0
Research Papers

# Magnetorheological Damping of Fragment Barrier Suspension SystemsOPEN ACCESS

[+] Author and Article Information
Kwon Joong Son

Mem. ASME
Department of Mechanical and
Design Engineering,
Hongik University,
Sejong 30016, South Korea
e-mail: kjson@hongik.ac.kr

Eric P. Fahrenthold

Professor
Mem. ASME
Department of Mechanical Engineering,
University of Texas at Austin,
Austin, TX 78712
e-mail: epfahren@mail.utexas.edu

1Corresponding author.

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT,AND CONTROL. Manuscript received August 23, 2017; final manuscript received February 12, 2018; published online March 30, 2018. Editor: Joseph Beaman.

J. Dyn. Sys., Meas., Control 140(9), 091002 (Mar 30, 2018) (8 pages) Paper No: DS-17-1421; doi: 10.1115/1.4039414 History: Received August 23, 2017; Revised February 12, 2018

## Abstract

Magnetorheological (MR) fluids, well established as components of a variety of suspension systems, may offer opportunities to improve the performance of fabric ballistic protection systems, which typically do not incorporate significant energy dissipation mechanisms. A series of ballistic impact experiments has been conducted to investigate the potential of MR fluid damped fabric suspension systems to improve upon current fabric barrier designs. The results indicate that for the simple fabric suspension systems tested, MR fluid damping does not improve upon the very high weight specific ballistic performance of state of the art aramid fibers.

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## Introduction

Woven fabrics manufactured from high strength aramid [1] or ultrahigh molecular weight polyethylene [2] fibers are widely used as fragment barrier materials to protect personnel, vehicles, and infrastructure from blast and impact loads. Example applications include body armor [3], fan blade containment systems [4], and orbital debris shielding [5]. In comparison to alternative fragment barrier materials, fabrics offer a combination of flexibility and high strength per unit mass which makes their use particularly attractive in personal protection as well as vehicle protection applications. The effectiveness of high performance fabrics in such applications has motivated research aimed at the development of new materials [6] or composites [7] with similar flexibility or improved ballistic performance. However, the development of fundamentally new materials is a major challenge, hence parallel research efforts are investigating the more effective use of available materials in new fragment barrier designs. Examples include the use of fabric coatings [8], variations in stitching [9], variations in fabric panel width [10], and functional grading of fabric stacks [11].

The effects of target mounting on the ballistic performance of woven fabrics are widely recognized [1214]; this sensitivity offers an opportunity to improve upon the ballistic performance of conventional fabric barriers. Recognizing the benefits of magnetorheological (MR) fluid based dampers developed for a variety of vehicle suspension [15] and occupant safety [16] applications, this paper describes the first experimental investigation of the use of MR fluid based dampers in fragment barrier suspensions. The experiments involved the assembly and testing of an MR fluid fabric damper, similar to the sponge [17] and foam [18] dampers described in the previous work, but employed in a new configuration and application. The MR fluid suspension concept tested here loads the saturated fabric in shear mode, makes judicious use of the MR fluid, and requires that only a small air gap be energized; hence, the concept investigated here differs markedly from some other proposals for the use of MR fluids in ballistics applications [19,20]. Like the latter proposals, the present work attempts to add a new energy dissipation mechanism to fragment barriers composed of high strength fibers which exhibit an elastic-brittle constitutive response under typical design loads. Unlike established applications [15] of MR fluid dampers, the experiments described here do not incorporate any tuning or damping control mechanisms. Hence, these experiments provide only a baseline measure of the energy dissipation properties of the tested fabric shear dampers, when used in a ballistics application.

