The Experimental Research And Measurement Of Material Surface’s Strain Field Based On Photoelastic Coating

Electrical measurement with electric resistance strain gauge is one of commonly used measurement methods for surface strain (stress).The measuring method based on strain-resistance effect has advantages of high sensitivity and small error,however, it is a kind of point measurement method can only measure very small areas of average strain for the component surface and can not illustrate the strain field distribution of the measured areas.Photoelastic coating method using strain-optical interference effect of photosensitive material to measure strain(stress) of component surface,it is a kind of surface strain field measurement method developed based on the traditional photoelastic measuring technique.The photoelastic coating method can show a large area strain (stress) field image of component surface. It can show a large area strain (stress) distribution and not just the average strain of a small area value.Therefore,the study on the measurement of strain in photoelastic effect can provide a visual pattern method for regional strain field measurement of component surface.The measurement results of resistance strain gauge method is not easy to interpret distribution of the surface strain field.To solve this problem, the article carried out the material surface strain measurement with photoelastic coatings.The research work of photoelastic production, material calibration, fringe image processing and so on are carried out. To carry out further research work,photoelastic coatings are applied to metallic and concrete strain field measurement.The main research contents are as follows:(1) Production process of photoelastic coating are studied.In the production process of photoelastic coating,some effective measures are adopted to solve proplems of the patch inside bubbles, uneven thickness, the surface is not smooth etc.The photoelastic coating material fringe value was calibrated with uniform beam,and stress enhancement effect on the calibration results of the coatings was revised.(2) Through the loading experimentd of several typical photoelastic shapes,the measurement and analysis methods of isochromatic, isocline, separation of principal stress are mastered.(3)To make the photoelastic fringe clarity and to be understood better,the image processing technique of photoelastic coating fringe was studied.Image denoising, the isochromatic analysis and skeleton extraction work is carried out and image processing software was compiled for fringe image processing.(4) Study on measureing application of photoelastic coating was carried out to measure the metal and concrete surface strain field.Photoelastic coatings are applied to measure the strain field of simply supported beam,comparing with strain gauge, strain value on weak spots obtained by photoelastic coatings was analysis. In loading test of concrete specimens, the variation of strain fringe in the process of which the surface crack of the concrete specimen appears, propagates and finally is fractured is obtained.