Mechanical properties of poly(ethylene terephthalate) at the near surface from depth-sensing experiments

Abstract

The viscoelastic-plastic properties of glassy poly(ethylene terephthalate) in the micron and submicron range have been investigated by means of load-displacement analysis from depth-sensing experiments. Experimental data have been modelled using two methods: firstly assuming the elastic behaviour during initial unloading to be that of a cylindrical punch; secondly using a power-law relation. The creep behaviour under the indenter has been examined. Furthermore, the influence of the maximum penetration depth and loading and holding times on the hardness values are discussed. Hardness data from the depth-sensing and imaging methods are shown to be in good agreement. When using the depth-sensing method, hardness values are shown to be constant with decreasing penetration depth (0.5 μm ≤ hmax 9 μm), provided that a correction procedure to account for the indenter tip defect is applied. Young's modulus derived from the compliance method has been studied and results are discussed in the light of the various testing conditions employed.