Behavior Of High-density Polyethylene Research Articles

Constitutive model calibration for the thermal viscoelastic-viscoplastic behavior of high density polyethylene under monotonic and cyclic loading

High density polyethylene (HDPE) can show viscoelastic-viscoplastic behaviors under monotonic loads and a stress softening after reloading under cyclic ones. This sets a challenge in simultaneously representing such response in material constitutive models. In addition, due to the adoption of novel accelerated tests at higher temperatures, e.g., 95 °C, the need for a higher temperature calibration is motivated. Therefore, the objective of this study is threefold: (i) to investigate the capability of the three network viscoplastic (TNV) model in capturing HDPE thermo-viscoplasticity under monotonic and cyclic loads, (ii) to report observations on HDPE at various strain-rates and temperatures from 23 °C to 95 °C including the α-relaxation region (iii) to explore the ratcheting behavior of HDPE, i.e., cyclic creep. The FEA analysis based on the calibrated TNV model was successfully able to predict the HDPE behavior under static, quasi-static and dynamic loads. The predicted strain range Δε and mid-range strain εs of the cyclic creep showed good agreements. This implies that the TNV model can be a reliable candidate for HDPE engineering assessments. Findings of this work will have many industrial applications, e.g., products manufacturers or resin producers, in which HDPE is used under complex loads. Similar procedures can be followed for other thermoplastics which lays the basis for establishing a standard calibration guideline.

The dielectric properties of system composed of insulator-conductor materials

This study includes investigates the electrical behavior of high density polyethylene (HDPE) having various concentrations of carbon black (C.B.) over a range of frequencies from (100Hz) to (20KHz).Experimental results display that the dielectric constant and a.c. conductivity increase with increasing C.B. concentrations in the samples which have the same thickness but different concentrations, especially in sample (90%HDPE+10%C.B.). The dielectric constant and a.c. conductivity increase with increasing of thickness of samples which have the same concentration of C.B. because the effect of the dipole moment on the sample has large thickness.

Short‐term creep experiments and modeling on the effect of nano-sized calcium carbonate particles and applied stress on nonlinear viscoelastic behavior of high-density polyethylene

Short‐term creep experiments and modeling on the effect of nano-sized calcium carbonate particles and applied stress on nonlinear viscoelastic behavior of high-density polyethylene

Accelerated aging and characterization of HDPE pin type insulators (15 kV)

The study of the behavior of polymeric material used for insulators in the electrical system is extremely important in order to evaluate their lifetime as well as their performance when exposed to different environmental conditions. In the present work, the behavior of high-density polyethylene (HDPE) pin type insulators (15 kV), under accelerated aging conditions, was studied. Samples were exposed to aging, for 200 h, 1000 h, and 2000 h, in accelerated weathering chambers, according to two different methods. In Method 1, the parameters were established based on natural aging in location conditions, and in Method 2, ASTM G155 standard parameters were used. All samples were characterized by rheometry, Fourier-transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The accelerated aging conditions, used in Methods 1 and 2, affected the aging of HDPE pin type insulators samples differently, the changes being more intense in Method 1.

Investigation of Tensile Creep Behavior for High-Density Polyethylene (HDPE) via Experiments and Mathematical Model.

Temperatures of −25 °C, +5 °C, and +35 °C were selected to study the creep behavior of high-density polyethylene (HDPE). The ultimate tensile strength of HDPE materials was obtained through uniaxial tensile experiments and the time–strain curves were obtained through creep experiments. When the loaded stress levels were lower than 60% of the ultimate strength, the specimens could maintain a longer time in the stable creep stage and were not prone to necking. In contrast, the specimens necked in a short time. Then, the time hardening form model was applied to simulate the time–strain curve and the parameter values were solved. The parameter values changed exponentially with the stresses, thereby expanding and transforming the time hardening model. The expanded model can easily and accurately predict creep behaviors of the initial and stable creep stages as well as the long-term deformations of HDPE materials. This study would provide a theoretical basis and reference value for engineering applications of HDPE.

