High Resolution Strain Gages for Ceramic Matrix Composites
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Solution Overview
Problem
Conventional strain gages, such as NiCr strain gages, are inadequate for accurately measuring strain at high temperatures due to limited gage factor and stability issues in harsh environments like gas turbine engines, where ceramic matrix composites (CMCs) are used, requiring a high-resolution strain gage capable of operating beyond 1000°C.
Innovation Solution
A strain gage comprising a ceramic matrix composite (CMC) layer with a conductive material like platinum, integrated with an oxygen diffusion barrier and silicide diffusion barrier, allowing for high-temperature operation and improved stability, using either thin or thick film technology to ensure compatibility with CMCs and eliminate the need for vacuum chambers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional NiCr strain gages are used, then they are well understood and generally available, but they provide insufficient gage factor and stability at high temperatures
Solution Approach 1:
The patent changes the material parameter from conventional NiCr alloy to semiconductor materials (silicon, germanium, silicon carbide) which exhibit fundamentally different piezoresistive properties. These semiconductor materials provide significantly higher gage factors and maintain stability at elevated temperatures up to 1000°C, directly resolving the contradiction between measurement precision and high-temperature reliability
Solution Approach 2:
The patent employs composite structures combining semiconductor strain gage elements with ceramic matrix composite substrates and protective coatings. This composite approach enables the strain gage to withstand harsh high-temperature environments while maintaining measurement accuracy, addressing both the precision and reliability requirements
2Ease of operation
If thin film sensors are used, then they have low profile and minimal mass, but they exhibit decreased stability at elevated temperatures due to small diffusion distances
Solution Approach 1:
The patent utilizes thin film deposition techniques to create low-profile strain gage structures that conform to the surface of turbine blades. The thin film configuration maintains the aerodynamic advantages of minimal mass and low profile while incorporating protective ceramic layers and diffusion barriers to enhance high-temperature stability
Solution Approach 2:
The patent introduces intermediate protective layers including ceramic matrix composite substrates and diffusion barrier coatings between the thin film semiconductor element and the harsh environment. These intermediary layers protect the thin film from thermal degradation while preserving its low-profile characteristics
3Reliability
If strain gages are designed to survive high temperatures and rotational forces, then they can monitor CMC components, but instrumentation becomes increasingly difficult without adversely affecting engine operation
Solution Approach 1:
The patent designs the strain gage system to serve multiple functions simultaneously: measuring strain, withstanding high temperatures, resisting rotational forces, and maintaining electrical connectivity. The integrated ceramic matrix composite structure provides both structural support and sensor functionality, reducing overall device complexity while achieving high-temperature reliability
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 solution provides significantly higher gage factors, improved stability, and enhanced resolution for strain measurements at extreme temperatures, enabling accurate mechanical strain monitoring independent of thermal strain, with the ability to operate up to 1768°C and beyond.
Implementation Method 1
The strain gage preferably comprises an oxygen diffusion barrier deposited on the conductive material in a vicinity of the openings. The oxygen diffusion barrier preferably comprises indium oxynitride or indium-tin-oxynitride.
Implementation Method 2
When the conductive material comprises a metal, or any material that is not a silicide diffusion barrier, the strain gage preferably comprises a silicide diffusion barrier deposited between the metal (or other material) and the CMC layer.
Implementation Method 3
A strain gage (or strain gauge) is a device that measures the strain on an object. While NiCr strain gages have been on the market for some time now and are generally well understood, the measured gage factor (or gauge factor) associated with NiCr strain gages are only sufficient for low to moderate temperature strain measurements.
Data Source
AI summary
Strain gages for use with ceramic matrix composites (CMCs), and methods of manufacture therefore. The strain gages use the CMC as a strain element. For semiconductor CMCs, for example SiC fiber-reinforced SiC CMC, their large gage factor enables high sensitivity, high accuracy strain measurements at high temperatures. By using a single elemental metal such as platinum, or another high temperature conductive material, the strain gages can operate at temperatures over 1600° C. The conductive material is preferably deposited on a dielectric or insulating layer, and contacts the CMC substrate through openings in that layer. The materials can be deposited using thin film vacuum techniques or thick film techniques such as pastes or inks. The strain gages can be configured to measure only the mechanical strain independent of the apparent or thermal strain. The strain gages can be incorporated into a bulk CMC structure during layup, and can optionally measure the strain of only desired fiber weave orientations.