Study of the Interface Matrix-Inclusion Properties on Fracture Properties in Composite Materials

E.BITTENCOURT; A.P.CISILINO

Ouro Preto, Brasil

Congreso; 18th International Congress of Mechanical Engineering COBEM 2005; 2005

Asociación Brasileña de Ciencias Mecánicas

The addition of a second phase (inclusions) in a homogeneous matrix can modify significantly the global behavior of the composite depending on geometry (dimensions and distribution) and physical properties of the second phase. The analysis of the composite behavior can be done through the determination of the so called “representative volume” that permits to define a new constitutive homogeneous tensor that characterizes the behavior of the whole composite. However, due to obvious limitation in terms of mesh, this procedure may lose information about the interaction between matrix and second phase (debonding for instance). Also, if the second phase is plastic, it will probably cavitate. The study presented in this work consists in the analysis of a single unit cell consisting in a cylindrical domain containing a spherical inclusion. The matrix of the material is PMMA, which is considered as linear elastic. The second phase (the inclusion) is rubber and is considered elasto-plastic. Experimental studies performed on PMMA specimens have demonstrated that the addition of rubber particles results in a substantial increment in toughness. This increase in the material toughness apparently comes from the existence of holes inside the PMMA matrix (regardless the presence of rubber) and in the cavitation of the rubber due to plastic strains. The plastic strain dissipates energy and promotes crack arrest. However, the cavitation may be inhibited by the occurrence of debonding between matrix and the rubber inclusion. The influence of all these variables on toughness will be studied using a finite element code that considers debonding. The algorithm used is based on the so called cohesive interface method (Needleman (1987)). Preliminary results show that debonding may reduce significantly toughness by eliminating plastic strain of the cavitation.