Static Tensile Strengths

Fig. 2-45 Summary of high-performance fatigue properties of different materials based on their percent of ultimate static tensile strength.

Cyclic fatigue measurements require the specimen to be subjected to cyclic stress or strain of a higher amplitude than that employed for the simple dynamic test just described. The deformation must be of sufficient intensity to bring about specimen failure after a certain number of cycles, N. The value of stress leading to failure for a given N is typically 20% to 40% of the static tensile strength. 

We do not have much data on the spall strength of many materials. Even when we do have data, the local conditions and history of that one particular specimen come heavily into play. Table 19.1, however, lists approximate values that can be expected for the spall behavior of several materials of common interest. The values for spall strength shown in Table 19.1 are considerably higher than the equivalent static tensile strengths of these same materials, ranging from a factor of 2.5 to as high as 10. 

The second important area of contribution involves the work of Rumpf [The Strength of Granules and Agglomerates, Knepper (ed.), Agglomeration, Interscience, New York, 1962, pp. 379-414 and Par-tiele Adhe.sion, Sastry (ed.), Agglomeration 77, AIME, New York, 1977, pp. 97-129], which studied the impact of interparticle force El on granule static tensile strength, or... 

Lin and coworkers [41] also investigated the static tensile strength and fatigue behavior of long glass-reinforced semicrystalline polyannide and amorphous polycarbonate composites. The static tensile measurement at various tanperatures and tension-tension fatigue loading tests at various levels of stress amplitudes were studied. 

The second important area of contribution involves the work of Rumpf (20,21) and Ausburger and Vuppala (22), which studied the impact of interparticle force H on granule static tensile strength, or... 

Fatigue Ratio The ratio of fatigue strength at a given number of cycles of stated alternating tensile stress to the static tensile strength. 

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