Issue 41

H. Šimonová et alii, Frattura ed Integrità Strutturale, 41 (2017) 211-219; DOI: 10.3221/IGF-ESIS.41.29 216        0 1 , 0 d d yy yy x y x d , (1)       AGG ITZ ,max ,min yy yy yy , (2) where d is a size of region, where the stress is averaged. For each configuration critical applied stress is evaluated by means of critical value of mean opening stress  c yy [21]:      Ic c 2 ITZ 2 yy K d (3) Then the critical applied stress is:      c appl,c appl yy yy (4) and it determines the magnitude of applied stress under which the crack will propagate through ITZ. In the following calculations it was taken K Ic = 0.5 MPa·m 1/2 . This value is estimated as equal to usual fracture toughness of matrix of the composite. Composites 04042016 and 09052016 As it was mentioned above the thickness of ITZ was taken from SEM measurement and in the composite 04042016 it was 55 μm, while in the composite 09052016 it was 40 μm. Figure 4 : Distribution of the opening stress  yy in ITZ and AGG; ITZ thickness 55 μm and 40 μm. In Fig. 4, the opening stresses  yy (for both composites) are shown in dependence on the distance from the crack tip x , where the value x = 0 μm refers to the crack tip. The step changes of the stresses  yy are apparent at the interface between ITZ and AGG. Here the average values  yy are evaluated over the whole ITZ thicknesses. The average values  yy and the stress ranges   yy for the composite 04042016 ( d = 55 μm) are stated in Tab. 4 while for the composite 09052016 ( d = 40 μm) they can be found in Tab. 5. 0 2 4 6 8 10 0 100 200 300 400 Opening stress [MPa] x [μm] 04042016 09052016 AGG ( d =55 μm) ( d =40 μm) ITZ