Deformation residual elastic

Too means the reduction of the purely elastic deformation). As yQ remains constant, we observe a residual elastic deformation29 ... 

The following symbols are used in Table 1.3 ot> is strength limit in extension e is defoimation at break E is modulus of elasticity Er is residual deformation (after elastic recoil) Hb is Shore hardness Eel is rebound elasticity T, is glass transition temperature... 

TWO SEPARATE ALTERED or damaged layers classically have been recognized on metal surfaces formed by cutting- or polishing-type processes namely, an amorphous-like "Beilby" layer and a plastically deformed layer. Modern work indicates that the Beiiby layer is not, in fact, formed by the common important methods of surface preparation but that a deformed layer always is. The detailed structure of this layer is reviewed. Some consideration is also given to residual elastic stresses, surface topography, and embedded abrasive. 

The presence of residual elastic stresses is inevitable in a surface which contains a plastically deformed zone whose thickness is limited compared with that of the bulk s pecimen. Alternatively, the relief of these stresses may cause distortion of the specimens in cases where the thickness of the two is comparable. Very little work has been done on this important subject and, so far as can be ascertained, none that can be related to the complexities of die plastically-deformed layer. Considerable complications are introduced because the residual stresses may be of thermal as well as mechanical origin and because those of mechanical origin may be altered by the thermal effects. 

To obtain and keep the required product quality, agglomerates that are formed by external pressure must maintain their shape and density after release of the pressing force and removal from the die. If residual elastic deformation is present within the compact, elastic recovery, accompanied by an increase in volume, will occur when the pressure is released and the part is ejected from the die or leaves the shaping tools. This causes structural defects such a microcracks, which lower the strength or separation of pieces by capping (Section 6.2.2) or lamination (Section 6.9.2). 

Following on from the Lawn analysis, all the subsequent relationships have the same two features Kc is made proportional to P(c y by keeping the model which places the cracks in a center loaded position from the deformed zone-elastic zone interface. The ratio E/Hy appears in them all because the residual stress arises from deformation mismatch. A selection of these expressions is given below with a and c defined according to Figure 5.2 ... 

Fig. 3.4 Calculated residual elastic stress Tel and plastic deformation Spi along a elastoplastic crystal (InP) using the Alexander-Haasen model. The To curve shows the elastic stress course in a purely elastic body. The relaxation of elastic stress,...

One of the characteristics of elastic Hertzian contact is that over the elastic shakedown limit, the place of the beginning of the plastic flow varies in function of the friction coefficient [7]. In the case of low friction coefficient it begins in a known depth below the surface due to the maximal shear stress. On the surface, at the contact point or on the contact line, the stress state is hydrostatic compression and the deformation remains elastic, even if a residual change happens below the surface. If the friction coefficient increases, the plastic flow can begin on the surface. 

If the film adhesion is high or the fracture strength of the surface is low, the actual fracture path may be in the substrate and not at the interface. The residual stress that can be attained depends on the elastic modulus of the film material. A soff material will not sustain a high stress it will deform. The elastic modulus of soft materials can be increased by gas incorporation during deposition.The film stress may vary through the thickness of the film. This film stress profile leads to curling of a film when it is detached from the substrate. 

Spherical indentor deformability tests of composites with PE synthesized on different fillers have shown [164] that the deformation of PFCM containing high percentages of filler (and polymer concentrations of less than 10% by mass) is substantially elastic and the specimen recovers completely after release of the load. As the polymer content increased to 60% by mass considerable residual deforma-... 

In Fig. 24(a) the purely elastic deformation and the plastic elastic flow processes are plotted and hatched in a different manner. Figure 24(b) shows the dependence of stress on time. It can also be seen, that with discharge at time t0 the purely elastic residual deformation disappears at once, whereas the plastic-elastic portion does so gradually (diffusion processes). 

Extensive theoretical investigations devoted to calculation of residual stresses have been carried out for metals. The principal theme of this work is assumption that residual stresses and strains are the result of differences between pure elastic and elastic-plastic deformations under fixed loading.127 128 The same mechanism, i.e., the appearance of plastic deformed zones, is responsible for the residual stresses arising during crystallization of metals, which occurs on quenching from the melt or cooling after welding. 

Non-destructive methods include holographic interferometry, resistance transducers, stress-sensitive covers, and other similar techniques. In practice, the following physical methods of non-destructive monitoring of residual stresses are commonly used X-ray diffraction, measurement of dielectric properties, and ultrasonic control. The main purpose of these methods is to monitor the structural transformations or distortions taking place as a result of residual stresses and local deformations. However, the application of methods such as X-ray diffraction to measure distortions in unit cel dimensions, ultrasonics to measure elastic wave propagation velocities, etc., all encounter numerous experimental problems. Therefore, in ordinary laboratory conditions only quantitative estimations of residual stresses can be obtained. 

Note that the internal viscosity is a residual of internal relaxation process in the case, when the slow deformation is considered. In a more general case, the elastic and internal viscosity forces acting on the chain, according to equations (2.2) and (2.28), can be written as... 

---