Question

Describe in simple terms how an XRD instrument can be used to perform a residual stress analysis of a strained steel sample. What needs to be measured, and how are the measurements performed

Answer 1

IN THE STEEL SAMPLE , WE USE XRD ( X-RAY DIFFRACTION) INSTRUMENT FOR CALCULATING THE RESIDUAL STRESS NONDESTRUCTIVELY.

FOR THIS WE HAVE TO CALCULATE THE STRAIN IN CRYSTAL STRUCTURE LATTICE,. SO , WE CAN MEASURE BY CALCULATING THE STRAIN FROM THE DIFFRACTION PEAK POSITIONS. . SO , WE JUST NEED TO MEASURE THE STRAIN FOR CALCULATING THE RESIDUAL STRESS.

WE PERFORMED MEASUREMENT BY PROVIDING THE ARITHMETIC AVERAGE IN THE DIFFRACTING VOLUME WHICH IS DEFINED BY THE SIZE OF IRRADIATED AREA AND DEPTH OF PENETRATION OF X- RAY BEAM. THE RESIDUAL STRESS IN THAT VOLUME IS ASSUMED TO BE UNIFORM BOTH ALONG THE SURAFCE AND AS A FUNCTION OF DEPTH.

ANY STRESS INDUCES A STRAIN WHICH LEADS TO CHANGE IN LATTICE SPACING. IN PRACTICE, A METAL POWDER WITH NO STRESS IS MEASURED FIRST TO SET THE ANGULAR SCALE OF THE DETECTORS FOR A CERTAIN MATERIAL.

AT LAST , STRESS IS CALCULTED BY MEASURING THE LATTICE DISTANCE WITH MULTIPLE TILT ANGLES AND PLOTTING THE RESULTS AS d and SIN^2X, D IS MEASURED LATTICE SPACING AND X IS THE TILT ANGLE.