scholarly journals Assessment of the stepped isothermal method for accelerated creep testing of high-density polyethylene

2021 ◽  
Author(s):  
Gerald Pilz ◽  
Stefan Wurzer ◽  
Matthias Morak ◽  
Gerald Pinter
Keyword(s):  
Creep Behavior ◽  
High Density Polyethylene ◽  
Creep Compliance ◽  
High Density ◽  
Creep Testing ◽  
Time Range ◽  
Master Curves ◽  
Isothermal Method ◽  
Temperature Levels

AbstractThermoplastic materials are increasingly used in demanding structural applications under, in some cases, long-term static loading over several decades. In this regard, the stepped isothermal method (SIM) with creep testing at stepwise increased temperature levels in combination with time-temperature superposition (TTSP) provides a very time efficient procedure for long-term creep characterization. In the present study, the creep behavior of an injection molded high-density polyethylene material (HDPE) was investigated by SIM in the thermally untreated state as well as after annealing.Due to experimental issues regarding the heating behavior of the specimens and non-linear viscoelastic behavior, particularly at elevated temperatures, bi-directional curve shifting was required in order to generate meaningful master curves for creep compliance. In a first step, an Arrhenius equation was used for the horizontal curve shifting, based on activation energies, determined in additional multi-frequency dynamic mechanical analysis (DMA). Continuous master curves were then obtained by empirical vertical shifting of the individual creep curve segments for the different temperature levels. In general, good agreement was observed between the resulting SIM master curves and the corresponding conventionally measured creep compliance curves at least for a time range up to 300 hours. Furthermore, significant differences in the creep tendency of the annealed material state compared to the thermally untreated condition revealed the distinct influence of the thermal history on the resulting creep behavior.

scholarly journals Flexural Creep Behavior of High-Density Polyethylene Lumber and Wood Plastic Composite Lumber Made from Thermally Modified Wood

Polymers ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 262 ◽  
Author(s):  
Murtada Abass A. Alrubaie ◽  
Roberto A. Lopez-Anido ◽  
Douglas J. Gardner
Keyword(s):  
Creep Behavior ◽  
Creep Deformation ◽  
High Density Polyethylene ◽  
Creep Compliance ◽  
High Density ◽  
Wood Plastic Composite ◽  
Creep Stress ◽  
Plastic Composite ◽  
Thermally Modified Wood ◽  
Modified Wood

The use of wood plastic composite lumber as a structural member material in marine applications is challenging due to the tendency of wood plastic composites (WPCs) to creep and absorb water. A novel patent-pending WPC formulation that combines a thermally modified wood flour (as a cellulosic material) and a high strength styrenic copolymer (high impact polystyrene and styrene maleic anhydride) have been developed with advantageous viscoelastic properties (low initial creep compliance and creep rate) compared with the conventional WPCs. In this study, the creep behavior of the WPC and high-density polyethylene (HDPE) lumber in flexure was characterized and compared. Three sample groupings of WPC and HDPE lumber were subjected to three levels of creep stress; 7.5, 15, and 30% of the ultimate flexural strength (Fb) for a duration of 180 days. Because of the relatively low initial creep compliance of the WPC specimens (five times less) compared with the initial creep compliance of HDPE specimens, the creep deformation of HDPE specimens was six times higher than the creep deformation of WPC specimens at the 30% creep stress level. A Power Law model predicted that the strain (3%) to failure in the HDPE lumber would occur in 1.5 years at 30% Fb flexural stress while the predicted strain (1%) failure for the WPC lumber would occur in 150 years. The findings of this study suggest using the WPC lumber in structural application to replace the HDPE lumber in flexure attributable to the low time-dependent deformation when the applied stress value is withing the linear region of the stress-strain relationship.

Wear of the high-density polyethylene socket in total hip arthroplasty and its role in endosteal cavitation

1997 ◽  
Vol 211 (1) ◽  
pp. 109-118 ◽  
Author(s):  
B M Wroblewski
Keyword(s):  
Hip Replacement ◽  
High Density Polyethylene ◽  
High Density ◽  
Wear Particles ◽  
Total Hip ◽  
Weakest Link ◽  
Ultimate Cause ◽  
Cause Of Failure ◽  
Secondary Healing

High-density polyethylene (HDP) has been used in clinical practice in total hip replacement since its introduction by Charnley in November 1962. Fears are being expressed that this may be the weakest link and the ultimate cause of failure of the arthroplasty. Long-term clinical experience suggests that loosening may be the primary cause while the presence of HDP wear particles is secondary. Healing of endosteal cavities can take place in the presence of HDP wear particles.

Polymers for Solar Domestic Hot Water: Long-Term Performance of PB and Nylon 6,6 Tubing in Hot Water

2004 ◽  
Vol 126 (1) ◽  
pp. 581-586 ◽  
Author(s):  
Chunhui Wu ◽  
Susan C. Mantell ◽  
Jane Davidson
Keyword(s):  
Creep Compliance ◽  
Hot Water ◽  
Master Curves ◽  
Burst Strength ◽  
Domestic Hot Water ◽  
Nylon 6,6 ◽  
Creep Modulus ◽  
Long Term Performance ◽  
Term Performance

Polymers offer a lightweight, low cost option for solar hot water system components. Key to the success of polymer heat exchanger components will be the long term mechanical performance of the polymer. This is particularly true for heat exchangers in which one of the fluids is pressurized hot water. For domestic hot water systems, polymer components must not fail after many years at a constant pressure (stress levels selected to correspond to 0.55 MPa in a tube) when immersed in 82°C potable water. In this paper, the long term performance of two potential heat exchanger materials, polybutylene and nylon 6,6, is presented. Two failure mechanisms are considered: failure caused by material rupture (as indicated by the hydrostatic burst strength) and failure caused by excessive deformation (as indicated by the creep modulus). Hydrostatic burst strength and creep modulus data are presented for each material. Master curves for the creep compliance as a function of time are derived from experimental data. These master curves provide a mechanism for predicting creep modulus as a function of time. A case study is presented in which tubing geometry is selected given the hydrostatic burst strength and creep compliance data. This approach can be used to evaluate properties of candidate polymers and to design polymer components for solar hot water applications.

Long-term water uptake behavior of lignocellulosic-high density polyethylene composites

2006 ◽  
Vol 102 (4) ◽  
pp. 3907-3911 ◽  
Author(s):  
Saeed Kazemi Najafi ◽  
Mehdi Tajvidi ◽  
Majid Chaharmahli
Keyword(s):  
Water Uptake ◽  
High Density Polyethylene ◽  
High Density ◽  
Polyethylene Composites
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