A ndrea Resente

Department of Industrial Engineering, University of Padova, Padova, Italy



An experimental investigation of the fatigue behaviour of notched and unnotched specimens made of 25% wt. short glass fibre reinforced recycled Polypropylene filled with mineral filler is presented.

To this end, plain and double-edge notched specimens (with notch radius ranging from 0.25 mm to 10 mm) were produced by injection moulding and tested under tension-tension fatigue, highlighting the effect of the notch root radius and the notch geometry. During the fatigue test, the damage evolution was monitored using a traveling microscope to define the number of cycles spent for the fatigue crack nucleation. The fracture surfaces were careful analysed both at the macroscopic and microscopic level, discussing the analogies existing between plain and notched specimens.

The fatigue tests were reanalysed in terms of net stress amplitude defining the traditional stress-life curves, each of them fitted on data derived for a given specimen geometry. Then, an energy-based approach was proposed for the assessment of fatigue life spent for the crack nucleation. The model is conceptually based on the actual damage evolution observed both during the fatigue tests and reported in the technical literature: the initiation of a macro crack results from the accumulation of damage in the matrix. Thus, the strain energy density evaluated in the matrix and averaged on a structural volume embracing the notch tip was adopted as fatigue damage index to correlate in a single scatter band the fatigue data of unnotched and notched specimens.



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