Study of Elastic Properties of Polymers From Microhardness Tests

Abstract

A numerical method of identification to derive the elastic properties of polymers from indentation experiments has been developed. Five different polymers were tested: amorphous and semi-crystalline polyethylene terephthalate (PET), semi-crystalline polyvinylidene fluoride (PVF 2 ), a copolymer of polyvinylidene fluoride and trifluorethylene, PCVF2/F3E) 60/40, and high pressure crystallised polyethylene (PE). The elastic properties of the polymers are calculated by two methods. On the basis of finite element solution, a simple function relating the load to the indentation depth and elastic modulus is first obtained. The elastic properties are then derived from the load-indentation depth and elastic modulus is first obtained. The elastic properties are then derived from the load indentation depth experimental data (loading curve). A second method to determine the elastic properties is based on using the experimental data of the unloading curve. Elastic properties obtained from loading and unloading curves are in good agreement.

Effect of Processing Conditions on Mechanical Properties of Pretreated Gelatin Samples

“…The comparison was made on the basis of two well known relations [11 ± 13]. The cited in [11] relationship is…”

“…The result is shown in Figure 6 both with some theoretical lines. The two straight lines (v 0.2 and v 0.5) represent the known [11] relation E Ã E/(1 À v 2 ) between the indentation modulus E Ã and the Young's modulus E, where v denotes the Poisson ratio. Since the Poisson ratio of gelatin may change with the degree of crosslinking, the two extreme cases of v 0.2 and 0.5 [12] were taken and the respective straight lines were drawn in Figure 6.…”

Research on the Influence of Stiffness of Copolymer(N-Tert-octylacrylamide/Acrylic acid/Methyl methacrylate/Butylaminoethyl Methacrylate/Hydroxypropyl Methacrylate) by Methyl Methacrylate and N-Tert-Octylacrylamide

“…The stiffness is a measure of the resistance offered by an elastic body to deformation.For an elastic body with a single degree of freedom,the stiffness is defined as δ F k = .F is the force applied on the body, δ is the displacement produced by the force along the same degree of freedom.The term stiffness is usually taken to mean a measure of modulus derived from the resistance of the material to indentation but has also been applied to scratch resistance and resilience.The mode of deformation under an indentor is a mixture of tension,shear and compression,and stiffness is by no means a fundamental property.The result depends on the indentor geometry and degree of indentation as well as the time of indentation after which the measurement is made.Although stiffness is almost inevitably included in properties of rubbers and very commonly applied to metals,it has been used rather less often for plastics.Despite the complexity of the deformation,approximate relationships between stiffness and modulus have been derived in some cases.by far the most effort in this direction has been for rubbers [1],but plastics have been considered by,for example,Jirous [2]for a spherical indentor and by Rikards and co-workers [3]and Gubicza and co-workers [4]using the vickers pyramid.Amitay-sadovsky and Wagner [5]evaluated the measurement of Young's modulus from Knoop microtests.Results are time dependent,subject to the non-linear response of strain to stress and a function of force and indentor geometry.The latter effects have been investigated by crawford and stephens [6].Time and load dependence for the Vickers test was observed by Suwanprateeb [7]who found large differences in results calculated from diagonal length and indentation depth.Work by Fett and co-workers [9] and by Bowman and Bivis [10]has sought to relate stiffness measurements to orientation conditions in a variety of thermoplastics,while Martinez-Salazar and co-workers [11.12]have attempted to relate stiffness to structure and morphology in poluethylene and Balta-Calleja [13]to crystalline polymers generally.Selden and Gustafson [14] have attempted to correlate stiffness and tensile properties for a number of materials.A comprehensive review of microhardness tests has been given by Lopez [15].…”