Abstract
The objective of this study is to evaluate and improve the accuracy and stability of a strain measurement method that uses the speeded-up robust feature (SURF) method to trace the displacement of feature points in microimages and obtain the strain in objects. The microimages were acquired using a smartphone with a portable microscope, which has a broad prospect of application. An experiment was performed using an unpacked optical fiber as the experimental carrier. The matching effect of the SURF method was analyzed in the microimage, and the M-estimator sample consensus (MSAC) algorithm was used to reject outliers generated by SURF. The results indicated that the accuracy of strain measurement using the proposed method is improved by modifying the feature point tracking method and measurement method. When compared with the fiber Bragg grating (FBG) data, the maximum standard error corresponded to 2.5 με, which satisfies the requirement of structural health monitoring (SHM) in practical engineering.
Highlights
Strain is an important parameter that reflects a structural state, which can be used to evaluate the mechanical properties, failure behavior, crack development, and residual stress of structural members and materials
In order to observe the stability of the proposed method, the experiment performed five repeatability experiments on each smartphone with different pixel values, and the results were compared with the fiber Bragg grating (FBG) measurement data
The accuracy and stability of the proposed method based on speeded-up robust feature (SURF) to track the displacement of feature points in microimages to measure the strain were verified via experiments
Summary
Strain is an important parameter that reflects a structural state, which can be used to evaluate the mechanical properties, failure behavior, crack development, and residual stress of structural members and materials. It plays an important role in the field of structural health monitoring (SHM). 20 years, several extant studies focused on and developed various methods for measuring strain. The application of the sensors requires a variety of expensive instruments. The sensors entail complex preparation, the instrument circuit layout is tedious, and it requires personnel with significant professional knowledge to operate
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