Fatigue Crack Testing With Constant Strain Energy Release Rate
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Solution Overview
Problem
Current methods for determining structural fatigue properties in composite structures are time-consuming and expensive, making it difficult to identify potential failure modes during design, testing, and certification.
Innovation Solution
A method and test system that utilize a load frame and computer to apply adjustable stimuli to a structure, maintaining a constant strain energy release rate, and automatically calculate crack propagation using virtual crack closure techniques and linear elastic fracture mechanics, reducing the need for manual measurements and adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If physical testing with representative damage is used to verify fatigue damage, then airworthiness compliance and certification are achieved, but the testing is time-consuming and expensive
Solution Approach 1:
The patent uses digital twins (virtual models) to replicate physical structures and their fatigue behavior. Instead of extensively testing physical specimens, the digital twin simulates crack propagation and fatigue damage under various loading conditions, providing certification data with much reduced testing time and cost while maintaining reliability
Solution Approach 2:
The patent replaces physical mechanical testing with computational mechanics simulations. The digital twin uses fracture mechanics models and material behavior algorithms to predict fatigue properties, substituting expensive and time-consuming physical tests with efficient computational analysis
2Reliability
If physical testing with representative damage is used to verify fatigue damage, then airworthiness compliance is achieved, but the cost is high
Solution Approach 1:
The digital twin creates virtual replicas of physical structures, allowing multiple test scenarios to be evaluated computationally rather than physically. This eliminates the need to manufacture and test multiple physical specimens, dramatically reducing material costs, equipment usage costs, and labor expenses while maintaining certification validity
Solution Approach 2:
The patent substitutes expensive physical testing infrastructure and procedures with computational mechanics models. The digital twin runs simulations on standard computing hardware rather than requiring specialized testing equipment, reducing capital investment and operational costs significantly
3Measurement precision
If manual measurement of crack size is performed, then crack propagation data is obtained, but the process is time-consuming and requires operator intervention
Solution Approach 1:
The digital twin automatically tracks and measures crack size through computational algorithms that analyze simulation data. The system self-updates crack propagation measurements without requiring manual intervention, maintaining precision while dramatically improving productivity by eliminating operator bottlenecks
Solution Approach 2:
The patent replaces manual measurement processes with automated computational methods. The digital twin uses image processing algorithms and fracture mechanics models to continuously monitor crack growth, substituting human operators with intelligent software that provides both precision and high-speed data collection
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 significantly reduces the number of cycles required for fatigue testing, providing accurate and reliable fatigue property data with fewer specimens, thereby saving time and resources while improving the precision of failure mode identification.
Implementation Method 1
determining fatigue properties of a structure... applying repeatedly an adjustable stimulus to the structure over a plurality of cycles
Implementation Method 2
updating the crack size based on the response in each of the plurality of cycles... calculating a new value of the crack size with an analytical technique based on a compliance calculation
Implementation Method 3
updating the adjustable stimulus in each of the plurality of cycles. The adjustable stimulus as updated maintains a strain energy release rate approximately constant based on the crack size
Data Source
AI summary
A method for determining fatigue properties of a structure includes mounting the structure in a load frame. The structure has a crack with a crack size. The method includes applying repeatedly an adjustable stimulus to the structure over multiple cycles. The adjustable stimulus is an adjustable load or an adjustable displacement applied to the structure. The method further includes storing the crack size at a start of the cycles, measuring a response of the structure subjected to the adjustable stimulus in each cycle, updating the crack size based on the response in each cycle, and updating the adjustable stimulus in each cycle. The adjustable stimulus as updated maintains a strain energy release rate approximately constant based on the crack size. The method includes calculating a growth rate of a crack propagation in the structure based on the response in each cycle, and storing the growth rate in a file.