Issue 29

M. Scafè et alii, Frattura ed Integrità Strutturale, 29 (2014) 399-409; DOI: 10.3221/IGF-ESIS.29.35 404 The strain gauge configuration allows the determination of sample bending during the test time, by means of the following factor: 1 2 1 2 [%] 100 Bending         (8) where ε 1 and ε 2 are the longitudinal strains measured respectively by strain gauge 1 and 2 [2]. The percent bending, as calculated in eq. (8), provides a reasonable indication of Euler buckling. Failure and midpoint bending are reported in tables from 2 to 7 as requested by ASTM D 6641. The latter is determined at the midpoint of the strain range used for chord modulus calculations [2]. Material E σ max E SG1chord E SG2chord ΔE % ν % Bending Midpoint Failure E1 71.4 97.0 100.0 3.0 100.0 2.4 -8.1 E2 79.4 98.8 94.4 -4.6 91.1 5.3 1.2 E3 71.9 93.7 95.1 1.5 81.2 3.6 4.7 E4 77.1 99.8 99.5 -0.3 - 7.0 3.4 E5 75.8 95.2 92.5 -2.8 - 2.7 0.4 E6 100.0 - - - - - - Mean Value 79.3 96.9 96.3 -0.6 90.8 - - Std. Deviation 10.6 2.5 3.3 - 9.4 - - CV % 13.4 2.6 3.4 - - - - Table 6 : Compressive test results of E samples (normalized results). Material F σ max E SG1chord E SG2chord ΔE % ν % Bending Midpoint Failure F1 21.0 4.9 5.2 5.6 6.7 18.0 - F2 19.9 5.2 4.9 -7.3 5.0 5.7 - F3 20.5 5.0 5.0 -0.8 5.5 8.4 - F4 20.8 4.7 5.3 11.9 - 9.4 - F5 20.6 4.7 5.1 8.8 - 9.0 - F6 21.2 - - - - - - Mean Value 20.7 4.9 5.1 3.6 5.7 - - Std. Deviation 0.5 0.2 0.2 - 0.9 - - CV % 2.4 4.1 3.9 - - - - Table 7 : Compressive test results of F samples (normalized results). Tab. 8 shows the compressive strength of UD material calculated by means of classical lamination theory. The four back- out factors (2 for cross-ply and 2 for angle-ply), determined through Eq. (3) and (4), are:  BF cross-ply A = 3.98  BF cross-ply B = 2.22  BF angle-ply C = 3.41  BF angle-ply D = 2.04 The compressive stiffness (E x and E y ) for BF determination were obtained averaging the mean values listed in Tab. 6 and 7. The 0° lamina compressive strength values obtained by Eq. (1) are reported in Tab. 8.