Trans RINA, Vol 152, Part B2, Intl J Small Craft Tech, 2010 Jul-Dec
The second layup consisting of Chopped strand mat (CSM) + Double Bias (DB) followed the same trend, with an ultimate failure at 573.93N with 93.03mm displacement. The load deflection plot for layup 2 is shown in Figure 4.2. Initial crack was observed between the second and third layers at a displacement of 61.04mm at a load of 57N. The crack initiation and progression of the specimen is shown in Figure 4.1. Further loading caused the crack to propagate in the longitudinal direction. Another major crack occurred between the third and fourth layers. During the final stages of loading, the outer layers were subjected to
interlaminar
compressive stress and the fibres in those layers buckled and sheared at the bend. The Double Bias layer is very flexible, hence large deflection with minimal increase in load is observed. The specimen failed at 573.6N with a displacement of 93.03mm. The experimental load- deflection plot for layup 2 is shown in Figure 4.2.
4.2(b) Layup 2 (Csm+Db) Acoustic Emission Correlation
The parametric distribution of AE events for CSM+DB layup is shown in Figure 4.3. The flexure modulus and
strength of double bias layer were low, 1158 MPa & 78MPa respectively compared to the other two layups. The first damage occurred at 10% of ultimate load at 247sec, as a crack between second and third layers. The AE parametric values at 247sec were Amplitude – 100dB, Energy – 2680eu, Rise time -708μs and duration - 53027μs. Further damage was characterized by matrix cracking and the delamination growth. The amplitude of the AE signal was widely distributed and steady from the initial failure till final collapse; hence progressive damage was analysed using other parameters mainly with elastic energy release. Delamination between third and fourth layer occurred at 416 sec with a duration of 5521μs energy of 1091eu and an amplitude of 91dB. The third highest peak in the duration plot occurred at 485 sec with a duration of 8602μs, energy of 1475eu and an amplitude of 95dB. Further AE data was widely scattered accounting for continuous matrix cracking and delamination growth.
Final collapse of the structure
occurred at 636sec with an amplitude of 92dB, duration of 2331μs at 573.6 N.
Figure 4.1: Progressive failure of Layup 2 specimens
Figure 4.2: Load-deflection plot for Layup 2 specimens
©2010: The Royal Institution of Naval Architects
B-99
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