Fatigue loading

The way in which this sort of approach may be used to design articles subjected to fatigue loading is illustrated in the following example. 

Suppose we replace the 90° layers with a laminae in an attempt to increase the axial stiffness and to increase the first-ply failure load as in Figure 7-61. The load-deflection curve slope after first-ply failure also increases when a laminae replace the 90° layers. However, the energy absorption decreases with such a stacking sequence change. The associated fatigue lives are not known unless both laminates are made and subjected to fatigue loading. 

Strength, particularly where the material will be subjected to fatigue loading or is susceptible to degrading mechanisms such as hydrogen-induced cracking ... 

Low cycle fatigue loading of 9.5%Cr steel at 650°C in air has been shown to enhance uniform scale formation as well as promote nodular scale forma-... 

Doll, W. and Konczol, L. Micromechanics of Fracture under Static and Fatigue Loading Optical Interferometry of Crack Tip Craze Zones. Vol. 91/92, pp. 137 — 214. 

Many plastic products seen in everyday life are not required to undergo sophisticated design analysis because they are not required to withstand extreme loading conditions such as creep and fatigue loads. Examples include containers cups toys boxes housings for computers, radios, televisions and the like and nonstructural or secondary structural products of various kinds in buildings, aircraft, appliances, and electronic devices. These type products require reviewing... 

The behavior of materials under dynamic load is of considerable importance and interest in most mechanical analyses of design problems where these loads exist. The complex workings of the dynamic behavior problem can best be appreciated by summarizing the range of interactions of dynamic loads that exist for all the different types of materials. Dynamic loads involve the interactions of creep and relaxation loads, vibratory and transient fatigue loads, low-velocity impacts measurable sometimes in milliseconds, high-velocity impacts measurable in microseconds, and hypervelocity impacts as summarized in Fig. 2-4. 

Type of loading. A simple static load is relatively easy to recognize, but there are cases that fail between impact and suddenly applied loads. One thus takes into account infrequently applied fatigue loading mixed with some shock loads, as for example cams, links, or feeding devices. 

In a recent study, Saintier et al. ° investigated the multiaxial effects on fatigue crack nucleation and growth in natural mbber. They found that the same mechanisms of decohesion and cavitation of inclusions that cause crack nucleation and crack growth in uniaxial experiments were responsible for the crack behavior in multiaxial experiments. They studied crack orientations for nonproportional multiaxial fatigue loadings and found them to be related to the direction of the maximum first principal stress of a cycle when material plane rotations are taken into account. This method accounts for material rotations in the analysis due to the displacement of planes associated with large strain conditions. 

Fatigue data analysis, 13 494-495 Fatigue failures, 13 481, 486-487 Fatigue loads, 13 481 Fatigue performance, sample size and surface finish in, 13.486 487 Fatigue properties... 

In short fiber composites, energy absorption mechanisms, such as interfacial debonding and matrix cracking, most often occur at the fiber ends (Curtis et al., 1978). The damage model proposed by Bader et al. (1979) assumes that short fiber composites fail over a critical cross-section which has been weakened by the accumulation of cracks, since the short fibers bridging this critical zone are unable to carry the load. In fatigue loading, sudden fracture takes place as a direct result from the far-field effect of the composite, rather than due to the near field of the crack tip... 

In fact, the strength variability of a given fiber-resin combination may be significantly different from the strength variability of a different combination of the same fiber with another resin system [35]. This is particularly the case when environmental and fatigue loading (long-term durability) are considered. 

Wiggins MJ, MacEwan M, Anderson JM, Hiltner A. Effect of soft-segment chemistry on polyurethane hiostability during in vitro fatigue loading. Journal ofBiomedical Materials Research A 2004, 68, 668-683. 

Hsieh Y-F, Silva MJ. In vivo fatigue loading of the rat ulna induces both bone formation and resorption and leads to time-related changes in bone mechanical properties and density. J Orthop Res. 2002 20 764-771. 

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... 

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