Theoretical Study Of The Mechanical Behavior Of Fiber Ropes With Hierarchical Helical Structures

Hierarchical helical structures are everywhere in artificial and biological materials,and most widely used in fiber ropes.In engineering applications,the rope with hierarchical helical structure is generally under a complex force status.Therefore,in order to ensure the rope can work safely and high efficiency,it is of great significance to study the mechanical behavior of fiber ropes with hierarchical helical structures.In this paper,based on considering different influencing factors(e.g.contact friction,fiber migration),we theoretically analyse the mechanical properties of the fiber rope with hierarchical helical structure,when the rope is subjected to axial tension,torsion and bending loads.The main contents of the research consist of following three parts.In the first part,we study the mechanical properties of the multi-strand fiber rope in ideal conditions,where there is no contact friction effect and fiber migration in the rope.Based on Costello's thin rod model and Poisson effect,we use a bottom-up method and a direct way to calculate the internal forces of the rope subjected to axial loads,respectively.And we obtain the changing curve of the internal forces and stresses of the rope with the axial strain or structural parameters(such as chirality,initial helix Angle,etc.).It's found that the bottom-up calculation method shows a better prediction of the total axial force,and the direct way is more appropriate to calculate the total axial torque.And the chirality,initial helix angles,and numbers of the fibers and plies can be used for accurate control of the mechanical performance of ropes.In the second part,we study the friction effect of the fiber rope with complex hierarchical helical structure.There are different frictional forms among fibers of different plies.In the study,we still use Costello's thin rod model and consider Poisson effect,but ignore the contact deformation of fibers.And we mainly analyze the distribution of contact and friction forces of fibers under the influence of the axial tensile strain of rope,the chirality of the fibers or plies and the initial helix angles of fibers.It's found that the chirality has no obvious influence on contact forces and friction forces of fibers.The contact forces and friction forces are related to the arrangement of spiral fibers in the ply.With the increase of the angle of the fiber centerline spiral around the axis of the ply,the cyclical trends of contact forces and friction forces of the fiber are approximately sine curve in the core strand and approximately “w”shape curve in the helical strands.In the third part,we study the influence of fiber migration on the mechanical behavior of fiber ropes with hierarchical helical structures.When the structural parameters are different,we obtain the changed trend of the internal forces and stresses of the rope in the migration period.The main principle is that the migration behavior of the fiber changes the internal structure of the rope,thus influences the mechanical properties of the rope.The results show that the internal forces and stresses of the fiber have periodic non-monotonic changes along the length of the rope.And there is a jump in the internal forces and stresses around the half-cycle point.That is,there is a risk of fiber breakage when the fiber migration changes direction.