Mechanical behaviour deformation

The intermetallic alloy NiAl is discussed as a potential base alloy for high temperature structural materials. Its use is currently limited by low room temperature ductility and fracture toughness. Consequently, substantial research efforts have been directed towards understanding its mechanical behaviour [1, 2] so that detailed experimental [3, 4, 5] and theoretical [6, 7, 8] analyses of the deformation of NiAl are available today. 

One of the aims of the present research at Leeds University, of which the spectroscopic studies form a major part, has been to gain an understanding of mechanical behaviour. Both the uniaxially oriented and the biaxially oriented materials discussed in this review have also been the subject of studies of mechanical anisotropy and deformation. It is therefore of some interest to indicate the key guidelines which are emerging from these related studies. 

Before analysing the mechanical behaviour of amorphous polymers, it is useful to briefly give information on their molecular characteristics, the main descriptors used for plastic deformation and fracture, the micromechanisms of deformation, and some of the experimental procedures. 

For these reasons, PMMA and its maleimide and glutarimide copolymers represent very suitable materials for investigating the effect of the chemical structure and of the solid state molecular motions on the plastic deformation, the occurrence of the various micro-mechanisms of deformation (chain scission crazes, shear deformation zones, chain disentanglement crazes), as well as the fracture behaviour. 

Basic mechanical behaviours, such as plastic deformation, deformation micromechanisms, and fracture, are successively presented. The characteristics of the studied polymers are gathered in Table 7. 

The main subject of the following discussion is the mechanical behaviour of networks in terms of the behaviour of the system of weakly coupled macromolecules. The network modulus of elasticity is small in comparison to the values of the elasticity modulus for low-molecular solids (Dusek and Prins 1969 Treloar 1958). Nevertheless, large (up to 1000%) recoverable deformations of the networks chains are possible. 

In Ref. 26 34) the mechanical behaviour of several epoxy-aromatic amine networks was analyzed in the rubbery state at temperatures of about T + 40 °C. Figure 14 gives some experimental results. If the rubber elasticity theory is obeyed, the following relation holds for uniaxial deformation ... 

The mechanical properties of polymers are of interest, in particular in all applications where polymers are used as structural materials. Mechanical behaviour involves the deformation of a material under the influence of applied forces. 

In the same way as the mechanical behaviour of solid polymers can be described in terms of moduli (ratios of stress and deformation), the flow behaviour of polymer melts can be characterised by viscosities (ratios of stress and rate of deformation). 

As in the elastic-mechanical behaviour of solid polymers, so in the flow behaviour of polymer melts the mode of deformation determines the nature of the characteristic property, in this case the viscosity. 

Kekulawala, K. R. S. S., Paterson, M. S., Boland, J. N. (1981). An experimental study of the role of water in quartz deformation. In Mechanical Behaviour of Crustal Rocks, The Handin Volume, Geophysical Monograph 24, edited by N. L. Carter, M. Friedman, J. M. Logan, D. W. Stearns, pp. 49-60. Washington, DC American Geophysical Union. 

Peach, C.J. 1993. Deformation, dilatancy and permeability development in halite/anhydrite composities. Preliminary Proc. 3rd Conf Mechanical Behaviour of Salt, Paliseau, France, pp. 139-152. 

The mechanical behaviour of oxide scales has been investigated by a complex of appropriate techniques (cf. for example [12]), where the attention has been focused on the analysis of the stress development in the scale, as well as the measurement of the scale adherence. In the case of weak scale adherence, spontaneous scale failure is often observed during oxidation or cooling of specimens. For systematic investigations of the fracture-mechanical properties of oxide scales, scale failure is induced by a controlled loading of the scale which is produced by an appropriate deformation of the whole specimen. 

In this particular case, a special attention was devoted to the coupling between the thermal and the hydraulic problems. In fact, a simple linear elastic model was assumed for the mechanical behaviour, although a coupling between intrinsic permeability and void ratio (and therefore volumetric deformation) has been considered. 

The creep compliance of rocks reflects their deformability whereas the cohesion reflects their strength. In Section 1, the expressions are derived for the time-temperature equivalence for rocks and the testing results obtained in Sections 2 and 3 have shown clearly that not only the deformability of the TGP granite rock but also its strength follow the time-temperature equivalent principle. The establishment of shift factor eq. (25) and the determination of its parameters make it possible to predict correctly the long-term mechanical response of rock at lower temperatures according to its short-term mechanical behaviour at higher temperatures. 

This numerical tool may be used for simulations of oil reservoir chalk in order to reproduce the compaction during water injection. The computations presented here correspond to a hypothetical reservoir. The results show that the model is able to reproduce the compaction during production phase. These deformations are related to an increase of effective stress. During injection phase, an additional compaction is predicted. Even if the reservoir pressure increases, the suction decrease leads to compressive deformations. Suction is a pertinent mechanism to explain the mechanical behaviour of chalk. 

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