Estudo do ensaio de determinação da tenacidade à fratura em deformação plana (KIc) em PMMA e análise das tensões desenvolvidas por fotoelasticidade. / Study of test for determining fracture toughness in plane strain (KIc) in PMMA and stress analysis developed by photoelasticity.

AUTOR(ES)

Joelmir Mariano de Souza

DATA DE PUBLICAÇÃO

2010

RESUMO

Single-Edge-Notch Bending samples produced out of compression-molded plates obtained from a commercial Poly(methyl metacrylate), PMMA, resin were investigated concerning the influence of the adopted pre-cracking methodology on plane strain fracture toughness results according to ASTM D 5045 standard. Two sets of 6 samples each were pre-cracked using a sharp-edge scalpel steel blade using two methodologies proposed in the technical literature: by gentle tapping on the blade and by controlled insertion at constant velocity, both using a device specially designed for these purposes. These sample were, then, submitted to the plane strain fracture toughness (KIc) test based on the hypothesis that different pre-cracking methods result in different damage levels of the matrix near the pre-crack tip and, hence, in different measured values for KIc. All samples produced valid results for KIc based on the geometric criteria adopted by the standard. The results confirm the original hypothesis showing that the two pre-cracking methods influence the measured value at a significance level of 5% for the comparison of the averages obtained in both sets. The most conservative value for plane strain fracture toughness of the investigated resin is obtained by pre-cracks introduced by gentle tapping on the blade (KIc = 1.15 ± 0.11 MPa m1/2). Based on these results new samples with a self-similar geometry were produced and submitted to photoelasticity tests to investigate the influence of the pre-cracking methods on the strain-field developed during three-point bending loading. The results confirm that the different methods produce different Moiré patterns close to the pre-crack tip, proving that the developed stress fields are different and that pre-cracks introduced by controlled insertion of the blade produce the largest perturbations of the strain field close to the pre-crack tip.

ASSUNTO(S)

fotoelasticidade método de introdução de pré-trincas photoelasticity plane strain fracture toughness in polymers (test) poli(metacrilato de metila) pmma poly(methyl metacrylate) pmma pre-cracking methods tenacidade à fratura em polímeros (ensaio)

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