Non-Circular Fastener Joints for Composite Driveshaft Shear-Out
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Solution Overview
Problem
Existing fastener joints in composite driveshafts, which use circular-shaped fasteners, suffer from 'shear-out failure' due to concentrated stress, leading to damage and reduced operational life under torsional loads, as the composite body is the weakest element in these joints.
Innovation Solution
The use of non-circular cross-sectional fasteners and corresponding openings in composite and metallic bodies, oriented perpendicular to the dominant load, distributes stress and reduces the risk of damage initiation and growth, allowing for secure connection while minimizing damage to the composite body.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If circular-shaped fasteners are used in composite driveshafts, then the assembly is simple to manufacture and install, but the composite body suffers from shear-out failure due to concentrated stress
Solution Approach 1:
The patent applies asymmetry by replacing circular fasteners with non-circular cross-section fasteners (such as rectangular, oval, or other asymmetric shapes). This asymmetric geometry redistributes the stress field around the fastener, preventing the concentrated stress that causes shear-out failure in circular fasteners. The non-circular shape creates a more favorable stress distribution pattern that protects the composite body while maintaining manufacturing feasibility through standard drilling and fastening processes.
2Device complexity
If circular fasteners are used, then the fastener design is simple, but the operational life of the composite driveshaft is reduced due to damage initiation and growth
Solution Approach 1:
The asymmetric non-circular fastener cross-section is designed to optimize stress distribution specifically for torsional and bending loads experienced by driveshafts. This geometric modification increases operational life by preventing damage initiation at the fastener-composite interface and inhibiting damage growth under cyclic loading conditions, while adding minimal complexity to the overall fastener system.
Solution Approach 2:
The patent changes the geometric parameters of the fastener from a circular cross-section to non-circular cross-sections with specific dimensional ratios and shapes. This parameter change optimizes the stress distribution characteristics, creating a more favorable stress field that reduces damage risk and extends operational life without significantly complicating the fastener design or installation process.
3Reliability
If non-circular fasteners are used, then stress is distributed and damage risk is reduced, but the fastener and opening geometry becomes more complex
Solution Approach 1:
The asymmetric non-circular fastener geometry is implemented with practical considerations for manufacturing. Standard drilling processes can still be used to create the openings, and the non-circular shape is achieved through common fastening methods. This approach maintains relatively simple device complexity while achieving the reliability benefits of reduced stress concentration and lower damage risk in composite driveshaft applications.
Data Source
AI summary
An assembly includes a composite body and a load body connected to the composite body by a fastener. The composite body is elongate along a body axis and has a first fastener opening extending radially therethrough. The load body has a second fastener opening extending therethrough. The fastener extends along an insertion axis through the first fastener opening and the second fastener opening to connect the composite body and the first load body together. The fastener has a non-circular cross-section orthogonal to the insertion axis.