Fatigue behaviour of 25% wt. short glass fibre reinforced recycled Polypropylene filled with mineral filler in presence of notches

An experimental investigation is presented regarding the fatigue behaviour of notched and plain specimens made of 25% wt. short glass fibre reinforced recycled Polypropylene filled with mineral filler. Plain and double-edge notched specimens (with notch radius ranging from 0.2 mm to 10 mm) were produced by injection moulding and tested under tension-compression fatigue to highlight the effect of the notch root radius and notch geometry. During the fatigue tests, the damage evolution was monitored using a traveling microscope to define the number of cycles spent for the fatigue crack nucleation. First, the fatigue tests were reanalysed in terms of net-stress amplitude and the traditional stress-life curves for each specimen's geometry were found. 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 during the fatigue tests, which was according to 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 plain and notched specimens.