Stress Response Mechanism Of Rare Earth Ion Doped YAG-Al₂O₃ Fluorescent Fibers Reinforced Aluminum Matrix Composites

Stress and strain in the deformation zone have very important impact on the performance of fiber reinforced aluminum matrix composites,but it is still difficult to detect and analyze the stress-strain intuitively.Rare earth ions have rich fluorescence lines and high fluorescence emission intensity.It is easy to find the position of the peak wavelength,which provide more possibilities for the selection of force-sensitive characteristic materials required for fluorescence spectrometry to measure stress.In this paper,the rare-earth ion(Tb³⁺/Eu³⁺)as a luminous center were doped into the YAG-Al₂O₃ composite short-nanofibers,Tb³⁺/Eu³⁺doped YAG-Al₂O₃ fluorescent nanofibers were prepared by an electrospinning method(Tb³⁺doped and Eu³⁺doped YAG-Al₂O₃composite short-nanofibers are abbreviated as(YAG:Tb³⁺-Al₂O₃)_csf and(YAG:Eu³⁺-Al₂O₃)_csf in the following description,respectively).This method makes the reinforcing fiber have excellent luminous performance.And afterwards these luminescent fibers were compounded with aluminum alloy powders and sintered to form fiber-reinforced composites((YAG:Tb³⁺-Al₂O₃)_csf and(YAG:Eu³⁺-Al₂O₃)_csf reinforced Al matrix composites are abbreviated as(YAG:Tb³⁺-Al₂O₃)_csf/Al and(YAG:Eu³⁺-Al₂O₃)_csf/Al composites in the following description,respectively).The effect of fibers addition amount on the mechanical properties of composites have been studied in detail and the changes of emission spectrum of the fluorescence fiber-reinforced aluminum matrix composites under different tensile stresses were studied by the spectral response.The response mechanism of fiber fluorescence emission peak frequency shift to tensile stress was expounded.The main findings are as follows:?1?A series of Tb³⁺/Eu³⁺were doped into YAG-Al₂O₃ composite short nanofibers by electrospinning.The crystal structure,microstructure and luminescent properties of fluorescent nanofibers were studied.The fluorescent nanofibers(YAG:Tb³⁺-Al₂O₃)_csfsf and(YAG:Eu³⁺-Al₂O₃)_csf showed stronger luminescence characteristics when Tb³⁺/Eu³⁺was added in an amount of 5 mol.%.The emission spectrum of(YAG:Tb³⁺-Al₂O₃)_csfsf emits green light at 543 nm,which belongs to the ⁵D₄-⁷F₅ transition of Tb³⁺.The emission spectrum of(YAG:Eu³⁺-Al₂O₃)_csf shows the ⁵D₀-⁷F_{J?J=0,1,2,3,4?}transitions of Eu³⁺and exhibits a strong orange-red emission at a wavelength of 592 nm.?2?Combining(YAG:Tb³⁺-Al₂O₃)_csf with aluminum alloy matrix,the effects of(YAG:Tb³⁺-Al₂O₃)_csf on the mechanical properties such as density,tensile strength and hardness of aluminum matrix composites were studied.The ultimate tensile strength?UST?of(YAG:Tb³⁺-Al₂O₃)_csf/Al composite is 300.1 MPa when the content of fiber was 1 wt.%.The barycenter wavelength of fluorescence emission spectrum of(YAG:Tb³⁺-Al₂O₃)_csf/Al composite as the sensing signal for tensile stress,the stress sensing equation was?=546.6817-0.0042?,and the sensitivity is 0.0042 nm/MPa.The barycenter wavelength of fluorescence emission spectrum was obviously blue shifted with the tensile stress.?3?(YAG:Eu³⁺-Al₂O₃)_csf prepared by electrospinning had a stress-luminescence property and can effectively improve the mechanical property of the aluminum matrix composites.(YAG:Eu³⁺-Al₂O₃)_csf/Al composites have stress-sensitive properties.With the increase of tensile stress,the barycenter wavelength of fluorescence emission spectrum shifts red.There is a good linear relationship between the applied stress and the barycenter wavelength of fluorescence spectral band,the stress-sensing equation?=594.69539+0.01437?.The frequency shift coefficient of(YAG:Eu³⁺-Al₂O₃)_csf/Al composites under tensile stress is 0.40523 cm^-1/MPa,which is approximately 73 times the pressure spectrum coefficient(5.5 cm^-1/GPa)of the standard fluorescence pressure spectrum material ruby.?4?The barycenter wavelength of fluorescence spectral band can be used as a force sensitive signal to detect tensile stress.Under the same experimental conditions,(YAG:Eu³⁺-Al₂O₃)_csf/Al composites show higher tensile stress sensing accuracy,and the frequency shift coefficient of(YAG:Eu³⁺-Al₂O₃)_csf is 34 times of(YAG:Tb³⁺-Al₂O₃)_csf.Consequently,the relationship between the barycenter wavelength of ⁵D₀?⁷F₁electron transition of Eu³⁺and stress can be applied to stress sensing,characterizing the internal stress-strain of the composite to a certain extent.