Tensile force measurement, procedure

The tensile force and birefringence were simultaneously measured as functions of the strain. In brief, the samples were suspended vertically between two clamps the lower clamp was fixed, and the upper clamp was connected to a force transducer (Statham strain gauge). The output of the transducer was monitored by a Hewlett-Packard chart recorder (7, 8). Values of the birefringence An were determined by using a single-frequency He-Ne laser according to well-established procedures (2, 7, 8). Values were calculated directly from the sample thickness and the relative retardation R, which was measured with a Babinet-type compensator. The measurements on the 660-21.3 X 10 samples were carried out at 0-90 °C, and those on the 880-21.3 X 10 samples were carried out at 25 °C. 

The TS of the compacted samples was determined by transverse compression with a custom-built tensile tester. Tensile failure was observed for all the rectangular compacts when compressed between flat-faced platens at a speed ranging between 0.006 and 0.016 mm/sec. Platen speed was adjusted between materials to maintain a time constant of 15 2 seconds to account for viscoelastic differences the constant is the time between the sample break point and when the measured force equals Fbreak/e in the force versus time profile, where the denominator is the mathematical e. Specially modified punch and die sets permitted the formation of square compacts with a centrally located hole (0.11 cm diameter) that acted as a stress concentrator during tensile testing. This capability permitted the determination of a compromised compact TS and thus facilitated an assessment of the defect sensitivity of each compacted material. At least two replicate determinations were performed for each mechanical testing procedure and mean values are reported. 

Another group of procedures subjects the sample to continuous forced oscillations. The resulting stresses and deformations can be measured independently of each other with the most commonly used instrument of this group, the rheovibron. Since the rheovibron applies a tensile stress, the moduli obtained are tensile moduli and not shear moduli, as is the case with the torsion pendulum. 

Measurement of the force on the stretched test pieces has been much improved by eliminating the heavy pendulum dynamometer and employing inertialess transducers which convert the force into an eleetrical signal. In all standard procedures tensile strength and modulus are expressed as foree per unit area of the initial cross section before stretching. 

Test Procedures - Generally, a displacement-control or strain-control test mode is used to avoid run-away tests that sometimes occur in force-control. A test mode rate is chosen so as to produce test specimen failure in 5-50 s. Failure within 1 minute or less should be sufficient to minimize slow-crack growth (SCG) effects in the tensile test. If slow crack growth is observed (e.g. under slow test mode rates), subsequent tests can be accelerated to reduce or eliminate slow crack growth. Extensometers and/or strain gages are used to determine gage length extension and/or local strain. The test specimen is tested in flexure to fracture. The test specimen is retained for failure analysis and post-test dimensional measurement. 

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