ECCOMAS Thematic Conference on Mechanical Response of Composites P.P. Camanho et.al. (eds.) Porto, Portugal, 12–14 September 2007 STUDY OF DELAMINATION IN COMPOSITES BY USING THE SERIAL/PARALLEL MIXING THEORY AND A DAMAGE FORMULATION Xavier Mart´ ınez 1 , Sergio Oller 1 and Ever Barbero 2 1 International Center of Numerical Methods in Engineering (CIMNE) c/ Gran Capit` a s/n; 08034 Barcelona, Spain e-mail: xaviermg@cimne.upc.edu; sergio.oller@upc.edu 2 Mechanical and Aerospace Engineering, West Virginia University P. O. Box 6106, Morgantown, WV 26505-6106, United States http://www.mae.wvu.edu/barbero/ Keywords: Delamination, continuum mechanics, Serial/Parallel mixing theory, damage for- mulation, End Notch Flexure test Abstract. This paper presents a new procedure to deal with the delamination problem found in laminated composites, based in a continuum mechanics formulation. The procedure proposed obtains the composite constitutive performance with the Serial/Parallel mixing theory, devel- oped by F. Rastellini. This theory characterizes composite materials by coupling the constitutive behaviour of the composite components, imposing an iso–strain relation among the components in the fibre (or parallel) direction and an iso–stress relation in the remaining directions (serial directions). The proposed procedure also uses a damage formulation to characterize the con- stitutive behaviour of matrix component in order to obtain the stress–strain performance of this material. With these two formulations, the delamination phenomenon is characterized naturally by the numerical simulation, being unnecessary the definition of special elements or computationally expensive techniques like the definition of contact elements or mesh separation. Matrix failure, as a result of the stress state found in it, leads to a reduction of the stiffness and strength ca- pacity of the composite in its serial direction. This reduction provides a composite performance equivalent to what is found in a delaminated material. To prove the ability of the formulation proposed to solve delamination problems, the End Notch Failure test is numerically simulated and the results obtained are compared with ex- perimental ones. The agreement found in the results with both simulations, numerical and experimental, validate the proposed methodology to solve the delamination problem. 1