Issue 46

I. Čamagić et alii, Frattura ed Integrità Strutturale, 46 (2018) 371-382; DOI: 10.3221/IGF-ESIS.46.34 381 The fracture toughness values, K Ic , of specimens, taken from the new PM, tab. 8, range from 118MPa m1/2 obtained by testing at 20  C and decrease to 88MPa m 1/2 at 540  C. Also, the fracture toughness values, K Ic , of specimens, taken from the exploited PM, tab. 9, range from 100MPa m 1/2 obtained by testing at 20  C and decrease to 64MPa m 1/2 at 540  C. The fracture toughness values, K Ic , of specimens, taken from WM, tab. 10, range from 130MPa m 1/2 obtained by testing at 20  C to 94MPa m 1/2 obtained by testing at 540  C. The fracture toughness values, K Ic , of specimens, taken from HAZ from the side of the new PM, tab. 11, range from 109MPa m1/2 obtained by testing at 20  C and decrease to 78MPa m 1/2 obtained by testing at 540  C. The testing of specimens taken from HAZ from the side of exploited PM, tab. 12, the poorer values of fracture toughness K Ic are obtained. Namely, Namely, the value of plane strain fracture toughness, K Ic , ranges from 93MPa m 1/2 obtained by testing at 20  C, and decreases to 61MPa m 1/2 obtained by testing at 540  C, [1]. The obtained values of critical crack length, a c , fig. 10, at new PM are almost unchanged when it comes to room and working temperature. This was to be expected, because for the calculation of critical crack length, ac, the real values of yield stress obtained by tensile testing were used. However, exploitation weakening of PM has led to the fact that value of ac at specimens taken from exploited PM decreases by about 24% and is about 29mm. The obtained values of critical crack length, a c , fig. 12, at WM in relation to the yield stress level are quite low, and range from 20,2mm for the room temperature and decrease to 17,5mm which is the obtained value of a c , at the testing temperature of 540  C. However, if values of critical crack length, a c , in relation to yield stress of the new and exploited OM are calculated, they are significantly higher and indicate the good resistance to brittle fracture of WM. The obtained values of critical crack length, a c , fig. 14, at HAZ from the side of the new PM are slightly changed when it comes to room or working temperature. However, exploitation weakening of PM has led to the decrease of the value, a c , at notched specimens in HAZ from the side of exploited PM and at the testing temperature of 5400C is 27mm, [1]. C ONCLUSION ased on the testing results of tensile properties of specimens taken from the welded joint of the new PM and WM at selected temperatures, it can be concluded that a decrease in strength properties, that is, yield stress and tensile strength was obtained with the increase of temperature. Likewise, the increase of testing temperature leads to the increase of elongation. The increase of elongation with the temperature increase is explained by the increased overall plasticity of the material at higher temperatures, but also by the significantly unfavorable ratio of homogenous and non- homogenous elongation. Also, the exploitation time significantly impacts the reduction of strength properties and strain properties, which can be related to the microstructures of the exploited and new PM, [1]. Based on the obtained testing results of the critical stress intensity factor K Ic , which was due to inability to satisfy the plane strain conditions determined indirectly through the critical J Ic integral, we can see that the values of K Ic also depend on the testing temperature, placement of notches and exploitation time. The heterogeneity of welded joint mechanical properties, i.e. welded joint components significantly impacts the obtained values of plain strain fracture toughness, KIc. The weakest resistance to the crack propagation at static action of force, that is, the lowest value, K Ic , is at notched specimens in HAZ, and the best resistance to crack propagation is at notched specimens at WM. The character of the curves, exclusively changes depending on the testing temperature, placement of the notches and exploitation time. By analyzing the obtained curves, we see the almost identical character dependence of the individual curves in each group, except that the difference between the specimens is in the values of maximum force, Fmax, which is in direct dependence on the fatigue crack length, a , [1]. Exploitation time significantly impacted the resistance to crack propagation, which generally should be related to the weakening of mechanical exploitation properties of the used material in relation to the new material. The resistance to crack propagation, at specimens taken from the exploited PM and from HAZ from the side of exploited PM is for approximately 20% lower than at specimens taken from the sample of the new PM, and HAZ from the side of the new PM. The obtained testing results of fracture mechanics parameters (K Ic , J Ic i a c ) indicate two things. First, tendency to brittle fracture in the conditions of static load acting, is the lowest at the notched specimens in WM and PM and is the highest at the notched specimens in HAZ, i.e. HAZ in the concrete case has the worst resistance to brittle fracture. Second, the obtained testing results of exploited material indicate a significant difference in the results compared to the new material. Testing results and their analysis have justified the selected welding technology for the replacement of a part of the reactor mantle. B