Ballistic performance of hybrid panels composed of unidirectional/woven fabrics

Abstract

This paper examines the effect of the layering sequence of unidirectional (UD)/woven fabric hybrid panels on perforation resistance (V₅₀) against a 5.56 mm fragment-simulating projectile and the blunt trauma resistance represented by the backface signature (BFS) caused by a .44 Magnum semi-jacketed hollow point projectile. Some of the woven fabric layers were impregnated with shear thickening fluid (STF) to modify their properties. When layers with a smaller in-plane constraint (neat woven fabric) were laminated behind layers with a larger in-plane constraint (UD or STF-impregnated woven fabric), an increase in perforation resistance was observed due to the decreased out-of-plane constraint. When the layering sequence was reversed, an increase in blunt trauma resistance (i.e. smaller BFS) was observed due to better coupling of yarn elongation in the frontal and rear layers.

Keywords

unidirectional/woven hybrid shear thickening fluid layering sequence ballistic performance backface signature

The quest for flexible and light-weight, thus comfortable, body armors has been the driving force for soft body armor development. The most widely used soft ballistic resistant products are made from woven fabrics or unidirectionally oriented high-tenacity fibers. Although unidirectional (UD) products have desirable ballistic resistant properties, they require complicated manufacturing processes, resulting in higher manufacturing costs compared with other types of ballistic resistant composites. Thus, using materials that have desirable properties for soft body armor, such as Kevlar®, Twaron®, Heracron®, Spectra® and Dyneema®, various construction methods have been developed, such as hybridization (multi-material), multi-layer design (ballistic sandwiches), perimeter stitching, etc. To reduce the cost and weight of soft body armor by using the hybridization method, where materials with different properties are layered, determining the proper order of the layers is very important. Once produced, the protective performance of such body armor will be direction dependent and, thus, if worn the wrong way, there is a large chance that the panel would fail to protect the wearer. Therefore, the strike face and wear face of the panel must be carefully labeled in this type of body armor.

Although several patents and commercially available soft armor systems consisting of multiple materials can be found, relatively few papers have been published on the ballistic performance of hybridized body armor.¹ This may be partly due to the fact that researchers do not wish to disclose proprietary information about their products, but the complexity of the mechanism responsible for the performance enhancement in hybrid panels also plays its part.

Improving the penetration resistance of a target by layering it with materials having different properties has been known since the late 1800s, when armor plating was first improved by hardening its surface.² Since then, the use of multi-layered armor plating has increased and further attracted the interest of researchers. Larsson and Svenson³ reported that hybrid composite panels of ‘carbon fiber fabric/polyethylene (PE) fiber fabric’ showed an ordering effect on the ballistic limit (5.46 mm fragment-simulating projectile (FSP)), where the ‘PE at the back (i.e. high-strength/high-stiffness carbon fiber component backed by high-ductility/high-toughness polyethylene component)’ hybrid composite showed significant improvement in perforation resistance compared with the ‘PE at the front’ hybrid composite. On the other hand, Grujicic et al.,⁴ using non-linear dynamics transient computational analysis, reported results opposite to the above paper using a hybrid panel of one layer of Kevlar fiber-reinforced epoxy and one layer of carbon fiber-reinforced epoxy. The results were rationalized using an analysis of the elastic wave reflection and transmission behavior at the inter-laminate and laminate/air interfaces.

There are very few published papers regarding this topic in the field of soft body armor application, and it is even harder to find studies using panels that have field-applied areal density levels. The few papers found deal with panels consisting of only a few layers. One such study is that of Cunniff,⁵ who studied the effect of the laminating sequence with compliant fabric panels using two heterogeneous systems of double ply panels made of woven fabrics. He investigated the effect of constraint in transverse deflection with one system composed of 1 ply of 1000 denier Kevlar 29 fabric (lower modulus) and 1 ply of 375 denier Spectra 1000 fabric (higher modulus), and the other composed of 1 ply of 1000 denier Kevlar 29 fabric (lower modulus) and 1 ply of 1040 denier Kevlar 49 fabric (higher modulus). While the former system showed nearly a factor of two difference in ballistic limit velocity (V₅₀) for the two possible stacking orders, the latter system showed equivalent V₅₀ regardless of laminating sequence. To explain the experimental result of the former system of Cunniff,⁵ Porwal and Phoenix⁶ developed a theoretical and computational model using typical mechanical properties (i.e. modulus and mass density) of Kevlar and Spectra layers, but the calculation result was unsatisfactory. In our previous study,⁷ we reported the effect of the laminating sequence of a shear thickening fluid (STF)-assisted woven fabric panel on the ballistic performance using a 9 mm full metal jacket (FMJ) bullet. The increase in ballistic performance (i.e. increased V₅₀ and decreased backface signature (BFS)) was observed when neat layers were backed with STF-impregnated layers, and this was presumed to be due to a better coupling of yarn elongation in frontal and rear layers and hence increased bullet expansion.

