Issue 37

D. Angelova et alii, Frattura ed Integrità Strutturale, 37 (2016) 249-257; DOI: 10.3221/IGF-ESIS.37.33 252 Crack Growth Monitoring Method A replication technique was used for short fatigue-crack growth monitoring according to technical standards [6]. This method consists of making a replica (stamp) of specimen’s surface and subsequent monitoring of crack length and its propagation. Replicas are taken onto two mutually opposite specimen surfaces, which ensures full coverage of its hourglass working area. Replication material used is synthetic acetate film type "Agar scientific". After each experiment all replicas with cracks are subjected to closer monitoring and then the crack lengths are measured at the corresponding number of cycles at their taking. Measurement of cracks is done by using an optical microscope. R ESULTS AND DISCUSSION ll specimens of Steels A (BRF) and B (TF) were tested to fracture. The corresponding Wöhler curves were obtained by applying the well-known standard procedure and data recording; the curves are plotted and presented with their analytical models in Fig. 3 (for Steel A) and in Fig. 4a (for Steel B) and together for comparison - in Fig. 4b. Figure 3 : Wöhler curve of Steel A and characteristic areas of the fractured specimen surfaces corresponding to some stress ranges. A