Browsing by Author "Bwembya, Emmanuel Mutale"

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    Lockin thermography parameter investigation
    (Stellenbosch : Stellenbosch University, 2017-03) Bwembya, Emmanuel Mutale; Schreve, K.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH SUMMARY: Infrared thermography has emerged as one of the leading nondestructive testing techniques used for composite materials testing. It is fast, safe, effective and data acquisition is done remotely. As such it has attracted significant research to improve its performance in detection of material flaws in carbon and glass fibre composites. The aims of this thesis were to investigate parameters that affect defect detectability with optical lockin thermography. These were the frequency, intensity, number of wave cycles of the excitation and material type for which both simulations and experiments were conducted. The materials contrasted were carbon fibre composite and mild steel as they display a large disparity in thermal properties and density. A major note to make was that the material with lower thermal conductivity and heat capacity produced better results in experimental data while results in simulated data were similar. Low values of thermal effusivity enhanced defect detection and reduced the effect of experimental noise. Furthermore, other results showed that low frequencies probe deeper into the material and as such increase the probability of detecting deep defects. In the case of intensity of thermal excitation, low excitation intensities resulted in a low temperature rise which if too low equalled the camera noise and deterred defect detectability. This was especially so for mild steel which has a high heat capacity. As for the number of wave cycles, increasing this parameter had little influence on increasing the probability of defect detection in simulations as the phase response of the curve was barely altered by using more cycles as there was no noise in simulated data. Experimental results showed improved results for both materials.