Fatigue damage

CHRONIC HEALTH RISKS acne-like skin rash papules, large comedones and pustules, affecting the face, neck, arms, and legs skin lesions headache vertigo anorexia liver damage fatigue dark urine yellow jaundice death. 

However, the word fatigue is used for such situations when there is no stabilization, but rather a gradually increasing damage. Fatigue under constant load is considered in more detail in Section 11.4, and here fatigue under cyclic load is described. 

Fig. 8.25 Constant damage fatigue finite life S-N curves...

In this study, the cumulative AE counts have been used to quantify the fatigue damage development in quasi-isotropic CFRP laminates and a model based on AE data has been formulated. 

Figure 6. Three stages of the fatigue damage growth in composite laminates [2]...

The higher the fatigue stress level the higher the rate of damage development (and the rate of cumulative AE counts)... 

O Brien, T.K., Characterization of Delamination Onset and Growth in a Composite Laminate in Damage in Composite Materials, ASTM STP 775, p. 140-167,1982 Poursartip, A. Ashby, M. F., Beaumont P.W.R., The Fatigue Damage Mechanics of Fibrous Laminates in Proceedings of the European Workshop on Nondestructive Evaluation of Polymers and Polymer Matrix Composites, Polymer NDE (edited by Khg. Ashbee), Technomic Publishing, p. 250-260, 1984... 

Extend the safe useful operation life of major HT/HP power plant items, subject to time-dependent creep and thermal fatigue damage, with benefits in terms of delayed costs for component replacement. 

As stated above the life of a ship will be determined by corrosion and fatigue damage. The assessment of corrosion and fatigue damage is discussed below. 

Cumulative Damage. Pressure vessels may be subjected to a variety of stress cycles during service some of these cycles have ampHtudes below the fatigue (endurance) limit of the material and some have ampHtudes various amounts above it. The simplest and most commonly used method for evaluating the cumulative effect of these various cycles is a linear damage relationship in which it is assumed that, if cycles would produce failure at a... 

In the case of the fibrous laminate not much work has been done, but it has been observed that a significant loss of stiffness in boron—aluminum laminate occurs when cycled in tension—tension (43,44). Also, in a manner similar to that in the laminated PMCs, the ply stacking sequence affects the fatigue behavior. For example, 90° surface pHes in a 90°/0° sequence develop damage more rapidly than 0° pHes. In the case of laminates made out of metallic sheets, eg, stainless steel and aluminum, further enhanced resistance against fatigue crack propagation than either one of the components in isolation has been observed (45). 

Cases can be classified as either hermetic or nonhermetic, based on their permeabiUty to moisture. Ceramics and metals are usually used for hermetic cases, whereas plastic materials are used for nonhermetic appHcations. Cases should have good electrical insulation properties. The coefficient of thermal expansion of a particular case should closely match those of the substrate, die, and sealing materials to avoid excessive residual stresses and fatigue damage under thermal cycling loads. Moreover, since cases must provide a path for heat dissipation, high thermal conductivity is also desirable. 

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