Thermoplastic stress-strain diagram

Figure 15.4 gives the stress-strain diagrams for a typical fiber, plastic, and elastomer and the average properties for each. The approximate relative area under the curve is fiber, 1 elastomers, 15 thermoplastics, 150. Coatings and adhesives, the two other types of end-uses for polymers, will vary considerably in their tensile properties, but many have moduli generally between elastomers and plastics. They must have some elongation and are usually of low crystallinity. 

Quasi-static tensile test - tensile properties without yield point - data Polymer Solids and Polymer Melts C. Bierdgel, W. Grellmann The following Table 4.2 shows a summary of available tensile properties of thermoplastics according to stress-strain diagrams of type a and d ( Fig. 4.3). Table 4.2 Tensile properties of thermoplastics without yield point. ... 

Fig. 8.12. Stress-strain diagrams of an amorphous thermoplastic at different temperatures [9]...

Rgure 1.16 Stress-strain diagrams of a thermoplastic material as a function of testing speed (loading rate) and testing temperature T... 

In the diagram, load per unit cross section (stress) is plotted against deformation expressed as a fraction of the original dimension (strain). Even for different materials the nature of the curves will be similar, but they will differ in (1) the numerical values obtained and (2) how far the course of the typical curve is followed before failure occurs. Cellulose acetate and many other thermoplastics may follow the typical curve for almost its entire course. Thermosets like phenolics, on the other hand, have cross-Knked molecules, and only a limited amount of intermolecular shppage can occur. As a result, they undergo fracture at low strains, and the stress-strain curve is followed no further than to some point below the knee, such as point 1. 

Figure 11-14. Schematic representation of the tensile stress aw as a function of strain e at constant temperature for an elastomer E, a partially crystalline thermoplast T, and a hard-elastic thermoplast HT. The ductile region is la-II-III. The necking effect shown below the diagram is typical of normal thermoplasts, but does not occur with elastomers or hard-elastic thermpolasts. The diagram is not drawn to scale for example, elastomers show a much larger elongation at break than do thermoplasts.

During the test, the load (F)- longation (AL) diagram up to the break of specimen is recorded necessary to calculate the stress ((T)-strain (s) diagram (Fig. 4.3) using the geometric conditions of specimen Aq and equipment L or Lq (Eqs. 4.1-4.3). Modem universal testing systems equipped with computer techniques are able to record stress a, time t and strains s and 8t simultaneously. For the determination of modulus of elasticity a strain rate of 1 %/min is applied and 50 mm/min are mostly used to characterize the tensile properties of thermoplastics. 

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