Contrôle non destructif | EPFL Graph Search

Le contrôle non destructif (CND) est un ensemble de méthodes qui permettent de caractériser l'état d'intégrité de structures ou de matériaux, sans les dégrader, soit au cours de la production, soit en cours d'utilisation, soit dans le cadre de maintenances. On parle aussi d'essais non destructifs (END) ou d'examens non destructifs. Utilisations Ces méthodes sont utilisées dans l'ensemble des secteurs industriels. On peut citer notamment :

l'industrie pétrolière (pipelines, tubes, barres, soudures, réservoirs) ;
l'industrie navale (contrôle des coques) ;
l'aéronautique (poutres, ailes d'avion, nombreuses pièces moteurs, trains d'atterrissage) ;
l'aérospatiale et l'armée ;
l'industrie automobile (contrôle des blocs moteurs) ;
la sidérurgie ;
la fonderie ;
la chaudronnerie et la tuyauterie en fabrication ;
l'industrie de l'énergie : réacteurs nucléaires, chaudières, tuyauterie, turbines (maintenance des installations) ;
le ferroviaire en fabrication et en

Vieillissement et fiabilité des parcs de poteaux bois des réseaux de lignes aériennes

Yann Benoit

The reliability of new overhead electric and telecommunication lines depends principally on the quality of their support structures. These structures are generally made of wood, metal or concrete. The complexity of a natural substance such as wood requires a thorough analysis of the various factors that influence its overall quality. In the case of wood poles, such factors include initial forest growth pattern, the species of wood and its preservative treatment, ageing characteristics, and its various mechanical defects such as knots, cracks etc. The accumulation of knowledge on the effect of the various variables that contribute to the overall quality of a wood support structure permits an optimum use of such a resource. For example, less variability and higher strength of wood support structures permits optimum loading and spacing between structures, thus reducing the number needed in a specific length of an overhead line. If one assumes that in Western Europe 1 wood pole is employed for every 2 inhabitants, and that this proportion increases in less densely populated countries such as the US and Scandinavia, the economics of optimum use of wood as a resource soon become apparent. In less developed countries, the proportions and the economics vary depending on the natural resources such as wood that they employ. The goal of this research is to establish, thanks to non destructive evaluations, a general ageing probabilistic law of the wooden pole based on two distinguished laws: one on the new pole in studying the influence of a grading of the bad elements based on a normal law: "left-truncation of a normal distribution", point 1; and another one based on the in-field wooden pole in exploiting the different parameters such as: the age of the pole, its chemical treatment, its species, its knots etc. in order to define the pole's damage law, point 2. Statistical distribution law of the new wooden pole after grading by non destructive sorting (ultrasounds) of the high mechanical performances supports: This new distribution law is a Gaussian law or evolves to a Log or Weibull's law with 3 parameters according to the inspected species. This grading allows a revalorization of the properties of the new poles and of the design values while guaranteeing an index of reliability required by the design standards, or in improving directly this nominal reliability (economic gain and reliability gain). Statistical distribution law of an aged in-field population (20-50 years old) approached by a bi-modal law which depends on: The distribution law of the new component (see point 1) and its minimal extreme law, which is asymmetrical, for an observation on 50 years. The statistical distribution at the time t of the residual mechanical performances of a group of supports making a local net, evaluated by non destructive methods. The non destructive evaluation is based on the measurements of physical variables (density, biological moisture content) and some descriptive variables from natural origins (diameter, knots, cracks...) and from accidental origins (diameter reduction, lightning cracks...). The statistical distribution at the time t is then obtained on the basis of a model of multivariate non destructive evaluation, generalized to the whole of species and treatments. This model is the other concrete goal to reach in this thesis. As a conclusion, the research demonstrates the influence and the interaction of the new pole grading (distribution at t0) on the modelisation of the distribution at ti (multivariate non destructive model). The data used for the mentioned modelisations come from a significant international database with a large amount of inspected wood poles and with studied cases. This database is the synthesis of about 15 years of research and development leaded by IBOIS-EPFL and its international partners. The probabilistic approaches are then validated by a huge database allowing thus to be directly exploitable. On this basis, all the standards dealing with the new poles and dealing with the controls and maintenances of a wooden pole networks, could be re-examined for a double gain: Concerning the economy: by increasing the capacity of the new poles profiting of an objective quality assurance, and by increasing the life time of the in-field pole, in knowing how to purge only the ones which are under the critical threshold of damage Concerning the reliability: by increasing the reliability of the network from the stage "new pole", by eliminating the weakest components, and by maintaining this reliability during all the life time of the network thanks to a cyclic preventive maintenance (every 5 to 8 years) and the replacement of only the weakened poles.

