Mean stress sensitivity factor

5 Stress-Based Fatigue Analysis High Cycle Fatigue 

The Morrow M factor appears to be a function of material and mean stress [49, 50] as schematized in Fig. 5.39 and for that reason is also known as mean stress 

For low values of the mean stress (—1 0) the Morrow s factor is indi- 

Large M values indicate high sensitivity. In the negative mean stress quadrant (— cxd 7 — 1) it is indicated by M2 while for high mean stress values (0 / 1) it s referred to as M3. Usually, M3 is lower than M by a factor of 3 

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Fig. 5.40 Haigh diagram showing the mean stress sensitivity factor M and its dependence on mean stress...

Scharf K-D, Berberich T, Ebersberger I, Nover L (2012) The plant heat stress transcription factor (Hsf) family structure, function and evolution. Biochim Biophys Acta 1819 104-119 Seki M, Umezawa T, Urano K, ShinozaM K (2007) Regulatory metabolic networks in drought stress responses. Curr Opin Plant Biol 10 296-302 Sfichi L, loannidis N, Kotzabasis K (2004) Thylakoid-associated polyamines adjust the UV-B sensitivity of the photosynthetic apparatus by means of light-harvesting complex II changes. Photochem Photobiol 80 499-506... 

Nevertheless, in food plants such as potatoes, toxicants regularly reach such high levels that a single meal can cause unpleasant symptoms in sensitive persons, although serious cases (more than a few hours of nausea and/or diarrhoea) are extremely rare, and no cases have been reported in developed countries for more than two decades (Percival and Dixon 1997). Many of the plant toxicants are phytoalexins, which means that they accumulate in varying amounts in response to mechanical damage, an infection or other stress conditions, so the concentrations within the same plant often vary by more than a factor of 100 depending on plant age and sample site (Morrissey and Osbourn 1999). 

Although Ey and are analogous to fj. and v, respectively, in that all these quantities are coefficients relating shear stress and velocity gradient, there is a basic difference between the two kinds of quantities. The viscosities n and v are true properties of the fluid and are the macroscopic result of averaging motions and momenta of myriads of molecules. The eddy viscosity and the eddy diffusivity are not just properties of the fluid but depend on the fluid velocity and the geometry of the system. They are functions of all factors that influence the detailed patterns of turbulence and the deviating velocities, and they are especially sensitive to location in the turbulent field and the local values of the scale and intensity of the turbulence. Viscosities can be measured on isolated samples of fluid and presented in tables or charts of physical properties, as in Appendixes 8 and 9. Eddy viscosities and diffusivities are determined (with difficulty, and only by means of special instruments) by experiments on the flow itself. 

Semiconductor fabrication processes permit construction of small, sensitive, stress sensors. In fact the levers used in atomic force microscopes are almost ideal for this purpose. The combination of the mechanical properties of silicon nitride and the geometry of the cantilever mean that the lever has a high resonant firequency and a low spring constant [32]. The low spring constant is beneficial for sensor applications because it means that a small applied force can be transduced to a measurable deflection, which lies at the heart of any sensor [33]. When combined with the highly sensitive optical lever AFM detection system, both of these factors mean that this arrangement is a fast and highly sensitive stress sensor. 

Displacement data provide a direct means of evaluating cavern stability. Displacements that have exceeded the predicted elastic displacements by a factor of 5-10 generally have resulted in decisions to modify support and excavation methods. In a creep-sensitive material, such as may occur in a major shear zone or zone of soft altered rock, the natural stresses concentrated around an opening cause time-dependent displacements that, if restrained by support, result in a build-up of stress on the support. Conversely, if a rock mass is not sensitive to creep, stresses around an opening normally are relieved as blocks displace towards... 

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