Flexural testing

Flexo inks Flexprene Flexricin Flexsorb FTP Flexsorb SE Flexure testing Flexzone3C [101-72-4]... 

Subscripts denote reinforcement morphology p = particulate, 1 = platelet, w = whisker, f = fiber, i = interlayer between reinforcement and matrix. Strength as measured in a four-point flexure test (modulus of mpture) to convert MPa to psi, multiply by 145. 

Flexure testing has also been used to measure the strength of a RGP material (33). The strengths measured from flexure tests can be empirically related to a material s resistance to breakage during typical lens handling. 

Another method of flexural testing that can be used is, for example, the cantilever beam method (Fig. 2-18), which is used to relate different beam designs. It provides an exam-... 

In many cases, even the method of conditioning prior to test will influence the ratings. For example, flexural tests run on standard conditioned specimens (50% relative humidity and 73.5°F) may rank materials differently from tests conducted on specimens which have been immersed in water or which have been heated to some elevated temperature after outdoor exposure. 

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 stress systems in such tests are complex, and not easily related to fundamental properties. But the results are relevant to the performance of materials in service, and for that reason, flexural tests are frequently used in engineering practice. 

Development of a Fully Automated Tensile and Flexure Test System... 

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. 

For tensile tests the Instron 1125 tester is fitted with pneumatic-hydraulic grips which can be opened and closed by remote control. We have installed microswitches to indicate when a specimen is in place, and pneumatic actuators to eject the specimens from the grips after each test. For flexure tests either a three or a four-point compression-cell flexure fixture is substituted for the grips. We have attached air jets to the lower supports to eject the specimens. 

Overall control is provided by the PDP-11/44, running DEC S RSX-llM operating system. RSX-llM is a multi-user multi-task operating system, and a number of other analytical instruments are interfaced to this computer system and are running concurrently. The automated Instron software is menu-driven because our experience has shown that menu-driven software is particularly effective for applications of this type. To perform either test the user accesses a main menu from which separate menus for instrument calibration, tensile tests, and flexure tests can be reached. The tensile and flexure menus have equivalent options the choices pertaining to automated testing are as follows ... 

Automated flexure tests are similar. The robot moves the bottom bar from the magazine to the measuring device where its width and thickness are determined, then it places the bar on the flexure test fixture. The PDP-11/44 begins the test by putting the crosshead in motion. Data collection begins when the first load is detected, and the test continues until the specimen bar breaks, the load cell maximum force is reached, or a specified maximum strain value is reached. Then the crosshead is stopped, the specimen is ejected from the fixture, and the crosshead is returned to its initial position. This process is repeated until the test series is complete. 

Data analysis routines may change with time, and it is desirable to be able to reanalyze old data with new analysis software. Our tensile test analysis software creates plots of engineering stress as a function of engineering strain, as illustrated in Figure 3. Our flexure test software plots maximum fiber stress as a function of maximum fiber strain, with the option of including Poisson s ratio in the calculations. Both routines generate printed reports which present the test results in tabular form, as illustrated in Figure 4. 

Of all the methods of determining strength, the flexural test appears to be the most satisfactory. While not ideal, it does have the advantage of... 

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. 

Young s modulus is often measured by a flexural test. In one such test a beam of rectangullar cross section supported at two points separated by ia distance Lq is loaded at the midpoint by a force F, as illustrated in Figure 1.2. The resulting central deflection V is measured and the Young s modulus E is calculated as follows ... 

Flexural tests, impact tests, and hardness tests... 

The standard methods for testing creep, the elongation and possible rupture of a plastic under sustained load, are ISO 899-1 [34] for tension and ISO 899-2 [35] for flexure. Tests last typically for 1,000 hours or six weeks. Tests at higher temperatures may be required either because of a higher service temperature or to provide a prediction of longer term behaviour by time-temperature shifting. 

ISO 178 2004 Plastics - Determination of flexural properties ISO 1209-1 1990 Cellular plastics, rigid - Flexural tests - Part 1 Bending test ISO 1209-2 1990 Cellular plastics, rigid - Flexural tests - Part 2 Determination of flexural properties... 

For a given grade of HD PE, Figure 4.5 displays an example of an SN or Wohler s curve concerning flexural tests with maximum stress of cr and average stress of 0. 

For a given grade of 20% talc-filled polypropylene, Figure 4.13 displays two examples of SN or Wohler s curves concerning flexural tests ... 

---