Passive infrared thermography measurement of transverse cracking evolution in cross‐ply laminates

Abstract

Over the last decades, various experimental methodologies have been used to study the matrix crack density evolution in cross-ply laminates. The main drawback of these techniques is their difficult use at intermediate and high strain rates. In this study, a new experimental protocol to evaluate matrix crack density evolution at intermediate strain rates is proposed and applied to [0∕90 3 ] s carbon/epoxy laminate. It is based on the use of passive infrared thermography to monitor the matrix cracking appearance. This methodology is used to first demonstrate that the crack appearance in the 90 • ply remains instantaneous from side to side with the increase of the strain rate. Finally, the rate insensitivity of the crack density as a function of the applied stress for the studied material in the studied range of strain rates (8.3 × 10 −4 up to 6.69 × 10 −2 s −1 ) is demonstrated. KEYWORDScomposite materials, crack density, infrared thermography, strain rate dependency, transverse cracking Strain. 2018;54:e12293.wileyonlinelibrary.com/journal/str

Rate dependency and ply thickness influence on transverse cracking evolution in cross-ply laminates

“…The measurement of the upper holder displacement is performed by means of a laser transducer (Keyence LK-HD500 and LK-H052) in order to be able to accurately capture the real speed applied to the specimen. The specimen longitudinal strain is measured using a non-contact technique to avoid any disturbance of the measurement that could be generated by the appearance of cracks (Berthe and Ragonet 2018). An optical extensometer Rudolph 200XR is used to capture two black-and-white transitions painted on the specimen surface.…”

“…Transverse crack propagation in [0 m /90 n ] s can be considered as almost instantaneous from side to side (Berthelot 2003;Huchette 2005). This hypothesis remains valid with the loading rate increase (Berthe and Ragonet 2018). Based on this assumption, only one edge of the different specimens has been monitored to maximize the IR camera frame-rate for the high loading-rate tests.…”

“…The protocol used in this study is based on a detection procedure which has been proposed by Berthe and Ragonet (2018). The extension of this methodology to thinner 90°plies and to higher loading rates will be studied in the sequel.…”

“…Only located within the total thickness of the 90°plies, these hot spot areas captured by the IR camera reveal the energy dissipated as heat during the process of creation of the transverse cracking mechanism (Figure 2(c) and Figure 2(d)). A dedicated methodology for the quantification of matrix crack density using IR thermal fields and over a wide range of quasi-static tensile loads has been proposed by Berthe and Ragonet (2018). This procedure has been validated with a cross analysis of the qualitative detection of the thermal events over the time and the quantitative detection of the load signals oscillations captured by the piezoelectric load cell that have been generated by crack occurrences.…”

“…However, the detection and the quantification by IR thermography of transverse cracks for dynamic loads remains little investigated in the literature due to the limitations on the acquisition frequency of the older generation of IR cameras. The present work proposes to extend the analysis performed in the quasi-static ranges in Berthe and Ragonet (2018) to a dynamic loading-rate range, through the use of a high-rate IR camera (Telops FAST M3K).…”