# Torsion of a non-circular cross-section with more than one material

• VKulkarni
In summary, the conversation discusses the process of tackling torsion of non-circular bars and two-material composites. The speaker is unsure of how the warping function changes across a material interface and how this affects torsional behavior. They ask if there is a process to calculate the new torsional constant for a composite section, similar to how one would calculate the area moment of inertia for a bending problem. The expert recommended a scholar who specializes in torsion problems and suggested a specific paper to look into. They also noted that the papers may require knowledge of BEM and advanced mechanics of materials to understand.

#### VKulkarni

I am trying to understand how to tackle torsion of bars that are non-circular and two-material composites. I understand the process of finding the torsion constant for non-circular sections but I am not sure how the warping function changes across a material interface.

For example, if I have a solid square bar made from HDPE and one on surface I bond a thin sheet of Aluminum, how does the torsional behaviour change? Is there a process to calculate the new torsional constant? If this were a bending problem, we could convert the composite cross-section into an equivalent section using the ratios of elastic moduli of the materials and then find the area moment of inertia of the new section. Is there an analogous process for torsion?