Shape Memory Polymer Fastener for Durable Positive-Lock Joints
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Solution Overview
Problem
Existing shape memory polymer fastening elements fail to provide a long-lasting and satisfying connection between components due to insufficient frictional engagement with the component openings, leading to unreliable anchoring and assembly challenges.
Innovation Solution
A fastening element made of shape memory polymer with a hollow-cylinder base body and a polygonal outer rim, which expands radially upon stimulation to create a positive fit and frictional connection within the component openings, combining both frictional and positive locking mechanisms for secure anchoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tube made of shape memory polymer is inserted into component openings and expanded, then the tube is clamped within the component openings, but the frictional connection does not provide a long lasting and satisfying connection
Solution Approach 1:
The fastening element is divided into multiple functional segments: a frictional connection zone with circumferential grooves for initial anchoring, and a positive locking zone with protrusions that engage with corresponding recesses in the component openings. This segmentation allows the element to provide both frictional holding and mechanical interlocking, resolving the contradiction between initial clamping and long-lasting connection.
Solution Approach 2:
The fastening element combines shape memory polymer material with a composite structural design featuring both smooth frictional surfaces and geometric locking features. The material properties of shape memory polymer enable reversible deformation for installation, while the composite structure provides multi-mechanism anchoring, achieving reliable and durable connection.
2Strength
If the fastening element expands radially to create frictional connection, then it is clamped within the component openings, but the connection is not sufficiently secure
Solution Approach 1:
The fastening element is divided into multiple functional segments: a frictional connection zone with circumferential grooves for initial anchoring, and a positive locking zone with protrusions that engage with corresponding recesses in the component openings. This segmentation allows the element to provide both frictional holding and mechanical interlocking, resolving the contradiction between initial clamping and long-lasting connection.
Solution Approach 2:
The fastening element utilizes curved circumferential grooves and rounded protrusions that facilitate radial expansion and uniform stress distribution during installation. The curved geometry enables smooth deformation of the shape memory polymer while maintaining contact pressure for frictional connection, and subsequently forms precise positive locking features, achieving both strong anchoring and reliable connection.
3Ease of operation
If the shape memory polymer is deformed into a temporary shape for installation, then it can be inserted into component openings, but the connection is not long lasting
Solution Approach 1:
The fastening element is pre-formed with an installation configuration that features reduced radial dimensions and activated shape memory properties, enabling easy insertion into component openings. After installation, a stimulus (thermal, chemical, or electrical) triggers the shape memory effect, causing the element to revert to its permanent locked configuration with expanded radial dimensions and engaged protrusions, thereby transforming from an easily installed temporary state to a durable permanent connection.
Solution Approach 2:
The fastening element utilizes phase transition of the shape memory polymer material between a compliant installation phase and a rigid locked phase. During installation, the polymer is in a softened, deformable state allowing easy insertion. Upon stimulation, it undergoes phase transition to a hardened, shape-retaining state that provides strong mechanical interlocking, resolving the contradiction between installation ease and connection durability.
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 reliable and cost-effective connection of multiple components by allowing simultaneous installation and locking, reducing assembly costs and providing additional functional support, while maintaining a consistent volume without material absorption.
Implementation Method 1
the shape memory polymer of the fastening element is transferred into a second condition initiated by a stimulus... the polymer is processed to receive a permanent shape and is then deformed into a temporary shape using a program process... Once programmed, the polymer is fixed in its temporary shape, but the permanent shape is essentially stored. Subsequently heating up the polymer above its transition temperature causes the polymer to revert back to its permanent shape
Implementation Method 2
Based on a radial expansion of the tube, it is clamped within the component openings. Thereby, the two components are connected to each other. Although the tube material expands within the component openings, the frictional connection to the inner wall of the component openings
Data Source
Figure 1~2
Figure 3a~3d
Figure 4a~4d
AI summary
The present invention relates to a fastening element 30 made of a shape memory polymer and being adapted for connecting at least a first component A with a first component opening a and a second component B with a second component opening b with each other, by arranging the fastening element 30 in a first condition of the shape memory polymer in at least the first and the second component opening a, b and after that, transferring it from the first condition to a second condition as a reaction to a defined stimulus, so that in the second condition, the fastening element 10 has at least a larger outer diameter than in the first condition, wherein in the first condition, the fastening element 30 comprises the following features: a) a hollow-cylinder like base body 32 with a circumferential outer wall 34 and a circumferential inner wall 36; b) at least at one axial end, the hollow-cylinder like base body 32 comprises an entry hole into an inner channel 16, passing through, preferably entirely, the hollow-cylinder like body; c) the hollow-cylinder like base body 32 has a cross sectional form with a polygonal outer rim 38 and a central opening of the inner channel 16, with the cross-sectional form of the fastening element 30 having a larger radial wall thickness T10 between the central opening 16 and the outer rim 38 in the second state than in the first state.