Transverse Impact Response of a Linear Elastic Ballistic Fiber Yarn

Abstract

Transverse impact response of a linear elastic Kevlar V R KM2 fiber yarn was determined at various striking speeds from Hopkinson bar and gas gun experiments incorporated with high-speed photography techniques. Upon transverse impact, a triangle shape was formed in the fiber yarn. Both longitudinal and transverse waves were produced and propagated outwards the fiber yarn. Both the angle of the triangle and Euler transverse wave speed vary with striking speeds. The relationship between the Euler transverse wave speed and the striking speed was determined. The transverse impact response of the fiber yarn was also analyzed with a model, which agrees well with the experimental results. The model shows that the longitudinal wave speed is critical in the ballistic performance of the fiber yarn. At a certain striking speed, a higher longitudinal wave speed produces a higher Euler transverse wave speed, enabling us to spread the load and dissipate the impact energy faster, such that the ballistic performance of the fiber yarn is improved.

Modeling and Experiments on Ballistic Impact into UHMWPE Yarns Using Flat and Saddle-Nosed Projectiles

“…This may happen during the first fraction of a microsecond if the fibers directly in contact with the projectile travel at velocity V, whereas those deeper into the yarn under the projectile travel initially at a considerably lower velocity until yarn compaction is complete. This is precisely the situation noted by Song et al [33,34]. The reader is referred to Appendix A for theoretical details.…”

“…Additional details on yarn modeling can be found in Chocron et al [32] who used four continuum elements for the yarn cross section and assumed a linear elastic, orthotropic constitutive model. Advances in high speed photography have subsequently allowed very detailed observation of the yarn impact event as for instance in work by Song et al [33,34] for 450 denier Kevlar KM2 yarn where a Hopkinson bar was used for transverse impact testing. It is clearly visible that no bounce occurs, and additionally, non-uniform through-thickness compression of the yarn occurs before the back of the yarn begins to move.…”

Recent advances in modeling and experiments of Kevlar ballistic fibrils, fibers, yarns and flexible woven textile fabrics – a review

“…For example, a Kevlar KM2 600 denier yarn consists of 400 individual fibers. The transverse impact experiments reported in the literature are at the yarn length scale 26 and fabric length scale 40 as it is extremely challenging to capture real time information at the fiber (micron) length scale. The dominant role and contribution of principal yarns (yarns directly in contact with projectile) to energy absorption and projectile deceleration is reported by several researchers 17,65 .…”

Dynamic modeling of Kevlar KM2 single fiber subjected to transverse impact

“…The impact results in bouncing of the yarn in front of the projectile and the breaking speed is predicted to be lowered up to 40% due to the increase in the axial strain. Also for linear elastic long fibers subjected to transverse impact Song et al (2011) derived equations (again assuming tension is the only restoring force) for the transverse wave speed and the angle c which the transverse wave makes with the horizontal direction. These simple analytical models provide an excellent baseline to compare our numerical results but are unable to capture projectile/fiber interactions.…”

“…Song et al (2011) conducted Hopkinson bar transverse impact experiments of Kevlar KM2 yarns at different striking speeds. They noted that transverse wave speed, unlike longitudinal wave speed, depends on both material properties (longitudinal wave speed) and loading conditions (impact velocity).…”