1、Basic Theory Consider a unit cube (quite a big one!) embedded in a component Notation, (ij) the stress component acting on face i in direction (parallel to axis) jBasic Theorydn Diffraction vector, titled with respect to sample surfaceTilt the sample through an angle and measure the d-spacing again.
2、 These planes are not parallel to the free surface. Their d-spacing is changed by the stress in the sample.dDefocused geometryStrain TermThe sin2 Plot : The Results! Shot Peened Steely = -0.0028x - 2E-05-0.00090-0.00080-0.00070-0.00060-0.00050-0.00040-0.00030-0.00020-0.000100.000000.00000.05000.1000
3、0.15000.20000.25000.3000Sin2 psiStrainShot Peened Steely = -0.00278x + 1.170381.169501.169601.169701.169801.169901.170001.170101.170201.170301.170401.170500.0000 0.0500 0.1000 0.1500 0.2000 0.2500 0.3000sin2 psidhklOmega2 = 02ChiDiffractedX-ray beamIncidentX-ray beamPhiNormal to sample surfaceSample
4、Goniometer circleOmega2 = 02ChiDiffractedX-ray beamIncidentX-ray beamPhiNormal to sample surfaceSampleGoniometer circleDiffraction GeometrySummary of the Angles Used in Residual Stress Analysis Choice of Measurement Conditions: Summary Ask someone who has experience with that particular material Don
5、t re-invent the wheel Choose radiation type carefully Avoid X-ray tubes which cause K -1 fluorescence Lots of “tricks of the trade” see the NPL Good Practice Guide for Residual Stress Measurements using the sin2 MethodInstrument Misalignment- Omega-2 misalignments-Omega- misalignments (side inclinat
6、ion method)Instrument misalignment causes, Shifts in the positions of the reflections and incorrect stress values The positive and negative measurements give different peak positions, this is called splittingWe must measure at least two standards to verify that the machine is working correctlyInstru
7、ment Misalignment- Recommended Standards A stress free powder Not an easy thing to make Beware stresses due to filing and oxidation Can be combined with resin for ease of use A stressed standard Be careful, always measure in the same direction Shot peened samples are good Usually verified by Round-Robin tests No certified standards (?) One set for each tube anode 04080120160200240280320-1400-1200-1000-800-600-400-2000200400 Residual Stress (MPa)Depth (m) 1.2% Strain, R=0 350oC / 1 cycle, Longitudianl 350oC / 1 cycle, Transverse As-peenedShear Stress, the positive & negative plots split
