Thermoplastic Composite Rivet Joint with Projection Interlock
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Solution Overview
Problem
The existing methods for joining thermoplastic composite members using self-piercing rivets often result in micro-cracks and weakening of the joint due to the brittleness of thermoplastics, leading to increased material usage and size when trying to maintain structural integrity, necessitating a redesign of the component form factor.
Innovation Solution
The proposed assembly and method involve a self-piercing rivet system where the rivet is driven through a first member and partially through a second member with a projection, deforming radially to interlock, using a washer if necessary, to minimize overlap and prevent fracturing, with features like curved projections and recesses to distribute stress and maintain structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the overlap of the thermoplastic member is increased to prevent micro-cracks and maintain structural integrity, then the reliability of the rivet joint is improved, but the weight and overall size of the assembly increase
Solution Approach 1:
The patent applies preliminary action by creating projections on the first member before riveting. These projections pre-position the rivet away from the edge of the thermoplastic member, ensuring sufficient overlap distance is maintained without requiring the thermoplastic member itself to be extended. This preliminary structural modification enables reliable joining while avoiding the weight penalty of increased overlap.
2Strength
If the overlap of the thermoplastic member is increased to avoid micro-cracks, then the strength of the joint is improved, but the overall size of the assembly increases
Solution Approach 1:
The projections are formed on the first member in advance to establish proper rivet positioning. This preliminary action ensures the rivet is placed at an optimal distance from the thermoplastic member edge, achieving sufficient overlap for strength without extending the thermoplastic member length.
Solution Approach 2:
The patent applies local quality by adding projections only in specific locations where rivets will be installed. This localized modification provides the necessary structural support and rivet positioning without requiring the entire thermoplastic member to be extended, thus maintaining compact overall dimensions while achieving strong joints.
3Ease of manufacture
If a sharpened rivet is used to pierce through the thermoplastic member, then the ease of manufacture is improved, but micro-cracks form due to the brittleness of thermoplastic
Solution Approach 1:
The projections are formed on the first member before the riveting process. This preliminary action pre-positions the rivet away from the edge of the thermoplastic member, ensuring sufficient overlap distance that prevents micro-crack formation during piercing and deformation, while still allowing the use of sharpened rivets for easy installation.
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 approach minimizes the overlap between thermoplastic and other members, enhancing structural integrity while reducing material usage and size, thus avoiding the need for redesign and ensuring a strong, lightweight joint.
Implementation Method 1
the sharpened end portion of the rivet is typically deformed or bent to secure the rivet to the metallic sheets, thereby interlocking the metallic sheets into an assembly
Data Source
AI summary
An assembly and method for minimizing an overlap of a composite member riveted to another member includes a first member having a first overlap area and a second member having a second overlap area. The overlap areas of the first and second members are in direct contact, thereby forming an overlapped region. The overlapped region may be thicker than the sum of the individual members. The second member includes an end defining a projection in the overlapped region. The rivet is disposed through the first member and at least partially through the second member in the projection, thereby interlocking the second member to the first member. The projections include a curved symmetrical body defining an apex. The rivet extends through the body such that a line extending from the center axis of the rivet is perpendicular to a tangent extending through the apex of the projection.