Polymer flexural test

Fig. 5.3. Young s moduli Efle, as determined by flexural tests on small samples after thermal treatment are plotted against the densities of those samples. The dots are situated along a single line since the annealed samples are denser and more rigid than the quenched samples prepared from the same polymer...

Fig. 6.1. Yield strengths of the five polymers are plotted against 1/MC that is the inverse molecular mass between crosslinks. The diamond represents polymer E. Test temperature 23 °C. a and b represent results of flexural tests on small samples (thickness 1.3 mm) a annealed, b quenched,...

Fig. 6.3. Yield strengths from flexural tests are plotted against the densities of the polymers. The annealed samples were noticeably stronger than the quenched ones of similar density. Rigidity (Fig. 5.3.) was governed by the density of the polymer whereas yield strength seemed to depend mostly on molecular conformations...

The yield strengths of the polymers A, B and E from flexural tests are plotted in Fig. 6.5 against the strain rate on a logarithmic scale. The crosshead speed was... 

Fig. 6.5. Yield strengths from flexural tests are plotted against strain rates at the surface of the samples. Tests were performed on polymers A, B, and E test temperature 23 °C. The slope of the three lines correspond to similar activation volumes v = 2 0.1 nm3...

The labor-intensive nature of polymer tensile and flexure tests makes them logical candidates for automation. We have developed a fully automated instrument for performing these tests on rigid materials. The instrument is comprised of an Instron universal tester, a Zymark laboratory robot, a Digital Equipment Corporation minicomputer, and custom-made accessories to manipulate the specimens and measure their dimensions automatically. Our system allows us to determine the tensile or flexural properties of over one hundred specimens without human intervention, and it has significantly improved the productivity of our laboratory. This paper describes the structure and performance of our system, and it compares the relative costs of manual versus automated testing. 

We perform flexural testing on polymer rods or beams in the same basic apparatus that we use for tensile or compressive testing. Figure 8.6 illustrates two of the most common flexural testing configurations. In two-point bending, shown in Fig. 8,6 a), we clamp the sample by one end and apply a flexural load to the other. In three-point bending, shown in Fig. 8.6 b), we place the sample across two parallel supports and apply a flexural load to its center. 

We use a variant of flexural testing to measure a sample s heat distortion temperature. In this test, we place the sample in a three point bending fixture, as shown in Fig. 8.6 b), and apply a load sufficient to generate a standard stress within it. We then ramp the temperature of the sample at a fixed rate and note the temperature at which the beam deflects by a specified amount. This test is very useful when selecting polymers for engineering applications that are used under severe conditions, such as under the hoods of automobiles or as gears in many small appliances or inside power tools where heat tends to accumulate. 

Flexural Properties. Both flexural modulus and flexural strength values were obtained. These values were measured at 23 °C and also over a range of temperatures for the MBAS polymer (see Figure 4). In the flexural tests, a molded bar is tested as a simple beam, the bar resting on two supports, and the load is applied midway between. The test is continued until rupture or 5% strain, whichever occurs first. The test fixture is mounted in a universal tester, and the tester is placed in an appropriate temperature environment. 

Recent tests have revealed surprisingly good fatigue and creep resistance for carbon/carbon composites. Figure 29 presents some results of torsion and flexure tests in which the fatigue properties of carbon-fiber-reinforced carbon (CFRC) 3D composites are compared with those of carbon-fiber-reinforced polymer (CFRP) 3D composites (53). 

Testing of ceramic composites has been around since the earliest fabrication of these materials. For particulate- and whisker-reinforced composites, testing methods which are suitable for monolithic ceramics are generally used. These methods include three- and four-point flexure, uniaxial tension and compression, and many others. For fiber-reinforced ceramic composites, flexural testing was also used initially. However, as was recognized in the polymer composites area, flexural testing alone could not provide the type of... 

ISO 4600 details a ball or pin impression method for determining the ESCR. In this procedure, a hole of specified diameter is drilled in the plastic. An oversized ball or pin is inserted into the hole, and the polymer is exposed to a stress cracking agent. The applied deformation, given by the diameter of the ball or pin, is constant. The test is multiaxial, relatively easy to perform, and with not very well-defined specimens, and the influence of the surface is limited. Drawbacks are the small testing surface and the undefined stress state. After exposure, tensile or flexural tests may be performed on the specimens. This leads to the determination of either the residual tensile strength or the residual deformation at break. 

