Multi-Actuator Fatigue Testing Apparatus for Arbitrary Multiaxial Loads
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Solution Overview
Problem
Conventional fatigue testing machines are limited in their ability to apply arbitrary combinations of loads across multiple degrees of freedom, restricting their capability to simulate real-world stress conditions on structural components, and they often face a trade-off between frequency and amplitude, lacking high authority mutiaxial loading capabilities.
Innovation Solution
A fatigue testing apparatus comprising a first platform, a second platform, actuator assemblies with servo-control and position encoders, a load cell for force and torque measurements, and a direct-strain imaging system, along with a local sense and control system that can apply complex, time-varying loads across six degrees of freedom, enabling high authority mutiaxial loading with multispectral content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional single degree-of-freedom fatigue testing machines are used, then the device complexity is low, but the adaptability to test arbitrary combinations of loads across multiple degrees of freedom is limited
Solution Approach 1:
The system segments the loading function into six independent actuator assemblies, each controlling one degree of freedom. This allows arbitrary combinations of loads to be applied independently to the specimen while keeping each individual actuator relatively simple, thus achieving high adaptability without excessive overall complexity.
Solution Approach 2:
The six actuator assemblies work together as a universal system that can apply any combination of loads across all six degrees of freedom. The system is designed to be multi-functional, capable of testing specimens under any arbitrary loading condition rather than being limited to specific load types.
2Adaptability or versatility
If conventional fatigue testing machines apply only cyclic forces, then the device complexity remains manageable, but the adaptability to simulate real-world stress conditions with arbitrary time evolution is restricted
Solution Approach 1:
The control system is designed to be dynamic and adaptive, allowing the loading parameters to change arbitrarily over time. Each actuator can independently vary its force magnitude and timing, enabling the system to simulate any time-evolution pattern of stress conditions rather than being limited to simple cyclic patterns.
Solution Approach 2:
The system uses feedback from load cells and position encoders to continuously monitor the actual forces and positions, allowing the control system to adjust and maintain arbitrary loading profiles with high precision, thus achieving adaptability without unmanageable complexity.
3Productivity
If high frequency loading is applied in conventional systems, then the productivity of fatigue testing increases, but the achievable kinematic amplitude and force magnitude decrease significantly
Solution Approach 1:
By segmenting the loading function across six independent actuators, the system can distribute the total force requirement among multiple actuators. This allows high-frequency operation while maintaining high force magnitude, as each actuator operates within its capability but their combined effect achieves the desired high authority loading.
Solution Approach 2:
The system merges the capabilities of six actuators to achieve combined force and displacement outputs that exceed what any single actuator could produce. This combination allows simultaneous achievement of high frequency, high amplitude, and high force magnitude.
4Measurement precision
If conventional systems achieve high kinematic amplitude, then the measurement precision of strain and deformation improves, but the available frequency range shortens significantly
Solution Approach 1:
The system is designed with universal capability to simultaneously achieve high kinematic amplitude and high frequency across all six degrees of freedom. The coordinated operation of multiple actuators allows the system to maintain large amplitudes even at high frequencies, unlike conventional single-degree-of-freedom systems where these parameters are inversely related.
Data Source
AI summary
Methods and apparatuses for multiple degree-of-freedom fatigue testing of a specimen. The apparatus includes a first platform, a second platform, a plurality of actuator assemblies, a load cell, a mounting plate, a specimen support, a direct-strain imaging system, and a local sense and control system. Each actuator assembly includes a servo-control, a position encoder, and a piston that is constructed to move in a linear direction in accordance with the servo-control. Each piston is rotatably connected to the second platform. The load cell is connected to the second platform and constructed to output force measurements in three orthogonal directions and torque measurements about the three orthogonal directions. The mounting plate is constructed to hold a portion a specimen. The specimen support is constructed to hold another portion of the specimen. The direct-strain-imaging system includes a camera that is constructed to record a plurality of images of the specimen during fatigue testing. The local sense and control system constructed to receive: a loading specification, the force measurements and torque measurements from the load cell, and position information from each position encoder, and output control commands to each servo-control of the plurality of actuator assemblies based on the received loading specification. The control commands are updated in time in accordance with the position information from each position encoder and the force measurements and torque measurements from the load cell.