A schematic description of the fragment barrier suspension concept investigated in this paper is provided in Figs. 13. Note that all practical fabric protection systems are composed of multilayer fabric stacks; an example is body armor, which may incorporate dozens of fabric layers. Figure 1 depicts one layer of a conventional fabric fragment barrier, like that which might be used in a vehicle spall liner [21], with the fabric attached by straps, clamps, or other means to a stiff elastic suspension. In Fig. 2, the stiff suspension for this layer has been replaced by an MR fluid damper. In a multilayer fabric barrier, this layer would be intended to both: (1) dissipate energy (rheologically) at the barrier boundary and (2) resist penetration (mechanically) at the projectile impact point (note that in some fabric barrier applications, such as body armor, the presence of very compliant elastic supports means that the fabric layers function essentially without any peripheral boundary support). Figure 3 depicts the specific MR fluid fabric damper configuration tested in this research. The MR fluid saturated portion of the fabric layer is positioned in an energized air gap (channel); impact of the projectile on the fabric layer pulls the fabric through the air gap, dissipating impact energy at the barrier boundary. The constraining effect of an additional elastically supported layer, if added behind the damper supported layer, means that the fabric in the damper supported layer will also mechanically resist projectile penetration.

The experiments described in this paper, which appear to be the first to study the use of MR fluid suspension dampers in a ballistics application, measured ballistic performance in a simple case: a two-layer barrier, with one layer (the strike face layer) supported by an MR fluid damper and the second layer supported by mechanical clamps. The advantage of testing a two-layer target is that the MR damper supported target layer resists penetration both rheologically (in the shear damper) and mechanically (at the projectile impact location, when supported by the second target layer). Employing fabric in this dual role is, in the authors' judgment, more representative of practical ballistics applications than testing involving only a single shear damper supported target layer. The experiments were performed at a magnetic field intensity sufficient to take the tested MR fluid to its maximum yield strength. The experimental results were compared to published test data [22] on one- and two-layer elastically supported (edge clamped) neat fabric targets, in order to evaluate the potential of MR fluid fabric dampers to improve upon the performance of conventional fragment barrier designs.

The remaining sections of this paper are organized as follows: Section 2 describes the materials used in the experiments, while Sec. 3 details the two barrier configurations tested in the experiments. Sections 4 and 5 describe the ballistic testing and the experimental results, and the concluding section offers the authors' interpretation of the test results. Appendix A describes pull tests conducted to confirm that the yield stress in MR fluid shear damper meets or exceeds the yield stress quoted in the MR fluid manufacturer's specifications. Appendix B describes a magnetic circuit model developed to confirm that the magnetic field intensity in the MR fluid shear damper meets or exceeds that required to take the MR fluid to its maximum yield stress.

## Materials

A variety of fiber and fabric types [23] have been employed in ballistic protection applications. The experiments described here employed an aramid fiber (Kevlar KM-2) in a plain weave configuration, representative of fabric protection systems deployed in contemporary body armor and orbital debris shielding applications. Table 1 provides the tested fiber [24] and fabric (fabric style 706 manufactured by Hexcel Corporation) specifications. The MR fluid used in the experiments is type MRF-140 CG, manufactured by Lord corporation. Its properties are listed in Table 2. The projectile used in the impact experiments was a 0.22 caliber (0.56 cm) fragment simulating projectile (FSP). The projectiles were fabricated from 4340 steel; weight was 1.14 g.

## Barrier Configurations

The ballistic impact experiments tested two different barrier configurations, hence, this section and those which follow refer to test types 1 and 2. Each type consisted of a single edge damped Kevlar layer (strike face) backed by a single edge clamped neat Kevlar layer. The MRF treatment applied to the strike face Kevlar strip varied with the test type. In test type 1, the MR fluid was mixed with a vacuum grease (1% mixture, by total volume, of type Apiezon H grease manufactured by M&I Materials Ltd. (Manchester, UK)). The mixture was then brush applied to a 5.08 cm × 5.08 cm region of the Kevlar strips (the region to be positioned in the air gap at the start of a ballistics experiment). Despite the addition of grease to the MR fluid, saturating the air gap with MR fluid in test type 1 proved difficult, motivating additional tests in a second configuration. In test type 2, the MRF-treated region of the Kevlar strip was reduced to 1.27 cm × 5.08 cm, and polyvinyl chloride tubing was used to confine the fluid. Figure 4 shows an example 22.86 cm × 5.08 cm Kevlar strip, edge treated with MR fluid for mounting in the target frame (note the untrimmed polyvinyl chloride tubing present on both ends of the target strip). Testing in the type 2 configuration was also motivated by an interest in testing ballistic performance for a configuration in which the MRF treated region of the Kevlar strip was fully detached from the shear damper over the course of the ballistic impact event.

