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Manufacturing Composite External Volumes with Enhanced Underwater Collapse Performance



OBJECTIVE: Develop an ability to manufacture high-quality composite pressure housings for external volumes (EVs) with an enhanced hydrostatic pressure collapse performance by understanding how filament winding methods and materials can be used to control the collapse response. 

DESCRIPTION: In order to adhere to Navy submergence requirements (MIL-STD-1688, MIL-STD-278, or other relevant commercial standard), all components and systems must be evaluated to assess their susceptibility to the underwater environment. Components external to submarine pressure hulls, such as EVs, are particularly difficult to evaluate due to the high potential for material flaws to cause catastrophic collapse under hydrostatic pressure loading. The catastrophic collapse of EVs can result in the release of a radiated pressure pulse that can negatively affect nearby components and other EVs. Composite materials provide unique characteristics and increased flexibility for application-specific customization. The Navy has successfully leveraged the benefits of composite materials for use as EV pressure housings, which are often used to isolate components from exposure to the harsh marine environment. The Navy seeks an enhanced understanding of how manufacturing methods affect material flaw distributions and subsequent collapse failure of EV composite pressure housings due to underwater hydrostatic pressure loading. The Navy lacks a knowledge of how filament winding techniques (e.g., width of winding strip and overwrap frequency) and materials (e.g., glass fiber reinforcement strength) affect the quality and hydrostatic collapse response of composite pressure housings. To quantify part quality, non-destructive methods will be used to measure flaw distributions and document shape quality measurements. Manufactured composite pressure housings will be selected for hydrostatic pressure collapse testing to determine which methods and quality parameters have the greatest effect on housing failure. Additionally, to aid the Navy with numerical collapse predictions, manufacturing procedures will be developed to create flat filament wound material characterization samples, which are representative of the housing materials. Material characterization samples will also be assessed for quality and tested to better quantify the flaw distribution that is present in the as-manufactured housings. By identifying which manufacturing methods have the most control over the collapse pressure of composite housings and developing manufacturing methodology to create representative material characterization samples, the Navy will have enhanced control over the response and prediction of collapse for EVs with composite housings. 

PHASE I: Investigate the effects filament winding methods, such as width of winding strip and overlapping frequency, have on housing quality. Cylindrical glass fiber reinforced composite pressure housings will be manufactured with a diameter and length between 6 inches and 36 inches. Only one- or two-part shapes (diameter and aspect ratio combinations) will be developed during Phase I, while multiple winding methods will be investigated. Part flaws will be quantified using non-destructive scanning methods (e.g., ultrasound) to measure size, distribution, and location of flaws. Shape quality will be quantified using techniques such as out-of-roundness and thickness measurements. Once high-quality manufacturing methods are obtained, with minimal flaws and acceptable shape measurements, a best practices and lessons learned guide to manufacture composite pressure housings will be developed. The Phase I Option, if exercised, will continue to investigate additional filament winding techniques that may result in high-quality, low-cost parts. 

PHASE II: Building on lessons learned during Phase I, determine the effects of manufacturing composite housings with a variety of glass fiber types (e.g., E-glass, S-glass, S-2 glass, etc.). Quantify part and shape quality of the housings. Facilitate Navy performed hydrostatic collapse testing of the housings manufactured during Phase I to quantify how quality, winding method, and glass fiber properties influences the housing collapse performance. Develop a capability to manufacture flat filament wound material characterization samples. Execute instrumented quasi-static and high-strain rate characterization of the filament wound materials. Manufacture a variety of parts from small-scale to large-scale with the previously identified best manufacturing methods and materials, and collapse tested to provide evidence of how scale effects quality and performance. Expand manufacturing capabilities to EVs, which consist of other fiber types (e.g., carbon fiber) and hybrid designs (e.g., composite wrapped metallic cylinders) to add to the manufacturer’s ability to produce a wide range of Navy EVs. 

PHASE III: Assist the Navy in transitioning this technology to a wide variety of other military and non-military undersea applications including, but not limited to, oil and gas extraction, exploratory work for deep-sea mining, and scientific exploration. These deep-sea activities are continually becoming more common due to decreases in terrestrial resources and improvements in marine technologies. As composite-housed components become more prevalent across all fields, the ability to design and manufacture them for increased safety by mitigating hydrostatic collapse is essential to continue safe human exploration and operations in the harsh environment of the deep sea. 


1. Pinto, M., Matos, H., Gupta, S. and Shukla, A. “Experimental Investigation on Underwater Buckling of Thin-walled Composite and Metallic Structures.” Journal of Pressure Vessel Technology, 2016, 138(6). doi: 10.1115/1.4032703.

KEYWORDS: External Volumes; EVs; Submarines; Composites; Hydrostatic Pressure Collapse; Filament Wound Composite Shells 

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