Sur la longueur moyenne d'extraction pour des composites à fibres longues

International audienceIn this Note, an expression of the average pull-out length is established when the length of a representative element varies with the external load. This expression is derived from a study of fracture locations generalized to varying lengths, and can be used to determine ultimate strengths of fiber−reinforced composites.Dans cette Note, une expression de la longueur moyenne d'extraction est obtenue lorsque la longueur d'un élément représentatif varie avec le chargement. Cette expression correspond à une généralisation des lieux de rupture dans le cas d'une longueur variable. Le résultat peut être utilisé dans le calcul de résistance de composites à fibres longues

A New Synthetic Indicator Taking Into Account the Dynamics of Individual Responses to the French Industry Survey

The interpretation of tendency surveys is very often based on changes in balances of opinion, which constitute the most commonly used summaries of responses of companies. This article suggests the construction of different indicators, which, on the one hand, take into account "stable" or "normal" response conditions, and on the other hand also take into account the dynamics of individual responses from one survey to the next. The responses of companies during two consecutive surveys are classified into nine categories: Increase-Increase, Increase-Unchanged, Increase-Decrease, Unchanged-Increase, etc. We focus on the percentages of companies that change their response from one survey to another. These percentages could give early signals of certain changes in the short-term economic situation and represent slightly advanced indicators. In particular, the article shows that, for certain questions, the percentages of Unchanged-Decrease and Unchanged-Increase responses do indeed display a number of tendencies earlier than the corresponding balances of opinion.Business Tendency Surveys, Synthetic Indicators, Short-Term Forecasting

Recent Advances and Perspectives in Digital Image Correlation

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Ultimate strength properties of fiber-reinforced composites

International audienceThe volume effect and stress heterogeneity effect (i.e., the effect of loading type) on the ultimate strength are analyzed for fiber-reinforced composites. The main failure mechanisms are assumed to be fiber breakage and fiber pull-out. Depending on the load redistribution around a broken fiber, two different regimes can be obtained. The results are applied to the prediction of ultimate strengths of SiC fiber-reinforced composites subjected to tension, pure flexure and three-point flexure

A Statistical Approach to the Rupture of Brittle Materials

International audienceSince initial defects are the main cause of the failure of structures made of brittle materials, the scope of this paper is to take these defects into account in the evaluation of the failure probability of a structure. Using the weakest link theory assumption and modeling the failure probability of a single link, a general relationship between the statistical distribution of defects and the failure probability is obtained. After determining the size of the critical defect, some correlations between the defect distribution and the Weibull's parameters are deduced from either Linear Fracture Mechanics or Continuum Damage Mechanics. The effect of the statistical distribution of defects within the material is computed and studied with respect to the distribution itself, the loaded volume of the structure and the heterogeneity of the stress field

On the characteristic scales involved in a fragmentation process

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Fatigue initiation in heterogeneous brittle materials

International audienceThe fatigue process can be schematically divided into an initiation stage and the propagation period. In this paper, we consider brittle materials where only the initiation phase needs to be studied, since the propagation is always unstable. We suppose that the initiation is due to some initial randomly distributed defects that grow according to a generalized Paris' law and become critical for a given number of cycles and for a given load level (characterized by a maximum equivalent stress over a cycle). The purpose of this paper is to present a statistical approach of the initiation stage in fatigue derived from a unified framework of the failure probability in the case of monotonic and cyclic loadings. We will show in particular that the iso-probability curves in a Woehler diagram, have a shape which is independent of the initial statistical distribution of defects. Applications of this study are to be found in the case of engineering ceramics