Fatigue problem

Cohen, R., Valve Stress Analysis for Fatigue Problems, ASHRAE Journal, January 1973, pp. 57-61. 

The problem- points in high-pressure machines are certainly the dynamic shaft- and piston-or plunger seals. Seals create special problems when they slide rapidly under high-pressure and if the fluid being sealed has no lubricating actions. Cyclic stress creates additionally fatigue problems in the seal. 

Volatility of PbO leads to the so-called fatigue of Pt/PZT/Pt capacitor structures polarization drastically decreases after the structure is exposed to repeated (about 10 cycles) polarization cycles. The fatigue problem may be overcome by application of ferroclcctries without volatile components leading to... 

Naphtho[l,2- 6]pyrans have been patented55 that are purple in the activated state. These contain, in addition to a methyl at the 2-position, a phenyl containing ortho and/or para amino functionality. While these compounds have intensely colored open forms, they appear to be of little use due to fatigue problems associated with the previously discussed potential of the colored species undergoing an irreversible sigmatropic 1,7-hydrogen shift. 

Sharp, J.D. and M.L. Drake, "Elimination of Resonant Fatigue Problems for Major Maintenance Benefits," ASME Publication Number 77-DET-135. 

Gregory, M.A. and Roebroels, G.H.J.J. (1991) Fiber/metal laminates a solution to weight, strength and fatigue problems , 30 Ann. Conf. of Metallurgical Society of CIM, Ottawa, Canada. 

Unplanned stresses may result from vibrations causing cavitation and corrosion-fatigue problems that can be considerably reduced with the adoption of appropriate stiffeners and/or flexible connections (Figure 12.46). 

The selection of surface finish is usually made on the basis of choosing the optimum economic method to meet the objectives related to suitability for the application. The choice may be compromised by global conditions, such as seeking machine or plant uniformity, or by narrow key functions of crucial importance, as with fatigue problems or stringent duty constraints. 

The vibration and fatigue problems likely as a result of the distorted shaft and overloaded bearings arc readily apparent and. not surprisingly, premature failure often occurs in such situations. 

Design loads this high should never be imposed for it is doubtful that any adhesive should ever bear loads greater than 20 per cent of its ultimate shear strength. Above this level, fatigue problems are likely, particularly in severe environmental conditions. However, such stresses may occasionally be reached during anticipated overload, or during accidental abuse. If in doubt answer Yes . 

Note checks on early moulding revealed fatigue cracks where the deep ribs (around the bearing) blend in with the shallow ribs towards the outside of the base. An increased fillet radius at this junction eradicated the fatigue problem. 

The presence of undesirable side reactions associated with photochromic transitions may also reduce the number of cycles of forward and reverse reactions. This concept known as a fatigue problem is associated with photochromic molecules and is represented by the following reaction ... 

Their belief was of course wrong, and the experience with the Comets eventually improved the state of the art of aircraft design. Once the fatigue problem was understood to be aggravated by the... 

---