What Is Acoustic Emission and How Does It Work?

If you work within industry or are looking at working in heavy industry, you’re probably aware of acoustic emission, but might not be sure what exactly sure what it is. When you’re working with heavy machinery in difficult conditions, the upkeep and state of the machinery on site is imperative. Any sort of mechanical breakdown can cause real upset in production and set the project back weeks whilst repairs are made.

Acoustic emission is used to monitor and collect information on materials under strain by constant use, to test the structural integrity of a weld or to study the formation of cracks. This makes Acoustic emission an integral part of the industrial system and in ensuring both quality of work and in keeping track of how well your machinery is working under the pressure of day to day use.

Let use a bridge for an example. Every day a bridge crossing over a river between two major cities is subject extreme forces made by the cars and people crossing over it each day. Every time a foot falls on the pathway or a lorry rolls its way over the tarmac, shockwaves are sent through the bridge. The shockwaves that travel through the bridge are perfectly manageable by the bridge. However, over time the bridge begins to look a little worse for wear and is in need of inspection.

This is where we can use acoustic emission to our advantage. We might not be able to physically see the stress cracks that all of those trucks, cars and people have caused to the bridge. They could be internal or in hard to reach places. So what we need is a test that we can use to monitor the structural integrity of the bridge internally as well external.

Acoustic emission does exactly that. Rather than supplying energy to object under the examination (in this case the bridge), acoustic emission testing simply listens to the energy being released by the object. The energy being released by the object whilst in use should be smooth an unaltered, if there is a blip or jump in the wave being recorded this could mean there is fault or crack.

Acoustic emission testing it unique among the types of non-destructive testing because of the nature of the way it is tested. Acoustic emission testing is best tested while the object is in use. So for example we could use a sensor while the bridge is being used the most, at rush hour, and detect how it is performing under pressure. The waves that emit from every footfall and tire tread that the bridge withstands will give an accurate performance of the bridges structural integrity and show where any faulty are, of if structural defaults are present.

When any material undergoes pressure, a reaction is induced. So if you squeeze a sponge ball it will compress. When you release the ball from your hand it will reform back to its original state. This is known as stress and strain. If a material cannot contain the stress that is being forced upon it, then the material will become deformed due to the strain forced upon it. This does not happen with the sponge ball, but try and bend a plastic ruler too far and you will see the results.

This comes in to play massively when we think about acoustic emission testing and industry. Think about all the stress and strain that heavy industry machinery undergoes every day, whether you’re extracting oil, mining, or even simple industrial tasks like packaging items into cans or boxes. All the machines that are used in these processes undergo stress over a prolonged period of time.

Over this period of time, the stress can take its toll on moving parts within the mechanism and can succumb to the strain, causing internal parts to bend, deform and even shatter, just like the ruler. This is not such a huge problem if you’re in a factory and call out a mechanic for a replacement. However, if you’re extracting ore in the middle of the Atlantic Ocean then you’re in a bit of a pickle. Acoustic emission is invaluable in these kinds of situations. Due to the simplicity and accuracy of the testing it can be done pretty much anywhere on any piece of machinery in any environment. Allowing you to access real time and accurate information about the internal lifespan of your machinery.

Acoustic emission testing is imperative for the upkeep and maintenance of heavy machinery in all sorts of industries due to its easy use in difficult conditions and its real time, accurate results. It allows for planned maintenance and can notify possible problems before they occur – meaning that production doesn’t have to stop due to the breakdown of a kit or machinery, but instead stops to prevent a problem from happening in the first place