Titanium Bolt Assembly With Flexible Spacer for FBO Load Relief
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Solution Overview
Problem
Bolts used in flange connections of gas turbine engine fan cases face integrity issues during Fan Blade Off (FBO) events, leading to potential failure in maintaining clamping load and ensuring containment of high-energy fragments.
Innovation Solution
A bolt assembly comprising a titanium alloy bolt and spacer, with the spacer designed for reduced stiffness and increased flexibility, allowing it to compress more and spring back, thereby reducing the load on the bolt and enhancing the overall integrity of the assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If steel or nickel-based superalloy bolts are used in flange connections, then high strength and creep resistance are achieved, but weight increases and elastic modulus becomes too high causing excessive load on bolts during FBO events
Solution Approach 1:
The patent changes the material parameters by selecting titanium alloy with specific properties (yield strength ≥500 MPa, elastic modulus <150 GPa, density <5 g/cc) to resolve the contradiction between strength and weight. This parameter optimization allows the bolt to maintain sufficient strength while reducing weight and elastic modulus to improve load distribution during FBO events.
Solution Approach 2:
The patent employs composite material strategy by combining titanium alloy bolt with stainless steel flange components, creating a hybrid material system that leverages the high strength-to-weight ratio of titanium and the high strength and stiffness of stainless steel, thereby resolving the strength-weight contradiction.
2Strength
If high elastic modulus material is used for bolts, then high strength is achieved, but load distribution worsens as bolts take up excessive load instead of the flange
Solution Approach 1:
The patent optimizes the elastic modulus parameter by selecting titanium alloy with elastic modulus less than 150 GPa (compared to 200+ GPa for steel and superalloys). This parameter change ensures the bolt is more compliant than the flange, allowing proper load distribution where the flange takes the majority of load during FBO events, thereby improving reliability.
3Strength
If traditional steel bolts are used, then sufficient strength is achieved, but weight increases and number of bolts required increases
Solution Approach 1:
The patent changes the density parameter by using titanium alloy with density less than 5 g/cc (approximately half of steel's 7.85 g/cc). This enables weight reduction through material substitution while maintaining sufficient strength through optimized yield strength ≥500 MPa.
Solution Approach 2:
The patent applies local quality principle by using titanium alloy specifically for the bolt components where weight reduction is most beneficial, while maintaining traditional materials for other components. This targeted material selection optimizes the overall system by reducing connection weight without compromising structural integrity.
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
The titanium alloy bolt assembly provides improved load distribution and increased reserve factor, maintaining bolt integrity during FBO events while offering weight savings due to reduced material density and diameter, ensuring effective containment and reduced risk of damage.
Implementation Method 1
the spacer is designed for reduced stiffness and increased flexibility, allowing it to compress more and spring back, thereby reducing the load on the bolt
Data Source
AI summary
Aspects of the disclosure regard a bolt assembly which comprises a bolt extending in a longitudinal direction through a flange connection, the bolt comprising a first portion and a second portion, the first portion comprising a threaded section at a first side of the flange connection and the second portion comprising a head portion at a second side of the flange connection. The bolt assembly further comprises a nut screwed on the threaded section and a spacer arranged between the nut and the flange connection or between the head portion and the flange connection. The bolt is comprised of a titanium alloy.