Fatigue Crack Propagation in Composite Resins

1.The Paris law (da/dN=C(DELTA K)^m) could be applied to The fatigue crack growth rate of Thematerials used in this study. Constant m was in the range of 24.3-32.2 for composite resins and19.7-21.0 for unfilled resins. The DELTA k__ <th> was in The range of 0.43-0.82 MPa·m^<1/2> forcomposite resins and 0.20-0.21MPa·m^<1/2> for unfilled resins. Constant m of dental composites wasextremely higher than that of metal(m=2-7)，但没有did not differ very much from each other. The fatigue crack growth rate of dental compositesdepended on DELTA k_ <th> rather than constant m. 2.Microstructural examination of fatigue fracturesurfaces by SEM indicated that the fatigue crack of dental composites propagated along the interfaceinorganic filler and matrix，3.某些组织fillers penetrated with fatigue cracks. fatigue crack growth rate was4.The fatigue more sensitive to degradation of composites by aging in than transverse strength.4composites measured as DELTA k_ <th> decreased by aging in water. SEM observationshowed that fatigue crack propagated in both matrix and filler-matrix interface after aging in waterfor three months.These results indicated that that crack deflection and crack bridging by inorganicfiller increased the fatigue resistance of composites，and decrease of fatigue resistance by aging in water was caused by the degradation of resinmatrix. From the present study，这应该是一个有效的研究方法，即fatigue crack propagation testtoughening and degradation of dental composites。

1.The Paris law (da/dN=C(DELTA K)^m) could be applied to the fatigue crack growth rate of the materials used in this study. Constant m was in the range of 24.3-32.2 for composite resins and 19.7-21.0 for unfilled resins. The DELTA K_<th> was in the range of 0.43-0.82 MPa・m^<1/2> for composite resins and 0.20-0.21MPa・m^<1/2> for unfilled resins. Constant m of dental composites was extremely higher than that of metal(m=2-7), but did not differ very much from each other. The fatigue crack growth rate of dental composites depended on DELTA K_<th> rather than constant m. 2.Microstructural examination of fatigue fracture surfaces by SEM indicated that the fatigue crack of dental composites propagated along the interface between inorganic filler and matrix, and that some organic fillers were penetrated with fatigue cracks.3.Fatigue crack growth rate was more sensitive to degradation of composites by aging in water than transverse strength.4.The fatigue resistance of composites measured as DELTA K_<th> decreased by aging in water. SEM observation showed that fatigue crack propagated in both matrix and filler-matrix interface after aging in water for three months.These results indicated that that crack deflection and crack bridging by inorganic filler increased the fatigue resistance of composites, and that decrease of fatigue resistance by aging in water was caused by the degradation of resin matrix. From the present study, it was shown that the fatigue crack propagation test was an effective method to investigate toughening and degradation of dental composites.