AMPTIAC Quarterly, Vol. 9, No. 2, Summer/Fall 2005 - Advanced ...

V 50 (ft/s)
3500
3000
2500
2000
1500
1000
500
0.20
0.22 cal. Fragment Simulating Projectile 0.50 cal. Fragment Simulating Projectile
FEM
EXP
0.16
Delamination Diameter (m)
0.12
0.08
0.04
Stitched
Stitched
0
Plain
Weave
Triaxial
Weave
3D
Orthogonal
Weave
3D
Triaxial
Weave
3D
Braided
Weave
Figure 10. Ballistic Performance Comparison of S-2 Glass-Based
Composite of Weave Structures[24].
0.00
Vinyl Ester
Epoxy
Figure 11. Effect of Stitching on Ballistic Performance of
S-2 Glass Fiber-Reinforced Composites[6].
quality. Polyesters and vinyl esters are low cost, easily processed
composites with above average mechanical properties, but have
low compressive strengths. As a result of this deficiency, they
are normally relegated to non-structural applications.
Phenolics, like the polyesters, have low compressive strength
properties, but provide higher temperature capabilities and low
smoke generation upon combustion.
Ease of processing and the potential release of toxic chemicals
are concerns with composites. Processing methods, such as resin
transfer molding, require resin materials to have low viscosities
in order for the finished product to have a low porosity, and thus
good performance. In the case of higher viscosity materials, like
epoxies, high processing temperatures and/or additives are used
to produce the required low viscosity for processing. High processing
temperatures, however, correspond to higher costs and
may also limit fiber selection, while additives can produce toxic
byproducts. The trade-offs of performance, ease of processing,
and costs are summarized in Table 2 for the three structural
resins. In most applications, vinyl ester resins have replaced
polyester resins as they are similar in many properties, but with
the added benefit of having superior mechanical properties.
FIBER-REINFORCED PMC ARMOR
The performance of fiber-reinforced PMC armors not only
depends upon the fiber and resin material properties, but also
the fiber structure, fiber volume, fiber compatibility with the
resin, and additives. Most commercial fiber composites for
armors consist of unidirectional, plain, or basket weave fiber
structures. Weaving fibers does not generally improve the
penetration resistance in composites, because the fibers are
confined by the resin and the energy can not be effectively
transferred to adjacent fibers as is the case of fiber mats. Three
dimensional weaves limit delamination and thus improve
multi-hit performance of composites. Figure 10 compares the
ballistic performance of various woven S-2 Glass fiber composites
subjected to a 0.22 caliber fragment simulating projectile
(FSP) using finite element modeling (FEM) and experiments
(EXP). Through-the-thickness stitching of composite plies is
another means of limiting delamination problems, as shown in
Figure 11 for S-2 Glass composites tested with a 0.50 caliber
fragment simulating projectile at 1550 feet per second.
The ballistic performance of fiber-reinforced PMC armors is
largely attributed to the fibers. Maximizing fiber volume in a
5000
0.30 cal. Fragment Simulating Projectile
5000
0.30 cal. Fragment Simulating Projectile
4000
4000
V 50 (ft/s)
3000
V 50 (ft/s)
3000
2000
1000
S-2 Glass, no background data
0
0 2 4 6 8 10 12
Areal Density (lb/ft 2 )
(a) V 50 versus Areal Density
Spectra 1000, 650 denier-plain weave
KM2, 850 denier-plain weave
Kevlar 29, 1500 denier-basket weave
2000
Figure 12. General Comparison of Fiber-Reinforced PMC Armors[18].
Spectra 1000, 650 denier-plain weave
1000
KM2, 850 denier-plain weave
Kevlar 29, 1500 denier-basket weave
S-2 Glass, no background data
0
0 0.2 0.4 0.6 0.8 1.0
Thickness (in.)
(b) V 50 versus Thickness
8
The AMPTIAC Quarterly, Volume 9, Number 2