Nonlinear Ultrasonic Imaging for Porosity Evaluation.

The influence of porosity on the mechanical behaviour of composite laminates represents a complex problem that involves many variables. Therefore, the evaluation of the type and volume content of porosity in a composite specimen is important for quality control and for predicting material behaviour during service. A suitable way to evaluate the porosity content in composites is by using nonlinear ultrasonics because of their sensitivity to small cracks.

Ultralight graphene oxide/polyvinyl alcohol aerogel for broadband and tuneable acoustic properties.

An ultralight graphene oxide (GO)/polyvinyl alcohol (PVA) aerogel (GPA) is proposed as a new class of acoustic materials with tuneable and broadband sound absorption and sound transmission losses. The interaction between GO sheets and PVA molecules is exploited in our environmentally friendly manufacturing process to fabricate aerogels with hierarchical and tuneable porosity embedded in a honeycomb scaffold. The aerogels possess an enhanced ability to dissipate sound energy, with an extremely low density of 2.

Deep-Subwavelength-Optimized Holey-Structured Metamaterial Lens for Nonlinear Air-Coupled Ultrasonic Imaging.

Ultrasound non-destructive testing (NDT) is a common technique used for defect detection in different materials, from aluminium to carbon-fiber-reinforced polymers (CFRPs). In most cases, a liquid coupling medium/immersion of the inspected component is required to maximize impedance matching, limiting the size of the structure and materials. Air-coupled inspection methods have recently been developed for noncontact inspections to reduce contact issues in standard ultrasonic inspections.

A nonlinear ultrasonic SHM method for impact damage localisation in composite panels using a sparse array of piezoelectric PZT transducers.

Structural health monitoring techniques (SHM) for material damage identification have demonstrated higher sensitivity and accuracy when relying on the assessment of nonlinear features exhibited in the material response under ultrasonic wave propagation. In this paper, a novel nonlinear ultrasonic SHM method is introduced for localisation of impact damage in composite laminates using an array of surface-bonded sensors. Unlike existing algorithms, this method enables quick selection of a suitable signal transmission frequency based on the combined sensor-material response, it does not rely on baseline data or complex measurements of signal arrival time, and it allows identification of malfunctioning sensors to minimise damage localisation errors.

A combined linear and nonlinear ultrasound time-domain approach for impact damage detection in composite structures using a constructive nonlinear array technique.

Discovery and evaluation concerns of barely visible impact damage in composite materials is a well-known issue in industries using these materials. This work proposes a frequency sweep method where damage assessment is conducted with respect to the time domain. Firstly, a combined linear and nonlinear ultrasound imaging technique is proposed, which focuses on the excitation of damage/defect regions using a frequency sweep methodology from multiple transducer locations.

Nonlinear elastic imaging of barely visible impact damage in composite structures using a constructive nonlinear array sweep technique.

Linear and nonlinear ultrasound imaging methods highlight different damage features: the linear method detects large stiffness changes, while the nonlinear technique identifies small impedance mismatches, such as microcracks or closed delaminations. Typically, nonlinear ultrasound techniques detect damage/defects in materials by measuring higher order harmonics. These harmonics can be difficult to measure due to low magnitude and signal to noise ratios (SNR): hence large excitation amplitudes are needed, which can further complicate the reliability of these methods as equipment nonlinearities can be generated.

Nonlinear imaging (NIM) of flaws in a complex composite stiffened panel using a constructive nonlinear array (CNA) technique.

Recently, there has been high interest in the capabilities of nonlinear ultrasound techniques for damage/defect detection as these techniques have been shown to be quite accurate in imaging some particular type of damage. This paper presents a Constructive Nonlinear Array (CNA) method, for the detection and imaging of material defects/damage in a complex composite stiffened panel. CNA requires the construction of an ultrasound array in a similar manner to standard phased arrays systems, which require multiple transmitting and receiving elements.