1991 Volume 40 Issue 454 Pages 825-831
If a stress at any applied stress range during cyclic loading can be dynamically measured by means of X-rays, it will contribute to investigate the fatigue behaviors because the stress measured by X-rays is an actual stress under loading. In this study, we propose a new method to measure continuously an X-ray stress during cyclic loading based on the time-resolved tecnique and on the single-exposure technique (SET) by use of two position-sensitive proportional counters (PSPC).
Single-exposure technique is available to measure a stress rapidly on a specimen which has a good linear sin2ψ relation. Therefore, we firstly developed a SET stress analyzer with dual PSPCs and a method to collect simultaneously two diffraction profiles at +η and -η sides in order to evaluate the stress determined by these diffraction angles as a mean value for the collection time of these profiles.Two PSPCs were connected in series each other, and X-ray signals from dual PSPCs were processed by only one multi-channel analyzer.
We examined a practical method to measure continuously an X-ray stress during cyclic loading. A cycle of applied stress was divided by 16 stress ranges. In each cycle of applied stress, a couple of diffraction profiles at each stress range was collected for a short detection time, and was accumulated in the separate memory of the multi-channel analyzer. Such time-resolved collection was continuously carried out over all the preset stress ranges. This process in each stress cycle was repeated for definite cycles.
In the application of this method, we verified that the actual stress at any applied stress range was measured as the algebraic sum of an applied stress and a residual stress when cyclic stresses were applied to a thin steel specimen at frequencies of 0.5, 2 and 8Hz.