Indentation of poly(formaldehyde), reinforced nylons and poly(ethyl terephthalate)

Indentation tests were performed on flat coupons of poly(formaldehyde), three types of reinforced nylon and reinforced poly(ethyl terephthalate) using a device developed for a typical universal tensile testing machine. Spherical, conical and cylindrical indenters were selected for this study and the effects of indenter shape combined with the rate of indentation on the behavior of these materials were examined. The load‐depth relationship during the indentation process revealed the emergence of step‐like transitions at high indentation rates. The effects of the assessed parameters on the indentation resistance, as defined in this study, were analyzed. Interest was also focused on the investigation of the deformation work as well as the plastic work taking place for a total depth that incorporated both the skin and part of the bulk of the material. The modeling of the data was based on a previously developed approach and the introduction of a modified parameter that took not only the geometrical characteristics of the indenter into account but also the indentation depth. The proposed method has proven to be useful since a steady state of the indentation pressure was observed for all materials after a certain depth of indentation. This was valid for the results obtained using both conical and cylindrical indenters. Polym. Eng. Sci. 44:1439–1447, 2004. © 2004 Society of Plastics Engineers.