Tensile stress-strain behavior

The effect of temperature on PSF tensile stress—strain behavior is depicted in Figure 4. The resin continues to exhibit useful mechanical properties at temperatures up to 160°C under prolonged or repeated thermal exposure. PES and PPSF extend this temperature limit to about 180°C. The dependence of flexural moduli on temperature for polysulfones is shown in Figure 5 with comparison to other engineering thermoplastics. 

Brittleness Brittle materials exhibit tensile stress-strain behavior different from that illustrated in Fig. 2-13. Specimens of such materials fracture without appreciable material yielding. Thus, the tensile stress-strain curves of brittle materials often show relatively little deviation from the initial linearity, relatively low strain at failure, and no point of zero slope. Different materials may exhibit significantly different tensile stress-strain behavior when exposed to different factors such as the same temperature and strain rate or at different temperatures. Tensile stress-strain data obtained per ASTM for several plastics at room temperature are shown in Table 2-3. 

Test rate and property The test rate or cross-head rate is the speed at which the movable cross-member of a testing machine moves in relation to the fixed cross-member. The speed of such tests is typically reported in cm/min. (in./min.). An increase in strain rate typically results in an increase yield point and ultimate strength. Figure 2-14 provides examples of the different test rates and temperatures on basic tensile stress-strain behaviors of plastics where (a) is at different testing rates per ASTM D 638 for a polycarbonate, (b) is the effects of tensile test-... 

Better cross-linking with the latter also improves post Tg viscoelastic responses of the rubber vulcanizates. Similar effect has also been observed with polychloroprene as investigated by Sahoo and Bhowmick [41]. Figure 4.8 represents the comparative tensile stress-strain behavior of polychloroprene rubber (CR) vulcanizates, highlighting superiority of the nanosized ZnO over conventional rubber grade ZnO [41]. 

Figure 1. Cyclic tensile stress-strain behavior of the spin-cast specimens, TR-41-1647, TR-41-1648, and TR-41-1649, at 25°C at a constant rate of tensile train, 50% /min. The tensile stress is expressed in terms of true stress. The specimens were air dried...

Figure 2. Cyclic tensile stress-strain behavior of TR-41-1649 and its blend with polystyrene (M 20,400) at room temperature at a constant rate of tensile strain, 50%/min. Curves (1) and (2) refer to the first and second stretching half-cycles, respectively, and the tensile stress is expressed in terms of nominal stress (29).

Stress—Strain Curves. The tensile stress-strain behavior of the blends in which PC is the continuous phase (blends with 5, 10, 20, and 25 wt% PST) also has been investigated. Some preliminary results regarding the influence of composition, strain rate, and temperature on the yield and fracture behavior of these blends will be reported. 

Fig. 11-23. Tensile stress-strain behavior for a molded sample of a nylon-6,6 at the indicated temperatures (°C). The arrows indicate the yield points which become mote diffuse at higher temperatures.

The TEM micrographs in Figs. 16a-16c of the undeformed regions of the reconstituted films prepared for mechanical tests revealed that particles were well dispersed and did not coagulate with each other. This proved that HIPS particles of narrow size ranges can be separated from a matrix and put into another matrix without coagulation and without particle deformation or disruption. The tensile stress-strain behavior of these samples is shown in Figs. 17a-17d, while in Table 3 the principal parameters of these curws are summarized. 

Figure 3.39 Tensile stress-strain behavior of FEP (MFR 7) as a function of temperature. ...

Fig ure 3.50 Tensile stress-strain behavior of various grades (MFRs) of ETFE at room temperature. 

The distinction between plastics, fibers, and elastomers is most easily made in terms of the tensile stress-strain behavior of representative samples (Rudin, 1982). The curves shown in Fig. 1.17 are typical of those obtained in tension for a constant rate of loading. The parameters of each curve are normal stress (force applied on the specimen divided by the original cross-sectional area), nominal strain (increase in length divided by original length), and the modulus (slope of stress-strain curve). The slope of the curve near zero strain gives the initial modulus. 

The low-speed mechanical properties of polymer blends have been frequently used to discriminate between different formulations or methods of preparation. These tests have been often described in the literature. Examples of the results can be found in the references listed in Table 12.9. Measurements of tensile stress-strain behavior of polymer blends is essential [Borders et al., 1946 Satake, 1970 Holden et al., 1969 Charrier and Ranchouse, 1971]. The mbber-modified polymer absorbs considerably more energy, thus higher extension to break can be achieved. By contrast, an addition of rigid resin to ductile polymer enhances the modulus and the heat deflection temperature. These effects are best determined measuring the stress-strain dependence. 

MECHANICAL BEHAVIOR 7.1. Tensile stress-strain behavior... 

