The end of the splice life, the break!

A splice, although designed to optimize load transmission and minimize the inherent strength loss of knots, is not a permanent connection. Its gradual degradation and eventual breakage are the result of the various mechanical stresses to which the fibers and strands that compose it are subjected throughout its use. These stresses act locally within the complex structure of the splice:

• Tensile stress is, of course, the primary stress. The splice transmits the tensile force applied to the rope. However, repeated tensioning and release cycles can induce fatigue in the fibers. Furthermore, a less than perfectly uniform load distribution between the different strands of the splice can create higher tensile stress points.

• Bending stress is omnipresent in a splice. The strands are bent to form tucks and insert into the sheath or core. When a splice passes over a pulley, sheave, eyelet, or is connected to a fixed point, the fibers are subjected to intense localized bending, causing significant stress concentrations and contributing to fiber fatigue, particularly at tight bend radii.

• Shear stress occurs primarily within the splice, at the interfaces between the strands that rub against each other under tension. This friction is essential for splice strength (progressive load transmission), but it also generates internal abrasion. Shear stresses can also occur if the splice is subjected to significant external friction or is subjected to lateral stress.

The splice's "end of life" is reached when the accumulation of damage caused by these stresses (individual filament breakage, internal or external abrasion, creep under load, fiber fatigue) weakens the local or global structure sufficiently so that it can no longer withstand the applied force, resulting in fracture.

Understanding these mechanisms is essential for designing durable splices and predicting their useful life. The fundamental stresses involved are:
Tensile (or Compressive) Stress:
σ=AF
Bending Stress:
σf=IM⋅y
Shear Stress:
τ=AsheareF

By analyzing how these stresses manifest and accumulate within the complex geometry of a splice and in its constituent materials, it is possible to optimize its design and more accurately assess its longevity under given operating conditions.