FINITE ELEMENT BASED SMALL PUNCH TESTING METHOD FOR STIFFNESS MEASUREMENT OF POLYMERS
X. Chen, C.P. Tsui, C.Y. Tang UDC: (620.179.2:678.71]:519.673)
Mechanical evaluation of a small size specimen is of great necessity. The small punch testing method, as one of the most commonly adopted techniques, was successfully used in determination of elastic modulus for small polymeric specimens. However, the ring support design in this method resulted in an inappropriate specimen-support contact, such as the large contact area and probably the partially non-contact condition, thus lowering the accuracy and sensitivity. In the present study, a finite element based small punch testing method has been developed to determine the elastic moduli of small polymer specimens. In order to measure the initial stiffness, a three-point support based small punch testing device rather than the conventional ring support type was designed and produced for conducting an indentation process. A finite element model for the indentation process was built for determining the elastic moduli of the polymer specimens from the measured initial stiffness through the computed correlation between the elastic modulus and initial stiffness. The differences between the elastic moduli of the PE, PP and PMMA specimens with certain Poisson’s ratios determined by the developed method and those from the standard tensile tests were found to be not statistically significant. With a reduction in the contact area and an elimination of the potential non-contact condition for the specimen-support contact, the developed finite element based method has been shown to be more accurate and sensitive in terms of the determined elastic modulus as compared with the ring-support based small punch testing method. This method may be served as a promising tool for determining the elastic modulus of small polymeric specimens with high sensitivity and accuracy.