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Analysis of fatigue behaviour of notched specimens made of fibreglass reinforced polyamide by means of a cohesive model

Abstract: Fatigue tests until fracture of five notched specimens of short glass fibre reinforced polyamide, with a humidity of 2.5%, were carried out at 23, 28, 33, 38 and 43 °C. A correlation between the environmental temperature and the number of cycles to failure was established. Three different regions of strain were observed, namely, transient, steady-state and pre-failure. Strain and strain-rate during the creep-fatigue process revealed the existence of non-temperature dependent critical strains between these regions. The fractographic study performed after failure suggested the suitability of describing the stress distribution in the remnant ligament through a cohesive model. This is based on the observed fact that, at the crack tip, the matrix and the fibres debond, giving rise to crazing mechanisms so that the ultimate bearing ability of the material relies on the matrix. The calculations involved in the cohesive model were based on the information provided by the fractographic study and the real-time measurements of the crack growth by means of an infrared thermographic camera. Based on this methodology, the cohesive stress of the material was estimated. In a last stage, the surface roughness of the samples was determined after being tested, revealing a reliable correlation between the roughness and the fracture micromechanisms undergone by the underlying material. This correlation makes it possible to use the surface roughness of an in-service component as a parameter to evaluate the level of microstructural damage that it has experienced.

 Fuente: Polymer Testing Volume 64, December 2017, Pages 337-344

 Editorial: Elsevier Ltd

 Fecha de publicación: 01/12/2017

 Tipo de publicación: Artículo de Revista

 DOI: 10.1016/j.polymertesting.2017.10.021

 ISSN: 0142-9418,1873-2348

 Url de la publicación: https://doi.org/10.1016/j.polymertesting.2017.10.021