Deformation behaviour, and

The transition of the polymer from the rubbery to the glassy state principally changes the deformation behaviour and mechanical response of the material. The dominant role of intermolecular forces in the glassy state of polymer fully suppresses the effect of the conformational elasticity of network chains, at least at low strains. 

It is postulated that the morphology of ABA type block copolymers with 20 % or more polyol is that of a continuous rubber network extending through a nylon phase, the deformation behaviour and ultimate strength being determined by the rubber phase. Improvement of impact strength is due to shear flow. 

The wear of fine monofilaments when they slide over one another has important practical consequences in the deformation behaviour and the durability of fibrous assemblies. The frictional forces at the internal micro-contacts provide the local restraints which generate the cohesive response of the assembly. The flexibility of ropes and the tactile properties of fabrics are in many respects governed by these local forces. The frictional work produces surface damage and wear hence the macroscopic response of an assembly is modified by deformation. Ultimately the damage is sufficient to undermine the strength of the fibres and the assembly strength is weakened. 

Mechanical Properties, Deformation Behaviour, and Rock Stress... 

On the basis on the carried out structural investigations of amorphous PET fibers simultaneous heat - mechanically modified at isothermal conditions and constant strain stress values it can be make the following conclusions The mechanical strain force applied simultaneously with the linear heating of the studied PET yarns affects significantly the deformation behaviour and samples crystallization kinetics. Moreover in contrast to the results obtained in the first experiment, all of the so treated specimens are partially crystaUine. The role of the tensile stress in the adjustment of the interacting processes of the fluid like deformation and stress-induced crystallization clearly reveals in the ultimate samples deformation. At stress values from 1.56 MPa to 2.16 MPa predominates the fluid like fibers extension, while the further stress increasing leads to the earlier crystallization start and thereby to decrease of the final fibers length. 

Predictions based solely on intermolecular forces do not always agree with experiment, and other factors such as deformation behaviour and wetting must be considered. The amorphous fraction of polymers used for adhesion is free to conform to the structure of the substrate [33]. 

According to the definitions given in Fig. 21.7, the influence of phase angle deviations with respect to the reference out-of-phase cycle (180° T-eme-phasing) on the TMF cyclic deformation behaviour and lifetime was investigated. 

Optimise the shape and size of a device to achieve required deformation behaviour and... 

Ariyama, T Cyclic deformation behaviour and morphology of polypropylene. J. Mater. Sci. 28, 3845-3850 (1993)... 

Pal] Palm, M., SauthofF, G., Deformation Behaviour and Oxidation Resistance of Single-phase and Two-phase T2i-Ordered Fe-Al-Ti Alloys , Intermetallics, 12, 1245-1259 (2004) (Experimental, Meehan. Prop., 89)... 

The application of load in materials produces internal modifications such as crack growth, local plastic deformation, corrosion and phase changes, which are accompanied by the emission of acoustic waves in materials. These waves therefore contain information on the internal behaviour of the material and can be analysed to obtain this information. The waves are detected by the use of suitable sensors, that converts the surface movements of the material into electric signal. These signals are processed, analysed and recorded by an appropriate instrumentation. 

A constitutive equation is a relation between the extra stress (t) and the rate of deformation that a fluid experiences as it flows. Therefore, theoretically, the constitutive equation of a fluid characterises its macroscopic deformation behaviour under different flow conditions. It is reasonable to assume that the macroscopic behaviour of a fluid mainly depends on its microscopic structure. However, it is extremely difficult, if not impossible, to establish exact quantitative... 

Whether or not a polymer is rubbery or glass-like depends on the relative values of t and v. If t is much less than v, the orientation time, then in the time available little deformation occurs and the rubber behaves like a solid. This is the case in tests normally carried out with a material such as polystyrene at room temperature where the orientation time has a large value, much greater than the usual time scale of an experiment. On the other hand if t is much greater than there will be time for deformation and the material will be rubbery, as is normally the case with tests carried out on natural rubber at room temperature. It is, however, vital to note the dependence on the time scale of the experiment. Thus a material which shows rubbery behaviour in normal tensile tests could appear to be quite stiff if it were subjected to very high frequency vibrational stresses. 

It is somewhat difficult conceptually to explain the recoverable high elasticity of these materials in terms of flexible polymer chains cross-linked into an open network structure as commonly envisaged for conventionally vulcanised rubbers. It is probably better to consider the deformation behaviour on a macro, rather than molecular, scale. One such model would envisage a three-dimensional mesh of polypropylene with elastomeric domains embedded within. On application of a stress both the open network of the hard phase and the elastomeric domains will be capable of deformation. On release of the stress, the cross-linked rubbery domains will try to recover their original shape and hence result in recovery from deformation of the blended object. 

