PSI - Issue 2_A

Uwe Mayer / Procedia Structural Integrity 2 (2016) 1569–1576

1572

Uwe Mayer / Structural Integrity Procedia 00 (2016) 000 – 000

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rate, T 0,5.3 and T 0,5.8 . Separate evaluations of the reference temperature result in T 0,5.3 = -5 °C and T 0,5.8 = +16 °C. According to the current version of ASTM E1921, the results could be evaluated all together as long as the individual loading rate differs not more than a factor 3 from the average loading rate. Considering these new results, obviously this range has to be narrowed. A series of 14 tests at 20 °C and a loading rate of about 2x10 5 MPa√m s -1 leads to T 0,5.3 = -12 °C. For the series of 14 tests with 1T C(T) specimens at 0 °C and a loading rate of about 2x10 5 MPa √ m s -1 only a small amount of plasticity was observed. Single temperature evaluation of the reference temperature leads to T 0,5.3 = -1 °C. The individual single temperature evaluation results for the reference temperature T 0,5.3 are 16 °C higher for test temperature -20 °C and 11 °C lower for test temperature +20 °C than this evaluation at test temperature 0 °C.

Fig. 2. T 0,5 -multi temperature evaluation for all 1T C(T) tests of the project

(b) T 0,5.8 -multi temperature evaluation for all 1T C(T) with dK/dt=7x10 5 MPa√m s -1

Fig. 3. (a) T 0,5.3 -multi temperature evaluation for all 1T C(T) with dK/dt=2x10 5 MPa√m s -1 ;

2.1. Possible modifications for the evaluation of test series at elevated loading rates

A proposal from Schindler and Kalkhof (2013), to solve this issue is the modification of the exponent p in the definition of the master curve. K Jc(med) = 30 + 70 exp [p·(T-T 0 )] (3) Instead of K Jc(med) = 30 + 70 exp [0.019·(T-T 0 )] (4) the shape of the master curve is changed to K Jc(med) = 30 + 70 exp [0.03·(T-T 0 )] (5) This proposal is analogous to the recently developed advanced master curve using a variable exponent taking into account the influence of temperature and yield stress on the shape of the quasi-static master curve, Wallin (2011).