific challenges such as the 3D crack initiation, based on a principal stress criterion, and its front propagation, in perpendicular to the principal stress direction, are conveniently addressed. No initial crack location is pre-defined and an unique crack is developed. Finally, computational outputs are compared with theoretical and experimental results validating the analysis

Mixed-mode damage into a CGRP cruciform subjected to biaxial loading

In this paper, a three-dimensional progressive damage model (PDM) is implemented within a chopped glass-reinforced polyester (CGRP) cruciform structure for modelling its damage under loading. Three different cruciform specimens subjected to biaxial tensile loading are studied. In order to simulate the computational behaviour of the composite, the constitutive model considers an initial elastic behaviour followed by strain-softening. The initiation criterion defined is based on the maximum principal stress of the composite and once this criterion is satisfied, stiffness degradation starts. For the computation of damage, the influence of the fibre and the matrix are taken into account within the damage rule. Realistic values of the energy dissipated during damage are computed. The computational results obtained by means of an explicit time marching solver are compared with experimental outcomes for validation purposes. Finally, it is concluded that the PDM is able to localise the damage effectively as well as predicting its initiation. In the best of authors' knowledge, this is the first time a three-dimensional PDM is implemented into a composite cruciform structure subjected to biaxial loading

An approach for dynamic analysis of stationary cracks using XFEM

A numerical implementation of the eXtended Finite Element Method (XFEM) is presented. The proposed approach solves the system of discrete equations using an explicit integration scheme and it is capable of addressing dynamic and static fracture mechanics problems. Special attention to the mass matrix construction is required in order to avoid instability issues such a null stable time increment. Hence, different mass lumping strategies are adopted for enriched elements. The in-house implementation of this approach, so-called X in-house FE platform called MULE. Numerical tests demonstrate that the proposed approach is able to provide an accurate calculation of static and dynamic stress intensity factors (SIFs) for different geometries and loading scenarios. Finally, in order to extend our point of view, an experimental analysis of a 10◦ off-axis carbon fibre laminate is carried out using Digital Image Correlation (DIC)

Damage detection and location in woven fabric CFRP laminate panels

The need for multifunctional carbon fibre composite laminates has emerged to improve the reliability and safety of carbon fibre composite components and decrease costs. The development of an electrical selfsensing system for woven fabric carbon fibre composite laminate panels which can detect and locate damage due to impact events is presented. The electrical sensing system uses a four probe electrical resistance method. Two different sensing mats are investigated, the main difference between them are the surface area of the electrodes and the distance between the electrodes. To investigate the damage sensitivity of the sensing system for woven fabric carbon fibre composite laminate panels, panels are produced with various thicknesses from 0.84 to 3.5 mm and are impacted at energies from 1 to 10 J to generate barely visible impact damage. Damage is detected using global electrical resistance changes, the changes in electrical resistance vary depending on carbon fibre volume fraction, spacing distance between the sensing electrodes in the sensing mats, the surface area of the electrodes, damage size, and damage type; it is found that the thicker the panel, the less sensitive the electrical resistance system is. The effect of the surface area of the sensing electrodes is high on the electrical resistance baseline, where the baseline increases by up to 55% when the surface area of the sensing electrodes increases from 100 mm2 to 400 mm2; while spacing distance between electrodes has a greater effect on damage sensitivity of the electrical resistance sensing system than the surface area of the sensing electrodes

Osteonecrosis de los maxilares: Documento de consenso

Nuestro objetivo ha sido elaborar un documento de posición sobre el riesgo de desarrollar una osteonecrosis de maxilares (ONM) en los pacientes que reciben bifosfonatos para el tratamiento de la osteoporosis, identificando y valorando el grado de evidencia que apoyan las recomendaciones. Para ello se revisaron los estudios publicados sobre la definición, epidemiología, fisiopatología, clínica, diagnóstico y tratamiento de la ONM, elaborándose tras su análisis las presentes recomendaciones. Éstas se efectuaron tras un proceso pre-especificado y reproducible, que incluyó un modelo aceptado para la evaluación y la cita de la evidencia que las apoyaban. El documento, una vez elaborado por los coordinadores, fue revisado y discutido por todos los miembros del panel, elaborándose las recomendaciones provisionales que finalmente fueron estudiadas y aprobadas por los expertos de las sociedades médicas relacionadas con el metabolismo mineral óseo, que se muestran en el Anexo 2