| The development of cyclic damage zones and the propagation of mode I fatigue cracks due to the application of cyclic loads is examined in polymers and polymeric composites, specifically polystyrene, rubber-modified polystyrene, polycarbonate, high density polyethylene and continuous carbon fiber-reinforced epoxy composites. These results are compared with metals and ceramics. The mechanisms of near tip deformation processes are examined and the effects of these microscopic deformation processes on the fatigue behavior of the polymeric materials are discussed. Particular attention is devoted to direct experimental measurement of the crack-tip stress fields ahead of the fatigue crack. Quantitative measurements of the different components of the stress tensor in the near-tip region are obtained using photoelastic and laser interferometric techniques. These results are compared to those obtained using finite element models. The study of near-tip fields ahead of fatigue cracks has practical implications for a variety of fatigue phenomena, such as, compression fatigue fracture, fatigue crack retardation after a tensile overload or exacerbated fatigue fracture due to a compressive overload in variable amplitude fatigue loading. |
