Core Bolt With Frangible Drive Element for Blind-Side Rework
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Solution Overview
Problem
Traditional fasteners require a torque wrench for installation and cannot be removed after installation without drilling out the head, posing challenges in confined spaces and limiting the flexibility of fastening systems for joining multiple substrates with working and blind sides.
Innovation Solution
A core bolt with a recessed torquing feature and a frangible drive element that allows for installation without a torque wrench and enables easy removal by breaking off the drive element post-installation, combining external wrenching and broached recess features in a single fastener.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional fasteners with external wrenching feature are used, then installation requires torque wrench and precision, but removal after installation requires drilling out the fastener head
Solution Approach 1:
The fastener is divided into two functional parts: a retained head portion with recessed torquing feature and a frangible drive element. The frangible drive element is designed to break off at a predetermined torque, separating the installation function (torque control via recessed feature) from the retention function (head remains in substrate). This segmentation allows precise installation without requiring the head to be removed later.
Solution Approach 2:
The frangible drive element is designed as a disposable component that breaks off after serving its purpose during installation. It is engineered to fracture at a specific torque level, sacrificing itself to leave the head portion retained in the substrate. This disposable element eliminates the need for complex removal procedures while maintaining installation precision.
2Manufacturing precision
If fasteners require torque wrench for installation, then accurate torque control is achieved, but automation and ease of operation in confined spaces is reduced
Solution Approach 1:
The frangible drive element automatically fractures at a predetermined torque without requiring external torque measurement or control systems. The fastener self-regulates the installation torque through its built-in fracture mechanism, eliminating the need for torque wrenches or automated torque monitoring systems. This enables automation while maintaining consistent torque application.
Solution Approach 2:
The fastener design changes the torque control mechanism from an external measurement-based system (torque wrench) to an internal fracture-based system. By designing the frangible element with specific material properties and geometry, the torque parameter is controlled through the fracture point rather than through measurement and adjustment, enabling automation.
3Shape
If fasteners break off flush with the fastener head, then clean appearance is achieved, but additional flushness shaving is required for rework
Solution Approach 1:
The separation of the frangible drive element from the retained head portion means that when the drive element breaks off, it leaves the head portion protruding slightly. This eliminates the need for flushness shaving during rework, as the retained head can be easily accessed and manipulated. The segmentation allows the fastener to maintain a clean appearance while enabling easy removal and reinstallation.
Data Source
AI summary
A core bolt of a fastener system for joining multiple substrates of a workpiece with a working side and a blind side is provided. The core bolt includes a head portion, a shank portion and a frangible drive element. The head portion includes a recessed torquing feature. The shank portion opposes the recessed torquing feature and extends from the head portion along a longitudinal axis to a distal end. The shank portion includes a threaded portion between the distal end and the head portion. The frangible drive element extends from recessed torquing feature and protrudes outward along the longitudinal axis to define a proximal end. A fastener system for joining multiple substrates of the workpiece includes a nut member and the core bolt. Methods for joining multiple substrates of a workpiece with a working side and a blind side are also provided.