Issue 50

M.A. Khiat et alii, Frattura ed Integrità Strutturale, 50 (2019) 595-601; DOI: 10.3221/IGF-ESIS.50.50 596 neighboring fibers by modeling the matrix by finite elements and the fibers by continuous one-dimensional springs. Their model also considered direct interactions of broken fibers with the next to nearest neighbors. Landis and McMeeking [5] later extended the work of Landis et al. [4] to account for the effects of interface sliding, axial matrix stiffness and uneven fiber positioning, on stress concentrations surrounding the broken fiber. Nedele and Wisnom [6, 7] also showed that the peak stress concentration on fibers close to the broken fiber occurred slightly out of the rupture plane. Case et al. [8] proposed an entirely different analysis technique to study the stress field in a general unidirectional composite material containing fiber fractures. The model is based on approximating annular ring of fibers to represent the unbroken neighboring fibers. Multiple fiber breaks were modeled by a fiber discount methodology. Case and Reifsnider [9] addressed the problem of a penny shaped crack in the center of multiple concentric cylinders. The problem was solved by applying standard elasticity assumptions, with appropriate choice of stress functions in each constituent. This solution was applied to the problem of a fiber fracture in a unidirectional composite material by making geometrical assumptions. Foster [10] proposed a direct numerical simulations and analytic Models to predict the strength of fiber reinforced composites under tensile and flexural loading. The main strength prediction model used in the present paper is the proposed by model Gao and Reifsnider [11]. In order to predict the unidirectional composite strength degradation, we incorporated in this model the mechanical characteristics changes. The strength degradation is a result of changes in ineffective lengths at fiber breaks and the corresponding stress concentrations in intact neighboring fibers. After the calculation of stress concentrations and ineffective lengths of composite Lin/Epoxy. Figure 1 : Schematic representation of unidirectional composite with broken fibers and adjacent regions [11]. M ICROMECHANICS OF TENSILE STRENGTH MODEL ao and Reifsnider [11], according to the model proposed by, tensile properties of fiber-reinforced composites are dependent on fiber strength and modulus, strength and chemical stability of matrix and efficiency of fiber/matrix interfacial bond in transferring loads. By introducing the micromechanical characterization with changes in temperature and moisture concentration, this model enables the prediction of changes in ineffective lengths at G Fiber Matrix Broken Composite Bulk Composite Zone of matrix yielding Crack U 0 U 1 U 2 x r 0 r 0 +d r 0 -d r f