BalacoM

MODE II FRACTURE TOUGHNESSOF GLASS FIBRE REINFORCED COMPOSITES: 

MODE II FRACTURE TOUGHNESS OF GLASS FIBRE REINFORCED COMPOSITES J F Silva1, P Vieira2, A M B de Morais3, A T Marques2, P M S T de Castro2 1 – ISEP, Porto, Portugal 2 – Universidade de Aveiro, Portugal 3 – Universidade do Porto, Portugal

Slide2: 

- several studies on fracture of laminated composites; - very little work done on filament wound composites; - special features of filament wound composites: - typically multidirectional [ ]n  high susceptibility to non-linearity and crack jumping; - more heterogeneous than laminates  higher scatter. STATE OF THE ART

manufacturing of glass/polyester plates:- []4 with  = 0.8, 5, 10, 30 and 60º;- PTFE film at mid-thickness to generate starter crack; - post-cure at 80 ºC during 24 h after winding.: 

manufacturing of glass/polyester plates: - []4 with  = 0.8, 5, 10, 30 and 60º; - PTFE film at mid-thickness to generate starter crack; - post-cure at 80 ºC during 24 h after winding. EXPERIMENTAL PROCEDURES

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mode II end-notched flexure (ENF) tests to measure GIIc

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linear P- curves for   10º RESULTS

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no crack jumping, but non-linearity problems for   30º - need to reduce span (2L) from standard 100 to 40 mm; - still premature yielding of [60º]4 specimens  stiffer specimens required; - GIIc results for [30º]4 are somewhat questionable.

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considerable scatter, especially from insert and for higher  values. measurements from insert :

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measurements from mode II precrack

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average GIIc increases with , except from 0.8º to 5º

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explanations - larger   larger plastic zone behind the crack tip  greater GIIc - GIIc decreases from 0.8º to 5º because: - fibre bridging is less effective? - batch variation?

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- Main difficulty in testing filament wound composites is non-linearity: - larger   greater GIIc, but also larger tendency for large scale yielding; - Specimen design (stacking sequence) can overcome problems? -subject of a research project funded by the Portuguese Ministry for Science and Technology (SAPIENS) CONCLUSIONS