Low-Cycle-Fatigue (LCF)

Subjected to cyclical stress component parts may fail prematurely. This can be an important criteria for the design of components. Therefore tests are performed in material testing for the determination of material characteristics. Here a distinction is made between two different kinds of fatigue. 

  • Low-Cycle-Fatigue (LCF) for fatigue caused by low loading
  • High-Cycle-Fatigue (HCF) by vibration endurance performance

 

This article deals with Low-Cycle-Fatigue. In LCF tests the material sample is tested with high oscillation amplitudes and plastic deformation. In many cases the loading causes the failure of the sample within 10000 cycles. The test frequency typically is between 0.01 and 5 Hz.

 

Measuring LCF

Since its foundation the H.-D. Rudolph GmbH deals with measuring strain during LCF tests. As the frequencies during the performance of such tests are rather low, the focus is on choosing a measuring device offering best possible resolution. Furthermore the instruments should be able to measure on very hot specimens (up to 3000° C). One advantage of the electro-optical measuring principle is the absence of mechanically moving parts, which guarantees wearfree operation.

 

If you want to measure during an LCF test, please feel free to contact us in order to find an instrument for the individual solution of your task. In order to give you a first overview, in the following please find a presentation of some standard solutions concerning LCF tests:

 

CMOS Line Scan Sensor ZS64A5K


The ZS64A5K is a CMOS line scan sensor with a very high resolution used for non-contact dimensional measurement. By means of a lens the object to be measured is imaged to the linear CMOS array in the sensor. The lens determines the measuring range. Standard lenses can cover measuring ranges from 1 mm to 5000 mm. 

 

ZS32

 Characteristics of the ZS64A5K:

  • High resolution of 1:64000
  • Measuring range 5 mm – 5000 mm
  • High sensitivity for shortest exposure times
  • Scan rate 4673/s
  • Narrow scanning width
  • Standard version: Detection of two edge positions, light/dark or dark/light
  • Measuring values: Edge A, Edge B, B-A or (A+B)/2
  • Optional version: Detection of max. eight edge positions
  • Analog, calibrated live measuring values

 

  

Digital Extensometer ZS128

Digital Extensometer ZS 32

With 4673 measurements per second and a resolution of 1:128000 the digital extensometer ZS128 electro-optically measures strain on material samples. The digital sensors guarantee high stability and maintenance-free operation. The immediate delivery of calibrated values takes place during dynamic as well as endurance tests. The extensometer is able to perform measurements of strain on material hot up to 3000° C.  

 

Characteristics of the ZS128:

  • Measuring ranges: 2 mm – 1000 mm
  • Working distances: 40 mm – 10 m
  • Resolution: 0.0016 %
  • Scan rate: 4673/s

 

 

Line Scan Sensors ZS16A and ZS16AHS

ZS32

ZS16A and ZS16AHS are line scan sensors designed for non-contact measurement of edge positions by means of digital line scanning. The object to be measured is imaged with a lens to the linear array in the ZS16A or ZS16AHS. The measuring range depends on the lens used. Standard lenses can cover measuring ranges from 1mm to 5000 mm. 

 

Characteristics of the ZS16A and ZS16AHS: 

  • High resolution: 1:16000 (interpolated)
  • Measuring ranges: 1 mm – 2000 mm
  • Working distances: 20 mm – 200 m
  • High sensitivity for shortest exposure times
  • Scan rate ZS16A: 1000/s
  • Scan Rage ZS16AHS: 4673/s 
  • Narrow scanning width
  • Analog output signals
  • Operating voltage: 18 – 36 V/DC
  • Calibrated live output signals for strain-controlled testing

 

Video LCF: