Unloading stress field

Residual Stress (Forming), Fig. 2 Stress field after unloading... 

The common stress field of rock-mass is complex of gravitational stress and tectonic stress. Erosion of valley and excavation will lead to unloading of stress field and the relaxation deformation of rock-mass, which may cause a series of changes of engineering properties of rock-mass. 

Fig. 7.6. Unloading of a crack by a phase transformation of particles. In the process zone, residual compressive stresses are superimposed to the external tensile stress field...

If the crack is large, it has moved so far away from the notch stress field that it feels only the far-field stress Acr. The notch is now in the region unloaded by the crack, and the fact that the notch opening is much wider than that of the crack is irrelevant for the mechanical behaviour. Thus we have to add the notch depth to the crack length, resulting in... 

Suppose, on the other hand, that energy is dissipated in the volume elements, so that unloading of an element returns only a fraction (1 — p) of its input energy to the stress field O is the hysteresis ratio and is proportional to tan 8 for small strains). Then it is necessary to divide the specimen into loading and unloading regions and integrate separately over these two domains. Hence in this case... 

These cracks are much shallower and are formed on unloading at the boundary between elastic, nonpermanently deformed material and the plastically deformed material close to the indenter the interface between these two regions is the source of a stress field because material that has been plastically strained has a different stress-strain behavior than the normal material. 

Analysis has shown that the component of the stress field is tensile in character, acting parallel to the sample surface and at a maximum about 13/2 below the surface )3 is defined in equation (1.16). On unloading, the... 

Similarly, different types of loading and unloading approaches can be used to extract desired properties as a function of penetration depth (Gan et al., 1996 Gan and Ben-Nissan, 1997 Fischer-Cripps, 2002). The apphcation of nanoindentation as suggested by Field and Swain (1993, 1995) can also be used to determine coating adhesion and residual stress from the load at which delamination occurs (taken from the pop-in that corresponds to a plateau or discontinuity in the load—displacement curve). 

The curve of the absolute maximum strain against the frequency of the unloaded MAS (Fig. 6.38) has been calculated and tested taking into account both the field limit and the stress limit at each frequency. It defines a law of current that depends on frequency. This new strain curve is above the classical curve of strain at constant current, based on the maximum current acceptable at resonance. It possesses a large pass band, which might be used in several applications such as active damping, low frequency projectors, etc. 

Fig. 3.49 for mechanical loads, that will force the unloading from A to C and a residual compressive stress will remain on the external surface. Alike point A any other element of material gone beyond yield point will rest in a residual stress state, which will be compressive on one side and tensile on the other, as shown in Fig. 3.68. This simple process is used in the most important thermo-mechanical treatment known as induction heating stress improvement (IHSl) developed in the 70s in the nuclear field to eliminate corrosion problems on sensitized stainless steel [66-69]. Its purpose is to eliminate tensile residual stress generated on the inner surface of a pipe made of austenitic stainless steels by a welding process.

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