The two most frequently used indices in measuring the ballistic resistance of soft body armors are the ballistic limit (V₅₀) and BFS. The V₅₀ is the impact velocity at which there is a 50% probability that a single projectile will completely perforate the target armor. The V₅₀ test is generally performed either with a clay body simulant placed behind the target or with no backing material (i.e. clamping), depending on the test protocol defined by the end user. The BFS is the perpendicular distance from the reference plane of the backing material surface to the deepest point of indentation caused by a non-penetrating impact on the target armor. This value is related to the energy that is transferred to the human thorax from the soft body armor by a non-penetrating projectile. In this study, the effect of the layering sequence of UD/woven fabric hybrid panels on (1) the perforation resistance against a 5.56 mm FSP and (2) the backface deformation by a .44 Magnum semi-jacketed hollow point (SJHP) bullet was investigated at the field-applied levels of protection.

Experiments

Materials

The cross-plied UD fabrics used in this study were ultra-high molecular weight polyethylene (UHMWPE) fiber-based Dyneema® SB31 (DSM, 0°/90° two-ply cross-plied) and p-aramid fiber-based Gold Flex® (Honeywell Inc., 0°/90°/0°/90° four-ply cross-plied). The areal density of a single layer of each fabric was 132 and 232 g/m², respectively. The woven fabric was a plain weave of 600 denier p-aramid yarns (Heracron® HF 100), having a fabric count of 13.4 × 13.4 (warp × weft) yarns/cm. The areal density of a single layer of the woven fabric was 179 g/m² in the dried state. The STF-treated woven fabrics were prepared by impregnating STF composed of 68 wt% silica nanoparticles (nominal average diameter; 45 nm) and 32 wt% polyethylene glycol (MW 200) into neat woven fabrics, and the add-on was controlled to be 15 or 20% owf (on the weight of fabric). The STF treatment modified the pullout and elongational properties of the yarns within the fabric to be close to UD fabrics, that is, higher frictional force in intersecting points and diminished retardation of elongation due to the crimp effect observed in a neat fabric.⁷ Table 1 shows the composition and layering sequence of the hybrid panels used in the ballistic test for perforation resistance performance (V₅₀) against a 5.56 mm NATO FSP, and Table 2 shows those of the panels used in the ballistic test for trauma resistance performance (i.e. BFS) against a .44 Magnum SJHP bullet.

Table 1.

Hybrid panels used in the ballistic test of perforation resistance performance (5.56 mm fragment-simulating projectile (FSP))

Panel		H-1F	H-2F	H-3F	H-3FR	H-6F
UD-1^a (A)	Number of plies	22	22	16	16	–
UD-1^a (A)	Weight fraction (%)	43.58	43.58	32.02	32.02	–
UD-2^b (B)	Number of plies	–	–	–	–	13
UD-2^b (B)	Weight fraction (%)	–	–	–	–	44.81
H34N^c (C)	Number of plies	15	15	17	17	15
H34N^c (C)	Weight fraction (%)	40.30	40.30	46.13	46.13	39.89
H34S^d (D)	Number of plies	5	5	7	7	5
	Weight fraction^e (%)	16.12	16.12	21.85	21.85	15.29
	STF add-on (%owf)	20	20	15	15	15
Fabric in panel (kg/m²)		6.48	6.48	6.41	6.41	6.60
STF in panel (kg/m²)		0.18	0.18	0.19	0.19	0.13
Total areal density (kg/m²)		6.66	6.66	6.60	6.60	6.73
Layering sequence (FMR)^f		ADC	CDA	ADC	ACD	BDC

UD-1; SB-31®.

UD-2; Gold Flex®.

H34N; neat p-aramid woven fabric.

H34S; shear thickening fluid (STF)-impregnated p-aramid woven fabric.

Weight fraction; weight of component layers divided by total weight of the panel.

FMR means the sequence of ‘Face-Middle-Rear’, where ‘Face’ is the strike face.

Table 2.

