Non-Circular Fastener Joints for Composite Shear-Out Resistance

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Solution Overview

Problem

Existing fastener joints in composite driveshafts with circular cross-section fasteners cause 'plowing' damage to the composite body under torsional load, leading to shear-out failure, making them the weakest element in the joint.

Innovation Solution

The use of fasteners with a non-circular cross-sectional shape, oriented perpendicular to the dominant load, and corresponding non-circular openings in the composite and metallic bodies to distribute stress and reduce damage initiation and growth, allowing for secure connection while minimizing damage to the composite body.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Force

If circular cross-section fasteners are used to connect composite bodies, then the fastener joint can transmit forces between components, but the fastener causes 'plowing' damage to the composite body under torsional load leading to shear-out failure

Engineering Contradiction:

Improveforce transmission capabilityVSAvoidcomposite body strength at fastener joint

Core Design Contradiction:

ForceVSStrength

Solution Approach 1:

The patent applies asymmetry by changing the fastener cross-section from circular to non-circular (e.g., rectangular, oval, or other asymmetric shapes). This asymmetric geometry allows the fastener to engage more effectively with the composite material, distributing shear stresses more uniformly and preventing the concentrated stress that causes plowing damage and shear-out failure in circular fasteners.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent changes the geometric parameter of the fastener cross-section from circular to non-circular. This parameter change fundamentally alters the stress distribution pattern within the composite body, reducing peak stresses and preventing damage initiation while maintaining force transmission capability.

Inventive Principle:

Principle #35Parameter changes

2Strength

If multiple fasteners are used to secure composite bodies, then the connection strength is improved, but the labor and manufacturing complexity increase

Engineering Contradiction:

Improveconnection strengthVSAvoidmanufacturing labor and complexity

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

By changing the fastener cross-section geometry to non-circular, the patent increases the load-carrying capacity and stress distribution efficiency of each individual fastener. This allows for reduced fastener density while maintaining overall connection strength, thereby reducing manufacturing complexity and labor requirements.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentEP3985267B1Fastener joints with enhanced strength for composite components

Publication Date: 2024.05.29 HAMILTON SUNDSTRAND CORP

Figure 1A
Figure 1B
Figure 2A~2B

AI summary

An assembly includes a composite body (116) and a load body connected to the composite body by a fastener (120, 220, 320, 520). The composite body (116) is elongate along a body axis and has a first fastener opening (132) extending radially therethrough. The load body has a second fastener opening extending therethrough. The fastener extends along an insertion axis (IA) through the first fastener opening and the second fastener opening to connect the composite body (116) and the first load body together. The fastener (120, 220, 320, 520) has a non-circular cross-section orthogonal to the insertion axis.