Fast residual stress determination by means of two-dimensional X-ray diffraction using the sin2ψ-method

Continuous movement in XRD residual stress measurement further reduces the measurement time.

Introduction

The conventional sin2ψ-method in accordance with EN 15305 [1] is an established tool for non-destructive residual stress measurements by means of X-ray diffraction. However, depending on the geometrical and structural properties of the investigated sample, its applicability on laboratory X-ray diffractometers can be limited. The arising difficulties are associated with the dimensioning of the used X-ray detector system, which may lead to insufficient counting statistics or impractically long measurement times. Two-dimensional X-ray diffraction offers new possibilities for residual stress analyses exploiting the full 2D position resolution of an X-ray area detector [2-4]. This work introduces a new approach based on the direct integration of 2D Debye-Scherrer ring sections to 1D intensity spectra for strain determination.

Xstress DR45 operated in modified-χ mode as per EN 15305.
Integration of 2D XRD data to 1D intensity spectra along the Debye-Scherrer ring
Integration of 2D XRD data to 1D intensity spectra along the Debye-Scherrer ring.
MaterialHklRadiationΔγ
α-Fe211Cr Kα156.4°45°
γ-Fe, INCONEL®311Mn Kα152.5°38°
α-Ti302Cu Kα148.7°34°
Al311Cr Kα139.3°27°
WC102Cr Kα135.8°25°
↑ Δγ values for different materials

Standard mode

  • Discrete tilt steps
  • Number of tilt angles ≥ 9 (5/5)
  • Equidistant data points (sin2χ)
  • Exposure time per tilt angle ≥ 1 s
Residual stress measurement standard mode.
Standard mode.
1D intensity spectra in standard mode.
1D intensity spectra in standard mode.

Sweep mode

  • Continuous tilt movement
  • Number of tilt angles ≥ 18 (9/9)
  • Non-equidistant data points (sin2χ)
  • Sweep time ≥ 5 s
Residual stress measurement sweep mode.
Sweep mode.
1D intensity spectra in sweep mode.
1D intensity spectra in sweep mode.

Comparison of standard mode and sweep mode
Comparison of standard mode and sweep mode.
Experimental results for a ferritic steel reference sample (σref = -593 MPa).
Experimental results for a ferritic steel reference sample (σref = -593 MPa).

Conclusions

The 2D position resolution of X-ray area detectors allows for a direct integration of the recorded Debye-Scherrer ring sections to 1D intensity spectra for strain determination. Experimental studies were conducted with the Xstress DR45 operated in standard mode with discrete tilt angles and in sweep mode with continuous tilt movement. For large collimator sizes (∅ 1-3 mm) the measurement time in sweep mode can be shortened by a factor of about 7 compared to standard mode, reducing to about 2 for small collimator sizes (∅ 0.3 mm). The results of this work demonstrate the statistical benefit from the replacement of linear X-ray detectors by X-ray area detectors, making the Xstress DR45 a well-suited diffractometer for fast residual stress measurements in various applications.

Written by

Sebastian Send (a),*, Dominik Dapprich (a),
Mikko Palosaari (b)
(a) Stresstech GmbH, Konnwiese 18, 56477 Rennerod, Germany
(b) Stresstech Oy, Tikkutehtaantie 1, 40800 Vaajakoski, Finland
*corresponding email: sebastian.send@stresstech.com

This poster is originally published in ICRS11.

References

[1] EN 15305, Non-destructive testing – Test method for residual stress analysis by X-ray diffraction, 2008.
[2] B. B. He, Two-Dimensional X-Ray Diffraction, second ed., John Wiley & Sons, Hoboken, 2018.
[3] B. B. He, Accuracy and Stability of 2D-XRD for Residual Stress Measurement, Proceedings of ICRS-10, Materials Research Proceedings 2 (2016), 265-270
[4] B. B. He, U. Preckwinkel, K. L. Smith, Advantages of Using 2D Detectors for Residual Stress Measurement, Advances in X-ray Analysis 42 (1998), 429-438

Article Type: Case study
Technology: X-ray diffraction
Product Line: Xstress DR45