Mean strain effects on cyclic deformation and fatigue behavior of polyether ether ketone (PEEK)

• Published in: Polymer testing Vol. 55; pp. 69 - 77
• Main Authors: Shrestha, Rakish, Simsiriwong, Jutima, Shamsaei, Nima
• Format: Journal Article
• Language: English
• Published: Barking Elsevier Ltd 01-10-2016; Elsevier BV
• Subjects: Crack initiation; Crack propagation; Cyclic loads; Defects; Deformation effects; Deformation mechanisms; Fatigue failure; Fatigue life; Fatigue tests; Fractography; Fracture mechanics; Fracture surfaces; Inclusions; Materials fatigue; Mean stress relaxation; Particle physics; Polyether ether ketones; Polymer; Scanning electron microscopy; Self-heating; Strain; Strain gauges; Studies; Tensile mean strain effect; Thermoplastics; Polymer; Tensile mean strain effect; Mean stress relaxation; Fractography; Self-heating
• ISSN: 0142-9418; 1873-2348
• DOI: 10.1016/j.polymertesting.2016.08.002

The fatigue behavior of polyether ether ketone (PEEK) thermoplastic was investigated under uniaxial strain-controlled cyclic loading condition with various mean strains (Rε = 0, 0.2, and 0.25). The mean stress responses of PEEK from all mean strain fatigue tests were found to be fully-relaxed. As a result, minimum mean strain effect on fatigue behavior of PEEK was observed. Fractography analyses utilizing a scanning electron microscope were performed on PEEK specimens under tensile mean strain cyclic loading. Two distinct stages of fatigue, crack initiation and physically small crack growth, were observed on all the fracture surfaces. Moreover, two types of inclusions, unmelted particles and void-like defects, were identified to be the cause of crack initiation. Void-like defects were found to have more detrimental effect on fatigue life of PEEK when compared to particles of similar size. The effect of inclusions on fatigue behavior of PEEK was observed to be more significant than that of the tensile mean strain.