Hey everyone,
I’m working on a robot model. I just modeled its wrist but when I go into render mode, it displays the material in a weird way, with spikes. The material is as simple as it can be (a white diffuse shader) which makes me think that the problem comes from the model of the wrist itself. Do you have any idea how I could fix this? (The project file is here: Robot.blend (1.62 MB))
Thanks 
You have some inconsistent face normals, some pointing outwards and some pointing inwards. To correct this select all vertices and Ctrl+N
The renderer can only render triangles, if you have non triangles in your scene these will be triangulated that can cause errors on non planar faces like the long triangles you see in your render.
Do you want the object flat or smooth shaded ? I’ll assume you want flat shaded as in the render.
You can set it as smooth shaded, mark each face as sharp (Ctrl+E) and use the Edge Split Modifier
or you could just enable Auto Smooth
It worked, thank you very much for your help! 