Fatigue behavior cyclic loading

Baste, U. (1993), Thermal shock and cyclic loading of ceramic parts in stationary gas turbines , in Schneider G. A. and Petzow G. (editors), Thermal Shock and Thermal Fatigue Behavior of Advanced Ceramics, Dordrecht Kluwer Academic, 87-97 Becher, P.F. (1981), Transient thermal stress behavior in Zr02-toughened A1203 , J. Am. Ceram. Soc., 64(1), 37-39. 

Fig. 6.5 Cyclic stress-strain behavior observed during the room temperature fatigue of unidirectional SiQ/LAS-II at a maximum stress below the 105 fatigue limit (loading frequency = 10 Hz, crmin/crmax = 0.1). The cyclic stress-strain curves show very limited, if any, hysteresis. Note that the strength and strain capability is retained after cyclic loading below the proportional limit stress. After Prewo.42...

Differences in the macroscopic and microscopic fatigue fracture behavior of ceramic composites under static and cyclic loading at high temperatures. 

By definition, ESC is influenced by the level of the applied multiaxial stress, ft is expected that below an assigned value of stress in a specific medium ESC will not occur. Fatigue crack growth experiments at various constant levels of A K can be applied to study the influence of the crack-tip loading on the ESC behavior in a systematic way. As an example, cast CT specimens of PMMA (Mn = 4.6 x 105) were tested in air and IPA at different levels of AK (0.6, 0.7, 0.8, 0.9 MPa -v/m). The tests were performed as described earlier, with the application of the medium after a certain time of cyclic loading in air. From the plots of the crack length ratio vs. number of cycles, the following observations can be made (Fig. 23) ... 

The crack growth behavior of polymers under cyclic loading has been intensively studied and the state of knowledge is also well documented by excellent, recently published review articles mong which the comprehensive book on Fatigue... 

Under cyclic loading, the fatigue life of S-PS ionomers decreases up to about 4 mol %, then rises rapidly between 4 and 6 mol %, and thereafter continues to rise slowly to about 10mol%. The transition in behavior near 5 mol% is attributed to the development of large scale aggregates, or ion clusters, that act as a reinforcing second phase that impedes crack propagation. 

The cyclic load form is important. The crack growth rate increases, and the fatigue threshold decreases as compared with that in air. The crack growth rate obeys a Paris Law with increase in crack growth rate and a decreased fatigue threshold compared with the behavior in air (73). 

The TDCB specimen is shown to be suitable for FRP-wood interface fatigue tests. The FRP-wood interface displayed the typical crack propagation behavior under constant cyclic loading as observed by others. 

Fujii T, Lin F, Morita Y. Fatigue behavior of plain woven glass-fabric laminates under tension/torsion combined loading (Effect of shear stress and cyclic condition on fatigue failure). Nippon Kikai Gakkai Ronbunshu, A Hen/Trans Jpn Soc Mech Eng Part A 1994 60 650—7 [in Japanese]. 

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. 

T. Ogasawara and Y. Mabuchi, Effect of Humidity and Cyclic Loading Condition on Fatigue behavior of Silicon Nitride , J. Ceram. Soc. Jap., Int. Edition, 101, 1993, 1122-1127. 

FIGURE 9. Cyclic tension-tension fatigue behavior of Piepieg HiPeiComp composites tested in air using sinusoidal loading. Black points ate for 815°C, gray points for 1093°C and white points for 1204°C. (Arrows indicate test run-outs.)... 

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