Reinforced plastic fatigue testing

Found MS. Review of the multiaxial fatigue testing of fiber reinforced plastics. In Multiaxial fatigue. ASTM STP 853 1985. pp. 381-95. 

Symonds DD, Davis G. Fatigue testing of impact damaged T300/914 carbon fibre reinforced plastic. Compos Sci Technol 2000 60 379-89. 

The rate dependence of fatigue strength demands carefiil consideration of the potential for heat buildup in both the fatigue test and in service. Generally, since the buildup is a function of the viscous component of the material, the materials that tend toward viscous behavior will also display sensitivity to cyclic load frequency. Thus, TPs, particularly the crystalline polymers like polyethylene that are above their glass-transition temperatures, are expected to be more sensitive to the cyclic load rate, and highly crosslinked plastics or glass fiber reinforced TS plastics are much less sensitive to the frequency of load. 

Fatigue strength of reinforced plastic materials is generally explored with laboratory tests of specimens in cycling machines. Test specimens are specially prepared or cut from the full structure. Such tests, however, cannot provide accurate information about the durability of a complete structure under actual operating conditions. Thus composite structures are sometimes built and subjected to full scale testing. The subject of fatigue is discussed fully in Chapter 5. 

Fatigue data are normally presented as a plot of the stress (S) versus the number of cycles (N) that cause failure at that stress the data plotted defined as an S-N curve. Test results are illustrated graphically in the form of curves. Examples of fatigue curves for unreinforced and reinforced plastics are shown in Figure 3-65. The values for stress amplitude and the number of load cycles to failure are plotted on a diagram with logarithmically divided abscissa and English or metrically divided ordinates. 

Reinforced Plastics Congress, British Plastics Federation, London, Paper No. 19, pp 145-151 Russell AJ, Street KN (1985) Moisture and temperature effects on the mixed-mode delamination fracture of unidirectional graphite/epoxy. Delamination and debonding of materials, ASTM 537 STP 876, American Society for Testing and Materials, Philadelphia, pp 349-370 Saito H, Kimpara I (2007) Effect of water absorption on compressive strength after impact and post impact fatigue behavior of woven and knitted CFRP laminates. Key Eng Matra-334-335 517-520... 

The importance of stress amplitude during fatigue is quite marked for this type of reinforcement (combination glass fabric). The difference between matrix dominated and fibre dominated properties is determined by the presence of a knee point in a static load/deflection test (Figure 1.5(c)). The average loss in strength per decade of cycles approaches 10%, which is typical of glass-reinforced plastics. 

The well-known S-N curves are - probably for historical reasons — the method most often used to describe fatigue behavior for fiber reinforced plastics. In this discontinuous (as defined in the previous section) procedure, the fatigue criterion is typically fracture, that is total failure of the test specimen. Statistic evaluation leads to statements regarding the probability of fracture P, Figure 1.65. 

As convincing as these considerations may be, comparisons of predictions made with actual tests on fiber reinforced plastics show that service lives calculated by Miner s Rule are overestimated by a factor of 1 to 10. According to VDI 2014/3 and with these findings, current state-of-the-art does not allow purely mathematical predictions, or are at least they should be be used with caution. In particular for complex parts, experimental fatigue strength tests are required [1013]. 

Watanabe M. Effect of water environment on fatigue behavior of fiberglass reinforced plastics. In Tsai SW, editor. Composite materials, testing and design (fifth conference), ASTM STP 674, American Society for Testing and Materials 1979. p. 345-367. 

K 7082 1993 Testing method for complete reversed plane bending fatigue of carbon fibre reinforced plastics... 

FIGURE 4.10 Apparent stress and temperature rise during constant deflection fatigue testing of a glass-reinforced PP at 1200 cpm. (From Cessna, L. C. and J. A. Levens, Proc. 4th Annual Plastics Conf., Eastern Michigan University, September, 1969, pp. 46-73.)... 

The focus in testing was to describe briefly the vast number of tests available to determine tensile, shear, peel, fatigue, creep, and impact properties. Wood, metal, plastic, and fiber-reinforced composite adherends were considered. Attention was also given to precautions which must be taken to obtain valid results. 

Reinforced thermosetting plastic pipes are somewhat more sensitive to fatigue than thermoplastic pipes. Accordingly, they are often pressure-rated for surge service on the basis of their HDB as determined by Procedure A of the aforementioned ASTM D 2992 from test... 

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