High magnification crack-tip field characterisation under biaxial conditions

This work presents a novel methodology for characterising fatigue cracks under biaxial conditions.The methodology uses high magnification Digital Image Correlation (DIC) technique for measuringdisplacement and strain crack-tip fields. By applying micro-speckle pattern on the metal surface it is possible toachieve high magnification for DIC technique. The speckles were created by electro-spray technique. Thevalidity of this novel technique is demonstrated by direct comparison with standard extensometermeasurements, under tension-compression and torsion conditions. In order to image the correct region, thenotch effect on the fatigue life was also evaluated

Colheita e processamento de amostras de sangue em suinos para fins de diagnostico.

Objetivos da colheita de sangue em suinos; Caracteristicas da amostra; Principais anticoagulantes; Material necessario para colheita de sangue; Material; Identificacao de amostras; Colheita de sangue; Contencao do suino de acordo com a idade; Vias de acesso ao sangue; Veia cava cranial; Veia jugular; Veia cefalica; Vasos da orelha; Vasos da cauda; Seio orbital; Comparacao entre as tecnicas de colheita de sangue; Sequencia indicada para colheita de sangue por puncao venosa; Processamento de amostra; Armanezamento e viabilidade do sangue; Valores sanguineos de referencia; Tipos sanguineos dos suinos.bitstream/item/58432/1/doc41.pd

Evaluation of new multiaxial damage parameters on low carbon steel

Most mechanical components are subjected to the complex fatigue loading conditions, where both amplitude and direction of loading cycles change over the time. The estimation of damage caused by these complex loading scenarios are often done by simplified uniaxial fatigue theories, which ultimately leads to higher factor of safety during the final design considerations. Critical plane-based fatigue theories have been considered more accurate for computing the fatigue damage for multiaxial loading conditions in comparison to energy-based and equivalent stress-based theories. Two recently developed fatigue theories have been evaluated in this work for the available test data. Test data includes significant amount of biaxial load paths

Study of short cracks under biaxial fatigue

In this paper a methodology for evaluating crack initiation under biaxial conditions is presented. The methodology consists of evaluating the crack length automatically with digital processing of highmagnification images of the crack. The methodology was applied to study five different strain conditions on a low carbon ferritic-pearlitic steel specimen with tubular shape. A hole of 150 ?m diameter was drilled to enforce the crack to initiate at a particular spot. Different combinations of axial and torsional strains were analysed during the initiation stage of the crack. The setup employed allowed detection of the crack to within 6 ?m from the edge of the hole on average and monitoring of the crack during early stages. Fatigue crack propagation curves clearly showed oscillations due to microstructure. It was also observed that these oscillations decreased as the torsional component of the strain was increased

Experimental and analytical study of cracks under biaxial fatigue

Most mechanical components experience multi-axial cyclic loading conditions during service. Experimental analysis of fatigue cracks under such conditions is not easy and most works tend to focus more on the simpler but less realistic case of uni-axial loading. Consequently, there are many uncertainties related to the load sequence effect that are now well known and are not normally incorporated into the growth models. The current work presents a new methodology for evaluating overload effect in biaxial fatigue cracks. The methodology includes evaluation of mixed-mode (KI and KII) stress intensity factor and the Crack Opening Displacement for samples with and without overload cycle under biaxial loading. The methodology is tested under a range of crack lengths. All crack-tip information is obtained with a hybrid methodology that combines experimental full-field digital image correlation data and Williams' elastic model describing the crack-tip field

Study of CT Images Processing with the Implementation of MLEM Algorithm using CUDA on NVIDIA’S GPU Framework

In medicine, the acquisition process in Computed Tomography Images (CT) is obtained by a reconstruction algorithm. The classical method for image reconstruction is the Filtered Back Projection (FBP). This method is fast and simple but does not use any statistical information about the measurements. The appearance of artifacts and its low spatial resolution in reconstructed images must be considered. Furthermore, the FBP requires of optimal conditions of the projections and complete sets of data. In this paper a methodology to accelerate acquisition process for CT based on the Maximum Likelihood Estimation Method (MLEM) algorithm is presented. This statistical iterative reconstruction algorithm uses a GPU Programming Paradigms and was compared with sequential algorithms in which the reconstruction time was reduced by up to 3 orders of magnitude while preserving image quality. Furthermore, they showed a good performance when compared with reconstruction methods provided by commercial software. The system, which would consist exclusively of a commercial laptop and GPU could be used as a fast, portable, simple and cheap image reconstruction platform in the future

Some experimental observations of crack-tip mechanics with displacement data

In the past two decades, crack-tip mechanics has been increasingly studied with full-field techniques. Within these techniques, Digital Image Correlation (DIC) has been most widely used due to its many advantages, to extract important crack-tip information, including Stress Intensity Factor (SIF), Crack Opening Displacement, J-integral, T-stress, closure level, plastic zone size, etc. However, little information is given in the literature about the experimental setup that provides best estimations for the different parameters.The current work aims at understanding how the experimental conditions used in DIC influence the crack-tipinformation extracted experimentally. The influence of parameters such as magnification factor, size of theimages, position of the images with respect the crack-tip and size of the subset used in the correlation is studied. The influence is studied in terms of SIF and T-stress by using Williams’ model. The concept of  determination of  the K-dominance zone from experimental data has also explored. In this regard, cyclic loading on a fatigue crack in a compact tension (CT) specimen, made of aluminium 2024-T351 alloy, has been applied and the surface deformation ahead of the crack tip has been examined. The comparison between theoretical and experimental values of KI showed that the effect of subset size on the measured KI is negligible compared to the effect of size of the image

Nueva ley de crecimiento de grietas por fatiga basada en la función de distribución de Gumbel: aplicación a la aleación Ti-6Al-4V

La caracterización del crecimiento de grietas por fatiga continúa siendo un tema de interés en la evaluación de la integridad estructural de componentes mecánicos. Desde la década de 1960, se han desarrollado numerosos modelos utilizando diferentes leyes para el crecimiento de grietas en función, generalmente, del rango del factor de intensidad de tensiones. En este trabajo se propone la función de distribución de Gumbel para ajustar la forma sigmoidal de las curvas de crecimiento de grietas largas por fatiga de una aleación de titanio Ti-6Al-4V y se describe la metodología para obtener los parámetros de la función. Además, se utiliza el modelo de Walker para tener en cuenta el efecto de la relación de carga y se obtienen los parámetros de la función para cualquier relación de carga. Los resultados presentados son comparados con los obtenidos utilizando el modelo basado en el cierre de grieta implementado en el software NASGRO. Estos resultados muestran que el método propuesto es igual o mejor que el de NASGRO para correlacionar los valores experimentales y predecir los efectos de la relación de carga en la velocidad de crecimiento de grietas.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Evidence Against the Sciama Model of Radiative Decay of Massive Neutrinos

We report on spectral observations of the night sky in the band around 900 angstroms where the emission line in the Sciama model of radiatively decaying massive neutrinos would be present. The data were obtained with a high resolution, high sensitivity spectrometer flown on the Spanish MINISAT satellite. The observed emission is far less intense than that expected in the Sciama model.Comment: 9 pages, accepted to Ap