Panels used in ballistic test of trauma resistance performance (.44 Magnum semi-jacketed hollow point (SJHP))

Panel		H-1M	H-2M	H-3M	H-4M	SW-M	SU-M
UD-1^a (A)	Number of plies	22	22	16	11	–	51
UD-1^a (A)	Weight fraction^d (%)	43.58	43.58	31.71	21.92	–	100.00
H34N^b (C)	Number of plies	15	15	17	22	37	–
H34N^b (C)	Weight fraction^d (%)	40.30	40.30	45.70	59.44	100.00	–
H34S^c (D)	Number of plies	5	5	7	6	–	–
	Weight fraction^d (%)	16.12	16.12	22.58	18.64	–	–
	STF add-on (%owf)	20	20	20	15	–	–
Fabric in panel (kg/m²)		6.48	6.48	6.41	6.46	6.62	6.73
STF in panel (kg/m²)		0.18	0.18	0.25	0.16	–	–
Total areal density (kg/m²)		6.66	6.66	6.66	6.63	6.62	6.73
Layering sequence (FMR)^e		ACD	CDA	ACD	ACD	All C	All A

UD-1; SB-31®.

H34N; neat p-aramid woven fabric.

H34S; shear thickening fluid (STF)-impregnated p-aramid woven fabric.

Weight fraction; weight of component layers divided by total weight of the panel.

FMR means the sequence of ‘Face-Middle-Rear’, where ‘Face’ is the strike face.

Ballistic performance tests

A schematic drawing of the firing site is shown in Figure 1. Chisel-nosed NATO FSPs (5.56 mm, 1.1 g) were used to investigate the perforation resistance of the hybrid panels. The FSPs were sabot-launched from a 7.62 mm rifled powder gun barrel, and the projectile velocity was controlled by varying the loading position of the FSP-inserted sabot in the gun barrel (Figure 2) and the type of color-coded cartridges for different velocity ranges. This test was conducted with a conditioned clay body simulant placed behind the target. Remington .44 Magnum SJHP (15.6 g) bullets were used to investigate the blunt trauma resistance of the hybrid panels at around 436 m/s (National Institute of Justice (NIJ) threat level III-A). To validate the BFS test results, both pre- and post-drop tests were conducted on the conditioned clay in a fixture with a 1.043 kg steel sphere at the height of 2 m (NIJ standard-0101.04). Right after the drop test, each panel (38 cm × 38 cm) interconnected at the four corners was mounted on a backing material fixture and secured with mounting straps. Figure 3 shows the panel size (38 cm × 38 cm) and shot locations for each test. The shot locations for 5.56 mm FSPs were 100 mm apart from adjacent shots, and the .44 Magnum SJHP shots (labeled CTE, LBE, and RBE) were aimed between 76 and 95 mm from the edge of the panel.

Figure 1.

Schematic drawing of the firing site.

Figure 2.

Velocity control principle in the 5.56 mm fragment-simulating projectile (FSP) test.

Figure 3.

Panel size and shot locations for each test: (a) 5.56 mm fragment-simulating projectile (FSP); (b) 44 Magnum semi-jacketed hollow point (SJHP).

Results and discussion

Effect of layering sequence on the perforation resistance of hybrid panels against an infrangible projectile

Figure 4 shows the ballistic limit test result of each hybrid panel against a 5.56 mm NATO FSP. From this result, the specific energy absorption (E_sp) value of each hybrid panel calculated from Equation (1) is shown in Figure 5:

Specific Energy Absorption (E_{sp}) = \frac{\frac{1}{2} \cdot m \cdot v_{50}^{2}}{Areal density}

(1)

Figure 4.

Ballistic limit test results of a series of hybrid panels (5.56 mm NATO fragment-simulating projectile (FSP)), where CP is complete perforation, PP is partial penetration, V₅₀ is average of V_tests and spread is V_test,max – V_test,min (all in m/s).

Figure 5.

Specific energy absorption values of hybrid panels (5.56 mm NATO fragment-simulating projectile (FSP)).

From the figure, we can see that the panels, which were layered in the order of decreasing stiffness (H-1F, H-3F and H-6F), possessed relatively higher perforation resistance compared with those that were layered differently (H-2F and H-3FR). ‘Stiffness’, here, is a comprehensive term, implying the modulus of the component yarn, the apparent modulus (a term that we used in our previous study⁷ to describe in-plane constraint) and the flexural rigidity of the fabric. As UD fabrics are generally not crimped and STF treatment reduces the ‘crimp effect (i.e. retardation of elongation of facing yarns)’ of the woven fabric, the modulus of the fabrics used in this study decreases in the order of UD > STF-treated woven fabric > neat woven fabric. For simplification, we will express UD fabrics as HM (high modulus), STF-treated woven fabric as IM (intermediate modulus) and neat woven fabric as LM (low modulus). Since the projectile was sabot-launched, the thermal effect on PE frontal layers would be negligible due to the insulation effect of the sabot on FSP from the exploding gas and direct touch with the gun rifling.