EPFL2004

Phase Gradient Estimation Techniques in Fringe Analysis

Rajshekhar Gannavarpu

The thesis introduces novel techniques in the field of fringe analysis for direct estimation of phase gradients or derivatives. A pseudo Wigner-Ville distribution based method is proposed to reliably estimate the phase derivatives from a single fringe pattern. The method's ability for estimating rapidly varying phase derivatives is enhanced by developing an adaptive windowing technique. Further, the two-dimensional extension of the method is presented to handle fringe patterns with severe noise. In addition, a generalized approach is described to enable direct estimation of arbitrary order phase derivatives. Subsequently, methods based on digital holographic moiré and multi-component polynomial phase formulation are introduced to measure the in-plane and out-of-plane displacements and their derivatives for a deformed object in digital holographic interferometry. These methods permit the simultaneous estimation of multiple phases and their derivatives without the need of multiple fringe patterns and complex experimental configurations, which is hitherto not possible with the current state-of-the-art fringe analysis methods. The major advantages of the developed techniques are the ability to directly estimate phase derivatives without relying on complex unwrapping, filtering and numerical differentiation operations, high computational efficiency and strong robustness against noise. In addition, the requirement of a single fringe pattern makes these techniques less error-prone in the presence of vibrations and external disturbances and enhances their applicability for dynamic measurements. Further, the developed techniques offer a potential solution to the challenging problem of simultaneous multi-dimensional deformation analysis in digital holographic interferometry. The reliable performance of these techniques is validated by numerical simulation and their practical applicability is demonstrated in digital holographic interferometry and fringe projection for slope and curvature measurement, defect detection, surface slope evolution studies and measurement of in-plane and out-of-plane displacements and their derivatives. These techniques offer substantial advancements in fringe analysis and exhibit significant application potential in areas such as non-destructive testing, biomechanics, reliability analysis, material characterization and experimental mechanics.

EPFL2012

Allometric equations for non-destructive biomass estimation of early stage sugarcane plants – Case study in Pernambuco, northeastern Brazil

Hadrien Baecher

Brazil recently became the 5th world power, and with a tremendous growing of its population and the resulting needs, this country is facing challenges in providing energy to every sector of its socio-economical activity. The actual global warming concern and the inevitable decline of fossil energy resources has lead to the research and development of new renewable energy sources as well as to the improvement of the already existing ones. Historically, sugarcane occupies a prominent place among the agricultural crops in Brazil and is in a period of increasing demand. The importance of this crop for the Brazilian economy makes research and development of new varieties and new agricultural techniques a priority. This study aimed to develop a non-destructive method to assess biomass production of live sugarcane plantations at an early stage of development. It highlighted the more relevant non-destructive parameters at different stages of the crop (60, 90, 120 days after planting) to evaluate above-ground biomass by establishing multiple linear regression models. The relevance of the following parameters were established: the diameter at ground level and the dimensions of the leaf F(0). The study was first carried out considering sugarcane as a species and then by comparing equations for five different sugarcane genotypes (varieties). It also assessed the feasibility of developing allometric equations that would be a useful tool to estimate root biomass from more easily measured above-ground plant parameters.

2013