基于虚拟聚焦理论的增材制造金属构件超声成像检测研究

Characteristics of additive-manufactured metallic material in three forming directions is obviously different and internal defects whose types are different from traditional forgings and castings are easily generated during additive manufacturing. With the development of additive-manufactured metallic components to complex and diversification, conventional nondestructive testing methods have not meet the inspection requirements. Hence, in this project nondestructive testing and evaluation of additive-manufactured metallic components are developed using ultrasonic imaging method based on virtual focusing. Ray-tracing algorithm is posed to calculate the path of ultrasonic wave propagation in additive-manufactured metallic material. New algorithms of virtual focusing are designed to detect anisotropy and complex components. The research contents are follows. First of all, propagation law and inspection characteristic of ultrasonic wave in additive-manufactured metallic material are researched and function mechanism between defects and ultrasonic wave is revealed. Then, the effect of anisotropic characteristic on ultrasonic propagation path is discussed in the additive-manufactured metallic component. The calculation methods of ultrasonic propagation path and time in additive-manufactured metallic components are established according to ray-tracing algorithm. Finally, the imaging algorithm based on virtual focusing is developed to inspect additive-manufactured metallic components. The ultrasonic imaging method based on virtual focusing and positioning and quantitative methods of defects are posed. The research results provide theory and experience for engineering application of ultrasonic imaging of additive-manufactured metallic components. The advanced and reliable nondestructive testing method are supplied for additive-manufactured metallic components according to research results.

增材制造金属材料不同成形方向上的组织特征差异很大，且制造过程中极易产生异于传统锻铸件的内部缺陷。随着增材制造构件向复杂化、结构多样化发展，现有无损检测手段已难以满足检测需求。项目拟采用虚拟聚焦成像方法实现对增材制造金属构件的超声检测，提出射线追踪算法解决声波传播路径计算问题，设计新型虚拟聚焦成像算法解决材料各向异性及型面复杂等检测难题。研究重点包括：1)阐释超声波在增材制造金属材料中的传播规律、检测特性及其与缺陷的作用机理；2)剖析增材制造金属构件的各向异性对声波传播路径的影响，基于射线追踪算法建立增材制造金属构件中超声波传播路径及时间的计算方法；3)开展增材制造金属构件的虚拟聚焦成像算法研究，建立增材制造金属构件的虚拟聚焦超声成像检测及缺陷定位定量表征方法。研究成果可为增材制造金属构件虚拟聚焦超声成像检测的工程应用提供理论基础，可为我国增材制造技术提供先进可靠的无损检测与评价技术。

增材制造金属材料不同成型方向上的组织特征差异很大，且在制造过程中极易产生异于传统锻铸件的内部缺陷。为了满足增材制造构件无损检测的发展需求，项目开展了基于虚拟聚焦理论的超声成像检测及评价技术研究。主要完成了以下工作：首先，采用立体切割技术测量了增材制造钛合金材料的弹性常数矩阵，基于Christoffel方程建立了各向异性材料声速的理论计算模型，采用上述模型分析了超声波在该材料中的传播规律；建立了基于时域有限差分方法的声场数值仿真模型，利用该仿真模型探讨了增材制造钛合金材料中超声波与缺陷的相互作用机理；采用基于全矩阵数据的声速测量方法，定量分析了材料不同成型方向上的声速和衰减变化，阐释了超声波在该材料中的检测特性，为增材制造金属构件的超声检测提供了理论指导。然后，通过探讨研究多种射线追踪算法，采用最短路径射线追踪算法和基于Snell定律的射线追踪算法建立了虚拟聚焦成像时超声传播时间的计算方法，为虚拟聚焦超声成像检测算法的研究奠定了基础。最后，开展了增材制造钛合金构件的全聚焦成像、多模态全聚焦成像算法及实验研究；验证了基于声速补偿的全聚焦成像算法，解决了由于材料各向异性而导致成像发散的问题；实现了基于当量试块比较法和6dB法的虚拟聚焦超声成像定量表征方法，并提出一种虚拟聚焦成像的声束校准方法，有效减小了缺陷定位、定量检测误差。研究成果为增材制造金属构件虚拟聚焦超声成像检测的工程应用提供了技术基础，为增材制造材料提供了一种先进可靠的超声成像检测及评价方法。