FIGURE 2. Typical tensile stress-strain behaviors measured on 2-D SiC/SiC composites possessing PyC based interphases and fabricated from untreated ortreated Nicalon (ceramic grade) fibers (a) strong fiber/coating interfaces... 

Tensile stress-strain behavior in bber direction of as-fabiicated CMC at 20°C and upper use tempoatoie in air... 

FIGURE 14. Room temperature tensile stress-strain behavior for 1-D and 2-D HP SiC/ SiaNa composites con-taming 30 vol% SiC monofilaments [31]. 

The room temperature tensile stress strain behaviors of 1 -D and 2-D SiC/Si3N4 monofilament composites showed high matrix cracking stress, but strain capability beyond matrix fracture is limited. Limited fiber pull out was observed on the tensile fracture surfaces [31]. 

Figure 2.3 Schematic representations of tensile stress-strain behavior for brittle and ductile materials loaded to fracture.

Fig. 8. Effects on tensile stress-strain behavior of prior creep at (a) 1000 °C, (b) 1100 °C and (c)...

F. Li and R. C. Larock, New soybean oil-styrene-divinylbenzene thermosetting copolymers III Tensile stress-strain behavior , / Polym Sci Part B Polym Phys, 2001,39, 60-77. 

Figure 4.116 Influence of temperature on tensile stress-strain behavior of Celanese Vectra B230 LCP [9].

The design of plastic parts requires the avoidance of failure without overdesign of the part, leading to increased part weight. The type of failure can depend on temperatures, rates, and materials. Some information on material strength can be obtained from simple tensile stress-strain behavior. Materials that fail at rather low elongations (1 percent strain or less) can be considered to have undergone brittle failure." Polymers that produce this type of... 

Fig. 7.40 Tensile stress-strain behavior, the cyclic curves are for a stress ratio, R of 0.1 and a frequency of 0.1 Hz at room temperature, a The submicron sized 3Y-TZP ceramics (0.35 pm) showing cyclic hardening, b the nanocrystalline 3Y-TZP ceramics (100 nm) showing cyclic softening [37]. With kind permission of John Wiley and Sons...

In addition to offering resistance to degradation at high temperatures, polysulfones maintain their mechanical properties at high temperatures without reinforcement. The effect of temperature on PSF tensile stress-strain behavior is shown in Fig. 13.2. It can be seen that the retention of useful properties extends to approximately 150°C for PSF. This useful temperature range approaches 180°C for PES and PPSF... 

Mechanical Properties. The tensile stress-strain behavior of ethylene-co-styrene polymers, including the effects of crystallinity and molecular weight, has been extensively reported and analyzed. Figure 5 presents tensile stress-strain data for a series of copolymers differing primarily in styrene content. The copolymers generally exhibit large strain at ruptiu e, and have been foimd to show uniform deformation behavior (46). 

Fig. 20. Typical uniaxial tensile stress-strain behavior of PS, medium-impact PS (MIPS), high-impact PS (HIPS), and ABS (30). To convert MPa to psi, multiply by 145. Courtesy of Springer-Verlag.

Fig. 21. Uniaxial tensile stress-strain behavior of HIPS/PS/PXE blends at 20°C showing the effects of matrix composition. Strain rate 4 x 10 s (29). To convert MN/m to psi, multiply by 145. Courtesy of Applied Science Publisher Ltd.

Attempts to improve the mechanical properties have focused on biocompatible plasticizers. Blending with PEG, the conventional name for low molecular weight (<20 000) PEG, improves elongation at break and softness of PLA. At ambient temperature, the desired mechanical properties are achieved by blending PLA with 30 wt% PEG Table 4.2 shows the effect of PEG content on the thermal and mechanical properties of quenched PLA/PEG blends. However, there is evidence that the blend is not stable and the attractive mechanical properties are lost over time. The dynamic mechanical relaxation behavior and tensile stress-strain behavior of PLA and PLA/PEG blends are shown in Figs. 4.19 and Fig. 4.20 respectively. 

Figure 4.20 Tensile stress-strain behavior of quenched PLA and PLA/PEG blends at ambient temperature. The insert shows the modulus and yielding regions on an expanded strain scale...

Figure 3.6 Tensile stress-strain behavior of ductile plastics...

Figure 7. True tensile stress strain behavior (strain gauge technique) of unpoled and poled depoled PSZT at room temperature.

The tensile stress-strain behavior of these copolymers measured at 23°C was also reported by the Dow scientists [56,57]. Copolymers exhibit a lower modulus as styrene content is increased over the range of 20-60 wt% styrene. The copolymer with 60 wt% styrene was highly elastic. 

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