Rheological Behavior of High Density Polyethylene (HDPE) Filled with Corn Stalk Biochar

AbstractCorn stalk (CS) was used as raw material to prepare biochar. Corn stalk biochar /HDPE composite (CSB/HDPE) was prepared by extrusion method with 3 wt% MA added. The effect of corn stalk biochar (CSB) on the rheological properties of HDPE under different conditions was studied. The interface performance of each component with HDPE was studied by using the Harmonic‐Mean interface equation. The purpose is to provide guidance for the processing and molding of materials by studying the rheological properties and interface properties of the materials. The results showed that, compared with CS, the interfacial tension between CSB and HDPE was lower; Research on dynamic rheological properties showed that an appropriate amount of CSB can improve the processing performance of HDPE; With the increase of CSB content, the stability of the composite system decreased, but the elasticity and viscosity increased correspondingly. The steady‐state rheological properties showed that shear induced compatibility occurs in the composite system at high shear rates; Compared with HDPE, 50 %CSB/HDPE was more sensitive to temperature and had higher viscous flow activation energy. In addition, the tensile strength and flexural strength of the composite material reached the maximum when the CSB content was 50 %, which were 28.69 MPa and 30.14 MPa, respectively. Overall, the study of rheological properties of materials provides guidance for the application of CSB in polymers and broadens the way of waste resources utilization.

Effect of impact angle and impact velocity on the slurry erosion behavior of high density polyethylene (HDPE)

High density polyethylene is widely used in many applications which deal with slurry because of its high erosion resistance characteristics. Slurry erosion is a type of erosive wear which takes place when a stream of liquid hits a solid body and results erosion in this body surface. Slurry erosion is affected by some parameters as material hardness, impact velocity, impact angle, slurry content, ambient temperature, particle hardness, particle size and particle shape. The changing of these parameters individually will result in useful analysis for the changing in slurry erosion rate with respect to the changed parameter. This experimental work aims to investigate the slurry erosion behavior of high density polyethylene under the effect of different impact velocities. A slurry impingement test rig will be used to make the wear test and wear rate of HDPE is investigated as a function of impact velocity and impact angle. Results showed that the maximum wear rate is at the lowest impact angle and maximum impact velocity. Weight loss is the indication of wear rate of the HDPE specimens after experiment and wear rate is defined as weight loss during the test time in [mg/h] unit

Behavior of high-density polyethylene at high strain rates

The Hopkinson split pressure bar (HSPB) was used for the testing of three polymers at strain rates between 102 to 103 s-1. Higher strain rates were achieved using the direct Hopkinson test. Experimental data were evaluated in time as well as in the frequency domain. A more detailed analysis in the frequency domain showed that the description of tested polymers can be described in the framework of the linear viscoelasticity. The use of the direct Hopkinson test showed the occurrence of a permanent strain.

Numerical and experimental study of the Behaviour of notched HDPE

It is important to study the Behaviour of high-density polyethylene (HDPE) under notch effects as it is widely used in industrial applications (Qi, 2018). However, there are only a few studies on the Behaviour of HDPE with defects, this work aims to study the deformation mechanisms under a tensile test experimentally performed on blank and notched specimens at constant speed and room temperature, and by developing our study by simulating HDPE using commercial software code.

Modeling Injection Molding of High-Density Polyethylene with Crystallization in Open-Source Software.

This work investigates crystallization modeling by modifying an open-source computational fluid dynamics code OpenFOAM. The crystallization behavior of high-density polyethylene (HDPE) is implemented according to theoretical and experimental literature. A number of physical interdependencies are included. The cavity is modeled as deformable. The heat transfer coefficient in the thermal contact towards the mold depends on contact pressure. The thermal conductivity is pressure- and crystallinity-dependent. Specific heat depends on temperature and crystallinity. Latent heat is released according to the crystallization progress and temperature. Deviatoric elastic stress is evolved in the solidified material. The prediction of the cavity pressure evolution is used for the assessment of the solution quality because it is experimentally available and governs the residual stress development. Insight into the thermomechanical conditions is provided with through-thickness plots of pressure, temperature and cooling rate at different levels of crystallinity. The code and simulation setup are made openly available to further the research on the topic.

