Quasi-plasticity

LGMs of the AT/alumina and AT/ZTA displayed some very interesting properties which include excellent machinability, low thermal expansion coefficient, improved thermal shock resistance, low hardness (about 5 GPa), low Young s modulus (E) (250 GPa) and excellent flaw tolerance [Pratapa, 1997 Pratapa Low, 1998 Skala, 2000 Manurung, 2001], These materials appeared to display a large degree of near-surface quasi-plasticity under the Hertzian or the Vickers indenter which effectively inhibits the formation and propagation of cracks. The ductile behaviour of these materials was... 

A. C. Fischer-Cripps and B. R. Lawn, "Stress Analysis of Contact Deformation in Quasi-Plastic Ceramics", Journal of the American Ceramic Society, vol. 79, pp. 2609-2618, 1996. 

Zhigalkin V.M., Usoltseva O.M., Semyonov V.N., Tsoi P.A. 2005. Deformation of quasi-plastic salt rocks under different conditions of loading. Report I deformation of salt rocks under uniaxial compression. Journal of Mining Science Vol. 41, No 6, 507-515. 

The tests of the specimens under compressive load proved a considerable increase of bearing capacity due to fibres. The descending branch of the load-deformation curve is long and its shape is strongly related to the kind of fibres used. In the case of elastic fibres a quasi-linear behaviour is observed, but for ordinary polymeric fibres the elastic quasi-plastic behaviour should be expected. Thanks to the artificial cohesion, the reinforced sand is used for construction of walls and slopes with steep gradients between 60° and 90° also in various geotechnical works (Aldea 2007). 

It is generally assumed that in brittle cement matrices the plastic phenomena, similar to those in metals, do not appear. In fact, when in specimens subjected to loading, certain apparently plastic deformations are observed that is, an increase of deformation at a constant load, then this effect is caused by microcracks and therefore the term quasi-plasticity is used. 

The fracture mechanics equations derived by Griffith after his tests on glass specimens directly concern the brittle behaviour of materials and are certainly better justified for hardened cement paste than for any other cement-based composite. The general application of the fracture mechanics is therefore associated with the additional assumptions that plastic or quasi-plastic effects are negligible, or with appropriate modifications of the linear formulae in LEFM. In that context the linear and non-linear fracture mechanics approach should be distinguished. 

On the load-displacement plots for concrete and mortar specimens, a slight quasi-plastic effect in the form of inflections appeared (Figure 10.38). This phenomenon may be related to rearrangement of the aggregate grains, after which an additional energy supply was required for further crack propagation. It was not observed on the curves for paste specimens. 

The observed quasi-plasticity phenomenon in case o-f granite and basalt concretes, was mainly caused by cleavable character o-f splits o-f the gravel grains in -failuring process and also by arising o-f characteristic terraces with cle-fts. 

These concepts were quantified in a series of studies [44-48] aimed at identifying the conditions required to obtain strain hardening or quasi-plastic behaviour, which is manifested also as a steady-state cracking behaviour. The... 

A piezo-composite consists of a piezoelectric active phase and a passive plastic phase [2]. In the 1-3-configuration adopted in our case, piezoelectric rods parallely aligned in thickness direction are imbedded in a three-dimensional plastic matrix (Fig. 1). The distance between the rods has to be chosen inferior to the half wave length of the shear wave in the matrix material ensuring that the whole compound is vibrating as a quasi-homogeneous material. 

Atomistically detailed models account for all atoms. The force field contains additive contributions specified in tenns of bond lengtlis, bond angles, torsional angles and possible crosstenns. It also includes non-bonded contributions as tire sum of van der Waals interactions, often described by Lennard-Jones potentials, and Coulomb interactions. Atomistic simulations are successfully used to predict tire transport properties of small molecules in glassy polymers, to calculate elastic moduli and to study plastic defonnation and local motion in quasi-static simulations [fy7, ( ]. The atomistic models are also useful to interiDret scattering data [fyl] and NMR measurements [70] in tenns of local order. 

Here ij denotes a plastic deformation velocity. Adding the relations (1.10), (1.11), we obtain the quasi-static elastoplastic model... 

Here ij denotes a velocity of a plastic part of the curvature. This model is quasi-static, and it reduces to the equivalent inequality... 

Solvation—Desolvation Equilibrium. From the observation of migration of plasticizer from plasticized polymers it is clear that plasticizer molecules, or at least some of them, are not bound permanently to the polymer as iu an internally plasticized resia, but rather an exchange—equiHbrium mechanism is present. This implies that there is no stoichiometric relationship between polymer and plasticizer levels, although some quasi-stoichiometric relationships appear to exist (3,4). This idea is extended later ia the discussion of specific iateractions. 

For a given amplitude of the quasi-elastic release wave, the more the release wave approaches the ideal elastic-plastic response the greater the strength at pressure of the material. The lack of an ideally elastic-plastic release wave in copper appears to suggest a limited reversal component, however, this is much less than in the silicon bronze. Collectively, the differences in wave profiles between these two materials are consistent with a micro-structurally controlled Bauschinger component as supported by the shock-recovery results. Further study is required to quantify these findings and... 

P.S. Follansbee and G.T. Gray III, The Response of Single Crystal and Polycrystal Nickel to Quasi-Static and Shock Deformation, in Advances in Plasticity 1989 (edited by A.S. Khan and M. Tokuda), Pergamon Press, Oxford, 1989, pp. 385-388. 

We imagine a finite-duration shock pulse arriving at some point in the material. The strain as a function of time is shown as the upper diagram in Fig. 7.11 for elastic-perfectly-plastic response (solid line) and quasi-elastic response generally observed (dash-dot line). The maximum volume strain = 1 - PoIp is designated... 

Figure 7.11. Quasi-elastic release (dash-dot line) from shock-compressed state. Solid line represents elastic-perfectly-plastic response.

Three general test procedures used to measure the permeability of plastic films are the absolute pressure method, the isostatic method, and the quasi-isostatic method. The absolute pressure method (ASTM D 1434, Gas Transmission Rate of Plastic Film and Sheeting) is used when no gas other than the permeant in question is present. Between the two chambers a pressure differential provides the driving force for permeation. Here the change in pressure on the volume of the low-pressure chamber measures the permeation rate. 

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