The factors affecting yarn strength and elongation are mainly the fiber properties and yarn structure of the yarns, among which the strength and elongation of blended yarns are also closely related to the property difference and blending ratio of blended fibers, and the external factors such as temperature, humidity and strength test conditions have basically the same effect on yarn strength and elongation as the fibers.

1. Fiber properties

Length and linear density of fiber:

When the fiber length is longer and the fiber is thinner, the friction resistance between the fibers in the yarn is larger, which is not easy to slip off, so the yarn strength is higher.

When the fiber length uniformity is good and the fiber is fine and uniform, the yarn will be dried evenly and weak rings are few and insignificant, which is beneficial to the improvement of yarn strength.

Fiber strength:

When the fiber is strong and extended, the yarn will be strong and extended. Strong fiber, low elongation unevenness, high yarn strength.

Surface friction properties of fiber:

When the friction coefficient of fiber surface increases, the sliding resistance between fibers increases, the slippage length lc decreases, the proportion of slippage fibers decreases, and the yarn strength increases. Increasing the crimp number can increase the sliding resistance between fibers.

2. Yarn structure

(1) the influence of staple yarn structure on its strength and elongation is mainly reflected in the twist.

When the twist factor increases when the wood fibers increase friction resistance, not easy to slip, it is of short fiber yarn strength strong positive, but when the twist factor increases at the same time, along with fiber tilt is more and more big, the fibers in the yarn strength of effective component of the axial force is reduced, the yarn fiber fracture simultaneity, fiber tilted at the same time the yarn diameter increase is unfavorable factors of yarn relative strength.

(2) the influence of partnership

The combination of single yarns makes the dry yarn evenly, and there is contact between single yarns, which increases the cohesive force between outer fibers of single yarn. The strength of strands is greater than the sum of the strength of individual yarns.

(3) the arrangement of fibers in staple yarns

The strength of rotor yarns is lower than ring yarns: in rotor yarns, there are more irregularly arranged fibers, such as fold, curl and circle, and less normal transfer fibers, resulting in poor contact between fibers and fibers, and more slippage fibers during stretching.

(4) bulk yarn

The tensile breaking strength of bulk yarn is smaller than that of traditional yarn, but the breaking elongation is larger.

Structure characteristics: after the blending of two kinds of fibers with great difference in thermal shrinkage, thermal shrinkage treatment is carried out to make the fibers with high shrinkage in the yarn fully shrink, and the normal fibers with low thermal shrinkage are forced to show bulking characteristics along the axial compression and wrinkling of the yarn.

Tensile fracture process: the number of fiber roots bearing external force is small and the tension of each fiber is uneven. As they begin to be stretched, only a small fraction of the fibers bear the force, while the other fibers crumple and relax. After one of the current fibers is pulled, the latter fiber stretches and bears the tensile force until the whole fiber breaks.

(5) textured yarn and stretch yarn

Depending on a variety of shaping methods, each fiber presents a helical spring - shaped or crimp - shaped oriented buckling curve.

During the first considerable stretch, the fibers are actually straightened with very little increase in tensile force, with very high elongation at break.