Subcritical crack growth and in vitro lifetime prediction of resin composites with different filler distributions

Abstract

Objectives: Verify the influence of different filler distributions on the subcritical crack growth (SCG) susceptibility, Weibull parameters (m and σ(0)) and longevity estimated by the strength-probability-time (SPT) diagram of experimental resin composites.

Methods: Four composites were prepared, each one containing 59 vol% of glass powder with different filler sizes (d(50)=0.5; 0.9; 1.2 and 1.9 μm) and distributions. Granulometric analyses of glass powders were done by a laser diffraction particle size analyzer (Sald-7001, Shimadzu, USA). SCG parameters (n and σ(f0)) were determined by dynamic fatigue (10(-2) to 10(2) MPa/s) using a biaxial flexural device (12 × 1.2 mm; n=10). Twenty extra specimens of each composite were tested at 10(0) MPa/s to determine m and σ(0). Specimens were stored in water at 37°C for 24 h. Fracture surfaces were analyzed under SEM.

Results: In general, the composites with broader filler distribution (C0.5 and C1.9) presented better results in terms of SCG susceptibility and longevity. C0.5 and C1.9 presented higher n values (respectively, 31.2 ± 6.2(a) and 34.7 ± 7.4(a)). C1.2 (166.42 ± 0.01(a)) showed the highest and C0.5 (158.40 ± 0.02(d)) the lowest σ(f0) value (in MPa). Weibull parameters did not vary significantly (m: 6.6 to 10.6 and σ(0):170.6 to 176.4 MPa). Predicted reductions in failure stress (P(f)=5%) for a lifetime of 10 years were approximately 45% for C0.5 and C1.9 and 65% for C0.9 and C1.2. Crack propagation occurred through the polymeric matrix around the fillers and all the fracture surfaces showed brittle fracture features.

Significance: Composites with broader granulometric distribution showed higher resistance to SCG and, consequently, higher longevity in vitro.