Progress Towards a Forward Model of the Complete Acoustic Emission Process

Abstract

Acoustic emission (AE) techniques have obvious attractions for structural health monitoring (SHM) due to their extreme sensitivity and low sensor density requirement. A factor preventing the adoption of AE monitoring techniques in certain industrial sectors is the lack of a quantitative deterministic model of the AE process. In this paper, the development of a modular AE model is described that can be used to predict the received time-domain waveform at a sensor as a result of an AE event elsewhere in the structure. The model is based around guided waves since this is how AE signals propagate in many structures of interest. Separate modules within the model describe (a) the radiation pattern of guided wave modes at the source, (b) the propagation and attenuation of guided waves through the structure, (c) the interaction of guided waves with structural features and (d) the detection of guided waves with a transducer of finite spatial aperture and frequency response. The model is implemented in the frequency domain with each element formulated as a transfer function. Analytic solutions are used where possible; however, by virtue of its modular architecture it is straightforward to include numerical data obtained either experimentally or through finite element analysis (FEA) at any stage in the model. The paper will also show how the model can used, for example, to produce probability of detection (POD) data for an AE testing configuration.

Finite Element Modelling of Cracks as Acoustic Emission Sources

“…Instead the rise-time is typically estimated based on the elastic properties of the bulk material. This type of source modeling has been successfully applied to many cases, and the basic concept has been used within the generalized theory of acoustic emission by Ono and Ohtsu [8,13], the work of Scruby [14] and numerous other analytical descriptions [7,9,15,16]. In recent years it has become convenient to use numerical methods to model acoustic emission sources.…”

“…In contrast to the source model, the theoretical description and numerical implementation of wave propagation is already well established [10,11,16,17,19,20,27]. However, it is important to consider the effects of attenuation, dispersion and propagation in guiding media to accurately capture the characteristics of the signal (e.g.…”

“…While analytical descriptions benefit from the low computational intensity [16] to describe wave propagation, for the numerical methods a main focus is the improvement of the calculation routines.…”

“…Here the detection process using piezoelectric sensors can have significant impact on the bandwidth of the detected signals and their relative frequency content. While some analytical approaches consider the sensors transfer function explicitly [16,21], some attempts have also been made to model the response of piezoelectric sensors themselves [22]. We recently proposed a finite element approach to directly include the piezoelectric sensor in a modeling environment to also account for the interplay between the sensor and the material it is attached on [23].…”

Acoustic Emission

“…This is typically done by phenomenological observations [6], by comparative measurement of test specimens with known types of AE sources [7,8] or subsequent microscopy [9]. Recent advances also allow the forward prediction of the emitted AE signal of a specific source type by analytical methods [10] or finite element modeling (FEM) [11][12][13].…”