Optical Fiber Sensor for Bonding Quality Detection
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Solution Overview
Problem
Ultrasonic testing cannot evaluate the strength of bonding in adhesive layers, as it cannot measure pressure applied during bonding, and requires time, labor, and a certified inspector, making it inefficient for assessing bonding quality, especially in carbon fiber composite materials.
Innovation Solution
A bonded structure with an optical fiber sandwiched between members, using birefringence to detect bonding conditions by deforming the optical fiber's shape under pressure, allowing for the determination of appropriate bonding based on multiple peaks in the light spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ultrasonic testing is used to detect bonding quality, then voids and defects can be detected, but bonding strength cannot be evaluated and the process requires time, labor, and certified inspectors
Solution Approach 1:
The patent replaces the mechanical ultrasonic testing system with an optical sensing system. An optical fiber sensor embedded in the adhesive layer detects bonding conditions through optical measurements, eliminating the need for mechanical contact and certified inspectors while providing real-time data during the bonding process itself
Solution Approach 2:
The bonding process itself generates the measurement data. The optical fiber sensor is embedded in the adhesive layer during bonding, and the bonding conditions (pressure, temperature, curing state) directly affect the optical properties of the fiber, allowing the system to self-monitor without separate inspection steps
2Strength
If pressure is applied to members during bonding, then bonding strength is improved, but the pressure cannot be measured by conventional methods
Solution Approach 1:
The optical fiber acts as an intermediary between the bonding pressure and the measurement system. The fiber is embedded in the adhesive layer and translates mechanical pressure into optical signal changes through birefringence, allowing indirect but accurate measurement of bonding pressure without interfering with the bonding process
Solution Approach 2:
The patent utilizes changes in optical parameters (birefringence, refractive index) of the optical fiber in response to pressure, temperature, and curing state changes during bonding. These parameter changes provide direct measurement of bonding conditions that correlate with bonding strength
3Reliability
If safety margins are increased or fasteners are used instead of adhesive bonding, then bonding reliability is improved, but weight increases and working efficiency decreases
Solution Approach 1:
The optical fiber sensor provides real-time feedback on bonding conditions (pressure, temperature, curing state) during the bonding process. This feedback allows operators to optimize the bonding process to achieve reliable bonds without excessive safety margins, eliminating the need for over-design while maintaining bonding reliability
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
Enables accurate determination of bonding quality without the need for certified inspectors or time-consuming processes, ensuring appropriate pressure application and reliable bonding in carbon fiber composite materials.
Implementation Method 1
the bonding condition between the first member and the second member is detected based on birefringence of the optical fiber... when a pressure is applied to the optical fiber only from a predetermined direction, the sectional shape of the optical fiber, which was originally a circular shape, is deformed to become, for example, an elliptical shape
Data Source
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AI summary
A joined structure (10) is provided with a laminate sheet (12A), a laminate sheet (12B), an adhesive (14) that joins the laminate sheet (12A) and the laminate sheet (12b), and an optical fiber (16) that is sandwiched between the laminate sheet (12A) and the laminate sheet (12B). As a result of the cross-sectional shape of the optical fiber (16) changing to an elliptical shape only when pressure is applied to the optical fiber (16) from a predetermined direction, birefringence that changes to a shape having a plurality of peaks (2, for example) occurs in the optical spectrum. The optical fiber (16) can be used as a sensor for detecting the joined state of the laminate layer (12A) and the laminate layer (12B) using the birefringence. As a result, it is possible to determine whether the members of the joined structure (10) are suitable joined.