Composite cylinder design software

MileStones

• Lightweight 105mm and 120mm barrel concepts. 
• Steel-lined 25mm Bushmaster barrel with PMC and MMC overwraps
• Steel-lined 81mm mortar overwrapped with MMC
• Ceramic bore M4 SOCOM heavy gun barrel replacement.

CCDS was used as the primary design tool for the first successful 105mm composite overwrapped gun tube. This tube was designed such that the composite and liner would retain interface compression at temperatures as low as -50°F yet absorb the high stresses and pressures at temperatures up to 400°F. The tube also meets or exceeds the critical velocities of the all-steel baseline barrel at all locations along the tube length. The composite overwrapped tube is 225lb lighter and has a CG shift of 2.3 inches over it steel counterpart which translates in a mass*C.G. reduction of 29%. This reduction in inertial mass allows for use of lighter targeting motors and provides for more accurate targeting in the field. 

In the design process, CCDS is used to determine the thickness of liner and overwrap, the overwrap material and lay-up, the thermal stresses and maximum service temperature, the dynamic strain attenuation, the interface stresses between liner and overwrap, the weight, center of gravity, and natural frequency, based on the pressure and thermal inputs for each barrel.

To achieve this, a hybrid glass/carbon composite is wound on the steel liner with an optimized winding angle such that the overwrap coupled with autofrettage absorbs breech pressures up to 90ksi while still maintaining interface compression at low temperatures. The carbon wrap is placed axially along the tube to provide a lightweight increase in axial stiffness and the glass is wound off-axis to absorb hoop stresses while maintaining interface compression.

The steel bore was manufactured and autofrettaged by Benet Labs in Albany NY, and was overwrapped by Spencer Composites Corp., based in Sacramento CA. The overwrapped barrel was sent to Benet Labs for static pressure testing up to 5ksi. Experimental data and CDS-WIND predictions were with 2% for all test results. The tube was then sent to Aberdeen Proving grounds for live fire testing. The barrel was tested with low pressure (20-30ksi) artillery rounds and high pressure (60-80ksi) tank rounds. Static strain results also matched CDS-WIND model predictions and FEA results for all firing cases. Dynamic strain results however revealed high strain amplification at low pressures and little to no strain amplification at high pressures which is counter to normally expected results. This abnormal strain amplification at low pressure may be attributed to the type of projectile being fired at these low velocities and the study of this phenomenon is ongoing.  

A higher risk design, which uses an all carbon thermoplastic system wound using a unique ‘tension profile’ is being used for the second generation composite overwrap tube. The risk associated with this design is accurate control and maintenance of high winding tension of the carbon composite prepreg as this tension is important for achieving intimate contact between the steel and all carbon composite overwrap under all thermal and pressure loading conditions.

Our current efforts involve supporting full-scale FCS testing, notch barrel testing, and the design of a thermoplastic carbon composite overwrap with a controlled tension profile that maximizes the efficiency of the composite while maintaining weight, C.G. and natural frequency requirements. This work involves modifying an existing robotic tow placement robot at UD-CCM to manufacture composite overwrapped cylinders under high tension. Concurrent efforts also involve continuing the advancement of the generic design tool CDS-WIND such as the addition of optimization methods. The CDS-WIND design tool is also being used by Magnum Technology in their ongoing work for the development of small caliber ceramic bore barrels to replace the M4 SOCOM heavy gun barrel.