Comparative Nano-indentation Creep Study of Ductile Metal, Ductile Polymer and Polymer-fly Ash Composite

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Anew study is conducted under same experimental creep conditions to investigate and compare the response of dissimilar materials (metals, polymers and composites) in relation to properties such as hardness and (unloading) ‘reduced modulus’ on changing the nano-indentation test parameters. The research uses nano-indentation technique to determine the resistance to plastic deformation in these broadly different materials as a function of maximum load, holding time and loading rate. Wear rate and cutting efficiency of these materials are examined and it is found that only maximum load alters these properties in the three materials. Hardness and ‘reduced modulus’ are found to be directly affected by increase or decrease in maximum load, holding time and loading rate.

H: Hardness;E_r: Effective Modulus; h: Indentation Depth; h_max: Maximum Indentation Depth at Maximum Load; h_c: Indentation Depth in contact with Indenter; hp: Height of Sink-in/pile-up; h_e: Elastic Recovery Height after Unloading; h_c/h_max: Degree of Sink-in/ pile-up; H/E_r ²: Rate of wear or Resistance to Plastic Deformation; A: Area of Indentation; S: Stiffness; β: Correction Factor for Indentation Shape; n value: Work Hardening Coefficient Value.

A concept of determining the mechanical properties of material on nano scale has given rise to the development of a powerful depth sensing nano-indentation technique which is capable of studying the various material properties such as unloading ‘reduced’ modulus, hardness, creep properties, and fracture toughness. Nano-indentation test procedure involves application of predetermined load in the range of μN to mN with the help of either spherical or pyramidal indenter in order to produce the indentation of the order of a few microns (measured in terms of nano-meters), followed by controlled unloading. The contact area of indentation is used to calculate hardness (H) of the material and the slope of unloading curve on load-displacement can be used for determining the ‘effective’ modulus or ‘reduced’ modulus (E_r). Later modification in the method was achieved by holding at maximum load constant for some time before unloading (creep). This modification was done in order to study the visco-elastic and visco-plastic behavior of the materials where conventional nano-indentation method was based on the assumption that material behave in an elastic-plastic manner.