Mode-I Interlaminar Fracture of Carbon-Epoxy Multidirectional Laminates

• Type: Article in International Conference Proceedings Book
• Date: 2005

Authors

A. B. Pereira (Author) Other; A. B. de Morais (Author) Other; Marcelo Francisco de Sousa Ferreira de Moura (Author) FEUP; A. G. Magalhães (Author) Other

Conference proceedings International

Title: 11th International Conference on Fracture

Pages: 1-6

11th International Conference on Fracture

Turin - Itália, 20 a 25 de Março de 2005

Indexing

ISI Proceedings

Scopus - 0 Citations

Scientific classification

FOS: Engineering and technology > Mechanical engineering

CORDIS: Technological sciences > Engineering > Mechanical engineering

Other information

Authenticus ID: P-008-7H3

Resumo (PT): An experimental study was conducted on the mode I interlaminar fracture of carbon/epoxy multidirectional specimens with starter delaminations in 0/0 and 0/θ interfaces. The specimens selected for Double Cantilever Beam (DCB) tests had [(02/90)6/02//(02/90)6/02] and [(02/90)6/02//θ/(02/90)6/02] stacking sequences, where // denotes the position of the starter delamination and θ = 22.5 to 90 degrees. The incorporation of the thick symmetric [(02/90)6/02] block of 20 plies aimed at minimising elastic couplings related problems, such as non-uniform width-wise distributions of the strain energy release rate GI, spurious modes and effects of residual stresses. This was verified in preliminary three-dimensional (3D) Finite Element (FE) analyses, which also showed the applicability of the Corrected Beam Theory data reduction scheme. The DCB specimens were tested according to the procedures defined in the ISO 15024:2001 standard for unidirectionally reinforced specimens. In the tests, intraply damage occurred in the θ-oriented ply soon after initiation from the starter crack, as it is commonly observed in multidirectional specimens. For θ = 22.5 and 45 degrees, a second crack propagated close to a neighbouring interface, while for θ = 67.5 and 90 degrees the starter crack ran inside the θ-oriented ply and proceeded in a wavy propagation trajectory. This resulted in extensive fibre bridging and pronounced R-curves with artificially high final values of the critical strain energy release rate, GIc. Therefore, only GIc values of initiation could be considered true interlaminar properties. Moreover, it was found that they were fairly independent of the ply angle θ. An additional FE analysis of the interlaminar stresses ahead of the crack tip was performed to interpret the delaminating interface effect on GIc values. The results indicated the existence of an interface independent fracture toughness, KIc, probably resin controlled, thus reinforcing the idea that the measured initiation GIc were pure interlaminar properties.

Language: Portuguese

Type (Professor's evaluation): Scientific