Skip to contentUnited States Department of Transportation - Federal Highway Administration FHWA Home
Research Home   |   Pavements Home
Report
This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-HRT-06-117
Date: December 2006

Appendix D

Previous | Table of Contents | Next

The NI-4552 Dynamic Signal Analyzer Board is used in conjunction with National Instruments VirtualBench DSA software to obtain time-domain data from ASTM C215 (impact method) testing of freeze-thaw test specimens and to convert that information to frequency response curves for use in determining resonant frequency.

Required Equipment

General Instructions

The beams are placed on the piano wire. The accelerometer is fixed on the beam, and the hammer hits the specimen. The impact hammer and the accelerometer are connected to the BNC 2140 box. The data is processed.

Figure 39 shows the several plots generated after tapping a freeze-thaw beam with the impact hammer. There are four plots in the figure. The first plot (from top to bottom) shows the time domain waveform for the impulse (hammer). This is typically one “spike” at the time of impact. In some cases (as in a double hit), there will be more than one spike. The second plot shows the time domain waveform for the response of the beam (accelerometer). This plot is typically a damped vibration that decreases with time. The third and fourth plots show the frequency response of the beam due to the hammer tap. The third plot shows the frequency response over the baseband range (in this example, 0 to 3200 Hz). The frequency response on the fourth plot is over the zoomed range (in this case 1900 to 2300 Hz), and the resonant frequency can be manually obtained from it by placing the cursor on the peak of the curve. The frequency response curves should look similar to those shown in this figure. At lose observation, in plots 3 and 4 (especially plot 4), the frequency response curve for a good hit will be smooth as in plot 4. It will not be wavy, it will not have two or more peaks, and it should be roughly symmetrical. It should not have one or both ends cut off—the ends should appear to level off.

There are four plots in the figure. The first plot (from top to bottom) shows the time domain waveform for the impulse. The horizontal axis represents the time waveform. The vertical axis is the Impulse ranging from negative 0.20 to positive 0.60 volts. The plot indicates one spike at almost the time of impact and is a straight solid line picking at 0.50 volts. The second plot shows the time domain waveform for the response of the beam. The horizontal axis represents the time waveform. The vertical axis is the impulse, ranging from negative 0.10 to positive 0.10 volts. This plot is a damped vibration that decreases with time. The third and fourth plots show the frequency response of the beam due to the hammer tap. The third plot shows the frequency response over the baseband range from 0 to 3200 hertz. The frequency response curve peaked at 2230 hertz. The frequency response on the fourth plot is over the zoomed range of the curve, from 1900 to 2300 hertz. The resonant frequency was obtained from it by placing the cursor on the peak of the curve (D X equals 330 hertz). The frequency response was calculated by adding “D X” to the left side of the zoomed range (1900 hertz).

Figure 39. Screen capture. Typical plot generated by NI 4552 and BNC 5140 setup.

 

Previous | Table of Contents | Next


The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT).
The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). Provide leadership and technology for the delivery of long life pavements that meet our customers needs and are safe, cost effective, and can be effectively maintained. Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
FHWA
United States Department of Transportation - Federal Highway Administration