CMC Cap Bolt Attachment for Turbine Engine Thermal Management
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Solution Overview
Problem
Ceramic matrix composite (CMC) components in turbine engines face challenges in attachment to metal structural components due to differing thermal growth rates and low ductility, leading to vibration and heat signature increase, necessitating a fastener that allows for thermal expansion mismatch and applies preload.
Innovation Solution
A fastener system comprising a metal bolt with a mechanically secured CMC cap, which allows for different thermal expansion rates and acts as a thermal shield, eliminating the need for thermal barrier coatings, and includes mechanical attachments like rivets or threaded members to secure CMC components to metal structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If CMC components are attached to metal structural components, then heat signature is reduced, but thermal expansion mismatch causes attachment failure
Solution Approach 1:
A CMC cap is introduced as an intermediary component between the metal bolt and the CMC component. The cap serves as a thermal shield that protects the bolt from direct heat exposure while allowing differential thermal expansion. This mediator resolves the contradiction by isolating the metal bolt from the high-temperature environment, enabling the attachment to maintain reliability despite thermal expansion differences.
Solution Approach 2:
The thermal properties of the bolt assembly are changed by adding the CMC cap, which has different thermal expansion characteristics compared to the metal bolt. This parameter change allows the assembly to accommodate thermal expansion mismatch between the metal structural component and the CMC component, maintaining attachment reliability while operating at reduced heat signatures.
2Strength
If metal fasteners are used to secure CMC components, then attachment strength is provided, but thermal expansion differences cause stress and potential failure
Solution Approach 1:
The CMC cap acts as a protective intermediary that shields the metal fastener from direct thermal exposure. This allows the metal fastener to maintain its mechanical strength while the cap accommodates the thermal expansion differences, preventing stress concentration and potential fastener failure.
Solution Approach 2:
The fastener system becomes a composite structure combining metal (bolt) and CMC (cap) materials. Each material is used where it performs best: the metal provides mechanical strength and fastening capability, while the CMC cap provides thermal shielding and compatibility with the CMC component's thermal expansion characteristics.
3Reliability
If CMC components are attached without preload, then vibration is reduced, but component damage occurs due to lack of clamping force
Solution Approach 1:
The CMC cap and bolt assembly automatically applies the necessary preload to the CMC component through the mechanical connection. The rigid CMC cap transfers the clamping force from the bolt to the CMC component, ensuring proper contact and preventing relative motion that would cause damage, while the system itself manages the preload application.
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 system effectively secures CMC components to metal structures, managing thermal expansion differences and reducing heat signatures by applying preload and acting as a thermal shield, thereby minimizing vibrations and heat absorption.
Implementation Method 1
The CMC cap also acts as a thermal shield for the bolt, aiding in the reduction of a heat signature of the turbine engine
Implementation Method 2
The mechanical device allows the CMC cap to have a different thermal expansion than the bolt
Data Source
AI summary
A fastener for a turbine engine includes a bolt and a ceramic matrix composite (CMC) cap mechanically secured to the bolt. CMC components are attached to an exhaust nozzle case with the fasteners. The fastener includes a bolt made of metal and having a head. A CMC cap is located on the head of the bolt and secured to the bolt by a mechanical device. The mechanical device allows the CMC cap to have a different thermal expansion than the bolt. The CMC cap also acts as a thermal shield for the bolt, aiding in the reduction of a heat signature of the turbine engine.