Multi-layer pattern creation for seamless front female body armor panel using angle-interlock woven fabrics

Abstract

Angle-interlock woven fabric offers an option for making female body armor as it can form integrally the required dome shapes because of its extraordinary moldability and satisfactory ballistic performance. A mathematical model is created to determine the pattern geometry for the front panel of female body armor, and the front panel can be quickly created using this mathematical model. However, the body armor is multi-layer, which indicates that the relationship between the thickness of the fabric and the pattern block projection for different layers of fabric needs to be investigated, in order to create the whole panel, to improve this novel approach for making seamless female body armor with satisfactory ballistic performance.

Keywords

female body armor moldability pattern block projection angle-interlock woven fabrics multi-layer pattern

It is true that women have become an important force in guarding national safety, which cannot be ignored. Women have been breaking barriers in civil guards and military organizations, and will continue to do so.^1,2 In these dangerous tasks, body armor plays an essential role in protecting wearers. However, male wearers alone are considered in most cases when improving body armor technology.^3–8 The apparent assumption is that most female officers and soldiers still wear unisex body armor, but in smaller sizes. Such an approach puts little emphasis on the difference in torso shape between men and women, and similar style and specifications are employed during manufacture. This is obviously unsuitable, due to the physiological differences between women and men; incorporating the female torso into a male-based system, may result in disproportionate protective and functional sacrifices. It has obvious drawbacks, but still has a large market because of easy operation and long-standing acceptance. A very common method for creating female body armor is cutting and stitching. However, such a method has its negative aspect: the seam that is created by stitching the materials to shape the bust area always becomes the weakest point against impact, due to the discontinuity of the yarns in that area sharply reducing the armor’s ballistic-resistant capability. The laboratory is often instructed to locate such places to test the minimum level of ballistic protection.

Fabric folding is also considered in making female body armor. The two-dimensional reinforcement could shape a three-dimensional form by folding, namely, bending one part to lie on another according to a certain axis.⁹ The downside is that folding also creates discontinuities in the structure, which decreases the torso protection capability. Further, the weakness of stitches against projectile impact still exists, as many stitches are required during the folding procedure. Additionally, wearers may feel uncomfortable under their armpits where sharp ridges may be formed by folding many layers.

The fourth method is overlapping. This female body armor comprises a contoured front protective panel composed of a plurality of superposed layers of ballistic protective piles of fabric made of aramid polymer yarns. The front protective armor panel is contoured by providing overlapping seams joining different sections of the panel.^10,11 This overlapping method also has a potential quality risk; close seams having conventional numbers of overlapping layers could permit small projectiles, that impact directly at the seam edges, to penetrate through the body armor by getting under the edges of the overlapping seam and following a path more or less parallel to the overlapped and seamed portions of fabric.

The final, most common, method used nowadays is molding; a kind of deep drawing process, where the specimen is mounted against a support medium, which mimics the compliance of a human torso. The process requires no additional finishing operations or the use of chemicals to fix the deep drawn shape. Subsequently, the molded fabric layers are placed on top of each other to obtain a garment part, and are joined by a seam located in the middle of the panel (for instance). The positive point of this system is that high wear comfort of the non-stitched bullet-resistant body armor is fully preserved. On the other hand, the molding method also has apparent drawbacks, such as unbalanced density in different areas, shear deformation, extension in the yarns, crimp loss, sliding of fibers, and local wrinkles.¹² Additionally, the method also has limitations in the size-choice for the bust area of female body armor.

The aforementioned five technologies are widely applied nowadays, but their own individual shortcomings prevent them from developing further. Scientists are continuing to investigate, and are trying to make three-dimensional female body armor directly.

