MONTANA STATE UNIVERSITY   
DEPARTMENT OF MECHANICAL ENGINEERING                                   

ETME 360 Spring 2014 – Measurements and Instrumentation Laboratory

EXERCISE 8 PIEZO-ELECTRIC TRANSDUCER APPLICATIONS:
ULTRASONIC THICKNESS MEASUREMENT      

R. Larson

Goal:
Create a three-dimensional thickness map of an aluminum test specimen, utilizing conventional inspection methods and ultrasonic NDT (non-destructive testing) inspection techniques. This exercise provides an exercise in piezoelectric transducer applications, and experience with operation of a digital storage oscilloscope. Creation of a detail component drawing using a CAD package is required.

References:
A. Wheeler & A Ganji, Introduction to Engineering Experimentation
ETME360 Lecture & laboratory instruction
 

Equipment:
10 MHz Ultrasonic Transducer with microdot co-axial cable
Digital Storage Oscilloscope
D.C. Power Supply, (HP 6216A or equivalent)
Pulser/Receiver Amplifier, either a commercial Panametrics model or an MSU-Fabricated (metal box) P/R Amp.
Micrometer, Ruler, Numbered Test Specimen
PRO-E, AUTOCAD, SOLID WORKS, or other similar CAD program


Laboratory Procedure:
Assemble the circuit shown in Figure 1.

Figure 1. Ultrasonic Inspection Apparatus

Set the power supply output to between 12 and 15 volts. (Do not exceed 15 volts!) Alternatively you may use one of the commercial pulser/receiver units that has an internal power supply.

Apply a small amount of water to the test specimen surface: This provides an incompressible sound path between the transducer and specimen. Remove the red protective cap from the transducer (if present) and hold the face of the transducer against the wetted specimen surface. Adjust the oscilloscope to display the series of echo peaks produced.

1.  WAVE  VELOCITY MEASUREMENT : Obtain data required to calculate specimen material sonic velocity:

    (a.) Accurately measure specimen thickness with micrometer or digital caliper
    (b.)  Place the ultrasonic transducer on the wetted specimen, at the location of known thickness.
    (c.)  Adjust the oscilloscope display so that two waveform “echo front” patterns are displayed. Then use oscilloscope
Δt markers to measure time differential between similar peaks on each of these echo patterns.
    (d.) 
Gather part thickness and oscilloscope delta-time data values sufficient to be able calculate longitudinal sound velocity.  

2. CONTOUR MAPPING : Obtain data required to map the specimen contours:

(a.)     Measure “time-of-flight” data at locations across the entire specimen surface. This data can be
used with the specimen sonic velocity value to determine thickness, in order to develop a "map" of specimen thickness: Spend some time planning how best to accomplish mapping.  If desired, you may LIGHTLY mark the specimen with PENCIL to define a search grid, or to mark the (hidden) boundaries found in your investigation. Please do not scratch the surface of the specimen, and be sure to clean off any marks at the end of the lab. Note that by decreasing the spacing between measurement sites, a contour map of higher resolution can be obtained: Assume that the center of the transducer is the point source for ultrasonic pulses.
(b.)     Record all important delta-t values and x-y locations.
(c.)      Be sure to record the specimen number on your data sheet.

Results: 
1. Perform research into the ultrasonic wave speeds of materials to find the speed of longitudinal sound waves in 6061 T6 Aluminum alloy, at a temperature of 25°C. CITE your source using formal citation notation. Compare your findings with the measured ultrasonic wave speed that you calculated in this lab exercise.

2. Using recorded sonic velocity data and the time of flight map, create an engineering drawing of the test specimen: 

Use a CAD program of your choice to create your drawing. The completed drawing must be formatted per accepted graphical communication standards and must be sufficiently complete to permit the machine shop to accurately fabricate a reproduction of the aluminum portion of your specimen, using 6061-T6 Aluminum material. You must include and clearly define ALL specimen dimensions, and  include "reasonable" dimensional tolerances. Dimensional data must be complete but not redundant; i.e., no omitted or  “double dimensions.”
 

The drawing is to describe the metal specimen only: Neglect the cover block. You may also neglect the tapped holes used to affix the wood block to the metal specimen, but include all other dimensions including part thickness, length, width, and pattern details. Your drawing should be based on and backed up by your group's experimental findings. Drawings containing details not supported with or indicated by the included measurement data will be penalized.

Your drawing must include a title block, and be signed by all group members. A signature denotes approval of all drawing elements, while no signature denotes no participation, and a zero grade!!

Compile other elements of your report (cover page, results, calculations in the usual manner.