Flexural fatigue

Data for thermal movement of various bitumens and felts and for composite membranes have been given (1). These describe the development of a thermal shock factor based on strength factors and the linear thermal expansion coefficient. Tensile and flexural fatigue tests on roofing membranes were taken at 21 and 18°C, and performance criteria were recommended. A study of four types of fluid-appHed roofing membranes under cycHc conditions showed that they could not withstand movements of <1.0 mm over joiats. The limitations of present test methods for new roofing materials, such as prefabricated polymeric and elastomeric sheets and Hquid-appHed membranes, have also been described (1). For evaluation, both laboratory and field work are needed. 

The performance properties of PEN present opportunities for replacement of rayon or polyamide in carcass construction. The use of PEN cord in these applications is currently being evaluated in both Asia and Europe. PEN has demonstrated acceptable flexural fatigue equivalent to polyethylene terephthalate (PET) and rayon. It has equivalent toughness to rayon, which is important for sidewall impact resistance. PEN s superior mechanical properties also afford opportunities to use less fiber in carcass construction enabling production of lighter-weight, more fuel-efficient tires. 

ASTM D671, Test Methodfor Flexural Fatigue of Plastics by Constant Amplitude of Force, Vol. 8.01, ASTM, Philadelphia, Pa., 1993. 

Prewo and co-workers were the first to study the fatigue behavior of fiber-reinforced ceramics.41,42 They conducted room temperature tension-tension and flexure fatigue experiments with 0° Nicalon SiCf/LAS-II composites. The fatigue experiments were conducted in air at a sinusoidal loading... 

Mechanical Characterization of Sulfur-Asphalt. The serviceable life of a pavement comes to an end when the distress it suffers from traffic and climatic stresses reduces significantly either the structural capacity or riding quality of the pavement below an acceptable minimum. Consequently, the material properties of most interest to pavement designers are those which permit the prediction of the various forms of distress—resilient modulus, fatigue, creep, time-temperature shift, rutting parameters, and thermal coefficient of expansion. These material properties are determined from resilient modulus tests, flexure fatigue tests, creep tests, permanent deformation tests, and thermal expansion tests. 

Figure 11 is a graph of initial bending strain vs. number of cycles-to-failure resulting from flexure fatigue tests for two of the recycled mixes... 

A.R. Chambers, J.S. Earl, C.A. Squires, M.A. Suhot, The effect of voids on the flexural fatigue performance of unidirectional carbon fibre composites developed for wind turbine applications, InternationalJournal of Fatigue 28 (2006), pp. 1389-1398. 

Figure 7b. Another example of a flexural fatigue fracture of cotton (1105X).

Figure 15.12 shows the fatigue resistance of carbon and glass fiber filled poly(phenylene ether ketone).The flexural fatigue depends on tensile properties of the composite. The yield strength of the matrix and the quality of the interface affect the fatigue properties of composites. 

The flexural fatigue endurance limit (ASTM D671) provides Information on the ability of a material to resist mechanical... 

Flexural Fatigue - Progressive localized permanent structural change occurring in a material subjected to cyclic flexural stress that may culminate in cracks or complete fracture after a sufficient number of cycles. 

Flexural Fatigue Strength - Maximum stress that can be sustained for a specified number of bending cycles without failure. 

Increasing the crosslink density of the elastomer dispersion results in improvements of the strength and tension set of the blend. The difference between the earlier commercial grades of partially cured EPDM/PP blends (TPR, Uniroyal) and the more recent commercial grades of completely cured EPDM/PP blend is in the improved elastomeric properties, viz. reduced compression and tension set and improved flexural fatigue. More important, the chemical resistance and resistance to oil swelhng is improved. Typical properties of commercial dynamically vulcanized EPDM/PP blend (Santoprene ) are shown in Table 15.13. 

ASTM D671. Flexural fatigue of plastics by constant amplitude of force, 1993. 

Until recently, data on the fatigue behavior of materials at cryogenic temperatures have been sparse, and information of this type for nonmetallic materials has been practically nonexistent. A preliminary search of published data revealed only a limited amount of information on fatigue characteristics of materials at cryogenic temperatures. Most of these data have been derived from flexural fatigue tests, and apply almost exclusively to metals. 

Schulte [46,47] has demonstrated how different organic solvents, such as hydraulic fluid encountered in the aerospace stmctures, lead to a reduction in the secant modulus of 45° glass fibre laminate under flexural fatigue and the number of cycles to failure. The matrix in this case was a polyether imide (PEI) which is plasticised by ingress of the fluid. A reduction in the matrix modulus means that the shear strength of the matrix will also be reduced with the consequence that the failure mechanism in flexure will change from matrix-fracture to delamination. 

Figure 16.41 Electrochemical impedance spectroscopy (ECIS) Nyquist plot of Re-hn impedance curves at various stages during low-cycle flexure fatigue testing of woven GFRP (specimen failure occurred at 7000 cycles) [99].

Superior long glass flexural fatigue behavior at afl cycles... 

This load causes a specified outer-surface stress level. The number of cycles to failure is then recorded. Both modes of flexural fatigue testing can be related to the performance of real structures, one to those that are flexed repeatedly to a constant deflection and the other to those that are repeatedly flexed with a constant load. 

Table Yin. Results of Flexural Fatigue Tests of Welded Beams ...

The results of the flexural fatigue tests of the weldments are summarized in Table VIII and plotted in Fig. 4. These limited data indicate that the 5183 and AMg6 welds had similar resistance to fatigue crack initiation. 

Fig. 4. Results of flexural fatigue tests of transversely butt welded plate.

C.H. Pameijer, F. Garcia-Godoy, B.R. Morrow, S.J. Jefferies, Flexural strength and flexural fatigue properties of resin-modified glass ionomers, J. Clin. Dent. 26 (2015) 23-27. 

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