Development of Ultrasonic C-Scan System. Ahmed Arabi Hassen, Jonathan Boyd and Uday K. Vaidya. Phone: ,

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1 Development of Ultrasonic C-Scan System Ahmed Arabi Hassen, Jonathan Boyd and Uday K. Vaidya Department of Materials Science and Engineering, University of Alabama at Birmingham, USA Phone: , 1. Abstract An ultrasonic C-scan was designed and constructed to expand the testing capabilities of the Department of Materials Science and Engineering (MSE) at the University of Alabama at Birmingham (UAB). The design aspect covers the tank and translational mechanisms, with the latter based on commercially available assemblies. The as-built assembly conforms to the preliminary engineering analysis and calculations and is consistent with the theoretical model presented. Testing on the tank and the drive mechanisms was performed. Ultrasonic inspection software that is compatible to the platform used by the motion software is needed for the optimization of the assembly. Keywords: Non Destructive Evaluation (NDE), ultrasonic C-scan, Inspection, Defects, FEA 2. Introduction Defects, flaws, or any irregularities can significantly alter the properties of various materials, which is generally undesirable; thus, various evaluation techniques are used to determine if a material contains defects or any discontinuities [1]. Defects are defined as any deviation from the nominal, ideal or specified geometric and/ or physical make-up of a structure or component and, for composite materials, most frequently arises during the manufacturing procedure [2]. Cracks and other damage indications on the surface of the material are easily detected. However, inspection for sub-surface and internal defects usually involves methods that require sectioning samples from a component for microstructural evaluation. Thus, nondestructive evaluation (NDE) methods are performed. NDE techniques involve material evaluation without damaging the component in question. These tests significantly decrease time and money in periodic assessments of components and product evaluation [3]. Ultrasonic inspection is considered as the most efficient method used for quality control and materials quality inspection in all major industries. High frequency sound waves, which are generated by a transmitting sensor, travel through the material via a coupling medium. These sound waves are reflected with some attenuation at interfaces, which can be associated to the presence of cracks, voids, inclusions, delamination, or other

2 discontinuities. A transducer receives and converts the signal to a voltage. Once the signals from the transducers are modified, a device displays the output as a time history of the sound waves travelling through the sample. ASM Handbook [4] presents the pulse- echo method as the most widely used ultrasonic method; this method is very often used for flaws location and thickness measurements. Ultrasonic data can be presented in different formats, which are A-, B-, and C-scan. A-scans show received ultrasonic energy as a function of time. B-scans display cross-sectional view of a specimen showing the depth or travel time of the sound waves with respect to the linear position of the transducer. C-scan display records echoes from the internal portions of test pieces as a function of the position of each reflecting interface within an area [5]. The ultrasonic signal amplitude or the time-of-flight is shown as a shade of gray or a color for each position that was scanned. Ultrasonic inspection is one of the most common and useful NDE techniques. In comparison with other NDE methods, it can detect and measure internal flaws with high degree of certainty. In addition, it requires minimal sample preparation, and testing can be carried out from a single surface [6]. Detailed images and results are acquired instantaneously. However, this technique has some limitations, it provides accurate detection of defects, which makes it more convenient to perform than other evaluation methods. In this paper a design and construction of an ultrasonic C-scan water tank unit is discussed. The assembled equipment can perform ultrasonic tests on various materials, primarily composites. That will expand the testing capabilities of UAB-MSE, which currently uses an ultrasonic A-scan unit. For the A-scan testing, ASTM E Standard Practice for Measuring Ultrasonic Velocity in Materials is used to identify the test procedure for measuring ultrasonic velocities in materials. The ultrasonic equipment involves an immersion tank and a translation mechanism that can be automatically adjusted and operated in the x, y, and z-axis. Also, it can accommodate a 24 by 24 composite panel. 3. Design The apparatus consists of an immersion tank, couplant (water), raster arms for translations, transducer, electronic signal generator, and an electronic interface to control, shows, and record output (LabView software). Design aspects will only cover the tank, tank frame, and raster arm. The components such as the translational mechanisms and electronics was purchased from manufacturers or constructed from existing assemblies. For achieving the optimum design some constrains should be considered for the design. The tank must be able to hold a water column of 12 inches and examine a 24 x 24 composite panel. It must be made of materials that can withstand the weight of the water and the sides of the tank must be rigid to minimize bending when under load. Any chemical reaction between the water and the inside surface of the tank and surrounding components must be avoided. The C-scan translational mechanisms must be adjustable and capable of traversing the x and y

direction with constant velocity. The raster arm must be adjustable in the z-direction and maintain a fixed position while traversing in the x and y direction. 3.1.

