| Unsteady fracture is the main reason for the components failure such as stress concentration and crack propagation. Stress-Strain measurement and crack propagation monitoring have been the major problem in engineering for the large scale structure equipment. Quantum Dots (QDs), fluorescence nano-semiconductor materials, have extensive application in biological probe, solar cells and light emitting diodes due to their unique quantum effect property. Recently, luminescent nanocrystal stress-strain gauge has been developed by utilizing QDs luminescence characteristics under different pressure.Based on core/shell structured photo-luminescence (PL) QDs, QDs-Epoxy Resin composite materials was prepared by mixing with epoxy resin. Through coating on the surface of a standard compact tension (CT) specimen, the crack propagation dynamic visual monitoring was studied. The mechanism of visual fluorescent signal was analyzed by affect of conditions variation including volume concentration of QDs, fluorescence intensity of crack area, crack width, crack tip and the synchronicity of crack. Meanwhile, metal stress-strain distribution via optical response was investigated. The mechanism of PL intensity response was proposed by stress-strain curves, stress relaxation and QDs concentration variation of QDs-epoxy resin blank sample under tensile experiment and the Ansys calculation between metal and coating. Finally, the residual strain distribution was detected using a flat with a preset hole in the middle. The main research content and conclusions in this dissertation were as follows: (1) Preparation and tensile property of QDs-epoxy resin composite material A bisphenol-A type epoxy resin (6002) and modified amine curing agent (593) are selected as carrier due to the epoxy reduced the influence of QDs PL properties and kept good coating performance at the same time. Through adding different concentration of QDs in the same volume of epoxy resin solution, the spectral intensity changed in the linear range on the basis of 1:4. Based on standard addition amount, QDs-epoxy resin composite material wad prepared.Based on tensile property and optical response of QDs-epoxy resin composite material, we determined the QDs-epoxy resin composite material variation tendency of stress strain curve and PL intensity response. After investigating the temperature stability of QDs-epoxy resin composite material, the suitable temperature range had been proposed. The aging of epoxy resin made quantum dot PL phenomenon disappear when the temperature rise to 150℃.(2) Metal crack propagation of type I monitoring by photoluminescence enhancement of QDs-epoxy resin composite material.A visualization method to monitor type I metal crack propagation was presented in this paper. Through the enhanced PL intensity of QDs mixed into an epoxy resin film, this crack detection method provides a visualization signal in a real-time and non-contact fashion. The method realized rapid response of PL signal, crack detection of micron grade width. Also it could descript crack growth state accurately. The article confirmed the prerequisite for PL signal through a high frequency fatigue testing for a coating with metal compact tensile specimen. At the same time, the obvious PL signals and dynamic visual process of tracking crack propagation were obtained after stretching. Crack width as small as 1μm can be detected with a precision of 0.1 μm and the crack width range of QDs-epoxy resin was measured as 1-100 μm by investigating with metal crack width, location and the form of crack tip.(3) Synchronous growth and mechanism analysis of PL responseTo improve the synchronicity between resin film crack and metal crack, the experiment controlled the adding proportion. Meanwhile, it also avoided the slight delamination in the interface and crack deflection and made sure that synchronous growing with metal crack. At last, the mechanism analysis for this behavior is based upon different models of cracks which have been briefly proposed based on the experimental results.(4) Metal stress-strain monitoring via optical response of QDs-epoxy resin composite materialThe stretch of the standard flat tensile test specimen results in a slight strain on a QDs-epoxy resin composite coating extended along with the standard flat tensile. The intensity of coating has been demonstrated a sensitive optical response kept a linear variation. The accumulation effect of PL intensity in several cycles was caused by many factors including structure changing of QDs-epoxy resin, stress relaxation and strain rebound. The magnitude of PL intensity increase was consistent with the residual strain increase of QDs-epoxy resin in several cycles. The mechanism of PL intensity was proposed through investigating the concentration of QDs stock solutions, settling, and changes in QDs activity due to the increase of load and unload segment. In the end, the stress distribution and strain variation were consistent with the changing of PL intensity through tensile the flat with a hole in the middle. |
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