An Integrated Systematic Approach to Linerless Composite Tank Development

The paper describes a program currently underway at Composite Technology Development, Inc. to dramatically improve the design and capabilities of lightweight linerless composite tanks. The program integrates material development and characterization, micromechanics-based analyses of composite materials and structural design and fabrication of prototype tanks. This integrated systematic approach, addresses the multi-scale and multi-disciplinary issues that are critical to linerless composite tank design by looking concurrently at material requirements, capabilities and tailoring, refinement of fabrication process, and structural design optimization. Unlike traditional composite over- wrapped pressure vessels, the linerless composite tanks depend on the composite shell itself to serve as a permeation barrier in addition to carrying all pressure and environmental loads. Designing these tanks requires accurate knowledge of the structural response of the tank on the macro-scale as well as the material behavior on the micro-scale. Limiting and managing the development of microcracks and microcrack-induced permeability in the composite shell dictates that new materials be tailored specially for this purpose. The paper describes how micromechanics-based analysis is used to: 1) define critical material- performance parameters that drive the development of new toughened matrices, and 2) predict microcrack formation and permeability in composite laminates under biaxial load. Key concepts are presented that help optimize the structural design of linerless composite tanks. Finally, the paper presents the progress to date in designing and fabricating linerless composite tanks using a newly developed, microcrack-resistant resin system.