1. Load separation in 17 mm wide CT specimen of Zr-2
Load separation in 17 mm wide CT specimen of Zr-2.5Nb pressure tube material
A K Binda,b*, S. Sunila, R. N. Singha,b, Abhishek Tiwarib, J. K. Chakravarttya
Bhabha Atomic Research Centre, Mumbai, India –
Homi Bhabha National Institute, Mumbai, India –

2. Purpose
To check load separability in 17 mm wide CT specimen of Zr-2.5Nb pressure tube material
To calculate h factor using load separation method

3. Outlines Introduction to Indian PHWR
Fracture testing of Pressure Tube(PT)
Difference between Conventional CT and 17 mm Curve CT specimen
Material and testing
Results
Conclusions

4. Introduction to Indian PHWR
Pressure tube type reactor. Pressure tube (PT) acts as miniature pressure vessel
Heavy water cooled and heavy water moderated reactor
Uses natural uranium as a fuel
Quadruple melted Zr-2.5Nb alloy are used as PT material because of high strength at operating temp., lower corrosion rate and lower hydrogen pick up rate

5. Introduction to Indian PHWR
Type of reactor MWe 540 MWe
No. of coolant channels
Wall thickness, mm

6. Fracture testing of Pressure Tube(PT)
Curved CT specimens with W=17 mm are most widely used for fracture test of pressure tube (PT) in longitudinal direction because:-
1. Obtaining a conventional CT specimen from PT is difficult and if obtained its fracture toughness may not be correct fracture toughness for PT thickness
2. Flattening of PT may alter texture and mechanical properties and will introduce residual stress in the PT
hpl and gpl of Conventional CT as given in ASTM E-1820 is used for Curved CT specimens
Based on bending theory, Chow and Simpson [ASTM STP ] showed that hpl and gpl of Curved CT specimen and Conventional CT will be same.
No data is available in open literature on hpl of curved CT specimen

7. Difference between Conventional CT and 17 mm Curved CT Specimen
Curvature of Curved CT specimen
Curved CT specimens does not meet thickness of W/B=2
Curved CT specimens of 220 MWe pressure tube also does not meet alternate thickness criteria of 2≤W/B≤4
Objective-: To calculate hpl of Conventional CT specimens just meeting the alternate thickness criteria of W/B=4 using load separation method a b
(a) Conventional CT specimen as recommended by ASTM E and (b) Curved CT specimen used for fracture testing of PT material

8. Material and testing Slit into 3 pieces at 120⁰
540 MWe PT spool (Inner Dia. 103 mm and thickness 4.5 mm)
Warm rolled at 400 ⁰C
Slit piece
Warm rolled plate from which Conventional CT was cut using EDM wire cut. Thickness after warm rolling mm

9. Typical (a) P vs. d and (b) P vs. dpl curves
Material and testing
Blunt crack Conventional CT specimens with a/W between 0.35 and 0.70 was cut warm rolled plates (B=4.25 mm)
For all specimens, W=17 and W/B=4
Each specimen was loaded up to maximum load and then unloaded
dpl calculated using initial elastic slope of the P vs. d curve a b
Typical (a) P vs. d and (b) P vs. dpl curves

10. Results
(a) P-dpl curve of the conventional CT specimens with different crack length and (b) Sij-dpl curve of the conventional CT specimens with different crack length for a reference crack, aj/W of 0.70.
For a/W of 0.45 and above, Sij was constant except a small region at the beginning
For a/W below 0.45, Sij was not constant indicating non separability of load

11. Results Sij vs. b/W curves are fitted with power law fit
Power law exponent m = hpl
hpl was constant and equal to 2.08 for a/W between 0.45 to 0.70
hpl was slighlty lower than that of reported by Sharobeam and Landes [IJF ].
(a) Sij vs. b/W curve of the conventional CT specimens for different reference cracks (b) Comparison of the hpl of conventional CT specimen calculated using load separation method with ASTM

12. Conclusions
Blunt conventional CT specimens with W/B=4 a/W between 0.35 to 0.70 were used.
Load separation does not exits for a/W below 0.45
hpl was constant between 0.45 to 0.70 and equal to 2.08
hpl was slightly lower than that of 2.13 as reported by Sharobeam and Landes [IJF ].