Dynamic Stiffness Measurement Using Laser and Impact Force
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Solution Overview
Problem
Existing methods for determining the stiffness of structures only measure static stiffness and fail to provide insight into dynamic stiffness, especially under low-frequency dynamic loads, which can vary significantly from static stiffness.
Innovation Solution
A system comprising a test member connected to the structure, a beam generator, an impactor, and a controller, where a beam of light is directed at a measurement surface, and the impactor applies a known impact force, allowing the controller to determine the movement of the measurement surface and calculate the stiffness based on this movement, enabling the measurement of both static and dynamic stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If static load testing with string pot is used to measure stiffness, then static stiffness measurement is achieved, but dynamic stiffness information is lost
Solution Approach 1:
The system transitions from static measurement to dynamic measurement by applying dynamic impact forces and measuring the structure's dynamic response. The impactor delivers time-varying forces while the laser measures dynamic displacement, enabling stiffness characterization across different frequencies including low-frequency dynamic conditions.
Solution Approach 2:
The system replaces the mechanical string pot measurement system with an optical laser measurement system. This substitution enables non-contact, high-precision measurement of dynamic displacements while maintaining the ability to measure static conditions, thereby expanding the frequency range coverage without sacrificing measurement precision.
2Adaptability or versatility
If dynamic impact testing is implemented to measure dynamic stiffness, then frequency-dependent stiffness information is obtained, but measurement complexity increases
Solution Approach 1:
The system achieves multi-functionality by integrating both static and dynamic measurement capabilities into a single unified platform. The laser measurement system can operate in both static and dynamic modes, and the data processing methodology can handle both static stiffness and dynamic stiffness (including frequency response functions), eliminating the need for separate testing systems.
Solution Approach 2:
The system utilizes parameter changes in the impact force (magnitude, duration, location) and the resulting dynamic response to extract stiffness information at different frequencies. By varying these parameters systematically, the system can characterize the structure's stiffness across a range of dynamic conditions without requiring fundamentally different measurement approaches.
3Adaptability or versatility
If comprehensive dynamic testing is performed to capture stiffness across frequencies, then low-frequency dynamic stiffness is measured, but testing time and labor increase
Solution Approach 1:
The impactor delivers a rapid impulsive force that excites the structure across a broad frequency range in a single brief event. This allows the system to capture dynamic stiffness information at multiple frequencies simultaneously during one quick impact, rather than requiring slow, sequential testing at each frequency point, thereby significantly reducing the total measurement time.
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 method allows for the accurate determination of both static and dynamic stiffness, reducing the time and labor required for measurements and providing a more comprehensive understanding of a structure's behavior under various frequencies and loads.
Implementation Method 1
directing a beam of light at a measurement surface carried by at least one of the test member or the structure
Implementation Method 2
The movement of the measurement surface may be determined as a function of changes in the length of the beam of light
Implementation Method 3
impacting an impact surface carried by the test member with a known impact force
Data Source
AI summary
In at least one implementation, a method for determining the stiffness of a structure may include connecting a test member to the structure, directing a beam of light at a measurement surface carried by at least one of the test member or the structure, impacting an impact surface carried by the test member with a known impact force, and determining the movement of the measurement surface that is caused by the impact. The movement of the measurement surface may be determined as a function of changes in the length of the beam of light and the stiffness of the structure may be a function of the magnitude of the measurement surface movement.