3 direction with constant velocity. The raster arm must be adjustable in the z-direction and maintain a fixed position while traversing in the x and y direction Immersion Tank The immersion tank was made of a transparent material that minimized the costs and complexities in the construction of the tank. The inner dimensions of the tank are x 28 x 18. The total weight of the tank with 12 of water is approximately 427 lb. The tank with 18 of water column weighs approximately 641 lb. The material selection was initially done using CES software. Considering the design constraints, properties of transparent materials were plotted and compared relative to each other. Since the properties considered on the CES plots weigh differently, a design evaluation matrix in Table 1 was also used to properly select the appropriate material. Cast acrylic (polymethyl methacrylate, PMMA) was chosen to be the best material to be used to build the immersion tank. Considering the load involved in this assembly, acrylic has sufficient rigidity and strength to satisfy the functional requirements. Although annealed and tempered glasses have higher modulus and strength under compression load, acrylic is more lightweight and is safer to use in case the experimenter/operator unintentionally drops the sample in the tank. Dissimilar to annealed glass, tempered glass will break to smaller and less sharp shards at impact; however, it is more expensive. Annealed glass is cheaper than acrylic, annealed glass has a price of 2.97 $/ square foot and acrylic has a price of 9.9 $/square foot, but the latter is easier to machine and handle. The tendency of acrylic to obtain surface scratches and to lose its clarity when in contact with water periodically was also noted. Therefore, acrylic meets the desired properties and design constraints for the tank. The tank frame was made of 80/20 aluminum extrusions, which provides support and stability as well as making it lightweight and convenient in terms of assembly/disassembly. The outer dimensions of the frame are as height, 32 width and length. A caster was attached to each leg of the frame for ease of maneuverability. The tank and the tank frame model are shown in Figure 1. Figure1: Tank frame model

Table 1: Immersion tank material selection Cast Acrylic Annealed Glass Tempered Glass Parameters Maximum Weighted Weighted Weight Rating Rating Rating Weighted Points Score Score Score Bulk Modulus

4 Table 1: Immersion tank material selection Cast Acrylic Annealed Glass Tempered Glass Parameters Maximum Weighted Weighted Weight Rating Rating Rating Weighted Points Score Score Score Bulk Modulus 10 20% Compressive Strength 10 20% Machinability 10 20% Density 10 15% Maintenance 10 10% Price 10 5% Durability (water & sunlight) 10 5% Safety 10 5% Total Score Continue Yes No No The design incorporates a gantry style system for movement in the x and y directions. Two rack and pinion systems drive both directions via stepper motors. The translation mechanism is secured on top of the 80/20 frame with fasteners that fit into the "T" slots of the aluminum extrusions. Flat rails are used as a guide for rolling linear carriages that will support the motors and bridge assembly that serves as a track for the z-axis translation mechanism, as shown in Figure 2. Utilizing these flat rails and linear carriages on both sides of the tank and bridge assembly prevent rotation or skewing of the bridge while traversing Figure 2: The translation mechanism assembly model, 1) Aluminum frame, 2) Y-Translation assembly and 3) X-Translation and bridge assembly

3.2. Translation Mechanisms A rack and pinion system translates the bridge in the x and y direction with the use of NEMA 23 stepper motors.

Flat, paint-coated rails, made of 1018 cold rolled steel, are used as a guide for rolling linear carriages that will support the motors and bridge assembly.

The z translation is comprised of 1/2-10- acme screw driven by a NEMA 23 motor. It has an anti-backlash nut and dual thrust bearings, which minimize end-play and backlash.

5 3.2. Translation Mechanisms A rack and pinion system translates the bridge in the x and y direction with the use of NEMA 23 stepper motors. The gear rack has a 20 pitch which mates with the 20 tooth, 20 pitch pinion drive. The gear rack is secured to the frame with rack clamps that ensure correct alignment. Flat, paint-coated rails, made of 1018 cold rolled steel, are used as a guide for rolling linear carriages that will support the motors and bridge assembly. Utilizing these flat rails and linear carriages on both sides of the tank and bridge assembly prevent rotation or skewing of the bridge while traversing, as shown in Figure 3a and 3b. The z translation is comprised of 1/2-10- acme screw driven by a NEMA 23 motor. It has an anti-backlash nut and dual thrust bearings, which minimize end-play and backlash. The assembly frame is pre-drilled and tapped for mounting on the bridge assembly. The assembly provides a total travel of 4 inches with a positive-stop limit switch for protection of the trust bearings, as shown in Figure 3c a) X-Translation and bridge assembly b) Y-Translation assembly 4 1 c) Z-Translation assembly Figure 3: Translation mechanism models, 1) Stepper motor, 2) Paint-coated rails, 3) Z-translation assembly and 4) Thrust bearings

