Study on development of fatigue life prediction system based on neutron strain scanning method

1.采用中子衍射法对试件中的载荷应力进行了测量，以检验测量应力值的准确性。将Kroner模型和自洽模型相结合，可由单晶弹性常数估算出单晶的衍射弹性常数。在塑性范围内，确定应力时应考虑塑性各向异性。提出了一种确定无应变晶格间距的新方法。微观应力和宏观应力可以用中子法分别计算。该方法在复合材料中的多次应用表明，这些应力与基于Esheby夹杂力学的理论预测相吻合。扫描方法被证明是测量大块样品中应变分布的有效方法。由于中子源强度低，中子法可以测量的最小体积为2 mm立方体。为了确定陡峭的应力梯度，需要提高空间分辨率。利用该方法研制的中子衍射仪成功地测量了几种工程材料和构件中的残余应力分布。在测量非常接近地表的应力时，“表面效应”会引起测量应力的误差。光束的小发散可以有效地减小这种影响。来自同步辐射的高能X射线将是测量表面附近应力分布的有用方法。将中子法与高能X射线和实验室X射线相结合，将是无损测量残余应力分布的一个有希望的新目标。

1. The loading stress in sample specimens was measured by the neutron diffraction method to check the accuracy of the measured stress value. The diffraction elastic constants can be estimated from the single crystal elastic constants by combining Kroner model with the self-consistent model. In the plastic range, plastic anisotropy should be taken into account for stress determination. A new method is proposed to determine the strain-free lattice spacing.2. The microstress and macrostress can be evaluated separately by the neutron method. Several applications of the method to composites showed those stresses which agreed with the theoretical predictions baed on Esheby inclusion mechanics.3. A scanning method was proved to be useful to measure the distribution of strain within the bulk samples. Because of a low intensity of neutron sources, the minimum volume that can be measured by the neutron method was 2mm cube. The improvement of the special resolution is necessary to determine steep stress gradients.4. The neutron diffraction system developed by the present method was successfully applied to measure the residual stress distributions in several engineering materials and components.5. To measure the stress very near the surface, "the surface effect" will cause the error of the measured stress. The small divergence of the beam is effective to reduce this effect.6. High energy X-rays from synchrotron radiation will be a useful method to measure the stress distribution near the surface. A combination of the neutron method with high-energy and laboratory X-rays will be a promising new toll for nondestructive measurements of residual stress distributions.