Tensile extension

In view of the development of the continuous chain model for the tensile deformation of polymer fibres, we consider the assumptions on which the Coleman model is based as too simple. For example, we have shown that the resolved shear stress governs the tensile deformation of the fibre, and that the initial orientation distribution of the chains is the most important structural characteristic determining the tensile extension below the glass transition temperature. These elements have to be incorporated in a new model. 

PP bead foams were subjected to oblique impacts (167), in which the material was compressed and sheared. This strain combination could occur when a cycle helmet hit a road surface. The results were compared with simple shear tests at low strain rates and to uniaxial compressive tests at impact strain rates. The observed shear hardening was greatest when there was no imposed density increase and practically zero when the angle of impact was less than 15 degrees. The shear hardening appeared to be a unique function of the main tensile extension ratio and was a polymer contribution, whereas the volumetric hardening was due to the isothermal compression of the cell gas. Eoam material models for FEA needed to be reformulated to consider the physics of the hardening mechanisms, so their... 

U Zero stress limit of activation energy for molecular chain scission Y(X) True tensile plastic resistance of homopolymer at a tensile extension ratio of A, Y Athermal plastic resistance of homopolymer with sorbed PB Yq Athermal plastic resistance of pure homopolymer a Craze half length... 

Cyclic tests provide the best representation of the conditions to which sealants are subjected in practice. They are very complex tests, however, and can be designed satisfactorily only if the material properties are well known from the results of tests using simpler loading patterns and if the rates are related to those of actual joints. Tensile extension at constant rate, stress relaxation under constant strain, and creep under constant stress are three of the simpler tests used to obtain the material properties of polymers. Tensile extension is not the simplest of the three tests (of the four basic variables only temperature can be kept constant), but it has been chosen because it is this type of loading that occurs in the sealant in a joint when the chance of failure is most probable. There is less likelihood of failure when the sealant is compressed in summer than when it is extended in winter. In addition, the tensile test is the least time-consuming and most laboratories are equipped for it. 

Three-Dimensional Representation. Whatever the configuration of the specimen, an infinite number of tensile curves can be obtained by changing either temperature or tensile extension rate. Figure 2, for one-part chemically curved silicone, and Figure 3, for two-part polysulfide model specimens, show a few examples that are obtained by varying the test conditions. The question arises, which of the tensile curves defines the mechanical properties of a sealant unambiguously ... 

For a tensile extension ratio A, with extension ratios 1/(A) in the lateral directions, the angle 9 in the deformed material is related to the value in the... 

Figure 3.33 (a) Predicted crystal orientation function vs. tensile extension ratio, from the pseudo-... 

The kinematics of the craze-induced plasticity is viewed, as shown in the sketch of Fig. 13.25, as a set of parallel crazes perpendicular to the tensile extension direction at an average spacing of Lq, thickening at a rate of S, the time rate of increase of craze thickness. The resulting average plastic-craze strain rate is... 

A plastic material is embrittled when its tensile extensibility falls below about 5%. A plastic degraded to this point falls apait on handling. 

Tensile extensibility is a particularly sensitive measure of the extent of weathering. Alternatively, the development of carbonyl functionalities (>C=0) or other spectral changes in samples determined in Fourier Transform Infra-Red Spectroscopy, FTIR, might be used to assess degradation, hi PE (Andrady et al., 1993b), the development of the carbonyl functionalities correlates well with the decrease in extensibility. Plastics such as PVC, PC, or PS (Ghaffar et al., 1976) turn yellow on photodegradation. Surface... 

FIGURE 10.1 Upper Change in percent original tensile extensibility of polypropylene laminate exposed in air and floating in seawater at a beach location Biscayne Bay, FL. Lower A floating rig used to expose plastics to surface water environment (in Miami Beach, FL). Reproduced with permission from Andrady and Pegram (1989b). 

Generally, the tensile extensibility of plastics dcCTcases exponentially with the time of exposure allowing the process to be modeled as follows. 

The physical movement of the fabric yarn may offer differential resistance depending upon the fabric properties such as cover factor, tensile extensibility, bending and shear rigidity, frictional hysteresis, thickness, and lateral compressibility. However, the extent of pucker would depend upon the amount of resistance to the yam offered by the fabric properties and the tension developed in the sewing thread. 

In conclusion, among all the sewing-thread properties discussed above, the one that is most significant from the seam pucker point of view is initial tensile modulus and tensile extension. 

Figure 6. Diagram showing the effect of tensile extension of a cylindrical bar. The change in the radius of the cylinder is used to determine the Poisson s ratio of the material.

Chen L, Zhang X, Li H Y, Li B, Wang K, Zhang Q and Fu Q (2011) Superior tensile extensibility of PETG/PC amorphous blends induced via uniaxial stretching, Chinese J Polym Sci 29 125-132. 

The tensile test is the most commonly performed test. Artifacts in measurement are seen because of deformation of material in the grip region. To overcome this problem, dogbone-shaped specimens are used. Truly accurate measurements, however, require the use of extensometers, localized displacement-measuring devices. Extensometers may be contact or noncontact. For design purposes, it is also of interest to measure the lateral contraction of the plastic in response to the applied tensile stress. The ratio of lateral contraction to tensile extension is termed Poisson s ratio. 

Nakajima et al. [101] studied the viscoelastic behavior of butadiene-acrylonitrile copol)rmer filled with carbon black. Capillary extrusion measurements with an Instron and dynamic oscillatory measurements with a Rheovibron suggested the occurrence of strain hardening in filled elastomer due to tensile extension causing structural changes in the carbon black filled elastomer. It is possible fliat the structure built by the carbon black in the elastomer increasingly jams against... 

Figure 11.17. TEM micrographs in the core region of an injection-molded polj=ainide 6/orgaiio-clay nauocoinposite (90/10) along a plane normal to the flow direction (a) before and (b) after subjected to a tensile extension of 60%. The preferred orientation of lamellae is seen even after delamination, pointed with arrows [116]...

The Doi-Edwards tube theory predicts the following damping function for tensile extension [24] ... 

FIGURE 10.8 Stress-strain data to break for two spandex fibers plotted according to Equation 9.93. Here a and a are the tensile extension ratio and stress, respectively. (Data from Higgins, T. D., Union Carbide Corporation, S. Charleston, private communication, 1969.)... 

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