The need to understand and monitor the integrity of structural components made of composite materials is becoming critical, due to an increase of the use of composites in aerospace, civil, wind energy, and transportation engineering. Off-the-shelf piezoelectric transducers embedded inside the composites or bonded onto the structure surface are a possible solution for on-line structural health monitoring and non-destructive evaluation: they can be used to generate Lamb waves, which are able to detect damage. This article focuses on the behavior of two sets of woven fiberglass/epoxy specimens, one with embedded, one with surface-mounted piezoelectric wafer transducers (lead zirconate titanate). The specimens are tested under axial tensile fatigue at high stress ratio, and the transducers are interrogated in pitch-catch mode at different stages of the specimens’ life, while they are subjected to the mean test load (the testing machine is paused). A novel signal processing technique based on wavelet thresholding/denoising and Gabor wavelet transform is discussed. This technique identifies changes in boundary conditions, loading/unloading prior to damage and during damage. It appears to correlate the contour area changes with the so-called characteristic damage state observed in the literature in composite laminates under tensile fatigue.

Overcharge of lithium-ion batteries can lead to the deposition of lithium ions on the surface of graphite electrodes. The phenomenon of lithium deposition causes reduced electrochemical performance and presents safety concerns for lithium-ion batteries in high-power applications. This study presents a technique using neutron radiography (NR) for in situ visualization of the effects of overcharge in a graphite/NCA (LiNi 0.8 Co 0.15 Al 0.05 O 2 ) lithium-ion cell. Patterns of deposition of solid material on the surface of the graphite electrode observed in the radiographs were confirmed by direct observation of the electrode. Inductively coupled plasma mass spectrometry was used to verify the elemental contents of the deposited material. NR is shown to be a promising tool for the study of lithium-ion batteries in high-power applications.

No abstract

No abstract

No abstract