PSI - Issue 13

N.V. Boychenko / Procedia Structural Integrity 13 (2018) 908–913

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Boychenko N.V. / Structural Integrity Procedia 00 (2018) 000–000

For all combinations of variable parameters considered in the paper (Table 1) the distribution of the elastic K 1 and the plastic K p stress intensity factors are determined along the crack front for two types of loading. These parameters are plotted against the normalized coordinate    2  . In all figures,  = 0.0 is the crack border (the specimen free surface), while  = 1.0 is the mid-plane of the specimen thickness. All values of K 1 and K p obtained in the study are listed in the tables at room, low (-60°C) and at high temperature (250°C) by Boychenko (2017a, 2017b, 2018).

Fig. 2. The elastic SIF distribution of along the crack front (1 - a/t=0.3, 2 - a/t=0.4, 3 - a/t =0.6 , 4 - a/t=0.8)

The elastic stress intensity factors distribution of along the crack front with the aspect ratio a/c = 0.3 for aluminum alloys D16T and B95 under the uniaxial tension (UT) and three-point bending (3PB) are plotted in Figure 2. As can be seen from Fig. 2 the elastic stress intensity factor depends on the crack size and position, and also on the loading type. At the same time, elastic SIF is not sensitive to the plastic properties of the considered materials. The K 1 distributions coincide for the corresponding positions of the crack fronts (a/t) in specimens with the properties of aluminum alloys D16T and B95 under the considered loading types. Furthermore, the elastic SIF is not sensitive to temperature in the considered range, since the same K 1 distribution corresponds to all temperature values (20°C, 250°C and -60°C) for two materials (aluminum alloy D16T and B95), depending only on the loading type and a crack front position. In other words, the elastic stress intensity factor exhibits dependence only on geometric parameters of specimen and crack and also on the loading type. This fact imposes restrictions on the use of the elastic stress intensity factor as a fracture resistance parameter. Figure 3 shows the plastic stress intensity factor distributions along the semielliptical crack front in specimens of alloys D16T and B95 under two loading types in the temperature range. As well as elastic SIF K p depends on the crack size and position, and on the loading type, but in contrast to the K 1 , the plastic SIF depends on the material properties and the temperature. It should be noted that the plastic properties of the material determine the quantitative effect on the plastic SIF. For identical crack front positions and loading conditions a higher value of K p is achieved in specimens produced from B95 alloy in comparison with specimens from D16T. This conclusion is valid for all combinations of variable parameters presented in Table 1. The plastic stress intensity factor for both materials under uniaxial tension and a three-point bending increases with temperature increasing from -60 to 250°C. Additionally, the plastic SIF K p gradually decreases with increasing aspect ratio a/c from 0.3 to 1. It can be observed that the plastic stress intensity factor distributions have a subsurface extremum for both of materials and loading types in temperature range for crack with aspect ratio equal to 0.3, whereas in the case of a semicircular crack (a/c = 1) K p assumes a constant value, independent of the position along the front.