Testing stress-strain curves

Pieces of the compression-moulded sheets were pressed into dogbone-shaped specimens of thickness 1.7 mm and a gauge width of 15 mm for the tensile tests. Stress-strain curves were obtained at room temperature with a Zwick tensile tester at a strain rate of 0.0001 s. The samples were strained up to 3.6% strain and the strain was measured with an extensometer with a gauge length of 50 mm. The tensile tests were done only on the composites with 50 vol% glass beads, with different amounts of the silane. 

O3, h). .. etc. from this family of curves, which form the relaxation curve. Furthermore, by determining the stress which belongs to a specified strain in the relaxation test after a long test time, one can experimentally verify the only calculated tensile test stress-strain-curves for very small deformation rates. The isochronous stress-strain diagram also directly indicates the non-linearity of the visco-elastic behaviour otherwise the curves would be straight lines. 

Fig. 1. Stress—strain curves for ionomer and polyethylene resins. Test speed is 5 cm/min. The reference matedal is high molecular weight conventional...

Gray and Follansbee [44] quasi-statically tested OFE copper samples that had been shock loaded to 10 GPa and pulse durations of 0.1 fis, 1 /rs, and 2 fus. The quasi-static stress-strain curves are shown in Fig. 7.10 with the response of annealed starting copper included for comparison. The yield strength of shock-loaded copper is observed to increase with pulse duration, as the work-hardening rate is seen to systematically decrease. 

Corrosion effect of forming Elongation X gauge length Standard hydropress specimen test True stress-strain curve Uniformity of characteristics... 

J7 In a tensile test on a plastic, the material is subjected to a constant strain rate of 10 s. If this material may have its behaviour modelled by a Maxwell element with the elastic component f = 20 GN/m and the viscous element t) = 1000 GNs/m, then derive an expression for the stress in the material at any instant. Plot the stress-strain curve which would be predicted by this equation for strains up to 0.1% and calculate the initial tangent modulus and 0.1% secant modulus from this graph. 

Most simple materia characterization tests are perfomned with a known load or stress. The resulting displacement or strain is then measured. The engineering constants are generally the slope of a stress-strain curve (e.g., E = o/e) or the slope of a strain-strain curve (e.g., v = -ey/ej5 for Ox = a and all other stresses are zero). Thus, the components of the compliance (Sy) matrix are determined more directly than those of the stiffness (Cy) matrix. For an orthotropic material, the compliance matrix components in terms of the engineering constants are... 

The mechanical properties were obtained using a tensile machine at room temperature and for a strain rate of 1000%/h. Each reported value of the modulus was an average of five tests. The tensile modulus Et was taken as the slope of the initial straight line portion of the stress-strain curve. 

The presence of hydrogen in pre-exposed specimens was revealed by straining specimens in vacuo. Hydrogen evolution occurred in the elastic region of the stress/strain curve, an effect that had been shown to be very much reduced by electropolishing pre-exposed specimens prior to testing... 

One of the most informative properties of any material is their mechanical behavior specifically the determination of its stress-strain curve in tension (ASTM D 638). This is usually accomplished in a testing machine by measuring continuously the elongation (strain) in a test sample as it is stretched by an... 

Real differences between the tensile and the compressive yield stresses of a material may cause the stress distribution within the test specimen to become very asymmetric at high strain levels. This cause the neutral axis to move from the center of the specimen toward the surface which is in compression. This effect, along with specimen anisotropy due to processing, may cause the shape of the stress-strain curve obtained in flexure to dif-... 

Even plastics with fairly linear stress-strain curves to failure, for example short-fiber reinforced TSs (RPs), usually display moduli of rupture values that are higher than the tensile strength obtained in uniaxial tests wood behaves much the same. Qualitatively, this can be explained from statistically considering flaws and fractures and the fracture energy available in flexural samples under a constant rate of deflection as compared to tensile samples under the same load conditions. These differences become less as the... 

Designers unfamiliar with plastic products can use the suggested preliminary safety factor guidelines in Table 2-11. They provide for extreme safety. Any product designed with these guidelines in mind should conduct tests on the products themselves to relate the guidelines to actual performance (Chapter 4, RP PIPES, Stress-Strain Curves). With more experience, more-appropriate values will be developed targeting to use 1.5 to 2.5. After field service of... 

It should be recognized that tensile properties would most likely vary with a change of speed of the pulling jaws and with variation in the atmospheric conditions. Figure 2-14 shows the variation in a stress-strain curve when the speed of testing is altered also shown are the effects of temperature changes on the stress-strain curves. When the speed of pulling force is increased, the material reacts like brittle material when the temperature is increased, the material reacts like ductile material. 

The important tensile modulus (modulus of elasticity) is another property derived from the stress-strain curve. The speed of testing, unless otherwise indicated is 0.2 in./min, with the exception of molded or laminated TS materials in which the speed is 0.05 in./min. The tensile modulus is the ratio of stress to corresponding strain below the proportional limit of a material and is expressed in psi (pounds per square inch) or MPa (mega-Pascal) (Fig. 2-7). 

If product use conditions vary appreciably from those of the standard test, a stress-strain curve, derived using the procedure of anticipated requirement, should be requested and appropriate data developed. 

The test can provide compressive stress, compressive yield, and modulus. Many plastics do not show a true compressive modulus of elasticity. When loaded in compression, they display a deformation, but show almost no elastic portion on a stress-strain curve those types of materials should be compressed with light loads. The data are derived in the same manner as in the tensile test. Compression test specimen usually requires careful edge loading of the test specimens otherwise the edges tend to flour/spread out resulting in inacturate test result readings (2-19). 

Test results provides the hypothesis that syntactic foam is rate insensitive and that the static uniaxial strain stress-strain curve actually represents the general constitutive relation. Disagreement between the experimental data and the predicted behavior is greatest at low stresses (1 kbar) where experimental stresses are about double those predicted analytically. The discrepancy decreases at the higher stress levels and virtually disappears at and beyond 7 kbar. This range... 

Extensometer An extensometer is an instrument to monitor strain in the linear dimension of a test specimen while a load or force is applied to it. The automatic plotting of load with strain produces stress-strain curves. 

Fig. 6.2. Yield strengths from tensile tests at 23 °C are plotted against the glass transition temperatures (T,max) of the five polymers [] result of extrapolated stress-strain-curve...

Flexural modulus is the force required to deform a material in the elastic bending region. It is essentially a way to characterize stiffness. Urethane elastomers and rigid foams are usually tested in flexural mode via three-point bending and tite flexural (or flex ) modulus is obtained from the initial, linear portion of the resultant stress-strain curve. 

---