Issue 49

R.V Prakash et alii, Frattura ed Integrità Strutturale, 49 (2019) 536-546; DOI: 10.3221/IGF-ESIS.49.50 540 elastic regime causes cooling of the specimen) of the CFRP specimens is not significant when compared to GFRP [13] or metallic materials as the carbon fibers have negative coefficient of thermal expansion. S. No Input Impact Energy (J) Fatigue Test Condition Residual Strength (kN) % Loss in Stiffness * % Damage Volume Fraction 1 Un-impacted - 53.67 - <0.5 1 23 J Constant Amplitude 53.67 30.20 4.83 2 23 J Lo-Hi Prog FALSTAFF Specimen failed in fatigue 5.92 1.88 3 35 J Hi-Lo Prog FALSTAFF 18.18 26.72 3.77 4 35 J Lo-Hi Prog FALSTAFF 11.83 37.64 4.09 5 51 J Hi-Lo Prog FALSTAFF Specimen failed in fatigue 52.59 5.60 6 51 J Lo-Hi Prog FALSTAFF 15.14 55.51 7.92 * The loss in stiffness is estimated w.r.t the un-impacted specimen stiffness (~ 27.02 kN/mm). Table 2 : The damage volume fraction of post-impacted specimens Vs. loss in stiffness. Fig. 3 (b) presents the plot of average temperature observed for the three area segments during tensile loading. It is noted that the highest temperature of 54.3 ° C is seen in area A1, followed by area A2 (42.4 ° C) and subsequently by area A3 (39.2 ° C). This peak temperature corresponds to specimen failure at the peak load. However, it is interesting to note that the temperature-time response for area A3 alone shows some spikes at ~ 70 seconds and once again at ~ 90 seconds) which was not seen in temperature response in other two areas of measurement. To verify if this has some correlation to damage progression, data of force-time response and temperature-time response was plotted. (a) (b) Figure 3 : (a) The temperature variation within the pristine specimen during the tensile test; (b) The position of area segments A1, A2 and A3 marked in a specimen under no load condition. Fig. 4 presents the correlation between temperature rise and tensile load during two ply-drop failures. The ply-drop failures in area A3 have resulted in fiber-matrix debonding and fiber breakage, and as a consequence, the final failure of