Mechanical property measurement stress-temperature curves

Mechanical Properties. The stress-strain curves were determined with an Instron tensile tester (Table Model 1130). The crosshead speed was 50 mm/min. The measurements were performed on wet 1.3-cm X 0.4-cm dog bone samples at room temperature. 

In Chapter 18 is discussed the measurement of mechanical, electrical and optical properties of polymers. Mechanical measurements include measurement of load bearing characteristics of polymers including stress/strain curves, stress temperature curves, recovery and rupture. Also measurement of impact strength characteristics by Izod and falling weight methods and many other polymer characteristics for polymer sheet, pipe, film, powders and rubbers and elastomers. 

The isothermal curves of mechanical properties in Chap. 3 are actually master curves constructed on the basis of the principles described here. Note that the manipulations are formally similar to the superpositioning of isotherms for crystallization in Fig. 4.8b, except that the objective here is to connect rather than superimpose the segments. Figure 4.17 shows a set of stress relaxation moduli measured on polystyrene of molecular weight 1.83 X 10 . These moduli were measured over a relatively narrow range of readily accessible times and over the range of temperatures shown in Fig. 4.17. We shall leave as an assignment the construction of a master curve from these data (Problem 10). 

The phenomenological ordering of polymers projected for use as constructing materials is not an easy matter. Sometimes the temperature stability is used as a criterion, i.e., the temperature up to which the mechanical properties remain more or less constant. Another attempt for classification, uses the E modulus or the shape of the curve of stress-strain measurements (see Sect. 2.3.5.1). In general one can say that semicrystalline thermoplastics are stiff, tough, and impact-resistant while amorphous thermoplastics tend to be brittle. Their E... 

The properties of the Nicalon /SiC (PIP) system followed a similar pattern (A/c(ou) = 400°C, A rc(omc) = 500°C), though this system failed through an interlaminar shear failure process (delamination) and the property reduction saturated at A T= 600°C. The Nicalon /SiC (CVI) system failed by fracture through fibre planes but its properties (ou, omc, WOF) had the same critical temperature difference, A Tc = 700°C. The pre- and post-quench stress-displacement curves for this material can be seen in Fig. 15.9. However, measurement of the Young s modulus of this system before and after quenching by means of a dynamic mechanical resonance technique showed the onset of decrease at ATC(E) = 400°C, i.e. significantly lower than the A 7C of the other properties. 

The mechanical properties were evaluated by two sets of tensile measurements. Typical stress-strain curves are shown in Figure 4. The modulus and stress decrease with increasing aging time. Similar results are observed for all aging samples at all three temperatures. Both testing methods provided essentially the same tensile data at 400% extension. The scatter of the tensile data is due to the experimental error associated with the measurement. 

The most common type of stress-strain tests is that in which the response (strain) of a sample subjected to a force that increases with time, at constant rate, is measured. The shape of the stress-strain curves is used to define ductile and brittle behavior. Since the mechanical properties of polymers depend on both temperature and observation time, the shape of the stress-strain curves changes with the strain rate and temperature. Figure 14.1 illustrates different types of stress-strain curves. The curves for hard and brittle polymers (Fig. 14.1a) show that the stress increases more or less linearly with the strain. This behavior is characteristic of amorphous poly-... 

The most important mechanical property of a plastic is its tensile stress-strain curve (Figs. 10-1 and 7-4). This curve is obtained by stretching a sample in a testing machine and measuring its extension and the load required to reach this extension. Plastics show viscoelastic behavior (as reviewed in Chapter 1) that is highly sensitive to temperature and, in some materials, to relative humidity variations so it is important to use samples of standard shapes, preconditioned at constant and standard temperature and relative humidity before testing. Requirements are explained in the ASTM specifications. 

The experimental work was performed to provide both material property Input to the design model and experimental verlflcatiori of model predictions. To this end small scale and scaled up joints were fabricated to determine their mechanical behavior. Experiments included measurements of elastic constants and of stress-strain curves as a function of temperature, tensile strength, shear strength, and fracture toughness. Some experiments were also performed on specimens fabricated entirely of the interlayer materials. 

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). 

Perhaps it is more understandable if we correlate adhesive performance to viscoelastic properties determined at the adhesive testing temperature. The bond is formed and destroyed during testing using conditions which differ in stress level, deformation rate, and extent of deformation at room temperature. Therefore, the measurement of viscoelastic properties at room temperature may be pertinent. Viscoelastic properties at constant temperature are determined by dynamic mechanical measurement over a range of frequencies, for example, from 0.1 to 100 rad/sec. We see that the frequency scan curves are approximately a reciprocal... 

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