# Impact Testing

### What is Impact Testing?

An impact test is a controlled procedure to determine the impact of an object heavily colliding with another. Typical parameters to be measured or calculated include impact force, impact time (pulse width), absorbed energy, amount of deformation (or breaking distance) and rebound factor (elasticity). Variables that influence the impact strength are shape, mass and velocity of the colliding objects, and temperature.

### What is impact force and how to measure it?

The impact force represents the strength of the impact and can be measured directly using special force sensors or dynamometers. However, it is necessary to calculate expected impact forces before measurement to know the approximate measuring range to be selected. The impact force can be calculated using different variables, for example change of velocity, breaking distance or impact time. Please refer to our impact force calculator made for practical use.

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### What is impact time?

The impact time or pulse width refers to the duration of the collision between two objects during an impact. It is the time interval over which the forces of the collision are applied and can have a significant effect on the magnitude and distribution of the forces involved.

### What is breaking distance?

The breaking distance or amount of deformation refers to the extent to which a structure changes shape or size in response to an applied force or load. For impact forces, the deformation often occurs in a compression of the structure. Typically the amount of deformation is measured in the change of length using micrometers, depending on the scale of deformation.

### What is energy absorption?

This parameter refers to the amount of impact energy which is absorbed by a structure or material during an impact. Structures as landing gears or crumple zones of vehicles slow down the colliding object and therefore absorb impact energy. As a result, the impact force is reduced and the impact time is extended. Energy absorption therefore is an important parameter for safety equipment design.

### What is the rebound factor?

The rebound factor is a measure of the elasticity of a collision between two objects. It is defined as the ratio of the velocity of separation of the two objects after the collision to the velocity of approach before the collision. Therefore the rebound factor can range from 0 to 1, with 0 representing a perfectly inelastic collision where the objects stick together after impact, and 1 representing a perfectly elastic (ideal) collision where the objects separate after impact without any loss of kinetic energy.

### Which applications include impact force testing?

Typical applications include landing gear tests, drop tests or crash tests. Test engineers need to know how objects and materials behave under real conditions: the landing gear of an aircraft has to absorb the landing impact; products and packages have to be tested for their robustness when falling down; and vehicles need to withstand the horizontal impact when crashing into differently shaped objects. To learn more about these applications, please refer to our impact force testing application page.

### Which challenges do occur in impact force testing?

Although piezoelectric sensors (force, acceleration) are predestined for impact force testing thanks to their high natural frequency, fast rise time and overload protection, care has to be taken when mounting the sensors on the overall test structure. The high acceleration forces during impact may potentially lead to resonances and hence inaccurate measurements. While calibration before testing is indispensable, suitable compensation measures (active or passive, e.g. with a top plate) have to be taken into consideration.