Center for Composite Materials - University of Delaware

Research Summary

Fiber Length Scale Finite Element Modeling of Kevlar KM2

Authors: Subramani Sockalingam, John W. Gillespie, Jr., and Michael Keefe

INTRODUCTION AND OBJECTIVES

• Kevlar flexible composites widely used on high velocity impact applications
• Role of fiber transverse properties not well understood
• To understand the fundamental fiber-level mechanisms during impact to establish ‘materials-by-design’

TOW TRANSVERSE COMPRESSION RESPONSE

Tow transverse compression response (TTCR) modeled considering all the 400 fibers in a tow to understand fiber-fiber contact and frictional interactions.

Fiber-Fiber contact plays a significant role in spreading and deformation of individual fibers.

TOW TRANVERSE IMPACT

Impact of a spherical projectile of radius 2.675 mm and 6.88 mg at the mid span of 1” long tow clamped at ends.

COMPARISON TO HOMOGENIZED MODEL

• The restoring force by reflected spreading wave shifts the axis of bending
• Axial tension + tension due to bending results in stresses twice as high as homogenized model at the clamped end

SUMMARY

• Systematic study of transverse mechanical properties of Kevlar KM2 at the fiber length scale
• Determined adequate mesh discretization to accurately capture the single fiber transverse compression response
• TTCR modeled considered all 400 fibers in a Kevlar KM2 tow
• Fiber-fiber contact plays a significant role in spreading of fibers, fiber-fiber compression and frictional interactions
• TTCR comparison to homogenized model indicate need for nonlinear material model to accurately represent transverse compression response
• 3D fiber level model subjected to high velocity impact
• Dynamic fiber kinematics – transverse wave, spreading wave
• Comparison to homogenized yarn level model
• Fiber-level model predicts axial stresses twice as high as the homogenized model at the clamped boundary

ACKNOWLEDGEMENTS

Research was sponsored by the Army Research Laboratory and was accomplished under Cooperative Agreement Number W911NF-12-2-022. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein.

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