In an attempt to visualize the effect of hybridization and layering sequence more clearly, we measured V₅₀ and calculated the E_sp of each component material under the same clay-backed conditions. The results are given in Table 3. Since the E_sp value may vary with the panel’s areal density, the average E_spvalue of non-hybrid panels with different areal densities (which were varied to obtain the field-applied levels of protection) was considered the E_sp value of each component material.

Table 3.

Specific energy absorption value of each component material used in the hybrid panels

Fabric	Ply	Areal density (kg/m²)	V₅₀ (m/s)	Impact energy at V₅₀ (J)	E_sp [J/(kg/m²)]	Avg. E_sp [J/(kg/m²)]
UD-1^a	49	6.47	625	214.84	33.22	32.83
UD-1^a	26	3.43	450	111.38	32.45
UD-2^b	31	7.19	620	211..45	29.40	29.81
UD-2^b	20	4.64	505	140.26	30.23
H34N^c	41	7.34	643	227.18	30.96	31.00
H34N^c	36	6.44	603	200.05	31.04
H34S15^d	36	7.41	590	191.20	25.80	25.80
H34S20^e	36	7.73	584	187.71	24.27	24.27

UD-1; SB-31®.

UD-2; Gold Flex®.

H34N; neat p-aramid woven fabric.

H34S15; shear thickening fluid (STF)-impregnated p-aramid woven fabric, add-on of 15%owf.

H34S20; STF-impregnated p-aramid woven fabric, add-on of 20%owf.

In Figure 6, the scale of the y-axis is the normalized E_spvalue of each hybrid panel obtained by summing the contributions of each component material. If the y-value equals unity (i.e. 1), it indicates that the hybridization effect is negligible. A y-value larger than unity indicates that the hybridization has a positive effect, and a y-value smaller than unity indicates a negative effect. Hybrid panels H-1F, H-3F and H-6F had y-values larger than unity, meaning the hybridization enhanced the perforation resistance of the component fabrics. These three panels were all layered in the HM-IM-LM sequence. On the other hand, judging from the y-values smaller than unity, for H-2F and H-3FR panels, hybridization decreased the perforation resistance of the component fabrics. Between the two negatively affected panels, H-2F, which was layered in the exact opposite sequence of the positively affected three panels, showed a higher decrease in perforation resistance. If we compare the two panels H-1F and H-2F, which had the same composition but were layered in reverse sequence, there is a 13.5% difference in perforation resistance. On the other hand, only 4% difference in perforation resistance was observed between the two hybrid panels, H-3F and H-3FR, which had the same composition and first-component layers, but reversed second- and third-component layers. The decrease in perforation resistance of H-2F and H-3FR panels is presumed to be due to the comparatively large resisting force of the successive rear layers. The following is our reasoning for this interpretation.

Figure 6.

Perforation resistance presented as a normalized value by the sum of the contributions of each component materials (5.56 mm NATO fragment-simulating projectile (FSP)).

A well-known relationship between the tension and the pressure acting on a bullet induced by the tension of a ballistic panel is shown in Figure 7. Analogously, the ith layer in an N-layered panel will be restrained by the force proportional to the sum of the tensions from the (i + 1)th layer to the Nth layer. The last layer (i.e. the Nth layer) that does not have successive rear layers is restrained by the drag force of the backing material, which may be clay or air. A schematic illustration showing the magnitude of such restraints in panels made of three layers of different components is given in Figure 8. The red double-sided arrow represents the restraint that will act on component F by components M and R, when component F fails. The blue double-sided arrow represents the restraint that will act on component M by component R, when component M fails. If we further expand this concept to an N-layered single component panel, each layer will be affected by the restraint of the rear layers, eventually forming a curve, as shown in Figure 9. Thus, when the elongation of yarns in each layer is better coupled (i.e. when a panel is LM-HM sequenced), the rear layer restraint acting on the ith layer will be higher than the reverse case.

Figure 7.

Relationship between the tension of facing yarns in a panel and the pressure acting on a bullet induced by the tension in a ballistic event.

Figure 8.

