Portable device to measure mechanical stress in polycrystals using X-ray diffraction NERKA
Residual stresses in the surface layers are among the factors that significantly affect the quality of many products characteristics. It is an urgent task to ensure the required quality indicators. In many cases the stress on the surface of the sample reflects the strained state of its cross section.
Residual stresses not only affect the durability of the product during its operation but they also influence the corrosion resistance, geometric accuracy, fatigue strength and durability. Existing non-destructive methods have limitations inhibiting their use in determining stresses in products of aluminum, nickel and other alloys.
We offer radiometric device NERKA for measuring mechanical (including residual) stress in the metal. The item fixes the crystal lattice strain in tension or compression and analyzes data in real time.
Description of the facility and it’s operation process
The device consists of the following parts:
- Portable X-ray tube with two anodes
- Semiconductor detector of diffracted radiation
- High-voltage power supply for 30 kV
- PC with software to control the installation, receive and process the information recorded by the detector
To determine residual stress the head tube is applied to tested unit surface and fixed in such a position. Then X-ray tube is switched on. It radiates X-ray beams in the direction of the monitored area (~ 10mm2) on the surface of the material.
X-ray radiation is only arise at the contact of the head tube with the sample, allowing to be in close proximity with the installation during the measurement.
The radiation is diffracted to the crystallites of the material falls on the position sensitive detector. Then the signals are transmitted to a PC. The signals are converted into diffraction angles value, which can show not only mechanical stress but also the material fatigue in the tested area.
The device allows to operate within 2 following methods:
1. Calibration curve method
Stress calculation is carried out on the calibration curve. Calibration is included in the software and the process is described in the device manual.
2. Calculation method
Stress calculation is processed according to the formulas of elastic deformation theory, where the known parameters are values of Young’s modulus and Poisson’s ratio.
It is noted that the empirical method (also known as a calibration curve method) is the most accurate, but when measuring an unknown sample with no possibility of calibration at discontinuous current machine the calculation method is the only to be used, as the Poisson’s ratio and Young’s modulus are known with some degree of accuracy.
The installation can be used in 2 following modes:
1. Analytical Measurement Mode
The entire process of the measurement and analysis takes approximately 2-5 minutes and displayed on the PC screen in stress MPa or kg / mm2. The measurement accuracy is 0.25 kg / mm2.
2. Dangerous areas detection mode
The analysis of controlled area takes from 0.5 to 1 minute. In case accepted value is exceeded indicator lights out on PC screen.
Residual stress measurement is applicable on the production of spare parts and items of machine-building, shipbuilding, construction, aviation, aerospace, nuclear, military and other industries (quality gear hardening, the trunks of large-caliber guns, hardening of turbine blades and others). It can also be used for batch control of state metalwork objects (load-bearing metal, the contours of reactors and others).
Information about NERKA can be found in this document (PDF, 350Kb)