Mechanoluminescence technique for real-time monitoring of cracks produced during application of loads on crystals

Abstract

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When a load is applied on to a crystal, then the fracto- mechanoluminescence (ML) emission takes place in the form of light pulses. The number of ML pulses and the time duration <i style="">t</i>_c for the appearance of ML increase with increasing value of the load and the average ML intensity from a single ML pulse decreases with increasing value of the load. For a given value of the applied pressure, the total number <i style="">N</i>_Tof ML pulses, the total ML intensity <i style="">I</i>_T and the time duration <i style="">t</i>_c of ML emission increase with increasing size of the crystals. As the total ML intensity is directly related to the area of newly created surfaces, the pressure dependence of the total ML intensity indicates that initially the total area of newly created surfaces increases with increasing value of the applied load and later on it tends to attain a saturation value for higher values of the applied load. As the strain rate is maximum at a particular time after the application of load on to a crystal, the rate of the emission of ML pulses is maximum at a particular time after the application of load on to the crystals. The dependence of <i style="">N</i>_T, <i style="">I</i>_T, and <i style="">t</i>_c on the applied pressure <i style="">P</i>_ofollows the following expressions, respectively

<i style=""> N</i>_T = <i style="">M</i>_o <i style="">V</i>^y [1 – exp{–δ_c (<i style="">P</i>_o – <i style="">P</i>_f)}]

<i style=""> I</i>_T = <i style="">D b M</i>_o <i style="">V</i> [1 – exp{–δ_c (<i style="">P</i>_o – <i style="">P</i>_f)}]

and, t_c=1/αln( P₀/P_f) where <i style="">V</i> is volume of crystal, <i style="">y</i> is an exponent, δ_c =1/<i style="">P</i>_c, <i style="">P</i>_c is the critical pressure, <i style="">P</i>_fis the fracture stress, <i style="">M</i>_o, <i style="">D</i>, <i style="">b</i>, and α are constants. A good agreement is found between the theoretical and experimental results.

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