Research Papers

Deep-Drawing Forming Trials on a Cross-Ply Thermoplastic Lamina for Helmet Preform Manufacture

[+] Author and Article Information
Lisa M. Dangora, Cynthia J. Mitchell

Department of Mechanical Engineering,
University of Massachusetts Lowell,
1 University Avenue,
Lowell, MA 01854

James Sherwood

Department of Mechanical Engineering,
University of Massachusetts Lowell,
1 University Avenue,
Lowell, MA 01854
e-mail: james_sherwood@uml.edu

Jason C. Parker

US Army Natick Soldier Research,
Development & Engineering Center,
15 Kansas Street,
Natick, MA 01760

1Corresponding author.

Manuscript received December 15, 2015; final manuscript received August 21, 2016; published online October 6, 2016. Assoc. Editor: Yannis Korkolis.This work is in part a work of the U.S. Government. ASME disclaims all interest in the U.S. Government's contributions.

J. Manuf. Sci. Eng 139(3), 031009 (Oct 06, 2016) (8 pages) Paper No: MANU-15-1668; doi: 10.1115/1.4034791 History: Received December 15, 2015; Revised August 21, 2016

With the evolution of modern warfare, there is a constant demand for enhanced soldier protection. The research efforts presented in this paper focus on improving the ballistic performance of composite combat helmets through the control of fiber orientations, reduction of seam density, and preservation of long fiber lengths. To accomplish these objectives, near-net-shape preforming is explored as an alternative method to the traditional cut and dart techniques used in the manufacture of combat helmets. An overview of current fabrication procedures is provided in addition to a discussion of the material selection and preform processing technique. Forming trials are conducted on Dyneema® HB80, a cross-ply thermoplastic lamina, using a laboratory deep-draw setup to explore the effects of processing parameters on the quality of the formed part. Undesirable wrinkling that manifests during deep-drawing of the material is found to be most effectively mitigated through the use of sufficient binder pressure. Furthermore, it is demonstrated that a loose ply stack up is more amenable to the production of high-quality preforms than a preconsolidated charge of material.

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Fig. 1

Generic darted pinwheel pattern cut into sheet goods to facilitate helmet forming. Plies align with overlaying crowns and staggered petals for full helmet coverage and even seam distribution.

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Fig. 2

Generic deep-draw process for forming a heated ply stack to the punch geometry as it is drawn into an open mold

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Fig. 3

(a) Laboratory preform setup consisting of a hemispherical male tool, an open female die, and a binder ring (shown here within an environmental chamber mounted on a universal testing machine) and (b) corresponding computational tooling with prescribed loading conditions and constraints

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Fig. 4

Degree of shear necessary for cross-ply to conform to hemispherical punch at a 1:1 draw ratio. Note: The results were generated using modeling technique described in Ref. [24] with a 3 mm element length.

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Fig. 5

A conservation of volume approximation is used to calculate the change in lamina thickness as a function of shear, which correlates well with experimental data

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Fig. 6

(a) FEA contour of thickness change from the nominal sheet value of 0.148 mm plotted on the undeformed lamina and (b) potential filler-ply pattern with cutouts to promote uniform preform thickness

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Fig. 7

Forming example where buckling forces exceed the pressure applied by the binder, causing the draw ring to lift and resulting in severe wrinkling

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Fig. 8

Deep-draw force profile at various temperatures for tests with a punch velocity of 6.35 mm/s and a binder pressure of 700 Pa

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Fig. 9

Severe wrinkling of hemisphere formed at 100 °C with 2900 Pa of binder pressure (6.35 mm/s)

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Fig. 10

Wrinkling moderated with increased binder pressure of 4000 Pa at 100 °C (6.35 mm/s)

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Fig. 11

Deep-draw force profile at various binder pressures for tests with a punch velocity of 6.35 mm/s and a forming temperature of 100 °C

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Fig. 12

Preconsolidated layup (a) before and (b) after deep-drawing (100 °C, 6.35 mm/s, 6.5 kPa)

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Fig. 13

Unconsolidated layup drawn to hemisphere geometry (100 °C, 6.35 mm/s, 6.5 kPa). Note that the smallest ply detached upon removal from the tooling and is shown here to the side.

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Fig. 14

Unconsolidated layup drawn to hemisphere geometry with filler ply secured in a sandwich between two full plies




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