But to verify whether the natural frequencies and mode shapes are correct in the model, as constraint assumptions were made during modelling, we performed modal analysis using an impulse force (shock impulse) or a dynamic force (sinusoidal wave or random input)
The results and analysis thereof, provide the mode shapes and their corresponding natural frequencies.
These results are compared with those from the modal analysis. If they differ, model updating of the finite element model is performed to ensure that the model behaves like the physical structure.
What if this is not possible?
Sometimes there are valid reason why this approach cannot be followed, like:-
The approach must be implemented via a closed feedback loop process, and over a long period of time. Building these capabilities takes time, but becomes a true investment for the future, as the constraints and assumptions taken for modelling are refined by the experimental results, and can be used for future modelling.
A good example of this, is a electronic circuit on a printed circuit board (PCB).
In our experience, during flight certification using RTCA/DO-160 and Mil-Std-810, there are components that fail during vibration testing on a vibration shaker.
These are usually
Fine wired components
Internals of components
Relatively heavy components detaching
Capacitor legs fatiguing due to vibration
Ceramic components cracking
These are typical failures that we have seen over the last 25 years on PCBs…
We have generated a lessons learnt data base that assists us in solving these failures cost effectively, and quickly.
There are also other aspects that contribute to failures on PCBS. And they are:
Designers not adequately informed of the complete nature of the tests that the component will undergo
A lack of structural dynamics understanding/p>
The incorrect fixings and the locations of the mounts or stand-offs./p>
This is where the true understanding of structural dynamics is an asset to any design and manufacturing company.
So if you need help with anything afore-mentioned, please get in touch.
We do not charge for phone calls and advice. We are just passionate about this field of engineering, and happy that we can help you.
What have we done for companies like yours?
Vibration testing of various assemblies on a vibration shaker table that includes:
Electric motors under high vibration levels, as experienced on a nacelle
Experimental modal analysis of commercial vehicle structures
Updating of fabricated structures to pass vibration testing
Modification of fabricated structures to manipulate the natural frequencies and mode shapes for a more healthier behaviour, i.e.
reduce high strain areas where fatigue occurred.
Isolating machinery from transmitting vibration
These are just a few examples. If you have any queries, please contact us on 01908 643 433.