NON-ISOTHERMAL STRESS CYCLE PARAMETERS INFLUENCE

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261 Non-isothermal Stress Cycle Parameters Influence on the Middle Alloy Steels Durability The durability, 2N [inversions] 1800 1600 1400 1200 1000 800 2N= -4735.3De + 2049.4 R 2 = 0.9403 t=600 o C 600 0 0.1 0.2 0.3 The relative total strain variation, De [%] 12 MN/m 28 MN/m 55 MN/m Figure 5. The durability vs. the relative total strain variation for maximum cycle temperature of 600 o C and different rigidities values. The durability, 2N [inversions] 900 800 700 600 500 400 300 2N= -979.11De + 939.29 R 2 = 0.9598 t=700 o C 12 MN/m 28 MN/m 55 MN/m 0 0.1 0.2 0.3 0.4 0.5 0.6 The relative total strain variation, De [%] Figure 6. The durability vs. the relative total strain variation for maximum cycle temperature of 700 o C and different rigidities values. The durability, 2N [inversions] 500 400 300 200 100 t=800 o C 12 MN/m 28 MN/m 2N=-318.63De+538.69 55 MN/m R 2 = 0.932 0 0.2 0.4 0.6 0.8 1 1.2 The relative total strain variation, De [%] Figure 7. The durability vs. the relative total strain variation for maximum cycle temperature of 900 o C and different rigidities values. Durability, 2N [inversions] 1600 1400 1200 1000 800 t=600 o C 2N = -78.434 t + 3885.8 R 2 = 0.8978 12 MN/m 28 MN/m 55 MN/m 25 27 29 31 33 35 37 39 The cycle duration, t [s] Figure 8. The durability vs. the cycle duration for maximum cycle temperature of 600 o C and different rigidities values
Adrian Catalin DRUMEANU, Niculae Napoleon ANTONESCU, Ion NAE, Marius Gabriel PETRESCU 262 Durability, 2N [inversions] 800 700 600 500 400 300 2N = -17.586 t + 1837.6 R2 = 0.865 t=700 o C 12 MN/m 28 MN/m 55 MN/m 60 70 80 90 The cycle duration, t [s] Figure 9. The durability vs. the cycle duration for maximum cycle temperature of 700 o C and different rigidities values Durability, 2N [inversions] 500 400 300 2N = -5.7139t + 1045.6 R 2 = 0.8853 t=800 o C 12 MN/m 28 MN/m 55 MN/m 200 100 110 120 130 140 150 The cycle duration, t [s] Figure 10. The durability vs. the cycle duration for maximum cycle temperature of 800 o C and different rigidities values It can be observed that between the parameters taking into account and the durability it exists a good correlation which is proved by the high values of the determination coefficient. This fact imposes to do a global evaluation of the interdependence between the durability and the main nonisothermal cycle parameters (the maximum temperature of the cycle, the system rigidity and the cycle duration), using multiple correlation regression. For this case, it is proposed the next equation: A 2N = tW τ a b c where: 2N is the durability, inversions; t is the maximum temperature of the non-isothermal cycle, o C; W is the system rigidity, MN/m; τ is the cycle duration, s; A, a, b, c are the equation constants which have the values A = 323594, a = 0.26, b = 0.182, c = 0.948. The characteristics of the regression equation (11) are: the maximum temperature value of the nonisothermal stress cycle t, in the range of 600…800 o C; the system rigidity W, in the range of 12…55 MN/m; the duration of the cycle τ, in the range of 25…150 s; the durability 2N, in the range of 200…1600 inversions; the determination coefficient value R 2 = 0.992. Regarding the equation regression (11), it can be remarked the good correlation between the independent variables which are considered and the dependent variable. This good correlation signifies the fact that the parameters of the non-isothermal stress cycle, which were considered, have the major influence on the tested steels durability. (11) 7. CONCLUSIONS The main conclusions, which can be detached from the experimental results above presented, are:
Page 1 and 2: SISOM - 2004, BUCHAREST, 20-21 May
Page 3 and 4: Adrian Catalin DRUMEANU, Niculae Na
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NON-ISOTHERMAL STRESS CYCLE PARAMETERS INFLUENCE

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