Numerical modeling of microhardness tests for polymer materials

A computational method in conjunction with indentation measurements is pres ented to determine stiffness properties of different polymeric materials. E xperiments were performed using a Vickers-type indenter. Five different pol ymers were tested: polyethylene naphthalate (PEN), copolymer amorphous poly ethylene terephthalate/polyethylene naphthalate (PET/PEN 70/30), copolymer crystalline polyethylene terephthalate/polyethylene naphthalate (PET/PEN 70 /30), a random copolyester of polyethylene naphthalate/hydroxybenzoate (PEN /PHB 50/50), and a blend of isotactic polypropylene/ethylene-co-propylene r ubber (i-PP/EPR 85/15). Elastic properties are determined from the unloadin g curve of indentation. Identification of plastic properties of polymers ar e performed from the loading curve of indentation. A novel approach based o n experimental design and finite-element analysis is discussed. Yield stres s and tangent modulus are obtained by minimizing the deviation between the calculated and the experimental data. Results are verified by the finite-el ement method. Good agreement between the experimental and numerical load-in dentation depth curves is observed.