Nicolas Dominguez

In the aeronautic industry, the performance demonstration of Non-Destructive Testing (NDT) procedures relies on Probability Of Detection (POD) analyses. This statistical approach measures the ability of the procedure to detect a flaw with regard to one of its characteristic dimensions. The inspection chain is evaluated as a whole, including equipment configuration, probe effciency but also operator manipulations. Traditionally, a POD study requires an expensive campaign during which several operators apply the procedure on a large set of representative samples. Recently, new perspectives for the POD estimation have been introduced using NDT simulation to generate data. However, these approaches do not offer straightforward solutions to take the operator into account. The simulation of human factors, including cognitive aspects, often raises questions. To address these diffculties, we propose a concept of operational NDT simulator [1]. This work presents the first steps in the implementation of such simulator for ultrasound phased array inspection of composite parts containing Flat Bottom Holes (FBHs). The final system will look like a classical ultrasound testing equipment with a single exception: the displayed signals will be synthesized. Our hardware (ultrasound acquisition card, 3D position tracker) and software (position analysis, inspection scenario, synchronization, simulations) environments are developed as a bench to test the meta-modeling techniques able to provide fast-simulated realistic ultra-sound signals. The results presented here are obtained by on-the-fly merging of real and simulated signals. They confirm the feasibility of our approach: the replacement of real signals by purely simulated ones has been unnoticed by operators. We believe this simulator is a great prospect for POD evaluation including human factors, and may also find applications for training or procedure set-up.

NDT performances evaluation in the aeronautic industry is made by estimating Probability of Detection (POD). It is a statistical estimation of the capability of a given NDT procedure to detect defects as a function of their size. The accuracy of the statistical estimation is directly linked the quality and quantity of collected data. The more data and the more realistic they are, the better the POD estimation. This practical production of data may have very high cost, sometimes obliging to decrease either the quantity or the quality (realistic) of data, or even both. In the last decade MAPOD and simulation-based POD approaches have emerged and been used for concept demonstration as a solution to decrease the cost of evaluating POD. Today tools are available to support these studies and are used in industrial laboratories. This paper reviews some examples of POD evaluation using simulation, describes the actual practice of the tools in the European aeronautical context and also draws some limits and perspectives for a future wider application of the simulation helped POD approach.

Carbon Fiber reinforced composites are increasingly used in structural parts in the aeronautics industry, as they allow to reduce the weight of aircrafts while maintaining high mechanical performances. However, such structures can be complicated to inspect due to their complex geometries and complex composite properties, leading to highly heterogeneous and anisotropic materials. Different potential damages and manufacturing flaws related to these parts are to be detected: porosities, ply waviness, delaminations after impact. Ultrasonic inspection, which is commonly used to test the full volume of composite panels, thus has to cope with both complex wave propagation (within anisotropic parts whose crystallographic orientation varies according to the layers structure) and flaw interaction (local distortion of plies such as ply waviness, small pores, structural noise due to periodicity patterns…). Developing NDT procedures for those parts therefore requires simulation tools to help for understanding those phenomena, and to optimize probes and techniques. Within the CIVA multi-techniques platform, CEA-LIST has developed semi-analytical tools for ultrasonic techniques, which have the advantages of high computational efficiency (fast calculations), but with limited range of application due to some hypothesis (for instance, homogenization approaches which don’t allow to take account of structural noise). On the other hand, numerical methods such as finite element (FEM) or finite difference in time domain (FDTD) are more suitable to compute ultrasonic wave propagation and defect scattering in complex materials such as composite but require more computational efforts. Hybrid methods couple semi-analytical solutions and numerical computations in limited spatial domains to handle complex cases with high computation performances. In CIVA we have integrated a hybrid model that combines the semi-analytical methods developed at CEA to FDTD codes developed at Airbus Group Innovations for composite applications. In this paper we give some examples of the hybrid method for the inspection of complex composite parts. Examples are related to curved composite parts with varying anisotropy (layers follow the curvature of the component), and effects of the inter-ply epoxy layer to structural noise.