Impact hammer test

Prepared by : Darawan Abdulwahid E-mail : darawan.me@gmail.com
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University of salahaddin | college of Engineering | Mechanical Department
Experiment NO.3
“Impact Hammer Test”
Prepared by :Darawan Wahid Rahman
Group : A1
Date: 17-Jan-2016

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Experiment NO.2 | “Impact Hammer Test”
Theory This is often also known as Modal Testing. It is a method of testing that allows us to calculate the
natural frequencies (modes), modal masses, modal damping ratios and mode shapes of a test structure. This
is commonly done using either impact hammer testing or shaker testing. Here we are going to deal only with
impact hammer testing. In theory, we would impact the structure under test with a perfect impulse. This
would be of infinitely short duration. This would result in a constant amplitude in the frequency domain. Of
course, in real life, such an impulse is not possible. Instead, we have a known contact time. The duration of
this time is directly linked to the frequency content of the force applied. In hammer impact testing (modal
testing) we use a special hammer with a load cell in its tip to measure the force of the impact. So, to test the
structure we need to use the instrumented hammer to generate our impulse and then measure the
response. This needs to be done at several points on the structure. There are several ways we can instrument
this:
 Place accelerometers at many positions on the structure and impact once. This is very time efficient as
it requires a single impact and data capture. In reality, we would perform a few impacts in order to
perform averaging, but it is still a very quick test. However, this would require a large investment in
transducers and an equally large investment in a measurement system with enough channels to
simultaneously record all of our responses.
 We could fix a single accelerometer to one position and then impact our structure at several locations.
This is known as a 'roving hammer' test. This uses the least resources, but takes longer as we have to
make several measurements. This is the most common form of hammer impact testing.
 Finally, we could impact our structure at a fixed position and move a single accelerometer around
several positions. This is known as a 'roving accelerometer' test. While this is still efficient in terms of
transducers and measurement system, it is least efficient in terms of time since moving an
accelerometer is time consuming. This method is usually used in situations where space considerations
make it possible to fix accelerometers, but there is not enough space to use a hammer.

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- Accelerometer :
An accelerometer is a device that measures proper acceleration ("g-force"). Proper acceleration is not
the same as coordinate acceleration (rate of change of velocity).
The Type 4513 (Description)
The Type 4513 accelerometer family are piezoelectric Shear accelerometers with integral electronics.
The transducers feature a 10–32 UNF side connector, an insulated base and are hermetically sealed. The
transducers have a high resolution, giving an excellent signal-to-noise ratio. They can be mounted by
means of a 10–32 UNF threaded stud, or adhesively mounted.

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Data acquisition: is the process of sampling signals that measure real world physical conditions and
converting the resulting samples into digital numeric values that can be manipulated by a computer.
Data acquisition systems, abbreviated by the acronyms DAS or DAQ, typically convert analog waveforms
into digital values for processing. Data acquisition applications are usually controlled by software
programs developed using various general purpose programming languages such
as Assembly, BASIC, C, C++, Fortran, Java, LabVIEW, Lisp, Pascal,Pulse Lab. Shop, etc.. we have more type
of Accelerometer, but in this experiment we worked with (model-7539_A)

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Hammer
Characteristics
The Type 8206 series feature built-in electronics and the output sensitivity is expressed in terms of
voltage per unit force (mV/N or mV/lbf). The hammers also have built-in acceleration compensation that
removes unwanted noise from the resonance of the hammer from the output signal. This results in a
clean, smooth output signal representing the excitation in both amplitude and phase. The impact
hammer is supplied with three interchangeable impact tips of aluminum, plastic and rubber. The choice
of impact tip determines the impulse shape (amplitude and duration) and the bandwidth of the
excitation. For increased head mass, a 40 gram head extender is available. The handle has been
ergonomically designed for optimal control of impact, thus reducing the risk of ®
double hits”.
Specifications
Technology CCLD/IEPE
Sensitivity 22.5 (100) mV/N (mV/lbf)
Sensitivity - Charge
Range Full Scale 222 (50) N (lbf)
Maximum Force 4448 (1000) N (lbf)
Maximum Compression 222 (50) N (lbf)
Maximum Tension
Frequency Range 5 kHz
Resonance Frequency (unloaded)
Head Mass 100/ 140 with head extender grams
Weight
Operating Temperature Range -73° to 60° C
Overall Length 221.5 mm
Dimensions 19/ 70.7 mm (inch)
Handle Material Anodized Al/ PUR handle
Case Material Stainless steel
Connector Electrical BNC
Mounting Provision
Accessories Included Head extender, cable, tips
Optional Accessories

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Appropriate :
 Sensors, to convert physical parameters to electrical signals.
 Signal conditioning circuitry, to convert sensor signals into a form that can be converted to digital
values.
 Analog-to-digital converters, to convert conditioned sensor signals to digital values.
Data acquisition applications are usually controlled by software programs developed using various
general purpose programming languages
Experiment setup: I connected the accelerometer of tne channel one and the Hammer of the channel
two on the data aquision via cabel . The acceleromert was connected at one posion on the beam as
shown on figure below, for obtainig the frequency I hit the beam by the hummer .

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Result:

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Impact hammer test

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