3D打印钛合金构件孔隙率的超声多次散射无损评价方法

With many distinct advantages, 3D printing titanium alloy is widely used in such high-end fields as aviation and military industries. Now that porosity is one of the most important factors affecting the mechanical performance and service life of 3D printing titanium alloy, evaluating it effectively is the bottleneck of the development of this technique. In this research, an ultrasonic nondestructive evaluation method is studied: titanium alloy test blocks of different porosities are produced by 3D printing, and the spatial topological structure of the pores in 3D printing material is analyzed using the theory of topological structure. Then the spatial correlation functions of the pores in the substrate are built to explore the mechanism of the influence of pores over ultrasonic single scattering. Besides, the path change of multiple scattering and the waveform transformation under the influence of the pores are studied, and the ultrasonic multiple scattering in the material is characterized by the higher-order components of the scattering intensity operators to develop the strategies on how to choose the cut-off points of the scattering order and the scattering weight distribution of each order. And the porosity parameters corrected by multiple scattering are identified by the spatial variance curve of each micro-element. Then the influence of the complex surfaces on the ultrasonic multiple scattering signals is analyzed by the multi-Gaussian model of ultrasonic beam, and a method to modify the backscattering coefficient is studied based on the diffraction attenuation compensation, eventually to establish the ultrasonic multiple scattering model to evaluate the porosity of the 3D printing titanium alloy. It is expected that this research will be of practical significance to improving the quality and performance of the 3D printing component and ensuring its safe application.

3D打印钛合金构件具备诸多独特优势，可广泛应用于航天、军工等高端领域，而孔隙是影响其机械性能与服役寿命的重要因素，难以有效便捷地测量孔隙率是该技术发展的瓶颈之一。本项目拟研究一种基于多次散射的3D打印钛合金孔隙率超声评价方法：首先3D打印出不同孔隙率的钛合金试块，运用结构拓扑理论分析3D打印材料中孔隙的空间拓扑模型，构建孔隙在基体中的空间相关函数，探求孔隙率对超声单次散射的作用机理；研究孔隙作用下的多次散射路径及波形转换，通过散射强度算子的高阶分量表征超声波在材料中的多次散射，研究各阶散射权重分布及截断散射阶数的选取策略，并通过各微元的空间方差曲线辨识多次散射修正后的孔隙率参数；利用多元高斯声束模型分析复杂型面对超声多次散射的影响，研究基于衍射衰减补偿的背散射系数修正方法，最终建立孔隙率的超声多次散射评价模型。预期成果对提高3D打印构件的产品质量、保证其使用安全具有重要理论意义及应用价值。

3D打印钛合金构件具备诸多独特优势，可广泛应用于航天、军工等高端领域，而孔隙是影响其机械性能与服役寿命的重要因素，难以有效便捷地测量孔隙率是该技术发展的瓶颈之一。本项目研究了一种基于多次散射的3D打印钛合金孔隙率超声评价方法：首先，3D打印出含不同孔隙率的钛合金试块，并利用静水力学法、扫描电镜分析法测定孔隙率，构建孔隙在基体中的空间相关函数；研究3D 打印钛合金材料单次以及多次散射理论，考虑构件表面粗糙度和晶粒分布，提出孔隙作用下的背散射系数提取方法，实现多次散射修正。然后，利用3D打印钛合金材料单次散射二次散射信号，研究基于高阶散射的微小孔洞检测方法，剔除了微小孔洞对孔隙率评价的影响。接着，研究面向复杂型面3D打印钛合金构件孔隙率评价的超声衍射补偿方法，分析超声探头焦距、3D打印钛合金构件表面曲率、声程等因素对衍射衰减的影响，进行衍射系数与衰减系数补偿；利用基于声速法和衰减法的孔隙率评价方法实现了3D打印钛合金材料孔隙率等性能的高通量快速检测。另外，开展了非线性超声无损检测的理论研究，研究了非线性声场传播特性、非线性系数测量以及三次谐波应用机理。最后，开展复杂型面3D打印钛合金构件超声C扫描与成像研究，设计并实现面向C扫描修正算法，结合二进位图像法与动态阈值法实现超声C扫描图像优化。在本项目资助下取得的成果主要有：①面向3D打印钛合金孔隙率评价的多次散射模型；②基于高阶散射的3D打印钛合金微小孔洞检测方法；③基于声速法和衰减法的3D打印钛合金孔隙率评价方法；④3D打印钛合金孔隙率非线性超声评价方法；⑤针对3D打印钛合金构件C扫描修正方法；⑥发表SCI学术论文23篇，EI论文3篇；⑦授权发明专利2项；⑧获得湖南省科技进步二等奖1项；⑨培养硕士研究生4名，博士研究生1名；⑩参加国际国内学术会议并作报告7人次。总体上看，研究成果对提高3D打印构件的产品质量、保证其使用安全具有重要理论意义及应用价值。