Pierre Calmon

Modeling tools for ultrasonic inspection of welds

Abstract Developments in quantitative ultrasonic nondestructive testing (NDT) of welds require simulation tools for cost-effective research and engineering works. The present paper reviews the specific developments in modeling of weld inspection at the French Atomic Energy Commission (CEA), made in keeping with the general pattern of CEA in simulation studies of ultrasonic examination. Two models have been developed for several years at CEA for this purpose. One is dedicated to the computation of the ultrasonic field radiated by arbitrary transducers into pieces (possibly anisotropic and heterogeneous) under examination. We specifically discuss how the metallurgical structure and associated elastic properties of welds is taken into account. The other simulates a testing experiment. It accounts for the interaction of the beam with defects (within a piece made of isotropic material) and specimen boundaries and simulates the transducer scan over the piece for synthesizing images comparable with measurements. We specifically discuss the influence of the possible complex geometry of the back-wall of a weld. Examples of application are given. They demonstrate the usefulness of such modeling tools in ultrasonic NDT of welds to study and optimize testing configurations, and to help NDT experts to interpret actual data.

Models for the computation of ultrasonic fields and their interaction with defects in realistic NDT configurations

Developments in quantitative ultrasonic non-destructive testing (subsequently denoted by NDT) require simulation tools for cost-effective research and engineering works. The present paper reviews the two models developed for several years at the French Atomic Energy Commission (CEA) for this purpose. The first one is dedicated to the computation of the ultrasonic field radiated by arbitrary transducers into pieces under examination. The second simulates actual testing configurations, that is, includes beam/defect interaction as well as the transducer scan over the piece so as to synthesise images typical of those actually measured in NDT experiments. Examples of their application in the context of nuclear engineering are given. They demonstrate the usefulness of such modelling tools in ultrasonic NDT either to study and optimise testing configurations, including transducer design or to help NDT-experts to interpret actual data, possibly by means of model-based automatic data inversion.

Modeling of ultrasonic fields radiated by contact transducer in a component of irregular surface.

The wedge of a contact transducer is imperfectly coupled to a component of irregular surface. A volume between the wedge and the component (filled by water or oil used as a coupling) is created that fundamentally modifies transducer radiation behavior. As a result, phenomena like beam spreading, skewing and splitting, generation of unwanted contributions that possibly lead to false alarms may occur. At first, the paper describes a model to account for the main effects observable in such a situation. The model is based on a matrix method which describes the behavior of transient elementary contributions as the variation of a pencil propagating into homogeneous regions (namely, the wedge, the coupling and the component) and through interfaces between them (refraction and reflection). The elementary contributions accounting for the finite size of the transducer are summed to predict transducer diffraction effects. In a second part, predicted fields are compared to measured results. The comparison concerns particle velocity fields measurements at the surface opposite to that (irregular) on which the transducer acts. The very good agreement obtained proves the validity of our approach.

Modeling of propagation and echo formation in a multilayered structure

In the aim of simulating the ultrasonic inspection of multilayered structure, we propose a hybrid model, based on transfer matrices and ray tracing formalisms. This approach allows one to predict the response of structures containing defects of finite size such as delaminations or adhesion defect.

IMAGING OF DEFECTS IN SEVERAL COMPLEX CONFIGURATIONS BY SIMULATION‐HELPED PROCESSING OF ULTRASONIC ARRAY DATA

Advanced ultrasonic array techniques such as full matrix acquisitions provide considerable amount of data making possible by the use of suitable processing algorithms enhanced capability of defects imaging and therefore improved localization and sizing. In general the applied processing consists in a coherent summation of signals (synthetic focusing) based on a time of flight inverse matching. Such algorithms have been connected to forwards models allowing to image defects in realistically complex configurations. In this communication we present results obtained on defects detected through complex surfaces on defects detected by multiple ultrasonic paths (tip diffraction, corner effect, mode conversions). The performances of the technique are evaluated both on simulated and experimental results.

Modeling of ultrasonic fields and their interaction with defects

Ultrasonic modeling at the French Atomic Energy Commission (CEA) is based onto continuous developments of two approximate models covering realistic commonly encountered NDT configurations. The first model, based on an extension of the Rayleigh integral, is dedicated to the prediction of ultrasonic fields radiated by arbitrary transducers. Being computed the field may be inputted in a model of the echo formation. This two step modeling yields the prediction of echo-structures detected with transducer scanning. The associated software is implanted in the CIVA system for processing and imaging multiple technique NDT data.

A model for predicting effects of surface wave propagation on the echo response from planar cracks

A system model is presented for predicting surface wave effects arising in crack diffraction. The model includes the computation of the time-dependent field incident upon the crack, radiated through the interface between the coupling medium and the piece. The crack scattering is computed by the Geometrical Theory of Diffraction (GTD) extended to the transient case for treating wideband transducers, typical of those used in nondestructive measurements. A transient model for reception by the transducer of the scattered field is developed for the prediction of inspection in immersion testing. It accounts for the specific symmetry of the diffracted waves (cylindrical waves arising from the near and far tips of the crack). Numerical results for a realistic testing configuration are given and discussed.

Integrated Models of Ultrasonic Examination for NDT Expertise

For several years, the French Atomic Energy Commission (CEA) has developed a system called CIVA for multiple-technique NDE data acquisition and processing [1]. Modeling tools for ultrasonic non-destructive testing have been developed and implemented within this system allowing direct comparison between measured and predicted results. These models are not only devoted to laboratory uses but also must be usable by ultrasonic operators without special training in simulation techniques. Therefore, emphasis has been on finding the best compromise between as accurate as possible quantitative predictions and ease, simplicity and speed, crucial requirements in the industrial context.

Modeling of Ultrasonic Attenuation in Uni‐Directional Fiber Reinforced Composites Combining Multiple‐Scattering and Viscoelastic Losses

A model coupling viscoelastic and multiple‐scattering losses is developed to predict ultrasonic attenuation in unidirectional fiber reinforced composite of high fiber volume fraction. Complex‐valued stiffness constants accounting for viscoelasticity are inserted in classical multiple‐scattering theory. Waves of various polarities (SH, SV, L) relatively to the fiber direction are considered. SH waves only require a scalar treatment, whereas the others require a vector treatment accounting for mode‐conversions. Comparisons of predicted attenuation coefficients with experimentally measured ones validate the model.

Simulation of phased array techniques for realistic NDE configurations

In this communication we briefly present the phased array simulation tools developed at the CEA in the aim of driving delays laws, predicting ultrasonic beams, simulating and processing acquired data. These tools allow to manage NDT inspections in complex configurations. We present some examples on such configurations illustrating the interest and reliability of simulation.