A phenomenological criterion for an optical assessment of PE-HD fracture surfaces obtained from FNCT

The full-notch creep test (FNCT) is a common test method to evaluate the environmental stress cracking (ESC) behavior of high-density polyethylene (PE-HD), e.g. for container materials. The test procedure as specified in ISO 16770 provides a comparative measure of the resistance against ESC using the time to failure of PE-HD specimens under constant mechanical load in a well-defined liquid test environment. Since the craze-crack damage mechanism underlying the ESC phenomenon is associated with brittle failure, the occurrence of a predominantly brittle fracture surface is a prerequisite to consider an FNCT measurement as representative for ESC, i.e. a time to failure dominated by craze-crack propagation.The craze-crack propagation continuously reduces the effective residual cross-sectional area of the specimen during the test, which results in a corresponding increase of the effective mechanical stress. Thus, a transition to ductile shear deformation is inevitable at later stages of the test, leading usually to a pronounced central ligament.Therefore, an optical evaluation of FNCT fracture surfaces concerning their brittleness is essential. An enhanced imaging analysis of FNCT fracture surfaces enables a detailed assessment of craze-crack propagation during ESC. In this study, laser scanning microscopy (LSM) was employed to evaluate whether FNCT fracture surfaces are representative with respect to craze-crack propagation and ESC. Based on LSM height data, a phenomenological criterion is proposed to assess the validity of distinct FNCT measurements. This criterion is supposed to facilitate a quick evaluation of FNCT results in practical routine testing. Its applicability is verified on a sample basis for seven different commercial PE-HD container materials.

Constitutive model calibration of the time and temperature-dependent behavior of high density polyethylene

HDPE is commonly used in pipelines and piping for industrial and societal infrastructure. Like most polymers, HDPE's mechanical properties are sensitive to temperature and show time dependent properties. The temperature effect on both the short and long term compressive and tensile behavior of HDPE, in a combined manner, have not been investigated thoroughly in the past. Especially the constitutive behavior of HDPE, incorporating temperature effects on its long and short term behavior, could be essential when designing such infrastructural components. Hence, the temperature effect on the short and long term response in tension and compression of HDPE is investigated in this study. The short term tensile and compressive stress-strain behavior at 23, 40, 60, and 80 °C were obtained through experiments at constant displacement rate and temperature. Tensile and compressive stress relaxation (e.g. long term) behavior at 23, 40, 50, 60, 70, and 80 °C were investigated through stress relaxation tests. The experimental results from the short term tests showed that both the tensile and compression moduli and yield strength of HDPE decrease linearly with the increase in temperature. It is also shown from the long term test that relaxation modulus in tension and compression are highly dependent on temperature. Based on the experimental results, the constitutive three network model (TNM) was calibrated and implemented in a FEA model, which was then validated through a three point bending (3 PB) relaxation test with a prescribed temperature profile. The FEA model and the calibrated model results agree markedly well with the experimental results, which indicates that the model can be used reliably to predict the temperature dependent short and long term behavior of HDPE in design and analysis of HDPE components.

Creep-Relaxation Modeling of HDPE and Polyvinyl Chloride Bolted Flange Joints

AbstractSimilar to many polymer materials, high-density polyethylene (HDPE) and polyvinyl chloride (PVC) show a clear creep behavior, the rate of which is influenced by temperature, load, and time. Most bolted flange joints undergo relaxation under compression, which is caused by the creep of the material. However, the creep property of the two polymers is different under tension and compression loading. Since the sealing capacity of a flanged gasketed joint is impacted by the amount of relaxation that takes place, it is important to properly address and predict the relaxation behavior due to flange creep under compression and thereby reducing the chances of leakage failure of HDPE and PVC bolted flange joints. The main objective of this study is to analyze the compressive creep behavior of HDPE and PVC flanges under normal operating conditions. This is achieved by developing a respective creep model for the two materials, based on their short-term experimental creep test data. Both numerical and experimental simulations of the polymeric flange relaxation behavior are conducted on an NPS 3 class 150 bolted flange joint of dissimilar materials, where one of the flanges is made of HDPE or PVC material and the other one is made of steel SA105. The study also provides a clear picture on how the compression creep data of ring specimen may be utilized for predicating the flange bolt load relaxation over time at the operating temperatures.

