Yazdanmehr Amir, Jahed Hamid
Fatigue & Stress Analysis Laboratory, Mechanical & Mechatronics Engineering Department, University of Waterloo, 200 University Ave. W., Waterloo, ON N2L 3G1, Canada.
Materials (Basel). 2020 Nov 17;13(22):5190. doi: 10.3390/ma13225190.
X-ray penetration in magnesium alloys is significant due to the low X-ray mass attenuation coefficient. To measure the surface residual stresses in magnesium alloys, a correction needs to be made to account for penetration depth. The residual stresses in as-received and shot peened AZ31B-H24 rolled sheet samples were measured using two-dimensional X-ray diffraction (2D-XRD) method. The electro-polishing layer removal method was used to find the residual stress pattern at the surface and through the depth. The results show that the corrected residual stresses in a few tens of micrometers layer from the surface differ from the raw stresses. To better estimate the residual stress distribution in the surface, the grazing-incidence X-ray diffraction (GIXD) technique was applied. Additionally, micrographs of the lateral cross-section of the peened specimens confirmed the presence of microcracks in this region, causing the residual stresses to vanish. Due to the low X-ray absorption coefficient of Mg alloys, this study shows how a small uncertainty in a single raw measurement leads to high uncertainty in the corrected residual stresses. The results were corroborated with the hole drilling method of residual stress measurements. The corrected X-ray diffraction (XRD) results are in close agreement with the hole drilling and GIXD results.
由于X射线质量衰减系数低，X射线在镁合金中的穿透性显著。为了测量镁合金中的表面残余应力，需要进行校正以考虑穿透深度。使用二维X射线衍射（2D-XRD）方法测量了铸态和喷丸处理的AZ31B-H24轧制板材样品中的残余应力。采用电解抛光层去除法来确定表面和不同深度处的残余应力分布模式。结果表明，距表面几十微米层内的校正残余应力与原始应力不同。为了更好地估计表面残余应力分布，应用了掠入射X射线衍射（GIXD）技术。此外，喷丸处理试样横向横截面的显微照片证实了该区域存在微裂纹，导致残余应力消失。由于镁合金的X射线吸收系数低，本研究表明单次原始测量中的小不确定性如何导致校正残余应力中的高不确定性。通过残余应力测量的盲孔法对结果进行了验证。校正后的X射线衍射（XRD）结果与盲孔法和GIXD结果密切一致。