The mounting fixture for the damped Kevlar layer was the same for both test types and is depicted in the schematic of Fig. 5. The damped target layer was mounted on a mild steel plate with dimensions 30.48 cm × 30.48 cm × 0.635 cm, containing a rectangular aperture with dimensions 10.16 cm × 6.35 cm. Brass shims attached (by brass bolts) to the steel plate supported an electromagnet (model ESA-241 from Industrial Magnetics, Inc.), providing an energized air gap in which an edge-saturated MRF fabric strip was allowed to slide. The suspension system for this fabric layer is, therefore, referred to as an MRF shear damper. Figure 6 shows an oblique view of a Kevlar strip mounted in the shear damper. Note that the orientation, in the laboratory reference frame, of the (strike face) Kevlar strip shown in Figs. 5 and 6 is horizontal.

The geometry, mounting, and standoff of the second (neat) Kevlar layer also varied with the test type. In test type 1, the second target layer was a Kevlar strip with dimensions the same as those used in the strike face layer. This second target layer was (1) mounted directly behind the strike face layer, (2) oriented vertically, and (3) clamped to the steel support frame with clinch buckles (the upper clinch buckle is labeled in Fig. 6). Figure 7 shows a postimpact, front side view of a target in a test type 1 impact experiment (C-clamps, not shown, were used to hold the magnets in place during the impact event). Figure 8 shows a back side view of a target in a test type 1 impact experiment, depicting perforation of the second target layer at an impact velocity of 426 m/s. In test type 2, the second target layer was a circular Kevlar panel, with diameter of 10.16 cm, clamped in place at a distance of 12.38 cm behind the strike face layer. Figure 9 shows a back side view of a target in a test type 2 impact experiment, depicting perforation of the second target layer at an impact velocity of 411 m/s.

A wide variety of barrier configurations are of course of interest in evaluating the potential of MRF shear damping to improve the performance of ballistic protection systems. The two configurations just described were selected for testing, since

• experimental data on the ballistic performance of one- and two-layer neat Kevlar targets in the test type 1 configuration are available, for direct comparison with the results of the experiments described in this paper, and

• by allowing for full detachment of the damped layer from the fixed mounting, the test type 2 configuration investigates a limiting case of interest in the study of boundary condition (suspension system) effects on the ballistic performance of fragment barriers.

## Impact Experiments

The impact tests were conducted at the Small Arms Range of Southwest Research Institute. Impact velocities were measured using chronographs, and projectile residual velocities (after target perforation) were measured using high speed video cameras. The experimental results are presented in Figs. 1013, as plots of residual velocity versus impact velocity and normalized energy absorption versus impact velocity, for both the type 1 and type 2 targets. The normalized energy absorption is defined as Display Formula

(1)$ΔE¯=Ei−ErEi, Ei=12 m Vi2 Er=12 m Vr2$

where Vi and Vr are the impact and residual velocities, respectively, and m is the projectile mass. The solid lines in the plots also show fits of the data to the correlations Display Formula

(2)$ΔE¯=(V50Vi)2, Vr=Vi2−V502$

where V50 is the fitted parameter. Although V50 represents an (extrapolated) estimate of the ballistic limit velocity for the tested targets, it is more properly a measure of the average energy absorption (Eabs) of the target over the impact velocity range considered in the experiments Display Formula

(3)$Eabs=12 m V502$

In this paper, V50 is a figure of merit used to compare the ballistic performance of the target types tested in this research to the ballistic performance of baseline one- and two-layer neat Kevlar targets mounted in the clinch buckles of the test article shown in Fig. 6. The baseline test data are provided in Ref. [22].