Thermo-mechanical properties of high density polyethylene with zinc oxide as a filler

This study investigates the microstructural, thermal, and mechanical behavior of high density polyethylene (HDPE)-based composites prepared using compression molding technique. HDPE was mixed with either micro-size zinc oxide (bulk ZnO) or zinc oxide nanoparticles (nano-ZnO) as fillers’ contents at 0, 10, 20, 30, and 40 wt%. The structural, morphological, and thermal properties of the composites were identified using X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectrophotometer (FTIR), and thermal gravimetric analysis (TGA). The results showed good dispersion and interaction mechanisms between HDPE and the fillers at low weight percentage. The thermal stability of HDPE was enhanced by adding both bulk and nano-ZnO, especially for higher filler loading. Tensile tests at different speeds and Vickers microhardness tests conducted at different indentation loads (0.25–5 N) at t = 60 s were performed to realize how the mechanical properties of the composites were influenced. The values of stiffness, ultimate tensile strength, and yield stress increased by increasing the filler loading to 20 wt% of either bulk ZnO or nano-ZnO. The values of ultimate tensile strain and ductility were deteriorated by increasing the filler loading. Nano-ZnO, at 20 wt% content in composite, showed higher mechanical properties than bulk composite, so it has been recommended for a better tensile performance at higher strain rates. Vickers microhardness measurements showed that the tested samples exhibited reverse indentation size effect (RISE) behavior. The obtained results were analyzed using Meyer’s law which was a preferred approach for analysis of HDPE/ZnO composite.

Effect of microcrystalline cellulose [MCC] fibres on the morphological and crystalline behaviour of high density polyethylene [HDPE]/polylactic acid [PLA] blends

The present study describes the fabrication and characterization of eco-friendly composites based on high density polyethylene (HDPE), poly (lactic acid) (PLA) with microcrystalline cellulose (MCC) fibres via melt extrusion followed by injection moulding. The morphology of PLA in both HDPE/PLA blends and HDPE/MCC fibres composites was irregular and immiscible. The tensile strength at max load and % elongation at break of all polyblend composites were reduced to ~17%, ~15%, and ~84%, ~89% than pure HDPE matrix, respectively. The toughness of HDPE and its polyblend composites were decreased to ~92% and ~91%, respectively. As higher number indicates greater resistance, the hardness of HDPE was improved by ~7% and ~10% after adding PLA followed by MCC fibres. As revealed from DSC analysis, the crystallinity of composites was considerably influenced by the MCC fibres content due to the transcrystallization effect. The crystallinity of HDPE/PLA with MCC fibres polyblend composites was decreased by ~41% as compared to the HDPE matrix because of disorientation of fibres as seen in X-ray diffraction analysis. Eventually, the results revealed that the presence or absence of MCC fibre loading had significant effects on the mechanical, morphological, and thermal properties of HDPE/PLA blends.

FLEXURAL AND QUASI-STATIC COMPRESSIVE BEHAVIOR OF INJECTION-MOLDED WALNUT SHELL (WS)/HDPE COMPOSITES

The present study focuses on flexural and quasi-static compression behavior of high-density polyethylene (HDPE)/walnut shell (WS) composites. Flexural and quasi-static compression specimens by 20, 40 and 60 wt. % of WS are synthesized by polymer injection (PI) molding. The flexural modulus and strength are observed to increase with increase in the wt.% of WS. Compared to pure HDPE, the flexural modulus and strength increased in the range of 205-403% and 49-58% respectively. Further quasi-static compression tests are carried at 0.001, 0.01, 0.1 s-1 strain rates. Compressive modulus of HDPE/WS specimens is lower as compared to pure HDPE samples for all the strain rates. Compressive yield strength of HDPE/WS specimens shows increasing trend with increase in the strain rates. Scanning electron microscopy (SEM) is employed to study the fractography of the samples.