Boussu and Bruniaux developed a three-dimensional design process for female body armor using the darts rotation technique, which can indeed improve the traditional two-dimensional design process by providing a comparatively precise fit to satisfy female morphology.¹³ The key technique here is to form the three-dimensional shape by providing many darts and stitches to two-dimensional flat fabric, such as plain weave-structure fabric, but it is not suitable for three-dimensional weave-structure fabric, such as angle-interlock woven fabric, which is already capable of shaping deep dome designs without darts or other assistance, due to its unique property of high moldability. The main task of the computer-aid software is to help to get precision with darts’ design, location, and quantity. The next step is similar to the common method used nowadays: overlapping or folding. Many darts and stitches are required to form the shape, and the process still cannot overcome the same issue that the traditional method meets: a projectile may hit the stitches or seams, which are the weakest points.

Mahbub et al. claimed to use a seamless knitting technology with CAD software to design a three-dimensional seamless female body armor vest.¹⁴ Two designs—a bra-vest design and loose-vest design—have been demonstrated. However, a key issue before the further design consideration is that the knitted fabrics used have not been tested to determine their bulletproof function based on the NIJ 0101.06 standard or other international standards. Bulletproof function is the basic and essential consideration in making body armor. Even using Kevlar yarn, invalid results for bulletproof function are possible if the weave structure, or the manufacture of the fabric, or the post processing are applied incorrectly. Another negative aspect is that it is a really time-consuming and high-cost procedure, as it is mentioned in the paper¹⁴ that the machines run at a very low speed, only around 0.3 m/s, otherwise the needle is very easily damaged. There is still a long way to go if this seamless knitting technology is to be used to make female body armor vests in industrial mass production.

In this paper, angle-interlock woven fabric is used for female body armor. This has been demonstrated to have good moldability which can fit the curvaceous female torso, and at the same time has been shown¹⁵ by ballistic impact testing to provide no less ballistic performance than other commercially used fabrics, according to the NIJ standard. Based on this extraordinary moldability and satisfactory ballistic performance, a mathematical model is presented to determine the pattern geometry for the front panel of female body armor. The raised bust area is divided into seven different parts for the model, using the simplest surfaces possible. This mathematical model takes the body figure size and bra size as the input, and the output is the profile of the front panel for female body armor. The front panel can be quickly created using this mathematical model.¹⁶ However, this solution creates only one layer of the front panel of female body armor which is not enough, as the body armor panel needs to be made of several layers.

Multi-layer front panel of female body armor

The relationship between the thickness of fabrics and the pattern block for different layers of fabrics needs to be investigated for the purpose of manufacturing the whole front panel of female body armor. One ballistic panel normally contains multiple pieces of fabrics, which indicates that the outer layer is larger than the inner layer, while still keeping uniformity in the design, as the contour surface induced by the female torso needs to be fully covered. The pattern block of the outer layer can be achieved by grading that of the inner layer if the interval (N_i) between them is known. N_i is equal to the increment of the bust girth. N_i exists because of the thickness of fabrics (N_t). N_t is obtained via measurement. Therefore, N_i can be calculated if the mathematical relationship between N_i and N_t is known. Figure 1 is the cross-section of the mannequin viewed from the top of the head. The dotted line indicates the bust girth (l) which is used to make the original block for the first layer of the multi-layer garment. The full line indicates the new bust girth (L) when the second layer is added. The gap (marked as the shaded area) between l and L is unchanged at any point because this gap is actually formed by the thickness of fabric, N_t. Therefore, keeping l, L, and Nt unchanged, their mathematical relationships could be considered on the assumption that they make a concentric circle, as shown in Figure 2.

Figure 1.

Cross-section of mannequin viewed from the top of the head.

Figure 2.

Concentric circle composed of l, L, and N_t.

