Fatigue fracture diagrams

Fig. 35. Fatigue fracture diagram for PC at 10 Hz, R = 0.1, showing the regions of craze and shear dominated crack growth...

Since no crack growth was observed in PBT, the fatigue fracture diagram is at first glance uninteresting (Fig. 38). It is, however, revealing, in that the endurance limit behavior can be mapped-out and the effects of the glass transition can be seen. 

Rg. 17. Schematic diagram showing the craze-dominated DCG regions constrained on the sides and terminated in the front by shear fatigue fracture regions... 

Figure 1.37 A diagram showing the surface of a fatigue fracture.

Permanent structural changes that occur in a material subjected to fluctuating stress and strain, which cause decay of mechanical properties. See S-N diagram. The ability of a material to plastically deform before fracturing in constant strain amplitude and low-cycle fatigue tests. See S-N diagram. ... 

The plotted characteristic numbers of cycles to fracture were determined by the Weibull method [21]. Each point represents a test series of ten specimens. In the diagram it can be seen clearly that fretting fatigue leads to a distinct deterioration of the specimen strength and life time. The higher the maximum Hertzian stresses the clearer the decline of the strength and life time is. 

In Figure 10 the number of fracture cycles and the characteristic number of fracture cycles for the respective test series is plotted against the maximum principal stress on the tensile loaded side of the specimens. The characteristic number of fracture cycles was determined by the method developed by Weibull [21]. In the Woehler diagram it can be seen clearly that fretting fatigue leads to a distinct deterioration of the life time. The higher the maximum stresses the clearer the decline of life time is. At Fn = 10 N (Pmax = 2311 MPa) the life time decreases at a maximum base load of OR.max = 210 MPa for about 80%. at Fn = 20 N (pmtx -2912 MPa) the life time decreases for about 91% compared to to life time under the same maximum base loading. 

Stress cycle diagrams (Woehler diagrams) remain the most commoniy used means for evaluating long-term cyclic, i.e., fatigue, behavior of fiber composite piastics. With this method, totai specimen faiiure, i. e., fracture, is equated with damage = 1, Fig. 1.65 [148]. 

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