Multivariate Characterization of Light Emission From ZnS:Cu-PDMS Self-Sensing Composites Under Cyclic Tensile Strains

The objective of this work is to understand multivariate elastic-mechanoluminescent (EML) light emission characteristics of copper-doped zinc sulfide (ZnS:Cu)-embedded polydimethylsiloxane (PDMS) self-sensing composites subjected to sinusoidal tensile loading and unloading cycles. To investigate the effect of tensile strain and strain rate on the EML light emission profiles (i.e., intensity and color) of the ZnS:Cu-PDMS composites, which are fabricated with different gage lengths (i.e., 150 and 4.7 mm). Each specimen is subjected to cyclic tensile loading and unloading with various maximum strains at various loading frequencies, and the EML light emission is video-recorded and subjected to image processing for quantifying intensity and color of EML light. The test specimen with 150-mm gage length is loaded and unloaded between 0% and a maximum tensile strain, which varies from 16% to 30%, at 1 Hz. The shorter specimen is subjected to tensile loading and unloading cycles between 0% and 15% strain at a frequency varying from 5 to 80 Hz. It is revealed that the EML light emission is triggered at a threshold tensile strain rate, and the light intensity increases as the composites undergo deformation during both loading and unloading cycles. This multistep EML light emission is attributed to the unique light emission mechanism of ZnS:Cu-embedded in soft PDMS matrix, which is a result of friction at the ZnS:Cu-PDMS interface, unlike other deformation-triggered light emitting EML materials.