Plastic deformational heating

In the viscoplastic model of Carroll and Holt [49], later extended by Khasainov et al., [52] Butler et al., [158] and Frey [164] (Fig. 17b), pores in a viscous material collapse slowly behind the shock front via ID (radial) plastic deformation. Heating results from viscoplastic work. In the small Reynolds number limit (see below), the viscous time constant Xyis is independent of pore diameter [52] ... 

A state-of-the-art production routine is P-ESR melting (pressurised electro slag remelting) which will be covered within the following section. Austenitic steels as well as martensitic steels can be manufactured and are suitable for forging and hot rolling. Some basic knowledge about the material characteristics is mandatory to avoid any potential issues at plastic deformation, heat treatment and to maintain the excellent corrosion resistance. 

The surfaces of titanium alloys can easily be damaged dming machining and grinding operations. Damage appears in the form of microcracks, built-up edges, plastic deformation, heat-affected zones, and residual tensile stresses. In service, failures can occur as a result of fatigue and stress corrosion. 

In this expression, K and n are constants these values vary from alloy to alloy and also depend on the condition of the material (whether it has been plastically deformed, heat-treated, etc.). The parameter n is often termed the strain-hardening exponent and has a value less than unity. Values of n and K for several alloys are given in Table 6.4. 

Traditionally, production of metallic glasses requites rapid heat removal from the material (Fig. 2) which normally involves a combination of a cooling process that has a high heat-transfer coefficient at the interface of the Hquid and quenching medium, and a thin cross section in at least one-dimension. Besides rapid cooling, a variety of techniques are available to produce metallic glasses. Processes not dependent on rapid solidification include plastic deformation (38), mechanical alloying (7,8), and diffusional transformations (10). 

Two approaches have been taken to produce metal-matrix composites (qv) incorporation of fibers into a matrix by mechanical means and in situ preparation of a two-phase fibrous or lamellar material by controlled solidification or heat treatment. The principles of strengthening for alloys prepared by the former technique are well estabUshed (24), primarily because yielding and even fracture of these materials occurs while the reinforcing phase is elastically deformed. Under these conditions both strength and modulus increase linearly with volume fraction of reinforcement. However, the deformation of in situ, ie, eutectic, eutectoid, peritectic, or peritectoid, composites usually involves some plastic deformation of the reinforcing phase, and this presents many complexities in analysis and prediction of properties. 

Some materials that are atomically ordered also develop a sHp-iaduced anisotropy as a result of plastic deformation. The origin is thought to be identical to that of thermomagnetic anisotropy, ie, short-range directional order, except that the order is brought on by deformation rather than by heat treatment ia a field (3,4). 

Fig. 9. Effect on fatigue strength of the plastic deformation of a carburized steel surface by shot peening (B) as compared to nitriding (A) and heat treating...

Most wrought alloys are provided in conditions that have been strengthened by various amounts of cold work or heat treatment. Cold worked tempers are the result of cold rolling or drawing by prescribed amounts of plastic deformation from the annealed condition. Alloys that respond to strengthening by heat treatment are referred to as precipitation or age hardenable. Cold worked conditions can also be thermally treated at relatively low temperatures to affect a slight decrease in strength (stress rehef annealed) to benefit other properties, such as corrosion resistance and formabiUty. 

The fact that shock waves continue to steepen until dissipative mechanisms take over means that entropy is generated by the conversion of mechanical energy to heat, so the process is irreversible. By contrast, in a fluid, rarefactions do not usually involve significant energy dissipation, so they can be regarded as reversible, or isentropic, processes. There are circumstances, however, such as in materials with elastic-plastic response, in which plastic deformation during the release process dissipates energy in an irreversible fashion, and the expansion wave is therefore not isentropic. 

Grady and Asay [49] estimate the actual local heating that may occur in shocked 6061-T6 Al. In the work of Hayes and Grady [50], slip planes are assumed to be separated by the characteristic distance d. Plastic deformation in the shock front is assumed to dissipate heat (per unit area) at a constant rate S.QdJt, where AQ is the dissipative component of internal energy change and is the shock risetime. The local slip-band temperature behind the shock front, 7), is obtained as a solution to the heat conduction equation with y as the thermal diffusivity... 

Al-Mg (5000 Series) and Al-Mg-Si (6000 Series) In the binary alloy system strength is obtained mainly by strain hardening. Stress corrosion is thought to be associated with a continuous grain boundary film of Mg,Alg which is anodic to the matrix . Air cooling prevents the immediate formation of such precipitates, but they form slowly at ambient temperatures. Thus only low Mg alloys are non-susceptible (Al-3% Mg). Widespread precipitation arising from plastic deformation with carefully controlled heat-treatment conditions can lower susceptibility. Al-5Mg alloys of relatively low susceptibility are subjected to such treatments. Mn and Cr... 

In retrospect, it should not be surprising that a time independent theory modeled after elasticity theory does not apply to a plastic flow process. Elastic deformation is conservative with the work done on the material stored as elastic strain energy. Plastic deformation is non-conservative with the work done on the material dissipated as heat, or converted into internal defects... 

In this book, elastic strain and plastic deformation will be differentiated by both words and symbols. Elastic strain is given the usual symbols e and y for extensional and shear elastic strains, respectively. For plastic shear deformation. 8 will be used, e and 8 are physically different entities, e and y are conservative quantities which store internal energy. 8 is not conservative. The work done to create it is dissipated as heat and structural defects. 

Plastic cans, 10 447 Plastic cements, 5 500t Plastic deformation ceramics, 5 624 heated coals, 6 733-736 of steel, 23 271... 

Polymer that, after heating and being subjected to a plastic deformation, resumes its original shape when heated above its glass-transition or melting temperature. 

Impurities, such as grit, shreds of cotton, even in small quantities, sensitize an expl to frictional impact. That is why utmost cleanliness must be exercised in the preparation of expls. There are differences in the sensitivity of azides to mechanical and thermal influences. They have been correlated with the structure of the outer electronic orbits, the electrochemical potential, the ionization energy and the arrangement of atoms within the crystal. Functions of the polarizability of the cation are the plastic deformability of the crystals, and their surface properties. The nature of cation in an azide, such as Pb(Nj)2, has little effect on the energy released by the decomposition, which is vested in the N ion. The high heat of formation of the N2 molecule accounts... 

Recrystallization occurs when a crystalline material is plastically deformed at a relatively low temperature and then heated [1]. The as-deformed material possesses excess bulk free energy resulting from a high density of dislocations and point-defect debris produced by the plastic... 

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