Schematic drawing of the magnitude of out-of-plane restraint in panels composed of three components and with the reverse stacking sequence (color online only).

Figure 9.

Rear layer restraint acting on the ith layer by the (i + 1)th last layers.

The reason we observed different hybridization effects among panels with different layering sequences is presumed to be due to this difference in restraining force of successive rear component layers. The restraining force of the rear layers will contribute to shortening the contact time of the preceding layer with a bullet. In other words, an impulsive force larger than the breaking force of the facing yarns can be reached in a shorter time if the rear layer restraining force is large, and as a result, the longitudinal wave front in the facing yarns will not travel so far. We may say this is a similar phenomenon to so called ‘shearing’ or ‘shear plugging’. The kinetic dissipation by the hybrid panel with an LM-IM-HM layering sequence will also be diminished likewise, leading to decreased perforation resistance.

To compare the results of our study (i.e. panels prepared to have areal densities for the field-applied levels of protection) with that of Cunniff⁵ (i.e. double layered hybrid panels), a probable explanation for Cunniff’s experimental results is given in ‘Appendix I’.

Effect of layering sequence on the trauma resistance of hybrid panels against a frangible bullet

In a previous study using a 9 mm FMJ bullet,⁷ we concluded that hybridization of neat woven fabric and STF-impregnated woven fabric has an ordering effect on the BFS, and this was presumed to be related to the coupling of yarn elongation in frontal and rear layers, which may further affect bullet expansion. Based on the results of this study, we have placed the neat woven fabric in front of the STF-treated woven fabric in all hybrid panels for better trauma resistance.

The experimental results with .44 Magnum shots are given in Table 4, which shows the results of four hybrid panels and two single component panels. Figure 10 shows the BFS value of each panel. The result shows a substantial difference in trauma-resistant performance between the two single component panels (i.e. all neat woven fabric panel (SW-M) and all UD panel (SU-M)). When compared with single component woven fabric panels, all the hybrid panels showed lower BFS values. In general, if a panel is composed of UD and neat woven layers, it will have a BFS value somewhere between those of each single component panel. Thus, this increase in trauma-resistant performance of the hybrid panels is partly due to the third component of STF-impregnated woven fabric layers. The H-3M panel, which had a relatively higher STF content, showed the smallest perforation ratio and BFS value, while all the other hybrid panels showed similar values of perforation ratio. With an exception of the H-4M panel, where the perforation ratio exceeded the weight fraction of the first-component UD layers, the bullet was stopped by the first-component layers in all the other hybrid panels. If we compare the three panels having different compositions but the same layering sequence, that is, H-1M, H-3M and H-4M, it seems probable that an optimal range exists for the content of the strikeface UD component and/or for the amount of STF to effectively decrease the backface deformation caused by the impact. Although the perforation resistance (V₅₀), against this frangible bullet, of these hybrid panels was not tested, it seems possible to enhance the perforation resistance at certain composition ranges of UD and STF fabric. Further investigation is necessary to confirm this explanation.

Figure 10.

Backface signature (BFS) test results of hybrid panels and single component panels (.44 Magnum semi-jacketed hollow point (SJHP)).

Table 4.

Backface signature (BFS) test result of a series of panels (.44 Magnum semi-jacketed hollow point (SJHP))

Panel	Shot location	Velocity (m/s)	BFS (mm)	Perforation ratio (%)^a
H-1M	CTE	442.2	40	25.8
	LBE	435.8	40	29.8
	RBE	443.7	38	15.9
	avg.	440.6 ± 4.2	39.3 ± 1.2	23.8 ± 7.1
H-2M	CTE	440.3	37	26.9
	LBE	439.2	35	21.5
	RBE	440.0	35	21.5
	avg.	440.5 ± 1.4	35.7 ± 1.2	23.3 ± 3.1
H-3M	CTE	438.8	33	19.8
	LBE	435.5	32	11.9
	RBE	439.2	33	21.8
	avg.	437.8 ± 2.0	32.7 ± 0.6	17.8 ± 5.2
H-4M	CTE	439.2	39	21.9
	LBE	435.0	44	21.9
	RBE	440.9	43	27.3
	avg.	438.4 ± 3.0	42.0 ± 2.6	23.7 ± 3.1
SW-M	CTE	439.74	50	29.7
	LBE	431.33	45	27.0
	RBE	435.79	47	29.7
	Avg.	435.6 ± 4.2	47.3 ± 2.5	28.8 ± 1.6
SU-M	CTE	431.9	41	23.5
	LBE	436.1	42	19.6
	RBE	441.5	42	25.4
	Avg.	436.5 ± 4.8	41.7 ± 0.6	22.8 ± 3.0