Although Figs. 1013 plot all of the test data collected in the fifteen type 1 and nineteen type 2 experiments performed in this study, only those experiments in which the projectile impacted region A of the strike face Kevlar strip, as defined in Fig. 14, were used in computing V50. The previous experimental and computational research [25] has demonstrated that projectiles impacting close to the target edges (as defined by region B in Fig. 14) underestimate the target's capacity to absorb impact energy and should not be considered in computing ballistic performance metrics.

## Impact Testing Results

The ballistic data collected in the impact experiments and the baseline comparative data obtained from the published literature were used to compute a ballistic figure of merit V50 for four target configurations: (1) test type 1, MRF-damper suspension without standoff, as described in this paper, (2) test type 2, MRF-damper suspension with standoff (and a 75% reduction in shear damping area), as described in this paper, (3) a single layer of neat Kevlar, mounted on clinch buckles in the target fixture shown in Fig. 6, and (4) a double layer of neat Kevlar, mounted on clinch buckles in the target fixture shown in Fig. 6. Table 3 lists the V50 values fit to each data set. Both the type 1 and the type 2 MRF-damper supported targets show a ballistic performance better than that of one layer of edge clamped neat Kevlar but inferior to that of two layers of edge clamped neat Kevlar.

The bar chart in Fig. 15 compares the energy absorption capability of the four target configurations, normalized to the energy absorption capability of one layer of edge clamped neat Kevlar. Adding a second layer of edge clamped neat Kevlar increases the target's ability to absorb impact energy by 84%. By comparison, adding a single layer of MRF edge damped Kevlar increases the target's ability to absorb impact energy by only 67%. In a damped configuration which adds standoff, but reduces the shear damping area by 75%, the MRF edge damped target absorbs only 23% more impact energy than one layer of edge clamped neat Kevlar. The ballistic performance of the MRF edge damped Kevlar targets was poor; in the simple damping configurations tested, MR fluid based damped suspension systems do not improve upon the excellent mechanical performance of high strength fabrics.

## Conclusions

Over the past half century, scientific research has produced two material classes (aramids and ultrahigh molecular weight polyethylene) now in widespread use as high performance ballistic fabrics. Although the weight specific performance of these materials is remarkable, the relatively slow pace of new materials development efforts has motivated research on the augmentation of existing fabrics, or their innovative use in new ballistic protection system designs. Magnetorheological fluids, well established as components of smart damping systems, may offer opportunities to improve the performance of fabric ballistic protection systems, which normally do not incorporate significant energy dissipation (irreversible entropy production) mechanisms. The experiments described in this paper appear to be the first to investigate the potential of MR damped suspensions to improve upon current fabric barrier designs. In the simple damping configurations tested in this paper, MR fluid based shear dampers do not improve upon the very high weight specific ballistic performance of state of the art aramid fibers.

## Acknowledgements

This work was supported by the Office of Naval Research. The ballistic impact experiments were conducted at Southwest Research Institute.

