Investigation of damage evolution in short glass fibers reinforced polyamide 6,6 under tensile loading using infrared thermography

AbstractMechanical properties of polymers are very sensitive to environmental conditions in particular temperature. In the case of mechanical testing, thermomechanical coupling induce heat sources to be activated during the deformation and damage processes so that the temperature of the specimen may vary during testing. Depending on the characteristic temporal and spacial scales of the deformation and damage processes involved by the loading this temperature increase might be uniform or highly localized. The aim of the study is to investigate the temperature field evolution of glass fibers reinforced polyamide 6,6 with 0% (PA66GF00), 10% (PA66GF10), 20% (PA66GF20) and 30% (PA66GF30) glass fiber. In addition to infrared thermography, digital image correlation (DIC) was used to quantify deformation localization zones and correlate them to identified heat dissipation sources. Until necking, the heat distribution was found to be nearly homogeneous on PA66GF00 with a well marked thermoelastic region, succeeded by an homogeneous heat increase due to viscoplastic dissipation. Necking is associated to strong heat increase that is localized on the the necking area. The thermal response of short fiber reinforced materials was found to differ markedly from the uncharged one. Strong heterogeneity of the thermal was observed and was associated to localisation processes at different scales (investigated by DIC). The effect of the applied strain rate on the observed thermal heterogenities was investigated. In addition to DIC, the volume damage evolution was monitored using X-ray computed microtomography in particular region

Analyse thermomécanique des lois de comportement par thermographie infrarouge

The knowledge of dissipative and non dissipative phenomena associated to quasi-static déformation processes, is a fundamental supplementary asset for determination of thermomechanical behaviour law. On depicts, in this paper, an experimental set-up, using infra-red technics, which allows to observe thermal and energetical phenomena during sample déformation. After restating the definition of the energy balance, in case of elastic-plastic materials, the relationship between the dissipation (or the stored energy of cold working) and the hardening state variables are recalled. The dissipation is continuously evaluated during monotonic tensile test. Numerized maps of surface temperature are used. The experimental arrangement is described ; then the physical model, which allows to relate the dissipation to the temperature signals, and the calibration method are successively introduced. Results on several materials are shown and their incidence on the behaviour law is succinctly mentioned.La connaissance des phénomènes dissipatifs et non dissipatifs associés aux processus quasi-statiques de déformation, représente un atout supplémentaire important pour l'élaboration de loi thermomécanique de comportement. On décrit, ici, un dispositif expérimental, utilisant les techniques de thermographie infrarouge, et permettant d'observer les phénomènes thermiques et énergétiques durant la déformation d'un échantillon en traction simple. Après avoir rappelé la définition du bilan énergatique, dans le cas de matériaux élasto-plastiques, on relie la dissipation et l'énergie interne bloquée durant l'écrouissage, aux variables d'état. La puissance mécanique dissipée est évaluée continûment durant l'essai. On utilise pour cela, les images thermiques fournies par la caméra infra-rouge. On présente le dispositif expérimental, puis successivement, on décrit le modèle physique permettant de relier l'énergie dissipée aux cartes de température de surface ainsi que le protocole d'étalonnage. En fin d'article, on présente quelques résultats obtenus avec plusieurs matériaux et on évoque rapidement leur incidence sur la forme des lois de comportement

Stabilizing Heteroscedastic Noise With the Generalized Anscombe Transform. Application to Accurate Prediction of the Resolution in Displacement and Strain Maps Obtained With the Grid Method.

International audienceThe objective of this paper is to show that it is possible to predict the noise level in displacement and strain maps obtained with the grid method, but that actual noise of camera sensors being heteroscedastic, it is necessary to stabilize this noise in grid images prior to employing the predicting formulas. The procedure used for this purpose relies on the Generalized Anscombe Transform. This transform is first described. It is then shown that experimental and theoretical resolutions in strain maps obtained with the grid method are in good agreement when this transform is employed

Dissipation and thermoelastic coupling associated with fatigue of materials

The fatigue behaviour is examined in terms of calorimetric effects. Aluminum alloy and steel have been chosen as reference materials. Heat sources accompanying the fatigue mechanisms are derived from thermal images provided by an infrared camera. A processing method allows identifying separately thermoelastic and dissipative sources. Thermoelastic effects are compared to theoretical predictions given by the basic, linear, isotropic thermoelastic model. Dissipation amplitudes are analyzed as a function of the loading frequency and stress amplitude applied to the fatigue specimen. Finally, the heterogeneous character of the fatigue development is studied both in terms of thermoelastic and dissipation sources

Categorical perception of facial gender information: behavioural evidence and the face-space metaphor

Categorization is a fundamental property of the human brain. We used an image-morphing procedure to investigate the categorical perception of facial gender information. Three experiments, an identification and two matching tasks, were reported. First, we showed that, even when facial image information changes linearly across unfamiliar male and female faces, gender is perceived categorically. This holds only when faces are presented in an upright orientation. Second, subjects discriminated more easily two unknown morphed faces presenting a gender change as compared to two unknown morphed faces belonging to the same gender, even when the physical distance between the pairs was identical. We discuss the results in terms of how representations of faces are encoded and stored in long-term memory.info:eu-repo/semantics/publishe