$Perforation Ratio (%) = \frac{Weight Fraction of Perforated Plies}{Weight of Total Laminated Plies} \times 100 .$

Meanwhile, the effect of layering sequence in hybrid panels could be clearly observed by comparing H-1M and H-2M. Although the two panels had the same composition, the panel that had the woven fabric component layers backed by UD component layers (H-2M) showed better trauma resistance than the panel that had the UD component layers backed by the woven fabric component layers (H-1M). The two panels were not layered in the exact opposite sequence (i.e. ACD- and CDA sequence, as shown in Table 2). However, we can analogously infer the performance of an ADC-sequenced panel (i.e. exact opposite sequence of H-2M), which we will name ‘H-XM’ for convenience. As previously mentioned, placing the neat woven fabric (component C) in front of the STF-treated woven fabric (component D) is more effective in reducing backface deformation by frangible bullet shots. Thus, it is possible to predict that an ADC-sequenced panel (H-XM) would have inferior trauma resistance compared with the ACD-sequenced panel (H-1M). Moreover, from the previous section we have seen that the H-3FR panel (ACD sequence) showed lower perforation resistance than the H-3F panel (ADC sequence), which can be interpreted as rear layer restraining forces are smaller for ADC-sequenced panels (i.e. less coupling takes place). Thus, if an H-XM panel (ADC sequence) is constructed, its BFS value will be higher than that of the H-1M (ACD-sequenced) panel, and an apparent ordering effect will be observed between the H-XM (ADC-sequenced) panel and the H-2M (CDA-sequenced) panel, that is, BFS; ADC(H-XM) > ACD(H-1M) > CDA(H-2M).

The following content is from our previous report,⁷ which is included here to aid in the understanding of the results from this study. When a bullet hits a multi-layered panel, the initiation of elongation of facing yarns in each layer is time dependent, that is, the initiation of elongation of facing yarns in the rear layers is presumed to be retarded by the time necessary for the compressive wave to reach the corresponding rear layers. Thus, the elongation of facing yarns in successive layers will occur sequentially rather than simultaneously. A schematic illustration of the elongation of a yarn bundle (solid line) composed of two yarns (dotted lines) is shown in Figure 11. As shown in the figure, cases (a) and (c) exhibit higher strength than case (b). However, case (a) cannot occur when the two yarns are located in different layers. In a one-component, multi-layered panel, the elongation of two yarns located in different layers can be represented as case (b), while the elongation of two yarns in hybrid, multi-layered panel (where the layers are sequenced to have increasing modulus) can be represented as case (c). This phenomenon was expressed as ‘better coupling of yarn elongation in frontal and rear layers’ or ‘synchronized elongation’ in our previous paper.⁷ Thus, the stronger yarn bundle (case (c)) will survive longer (i.e. at higher stress) than the weaker yarn bundle (case (b)) and will bear higher stress. From the tension–pressure relationship shown in Figure 7, one can expect the bullet to expand more at higher tension. As the bullet expands, the number of facing yarns increase accordingly; thus, a larger fraction of the impact energy can be dissipated through the tensile dissipation route resulting in decreased BFS.

Figure 11.

Schematic illustration of elongation of a yarn bundle (solid line) composed of two yarns (each dotted line): (a) simultaneous elongation of two yarns with the same modulus; (b) sequential elongation of two yarns with the same modulus; and (c) sequential elongation of two yarns with different modulus (i.e. with increasing modulus).

Conclusion

The effect of the layering sequence of UD/woven fabric hybrid panels on (1) the penetration resistance (V₅₀) against a 5.56 mm FSP and (2) the trauma resistance (BFS) against a .44 Magnum SJHP projectile was examined in this study. Sequencing the component layers of hybrid panels in the order of decreasing stiffness enhanced the penetration resistance of the panels against infrangible bullets, which is presumed to be due to less restraint by subsequent rear-component layers. On the other hand, sequencing the component layers of hybrid panels in the order of increasing stiffness enhanced the trauma resistance of the panels against frangible bullets, which is presumed to be due to a better coupling between the facing yarns in the frontal and rear layers (i.e. leading to increased bullet expansion). Such direction-dependent ballistic performances of multi-material panels should be considered when designing more efficient and comfortable soft body armors and, obviously, the users should be cautioned to wear the armors the right way.

Footnotes

Funding

This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (R11-2005-065).

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