Shawn M. Walsh’s research while affiliated with Army Research Laboratory and other places

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Publications (29)


Ballistic impact response of Ultra-High-Molecular-Weight Polyethylene (UHMWPE)
  • Article

July 2015

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998 Reads

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120 Citations

Composite Structures

Timothy G. Zhang

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Lionel R. Vargas-Gonzalez

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Shawn M. Walsh

In this paper we report findings from ballistic experiments conducted on Ultra-High-Molecular-Weight Polyethylene (UHMWPE) flat panels. We measured ballistic limit velocities, V50 of panels of different thicknesses using a fragment simulating projectile (FSP) and characterized back face deformation (BFD) using a spherical projectile. UHMWPE panels with different architectures (hybrid and non-hybrid) were evaluated. For the back face deformation (BFD) experiments, the thickness of post-impact intact material and interior delamination were characterized using X-ray Computer Tomography method. These measurements were used to evaluate the effects of fiber orientation and boundary constraints on material deformation and failure response to ballistic loading conditions. The expansion rate of the back face deformation zone in the transverse direction (to the direction of impact) decreased with time. This transverse expansion speed was higher in hybrid panels compared to the [0/90] cross-ply panels, which resulted in earlier influence of boundary constraints on back face deformation for hybrid panels. One major delamination occurred in the hybrid panels at cross-ply [0/90] and non-cross ply interface. The lateral extent of this delamination was larger when the panel edges were clamped as compared to the free panel edge case.



Comparison of Numerical and Experimental Results of Small Scale Compressed Gas Blast Experiments Involving a Surrogate Head Form

November 2012

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23 Reads

Exposure to a shock wave from an explosive blast can result in injury to the human body even if external signs of trauma are not present. Gaining a better understanding of the mechanisms contributing to those injuries can result in the design of better personal protective equipment (PPE). Compressed gas blast experiments can be conveniently used to explore the mechanical response of PPE systems and instrumented surrogate head forms to blast loading scenarios in a laboratory environment. Likewise, numerical simulations can be used to study relevant field variables related to the compressed gas blast and its effects on the target. In this regard, experimental data is needed to validate simulation results. This paper presents an experiment that uses a small scale compressed gas blast generator to explore the pressure distribution around a surrogate head form due to blast loading. The compressed gas blast generator is an open-end shock tube which creates a shock wave when the diaphragm that separates the high pressure and low pressure (ambient air) regions ruptures. The overpressures on selected locations of the surrogate head form were measured with piezoelectric pressure sensors and the data was processed to obtain positive phase durations and positive phase impulses. The surrogate head form was positioned off-axis from the exit of the compressed gas blast generator to preclude the discharge flow from affecting the overpressure measurements. A three-dimensional Coupled Eulerian-Lagrangian (CEL) model of the experiment described above was prepared in Abaqus/Explicit. Selected numerical and experimental results were compared and there was good agreement between them.


Control of the interfacial properties of ultrahigh-molecular-weight polyethylene/magnesium hybrid composites through use of atmospheric plasma treatment

February 2012

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9 Reads

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7 Citations

Polymer Composites

This work aims to explore the use of lightweight magnesium alloys as an advanced composite material in conjunction with lightweight thermoplastic materials, such as ultrahigh-molecular-weight polyethylene (UHMWPE). High throughput, environmentally friendly, atmospheric plasma treatment methods were used to control the interfacial properties and improve the adhesion behavior of metallic/UHMWPE composites. Helium-oxygen dielectric barrier discharges were used, and the plasma-activated UHMWPE surfaces were characterized through analytical and mechanical characterization methods. Oxygen content on the treated polymer surfaces increased 18.1–36.0%. A reduction in silicon content combined with characterization through microscopy reveal a preference for the attack of the matrix over the polyethylene fibers. Wetting angles for the treated samples decreased as much as 53.7%. Treated UHMWPE/Mg hybrid samples exhibited lap shear strengths up to 113.7% greater than the control. Both the plasma-induced surface functionalization with oxygen-containing polar groups (carboxyl, carbonyl, and hydroxyl groups) and the preferential mild etching of the polymer matrix over the fibers lead to the improvement in adhesion. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers


