Neutron Surface Residual Stress Scanning Using Optimisation of a Si Bent Perfect Crystal Monochromator for Minimising Spurious Strains
Neutron Surface Residual Stress Scanning Using Optimisation of a Si Bent Perfect Crystal Monochromator for Minimising Spurious Strains
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DOI：
10.4028/www.scientific.net/msf.681.399
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发表时间：
2011-03
期刊：
影响因子：
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通讯作者：
J. Rebelo-Kornmeier;J. Gibmeier;M. Hofmann;R. Wimpory
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文献类型：
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作者：
J. Rebelo-Kornmeier;J. Gibmeier;M. Hofmann;R. Wimpory
对于表面处理钢样品的非破坏性应力分析，实验室X射线或高能同步辐射在反射模式下的应用覆盖了从几微米到大约150 - 200 µm深度的区域。要访问深度超过200 µm的深度区域，可以使用增量层去除技术，并对新生成的表面重复应用X射线应力分析。然而，该过程是破坏性的、费力的，并且此外，必须检查是否由于应力松弛而必须应用校正。通过使用中子辐射穿透深度通常可以达到几毫米，非破坏性[1]。然而，中子测量在表面是至关重要的。当扫描样品表面时，由于由初级和次级光学器件限定的计量体积部分地在样品外部的事实，出现了由所谓的寄生应变引起的像差峰值偏移。这些像差峰位移与残余应变相关峰位移的数量级相同[2-6]。在该示例性研究中，将证明，通过优化Si（400）单色器的弯曲半径，当与用传统Ge（311）镶嵌单色器获得的值相比时，即使当计量体积主要在表面之外时，寄生表面应变也可以大大减小。实验的目的是在德国慕尼黑FRM II研究堆的STRESS-SPEC仪器上找到Si（400）单色器的最佳单色器设置。对于参数研究，使用细晶粒建筑钢S690 QL的无应力钢样品。从系统研究中得到的Si（400）单色化的优化条件被应用于SAE 4140钢的喷丸板。采用穿透式表面应变扫描法分析了残余应力的分布。获得的残余应力梯度与在BRITE-EURAM项目ENSPED（欧洲表面和预应力工程与设计网络）范围内的循环试验中获得的表征良好的残余应力深度分布非常一致[7]。结果表明，表面残余应力分布可以用表面下200 µm的中子测量，而无需耗时费力的表面效应校正。
For non destructive stress analysis of surface treated steel samples the application of laboratory X rays or high energy synchrotron radiation in reflection mode covers the region from some micrometers up to a depth of about 150 - 200 µm. To access depth regions deeper than 200 µm the incremental layer removal technique in combination with the repeated application of X‑ray stress analysis for the newly generated surfaces can be used. However, this procedure is destructive, laborious and furthermore, it has to be checked whether corrections have to be applied due to stress relaxation. By using neutron radiation penetration depths generally up to several millimetres can be achieved non destructively [1]. However neutron measurements are critical at the surface. When scanning a sample surface, aberration peak shifts caused by so called spurious strains arise due to the fact that the gauge volume defined by the primary and secondary optics is partially outside of the sample. These aberration peak shifts can be of the same order of magnitude as the peak shifts related to residual strains [2-6]. In this exemplary study it will be demonstrated that, by optimising the bending radius of a Si (400) monochromator, the spurious surface strains can be strongly reduced when compared to the values obtained with a traditional Ge (311) mosaic monochromator, even when the gauge volume is mainly out of the surface. The objective of the experiments is to find the optimal monochromator settings for the Si (400) monochromator at the STRESS-SPEC instrument at the research reactor FRM II, Munich, Germany. For the parametric studies a stress free steel sample of the fine grained construction steel, S690QL was used. The optimised conditions for the Si (400) monochromator that resulted from the systematic studies were applied to a shot peened plate of steel SAE 4140. The residual stress distribution is analysed by means of through surface strain scanning. The residual stress gradient obtained is in very good agreement with the well characterised residual stress depth profile obtained within a round robin test in the scope of the BRITE-EURAM-project ENSPED (European Network of Surface and Prestress Engineering and Design) [7]. The results indicated that surface residual stress profiles can be measured with neutrons up to 200 µm underneath the surface without time consuming and laborious surface effect corrections.