In Figure 2, l is the perimeter of the inner circle, which can be expressed as

l = 2 π r

(1)

where r is the radius of the inner circle. r can then be expressed as

r = \frac{l}{2 π}

(2)

L is the perimeter of the outer circle, which could be expressed as

L = 2 π R

(3)

where R is the radius of the outer circle and could be achieved by

r + N_{t}

. As it is known that

r = \frac{l}{2 π}

the equation for L can be converted into

L = l + 2 π N_{t}

(4)

Equation (4) minus equation (1) gives $L - l$ , which is the increment of the bust girth between the first layer and the second layer—in other words, the interval N_i. Therefore, the mathematical relationship between N_i and N_t can be shown as

N_{i} = 2 π N_{t}

(5)

Equation (5) means that the ratio between the intervals and the thickness of fabrics is $2 π : 1$ . The thickness of angle-interlock woven fabrics used in this research is around 0.3 cm. Therefore, the corresponding intervals between the outer layer and inner layer of fabrics could be calculated around 2 cm according to equation (5). To keep continuity and accuracy of research, the block projection of a single layer in the former research (shown in Figure 3),¹⁶ is used here as the basic original block projection to make the multi-layer block projection based on the grading rule, with the assistance of PAD software system (PAD Systems International Ltd., Hong Kong, China). Table 1 illustrates (a) the coordinate movements of original block projection with 2 cm intervals after grading, and (b) the coordinate values of new block projection. The pattern blocks for more (larger) outer layers may also be achieved using this ratio for grading. Just as the number of layers increases, so the thickness of fabrics is increased by the same amount (2 cm) for each layer.

Figure 3.

Block projection: (a) making key points; (b) grading.

Table 1.

New block projection: (a) the coordinate movements with 2 cm intervals, (b) the coordinate values.

(a)
Original key points	Coordinate change		Original key points	Coordinate change
Original key points	X	Y	Original key points	X	Y
A	0.00	0.16	B	0.01	0.15
C	0.08	0.22	E	0.10	0.28
F	0.22	0.28	G	0.24	0.22
I	0.26	0.16	J	0.28	0.12
K	0.30	0.08	M	0.35	0.06
N	0.40	0.04	Q	0.50	0.00
S	0.50	−0.10	T	0.50	−0.20
V	0.22	−0.20	W	0.10	−0.20
Z	0.00	−0.20
(b)
Key points	Coordinate values
	X	Y
A_n^a	0.0	10.5
B_n	4.5	12.7
C_n	8.0	19.2
E_n	9.5	24.1
F_n	17.3	21.5
G_n	16.5	16.4
I_n	16.6	11.5
J_n	17.2	7.8
K_n	18.2	4.3
M_n	19.5	2.3
N_n	21.4	0.5
Q_n	22.3	0.0
S_n	22.3	−8.4
T_n	22.3	−16.0
V_n	13.0	−16.0
W_n	5.9	−16.0
Z_n	0.0	−16.0

key points for new block projection after 2 cm intervals.

After the new block projection has been produced, the pattern block with the bust-cup part can be designed using the same mathematical modeling developed previously.¹⁶ Figure 4 shows the front panel pattern of body size 12 with bra size 85C after shaping.

Figure 4.

The front panel pattern of body size 12 with bra size 85C after shaping.

Based on the new pattern block, the outer layer of appropriately-profiled angle-interlock ballistic fabric can be produced, subtly graded to fit the inner layer to make a two-layer front panel of female body armor. Figure 5 shows the result: (a) top view: the outer layer entirely fits the inner layer; (b) side view: two neighboring layers of fabrics are laid together very closely; (c) view for verification: the inner layer of the front panel of female body armor has already been shaped to be matched with the outer layer, which is demonstrated by peeling off a corner of the outer layer and a half of the outer layer.

Figure 5.

Two-layer front panel of female body armor: (a) top view, (b) side view, (c) view for verification.

Conclusions

The use of angle-interlock fabric for female body armor will diminish the drawbacks, such as wrinkles and fabric discontinuity, which negatively influence ballistic protection. Based on the ballistic evaluation and the mathematical model of angle-interlock fabrics reported in the previous research,^15,16 this paper determined the mathematical relationship between the thickness of the fabric and the pattern block projection of different layers of female body armor. The new pattern block projection of the different outer layers can be calculated and graded from the pattern block projection of the inner layer of fabrics. Then, with the assistance of the same mathematical modeling developed previously, the front panel for each outer layer can be created to make a multi-layer front panel of female body armor.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

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