Cyclic Behavior of High Density Polyethylene (HDPE)

2010 ◽  
Author(s):  
Necmi Dusunceli ◽  
Bulent Aydemir ◽  
Niyazi U. Terzi ◽  
A. D’Amore ◽  
Domenico Acierno ◽  
...  
Keyword(s):  
High Density Polyethylene ◽  
High Density ◽  
Cyclic Behavior

Modeling Viscoelastic and Viscoplastic Behavior of High Density Polyethylene (HDPE)

2006 ◽  
Vol 128 (4) ◽  
pp. 572-578 ◽  
Author(s):  
Ozgen U. Colak ◽  
Necmi Dusunceli
Keyword(s):  
Strain Rate ◽  
Rate Equation ◽  
High Density Polyethylene ◽  
Elastic Strain ◽  
High Density ◽  
Cyclic Behavior ◽  
Compression Tests ◽  
Rate Dependency ◽  
Loading And Unloading ◽  
Simulation Results

The viscoelastic and viscoplastic behaviors of high density polyethylene (HDPE) under uniaxial monotonic and cyclic loading are modeled using the modified viscoplasticity theory based on overstress (VBO). The viscoelastic modeling capabilities of the modified VBO are investigated by simulating the behavior of semicrystalline HDPE under uniaxial compression tests at different strain rates. In addition, the effects of the modification (introducing the variable “C” into an elastic strain rate equation) on VBO that has been made to construct the change in the elastic stiffness while loading and unloading are investigated. During first loading and unloading, the modification in the elastic strain rate equation improves the unloading behavior. To investigate how the variable “C” that is introduced in the elastic strain rate equation evolves during reloading, the cyclic behavior of HDPE is modeled. For a complete viscoelastic and viscoplastic behavior, the relaxation and creep behaviors of HDPE are simulated as well in addition to stress and strain rate dependency. The influences of the strain (stress) levels where the relaxation (creep) experiments are performed are investigated. The simulation results are compared with the experimental data obtained by Zhang and Moore (1997, Polym. Eng. Sci., 37, pp. 404–413). A good match between experimental and simulation results are observed.

Composition and Surface Topography Effects on Apatite-Forming Ability of Ceramic-Polymer Composites

2003 ◽  
Vol 774 ◽  
Author(s):  
Susan M. Rea ◽  
Serena M. Best ◽  
William Bonfield
Keyword(s):  
Surface Topography ◽  
High Density Polyethylene ◽  
High Density ◽  
Apatite Layer ◽  
Biologically Active ◽  
Human Blood Plasma ◽  
Apatite Formation ◽  
Polyethylene Matrix ◽  
Composite Surface ◽  
X Ray

AbstractHAPEXTM (40 vol% hydroxyapatite in a high-density polyethylene matrix) and AWPEX (40 vol% apatite-wollastonite glass ceramic in a high density polyethylene matrix) are composites designed to provide bioactivity and to match the mechanical properties of human cortical bone. HAPEXTM has had clinical success in middle ear and orbital implants, and there is great potential for further orthopaedic applications of these materials. However, more detailed in vitro investigations must be performed to better understand the biological interactions of the composites and so the bioactivity of each material was assessed in this study. Specifically, the effects of controlled surface topography and ceramic filler composition on apatite layer formation in acellular simulated body fluid (SBF) with ion concentration similar to those of human blood plasma were examined. Samples were prepared as 1 cm × 1 cm × 1 mm tiles with polished, roughened, or parallel-grooved surface finishes, and were incubated in 20 ml of SBF at 36.5 °C for 1, 3, 7, or 14 days. The formation of a biologically active apatite layer on the composite surface after immersion was demonstrated by thin-film x-ray diffraction (TF-XRD), environmental scanning electron microscopy (ESEM) imaging and energy dispersive x-ray (EDX) analysis. Variations in sample weight and solution pH over the period of incubation were also recorded. Significant differences were found between the two materials tested, with greater bioactivity in AWPEX than HAPEXTM overall. Results also indicate that within each material the surface topography is highly important, with rougher samples correlated to earlier apatite formation.

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