ANALYSIS OF CRACK PROPAGATION DURING FATIGUE TESTS IN INJECTION MOULDED NOTCHED SPECIMENS MADE OF SHORT GLASS FIBRE REINFORCED POLYAMIDE

In this work, we present the results of fatigue tests on injection moulded, notched specimens made of short glass fibre reinforced polyamide 66, containing 50%w of fibres. Specimens have three different notch radii (2 mm, 1 mm and 0.5 mm). The local fibre orientation was assessed by analysing the fibre orientation distribution using the optical method. Crack nucleation and propagation was monitored during fatigue tests by microscope observations in back light conditions. This technique allowed for observing and measuring the crack length. The role of propagation was quantified and discussed, by comparison with data previously obtained using a lower amount of reinforcing fibres and PA 6 matrix. It appears that with a higher content of fibres, most of the fatigue test is spent in nucleating the cracks, while propagation takes places over the last few cycles. In previous tests, with 30% glass fibres and PA6 matrix, crack propagation was dominant (more than 50% of total fatigue life), particularly for a small notch root radius.