Arnold JC (1994) The use of flexural tests in the study of enviromental stress cracking of polymers. Polym Eng Sci 34(8) 665-670... 

For mechanical test such as tensile test and flexural test, the impregnation of polymer-blend to the carbon fiber was carried out several soakings of the fiber in the polymer-blend dispersion consists of PTFE (98.2 wt%) and fluorinated-pitch (1.8 wt%). A sheet of chemical crosslinked pre-forming sample was prepared under the pressure at around 20 MPa and then heat-treated at 350 °C 5 °C for 30 minutes. Samples were irradiated by EB up to 1000 kGy at 335 °C 3 °C in nitrogen gas atmosphere. 

Flexural tests may be carried out in tensile or compression test machines. In standard tests, three-point bending test is preferred, although it develops maximum stress localized opposite the center point (support). If the material in this region is not representative of the whole, this may lead to some errors. Four-point test, offers equal stress distribution over the whole of the span between the inner two supports (points) and gives more realistic results for polymer blends (Figure 12.3). Expressions for the calculation of flexural strength and modulus for differently shaped specimens are given in Table 12.4. 

Figure 4.50i l indicates the adhesion of latex-modified mortars to ordinary cement mortar as a substrate, measured by four types of test methods. CJenerally, the adhesions in tension, flexure, and direct compressive shear of the latex-modified mortars to ordinary cement mortar increase with a rise in the polymer-cement ratio regardless of the type of polymer and test method. The adhesion in slant (indirect) compressive shear of the latex-modified mortars attains a maximum at a polymer-cement ratio of 5 or 10%, and is extremely large compared to the adhesions determined by other test methods irrespective of the polymer type and polymer-cement ratio. The reasons for diis may be due to the effects of the combined shear and compressive stresses and their relaxation by the polymer films formed on the bonding joints. Considering the above adhesion data, it is most important to select the best test methods to successfully reproduce service conditions in the applications of the latex-modifled mortars. 

Plastic and polymer mechanical tests include tensile, tear, shear, flexural, impact, and compression tests. These are summarized in the following sections. 

Fig. 12 Scheme of a three-point flexural test, (a) Scheme of the shape-memory effect (SME) in polymers as defined by four critical temperatures. The value of 7 is a material property. Tiow is always less than Tg, whereas Tiugh may be above or below Tg, depending on the desired recovery response. (b) Schematic of the three-point flexure thermomechanical test setup. Taken from lef. [63], Copyright 2005. Reprinted with permission of John Wiley Sons, Inc. 

A similar behavior was observed in three-point flexural tests for epoxy based polymer networks (Tg = 90°C), where Tgw, Tg max, and (Tmax increased when ]8h was raised from 2.5 to 10Kmin [64]. 

The very nature of polymers makes their mechanical response very sensitive to variations in the rate at which the polymer solids are deformed. The strain rates considered in this chapter are well above these for standard tensile or flexural tests and well below the ballistic deformation rates at which bullet-proof vests and other polymer applications are tested (78). Impact speeds vary from 1 to 10 m/s compared to 10 m/s for standard tensile tests. The actual strain rates within the loaded solid body depend on the loading and specimen geometries. 

Zhou and co-workers [27] studied the effect of surface treatment of calcium carbonate with sulfonated PEEK on the mechanical properties of the polymer. Tests used included tensile tests, flexural tests, notched Izod impact tests, TGA, DSC and SEM. The modulus and yield stress of the composites increased with CaCOs particle loading. This increase was attributed to the bonding between the particles and the PEEK matrix, was proved by the SEM of the tensile fracture surface of the composites. The treated fillers were found to give a better combination of properties, which indicated that the sulfonated PEEK played a constructive role in the calcium carbonate/PEEK composites. 

G.D. Sims and A. Vanas, Round-robin on fatigue test methods for polymer matrix composites. Part I, Tensile and flexural tests of unidirectional material, NPL Report DMM(A)180, 1989. 

FIGURE 40.4 Flexural testing of hybrid alumoxanes. Flexural modulus (a) and flexural fracture strength (b) of hybrid alumoxane nanocomposites as a function of nanoparticle loading weight percentage. Error bars represent mean standard deviation for n = 5. The symbol indicates a statistically significant difference compared to the pure polymer resin (p <. 05). 

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