Gas Turbine Fastener Assembly With Load-Absorbing Spacers
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Solution Overview
Problem
Gas turbine engine casing flanges experience high tension and bending forces due to unbalanced rotor stages, leading to bolt failure and limited space for extended fasteners or spacers.
Innovation Solution
A fastener assembly comprising a bolt with a supporting shaft and a thread portion, along with spacers that absorb tensile loads and allow for bolt bending, enabling the assembly to accommodate flange separation from the casing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the bolt is made longer to accommodate extended axial length fastener or spacers, then the ability to withstand tension and bending forces improves, but the available space within the casing flange is exceeded
Solution Approach 1:
The fastener assembly is divided into distinct functional segments: a bolt portion for withstanding forces, spacer portions for occupying space and providing flexibility, and a fastener portion for engagement. This segmentation allows each component to be optimized for its specific function while keeping the overall assembly within spatial constraints.
Solution Approach 2:
Spacer portions are introduced as intermediary elements between the bolt and fastener, and between the bolt head and the flange. These spacers absorb tensile loads, provide necessary axial length, and allow controlled bending to accommodate flange separation without subjecting the threaded portion to excessive bending forces.
2Strength
If the bolt is made more rigid to withstand significant tension and bending forces, then the strength improves, but the ability to accommodate flange separation through bending is reduced
Solution Approach 1:
Different portions of the fastener assembly have different rigidity characteristics. The bolt portions (especially the supporting shaft and thread portion) are designed with high rigidity to withstand forces, while the spacer portions are designed with controlled flexibility to allow bending. This local differentiation of mechanical properties enables the assembly to simultaneously achieve strength and adaptability.
Solution Approach 2:
The fastener assembly transitions from a static rigid structure to a dynamic system where the spacer portions can elastically deform under load. This dynamic behavior allows the assembly to accommodate flange separation during FBO events while maintaining overall structural integrity through the rigid bolt portions.
3Strength
If the threaded portion of the bolt is subjected to significant forces, then the fastening capability improves, but the risk of bolt failure increases
Solution Approach 1:
Spacer portions are positioned between the fastener and the first flange, and between the bolt head and the second flange, to act as intermediaries that absorb tensile loads. This protects the threaded portion from experiencing the full magnitude of bending forces while still maintaining effective fastening capability.
Solution Approach 2:
The spacer portions are designed to absorb and cushion the tensile loads before they can be transmitted to the threaded portion of the bolt. This preemptive load absorption reduces the stress on the threaded portion, thereby preventing bolt failure under extreme loading conditions.
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 fastener assembly effectively reduces bending strain on the bolt thread portion, absorbs significant tensile loads, and allows for load sharing with adjacent fasteners, enhancing the durability and reliability of the gas turbine engine.
Implementation Method 1
At least one of the first spacer and the second spacer absorbs a portion of a tensile load acting on the bolt
Implementation Method 2
The fastener assembly accommodates separation of at least one of the first flange and the second flange from the casing of the gas turbine engine by allowing bending of the bolt along the pitch diameter shank
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A fastener assembly (10) for affixing two flanges to a casing (12) of a gas turbine engine is provided. The fastener assembly (10) includes a bolt (20), a fastener (30), and first and second spacers (50). The bolt (20) has a supporting shaft (22) extending from a head and a thread portion (24). The supporting shaft (22) has a diameter larger than a diameter of the thread portion (24). The fastener (30) is configured to releasably mate with the thread portion (24). The first spacer (40) surrounds a portion of the thread portion (24) and is disposed between the fastener (30) and a first flange (14). The second spacer (50) surrounds the supporting shaft (22) and is disposed between a second flange (16) and the bolt head. The supporting shaft (22) engages holes in the first flange (14), the casing (12), and the second flange (16). At least one of the first and second spacers (50) absorbs a portion of a tensile load acting on the bolt (20).