## Nomenclature

• Ac =

center pole area

• Ae =

edge pole area

• $Aceff$ =

effective flux area for the center pole

• $Aeeff$ =

effective flux area for the edge pole

• Bc =

magnetic flux density for the center pole

• Be =

magnetic flux density for the edge pole

• d =

length of the edge pole

• Eabs =

average energy absorption

• Ei =

impact kinetic energy

• Er =

residual kinetic energy

• E0, E1 =

fitted coefficients in the magnetic circuit model

• Hc =

magnetic field intensity for the center pole

• He =

magnetic field intensity for the edge pole

• lg =

length of the air gap

• m =

projectile mass

• Rc =

center pole reluctance

• Re =

edge pole reluctance

• Ri =

magnetic core reluctance

• Rp =

plate reluctance

• Vi =

impact velocity

• Vm =

magnetomotive force

• Vr =

residual velocity

• V50 =

ballistic limit velocity

• $ΔE¯$ =

normalized energy absorption

• μ0 =

free space permeability

• $Φ$ =

magnetic flux

## Appendices

###### Appendix A: Pull Tests

Static pull tests were conducted on MRF Kevlar strips mounted in an MRF shear damper like that used in the test type 1 experiments. These experiments were conducted to confirm that the magnetic clamping method shown in Fig. 6 can produce a shear yield stress at least as high as that associated with the tested MR fluid at saturation magnetization (60 kPa, as indicated in Table 2). Figure 16 shows (a) the test setup and (b) an oblique view which depicts the brass shims that provide an air gap of length 0.4064 mm between the electromagnet and the mild steel mounting plate. A series of ten dead weight pull tests were performed to measure the shear force required to overcome the magnetic clamping force on the fabric specimen. The average critical force was used to estimate the shear yield stress in the MR fluid fabric damper. Figure 17 shows a plot of the experimentally measured shear yield strength for the damper. The error bar associated with each data point is determined by the incremental added weight which precipitated shear failure. The horizontal solid line in the graph represents the measured average yield strength of 99.1 kPa, which is greater than the manufacturer's specified yield strength (60 kPa) for the MR fluid. The measured shear strength apparently exceeded the MR fluid yield stress due to mechanical friction in the test fixture. Based on the pull test results, it appears that the edge damper suspension used in the ballistic impact experiments applies a shear load per unit area which meets or exceeds the yield stress for the tested MR fluid.

###### Appendix B: Magnetic Circuit Model Incorporating Fringing Effect

A magnetic circuit model was required to estimate the magnetic field strength in the air gap between the electromagnet and the mild steel mounting plate, since the gap length was too small (lg = 0.4064 mm) to access using the available Gaussmeter probe. The magnetic field strength calculated from the circuit model was used to estimate the field applied to the MR fluid occupying the air gap.

Figure 18 shows (a) the configuration of the commercial electromagnet (model ESA-241 from Industrial Magnetics, Inc.) used in the experiments, (b) a sketch of the magnetic circuit, and (c) a schematic of the magnetic circuit model. As illustrated in Fig. 18(a), the electromagnet has a rectangular pole at the center and much narrower rectangular poles along the four edges of its bottom face. Applying Kirchhoff's voltage law to the loop in the circuit model (Fig. 18(c)), the magnetomotive force may be expressed as the algebraic sum of the voltage drops due to magnetic reluctance in the circuit Display Formula

(B1)$Vm=Φ(Ri+Rp+Rc+Re)$

where Vm is a magnetomotive force, $Φ$ is a magnetic flux, Ri is the intrinsic reluctance of the magnet core, Rp is the reluctance associated with the mild steel plate, $Rc=lg(μ0Aceff)−1$ is the air gap reluctance of the center pole (which has effective flux area $Aceff$ and air gap lg), and $Re=lg(μ0Aeeff)−1$ is the total air gap reluctance of the four edge poles (which have effective flux area $Aeeff$). The permeability of free space is μ0. Applying continuity, the magnetic flux through the magnetic circuit shown in Fig. 18(c) can be written as Display Formula

(B2)$Φ=BcAceff=BeAeeff$

where Bc and Be are the magnetic flux densities through the air gaps over the central island pole and over the four edge poles, respectively.

Using Eqs. (B1) and (B2), the magnetic flux density can be expressed as a function of lgDisplay Formula

(B3)$Bc(lg)=[Aceff(Ri+Rp)Vm+(1+AceffAeeff)lgμ0Vm]−1=1E0+E1lg$

where E0 and E1 are coefficients to be obtained by fitting experimental data.

