Deformation—time curves

Figure 9.8. Deformation-time curves, (a) Material showing substantial ordinary elastic, high elastic and viscous components of deformation, (b) Material in which high elastic deformation...

Figure 3.7 shows schematically the above types of deformational response as a result of a fixed stress imposed on a body showing ordinary elastic deformation only (Figure 3.7b), a second body showing high elastic deformation only (Figure 3.7c), and a third body showing viscous deformation only (Figure 3.7d). In each case, the stress is imposed at time to and held at a constant value until time ti, when it is removed. Real polymers exhibit deformation-time curves which are a combination of the three basic responses, and a simple relationship for a combined or total strain e...

Long-term deformation such as shown by creep curves and/or the derived isochronous stress-strain and isometric stress-time curves, and also by studies of recovery for deformation. 

As a plastic is subjected to a fixed stress or strain, the deformation versus time curve will show an initial rapid deformation followed by a continuous action. Examples of the standard type tests are included in Fig. 2-1. Details on using these type specimens under static and dynamic loads will be reviewed throughout this chapter. (Review also Fig. 8-9 that relates elasticity to strain under different conditions.)... 

Fig. 7 a and b. Scheme of the thermomechanical behaviour of a well phase-separated thermoelasto-plastic. Stress-strain (or time) curves. Plots of heat effects versus time. First loading (ABC) and unloading (CD) cycle. Second loading (AC) and unloading (CD) cycle. The yielding point occurs at B. AD indicates the residual deformation after the first cycle. AB on the dQ/dT-time curve is the endo-effect resulting from the initial small-strain deformation AB U9)... 

Hydrogenation of the Lu2Fei7 single crystal leads to a decrease of magnetostrictive deformations (see curve 7, Fig. 7). The experimentally obtained values of magnetostriction for the LuJenH] 5 hydride were three times less than that one in Lu2Fei7. 

In bodies showing retarded elasticity, the deformation is a function of time as well as stress. Such a stress-strain curve is shown in Figure 8-10. The upward part of the curve represents increasing values of stress when the stress is reduced, the corresponding strains are greater on the downward part of the curve. When the stress reaches 0, the strain has a finite value, which will slowly return to zero. There is no permanent deformation. The corresponding relaxation (stress-time) and creep (strain-time) curves... 

Vogel, P. J., and Schmidt, P. C. (1993), Force-time curves of a modern rotary tablet machine. Part 2. Influence of compression force and tableting speed of the deformation mechanisms of pharmaceutical substances, Drug Dev. Ind. Pharm., 19,1917-1930. 

Figures 1,2 show typical curves of shear stress versus deformation time of aminoplastic at 120 °C for different r.p.m. of the plastometer rotor, from 2 = 0.05 to 50 min (i.e. for shear rates from 1.4 x 10 to 1.5 x 10 s ).

The vane yield stress technique is a useful technique that applies small deformations in the initial stages and large deformations in the latter stages. From the initial linear portion of the torque-time curve at a low shear rate, for example, 0.01 s , the shear modulus (G) can be calculated as ... 

Figure 20.2. Effects of platelet orientation relative to the direction of deformation, predicted by using the model of Brune and Bicerano [11]. The orientation angle is defined as the angle between the symmetry axis of the platelets and the direction of deformation, so that it is 90° if the platelets are aligned perfectly along the direction of deformation while it is 0° if the platelets are aligned completely perpendicular to the direction of deformation. The curves are labeled by the platelet aspect ratio Af. The platelet volume fraction was =0.025, the platelets were assumed to have a Young s modulus of 100 times that of the matrix, and a Poisson s ratio of 0.4 was assumed for both the matrix polymer and the platelets in these calculations.

Fig. 22.9 Relaxation of the fibrils in a probe test for the SIS adhesive, (a) Force vs. time curves for consecutive tests where the displacement was stopped at various levels of deformation of the fibrils, and left to relax for 120 s. (b) Relaxation curves for different stops, normalized by the stress at the beginning of the stop.

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