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Impact force testing:

Equipment for accurate and repeatable measurement

Measuring impact forces is indispensable in a variety of applications, such as drop tests, crash tests or landing gear tests for example.
In order to accurately measure the force during an impact – an object heavily colliding with another – appropriate set-ups including sensors for highly dynamic measurements are required. We not only provide special force sensors and dynamometers for impact testing but also consulting and services for reliable set-ups and complete measuring chains.

Why impact force testing benefits from piezoelectric sensors

Even though strain gauge sensors are commonly used also for impact testing, piezoelectric sensors and quartz technology offer tangible advantages for practical usage: PE sensors present a very high stiffness which is unreachable for strain gauge technology – and therefore much higher frequencies can be measured. In addition to that, the overload protection as well as the rangeability via voltage output and charge amplifier make PE sensor easier to handle in complex impact force measurements. Last but not least, piezoelectric technology come with advantages in operational stability and reliability over the long term.

ETH pendulum impact hammer test | © ETH Zurich 

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Wide frequency range

Measures from quasi-static to >50 kHz

Operational stability

Very high rigidity, high linearity
and negligible hysteresis

Rangeability

Via charge amplifier resolution (noise)

Drop testing

To precisely capture the impact force, drop testing often included a drop tower instrumented with piezoelectric sensors.

For vertical impact force measurement a drop tower is a commonly used structure: it contains a platform for drop-off and a set of force sensors at the bottom, typically mounted between a top and a base plate. Such drop testing requires high stiffness of the sensor array and fast rise times to correctly measure the impact peak force. Piezoelectric force sensors come with features such as wide frequency range, high operational stability and overload protection which make them favorable for drop testing applications, especially for high impact forces.

In order to select the right force measuring range, test engineers calculate expected impact forces either via the pulse width method or the work-energy principle. Further desired parameters include impact energy, rebound factor and breaking distance.

Crash testing

Kistler sensors measure forces during crash tests

Horizontal impacts of moving objects require special structures to measure impact forces and absorbed impact energy. Vehicles such as cars, trains and planes have to be tested thoroughly to determine how objects and materials behave under real conditions. Kistler has more than 50 years of experience in crash testing applications and provides tried-and tested structures – such as rounded walls or poles – for established test protocols as well as special applications.

For example, the world’s first crash wall for high-speed trains is comprised of six segments with 36 force sensors each. The sensors with a maximum measuring range of 1,000,000 N can be flexibly combined to meet all load requirements, with the highest impact force being equivalent to a mass of 10,000 metric tons.

Landing gear testing

A landing gear testing setup to measure impact forces under real conditions with the help of a piezoelectric dynamometer.

A special type of drop testing, landing gear tests require an appropriate structure to determine the energy absorption capability at maximum take-off and landing weight of an aircraft. To calculate the maximum impact energy, a stationary drop tower including a drop carriage is applied to simulate the aircraft weight. The landing gear is mounted below the carriage and above a second platform which is equipped with force sensors. These triaxial load cells measure vertical forces as well as drag and side loads caused by the rapid acceleration of the wheels.

Piezoelectric dynamometers (multi-component force and moment sensors) are ideal for landing gear testing thanks to their rangeability, durability and multi-axis measurement capability. As a result, shock absorption, different configurations and directional stability can all be measured with the same equipment.

Material testing

Different materials can be evaluated through impact force tests with piezoelectric sensors and compliant data analysis.

Impact tests on materials aim at measuring their ability to withstand deformation when exposed to a dynamic load. There are different types of material testing as well as established standards for different materials (e.g. ASTM E23 / ISO 148-1 for metals). To conduct such an impact test, a prepared specimen has to be fixed accordingly to be hit by a weight either from the side – for example in a pendulum structure – or from above.

Material testing is highly sensitive to any parameter change such as different forces, specimens or their exact position. Furthermore, the interpretation of the measurements results can be challenging. Thanks to our vast experience and the superior qualities of PE sensor technology, we offer genuine products and consulting to support you with a highly consistent testing procedure and data analysis.

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