Fatigue loading rate

Lundberg, G. and Palmgren, A., Load Ratings and Fatigue Life for Roller Bearings, Std. 11-1978. 

Standard 9 Load Ratings and Fatigue Life for Ball Bearings... 

ANSI/ABMA Load ratings and fatigue life for 281 622 5512 Part I NF ISO 281 B1518... 

Other test modes, such as constant loading rate and variable strain rate, have been used on a limited basis as research techniques to investigate such phenomena as the path dependence of failure, but no general description of these tests can be provided. Of course the entire area of dynamic testing and fatigue uses various specialized test conditions, but these are discussed later. 

Figure 10. Relationship of crack propagation resistance to strain rate and temperature. Thermally stabilized 2I/4 Cr-1 Mo in high-N Li. Stress intensity factor, K = 20.0 and fatigue load ratio, R — 0.0. ...

Loads on a fabricated product can produce different t3q>es of stresses within the material. There are basically static loads (tensile, modulus, flexural, compression, shear, etc.) and dynamic loads (creep, fatigue torsion, rapid loading, etc.). The magnitude of these stresses depends on many factors such as applied forces/loads, angle of loads, rate and point of application of each load, geometry of the structure, manner in which the structure is supported, and time at temperature. The behavior of the material in response to these induced stresses determines the performance of the structure. 

The rate dependence of fatigue strength demands carefiil consideration of the potential for heat buildup in both the fatigue test and in service. Generally, since the buildup is a function of the viscous component of the material, the materials that tend toward viscous behavior will also display sensitivity to cyclic load frequency. Thus, TPs, particularly the crystalline polymers like polyethylene that are above their glass-transition temperatures, are expected to be more sensitive to the cyclic load rate, and highly crosslinked plastics or glass fiber reinforced TS plastics are much less sensitive to the frequency of load. 

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