Fatigue of polymers

Abstract

The general nature of fracture in polymers, when subject to alternating loads as distinct from static or steadily increasing loads, is reviewed; and the molecular mechanisms and micromechanics aspects of the fatigue fracture process are discussed. Some attention is given to thermal fatigue, where fracture results primarily from a large specimen temperature rise due to hysteresis heating. However, primary emphasis is devoted to mechanical fatigue, in which fracture is a result of initiation and propagation of a crack, as a result of the periodic nature of the applied load.Attention is given to the important internal, or material, variables such as polymer structure, molecular weight, crosslinking, and filler or diluent type and content; and to significant external variables such as stress or stress intensity factor amplitude, mean stress, temperature, frequency and environment. Various methods that can be utilized to provide significant degrees of enhancement in the fatigue resistance of polymers are outlined and discussed.

Do Surface Porosity and Pore Size Influence Mechanical Properties and Cellular Response to PEEK?

“…There was no change in modulus with the addition of surface porosity when using A LB . As a result of the cyclic loading experienced by orthopaedic implants and the often detrimental decrease in the fatigue resistance of polymers with surface flaws [33,39,46], it was important to evaluate the fatigue resistance of PEEK-SP. All pore sizes demonstrated a high fatigue resistance at one million cycles when using A LB despite a decrease in endurance limit from injection-molded PEEK.…”

Retardation and repair of fatigue cracks in a microcapsule toughened epoxy composite – Part I: Manual infiltration

“…Susceptibility to cyclic loading is particularly problematic because a crack will grow, however slowly, above a threshold range of stress intensities ΔK th that is significantly lower than the critical stress intensity K IC . Prevention of fatigue failure currently depends on accurate life prediction and implementation of inspection procedures.Polymer fatigue has been studied extensively in both homogeneous and composite structures (e.g., [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]). In most polymers, fatigue crack growth rates (da/dN) are accurately described by the Paris power law [16],…”

Investigations on Damage in a Filled Epoxy Resin

“…This observation was confirmed later by various authors. [2,5] On figure one, the softening of the stress-strain hysteresis curve is clearly visible and proves that a damage process is happening. The fact that the maximal stress diminishes is in full accordance with the TEM images which show delamination.…”

“…The literature on polymers shows that two distinct mechanisms govern the fatigue process: crazing and shearbands. [2,5,6] Under a tensile loading, the onset of crazing is observed. Crazes are micro-cavities perpendicular to the maximum principal stress with load bearing fibrils connecting the craze walls.…”