Magnetic field measurements (at air gaps larger than those used in the ballistic testing) indicated that fringing effects around the edge poles were not negligible, while fringing effects for the center pole were insignificant (see Fig. 19). Hence in this analysis, the effective flux area $Aceff$ was assumed to equal the center pole surface area Ac, while the effective flux area $Aeeff$ was expected to be greater than the total edge pole surface area Ae. Figure 19 shows a schematic of one of the four edge posts and the magnetic fringing effect at an edge pole. Regardless of the existence of magnetic fringing, in Fig. 20, $Φ1$ must equal to $Φ2$. Hence, applying the fringing model of Ref. [26], it is assumed that Display Formula

(B4)$Aeeff=Ae+4dπ[1+ln(πh4lg)]lg$

where d is the length of the longer side of the (rectangular) edge pole. Substituting, Eqs. (B3) and (B4) into Eq. (B2) yields an expression for the magnetic flux at the edge poles as Display Formula

(B5)$Be(lg)=AcAeeffBc=Ac[Ae+4dπ[1+ln(πh4lg)]lg](E0+E1lg)$

Figure 21 plots the magnetic field intensity as a function of the length of the air-gap lg. In this plot, magnetic field intensity (H) is shown in lieu of magnetic flux density B, since H is normally used to describe MR fluid properties. The parameters E0 and E1 were determined by regression of the models against measured data at air gaps larger than those used in the ballistic testing. The field measurements indicated that the model accurately represents the variation of the field strength with changes in the air gap. Estimated field intensities for the small air gap used in the experiments (0.4064 mm) were computed from the model; they are Hc = 809 kA/m and He = 596 kA/m, both of which are sufficient to induce saturated magnetization for the MR fluid used in the impact testing.

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David, N. V. , Gau, X.-L. , and Zheng, J. Q. , 2009, “ Ballistic Resistant Body Armor: Contemporary and Prospective Materials and Related Protection Mechanisms,” ASME Appl. Mech. Rev., 62(5), p. 050802.
Naika, D. , Sankarana, S. , Mobashera, B. , Rajana, S. D. , and Pereira, J. M. , 2009, “ Development of Reliable Modeling Methodologies for Fan Blade Out Containment Analysis—Part I: Experimental Studies,” Int. J. Impact Eng., 36(1), pp. 1–11.
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## References

