Shape Memory Alloy Fittings for Composite Structural Interlocking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Composite structures, commonly used in aircraft due to their light weight and structural capabilities, pose challenges in forming connections without compromising their integrity, as they are sensitive to disturbances and require robust yet non-stressful joining methods.
Innovation Solution
The integration of shape memory alloy fittings with composite structural members, where the alloy changes shape upon heating, allowing for interlocking with composite structures, providing a secure and stress-free connection through thermal activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional joining methods (fasteners, adhesives, welding) are used to connect composite structures, then connection strength is achieved, but stress concentrations and potential damage to composite materials occur
Solution Approach 1:
The invention utilizes temperature as a parameter to change the shape memory alloy from martensite phase (soft, deformable) to austenite phase (hard, shape-retaining). By heating the SMA above its transformation temperature, the material transitions from a compliant state that allows insertion to a rigid state that provides interlocking, thereby achieving strong connections without stress concentrations that would damage composite materials
Solution Approach 2:
The core mechanism employs phase transition of shape memory alloy between martensite and austenite phases. In the martensite phase at lower temperatures, the SMA fitting is soft and can be deformed to insert protrusions into composite openings. Upon heating to austenite phase, the SMA returns to its original shape, creating interference fits that securely lock the connection without generating harmful stress concentrations in the composite structure
2Ease of manufacture
If composite structures are disturbed or reworked to form connections, then connections can be formed, but structural integrity and component distinctness are compromised
Solution Approach 1:
The SMA fittings are pre-formed with specific geometries including protrusions that will interlock with composite openings. The fittings are prepared in advance with martensitic properties allowing easy deformation for insertion, then activated in situ through heating to achieve the final locked configuration, eliminating the need to disturb or rework the composite structure itself
Solution Approach 2:
The invention replaces traditional mechanical joining systems (fasteners, adhesives requiring surface preparation, welding) with a thermal-actuated shape memory system. The SMA fitting is inserted in a soft state and then thermally activated to lock in place, providing a connection method that does not require disturbing the composite structure's integrity or its component distinctness
3Object-affected harmful factors
If shape memory alloy fittings are used to interlock with composite structures, then stress-free connections are achieved, but additional heating and activation steps are required
Solution Approach 1:
The SMA fittings can be activated through self-heating mechanisms where the material's own properties enable temperature elevation to the austenite transformation point. This may involve resistive heating from applied electrical current or exothermic reactions, allowing the fitting to autonomously transition from insertion mode to locked mode without requiring complex external heating equipment or multi-step activation procedures
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
This solution enables secure, stress-free connections that maintain the structural integrity of composite materials, allowing for load transfer and redundancy, while avoiding stress concentrations and preserving the material's properties, even in complex geometries and varying loads.
Implementation Method 1
The interlocking protrusion is configured to change it shape when the interlocking protrusion is heated above the activation temperature of the shape memory alloy used to make the second structure
Implementation Method 2
The activation temperature is sometimes referred to as a transformation temperature as it corresponds phase transformation of the shape memory alloy
Data Source
AI summary
Provided are assemblies having composite structures interlocked with shape memory alloy structures and methods of fabricating such assemblies. Interlocking may involve inserting an interlocking protrusion of a shape memory alloy structure into an interlocking opening of a composite structure and heating at least this protrusion of the shape memory alloy structure to activate the alloy and change the shape of the protrusion. This shape change engages the protrusion in the opening such that the protrusion cannot be removed from the opening. The shape memory alloy structure may be specifically trained prior to forming an assembly using a combination of thermal cycling and deformation to achieve specific pre-activation and post-activation shapes. The pre-activation shape allows inserting the interlocking protrusion into the opening, while the post-activation shape engages the interlocking protrusion within the opening. As such, activation of the shape memory alloy interlocks the two structures.