Fatigue resistance and stiffness of glass fiber-reinforced urethane dimethacrylate composite

Abstract 

Statement of problem

Retentive properties of cast metal clasps decrease over time because of metal fatigue. Novel fiber-reinforced composite materials are purported to have increased fatigue resistance compared with metals and may offer a solution to the problem of metal fatigue.

Purpose

The aim of this study was to investigate the fatigue resistance and stiffness of E-glass fiber-reinforced composite.

Material and methods

Twelve cylindrical fiber-reinforced composite test cylinders (2 mm in diameter and 60 mm in length) were made from light-polymerized urethane dimethacrylate monomer with unidirectional, single-stranded, polymer preimpregnated E-glass fiber reinforcement. Six cylinders were stored in dry conditions and 6 in distilled water for 30 days before testing. Fatigue resistance was measured by a constant-deflection fatigue test with 1 mm of deflection across a specimen span of 11 mm for a maximum of 150,000 loading cycles. The resistance of the cylinder against deflection was measured (N) and the mean values of the force were compared by 1-way analysis of variance (α=.05). The flexural modulus (GPa) was calculated for the dry and water-stored cylinders for the first loading cycle. Scanning electron microscopy was used to assess the distribution of the fibers, and the volume percent of fibers and polymer were assessed by combustion analysis.

Results

The test cylinders did not fracture due to fatigue following 150,000 loading cycles. Flexural modulus at the first loading cycle was 18.9 (± 2.9) GPa and 17.5 (± 1.7) GPa for the dry and water-stored cylinders, respectively. The mean force required to cause the first 1-mm deflection was 33.5 (± 5.2) N and 37.7 (± 3.6) N for the dry and water stored cylinders, respectively; however, the differences were not significant. After 150,000 cycles the mean force to cause 1-mm deflection was significantly reduced to 23.4 (± 8.5) N and 13.1 (± 3.5) N, respectively (P<.0001). Scanning electron microscopy highlighted fiber- and polymer-rich areas within the specimens and indicated that individual fibers were well impregnated with resin. The combustion analysis studies identified the fiber content to be 35.9 vol%.

Conclusion

The results of this study suggest that the fatigue resistance of the fiber-reinforced material examined was increased; however, the reduction in flexural modulus of fiber-reinforced composites may restrict their use where high rigidity is required, such as in removable partial denture clasps.