When testing devices that feature unique material behavior, it may not be possible to control the test directly using simple load, position or strain control. This is especially apparent when relationships between two control parameters change drastically under cyclic loading. For example, if the device loading increases exponentially as the displacement increases linearly, it can be impossible to properly tune the system using typical techniques. In order to overcome this obstacle, the system effectively has to ‘learn’ how to achieve the specified test targets because one tuning condition is not applicable to the full range of cyclic test conditions.
When we learn something, we typically start with a basic concept, and then expand outward from there. The same approach is used in Advanced Amplitude Control (AAC). The system is first programmed to run a starting waveform – this is a basic waveform representing only a portion of the full cyclic waveform that can more easily be controlled. We pair the starting waveform with the full cycle test targets – for this example, these would be minimum and maximum load values. Given these two pieces of information, the system then has to learn how to grow the starting waveform into a waveform that achieves the full cycle test targets. Using multiple feedback loops, the system is able to make necessary adjustments to reach the targets without relying on initial tuning inputs.
This capability allows our test setups to keep up with the creative device designs and materials developed by our customers. AAC is featured on eight (8) of our Instron axial test systems. We use AAC most commonly with hyperelastic materials such as rubber, or with unique fixture geometries such as semi-spherical probes.
MDT has multiple fatigue system types and will determine which one is the best fit for your application. With our custom fixture design capabilities and in-house machine shop, we can optimize the fixturing to get the best performance from each test system. Contact us with your test requirement today.