Strain-cycle diagram

The close relation between the composition and the mechanical properties of these polymers is reflected in the stress-strain diagrams measured at 300 K and 348 K (Figs. 47 and 48). Hence, at ambient temperature for the spedfied experimental conditions a distinct increase of initial modulus (11. 45 and 1 MNm ), stress-hysteresis (ratio of area bounded by a strain cycle to the total area underneath the elongation curve 60,80 and 90 %) and extension set (30,65 and 100 %) can be obsened with increasing hard segment content of polyester urethane (a) to (c). 

As an example, for room-temperature applications most metals can be considered to be truly elastic. When stresses beyond the yield point are permitted in the design, permanent deformation is considered to be a function only of applied load and can be determined directly from the stress-strain diagram. The behavior of most plastics is much more dependent on the time of application of the load, the past history of loading, the current and past temperature cycles, and the environmental conditions. Ignorance of these conditions has resulted in the appearance on the market of plastic products that were improperly designed. Fortunately, product performance has been greatly improved as the amount of technical information on the mechanical properties of plastics has increased in the past half century. More importantly, designers have become more familiar with the behavior of plastics rather than... 

Figure 8.26 Schematic diagrams to illustrate the permanent set mechanism during extension and retraction in the first cycle (a) before deformation, (b) during extension below the permanent set strain (about 1.0), (c) during extension at strains larger than the permanent set strain, and (d) during retraction to zero stress (reproduced from Reference (36) with permission from American Chemical Society.)...

A far lower strain of the cycle, positive charges on the carbonylic carbon atoms and higher orders of the corresponding bonds are characteristic of l, 8 -naphthoylene-1,2-benzimidazole, the molecular diagram of which is as follows [37, 39, 57, 58] ... 

Permanent structural changes that occur in a material subjected to fluctuating stress and strain, which cause decay of mechanical properties. See S-N diagram. The ability of a material to plastically deform before fracturing in constant strain amplitude and low-cycle fatigue tests. See S-N diagram. ... 

Notable features were the pronounced hysteresis, unrecovered strain and Mullins effect (whereby re-loading follows a stress-strain path closer to the unloading path than the original loading path). From curves such as these we calculated several quantifiers of the inelasticity. Consider the first cycle for material PU1, shown above. It defines three zones A, B and C in the stress-strain diagram. 

Fig. 4.11 Loading-unloading-reloading cycle for material PUl, with definitions of zones A, B, C of the diagram, maximum nominal strain and residual nominal strain Cr [69, 175]...

Every experiment consists of two parts, part 1 deals with the interaction between pattern and brain, and part 2 with the emotional self-assessment of each pattern. Fig. 11.8 shows a diagram of the slides used in the first part of the experiment, in which the brainwaves of every participant s response to each fabric were recorded. A preparation slide was first presented for 8 s then, a circle was shown with instructions of eye movements such as eyes close , eyes open and blink eyes , aiming at reducing eye strain during the experiment, followed by a grey screen between 2.5 and 3.5 s, which was set at the baseline period before presenting the actual fabric pattern stimulus for 11 s. This cycle was repeated four times. A 20 s break instruction followed on the screen, the circle then reappeared and this sequence was repeated... 

Fig. 23. Stress-strain diagram for a loading (1), unloading (2), and reloading (3) cycle of a PTMT film...

F%. 48a-c. Stress-strain diagrams of the loadin unloading cycles of the polyester urethanes a, b and c iiKasured at 348 K... 

Figure 2-47. Stress-strain diagram of an elongation-recovery cycle of the reference elastomer at 27 "C.

From typical diagrams of solicitation the following characteristics were determined the dynamical strain, 8 (%), in function of solicitation steps and number of cycles the force at which the relaxation is released, F, bellow 3 min the residual force, F, for any step of solicitation in the range from 0 to 3 min (cN/tex) for each step of solicitation in function on number of cycles. 

The chapter commences with a general overview of catalysis in the context of reaction coordinate diagrams and a simple thermodynamic cycle. Next, the most common factors invoked to explain transition state binding are explored differential solvation, proximity, nucleophilic and electrophilic activation, and strain. We also look at covalent catalysis, which fundamentally involves a mechanism change. 

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