Engine Titanium Consortium - Center for Nondestructive Evaluation ...

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The drawback of this method is that it ignores the effects of distortion of the ultrasonic beam during propagation through the metal microstructure. Phase I work has shown that beam distortion can be a major contributor to the response from flaws and backwalls. Even when beam distortion effects are minor and energy loss dominates, the material attenuation is found to vary significantly with position in a given billet in conjunction with noise banding as was shown in Figure 6. The effects of noise banding and nonuniform attenuation can lead to an incorrect measurement of flaw response, and a true inspection sensitivity different from that assumed from calibration. The current attenuation compensation technique will be evaluated by applying it to several billet segments, then drilling a number of flat-bottom or side-drilled holes into the sections, and comparing the measured amplitudes of those holes to those expected from the attenuation analysis. Improvements will focus on selection of a transducer which will minimize the effects of beam distortion and provide an attenuation estimate which enables good prediction of the hole echo amplitudes. Billet Specification: The specification for billet inspection (AMS 2628) will be updated to reflect improvements achieved by this subtask. Results will also be reported in required FAA format. Objective/Approach Amendments: Objective and approach remain as originally proposed in July 1998. Progress (January 1, 2002 – March 31, 2002): Several consortium conference calls were conducted during the quarter to discuss the details of the subtask. A number of technical issues were discussed and decisions reached. The technical issues and discussions are summarized into three primary areas, (1) Attenuation-Compensation, (2) 10” Billet Transducers and (3) 14” Chord Block Transducer and discussed separately below. One goal of Subtask 1.2.1 is to critically examine existing methods for attenuation compensation during billet inspection, and, if necessary, recommend improvements. Existing methods typically use the average strengths of back-wall echoes to estimate the attenuation difference between a billet under inspection and a calibration standard. During the Jan-Mar quarter, a series of experiments were performed to determine how well back-wall (BW) amplitude variations mirror the amplitude variations for an array of nominally-identical small internal defects. The measurements were carried out at GEAE and Honeywell, and results were analyzed at ISU. A 15”-long section of 6"-diameter Ti 6-4 billet was obtained which displayed large variations in BW amplitude during scanning. These variations presumably arise from differences in the local "effective" attenuation of the billet, with both energy loss and microstructure-induced beam distortion effects contributing to that attenuation. A series of #4 FBHs were drilled 0.3” deep into the OD of the billet, some at locations having large BW amplitudes, and others at locations having small BW amplitudes. The billet section was then inspected using several transducers (with different beam sizes at the back wall) to determine the degree of correlation between the FBH amplitudes and the nearby BW amplitudes. Initial measurements at GEAE used two 5-MHz fixedfocused transducers: (1) a multizone probe designed to focus near the center of 6"-diameter billet when operated at a 3” water path; and (2) a multizone probe designed to focus near the center of 13" billet, with the water path modified to 6.6” so as to best focus the beam near the BW of the 6" billet under study. Additional inspections were made at Honeywell using a 114-element, 5-MHz, phased-array transducer. The array transducer was used to simulate inspections for two other Quarterly Report – January 1, 2002 –March 31, 2002 print date/time: 6/6/2002 - 8:39 AM – Page 23
fixed-focus transducers that were not readily available. We note that 6"-diameter billet was chosen for these initial experiments because existing transducers were available which could approximately focus a sound beam near the back wall in such a billet (one of the focal conditions of chief interest). #4 FBHs were then chosen to simulate internal defects, because such targets were large enough to be easily seen for the range of focal conditions being investigated. C-scan images for four measurement trials are shown in the upper panels of Figures 1-4, respectively. The upper-left panel of each figure shows the rectified peak amplitude of the BW echo as a function of position for a full-round inspection of the 15”-long billet section. The upperright panel displays images of the FBHs, obtained by performing a second scan at increased gain, using a time gate that enclosed the FBH echoes, but excluded the BW echoes. Annotations on the upper panels list the peak FBH amplitudes and the average BW