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Stroke measurement in material testing machine

Material testing machines apply load to a test sample until it breaks and record the force-deflection graph for material characterisation during deformation. The machine itself consists of a stable frame with base structure and has fixed and movable parts. In between is the test sample. A spindle or hydraulic cylinder with a punch acts on the moving part and applies a defined increasing force to the test sample until it breaks. At the moment of fracture, the forces released act as a shock to the entire system and cause strong mechanical stress on the measuring systems.

 

Concrete test sample after fracture in material testing machine

 

Digital (incremental) length gauges based on the Magnescale principle are used for displacement measurement. The function of the Magnescale gauges is based on a magnetic scale with north-south magnetic pitch and MR element. The use of a break-sensitive glass scale is avoided, therefore damage to the scale due to vibration or shock is not possible.

 

Digital gauge for materials testing machine with magnetic scale

 

The pushrod bearings of the DK and DF series are designed with a special linear ball bearing for high loads and high shock resistance. The pushrods themselves are tempered and have a hard chrome layer. This increases the wear resistance extremely and the lifetime is over 100 million full stroke cycles. An additional friction-reducing DLC sliding layer reduces slip-stick behaviour.

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