Impact and Ballistic Response of Hybridized Thermoplastic Laminates

February 2011

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123 Reads

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12 Citations

Recent Army research has focused on the use of thermoplastic-based polymer laminates for mass-efficient ballistic helmets. The focus of this work was to develop an understanding of how hybridization of ultra-high molecular weight polyethylene (UHMWPE) thermoplastic with various other thermoplastic and thermoset materials would affect ballistic performance and back face deformation. Panels of various material combinations and of varying architectures were processed and tested. Architecturally hybridized panels of UHMWPE exhibited the highest resistance to dynamic backface deformation. Generally, there were tradeoffs between ballistic performance and backface deformation within the variations of architecturally hybridized composites. However, several of the panels (the 50/50 and 90/10 hybrid series) exhibited projectile resistances comparable, and in a few cases superior, to that of the [0/90] plate while still exhibiting a higher level of deformation resistance.


Comparative Study of the Dynamic Response of Different Materials Subjected to Compressed Gas Blast Loading

January 2011

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4 Reads

Understanding the dynamic response of materials under blast and impact loading is of interest for both military and civilian applications. In the case of blast loading, the mitigation characteristics of materials employed in personal protective equipment (PPE) is of particular importance. Without adequate protection, exposure of the head to blast waves may result in or contribute to brain tissue damage leading to traumatic brain injury (TBI). The development of simple but representative laboratory experiments that can be used to study the mechanical response of different materials and/or material combinations to blast loading could be very useful for the design of PPE such as helmets. This paper presents a basic experimental setup that can be conveniently used to perform such studies using small scale compressed gas blasts. An open end shock tube is employed to generate the blasts used to load flat plate samples placed in a special rigid holder. Acceleration time histories at selected locations in the sample are used to generate data to compare the dynamic response and blast mitigation effectiveness of different specimens. High speed schlieren video is used to correlate the arrival of the shock wave and air flow that follows with the motion of the test sample.


Influence of alcohol pre‐infusion on the quality of VARTM composites

December 2008

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22 Reads

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2 Citations

Polymer Composites

In the vacuum assisted resin transfer molding (VARTM) process, part-to-part variations such as the uncertainty in the permeability and race tracking phenomenon make it difficult to achieve consistent mold filling and ensure part quality of composites. Alcohol pre-infusion was presented in this study as a novel real-time monitoring and control approach for the flow process in the VARTM process, alcohol test fluid is infused before the actual resin infusion to locate the potential dry spots without using the large quantity of sensors. Then corresponding process control strategy is designed, such as opening the auxiliary gate at specific moment on those predicted dry spot locations to compensate flow defects. Moreover, alcohol can be easily removed by heat without changing the local permeability. The influence of alcohol pre-infusion on the quality of VARTM composites were investigated in this study. The mechanical tests were conducted to verify that the alcohol pre-infusion approach has no significant effect on composite properties because alcohol can be removed from fiber by heat and air flow. Specifically, DMA, TGA, and FTIR spectrum proved that negligible difference existed on the resin–fiber interface between the composites with or without alcohol pre-infusion. Finally, the microscopy results revealed a similar failure path in a resin matrix. TMA results also demonstrated similar dimension stability. This alcohol pre-infusion approach was effective when compared with computer simulation and could eliminate the occurrence of dry spots and voids without using sensors or data-acquisition system. The control schemes were shown in a case study to be capable of compensating the flow defects and achieving desired fill patterns in the face of permeability uncertainty. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers


