Fastener Insert for Open Cellular Sandwich Structures
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Solution Overview
Problem
Existing methods for integrating mechanical fasteners into sandwich structures with open cellular cores face challenges such as core damage, poor load transfer, and insecurement, particularly with self-propagating photopolymer waveguides, which limit the fastener's pull-out resistance and structural efficiency.
Innovation Solution
A sandwich structure configuration that includes a polymer component supporting a mechanical fastener connector insert, surrounded by self-propagating photopolymer waveguides, which form a micro-truss structure for enhanced securement and load transfer, and face sheets secured to the core assembly using these waveguides for improved structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a mechanical fastener connector is directly coupled to the sandwich structure without securement, then the installation process is simplified, but the fastener pull-out resistance is severely limited due to the poor shear strength of the core
Solution Approach 1:
A polymer component is introduced as an intermediary element between the mechanical fastener connector and the sandwich structure. This polymer component embeds the fastener connector and provides a secure mounting interface, preventing direct coupling to the weak core while maintaining installation simplicity. The polymer component acts as a mediator that transfers and distributes the fastener loads to the surrounding core material through its superior mechanical properties.
2Reliability
If machining a hole in or through the sandwich structure is used to install a mechanical fastener connector, then the fastener can be securely installed, but considerable damage is caused to the core which detrimentally affects its intended performance
Solution Approach 1:
The polymer component is prepared in advance with a pre-formed recess or cavity that accommodates the mechanical fastener connector. This preliminary preparation eliminates the need for post-installation hole machining through the sandwich structure. The polymer component is then positioned and secured to the core surface, allowing the fastener to be installed without penetrating or damaging the core material.
3Strength
If adhesive or frictional mechanisms are used to prevent the mechanical fastener connector from being pulled out, then securement is provided, but adhesive mechanisms create difficulty in quantifying failure load due to variability in adhesive application and frictional mechanisms rely on the poor shear resistance of the core
Solution Approach 1:
The polymer component provides a mechanical interlocking system that replaces adhesive or friction-based securement mechanisms. The recess in the polymer component mechanically engages with the mechanical fastener connector, creating a positive lock that does not depend on adhesive application quality or core shear strength. This mechanical engagement provides consistent and predictable securement that can be reliably quantified.
4Reliability
If self-propagating photopolymer waveguides are used to secure the mechanical fastener connector within the core, then some securement is achieved, but enhanced securement is needed and load transfer depends on the interfacial area and poor shear strength between the fastener and core
Solution Approach 1:
The solution combines multiple materials with complementary properties: the polymer component provides mechanical support and securement, while self-propagating photopolymer waveguides provide additional bonding and load distribution. This composite approach creates a multi-functional system where the polymer component's mechanical interlocking works synergistically with the photopolymer waveguides' adhesive properties, achieving both enhanced securement and improved load transfer capacity beyond what either material could provide alone.
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 reduces core damage, enhances load transfer efficiency, and provides improved securement of mechanical fasteners within the sandwich structure, allowing for better resistance to fastener pull-out and improved structural performance.
Implementation Method 1
the mechanical fastener connector was positioned within a reservoir of photopolymer and self-propagating photopolymer waveguides were formed around the mechanical fastener connector within a photopolymer reservoir
Data Source
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AI summary
A sandwich structure configured to be secured with a mechanical fastener includes a core assembly, which includes a polymer component configured for supporting a mechanical fastener connector insert. The core assembly further includes an open cellular component formed from a plurality of self-propagating photopolymer waveguides positioned around the polymer component, wherein a first portion of the plurality of self-propagating photopolymer waveguides is secured to and extends from the polymer component. Further included is a first face sheet secured to a first side of the core assembly, wherein the first portion of the plurality of self-propagating photopolymer waveguides has a distal end spaced apart from the polymer component and secured to the second face sheet.