Current injection phase thermography for low-velocity impact damage identification in composite laminates

Abstract

An innovative non-destructive evaluation (NDE) technique is presented based on current stimulated thermography. Modulated electric current is injected to Carbon Fibre Reinforced Plastics (CFRP) laminates as an external source of thermal excitation. Pulsed Phase Thermography (PPT) is concurrently employed to identify low velocity impact induced (LVI) damage. The efficiency of the proposed method is demonstrated for both plain and with Carbon Nanotubes (CNTs) modified laminates, which are subjected to low-velocity impact damaged composite laminates at different energy levels. The presence of the nano reinforcing phase is important in achieving a uniform current flow along the laminate, as it improves the through thickness conductivity. The acquired thermographs are compared with optical PPT, C-scan images and Computer Tomography (CT)representations. The typical energy input for successful damage identification with current injection is three to four orders of magnitude less compared to the energy required for optical PPT.

Recent Advances in Active Infrared Thermography for Non-Destructive Testing of Aerospace Components

“…This, in turn, determines the anisotropy of the heat flow propagation through the laminate. As a consequence, in order to increase the number of random contacts and enhance the heating front propagation, 0.5% w / w of carbon nanotubes (CNTs) was included within the epoxy matrix [ 151 ]. The nanomodified samples were subjected to low velocity impacts at different energies (3 and 4 J) and the material damage was evaluated in “live mode” by first recording the surface temperature during the application of electrical current at 10 A for 60 s and then during the cooling down process for other 150 s. Results from these tests showed that the difference in the temperature field between damaged and undamaged areas was higher during the heating phase rather than the cooling one.…”

Improvement of the Impact Properties of Composite Laminates by Means of Nano-Modification of the Matrix—A Review

“…These differences were because of the type and content of the nanoparticles and different manufacturing methodologies that were found to be very important factors in impact performance of composite materials. Aligned CNTs offer excellent mechanical toughness improvements for traditional composite laminates, and additionally enable multifunctional capabilities; i.e., to improve the impact performance (reduced damage area and better CAI) [73,120] and also as a promising damage monitoring technique of the carbon fiber laminated composites [118,120,121]. The compression strength and compression-compression fatigue after impact performance was improved [111].…”

On the fatigue response of a bonded repaired aerospace composite using thermography

“…Carbon fibres are thermally anisotropic, as they possess a negative CTE in the longitudinal direction and a positive CTE in the transverse direction [42][43][44]. However, Wong reported positive CTE values at the two principal directions [32].…”