Table 1 . Comparison of Pt particle size, cell output, Pt loading, and Pt utilization corresponding to CNT-supported catalyst. 
Figure 5. Cell polarization curves and electrode overpotential as a function of current density at 80 °C for a) Cell I and b) Cell II with humidified H 2 /O 2 as the fuel/oxidant at a back pressure of 1.36 atm. 
Highly-Efficient Buckypaper-Based Electrodes for PEMFC
  • Article
  • Full-text available

October 2008

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371 Reads

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14 Citations

ECS Transactions

The Pt catalytic electrode was developed using carbon nanotube film (buckypaper) as a supporting medium through use of the electrodeposition method. Buckypapers are free-standing thin films consisting of single-walled carbon nanotubes (SWNT), multi-walled carbon nanotubes (MWNT) or carbon nanofibers (CNF) held together by van der Waals forces without any chemical binders. Mixed buckypapers may be developed by layered microstructures with a dense and high-conducting SWNT networks at the surface, as well as large porous structures of MWNT or CNF networks as supports. This unique microstructure may improve Pt catalyst accessibility and the mass exchange properties. Pt particles were uniformly deposited in porous buckypaper and had an average particle size of about 6 nm. A promising electrochemical surface area of about 40 m2 g-1 was obtained from these electrodes. A Pt utilization of as low as 0.5 g kW-1 was achieved for the cathode electrode at 80 oC. Pt utilization efficiency may be further improved by optimization of the electrodeposition condition in order to reduce the Pt particle size.

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Modeling and analysis of thickness gradient and variations in vacuum‐assisted resin transfer molding process

May 2008

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114 Reads

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48 Citations

Polymer Composites

As vacuum-assisted resin transfer molding (VARTM) is being increasingly used in aerospace applications, the thickness gradient and variation issues are gaining more attention. Typically, thickness gradient and variations result from the infusion pressure gradient during the process and material variations. Pressure gradient is the driving force for resin flow and the main source of thickness variation. After infusion, an amount of pressure gradient is frozen into the preform, which primarily contributes to the thickness variation. This study investigates the mechanism of the thickness variation dynamic change during the infusion and relaxing/curing processes. A numerical model was developed to track the thickness change of the bagging film free surface. A time-dependent permeability model as a function of compaction pressure was incorporated into an existing resin transfer molding (RTM) code for obtaining the initial conditions for relaxing/curing process. Control volume (CV) and volume of fluid (VOF) methods were combined to solve the free surface problem. Experiments were conducted to verify the simulation results. The proposed model was illustrated with a relatively complex part. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers


Citations (19)


... This approach was previously followed by the authors of this paper [5,6]. Typically, para-aramid prepreg plates are processed by applying conditions of 1.4 MPa-2.5 MPa and 150 • C-170 • C for 60 min-90 min, whereas UHMWPE prepreg plates, such as Dyneema ® and Spec-traShield ® , require higher pressures (typically 13 MPa-40 MPa) and lower temperatures (120 • C-130 • C), with similar processing times [7][8][9][10][11]. Nevertheless, ballistic helmet processing is considerably more complex. ...

Reference:

Thermoplastic-Based Ballistic Helmets: Processing, Ballistic Resistance and Damage Characterization
Ballistic impact response of Ultra-High-Molecular-Weight Polyethylene (UHMWPE)
  • Citing Article
  • July 2015

Composite Structures

... High-strength ABS thermoplastic material has been attracting a substantial effort in developing a new war fighter head protection which is lighter and more resistant to ballistic, blunt and blast impact [5]. To define the impact behavior of ABS materials, low velocity impact experiments were conducted on ABS materials at energy levels of 20 J and 100J. ...

INNOVATIVE MATERIALS AND DESIGN FOR THE IMPROVEMENT OF WARFIGHTER HEAD PROTECTION
  • Citing Article

... As a result, the BP film forms a structure that can be considered as a CNT skeleton where the CNT are held together by the tube-tube junctions [6,13,14]. Several studies have been addressed to explore the potential applications of BP including polymer composites with high CNT loading (up to 60 wt%), supercapacitors, hydrogen storage materials, gas separators, electrodes, actuators, sensors, and artificial muscles [14,15,16,17]. ...

