Fatigue behavior

Since engineering plastics are often subject to cyclic or repeated stresses, the question of fatigue behavior is important. In general, relatively little attention has been given this phenomenon in plastics, with the exception of measurements of lifetime as a function of stress, frequency, and number of 

As with tensile and impact behavior of rubber-toughened plastics, a major energy-absorbing mechanism appears to be crazing. Thus, at least qualitatively, low-frequency fatigue behavior of rubber-modified plastics appears to involve the same phenomena as are seen in tensile and impact loadings. 

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The constant, C, is proportional to the ductility of the material in tension the exponent, b, is near 0.5 for most materials over a wide temperature range. This equation applies usually in the range 1—10 cycles, and typical data are shown in Figure 4a (5). The exponent rises when creep or environmental interactions affect fatigue behavior. 

High temperature fatigue and fretting fatigue behavior has also been improved by implantation (113,114). This has been achieved by using species that inhibit oxidation or harden the surface. It is generally accepted that fretting behavior is closely coimected to oxidation resistance, perhaps due to third party effects of oxidation products. Oxidation resistance alone has also been improved by ion implantation (118—120). 

In the case of the fibrous laminate not much work has been done, but it has been observed that a significant loss of stiffness in boron—aluminum laminate occurs when cycled in tension—tension (43,44). Also, in a manner similar to that in the laminated PMCs, the ply stacking sequence affects the fatigue behavior. For example, 90° surface pHes in a 90°/0° sequence develop damage more rapidly than 0° pHes. In the case of laminates made out of metallic sheets, eg, stainless steel and aluminum, further enhanced resistance against fatigue crack propagation than either one of the components in isolation has been observed (45). 

Figure 4-443. Fatigue behavior of ferrous and nonferrous alloys. (From Ref. [183].)...

The fatigue behavior of a material is normally measured in a flexural but also in a tensile mode. Specimens may be deliberately cracked or notched prior to testing, to localize fatigue damage and permit measuring the crack-propagation rate. In constant-deflection amplitude testing a specimen is... 

Factors That Affect the Fatigue Behavior of Rubber.676... 

FACTORS THAT AFFECT THE FATIGUE BEHAVIOR OF RUBBER... 

In order to accurately model the fatigue behavior of rubber, fatigue analysis methods must account for various effects observed for rubber during constant amplitude testing. Effects associated with load level, 7 -ratio (ratio of minimum to maximum loading level), and crack closure are presented in this section. 

This behavior is similar to the cut growth and fatigue behavior of rubber compounds. The rate of the growth of a cut is a function of the tearing energy [38,39] which itself is proportional to the stored elastic energy density in the test piece. The exact value depends on the shape of the test piece. 

Probabibstic fatigue behavior, 13 494 Probabibstic performance assessment, 17 548... 

ASTM specifications for, 24 862-864 dental applications, 8 311-314 defects in, 24 855 fatigue behavior of, 24 841, 845 hip implants, 3 734 mechanical properties of, 24 841, 843-844t... 

Khandkar, A. C. Elangovan, S. Liu, M. Timper, M. Therwal Cycle Fatigue Behavior of High Tewperature Electrodes, Cera-matec, Inc. 1994. 

Karger-Kocsis J. (1991). Microstructural aspects of fracture and fatigue behavior in short fiber-reinforced, injection-molded PPS-, PEEK- and PEN-composites. Poiym. Bulletin 27, 109-116. 

Fatigue Behavior of Acrylic Interpenetrating Polymer Networks... 

The polyurethane formulation Involved a proprietary crossllnkable system based on poly(propylene glycol) and methylene dllsocyanate (NCO/OH ratio = 1.0). For studies of viscoelastic, energy absorption, and fatigue behavior, the weight fractions of PUMA were 0, 0.25, 0.50, 0.75, and 1.0 for studies of tensile and tear strength, the ratios were 0, 0.10, 0.20, 0.25, 0.30, and 0.40. Reactants were mixed at room temperature, degassed, poured Into a mold, and cured at 60 C for 48 hr. 

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