Alexandre Clément

The αδ method for modelling expert judgement and combination of non-destructive testing tools in risk-based inspection context: application to marine structures

Owners of civil infrastructure base their maintenance decision schemes mainly on both structural integrity assessment and consequence analysis. Some inputs come from information collected by inspections with non-destructive or destructive tools. Uncertainties and errors of measurement can lead to bad decisions but are rarely integrated into the decision process. Currently, risk-based inspection (RBI) provides the basic concepts for optimising the maintenance plans of existing structures while insuring satisfactory safety and availability of the structure during its service life. It relies both on reliability computations and probabilistic modelling of inspection results. This last point leads to introduce the probability of detection and the probability of false alarms that are usually considered as parameters in RBI. However, when data from inter-calibration campaigns are available, the whole receiver operating characteristics curves should be used. Then, the comparison of non-destructive testing tools in terms of cost or benefit is difficult as well as the method for optimising a given technique. This article presents the αβ method that gives a new performance indicator in this context. It is applied to the field of inspection of harbour structures.

Moisture diffusion in composites tubes: Characterization and identification of microstructure-properties relationship

This work aims at highlighting some microstructure-properties relationships; namely: the effect of the microstructure on the diffusive behavior of composites tubes obtained by filament winding technique. Composites tubes are made from either glass or carbon fibers impregnated with the same epoxy matrix cured at 150℃. Specimens were rings cut from tubes. Three winding angles were investigated: ± 42°, ±56° or ±78°. Glass and carbon/epoxy tubes present a strongly different void content, respectively, 1.7% and 5.7%. Immersion aging tests were conducted in distilled water at 70℃. Results show that despite both glass and carbon composites are made of the same resin, moisture uptake exhibits strong discrepancies between glass/epoxy and carbon/epoxy samples. An investigation of the most appropriate diffusion model for glass and carbon/epoxy specimens is developed in this paper, based on an experimental study of the microstructure of these composites owing to various complementary characterization methods. Glass/epoxy rings exhibit a Fickian diffusion, whereas carbon/epoxy specimens do not match a Fickian diffusion. A dual-stage Fickian law is discussed and seems to fit quite well in experimental observations.

Multiphysics Modeling of the Hygro-Mechanical Behavior of Heterogeneous Materials

The present chapter investigates the modeling of the hygro-mechanical behavior of composites used in marine environment. The purpose of the proposed models is to analyze the effect of water absorption on a composite structure through mechanical quantities such as stress fields. The case of non-Fickian diffusion processes is first addressed with the Langmuir model allowing representing anomalies of diffusion. The elastic constitutive equations thus depend on the moisture content involving a hygroscopic strain field. The capabilities of the model are shown with a numerical study on a composite material. Second, we propose to introduce couplings between the water diffusion and the mechanical states. To achieve this, we mix the classical Fick model with the free volume theory and implement the model in a finite element software. A numerical study regarding the impact of such coupling on a pure resin case is carried out. We finally propose to take into account the uncertainties sometimes observed on the experimental data which enable the characterization of the diffusion properties. Some of the material properties of the hygro-elastic model thus become random and are modeled with random variables. The propagation of these uncertainties is made with a stochastic spectral approach based on polynomial chaos expansions. The efficiency of the proposed technique is shown with a numerical application involving a polyamide neat resin.

Risk assessment based on performantial criterion for inspection of offshore structures in presence of large cracks

ABSTRACT When performing risk analysis, it is often uneasy to find the link between limit state and consequences. This paper focuses on efficiency based limit states in case of large cracks on offshore structures. Randomness and uncertainties on loading as well as on crack measurement and detection are introduced.