PSI - Issue 2_A

2

Abhishek Tiwari et al. / Procedia Structural Integrity 2 (2016) 690–696 Author name / StructuralIntegrity Procedia 00 (2016) 000–000

691

Nomenclature β

fitting parameter used in σ *- V * post processing

yield strength

σ YS σ*

critical maximum principal stress encompassing volume responsible for cleavage

σ e σ h

equivalent/von-Mises stress hydrostatic stress component

ratio of equivalent stress and hydrostatic stress components integrated q in the sampled active volume, V * encompassed by σ *

q

q W K JC

elastic plastic fracture toughness based on J -integral K JC ,(1T) elastic plastic fracture toughness based on J -integral for specimen of thickness 1 inch T 0 reference transition temperature defined by ASTM E1921-13a T stress second term of William’s stress function Δ T stress Change in T stress as a function of increasing crack length V reference volume used for normalizing Weibull stress or Weibull triaxiality V 0 threshold active volume used as fitting parameter V * critical Volume responsible for cleavage encompassed by σ* (σ 1 > 2×σ YS at crack tip) W width of a fracture specimen Z ’ curve fitting parameter TPB three point bend SSY Small Scale Yielding

The conventional Master Curve approach, which is used to characterize the fracture behaviour of ferritic and ferritic/martensitic steels, restricts the crack depth to be in the range of 0.45 ≤ a/W ≤ 0.55 (ASTM E1921-13a, 2013). The fracture toughness is known to decrease with increasing crack depth owing to increase in constraint (Chen et al., 2007). Despite the fact that the fracture parameters corresponding to shallower crack depth are unconventional due to its non-conservative values, in transition region a correlation to assess the shift in reference transition temperature with different crack depth is of great importance. The fracture toughness of ferritic and ferritic/martensitic steels having BCC structure, generally shows a transition not only with temperature, but also with crack depth being tougher for shallower crack and brittle for deeper crack in DBT region. This is attributed to constraint loss for shallow cracks. In this work, the MC methodology is used to estimate reference transition temperature for different crack depths and the loss of constraint is examined numerically. The details on Master Curve methodology is not described in this work and can be found elsewhere for e.g. Wallin (1999), ASTM E1921-13a (2013). 2. Experimental details and material The Indian Reduced Activation Ferritic Martensitic Steel (In-RAFMS) is a newly developed steel in the category of reduced activation ferritic martensitic steel for fusion reactor blanket application. The chemical composition of the steel is shown in Table.1. The steel plates were solutionized after hot rolling to 1250K for 30mins and tempered for 60mins at 1033K. The steel comprises tempered martensitic structure with carbides precipitated at lath and pre austenitic grain boundaries (Laha et al.,2013). The fracture specimens were fabricated in the form of sub-sized charpy specimen with 5mm thickness.

Table 1. Chemical composition of In-RAFMS

C

Cr

W

V

Ta

Si

Mn

S

N

Ni,Sn,Co

0.08

9.15 1.37 0.24 0.08 0.026 0.53 0.002 0.02

≤0.004