May 2013 NDCM-XIII Le Mans1 Materials Evaluation

Variations in Crack Detectability Due to Load History and State of Stress John C. Duke, Jr. and Nicole Capella Damage Science and Mechanics Laboratory Virginia Tech May NDCM-XIII Le Mans

Presentation Overview Presumptions and Assumptions The Ultimate Objective Comparison of Crack Detection and Sizing Different Load Conditions during Detection Ultrasonic and Eddy Current Scanning, Fracture Surface examination Future Considerations May NDCM-XIII Le Mans

Presumptions and Assumptions The structure built is the same as the design. –The loading of components is consistent with the design model. –All critical cracks/flaws (manufacturing) are detected and sized correctly (90/95 POD) The properties of the materials used are the same as the handbook values. –Crack growth is predictable –Service regime is the same as the design regime May 2013 NDCM-XIII Le Mans4

What Designers Assume As technology improves smaller flaws can be detected and sized properly. Computational tools can be used to verify damage tolerant response… NASAGRO, etc. Computational tools can be used to determine POD --- model assisted POD MAPOD The design assumptions are valid May 2013 NDCM-XIII Le Mans5

May 2013 NDCM-XIII Le Mans6 Damage development begins with the 1 st cycle Life: 1.1 million cycles (N=0    failure  ) 50 μm

Small cracks grow faster than short cracks May 2013 NDCM-XIII Le Mans7

The Ultimate Objective Characterize the condition of the structure Assess how the condition of the structure will affect performance under the expected service regime Alter the regime if necessary or repair the condition to allow for enhanced performance May 2013 NDCM-XIII Le Mans8

Reliability Variability in actual material properties Variability if actual level and state of stress experienced by flaws Variability of size of flaws Variability between assumed and actual loads Variability of “ideal” PoD and actual PoD May 2013 NDCM-XIII Le Mans9

The Study Two 7075 T651 COD specimens cycled to initiate and grow cracks Subject cracks to different loading conditions during examination by Eddy Current and Ultrasonic Examination Load precracked specimens quasi- statically to fracture; monitor AE measure COD versus load. May 2013 NDCM-XIII Le Mans10

May 2013 NDCM-XIII Le Mans11 Specimen 1Specimen 2

May 2013 NDCM-XIII Le Mans12 Specimen 1 unwedged 15 MHz (focus 1.5 in) Specimen 1 wedged 15 MHz (focus 1.5 in)

May 2013 NDCM-XIII Le Mans13 Specimen 2 no load 15 MHz (focus 1.5 in)

Specimen 2 different loading during examination (7.3>6.6mm, 6.9 mm>6.2mm) May 2013 NDCM-XIII Le Mans14

May 2013 NDCM-XIII Le Mans15 Specimen 1 Wedged top 5.6mm bottom 7.1 mm

Comparison of Loading to Failure May 2013 NDCM-XIII Le Mans16

May 2013 NDCM-XIII Le Mans17 Specimen 1 Specimen 2

May 2013 NDCM-XIII Le Mans18 Specimen 1 Specimen 2 top

Summary The size of the ultrasonic beam influences crack sizing The size of eddy current probe influences crack sizing The state of stress experienced by the crack during examination influences sizing by both UT and ECT Load spectrum during cycling affects crack growth and AE response Much more NDMC is possible May 2013 NDCM-XIII Le Mans19

Questions/Reactions VT Damage Science and Mechanics Laboratory May 2013 NDCM-XIII Le Mans20