Generation of controlled delaminations in composites using symmetrical laser shock configuration

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. b s t r a c tStructural Health Monitoring (SHM) is defined as the process of implementing a damage identification strategy for aerospace, civil and mechanical engineering infrastructures. SHM can be organized into five main steps: detection, localization, classification, quantification and prognosis. Our work considers SHM quantification level and in particular the evaluation of the severity of delamination-type damage in CFRP composite laminates. Prior to quantification algorithms implementation, it is important to properly prepare the supports on which algorithms will be tested. Teflon inserts and conventional impacts are commonly used techniques to generate or simulate delaminations. However, with such rudimentary techniques it is difficult to generate controlled delamination-type damage in a realistic way. In the present work, we investigate symmetrical laser shock approach, as a new method to calibrate delaminations in composites. By tuning the time delay between the two laser beams and laser energy, throughthickness damage position and severity can respectively be adjusted. The effect of multiple contiguous laser impacts was also investigated. Post-mortem analyses using A-scan and C-scan testing as well as penetrant testing were performed in order to characterize laser impact induced damage.Results are encouraging and demonstrate the high potential of symmetrical laser shock for damage calibration in both size and location.

Upcoming damage size quantification in aeronautic composite structures based on imaging results post-processing

“…The crossing of the two waves creates local high tensile stress which can result in damage at a through thickness depth if the energy level of the laser irradiation is high enough. More details about controlled delaminations in composites can be found in Ghrib et al (2017). (Ghrib et al, 2017).…”

Development of the symmetrical laser shock test for weak bond inspection

“…where the indices r and l refer to the material respectively on the right and on the left of the area where the maximum tensile stress should be located, t li is the thickness of ply number i, ρ li the density of the ply, and Z li its shock impedance. Ghrib [21] has shown that by using this time delay, one can generate the maximum tensile stress in a specific location of the material, and for example generate a delamination in between two selected plies inside of a laminate structure. This technique has not yet been used to assess bonding quality on real aircraft parts.…”

Signal-based Versus Nonlinear Model-based Damage Sensitive Features for Delamination Quantification in CFRP Composites

“…Damage is introduced into samples (See Figure 2) in a calibrated way using LSWT and more particularly symmetrical laser shock configuration (See Figure 1). LSWT is chosen as an alternative to conventional damage generation techniques such as conventional impacts and Teflon inserts since it allows for a better calibration of damage in type, depth and size [3][4][5]. Four CFRP test coupons are considered.…”

“…The first one is kept in a healthy state. The second one was subjected to a symmetrical laser impact at 0 ns time delay and at 100% of the maximum energy of the two laser beams [5]. This resulted in approximately 7 mm diameter delamination which occurred at 1.1mm depth.…”