PSI - Issue 13

Yuki Nishizono et al. / Procedia Structural Integrity 13 (2018) 1817–1827 —‹ ‹•Š‹œ‘‘ Ȁ –”—…–—”ƒŽ –‡‰”‹–› ”‘…‡†‹ƒ ͲͲ ሺʹͲͳͺሻ ͲͲͲ – ͲͲͲ

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1820

( p ̅̅̅ ) = y (1 + p ̅̅̅ − ) ( p ̅̅̅ , p ̅̅̅ . ) = static ( p ̅̅̅ ) ⋅ [1 + ( p ̅̅̅ . ) 1 ]

(2)

(3)

3. Preliminary experiments

The authors analyzed the relationship between test specimen shape and crack driving force transition by a number of dynamic 3D elasto-plastic FEAs in which the input data such as crack front shape and crack velocity history are assumed to be constant and crack driving force varies with crack propagation, which is the simplification for the affinity with the conventional explanation of crack propagation as described in Chapter 1, and obtained the appropriate test specimen shape. In this chapter, the authors carried out “Preliminary experiment s ” for confirming the validity of selected test specimen shape. 3.1. Selection of test specimen shape The press-notched bend test is a single edge notched bend test, which was standardized as a simplified evaluation method of arrest toughness in steel materials in 2015 (The Japan Welding Engineering Society, 2015). In this test, arrest toughness ca−PB can be evaluated by measuring 0 and . The calculation formulas are shown in Eqs. 4~6. Although this evaluation method is highly versatile because of its simplicity, the static calculation formulas assuming 2D elastic body may not be able to accurately characterize the dynamic crack driving force. Actually, it has been pointed out that ca−PB deviates significantly from ca evaluated by the wide plate tensile test in the Arrhenius type temperature dependence, as shown in Fig. 1 (Kawabata et al., 2017). It has also been pointed out that the crack arrested positions in the press-notched bend tests tend to concentrate in the limited region and the region corresponds to the vicinity of neutral plane in bend where the dynamic crack driving force d decreases at a high rate (Kawabata et al., 2017). Fig. 2 shows the typical d transition in the press-notched bend test and the ideal d transition aimed in this study. In a simplified test without temperature gradient, it is desirable that d decreases monotonically at a low rate with crack propagation. In addition, d at a peak needs to be higher than that in the press-notched bend test in order to evaluate arrest toughness in high range required for modern steel plates, e.g. used for container ships. The authors focused on the influence of the tensile and compressive stress distribution formed by bending load on d transition and optimized test specimen shape. As a result, the authors confirmed that d transition in the test design shown in Fig. 3 is very close to the ideal d transition. The position of neutral plane in this test design greatly differs from that of the press-notched bend test since the longitudinal compressive stress in the bottom of specimen is enhanced. This newly developed specimen is denoted tapered three-point bend test specimen. ca−PB = 3 0 2 √ [1 + + 1 6 8 ( 0 ) ∫ 2 ( ) 0 ] −1 × ( ) √ ( ) Where = , 0 = 0 , = (4) ( ) = 1.99 − (1 − )(2.7 2 − 3.93 + 2.15) √ (1 − ) 3 2 (2 + 1) (5) ( ) = ( 1 − ) 2 × (12.77 4 − 34.94 3 + 36.82 2 − 19.57 + 5.58) (6)