Deformation avoiding

Once the precipitates grow beyond a critical size they lose coherency and then, in order for deformation to continue, dislocations must avoid the particles by a process known as Orowan bowing(23). This mechanism appHes also to alloys strengthened by inert dispersoids. In this case a dislocation bends between adjacent particles until the loop becomes unstable, at which point it is released for further plastic deformation, leaving a portion behind, looped around the particles. The smaller the interparticle spacing, the greater the strengthening. 

Access for the deformation tool is an important consideration. Awkward positions should be avoided and ideally processing should be performed from above. 

Ductility. As a warning against the quick conclusion that high ductility is the premium quality desired, it. should be pointed out that the amount of deformation is closely related to the hot strength with which deformation is resisted. A very strong alloy may avoid yielding, or yield so little that there is no need for much ductility. 

Up to this stage we have considered the deformation behaviour of fibre composites. An equally important topic for the designer is avoidance of failure. If the definition of failure is the attainment of a specified deformation then the earlier analysis may be used. However, if the occurrence of yield or fracture is to be predicted as an extra safeguard then it is necessary to use another approach. 

If no laminae have failed, the load must be determined at which the first lamina fails (so-called first-ply failure), that is, violates the lamina failure criterion. In the process of this determination, the laminae stresses must be found as a function of the unknown magnitude of loads first in the laminate coordinates and then in the principal material directions. The proportions of load (i.e., the ratios of to Ny, to My,/ etc.) are, of course, specified at the beginning of the analysik The loaa parameter is increased until some individual lamina fails. The properties, of the failed lamina are then degraded in one of two ways (1) totally to zero if the fibers in the lamina fail or (2) to fiber-direction properties if the failure is by cracking parallel to the fibers (matrix failure). Actually, because of the matrix manipulations involved in the analysis, the failed lamina properties must not be zero, but rather effectively zero values in order to avoid a singular matrix that could not be inverted in the structural analysis problem. The laminate strains are calculated from the known load and the stiffnesses prior to failure of a lamina. The laminate deformations just after failure of a lamina are discussed later. 

To ensure that the water flows through the whole of the system as smoothly as possible and with the minimum of turbulence, it is vital that the layout of pipework should be planned before fabrication starts. It should not be the result of haphazard improvisation to avoid more and more obstacles as construction proceeds. Pipe runs should be minimised or run as directly as possible with every effort made to avoid features that might act as turbulence raisers. For this reason the number of flow controllers, process probes, bends, branches, valves, flanges, intrusive fittings, or mechanical deformation or damage to the pipework, should be kept to a minimum. 

However this technology has also some limitation. For example, pupil diameter is an overall parameter and for a 100 m primary telescope, the internal pupil diameter cannot be reduced below 1 m. According to the maximal size of the wafers (8 inches), a deformable mirror based on MOEMS technology cannot be build into one piece. New AO architectures are under investigation to avoid this limitation (Zamkotsian and Dohlen, 2001). 

In order to arrive ultimately at the entropy change accompanying deformation, we now proceed to calculate the configurational entropy change involved in the formation of a network structure in its deformed state as defined by a, ay, and (We shall avoid for the present the stipulation that the volume be constant, i.e., that axayag=l.) Then by subtracting the entropy of network formation when the sample is undeformed (ax = ay = az=l)j we shall have the desired entropy of deformation. As is obvious, explicit expressions will be required only for those terms in the entropy of network formation which are altered by deformation. 

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