Tear volume test

Figure 24-6 Schirmer tear volume test strips. Strips are available with or without markings some strips are impregnated with dye to allow easy visualization of wetting distance (top).

In TPE, the hard domains can act both as filler and intermolecular tie points thus, the toughness results from the inhibition of catastrophic failure from slow crack growth. Hard domains are effective fillers above a volume fraction of 0.2 and a size <100 nm [200]. The fracture energy of TPE is characteristic of the materials and independent of the test methods as observed for rubbers. It is, however, not a single-valued property and depends on the rate of tearing and test temperature [201]. The stress-strain properties of most TPEs have been described by the empirical Mooney-Rivlin equation... 

Fig. 3.12. Arc height (or centrepoint deflection) as a function of water pressure measured in a burst test on a 2.5 mm thick HDPE geomembrane (Kreiter and Hut-ten 1990). The clamp free diameter was 1050 mm. The pressure was stepwise increased by 0.2 bar (0.02 N/mm ) per two minutes. The material starts to yield at approximately 1.3 bar (0.13 N/mm ). When yielding has started, the rate of water flow is not sufficient to compensate for the volume increase under the geomembrane the pressure drops. Finally, the yielded range tears the test ends with a spectacular water fountain. The small diagram shows the decrease in the thickness of the geomembrane in the centre of the arched test specimen...

Experiment Heat c.c. of phenyl mustard oil in a test-tube with the same volume of yellow mercuric oxide for some time, until the oil boils. The yellow oxide is changed to the black sulphide, at the same time the extremely disagreeable odour of the phenyl isocyanate arises the vapour of the compound attacks the eyes, causing tears. 

As seen in Fig. 10 the steel surface of the wheel is modified by PTFE-PA material. The surface morphology is the same as the disc surface (used the PTFE-PA-6 test specimen). The examined PTFE PA-6 material consisting of 15-wt% PTFE micropowder (= 8.1 vol%) has only a small volume content but the AFM picture shows nearly 50% of the area of low adhesion. This means a surface modification takes place during tribological application. PTFE particles are degraded, removed and distributed on the surface by wear and tear and fixated on PA... 

Here fFis the elastic strain energy per unit volume, c is the length of the tear, and the subscript 1 denotes differentiation at constant specimen dimensions. Thomas (208) has shown how T may be evaluated from experiments on a simple test piece consisting of a rectangular sheet cut... 

The strain rates and temperatures prevailing in abrasion are very different from those used in routine laboratory testing of tensile or tear strength. Because of friction, local temperatures may far exceed those of the test track or of the bulk of the rubber (229-230). Even at small sliding velocities the effective strain rate is very large, as small volume elements of rubber are deformed repeatedly to high strains by the many surface... 

Inherently, all injection valves have one thing in common, that is, they have moving parts that might eventually become worn. Yet, the recent generation of FIA valves, made of a suitable combination of polymers, have proven very reliable in continuous use—in fact, van der Linden [1059] has reported that rotary valves subjected to exhaustive tests even after 50,000 switches still functioned properly, and no wear or tear was noticeable provided that the sample and carrier stream were virtually free from particles. Even better performance is feasible with valves if powered by stepper motors, which results in superior reproducibility of injection and excellent duration. Nevertheless, it would, particularly for special applications, be beneficial to be able to meter the sample volume and subsequently transfer it reproducibly into the carrier stream by means requiring no mechanically moving parts. 

Here v represents the Poisson ratio, defined as the ratio between the linear contraction and the elongation in the axis of stretching. In the case of constant volume (an incompressible body like rubber), i> = 0.5 and therefore E = 3G for rigid materials p < 0.3. There is also a direct test for tear strength, mainly in the case of thin films, similar to those used in the paper industry. 

Figure 1 shows a compact tension specimen in which a starter crack propagated at a controlled rate such that the test could be stopped prior to specimen failure. Whitened areas above and below the fracture surfaces are a result of particle cavitation. This particular material was a flexibilized vinyl ester containing a rubber particulate phase. The large volume of material involved in the fracture process resulted in high toughness and a ductile tearing mode of fracture as opposed to the brittle fracture mode of the base resin. 

Silver amide, AgNH2, is a white precipitate which darkens and shrinks in volume on exposure to air. The compound can be prepared by mixing a solution of potassamide with silver nitrate or iodide in liquid NH followed by washing by decantation and careful drying. This compound is extremely sensitive and can shatter test tubes and tear holes in several layers of towels wrapped around the tube for the protection of the operator. 

Samples were cured from each of the three compounds and then a large numher of physical and chemical properties were examined, including tensile properties, tear strength, resilience, abrasion resistance, ageing, and performance and swelling in test fluids. The results revealed that the abrasion volume of blends of virgin NR and the Novel reclaim is lower than that of the Control reclaim and comparable to the Control NR. Although the tensile properties of the Novel reclaim were found to be lower than Control NR, the workers concluded that they would be acceptable for a tyre tread application and overall it was concluded that the 85 15 Novel reclaim product could be used as an alternative to both the other two compounds for tyre tread manufacture. 

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