PAMM·Proc. Appl. Math. Mech.15, 157 – 158 (2015) /DOI10.1002/pamm.201510069
Effects of a circular defect size and position on the damage progression in hybrid laminates under compressive loading
Nacer Tala-Ighil1,∗, Ahcene Mokhtari1,andAmine Brick Chaouche1
1 Welding and NDT Research Center (CSC). BP 64 CHERAGA - ALGERIA
The effects of a circular defect size and position on the post-damage response of the FMLs laminates under compressive loading has been studied. Compression tests are performed on composite plates comprising a hole having different diameters (8 mm, 12 mm and 16 mm) and located at different positions (25%, 50% and 75%) in the loading direction. A numerical analysis using the finite element method FEM has permits the identification of the initiation zones and the description of the damage evolution in these laminates. The results of the numerical simulation are in good agreement with the experimental results. The FEM has well predicted the critical damage zones.
c
2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1 Introduction
The composite structures made from glass fiber reinforced with polymer matrices have resistance to compression considerably lower when holes (defects) are present. The hardness of the polymer matrix, the properties of the interface matrix/fiber and fiber stability are the main factors that affect the resistance to compression of notched laminates. The importance of these factors results in complex damage modes which involve the matrix cracking, delamination, local buckling and shear failure.
The importance of the damage tolerance analysis of composite materials was shown by many authors [1]. An approach was presented by Wang [2] related to the delamination problem of the composite laminates edges. Davis and Jones [3]
have examined the effect of manufacturing defects on the fracture of composite structures. An experimental and numerical study on the residual stresses in the composite laminates subjected to an impact loading was done by the authors [4]. The progressive evolution of the damage in the laminates under compressive loading containing a circular hole has been studied experimentally [5], it was observed that the rupture was initiated at the instability localized at the surface of the hole edge. In this paper, a numerical study of the effects of a circular defect size and position on the post-damage response of the FMLs laminates under compressive loading is performed. As shown on fig.1, different diameters (8 mm, 12 mm and 16 mm) of the defect (hole) and different positions along the loading direction (25%, 50% and 75%) on the composite plates are considered.
2 Finite Element Modelling
The damage has been Modelled by the combined use of the Cohesive Zone Model [6] (CZM), the Linde mechanical model [7]
and the Hill model [8]. The Linde’s model is simple and efficient to predict the rupture of the composite plies. The intra- laminar damage model used can capture the initial linear elastic behavior and the damage evolution caused by the gradual degradation of the plies. The damage variabledis introduced. The damage evolution at a material point is defined in terms of damage variable and the equivalent strain. The damage variables are defined [9] as:
df c= 1−
1 ef c
e
−C11f c11f c11(ef c−1)GfcLc
dmc= 1−
1 emc
e(−C11mc11mc11(emc−1)GmcLc ) (1)
WhereGf candGmcare the energies dissipated by the damage for the fiber and the matrix compression failure modes, respectively. ef c andemc are the compressive failure strains for the fiber and matrix, respectively. Lc is the characteristic length. ij are the strain component andCij are the components of the undamaged elasticity matrix. The adhesive layers were modeled with the cohesive element that is able to capture the interlaminar damage onset and growth in the composite laminates [7] and The aluminum layers were modeled as an elastoplastic material [8].
A 3D finite element analysis was conducted to provide answers to how the structure reaches its ultimate load, the interaction of damage and the load redistribution in composite structures. For reasons of symmetry in both directions (Ox) and (Oy), we consider only a portion of the specimen. The geometry, the mesh and the boundary conditions of the simulated model are presented in Fig.2. The plates are composed from three layers: metal (aluminum), composite and adhesive between the metal and the composite. The metal and the composite layers are discretized by theC3D3Relement while theCOH3D8
∗ Corresponding author: e-mail [email protected], phone +213 21 36 18 50, fax +213 21 36 18 50
c
2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
