No abstract

Carbon fiber reinforced composites are widely used in the aerospace industry, but barely visible impact damage can lead to delamination and compromise the structural integrity. The scattering of the fundamental anti-symmetric guided wave mode (A 0 Lamb mode) at an artificial circular delamination in a quasi-isotropic laminate was investigated experimentally. A 5 cycle Hanning windowed wave pulse was used as the excitation signal for the experiments. Fast Fourier Transform was employed to identify the guided wave amplitude of the scattered field along various directions. The experimental wavefield was captured using a laser Doppler vibrometer. Experimental results are presented for the scattering pattern and scattering amplitude as a function of distance from the damage. The results of this study can help to improve delamination detection techniques using guided waves and to gain physical insights into the scattering of guided waves at a delamination.

Carbon fiber laminates, consisting of highly anisotropic fiber-matrix ply-layers, are widely used in aerospace applications due to their good strength to weight ratio. However, poor interlaminar strength makes them prone to barely visible impact damage (BVID), significantly reducing the load bearing capacity of aircraft components. Guided ultrasonic waves have been widely used for structural health monitoring (SHM) of composite structures. Guided wave propagation and scattering at circular delaminations in a quasi-isotropic laminate was modelled using full three-dimensional (3D) Finite Element (FE) simulations in ABAQUS. Non-contact laser measurements were performed to obtain the scattered wavefield at a film insert delamination. The influence of ply layer anisotropy and incident wave direction were investigated both numerically and experimentally. Scattering directivity patterns were calculated using a baseline subtraction method and 2D scattering matrices were obtained for all incident wave directions. Circular magnets were used as a scattering target and numerical and measured scattering patterns were compared with those of the insert delamination. Strong directional dependency was observed for incident and scattered waves around both delamination and magnets, indicating energy focusing along the outer ply layers of the laminate. For the delamination a strong forward wave was observed, with low amplitude in other directions, whereas the magnet blocked forward transmission of the wave, demonstrating distinct scattering behavior. The anisotropic effects and different scattering patterns should be considered for guided wave sparse array SHM to ensure the robustness of imaging algorithms.

Carbon fibre reinforced composite laminates are widely used in aerospace structures but are prone to barely visible impact damage (BVID). Depending on impact severity, delaminations can form below the surface of the laminate, reducing the load bearing capacity. Efficient structural health monitoring (SHM) of composite panels can be achieved using guided waves propagating along the structure. Propagation and scattering of the A0 Lamb wave mode in a quasi-isotropic composite laminate was modelled using full three-dimensional (3D) Finite Element (FE) simulations. Individual ply layers were modelled using homogeneous unidirectional composite material properties to accurately capture the anisotropy effects. FE predictions for scattering and energy trapping at delaminations were compared to experimental measurements. Noncontact, full-wavefield guided wave measurements were obtained using a laser vibrometer. Good agreement was found between experiments and FE predictions. The effect of delamination shape and depth was investigated through a numerical parameter study. The angular dependency of the amplitude of the scattered wave was calculated. The influence of ply layer anisotropy on wave propagation in an undamaged laminate was investigated numerically. The sensitivity of guided waves for the detection of delaminations due to barely visible impact damage (BVID) in composite panels has been verified.

Composite structures, consisting of highly anisotropic layers of polymer matrix reinforced with high strength carbon fibers, are widely used for aerospace applications due to their low weight and high strength. However, impact during aircraft operation can lead to barely visible and difficult to detect damage. Depending on impact severity, delaminations can occur that reduce the structural integrity and load carrying capacity. Efficient structural health monitoring (SHM) of composite panels can be achieved using guided ultrasonic waves propagating along the structure. Guided ultrasonic wave propagation and scattering at circular delaminations was modelled using full three-dimensional (3D) Finite Element (FE) simulations in ABAQUS. Individual ply layers were modelled using unidirectional composite material properties to accurately capture the anisotropy effects. The guided ultrasonic wave propagation and scattered field at an artificial delamination was measured using a noncontact laser interferometer and quantified. Good agreement between experiments and Finite Element predictions was found and the energy trapping on top of a shallow delamination was verified. The influence of delamination shape and depth was investigated from a FE parameter study. The sensitivity of guided waves for the detection of delaminations due to barely visible impact damage (BVID) in composite panels has been verified.