Which surface of a groove is considered as the joint member surface included in the groove?

The groove face is the correct choice because it refers to the actual surface of the groove that is directly involved in the welding process. This face is the area of contact between the two joint members being welded and is essential for ensuring proper fusion and strength of the weld. The groove face is designed to allow for the flow of molten material during welding, which solidifies to form the joint.

On the other hand, the joint root refers to the deepest point of the groove, and while it is important in terms of penetration and weld quality, it is not the contact surface of the joint itself. The bevel angle refers to the angle created between the groove face and the base metal, which influences the weld size and shape but does not represent the surface in question. Lastly, penetration discusses how deeply the molten metal flows into the joint, which is related to weld quality but again does not identify the actual surface of the groove. Thus, understanding these definitions clarifies why the groove face is identified as the joint member surface included in the groove.