The effect of laminate stacking sequence of CFRP filament wound tubes subjected to projectile impact
Introduction
The chemical industry relies on pipes and vessels, produced by filament winding, in order to contain and transport hazardous substances, while the defence industry makes extensive use of filament winding in order to produce ordinance such as missile bodies and rocket motors. The automotive industry has investigated the use of filament wound fuel tanks for use in natural gas powered vehicles, while the aerospace industry uses it widely in satellite launch vehicles and aircraft components. Projectile impact in many of the aforementioned industries and applications, respectively, can result in leakage of hazardous substances due to structural failure, contents reacting violently to a projectile’s kinetic energy, or failure of sub-systems. In the armaments industry the issue of insensitive munitions has become a prime consideration in design procedures, where products are increasingly required to sustain high velocity impact without causing catastrophic failure. The tendency for a charge of high explosive or rocket fuel to detonate as result of projectile impact is strongly dependent on the energy imparted to the component.
The danger an impacting projectile presents to personnel, contents, and systems is therefore related to its kinetic energy. Tubes that differ only in the winding sequences are investigated to establish the effect of the stacking sequence on the kinetic projectile energy dissipation performance.
Section snippets
Background
In carbon fibre reinforced polymer (CFRP) laminates an impact is deemed to be of the high velocity type when the impact velocity exceeds 1% of the speed of sound in the laminate thickness direction [5] of a magnitude of 1500 m/s depending on the type of carbon fibre used. Hence impact velocities above 15 m/s constitute high velocity impact. For high velocity impact events, the overall compliance and the strain absorbing capability of the laminate is not expected to play a significant role: At
Specimens and experimental set-up
The specimens are filament wound tubes using a T800 carbon fibre and toughened epoxy. The stacking sequence is [−35°/+35°/90°3/−35°/+35°/90°3/−35°/+35°] for laminate A and [90°6/(−35°/+35°)3] for laminate B.
The fibre and matrix material properties are obtained from the manufacturer of the materials and the tubes [13], [14]. Some material properties could not be so obtained in which case a value from a similar material is substituted.
Material properties: (Note: Lamina and laminate properties
Energy release rates
The energy release rates used in the investigation are obtained from a instrumented perforation drop test and in addition from Refs. [5], [6], [12]. From these references, the energy release rates for delamination and matrix cracking are considered to be of the order of 500 J/m2. The drop tests yield an energy release rate for shear fracture in the laminate thickness direction of between 21 and 25 kJ/m2, which compares favourably to values quoted in Ref. [12]. Fig. 10 shows a typical result for
Discussion
The higher ballistic limit of laminate B indicates that the laminate B stacking sequence is better performing in terms of kinetic projectile energy dissipation.
The extent of material failure is reported to be strongly related to the impact energy and that delamination is the significant failure mode [7]. The strong correlation of the total delamination area with the impact energy for laminate A specimens and the good t-test values for laminate B specimens are an indication that the approach
Conclusions
Laminate B with the stacking sequence [90°6/(−35°/+35°)3] is the better overall projectile kinetic energy dissipater compared to laminate A with the stacking sequence of [−35°/+35°/90°3/−35°/+35°/90°3/−35°/+35°]. Laminate A is found to be a better kinetic projectile energy dissipater only for impact velocities between the ballistic limits of laminate A and laminate B. For the projectile used in this investigation, the ballistic limit for laminate A is determined to be approximately 70 m/s and
Glossary
In this paper, the terms penetration, perforation, and ballistic limit are used with the definitions based on Refs. [1], [2], [3], [4] as follows.
Penetration: Entrance of the projectile into the laminate without completing its passage through the laminate.
Partial penetration: The nose of the projectile enters the laminate, or is embedded in the laminate.
Complete penetration: The nose of the projectile exits the laminate.
Perforation: Passage of the projectile completely through the laminate.
Acknowledgements
The authors would like to thank the Management and Staff of Somchem/Denel for the material and practical support provided. Thanks go also to the technical and administrative support staff of the Department of Mechanical Engineering. Further thanks to the South African National Research Foundation for financial support.
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