Fatigue behavior loading

In order to accurately model the fatigue behavior of rubber, fatigue analysis methods must account for various effects observed for rubber during constant amplitude testing. Effects associated with load level, 7 -ratio (ratio of minimum to maximum loading level), and crack closure are presented in this section. 

The engineering properties of aggregate mixtures employing elemental sulfur as a binder are not suitable for highway pavement applications such mixtures possess adequate compressive strength, but are extremely brittle and lack satisfactory fatigue behavior to resist repetitive traffic 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. 

Prewo and co-workers were the first to study the fatigue behavior of fiber-reinforced ceramics.41,42 They conducted room temperature tension-tension and flexure fatigue experiments with 0° Nicalon SiCf/LAS-II composites. The fatigue experiments were conducted in air at a sinusoidal loading... 

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...

Summarizing, from numerous experimental investigations of fatigue behavior, it has been established that a fatigue limit exists for the tension-tension fatigue loading of fiber-reinforced ceramics, at least to 108 cycles. In... 

The fatigue performance of these materials in a pavement cannot be inferred directly from these values of Kx and K2, for the actual fatigue behavior will depend upon such variables as thickness and stiffness and size of tire footprints. In addition, it is well known that laboratory fatigue data does not represent accurately the actual fatigue strength of pavements. A given material in a pavement can take 10-100 times as much strain under seal traffic loads as it can when loaded under laboratory conditions to the same number of load cycles. 

Studies of the fatigue behavior of vapor-deposited pyrolitic carbon fibers (4000 to 5000 A thick) onto a stainless steel substrate showed that the film does not break unless the substrate undergoes plastic deformation at 1.3 x 10 strain and up to one million cycles of loading. Therefore, the fatigue is closely related to the substrate, as shown in Figure 39.17. Similar substrate-carbon adherence is the basis for the pyrolitic carbon deposited polymer arterial grafts [Park and Lakes, 1992). 

The fatigue behavior of the phenolic FRP-wood interface bond was investigated [7], using a TDCB specimen for constant strain energy release rate range AG. The load ratio effect... 

Fatigue behavior of continuous fiber composites under multiaxial loading... 

It is important to note that the uniaxial loading of an off-axis plate generates a local (inherent) multiaxial stress state. It is therefore worth mentioning the investigations by Kawai and coworkers for the description of the off-axis fatigue behavior of UD and woven reinforced laminates [61,71,72] and their fatigue damage mechanics model [61]. The model is based on the nondimensional effective stress concept, which is the square root of the Tsai—Hill polynomial. 

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