Macroscopic stress measurements by neutron diffraction and the part played by the 'Stress-free' reference
Macroscopic stress measurements by neutron diffraction and the part played by the 'Stress-free' reference
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通过中子衍射进行宏观应力测量以及“无应力”参考所发挥的作用
DOI：
10.2355/isijinternational.46.959
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发表时间：
2006
影响因子：
1.8
通讯作者：
D. Carr
中科院分区：
文献类型：
--
作者：
T. Holden;H. Suzuki;D. Carr
在过去的十年中，人们对如何根据中子衍射实验中测量的应变计算宏观应力有了更深入的理解。借助特定反射测量的应变可以具有对应于应力场的分量以及对应于2型应力或晶间应力的分量。后者源于不同晶粒取向之间的不均匀塑性变形。一种方法是从元件上切下小的参考试样，其尺寸与应力场的变化相比要小。切割破坏了应力场，但保留了所有化学和晶间效应，因为它们是在晶粒尺寸的范围内。然后，完整样品和试样之间的差异给出了与宏观应力相关的应变的近似值。针对轻微弯曲和严重弯曲的蒸汽发生器管道以及变形的压力管的情况，给出了晶间应变和宏观应变和应力如何叠加的示例。焊缝通常代表冷却时发生塑性变形的情况。此外，微观结构和成分变化通常与熔化有关，因此将参考试样作为焊接区域位置的函数非常重要。给出了遵循该程序的奥氏体不锈钢和锆合金焊缝的示例。
In the last decade a more sophisticated understanding of how to calculate the macroscopic stress from strains measured in neutron diffraction experiments has developed. Strains measured with the aid of a particular reflection may have a component corresponding to the stress field as well as a component corresponding to a type-2 or intergranular stress. The latter originates in inhomogeneous plastic deformation among different grain orientations. One approach is to cut small reference coupons from the component, small in size compared with the variation of the stress field. Cutting destroys the stress field but leaves any chemistry and intergranular effects intact since they are on the scale of the grain size. The difference between the intact sample and the coupon then gives an approximation to the strain associated with the macroscopic stress.Examples of how the intergranular and macroscopic strains and stresses are superposed, are presented for the cases of slightly bent and severely bent steam generator tubing, and for a deformed pressure tube. Welds often represent a situation where plastic deformation has occurred on cooling. In addition, microstructural and compositional changes are often associated with melting, so it is important to have reference coupons as a function of position through the weld zone. Examples of austenitic stainless steel and Zr-alloy welds are presented where this procedure was followed.