Composite Tank Joint Softening Strip for Cryogenic Stress
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Composite cryogenic tanks face peak stress issues in bonded joints due to line loads, leading to potential leaks and thermally-induced stresses, with existing materials becoming stiff at low temperatures and having incompatible thermal expansion coefficients.
Innovation Solution
A composite tank design incorporating a softening strip made of three-dimensional fabric with flexible fibers coated in a compliant thermoplastic binder, such as fluoropolymer, which remains flexible at cryogenic temperatures and is co-bonded with the tank components to linearize stress and reduce peak shear stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional softening strip materials (e.g., rubber) are used at ambient temperatures, then shear stress peaking is reduced, but the material hardens at cryogenic temperatures and loses its stress-controlling capability
Solution Approach 1:
The patent changes the material parameters of the softening strip by using a thermoplastic polymer with a melting point higher than the cure temperature of the composite resin. This allows the material to remain flexible at cryogenic temperatures while maintaining the ability to reduce shear stress peaking in the joint.
Solution Approach 2:
The softening strip is formed as a composite material consisting of a thermoplastic polymer matrix reinforced with a three-dimensional fabric. This composite structure provides both the flexibility needed at cryogenic temperatures and the structural integrity to effectively control stress in the joint.
2Temperature
If softening strip materials are selected for flexibility at cryogenic temperatures, then stress control is maintained, but the coefficient of thermal expansion becomes incompatible with composite components, creating thermally-induced stresses
Solution Approach 1:
The patent carefully selects thermoplastic polymers with thermal expansion coefficients that are compatible with the composite components. This parameter matching ensures that thermally-induced stresses are minimized while maintaining material flexibility at cryogenic temperatures.
3Strength
If a softening strip is added to reduce peak stresses, then joint strength is improved, but the manufacturing process becomes more complex
Solution Approach 1:
The softening strip is pre-formed with a three-dimensional fabric reinforcement structure before being integrated into the joint. This preliminary preparation allows for easier integration during the bonding process while ensuring the strip has the necessary structural properties to reduce peak stresses effectively.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces peak stresses and maintains stability at cryogenic temperatures, preventing leaks and minimizing thermally-induced stresses, thereby enhancing the structural integrity of composite cryogenic tanks.
Implementation Method 1
The plastic binder is a polymer that is compliant at both room temperatures and at cryogenic temperatures. The plastic binder may be a fluoropolymer exhibiting elastic compliance at temperatures below approximately -150°F
Implementation Method 2
Such materials typically have a coefficient of thermal expansion (CTE) that may be incompatible with other composite components of the joint which have a relatively low CTE. This mis-match of CTE's may create undesirable thermally-induced stresses in the joint at cryogenic temperatures
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A composite resin tank includes a wall joined to a dome along a joint. A softening strip is located in the joint.