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

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.