6 4. Weight Calculations Since the immersion tank will be filled to at least 12 inches of water at all times, weight calculations were performed to determine the thickness of acrylic to be used and also the profile of 80/20 aluminum extrusion that will be sufficient to support the weight of the filled tank and the attached translation components [7]. Calculations were also performed considering an18 water height in the tank, which is the maximum height that the tank may be filled. By first performing weight calculations, the pressure acting on the base plate and sides of the tank may be calculated. The total load of filled tank is lbs. At this design, there are four crossmembers and two main supports that will support the weight of the filled tank. When the water filled to 18, each cross member will carry lbs each. Since he cross-members are supported by the main supports, each main support carries half of the entire load, so it can be said that the main supports carry 50% of the entire load, about lbs. Each vertical support carries ¼ of the entire load, which is lbs. 5. Finite Element Analysis Finite Element Analysis (FEA) was performed to determine how much and in what areas there will be stress. The pressure values may be used to perform FEA on the tank to determine the location and magnitude of deflection. ANSYS was chosen to run the finite element analysis of the acrylic tank filled with a water column of 18. The model was created using 4 node Shell 181 elements. These elements were given a thickness of 3/8. The model was created; the material properties of acrylic were applied to the model and the boundary conditions then applied to the model. The pressure created from the 18 water column was applied to the model. A constant pressure of 0.65 psi was applied to the inside of the base of the model and a gradient (slope) pressure was applied to all inside walls of the model. After the loads were applied, constraints could be applied. Displacement constraints created from the supports of the frame were applied in all degrees of freedom. Once the static analysis was complete, data was collected to determine if the tank could handle the applied boundary conditions. First, a displacement vector sum contour plot was created. This plot revealed the areas of maximum deflection of An isometric view and bottom view of the displacement vector sum can be seen in Figure 4a and 4b. A Von Mises stress contour plot was also plotted as shown in Figure 5. This plot showed were the highest and lowest stresses occurred and also the values of those stresses in psi. The highest stress was shown to be psi. With a stress of psi the tank has a safety factor of 6.5.

a) Isometric view b) Bottom View Figure 4: Displacement vector sum resulted from the pressure created by 18 water column Figure 5: Von Mises stress due to the load created by 18 water column 6.

The weight carried by each cross member and main support were calculated to be 109.17 lbs and 355.03 lbs. Using these values, uniform and point loads were calculated.

7 a) Isometric view b) Bottom View Figure 4: Displacement vector sum resulted from the pressure created by 18 water column Figure 5: Von Mises stress due to the load created by 18 water column 6. Beam Calculations To determine the deflections in the aluminum extrusions that support the filled immersion tank, several calculations were performed. The weight carried by each cross member and main support were calculated to be lbs and lbs. Using these values, uniform and point loads were calculated. Upon plugging these loads into beam deflection formulas, the maximum deflections of main supports and cross members were determined to be inches and inches respectively. This data shows that the supporting structure can easily withstand a load created by the tank being completely filled with water.

7. Construction and assembly 7.1. Mechanical component A 96 x 48 acrylic sheet with a thickness of 0.

8 7. Construction and assembly 7.1. Mechanical component A 96 x 48 acrylic sheet with a thickness of was pre-cut by Interstate Plastics using a table saw to obtain panels with the following dimensions: 36 x (base), 36 x 18 (front and back), 28 x 18 (side). A test fit was done after the acrylic pieces were received. The acrylic pieces to be joined must have smooth edges to ensure strong joints. Weld was applied on one horizontal edge at a time with about 5 minutes curing. The same procedure was followed in sealing the vertical edges. The sealed tank was left to cure for 2 days T5 aluminum extrusions were pre-cut to desired dimensions. 5/16-18 fasteners were used for joining. 90 o inside corner connectors with set screws and corner brackets were fastened on the top and bottom corners of the frame, respectively. The gussets were fastened below the bedrails to support the weight of the tank. Each caster was then connected to a base plate and to the legs of the frame. The C-scan assembly can be seen in Figure 6. A 0.25 thick cold-rolled AISI/SAE 1018 was cut to 38 long and 2 wide and mounted as rails on the frame to serve as a guide for the linear carriages that will support the motor for the y-axis. Similarly, 36 x 2.5 rail was bolted to the bridge. The steel rails were cleaned, primed and painted prior to assembly for aesthetics purposes and improvement of resistance to corrosion. Gear racks, which have 20 pitch and mate with the 20 tooth, 20 pitch pinion drive, were cut to 38 for the y-axis translation and 36 for the x-axis (i.e. bridge assembly). Rack clamps were used to secure the racks and ensure a straight alignment. The gear rack and the pinion system were bolted with fasteners that fit into the T-slots of the aluminum extrusion frame assembly Figure 6: Typical view of the C-scan assembly, 1) Acrylic tank, 2) Aluminum frame, 3) Stepper motor, 4) Ultrasonic sensor, 5) X-Translation and bridge assembly and 6) Z-Translation assembly

