Final answer:
When subjected to twisting, a thin-walled three-cell cross-section experiences shear stress, resulting from parallel forces relative to the cross-sectional area that cause deformation. Other stress types such as bending, tensile, and compressive stress can occur but are not directly related to the twisting motion.
Step-by-step explanation:
When a thin-walled three-cell cross-section is subjected to twisting, the primary type of stress experienced is shear stress. While other types of stress like bending stress, tensile stress, or compressive stress could occur in structural members, twisting specifically causes shear stress within the material. Shear stress arises from forces acting parallel to the section's cross-sectional area, creating a deformation represented by the symbol Ax, and is often confronted in engineering problems addressing torsion in members.
For example, if we consider a long shelf loaded with heavy books, the top of the shelf experiences compressive stress while the bottom experiences tensile stress. This is due to the bending of the shelf under the weight. However, when looking specifically at a twisting or torsional scenario, it is the shear stress that predominately characterizes the material's response. Sideways stress or shearing force leads to shear deformation that behaves similarly to tension and compression and can be described with corresponding equations.
To summarize the concept, the shear modulus is a property that relates shear stress to shear strain in a material and plays a significant role in torsional analysis. The shear modulus helps predict the amount of deformation (Ax) an object will experience when shear forces are applied relative to its original length (Lo).