## 5 Creation of Didactic Material  
The methodology used for the creation of the didactic material, illustrated in Figure 6, consisted of three distinct phases: (i) development of 2D drawings; (ii) preparation of radiographic images (both simplified for initial application, and realistic (Figure 7) for a higher level of difficulty); and (iii) development of the IVP. Since there is no specific program that directly simulates the appearance of a radiographic part, this article describes how the authors achieved this effect. During the first phase, two-dimensional drawings of the orthogonal views of the part, including its internal defects, were generated according to TD norms (e.g., representing hidden edges with dashed lines, Figures 1b and 3b). Microsoft Word(r) drawing tools were used for this purpose due to their ease of use. However, despite requiring specific knowledge to be used, the authors recommend using a student version (free if used for educational and non-commercial purposes) of Autodesk AutoCAD(r) as it offers a large number of tools specifically oriented to the generation of drawings according to TD norms. Figure 5: IVP to allow students to freely explore the parts and their internal defects: (**a**) opaque view; (**b**) translucid view, where inner inclusions are shown. Figure 6: Methodology used for the creation of the didactic material. The second phase began by taking as a basis the 2D drawings generated in the first phase, creating from them images of the part to which depth gradients were applied, i.e., different shades of gray were used to represent the different thicknesses of the parts (simplified radiographs, Figures 1c and 3c). To carry out this operation, the image modification program Adobe Photoshop(r) was used, which offers a multitude of options for manipulation and creation of gray gradients. These images were then processed using Blackmagic Design Fusion(r) (BDF, Figure 7a), used in digital compositing of video and film, which blurred the edges of the figures to obtain images similar to real radiographies (Figure 7b). As an alternative to BDF, The Foundry Nukte(r) could be used, which is a program widely used in film production. In spite of this, the authors chose BDF because to obtain similar results, the price is much lower and the working environment is more user-friendly. The third phase was carried out by three-dimensionally modeling the part and its internal defects, using Autodesk 3 DS Max(r), which is a program that has advanced modeling, material application, and lighting options, and offers a student version that is free if used for non-commercial educational purposes. Alternatively, the authors believe that Blender(r), which has many of the features of Autodesk 3 DS Max(r) and is free of charge, could be used as an alternative. Once the 3D model was created, the IVP was developed (Figure 5), i.e., a computer application was generated that allows the user to interact with the different 3D models created in the previous phase (e.g., by rotating them or zooming in/out the point of view). To carry out this operation, Epic Unreal Engine 4(UE4) was used, which is a free game engine (if not used for commercial purposes) that allows programming a multitude of functionalities without typing code, using a visual scripting system. The authors consider that Unity Technologies Unity(r) could be used as an alternative to UE4, since it has many of the features of UE4, both being widely used in the educational world [43, 44]. It should be noted that the programs used to create the didactic material and the alternatives suggested by the authors have a large community of users who share experiences and knowledge on the Internet. This fact favors the existence of a large amount of updated and free information about the use of these programs and the resolution of possible problems that may arise during their use. However, there are several alternative programs to those described in this article that could be used in each of the three phases of creation of the methodology explained in this article.