Yang, H. H. , 1993, Kevlar Aramid Fiber, Wiley, New York.
Peacock, A. J. , 2000, Handbook of Polyethylene: Structures, Properties, and Applications, Marcel Dekker, New York.
David, N. V. , Gau, X.-L. , and Zheng, J. Q. , 2009, “ Ballistic Resistant Body Armor: Contemporary and Prospective Materials and Related Protection Mechanisms,” ASME Appl. Mech. Rev., 62(5), p. 050802.
Naika, D. , Sankarana, S. , Mobashera, B. , Rajana, S. D. , and Pereira, J. M. , 2009, “ Development of Reliable Modeling Methodologies for Fan Blade Out Containment Analysis—Part I: Experimental Studies,” Int. J. Impact Eng., 36(1), pp. 1–11.
Christiansen, E. L. , Crews, J. L. , Williamsen, J. E. , Robinson, J. H. , and Nolen, A. M. , 1995, “ Enhanced Meteoroid and Orbital Debris Shielding,” Int. J. Impact Eng., 17(1–3), pp. 217–228.
Zhang, M. , Fang, S. , Zakhidov, A. A. , Lee, S. B. , Aliev, A. E. , Williams, C. D. , Atkinson, K. R. , and Baughman, R. H. , 2005, “ Strong, Transparent, Multifunctional, Carbon Nanotube Sheets,” Science, 309(5738), pp. 1215–1219. [PubMed]
Martinez-Morlanes, M. J. , Castell, P. , Martinez-Nogues, V. , Martinez, M. T. , Alonso, P. J. , and Puertolas, J. A. , 2011, “ Effects of Gamma-Irradiation on UHMWPE/MWNT Nanocomposites,” Compos. Sci. Technol., 71(3), pp. 282–288.
Ahmad, M. R. , Ahmad, W. Y. W. , Salleh, J. , and Samsuri, A. , 2007, “ Performance of Natural Rubber Coated Fabrics Under Ballistic Impact,” Malays. Polym. J., 2(1), pp. 39–51.
Ahmad, M. R. , Ahmad, W. Y. W. , Salleh, J. , and Samsuri, A. , 2008, “ Effect of Fabric Stitching on Ballistic Impact Performance of Natural Rubber Coated Fabric Systems,” Mater. Des., 29(7), pp. 1353–1358.
Cork, C. R. , and Foster, P. W. , 2007, “ The Ballistic Performance of Narrow Fabrics,” Int. J. Impact Eng., 34(3), pp. 495–508.
Burt, R. R. , and Christiansen, E. L. , 2003, “ An Enhanced Shutter to Protect Spacecraft Windows From Meteoroids and Orbital Debris,” Int. J. Impact Eng., 29(1–10), pp. 139–152.
Zeng, X. S. , Shim, V. P. W. , and Tan, V. B. C. , 2005, “ Influence of Boundary Conditions on the Ballistic Performance of High-Strength Fabric Targets,” Int. J. Impact Eng., 32(1–4), pp. 631–642.
Singletary, J. , Steinruck, T. , and Fitzgerald, P. , 2007, “ Effects of Boundary Conditions on V50 and Zone of Mixed Results of Fabric Armor Targets,” 23rd International Symposium on Ballistics, Tarragona, Spain, Apr. 16–20, pp. 865–871.
Zhang, G. , Batra, R. , and Zheng, J. , 2008, “ Effect of Frame Size, Frame Type, and Clamping Pressure on the Ballistic Performance of Soft Body Armor,” Composites, Part B, 39(3), pp. 476–489.
Kciuk, M. , and Turczyn, R. , 2006, “ Properties and Application of Magnetorheological Fluids,” J. Achiev. Mater. Manuf. Eng., 18(1–2), pp. 127–130.
Deshmukh, S. S. , and McKinley, G. H. , 2007, “ Adaptive Energy-Absorbing Materials Using Field-Responsive Fluid-Impregnated Cellular Solids,” Smart Mater. Struct., 16(1), pp. 106–113.
Chrzan, M. J. , and Carlson, J. D. , 2001, “ MR Fluid Sponge Devices and Their Use in Vibration Control of Washing Machines,” Proc. SPIE 4331, pp. 370–378.
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## Figures

Fig. 1

Fabric target with fixed edge support

Fig. 2

Fabric target supported by edge dampers

Fig. 3

Fabric target, edge supported by an MRF shear damper (dashed line marks the target centerline)

Fig. 4

MRF-treated Kevlar fabric strip

Fig. 5

Schematic: MRF-Kevlar shear damper

Fig. 6

Photograph: MRF-Kevlar shear damper

Fig. 7

Test type 1: postimpact view

Fig. 8

Test type 1: FSP impact at 426 m/s: (a) t = 0 μs, (b) t = 50 μs, (c) t = 100 μs, and (d) t = 150 μs

Fig. 9

Test type 2: FSP impact at 411 m/s: (a) t = 0 μs, (b) t = 50 μs, (c) t = 100 μs, and (d) t = 150 μs

Fig. 10

Projectile residual velocity for the type 1 MRF damped targets

Fig. 11

Normalized energy absorption for the type 1 MRF damped targets

Fig. 12

Projectile residual velocity for the type 2 MRF damped targets

Fig. 13

Normalized energy absorption for the type 2 MRF damped targets

Fig. 14

Test classification schematic

Fig. 15

Relative performance of the MR fluid damped and elastically supported targets

Fig. 16

Pull test setup

Fig. 17

Pull test results

Fig. 18

Electromagnet and associated magnetic circuit

Fig. 19

Fringing effects at the edge poles

Fig. 20

Mild steel plate and edge postschematic, with air gap

Fig. 21

Magnetic field intensity versus air gap

## Tables

Table 1 Style 706 Kevlar fabric specifications
Table 2 Properties of fluid type MRF140-CG
Table 3 Ballistic figures of merit

## Discussions

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