Issue 50

M.A. Khiat et alii, Frattura ed Integrità Strutturale, 50 (2019) 595-601; DOI: 10.3221/IGF-ESIS.50.50 598 The solutions of both differential equations are given by: 1 2 0 2 3 ( ) x x c U x C e C e x Ec         (8) 1 2 1 1 1 2 3 ( ) (1 ) (1 ) x x c c U x C e C e x A A E             (9) All applications are made on unidirectional graphite epoxy specimen with length L, width W and thickness T. Mechanical and geometrical characteristics of the studied considered material are given in Tabs. 1 and 2, these data are drawn from E f (GPa) E m (GPa)  0 (MPa)  0 (GPa)  V f  27.6 4.2 25.2 3.10 0.43 0.53 1.0 Table 1 : Mechanical properties of Lin/epoxy specimen. l (mm) w (mm) t (mm) r f (mm) n i 152.4 12.7 1.016 0.0035 43 Table 2 : Geometrical characteristics of Lin/epoxy specimen. Figure 2 : Evolution of the ineffective length according to the number of broken fibers with progressive variation of moisture concentration for T=20° and  = 0.5  0 . I NEFFECTIVE LENGTHS AT FIBER BREAKS he ineffective length is defined as the length along a fiber from the break location that it takes for the fiber to regain its ability to carry full load. Therefore it must include the zone of matrix yielding a (   a), as in constitutive laws of unidirectional composites, we distinguish three regions: a plastic, transitory and elastic zone, where σ f is the T