Yamaguchi, M. and Umakoshi, Y. (1990) The deformation behaviour of intermetallic superlattice compounds. Prog. Mater. Sci. 34, 1. 

For most traditional materials, the objective of the design method is to determine stress values which will not cause fracture. However, for plastics it is more likely that excessive deformation will be the limiting factor in the selection of working stresses. Therefore this chapter looks specifically at the deformation behaviour of plastics and fracture will be treated separately in the next chapter. 

These latter curves are particularly important when they are obtained experimentally because they are less time consuming and require less specimen preparation than creep curves. Isochronous graphs at several time intervals can also be used to build up creep curves and indicate areas where the main experimental creep programme could be most profitably concentrated. They are also popular as evaluations of deformational behaviour because the data presentation is similar to the conventional tensile test data referred to in Section 2.3. It is interesting to note that the isochronous test method only differs from that of a conventional incremental loading tensile test in that (a) the presence of creep is recognised, and (b) the memory which the material has for its stress history is accounted for by the recovery periods. 

At room temperature, NiAl deforms almost exclusively by (100) dislocations [4, 9, 10] and the availability of only 3 independent slip systems is thought to be responsible for the limited ductility of polycrystalline NiAl. Only when single crystals are compressed along the (100) direction ( hard orientation), secondary (111) dislocations can be activated [3, 5]. Their mobility appears to be limited by the screw orientation [5] and yield stresses as high as 2 GPa are reported below 50K [5]. However, (110) dislocations are responsible for the increased plasticity in hard oriented crystals above 600K [3, 7]. The competition between (111) and (110) dislocations as secondary slip systems therefore appears to be one of the key issues to explain the observed deformation behaviour of NiAl. 

D.R. Pank, M.V. Nathal, D.A. Koss. Deformation behaviour of NiAl-based alloys containing iron, cobalt and hafnium, in High Temperature Ordered Intermetallic Alloys V, 1. Baker, R.Darolia, J.D.Whittenberger, Man H. Yoo, ed., MRS, (1993), Vol. 288... 

Fig.l. Prediction of the deformation behaviour of the material where three different processes may be rate and stress- controlled dashed line) ... 

Pakula T., Saijo K., Kawai H., and Hashimoto T. Deformation behaviour of styrene butadiene styrene triblock copolymer with cyhndrical morphology, Macromo/ecu/er, 18, 1294, 1985. 

Apostolov A.A. and Fakirov S., Effect of the length on the deformation behaviour of polyetheresters as revealed by smah angle x-ray scattering, J. Macromol. Set, Phys. B, 31, 329, 1992. 

Fakirov S, Fakirov C, Fischer EW, and Stamm M. Deformation behaviour of poly(ether ester) thermoplastic elastomers as revealed by SAXS. Polymer, 1991, 32, 1173-1180. 

Mechanical properties per se concerns with the qualities which determine the behaviour of a material towards applied forces. The ability to support weight without rupture or permanent deformation, to withstand impact without breaking, to be mechanically formed into different shapes - all these depend upon a combination of mechanical properties characteristic of metals. Four types of behaviour of a material under stress are very important linear or elastic behaviour, plastic behaviour, creep behaviour and fatigue behaviour. 

In contrast to the behaviour of a solid, for a normal fluid the shear stress is independent of the magnitude of the deformation but depends on the rate of change of the deformation. Gases and many liquids exhibit a simple linear relationship between the shear stress r and the rate of shearing ... 

The function iKt-t ) may be interpreted as a memory function having a form as shown in Figure 3.14. For an elastic solid, iff has the value unity at all times, while for a purely viscous liquid iff has the value unity at thfe current time but zero at all other times. Thus, a solid behaves as if it remembers the whole of its deformation history, while a purely viscous liquid responds only to its instantaneous deformation rate and is uninfluenced by its history. The viscoelastic fluid is intermediate, behaving as if it had a memory that fades exponentially with time. The purely elastic solid and the purely viscous fluid are just extreme cases of viscoelastic behaviour. 

Lauke B. and Schultrich B, (1983). Deformation behaviour of short fiber reinforced materials with debonding interfaces. Fiber Sci. Technol. 19, 111-126. 

The terms are arranged into sections dealing with basic definitions of stress and strain, deformations used experimentally, stresses observed experimentally, quantities relating stress and deformation, linear viscoelastic behaviour, and oscillatory deformations and stresses used experimentally for solids. The terms which have been selected are those met in the conventional mechanical characterization of polymeric materials. 

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