PSI - Issue 14

Filin V.Yu. et al. / Procedia Structural Integrity 14 (2019) 758–773 Author name / Structural Integrity Procedia 00 (2018) 000–000

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J = 35.7 N/mm. (vii) We find an estimate of the reserve factor n 1 for a high data scatter ( V = 0.50), see the formula (32) for explanations, taking into account the repeatability of the design case ( n case = 2)   case n n V 5 1 2 1   , (27) formula (26) was obtained by Monte-Carlo method of numerical experiments and counting the fracture/no fracture cases. In this example we get n 1 = 5.1. Then the required fracture toughness of the material J c should amount to 182 N/mm that approximately corresponds to CTOD = 0.21 mm. Note than in a real assessment other design cases should be also considered, e.g. pressure test. The obtained hypothetic figures are technically attainable and slightly less conservative than estimates derived from BS 7910. However, for embedded flaws the suggested method gives much less conservative results, as the residual stress at mid-thickness of welded joints with symmetrical groove is compressive. A lot of standards have been developed for various specimen geometries. The most known are listed below.  BS 7448, part 1 (1991) and ISO 12135 (2016) deal with single-edge notch bend specimens (SENB) and compact tension straight notch and stepped notch specimens C(T).  ASTM E1290 (2008) for CTOD measurement deals with SENB, stepped notch C(T) and arc shaped bend specimens A(B).  ASTM E1820 (2017) for J measurement deals with SENB, stepped notch C(T) and disk-shaped compact specimens DC(T).  GOST R 52927 (2015) Appendix B for CTOD measurement deals with SENB, straight notch and stepped notch specimens C(T).  BS 8571 (2014) deals with single-edge notch tensile specimens SENT, pin loaded or clamped-end. Testing of welded joints is described in two known standards.  ISO 15653 (2018) deals with SENB specimens and a specific case of shallow-notch SENB specimens.  ASTM E2818 (2011) in general refers to ISO 15653. All the above standards use simplified dependencies and approximations. For SENB, C(T) and similar specimen types they are based on an assumption that the load-displacement record obtained at the test depends only on the remaining section ligament, ( W-a ) in Fig. 4. 3.3 Experimental evaluation of critical J-integral J c and CTOD

Figure 4 — Ligament for deep-notched specimens predominantly loaded by bending

When a moment M makes a specimen bend to an angle  ,

θ



с

c

2

2

 0

 0

J c

Md

Pd

,

(28)



 



 t W a (

)

 t W a (

)

i.e., a critical value of J-integral is a double area under the diagram “load P vs. load line displacement  ” divided by ligament area. Index “c” relates to one of the critical events occurring during the test like a specimen fracture, pop-in or attainment of the maximum load. Polynomial approximations are applied for SENT specimens. CTOD test method if not based on correlation formula (10) as well as all the test methods for shallow-notched