AAE552-Session21

AAE552-Session21 - AAE 552 Spring 2009 A. F. Grandt AAE...

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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 21 – 2 March 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 21 27 February 2009 Last Time: Finish CT Backscatter X-ray Image Quality Today: Applications Safety issues Summary Start Ultrsonics 4 Chapter 11: Radiography Topics Overview Absorption/Scatter Radiation sources Image formation Image quality Examples Computed Tomography Safety issues Summary 5 Assignment Please read Textbook : Chapter 11 - Radiography Chapter 12 - Ultrasonics Exam #1 – Session 29 (Friday, 27 March 2009) Final Exam – Wednesday, 6 May 2009 (comprehensive) Image Quality 6
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AAE 552 Spring 2009 – A. F. Grandt 2 7 Scatter Control Sources of scatter Internal – x-rays thru object Side – from walls, etc Back scatter – after pass thru object - from floor, etc. Build-up Factor (BF) Measure direct/indirect radiation that strikes image plane BF = (I direct + I scatter )/ I direct = 1 + I s /I d BF can vary from 2 – 20 Smaller with increased energy Source Test Object Film Floor 8 Scatter Control Control scatter Filters Screens Shield Source Sides Back Lead backing on film package Source Test Object Shields Film 9 Geometric Factors Size Controlled by placement of source, object, film Geometric unsharpness U g Caused by finite source width Film unsharpness U f Inherent to film/process Image Quality Indicators Used to determine “quality” of recorded image 10 Image Size Depends on Placement of Source, Object, and image Plane (Fig. 11.10) Note size increases as object/image distance b increases image a b W o object source W o W i = a + b a 11 Source Density of film Object Film U g S a b U g Geometric Unsharpness U g due to Finite Width Source (Fig. 11.11) S/a = U g /b Note U g decreases as b decreases 12 ideal Film base emulsion Lead source U f actual Film density lighter darker Film Unsharpness U f Due to Emulsion Excitation (Fig. 11.12)
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AAE 552 Spring 2009 – A. F. Grandt 3 13 Film Unsharpness U f Inherent to film and processing Can be calibrated Increases with x-ray energy Film Unsharpness U f X-ray energy 14 Total Unsharpness Complex combination of geometric and film unsharpness Define following cases High-sensitive technique Let U g = U f Low-sensitive technique Let U g = 2 U f Optimize set-up parameters for x-ray Given U f specify spot width S, object – plane distance b, and source – object distance a for desired U
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AAE552-Session21 - AAE 552 Spring 2009 A. F. Grandt AAE...

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