Effect of heterogeneity at the fiber–matrix scale on predicted free-edge stresses for a [0°/90°]_s laminated composite subjected to uniaxial tension

Abstract

The effect of the free-edge on the interlaminar stresses that develop in a thin-ply [0°/90°]s laminated composite under uniaxial tension was explored using finite element models that directly modeled the random heterogeneous microstructure and a model that treated the plies as homogeneous, orthotropic materials. The deformed cross-sections were compared for the two cases, showing that the homogeneous model generally captured the displacement field well but the heterogenous model exhibited local perturbations due to the microstructure. The interlaminar normal stress distributions along the ply interfaces were very different for two models. The heterogeneous model exhibited a complex pattern of stresses that were sensitive to nearby fibers. A comparison of the interlaminar shear stress distributions for the two models showed better agreement, though the heterogeneous model greatly differed from the homogeneous model when fibers or matrix pockets were close to the ply interface. After separating the effect of the fibers and the free-edge effect, the stresses that develop due to the free-edge effect matched well between the two models, except very close to the free-edge. It was shown that the Poisson’s ratios of the fibers and matrix significantly affect the stress distributions along the ply interface, and a matrix Poisson’s ratio could be selected that reduces the effect of the microstructure on the interlaminar normal stress. The study highlighted that a full 3D analysis can provide new insights for classical problems, and more optimal design of composites will require consideration of microstructural effects.

Multiscale analysis of interlaminar stresses near a free-edge in a [±45/0/90]s laminate

“…The complex stress pattern was due to the interactions of fibers near the interface. As noted in McLendon and Whitcomb 11 and Ballard and Whitcomb, 15 compressive stresses form when fibers come into close proximity. Ballard and Whitcomb 15 also observed that tensile stress concentrations form near matrix pockets.…”

Mitigations of machine-damaged free-edge effects on fiber-reinforced composites

“…For many years, researchers have used classical laminate theories, finite difference models, and finite element analysis (FEA) to characterize the effects of the free edge for various types of layup with great success. 21 Consequently, some researchers have employed multiscale strategies to capture the effects of fibers in critical regions. 22 During the manufacturing and machining (e.g., curing, cutting, terming, and drilling) processes of these composites, there will be some machine damage and free-edge formation on the composites, which in turn reduce the overall mechanical properties through associated inter-laminar tension and shear stresses; they are also very detrimental to the structural applications of composites in those industries due to premature failure.…”

Experimental and numerical investigation of stiffener effects on buckling strength of composite laminates with circular cutout

“…36 developed a micromechanical damage model for failure prediction in laminated composites. In another work, Ballard and Whitcomb 37 considered a multi-scale model to investigate the micro-scale free-edge effect in laminated composites. Moreover, Liu et al.…”

“…However, to consider the effect of micromechanics of the damage, many studies carried out modeling in micro-scale. [36][37][38][39][40][41] Using multi-scale modeling, Mohammadi et al 36 developed a micromechanical damage model for failure prediction in laminated composites. In another work, Ballard and Whitcomb 37 considered a multi-scale model to investigate the micro-scale free-edge effect in laminated composites.…”

“…[36][37][38][39][40][41] Using multi-scale modeling, Mohammadi et al 36 developed a micromechanical damage model for failure prediction in laminated composites. In another work, Ballard and Whitcomb 37 considered a multi-scale model to investigate the micro-scale free-edge effect in laminated composites. Moreover, Liu et al 40 and Nguyen and Wang 41 used micromechanics modeling for investigation of progressive failure in woven composite laminates containing cutouts.…”