MOTIVATION

• Ultra high molecular weight polyethylene shows high stiffness and performs better to prevent penetration.
• Modeling impact on soft body armor pack can provide important knowledge about the performance of UHMWPE under impact.

OBJECTIVES

• Perform impact analysis on soft body armor pack (SBAP) using SHELL elements
• In order to perform impact analysis on SBAP, we need to:
• Determine the properties of unidirectional UHMWPE/PU lamina using transversely isotropic fiber properties

APPROACH

• Assemble UHMWOE fiber and matrix properties from literature
• Use continuous fiber mirco-mechanics (CFM) to calculate the properties of unidirectional lamina
• Determine shell element properties for impact analysis
• Conduct impact on a single [0/90] lamnia
• Conduct impact on multiple [0/90] laminas
• Identify the mechanics of SBAP deformation under impact

MATERIAL PROPERTIES

MATERIAL MODELING

FINITE ELEMENT MODELING
• UHMWPE [0/90] lamina is modeled with shell elements
• Coarse mesh at the edge
• Finest mesh in the Impact center
• In-plane dimension is 360 mm x 360 mm and thickness 0.127 mm
• RCC projectile, L/D=1
• Gap between laminas 0.003mm
• For multi-layer simulations, a total of 38 layers have been considered

Impact on single layer
Impact velocity 50m/s
• Dynamic deformation cone grows with time
• Cone edge makes a kink with the undeformed lamina
• The kink travels in the radial direction
• No failure is seen in the first 200 µs

Impact velocity 100m/s
• Failure seen in the first 200 µs

IMPACT ON MULTIPLE LAYERS

• The Soft Body Armor Pack (SBAP) is Made of 38 UHMWPE/PE [0/90] Sub-Laminates
• Gap Between Each Layer is 0.003 mm
• After Impact Laminates Engage in Contact with the Projectile from 0-8 µs and thus Deformation Cone Evolves
• Later It Grows In Through Thickness and Radial Direction

DEFORMATION OF SBAP

• Dynamic deformation cone grows with time
• The laminas under the projectile appears to be tightly packed under the compressive force
• At the kink,
• Laminas exfoliate through the thickness because there is no compressive force to hold them down
• At time 135 µs the projectile rebounds and no tension failure is found in this case

PROJECTILE DYNAMICS

CONTACT FORCE
• Contact force linearly grows to a maximum in between 0-8microsecond
• Loading-unloading behavior shows a saw-tooth appearance
• Impact contact force reduces as the projectile decelerates

PROJECTILE VELOCITY
• Projectile rigid body velocity also decrease with time
• Negative velocity shows rebound

VELOCITY DISPLACEMENT
• For impact velocity 200 projectile stops at a maximum distance 11.5 mm
• For impact velocity 400 the projectile stops at a about 23.5 mm

FUTURE WORKS

• Compare results with ballistic experiments with & without clay backing
• Compare single Layer impact with Phoenix & Porwal (2003) membrane theory