9 7.2. Electrical, electronic components and interface Once mechanical assembly was complete, 3-stepper motor, emergency stop switch, and limit switches were mounted. Each motor was plugged into the controller at its respective axis location and tested for motion. Once motion was achieved, the motors were fixed to the motion assemblies and tuned for optimal velocity and acceleration. This led to smooth linear movement along the linear rails. Geckodrive G540 stepper motor controller was used and it can be operated using LapViwe software. Using LapViwe, code was conducted in which the scanning rate and the number of the data point collected can be adjusted according ASTM E1454. After the motion assemblies were in working order, limit switches were placed on the unit. The linear carriages were allowed to travel to their limits in both X and Y directions where they contacted the limit switches. The Z- axis assembly has a built-in positive-stop limit switch, which restricts the motion along this axis to 4. The fund received by the ASTM (Graduate Design Project Grants), was used to attach inductive proximity switches as an alternative for the regular contact type limit switches. These sensors have a high accuracy and feature a 0.15 (4 mm) detection distance against steel and (2.5 mm) distance against aluminum. Moreover, the fund was used to get ultrasonic immersion transducer that is designed to transmit and receive ultrasound in water with a frequency of 10 MHz. This high frequency is suitable for inspecting and scanning composite materials due to their high damping characteristics. 8. Summary A C-scan ultrasonic facility has been developed and installed. The mechanical part of the C-scan consists of a mechanical scanner, motion control subsystem, ultrasonic transducer and an immersion tank. The acquisition and analysis part is consists of computer that contains ultrasonic pulser-receiver card, analog-to-digital converter card and system operating software. The mechanical elements of the ultrasonic C-scan unit have been designed, constructed and tested constructed. Stepper motors drive a belt driven rack and pinion system for X, Y translations and Z translation were mounted and tested. The motion and the speed of the scanning rate were controlled using LabViwe software. However, the communication of the unit to the pulser-receiver unit is pending. 9. Future modification Some of the requirements for optimization of the ultrasonic c-scan include completing the entire electrical and electronic components to the testing system. This control system should be synchronized with an ultrasonic pulser/reciver unit that mounted to Personal Computer (PC) with LabViwe software. The ultrasonic pulser/reciver unit should be consists of pulser/reciver multi-channel card with an Analog to Digital Convertor

10 (ADC) unit, multi-channel sequencer, digitizer board and programmable gain amplifier. ASTM E1454, Standard Guide for Data Fields for Computerized Transfer of Digital Ultrasonic Testing Data, will be used to standardize the form of transferring the digital ultrasonic data. In addition, this standard describes the structure of a data file for all of the ultrasonic information collected in a single and multiple scan. The machine calibration and the employment of the ASTM standards in UT testing will be investigated. We will conduct the testing according to ASTM E and ASTM E1454. A standard reference blocks will be used to calibrate the equipment periodically. 10. References 1. Theodoros Hasiotis, Efstratios Badogiannis, Nicolaos Georgios Tsouvalis, Application of Ultrasonic C- Scan Techniques for Tracing Defects in Laminated Composite Materials, strojniški vestnik -, Journal of Mechanical Engineering 57(2011)3, , (2009) 2. Lloyd, P.A., Ultrasonic system for imaging delaminations. Composite Materials, Ultrasonics, vol. 27, p. 8-18,(1989) 3. Melbourne, Victoria, In-situ ultrasonic c-scanner, Department of defence, defence science and technology organization, aeronautical research laboratory, Technical Report 4, (1992) 4. SM Handbook, Volume 17: Non- destructive Evaluation and Quality Control. American Society for Metals, 9th Ed., p. 516, (1992) 5. Anish Kumar, K. V. Rajkumar, P. Palanichamy, T. Jayakumar, R. Chellapandian, K.V. Kasiviswanathan and Baldev Raj, Development and applications of c-scan ultrasonic facility, BARC newsletter, issue no. 285 (October 2007) 6. ASNT, Non-destructive testing handbook, Volume 7: Ultrasonic testing, American Society for Nondestructive Testing, 2nd Ed., (1991) 7. Hibbeler, R.C., Mechanics of Materials 7th Edition, Prentice Hall, (2010)

SECTION ALUMINUM GATES

P.O. Box 1058 370 South Athol Rd. Athol, Massachusetts 01331 Phone: (978) 249-7924 Fax: (978) 249-3072 SECTION ALUMINUM GATES PART 1 GENERAL 1.01 SCOPE OF WORK A. The CONTRACTOR shall furnish all labor,