What Is A Hammer Test Or Hammer Impact Test?

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.

If you need to perform hammer impact tests (also known as bump testing, tap testing, or hammer resonance testing) then take a look at the Prosig Hammer Impact Test System. Prosig’s solution is not only the most simple to use and understand, but its 100% reliable giving perfect results every time. The complex mathematics of windowing, transfer function type, frequency range is all taken care of for you. What’s more, the automated peaking picking algorithm will find the modes automatically for you. Need to export test results to Word or Excel for FEA validation? No problem. It’s all included.

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.
Thrre different instrumentation configurations for performing a hammer impact test (Click for larger display)
Three different instrumentation configurations for performing a hammer impact test on a simple vertical beam (Click for larger display)

Once the instrumentation aspects of the test are decided, one needs to consider the software that will assist with the capture of the data and produce the results. A good test system will:

  • Lead a user through all the steps necessary to configure the test and prepare the measurement system
  • Step through the measurement process
  • Provide clear feedback at each stage. For instance, use audio feedback so that the user can concentrate on performing the test without having to refer to the computer screen at each stage

You can see an example of software used to setup and carry out a hammer test (Roving Hammer type) in the following video by James Wren

 

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Chris Mason

General Manager at Prosig
My passion for technology and innovation began as a teenager with Sinclair ZX80's, Commodore PETs & Apple ]['s. This became a career in software development, product development, team leadership, web development, and marketing. Now I am a General Manager responsible for growth, innovation, strategy & leadership. I gained an HND in Maths, Stats & Computing from Portsmouth Polytechnic in 1983 and completed an MBA at the University of Winchester in 2019 where I focused on innovation and strategy.
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Elena
Elena
8 years ago

This is my first time trying to do vibrational testing, and I was wondering if there is a way to do this all by hand using just simple data acquisition hardware and matlab. Are there any good references as to the equations necessary if you have a simple system with few significant modes of vibration?

James Wren
8 years ago
Reply to  Elena

Hello Elena,

Thank you for posting on our blog.

Yes it is possible to do this by hand.

The best references are actually on our web site, all the formula’s are included, please see here,

https://blog.prosig.com/2009/10/19/a-simple-frequency-response-function/

Walid Abdullah
Walid Abdullah
5 years ago

I need an offer to hammer test ASAP& my company in Cairo, Egypt , do you have an agent in Egypt??

James Wren
5 years ago
Reply to  Walid Abdullah

Hi Walid,

Thanks for posting on our blog, I have reached out to you by email to discuss your requirements further.

Christopher Marsh
Christopher Marsh
5 years ago

James,

I am in the process of determining dynamic stiffness for certain automotive parts. We have a vibration table and a Modal Hammer for impulse excitation. What process would I take to determine the Dynamic Stiffness of these specimens. The stiffness units will be in N/mm. I understand the impact hammer will impact the part and record the force, while an accel on the part will measure acceleration and frequency experienced by the part, but how do all these components come together to calculate dynamic stiffness. Is a specific software required?

Thank you,

Chris Marsh

James Wren
5 years ago

Hello Christopher,

Thank you for posting a question on our blog.

I would like to refer you another article,

https://blog.prosig.com/2014/04/10/how-do-we-design-or-modify-a-system-to-avoid-resonance/

This should take you through step by step the process to find the stiffness and change it.

I believe the SI unit for stiffness is N/m.

Mahabir Prasad
4 years ago

Dear Sir,
I have impulse hammer and accelerometer time data from field. I also know
the distances between source(hammer) and receiver (Accelerometer). Does it
possible to calculate the velocity of wave by using these data? if Yes, how. I do not have two
relative accelerometer data set, which is normally used literature.
Thanks in advance
Mahabir Prasad

Kabo
Kabo
1 year ago

Hi sir, Please I wanted to perform a hammer impact test but my question is this, does it matter the position one place the components? In my case, it is a cylindrical metallic pipe. If i’m to conduct the experiment, does the impact direction (x, y or z) affects the stiffness? I mean can I use any direction?

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