amplitudes in small regions centered about each FBH location. In all cases, the listed amplitudes are the percentage of Full Screen Height (FSH). One notices in each figure that the BW and FBH both amplitudes vary considerably, and that large (small) FBH amplitudes are usually associated with large (small) BW amplitudes at similar positions. The correlation between FBH and BW amplitudes is further illustrated in the lower panels of Figures 1-4. For each of the four inspections, the absolute amplitudes of the BW and FBH signals have been adjusted to have a mean value of 50% FSH for the suite of FBH targets. These rescaled amplitudes are shown in the lower-left panel, with the principal FBH targets numbered 1-13 (from top to bottom and left to right in the C-scan images). The lower-right panels display "correlation plots" of the rescaled FBH amplitudes versus the rescaled BW amplitudes. If there were perfect correlation between the two types of echoes, the plotted points would all fall along a straight line passing through the origin and having a slope of unity. In each case, a best-fit line through the origin is shown, and its slope is seen to be close to the ideal value of 1 in each case. Overall, the BW and FBH amplitudes were found to be generally well correlated, with the degree of correlation being largest when the beam was focused near the FBH targets. The results summarized in Figures 1-4 indicate that BW echoes can be used to track attenuation variations within a billet. Presumably, BW echoes can also be used to ascertain the attenuation difference between a billet under inspection and a calibration standard. Because of the significant variation in BW and FBH amplitudes with billet position, the results suggest that attenuation compensation procedures should make use of extreme BW amplitude data values rather than only average values. Quarterly Report – January 1, 2002 –March 31, 2002 print date/time: 6/6/2002 - 8:39 AM – Page 24
Page 1 and 2: Engine Titanium Consortium Quarterl
Page 3 and 4: Project 1: Task 1.1: Subtask 1.1.1:
Page 5 and 6: findings for the first billet studi
Page 7 and 8: measured P(L) curve, and tabulate t
Page 9 and 10: 1.2 1.0 0.8 V-DIE-A coupon "D" (axi
Page 11 and 12: Attenuation (dB/in) . Waspalloy Att
Page 13 and 14: Deliverables: Fundamental propertie
Page 15 and 16: Small Diameter Billet Assessment: A
Page 17 and 18: Under normal circumstances one woul
Page 19 and 20: Plans (April 1, 2002 - June 30, 200
Page 23: system will be at GE, and evaluatio
Page 27 and 28: Back-Wall Scan FBH scan 20% 57% 49%
Page 29 and 30: 63% Back-Wall Scan 74% FBH scan 58%
Page 31 and 32: Figure 6. Noise and target amplitud
Page 33 and 34: Original Date Revised Date Descript
Page 37 and 38: Objective/Approach Amendments: Obje
Page 39 and 40: (a) Transducer is: 15 MHz 0.5”-Di
Page 41 and 42: FOM (std. units) 0.20 0.18 0.16 0.1
Page 43 and 44: Peak> Range of Ave. Range of Peak G
Page 45 and 46: The average noise characteristics,
Page 47 and 48: Noise C-scans through the “Flat S
Page 49 and 50: 4.0” Convex Block; Flat Side Insp
Page 51 and 52: % FSH Noise Measurements from flat
Page 53 and 54: Original Revised Description Status
Page 57 and 58: possible candidates. Development wo
Page 59 and 60: Forging Calibration Standard #1 1.7
Page 61 and 62: Surface Finish Studies The plans fo
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Page 65 and 66: size was adequate to support a 0.04
Page 67 and 68: phased array instruments. The desig
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Page 71 and 72: Task 2: Task 2.1: Subtask 2.1.1: In
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Figure 2. A preliminary design of t
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Publications and Presentations: Dat
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Survey of common practices (industr
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include air drying, oven drying, an
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aluminum oxide blasting is conceali
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Original Date Revised Date Descript
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Project 3: Task 3.1: Subtask 3.1.1:
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the methodology. These may be thoug
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model parts across 17 micrograph pl
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Z Y X Figure 4. Angle View of Void
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A report documenting the relative e
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naturally occurring flaws in forgin
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Milestones: Revised dates of TBD ar
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7a-7l 6 8 9 10 Key additional ingre
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incorporating the results of the pr
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