Failure under Cyclic Loading

One way to predict failure under cyclic loading of fluoropolymers is to use traditional S-N fatigue data curves. To predict failure, the material must first 

Further discussion of the fatigue and failure behavior of polymers in general is presented in a number of specialized text books. F 

The following two examples provide first a relatively simple example analysis followed by a second more sophisticated effort that exercises many aspects of advanced fluoropolymer mechanical analysis. 

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This effect can cause failure under cyclic loads, but this is not true fatigue, for it is not the number of cycles, but the total loading time that determines failure. 

Ward et a/."" have shown that, under cyclical loading, the oxidation rate of steels is similar to that under unstressed isothermal conditions, provided the fatigue stress is below the stress required to exceed the scale failure strain. If, however, the failure strain is exceeded, the oxidation rate is accelerated due to repetitive scale failure, and linear kinetics are observed. 

L. X. Han and S. Suresh, High Temperature Failure of an Alumina-Silicon Carbide Composite under Cyclic Loads Mechanisms of Fatigue Crack-Tip Damage, J. Am. Ceram. Soc., 72[7], 1233-1238 (1989). 

Fatigue Failure Mode. The experiments conducted by Lin et al. were conducted under cyclic loads that resulted in the fatigue life of spot friction welds from 10 to 10. Based on the experimental observations, the failed spot fric-hon welds with fatigue lives from 10 to 10 ... 

P.-C. Lin, J. Pan, and T. Pan, Eatigue Failures of Spot Friction Welds in Aluminum 6111-T4 Sheets under Cyclic Loading Conditions, SAE Technical Paper 2006-01-1207, Society of Automotive Engineers... 

In design analysis, G can be used to assess the onset of fracture under extreme loads and the onset of crack growth under static loads (creep failure), but more often the rate of crack growth under cyclic loads (fatigue failure). 

Loading Level 1 Matrix cracks begin to develop while the hbers remain intact. Under cyclic loading, these cracks propagate until they reach a hber—matrix interface or some other inhomogeneity. If the cyclic load is sufficiently low, these cracks will not propagate any further, and no more fracture surfaces will be created until the fatigue limit of the hbers is reached and overall composite failure occurs. 

K Schulte, Damage development under cyclic loading . Damage Development and Failure Processes in Composite Materials, eds I Verpoest and M Wevers, Leuven, KU-Leuven, 1987, pp 39-54. 

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