Highly-Efficient Buckypaper-Based Electrodes for PEMFC

ECS Transactions

... Changes in the design and materials of helmets were particularly marked from those used in World War I to the Personal Armor System for Ground Troops (PASGT) and Advanced Combat Helmet (ACH) helmets, widely adopted today. A modern ballistic helmet, for example, protects the user's head against low velocity projectiles, such as pistols and revolvers, as well as against shrapnel from explosive devices [5,6]. In this case, there is a common misconception that modern ballistic helmets can protect wearers from the threat of most firearms. ...

Thermoplastic matrix combat helmet with graphite-epoxy skin
  • Citing Article
  • January 2007

... When researchers experiment with and develop new composite materials for ballistic helmets, they face the challenge of adapting their project to existing production methods or even creating new methods. Walsh, Scott and Spagnuolo [17] produced several carbon fiber/thermoset matrices (IM7 ® /epoxy) and aramid fiber/thermoplastic matrix (KM2 ® /polyolefin) hybridized ballistic plates. Although this approach presents a faster solution, coprocessing both parts demands that the resin curing cycle occurs for the same duration and at the same temperature of thermoplastic melting and consolidation. ...

The Development of a Hybrid Thermoplastic Ballistic Material With Application to Helmets
  • Citing Article
  • January 2005

... Ultra-high molecular weight polyethylene (UHMWPE) composites are fiber based polymer composites which have grown in popularity as bullet and fragment mitigating armor packages [1][2][3][4][5][6]. While there has been some experimentation conducted to characterize the responses of the laminate while varying projectile speed or material thickness [1,7] little work has been done to characterize additional effects such as the impact of various boundary conditions or the effectiveness of multi-plate stacks of the composite relative to a consolidated whole, especially so in a single study [8,9]. ...

Examining the Relationship Between Ballistic and Structural Properties of Lightweight Thermoplastic Unidirectional Composite Laminates
  • Citing Article

... Two effective methods can be used to obtain a uniform and stable water layer in the friction process. The first is to enhance the surface hydrogen bonding environment; this can be achieved by increasing the content of surface hydroxyl through special treatments such as thermal [92][93][94] or plasma treatment [87,[95][96][97]. The intensity of the peak at 3,200 cm −1 in the SFG spectra corresponding to the interface hydroxyl of the treated friction pair can be enhanced significantly compared with that before treatment. ...

Control of the interfacial properties of ultrahigh-molecular-weight polyethylene/magnesium hybrid composites through use of atmospheric plasma treatment
  • Citing Article
  • February 2012

Polymer Composites

... The second category includes various 3D methods that relate the principal permeability with the flow front position of a 3D transient flow through a textile specimen [18][19][20][21]. The permeability tensor can be obtained in this case either analytically by solving governing equations [20,22] or numerically by matching the actual flow front on a case-bycase basis [21,23]. Due to the complexity in flow front tracking and data analysis, 22 out of the 28 tests reported by 26 participants in an international benchmarking project (hereafter referred to as Benchmark III) [24] were obtained by the unidirectional approach with saturated flow conditions. ...

Determination of the Transverse Permeability of a Fiber Preform
  • Citing Article
  • November 1999

Journal of Reinforced Plastics and Composites

... Since SHM provides real-time diagnostic and prognostic information and NDE provides absolute information, both are needed in general; however, this work focuses on SHM research because damage is often most easily observed in operation under dynamic loading. For example, fatigue cracks in metals and delaminations in composites open and close when subjected to operating stresses but tend to close partially off-line (see [24]). Also, SHM can assess structural integrity in operating environments of varying severity. ...

Development of a structurally compatible sensor element
  • Citing Article
  • July 2001

Proceedings of SPIE - The International Society for Optical Engineering