Dynamic fatigue test

Test I3 Dynamic-Fatigue Test by Constant-Force Pounding. 

To measure n (defined in Eq. (12.30)) directly from velocity versus K curves is often difficult and time consuming. Fortunately, a simpler and faster technique, referred to as a dynamic fatigue test (not to be confused... 

The durability of a flexible foam may be determined by using a shear or a pounding force on the foam. Tests described here are designed to assess the suitability of foam for use in upholstery and are therefore primarily aimed at cellular latex or polyether urethane types of foam. A dynamic fatigue test using a roller shear at constant force is described in ASTM D 3574, Test U. However a much more popular fatigue test for cellular upholstery materials is determined by constant load pounding. 

Determine the value of n from dynamic fatigue tests (several stressing rates). 

FIGURE 12. Results of dynamic fatigue testing at 1000°C inairfor 10-YSZ, 10-YSZ/30mol% alumina particulate composite, and lO-YSZ/30 mol% alumina platelet composite. The solid lines represent the best-fit line. Slow crack growth parameter n is included. 

TABLE 3. Summary of slow crack growth parameters determined for three different composites by dynamic fatigue testing in flexure at 1000°C in air... 

Advances in Urethane Science and Technology 1.2.3.2f Dynamic Fatigue Test... 

Table 1.22 shows the dynamic fatigue test results for Lyondell and Dow cushion foams tested for 80,000 cycles and 60 minute recovery time. Results indicate that equivalent dynamic fatigue values are ohtainahle with use of the new non-fugitive and cell opening catalysts, based on nominal test error of 3. 

Tapered double cantilever beam This is again mode I, but the value of dClda can be made constant by tapering of the arms of the specimen (see Fig. 2b). Thus, Gj is independent of crack length and this design is well suited to tests where the value of a is difficult to measure, for example, environmental tests (see Durability fundamentals) and dynamic fatigue tests. This is also used in ASTM D 3433. The value of Gic is given by... 

Alternating-stress amplitude n. A test parameter of a dynamic fatigue test, others being frequency and environment. It is one half the algebraic difference between the highest and lowest stress in one full cycle. 

Method C Dynamic fatigue test by constant force pounding... 

Method D Dynamic fatigue test for carpet cushion... 

Method C—dynamic fatigue test by constant force pounding—is conducted to determine the loss of force support at 40 percent indentation force deflection (IFD), a loss in thickness and structural breakdown as assessed by visual inspection. The test evaluates the specimen by repeatedly deflecting the material by a flat horizontal indentation exerting a specified vertical force on the test specimen. This test may be conducted by using either 8000 or 80,000 cycles. The percent loss in thickness and percent loss of 40 percent IFD and results of visual examination are reported. 

Method D, the dynamic fatigue test for carpet cushion, was developed to evaluate the specimen by repeatedly deflecting the carpet cushion by a rubber-covered roller exerting a specified force on the test specimens. The test determines the retention of force support at 65% compression force deflection (CFD), loss of thickness, and structural breakdown as determined by visual inspection. 

When designing dynamic fatigue tests the experimentalist has a wide range of variables to consider which contribute in different ways to the fatigue process. The following list is an extended version of that compiled by Andrews [4], namely ... 

Fig. 5.61 Dependence of failure stress of a variety of engineering polymers upon the number of cycles accumulated during a dynamic fatigue test at 2(fC. The polymers used were poly (methyl methacrylate) (PMMA), rigid poly (vinyl chloride) (PVC) and an acrylonitrile-butadiene-styrene copolymer (ABS). (After Bucknall, Gotham and Vincent Chapter 10 in Polymer Sciencey ed. Jenkinsy North-Holland, 1972.)...

Furthermore, mechanical properties in an aluminum environment at 960 to 1000°C were studied by strength versus stress rate and tests (81). According to dynamic fatigue tests on... 

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