Push-out and pull-out tests are used for destructive evalu ation of implant-bone interface strength. Because nonde structive mechanical tests would allow maintenance of an intact interface for subsequent morphological study, we de veloped such a test to determine the shear modulus of the interface by measuring the shear deformation of a thin layer adjacent to the implant. A polyurethane foam model was used to test the experimental setup on a group of nine cylindrical implants with three different lengths (15-48 mm) and three different diameters (5-9.7 mm). The shear modu lus of the interface, as calculated from the pull-out test, was validated against the shear modulus of the foam derived from tensile tests. The two values of shear modulus were well correlated (R2 = 0.8, p < 0.001), thus encouraging further application of the setup for tests of implant-bone interface mechanics. In addition, we also examined the effects of im plant length and diameter. The length of the implants had a significant influence on the interface shear modulus (p < 0.05), indicating that comparisons of this variable should only be made of implants with the same length. The length and diameter of the implants were not critical parameters for the ultimate fixation strength.
A method is presented for predicting rheological characteristics, such as shear dependent (non-Newtonian) viscosity a i d components of linear oscillatory (complex) response functions for polyethylene melts from molecular weight distribution data obtained from gel permeation chromatographic (GPC) analysis. The results are compared with measured values ofthe rheological functions obtained from a variety of instruments over an extensive range of shear rates and frequencies. The agreement between predicted and measured rheological functions is quite good for high density resins. However, for a low density resin the agreement is not as good, although still reasonable over a considerable range of conditions. It is concluded that the quality of the GPC data is the key factor in the degree of success of the method * Present A d d r e s~.
This article describes the use of the Rheovibron Model DDV‐III‐B with a parallel plate modification of the sample holders to obtain oscillatory data in the shear mode for several high density polyethylene melts. A detailed analysis of the Rheovibron to obtain the dynamic shear: moduli of polymer melts using the new sample holders is given, as well as a procedure for determining the instrument compliance and inertia parameters which must be considered in analysis of the data. Using the principle of time‐temperature superposition, the data are extended to an equivalent frequency range of 1500 rad/sec. These data are compared with those obtained using the Weis‐senberg Rheogoniometer Model R‐17 for the same polymers. It is concluded that reliable measurements for dynamic shear moduli for polymer melts using the Rheovibron Model DDV‐III‐B with the modified sample holders can be made for melts with indices of about 5 or less (i.e., zero shear viscosities of 6.0 × 104 poise or greater).
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