Application of a master curve and the modified superposition principle for modeling creep and loading rate effects at small strains in high-density polyethylene

Studying the nonlinear viscoelastic behavior of high-density polyethylene (HDPE) at small strains and stresses is still a matter of interest in engineering applications such as laying submerged pipelines. Although sound modeling of such behavior requires complex phenomenological or micromechanical constitutive laws, many works have focused on the development of simplified procedures for approximating this type of nonlinear response. Usually, when these simplified methods are employed to reproduce creep behavior, they are not capable to simultaneously provide good estimates for traction tests even at constant stress or strain rates. This work describes a methodology, which has shown a good compromise to reproduce both types of responses within a given stress range. The procedure can be understood as an interpolative approach based on a master curve and the modified superposition principle to account for nonlinear effects. With this strategy, it is possible to predict the nonlinear creep behavior for an HDPE sample subjected at any constant stress level within a given experimental range. Once this predictive capability is achieved, we use an incremental algorithm based on the modified superposition principle to simulate traction tests at constant strain rates. We show that the combined application of the proposed master curve approach and the modified superposition principle results in good approximations for creep tests and simultaneously leads to remarkable agreement with experimental traction tests reported in the literature.

Melt spinning flow behaviour of high-density polyethylene blended with low-density polyethylene

ABSTRACTThe melt spinning flow behaviour of a high-density polyethylene (HDPE) blended with a low-density polyethylene (LDPE) was studied using a melt spinning technique in temperature ranging from 160 to 200°C and die extrusion velocity varying from 9 to 36 mm s−1. The results showed that the melt apparent extension viscosity of the blends was higher than those of the LDPE and HDPE; the melt apparent extension viscosity decreased with increasing temperature; while the melt apparent extension viscosity increased with increasing extension strain rate when the extension strain rate was lower than 0.2 s−1, and then decreased; the melt apparent extension viscosity reached up to a maximum value when extension strain rate was about 0.2 s−1; the relationship between the melt apparent extension viscosity and the LDPE weight fraction did not follow the mixing rule.

Antimicrobial performance of polyethylene nanocomposite monofilaments reinforced with metal nanoparticles decorated montmorillonite.

A comparative study on the antimicrobial behavior of high density polyethylene (HDPE) nanocomposite monofilaments based on three types of metal nanoparticles (NPs) decorated montmorillonite (MMT) has been presented. Modified MMT decorated with silver, copper and zinc oxide nanoparticles were synthesized in-lab and used as a reinforcing agent in preparing HDPE/modified MMT nanocomposite monofilaments via melt compounding and fiber spinning route in presence of compatibilizer. The concentration of modified MMT was varied from 1 to 5 wt. % in the nanocomposite monofilament. A mixture of intercalated and exfoliated morphology was observed from TEM and WAXD analyses with absence of clay agglomerations. DSC studies indicated MMT acting as heterogeneous nucleating agent with increased degree of crystallinity, crystallization temperature and rate of crystallization. The HDPE/modified MMT nanocomposite monofilaments showed remarkable decrease in bacterial colonies against Gram (-) E. coli and Gram (+) S. aureus with HDPE/Ag-MMT monofilaments showing the highest activity (>99%). The dissolution kinetics of metal ions/NPs from modified MMT nanostructure was studied to understand its effect on antimicrobial action. The antimicrobial filaments are potential candidates to replace neat HDPE counterparts in moist environment applications such as ropes, sacks, agricultural items and geotextiles where microbial growth is a cause of concern.

Multiaxial Fatigue Behavior of High-Density Polyethylene (HDPE) Including Notch Effect: Experiments and Modeling

High-Density Polyethylene (HDPE) is used in many industries with many applications from automotive industry to biomedical implants. It can be manufactured using different processing techniques including compression molding, injection molding, and blow molding. Multiaxial loading and non-proportionality between different loading sources are inevitable in many applications. It is shown that the common multiaxial fatigue criteria such as von Mises equivalent stress are not able to correlate the multiaxial fatigue data. In this study, multiaxial fatigue behavior of neat HDPE is investigated using hollow tubular specimens through experimental fatigue tests. Axial, torsion, and combined in phase and out-of-phase axial-torsion fatigue tests were conducted. Stress concentration effect on multiaxial fatigue behavior was also studied. Experimental results and analytical models used to account for the aforementioned effects are presented and discussed in this paper.