Material Performance Testing with Averaged Load Line Displacement
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Solution Overview
Problem
Existing material testing systems for fracture properties, such as the I-FIT and AASHTO TP 124-16, suffer from inaccuracies in Load Line Displacement (LLD) measurements due to unaccounted variations in the load head deformation, leading to incorrect Flexibility Index (FI) results.
Innovation Solution
Implementing multiple LLD measurement devices, such as non-contact magneto restrictive position transducers, on opposing sides of the specimen to accurately measure and combine displacement data, correcting for machine compliance and ensuring consistent LLD rate through feedback control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single LLD measurement device is used to measure displacement, then the device complexity is reduced, but the measurement precision deteriorates due to unaccounted load head deformation
Solution Approach 1:
The measurement system is segmented into multiple independent LLD measurement devices positioned at different locations (e.g., opposite sides) of the load head. Each device measures displacement independently, and the measurements are combined through averaging to cancel out deformation biases, achieving higher measurement precision without requiring a single complex measurement system.
Solution Approach 2:
Multiple LLD measurement readings from different positions on the load head are merged through averaging to produce a single corrected displacement value. This combining approach eliminates the need for complex individual measurement devices while improving overall measurement accuracy by canceling out systematic errors.
2Reliability
If multiple LLD measurement devices are used on opposing sides of the specimen, then the measurement precision is improved by canceling biases, but the device complexity increases
Solution Approach 1:
The measurement devices are positioned asymmetrically on opposing sides of the load head, which allows them to capture different deformation patterns. By placing sensors at symmetric but opposite locations, the system exploits the asymmetry in deformation modes to cancel out biases when averaging the readings, thereby improving reliability.
Solution Approach 2:
The system uses the combined measurements from multiple devices to provide feedback on the actual displacement, which is then used to control the actuator and maintain the target LLD rate. This feedback loop ensures consistent and reliable test results by continuously correcting for measurement biases.
3Measurement precision
If LLD measurements are not corrected for machine compliance, then the ease of operation is maintained, but the measurement precision deteriorates leading to incorrect FI results
Solution Approach 1:
The system performs preliminary measurements using multiple LLD devices before the actual test to establish baseline deformation characteristics. This preliminary action allows the system to pre-calculate correction factors or averaging weights that compensate for machine compliance during the actual test, maintaining ease of operation while improving precision.
Solution Approach 2:
The measurement system self-corrects for machine compliance by using its own multiple sensors to detect and average out deformation biases. The system serves itself by internally compensating for errors without requiring external calibration or complex manual corrections, thereby maintaining ease of operation while improving FI measurement accuracy.
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
Enhances the accuracy and reliability of FI measurements by canceling out measurement biases, resulting in more consistent and reliable test results.
Implementation Method 1
non-contact magneto restrictive position transducers
Data Source
AI summary
A material testing apparatus includes an actuator to apply a force to a load head according to electronic control signals. The load head supplies a load to a material specimen in a first dimension. A plurality of load line displacement (LLD) reference points extend radially outward from the load head; and a plurality of LLD measuring devices correspond to the plurality of LLD reference points. Each LLD measuring device is positioned to detect a position of a corresponding LLD reference point along the first dimension and is configured to transmit position signals to a controller programmed to perform a performance test on the material specimen using feedback control based on a combination of the position signals, including an average of the position signals.