Designing composite materials to withstand torsional loads involves considering the unique properties and behaviors of composite materials in response to such loading conditions. Torsional loads design involves taking into account the twisting of a structural element around its longitudinal axis.
Best laminate for torsional loads design
The shear modulus of numerous fiber-reinforced composites exhibits a diminished value in comparison to steel. Consequently, to achieve commensurate torsional stiffness, a fiber-reinforced composite tube necessitates a larger diameter or increased thickness relative to its steel counterpart. Within diverse laminate configurations, [±45]s laminates are preeminent, possessing the highest shear modulus and constituting the predominant laminate variant employed in applications centered solely on torsion.
In a general context, the shear modulus of a laminate exhibits an upward trend with escalating fiber modulus. For instance, the shear modulus of a high-modulus carbon–epoxy [±45]s laminate attains 78.3 GPa, mirroring parity with steel. Conversely, a high-strength carbon–epoxy [±45]s laminate achieves a shear modulus of 32 GPa, marginally surpassing that of aluminum alloys. Glass fiber laminates manifest even lower shear modulus values, and the application of Kevlar 49 fiber laminates in torsional scenarios is infrequent due to their suboptimal shear strengths. In comparison, the shear strengths of carbon fiber laminates parallel or slightly surpass those of mild steel and aluminum alloys.
Torsional loading of thin-walled tubes
The computation of the maximum torsional shear stress in a thin-walled tube constructed from balanced symmetric laminates is expressed as follows:
The torsional loading of thin-walled tubes represents a conventional methodology for evaluating in-plane shear modulus and strength. In this testing paradigm, stresses uniformly distribute circumferentially and longitudinally along the specimen, while shear strains maintain practical constancy throughout the thickness of the specimen wall. The classification of a structure as ‘a thin-walled tube’ in the context of torsion is contingent upon the extent of material anisotropy.
It is pertinent to note certain drawbacks associated with this approach, including the requisite use of relatively sizable specimens, specialized test fixtures, inserts to mitigate the buckling potential in select specimens, and the utilization of wound or specially configured specimens. Despite these limitations, the outcomes derived from torsional shear tests exhibit favorable comparability with results obtained through alternative methodologies utilizing flat specimens.
