Neutron residual stress analysis for multiphase materials with depth gradients of the strain free / independent lattice parameter D0

延续期研究项目的目标不变，研究相特异微残余应力对粗多相材料参考晶格参数D0确定的影响，并提供适当的测量和评价策略。对于利用中子衍射对残余应力深度梯度进行无损分析，了解这一参考值是非常重要的。因此，重点是利用非常小的深度增量通过表面应变扫描实现中子，其特定目的是无损地确定非常接近表面的残余应力深度分布。在这种情况下，表面效应和相关的伪应变的预测和校正是至关重要的。在第一个资助期内，对粗两相双相钢的相特有残余应力的发展进行了基础研究。结果表明，相特异织构对相特异（残余）应力的发展有很大的影响，对分析有很大的影响。此外，研究表明，对弹塑性材料载荷下材料体积的微观力学过程的基本理解对于理解残余应力的发展，特别是对于正确的残余应力评估和结果评估具有重要意义。晶间应变使基于确定{hkl}的晶格应变与机械材料载荷之间存在高度非线性关系。在项目继续的范围内，将制定一个自洽材料模型，用于塑性各向异性效应的数值预测，并将其扩展到粗两相、有织构的双相钢的应用。为了验证模型和评估晶粒取向相关的应变和应力，将使用中子衍射确定补充的相特定应变极数。此外，进一步开发模拟程序SIMRES来计算穿透表面中子应变扫描过程中表面效应引起的伪应变将是未来研究的课题。在后续项目中，现有模型将被扩展到能够处理特定阶段的纹理和纹理梯度以及化学梯度（d0梯度）。仿真软件的这些增强功能将与我们的捷克合作伙伴J. Šaroun密切合作实现。最后，在项目结束时，对机械表面处理双相钢和表面硬化状态进行的残余应力分析将使用实施的软件增强功能重新评估，最终结果将与使用补充方法确定的残余应力分布进行比较。

The aim of the research project for the continuation period remains unchanged and covers the investigation on the influence of phase-specific micro residual stresses on the determination of the reference lattice parameter D0 for coarse multi-phase materials and to provide appropriate measuring and evaluation strategies. For non-destructive analysis of residual stress depths gradients using neutron diffraction the knowledge of this reference value is of high importance. Hereby, the focus is on the realization of neutron through surface strain scans by using very small depth increments with the particular aim to determine residual stress depth distributions non-destructively that are very close to the surface. Here, the prediction and the correction of the surface effects and the associated spurious strains are of vital importance. In the first funding period fundamental investigation on the development of phase-specific residual stresses for coarse two-phase duplex steels have been carried out. The results indicate that phase-specific textures have an immense impact on the development of phase-specific (residual) stresses and strongly affect the analyses. Moreover, it was shown that the fundamental understanding of the micromechanical processes in the materials volume at elasto-plastic materials loading is of enormous importance for the understanding of residual stress development and particularly for the correct residual stress evaluation and for the assessment of the results. Intergranular strains bring out highly non-linear relationships between the diffraction based determined {hkl} dependent lattice strains and the mechanical materials loading. Within the scope of the project continuation a self-consistent material model for the numeric prediction of the plastic anisotropy effects will be formulated and extended to the application on coarse two-phase, textured duplex steels. For the validation of the model and for the assessment of grain orientation dependent strains and stresses supplementary phase-specific strain polefigures will be determined using neutron diffraction. Furthermore, the further development of the simulation routine SIMRES for calculating spurious strains caused by the surface effects during through surface neutron strain scanning will be subject of future investigations. In the continuation project the existing model will be extended to be able to handle also phase-specific textures and texture gradients as well as chemical gradients (D0-Gradients). These enhancements of the simulation software will be realized in close collaboration with our Czech partner J. Šaroun. Finally, at the end of the project period the residual stress analyses carried out for the mechanically surface treated duplex steels and the case hardened stated will be re-evaluated using the implemented software enhancements and the final results will be compared with residual stress distributions that are determined using complementary methods.