Gas Turbine Rotor Overspeed Treatment for Crack Life Extension
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Solution Overview
Problem
Gas turbine engine rotors are frequently scrapped due to crack propagation, leading to costly replacements, as existing methods fail to effectively extend the operational life of these high-value components beyond their predetermined life cycle limits.
Innovation Solution
The method involves rotating the rotor at speeds greater than 30% above normal operational cruise speed, with controlled temperature and cyclical loading to introduce compressive stresses around cracks, creating plasticized zones that inhibit crack propagation, thereby extending the rotor's operational life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If rotor is operated beyond predetermined life cycle limits, then operational life is extended, but crack propagation risk increases
Solution Approach 1:
The method applies preliminary compressive stress treatment to the rotor before it reaches its predetermined life cycle limits. By introducing beneficial compressive stresses through controlled overspeed rotation and thermal processing, the rotor is pre-conditioned to resist crack propagation, enabling safe extension of operational life beyond original limits.
Solution Approach 2:
The method changes physical parameters of the rotor by subjecting it to controlled thermal conditions (heating to specific temperature ranges) and mechanical stress conditions (rotation at speeds 10-50% above normal operational speeds). These parameter changes create plasticized zones and compressive stress fields that alter the rotor's resistance to crack propagation.
2Stress or pressure
If rotor speed is increased above normal operational cruise speed, then compressive stress is generated around cracks, but mechanical loading increases
Solution Approach 1:
The method employs periodic cycles of controlled overspeed rotation interspersed with thermal processing. The rotor is rotated at elevated speeds (10-50% above normal cruise speed) for specific durations, then subjected to thermal treatment. This periodic application of mechanical and thermal stimuli creates cumulative beneficial compressive stresses while managing peak mechanical loading through controlled cycle repetition.
Solution Approach 2:
The method utilizes thermal expansion and thermal stress principles by heating the rotor to specific temperature ranges (e.g., 100-500°C or 212-932°F) during the treatment process. The thermal conditioning modifies material properties and creates thermal stresses that, when combined with mechanical overspeed rotation, generate the desired compressive stress fields around crack regions.
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 effectively increases the operational life cycle of gas turbine engine rotors by slowing crack propagation, allowing for additional use of expensive components beyond their initial life cycle limits, as demonstrated by the creation of beneficial compressive stress regions around cracks.
Implementation Method 1
rotating the rotor at speeds greater than 30% above normal operational cruise speed, with controlled temperature and cyclical loading to introduce compressive stresses around cracks, creating plasticized zones that inhibit crack propagation
Data Source
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AI summary
A method of refurbishing a gas turbine engine rotor is disclosed and includes an initial step of inspecting a rotor for defects such as cracks. A strain is then generated around any detected cracks in the rotor to create enhanced plasticized zones about the detected defects that delay defect propagation. Strain is generated by rotating the rotor at speeds greater than operational speeds to induce the desired strain and delay the propagation of defects.