Flex fatigue fracture

Figure 8. Fracture by flex fatigue of a wool fiber of similar type to that of Fiaure 2. Samvle was fractured at 65% rh and 21 °C (442X).

Fi. 10. (a.b) Polye.sler fibres after a single bend, (c-e) Flex fatigue in polyester kink-band fracture, (f) Flex fatigue shear splitting in nylon, (g) Flex fatigue shear splitting in polyester. For further explanation. 

Flex fatigue is a term that is commonly used in the testing of elastomers. Flex fatigue is the result of a rubber fracturing after being subjected to fluctuating stresses. 

The fracturing of an elastomer after being subjected to fluctuating stresses is known as flex fatigue. 

For metals, FDA regulations specify ASTM F2129 (standard test method for conducting cyclic potentiodynamic polarization measurements to determine the corrosion susceptibility of small implant devices). Some devices may also require testing for stress corrosion (failure due to corrosion accelerated by tensile stress). There are many test methods for fatigue fracture, so it is incumbent on the manufacturer to select the most appropriate one(s) for device in question. Pacemaker leads, for example, are often tested in a fixture that flexes them 90 over a specified radius at twice the typical cardiac cycle rate (Fig. 10) [31]. Presently, FDA requires satisfactory performance over 4 hundred million cycles (equivalent to about 10 years in human use). 

Repeated flexing of the proximal stem in a fatigue mode over a period of months or years results in a widening of the separation between the metal and cement laterally and ultimately in an actual deformity or fracture of the metal stem. 

Continuous flexing of a PBA will fracture component leads and, more important, surface-mounted component solder joints, due to mechanical fatigue failure. (Mechanically induced flexing or vibration in assembled PBs is used under controlled conditions to induce failures in solder joints for quality and reliability studies.)... 

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