Fig. 1. Framework for detecting wrinkle deformation of bend tube

Fig. 2. Shape introduction of spine line

Fig. 3. TCT model in spine line plane

Fig. 4. Contour lines extracted by parallel planes

Fig. 5. Contour lines extracted by polar angles of ridge sections. (a) Ridge sections; (b) surface composed of rays corresponding to same polar angle

Fig. 6. Method of establishing polar coordinate systems on sections at different parts of bend tube. (a) First straight tube; (b) bend part; (c) second straight tube

Fig. 7. Diagram of generating contour lines on inner side of bend

Fig. 8. Diagram of flattening contour lines

Fig. 9. 3D scanning system

Fig. 10. Bend tubes and their contour lines

Fig. 11. Error analysis of spine line reconstruction

Fig. 12. Reconstruction results of tube A′. (a) Matching result of TCT model; (b) error of spine line point

Fig. 13. Reconstruction results of tube B′. (a) Matching result of TCT model; (b) error of spine line point

Fig. 14. Bend tube with obvious wrinkles. (a) Physical diagram of bend tube; (b) scanning result of tube; (c) detection result of wrinkle deformation; (d) contour line corresponding to largest wrinkle deformation after flattening

Fig. 15. Standard part and its contour lines

Fig. 16. Contour line analysis result of standard part