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Material Performance Centre University of Manchester UNTF 2010 Andrew Wasylyk UNTF 2010 Assessment of Ductile Tearing and Plastic collapse in 304 SS Andrew.

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Presentation on theme: "Material Performance Centre University of Manchester UNTF 2010 Andrew Wasylyk UNTF 2010 Assessment of Ductile Tearing and Plastic collapse in 304 SS Andrew."— Presentation transcript:

1 Material Performance Centre University of Manchester UNTF 2010 Andrew Wasylyk UNTF 2010 Assessment of Ductile Tearing and Plastic collapse in 304 SS Andrew Wasylyk

2 UNTF 2010 Aim Assessment of defect behavior against crack initiation toughness can be highly pessimistic representations of failure load by unstable tearing or plastic collapse for low yield high toughness materials We aim to quantify the dynamically evolving relationship between failure by crack initiation, crack instability and plastic collapse. Use a combination of experimental and modeling approaches to quantify the relationship between crack initiation, ductile crack growth and the development of local and global plasticity in standard and novel specimens What? Why? How?Conclusions!

3 Andrew Wasylyk UNTF 2010 plastic zone Fracture process area Plastic zone Fracture Modes: Competition What? Why? How?Conclusions! *Anderson, Fracture Mechanics: Fundamentals and Applications, 2005

4 Andrew Wasylyk UNTF 2010 Problems and issues Materials with low yield and high tearing modulus can exhibit increase in toughness with crack propagation Represented by a J-Resistance curve Structural components can experience loss of constraint and plastic collapse – this process competes with tearing In order to take advantage of the increase in toughness through crack growth, a better understanding of the interaction of these mechanisms is required What? Why? How?Conclusions!

5 Andrew Wasylyk UNTF 2010 The J-Resistance curve is highly dependant on the test specimen constraint High constraint test specimens provides conservative (lower bound) values of fracture toughness when analysing low constraint structures J-Resistance curve: Constraint effect What? Why? How?Conclusions!

6 Andrew Wasylyk UNTF 2010 J vs Load can be superimposed on the J- Resistance curve The intersections between the two curve represent the onset of stable then unstable crack growth Constraint has a high influence on the prediction of the extent of stable crack growth Onset of Stable crack growth Onset of unstable crack growth High constraint Specimens can lead to conservative predictions of structural instability. Adequate constraint correction can lead to more accurate predictions enabling known conservatism to be quantified J-Resistance curve: Ductile Tearing Prediction What? Why? How?Conclusions!

7 Andrew Wasylyk UNTF 2010 Approach to study Aim: Development of a generic approach to defect tolerance assessment of components showing high ductility characteristics that take account of the inter-relationship of Δa, P & J Analysis of the dynamic relationship between crack initiation, propagation and development of local and global plasticity. Experimental studies including Image Correlation and conventional and micro mechanistic FE modelling Material used: 304 (L) Stainless Steel Has low initiation toughness and high tearing modulus. Used in nuclear cooling system piping Fully Austenitic Highly ductile Low carbon content What? Why? How?Conclusions!

8 Andrew Wasylyk UNTF 2010 Fracture Mechanics Experiment: Fracture toughness testing of scaled down Compact Tension specimens of thicknesses B=25, 15, designed according to British Standard Experimental set-up: Specimens are first fatigue-cracked to crack length (a) to specimen width (w) ratio of Fracture toughness testing under displacement control promoting stable crack extension Experiment will be monitored using: Image Correlation Load Line Opening Displacement What? Why? How?Conclusions! Experiments

9 Andrew Wasylyk UNTF 2010 Material Properties What? Why? How?Conclusions!

10 Andrew Wasylyk UNTF 2010 Material Properties What? Why? How?Conclusions!

11 Andrew Wasylyk UNTF 2010 Image Correlation Optical tracking of local displacement of features on the surface of the specimen Surface preparation: –25mm CT: White paint coating with random black speckles –15mmCT: Oxalic Acid electro- etching, I=6V,t=12min Displacement mapping obtained using Digital Image Software (DaVis). Equivalent plastic strain calculated using strain components obtained from DIC What? Why? How?Conclusions!

12 Andrew Wasylyk UNTF 2010 Unloading Compliance What? Why? How?Conclusions!

13 Andrew Wasylyk UNTF 2010 Unloading Compliance What? Why? How?Conclusions!

14 Andrew Wasylyk UNTF 2010 J-Resistance Curves What? Why? How?Conclusions!

15 Andrew Wasylyk UNTF 2010 J-Resistance Curves What? Why? How?Conclusions!

16 Andrew Wasylyk UNTF 2010 Finite Element: Plastic collapse What? Why? How?Conclusions!

17 Andrew Wasylyk UNTF 2010 Conclusions Specimen size had little effect on J initiation values corrected for crack tip blunting Yielding of the remaining ligament (Limit Load) occurs before crack initiation. Extensive plasticity occurs (>2% strain) occurs before significant tearing is observed. Specimen size had little influence on the relationship between initiation and Yielding of the remaining ligament Specimen size influenced the crack propagation instability What? Why? How?Conclusions!

18 Andrew Wasylyk UNTF 2010 Questions???


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