Abstract
Composite materials are today used for various ind ustrial applications. However, delamination on free edges, where stress gradients are strong, s till remain a problem. In the aim of a better under standing of such phenomenons, Digital Image Correlation (DIC) measurements have been carried out on ((15 n/- 15n)2)s laminates under uniaxial tensile strain. Three dif ferent composites with different mechanical properties and microstructure have been tested as w ell as two samples geometries: flat and with ply dr op. Experimental results show high shear strain concent rations near 15°/-15° interlaminar interfaces on fr ee edges which depend on material mechanical properties and microstructure and increase in the vicinity o f a geometrical singularity.
Highlights
The use of composite materials has become more and more widespread in many industrial applications
It has long been known that the difference between elastic properties of adjacent plies induces strong three-dimensional interlaminar stresses on laminate free edges, which could initiate delamination [1]. This stress state cannot be predicted by Classical Laminates Theory (CLT) and some stacking sequences can be more critical than others [2]
Very high shear strain concentrations have been measured in the vicinity of 15°/-15° ply interfaces, varying non-linearly as a function of the tensile strain, as well as residual shear strains after unloading
Summary
The use of composite materials has become more and more widespread in many industrial applications. It has long been known that the difference between elastic properties of adjacent plies induces strong three-dimensional interlaminar stresses on laminate free edges, which could initiate delamination [1] This stress state cannot be predicted by CLT and some stacking sequences can be more critical than others [2]. Composites with carbon fiber and epoxy matrix with a [(15n/-15n)2]s stacking sequence have been tested under uniaxial tensile loading These composites have different microstructures and elastic properties to highlight the influence of such characteristics on free edge strain concentrations. For two of the three studied composite materials, fibre arrangement inside each layer is almost “regular”, with quite rectilinear interfaces (dashed lines on Fig. 1a) This microstructure will be called “pure unidirectional” (pure-UD) in comparison to the third one for which a much more heterogeneous repartition of the fibres, due to an alternation of areas with high fibre or resin contents, has been noticed. The elastic properties have been measured from tensile and shear tests, and their average values are given in table 1
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