AAE552-Session7

AAE552-Session7 - AAE 552 Spring 2009 A. F. Grandt AAE 552:...

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AAE 552 Spring 2009 – A. F. Grandt 1 1 AAE 552: Nondestructive Evaluation of Structures and Materials A. F. Grandt, Jr. Professor of Aeronautics and Astronautics Purdue University W. Lafayette, IN 47907 Session 7 – 28 January 2009 2 Contact Information Alten F. (Skip) Grandt, Jr. Email: aae552@ecn.purdue.edu Telephone: Office: 765-494-5141 Home: 765-463-4276 FAX: 765-494-0307 Course webpage accessed at: http://www.itap.purdue.edu/tlt/blackboard 3 AAE 552 Session 7 28 January 2009 Last Time: Accept/reject Inspection errors Factors that influence NDE POD Today: Probability of Detection (POD) NDE design requirements Evaluating maturity of technology 4 Assignment Please read : Textbook Chapter 4 Web page NASA NDE Guidelines and Requirements 1978 USAF POD Study Please Submit : Session 9 (2 February) – Abstract for Paper #1 – see webpage for more details 5 Ideal versus Actual Accept/Reject Decision Type I error – Reject good parts (economic) Type II error – Accept bad parts (safety) a* Crack size a 100% Probability of rejection Type II Error (safety) Type I Error (economic) “Ideal” Actual Fig 4.2 6 Factors that Influence Inspection Results (Section 4.6) Correct method selected for inspection Method applied correctly Procedures, training, calibration, etc. Test environment Access, working conditions, etc Variability Inherent in equipment, material, anomalies, etc. Variability in fatigue process Human factors
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AAE 552 Spring 2009 – A. F. Grandt 2 7 Human Factors Human Factors play large role in accuracy of NDE Mental acuity of inspector Fatigue Alertness Response to environment Emotional outlook, confidence Proficiency, training Expectations, prior knowledge 8 Inspector Qualifications (depends on method/employer) Trainee – minimal training/experience Level 1 – qualified to conduct particular NDE method Set up and supervised by another individual Qualified to run instrument 4-10 hrs training plus exam Level 2 More training experience than level 1 Can set up inspection, instructions for level 1 Level 3 Administrative/supervisory role Requires degree, at least 1 year of experience 9 Possible Inspection Results (Fig. 4.7) A1 -- Cracks are detected (correct rejection) Type II error (Safety problem) A2 -- cracks are undetected (incorrect acceptance) N1 specimens contain cracks Type I error (Economic problem ) A3 -- cracks are detected (false rejection ) A4 -- no cracks are detected (correct acceptance) N2 specimens are uncracked N total specimens N = N1 + N2 POD = A1/N1 10 Probability of Detection Note: will be “scatter” in experimentally determined POD vs a curve – determine “confidence” bounds Probability of Detection (POD) 1.0 0.9 0.0 Crack Size (a) a nde 90/95 Crack Size 95% Confidence Mean 90% POD 95% confidence Figure 4.10 Charles A. Annis • Statistical Consultant
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AAE552-Session7 - AAE 552 Spring 2009 A. F. Grandt AAE 552:...

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