Behavior Of Polymeric Materials Research Articles

Permittivity and Loss Characterization of Polymer Films for Terahertz Applications

With the development of science, terahertz (THz) technology has matured gradually. More attention has been given to THz technology in recent years due to its superiority for non-destructive testing. Dielectric polymers are widely used in electrical engineering because of their unique electrical properties. Spectral detection plays a vital role in studying the internal motion and micro-scale forces. THz time-domain spectroscopy (THz-TDS) is a powerful complement to other spectroscopy techniques because of its unique frequency band that energetically vibrates and rotates the polymer structure. Herein, we apply THz-TDS with an effective frequency of 0.1–1 THz at 55% relative humidity. TDS at 0.1–1 THz to conduct fundamental research on several commonly utilized dielectric non-polar and polar polymer films including PC, FTPE, PMMA, HDPE, PA6, PET, PP. In this study, the THz complex refractive index and dielectric constants of various polymer films are determined and compared with previously reported values. In addition, the loss mechanism of THz radiation in polymers is characterized by correlating the absorption coefficients of the materials with the loss tangents. Herein, we demonstrate that the sample preparation significantly impacts the loss behavior of polymer materials and quantify the effect of crosslinking on the dielectric constant across the entire frequency band. The findings presented herein are expected to contribute to the design and development of optical and electronic devices in the future.

A technical approach toward pre-crack generation and its effect on the fracture behavior of polymeric materials

Regarding the urgent need for a proper pre-crack generation method in polymeric materials, this study addressed the design and fabrication of a broaching machining apparatus. The performance of this device was examined by preparing polyvinyl chloride (PVC) samples with high sensitivity to the crack-tip radius. Pre-cracks generated by broaching and slotting and then examined by SEM analysis. The fracture parameters were determined by the essential work of fracture (EWF) method. Studies indicated that the energy required for crack growth was on average 24 % lower in the broached samples, suggesting a higher stress concentration in the crack-tip by the broaching approach. The numerical analysis also revealed the more coincidence of the modeled energy values with the broaching method results, further highlighting the higher resemblance of the cracks made by this method to the ideal cracks. Interestingly, the radius of the plastic region in the slotting method was three times larger than in the broaching method, indicating the sharper tip of the pre-cracks in the broaching method. The application of the broaching method for pre-crack generation can lead to more accurate results in the mechanical fracture tests.

Effect of Build Parameters on the Mechanical Behavior of Polymeric Materials Produced by Multijet Fusion

The figure depicts the multi-jet fusion printing of specimens used to study the effect of changing build parameters on mechanical properties. At each layer, heat is applied to a surface with fusing agent (black) deposited atop fresh powder. A transparent build volume shows the temperature distribution (white-red color map) on the printed layer. Further details can be found in the article number 2100974 by Grace X. Gu and co-workers. For the image, we would like to credit: "Fabiola Leyva from HP Labs".

Measurement and Analysis of Deformation Behavior of Polyethylene Tube Subjected to Linear Loading and Unloading Stress Paths with Large Strain

A material testing apparatus for measuring the biaxial deformation behavior of a polymer tube has been developed to quantitatively evaluate the deformation behavior of polymeric materials. The testing apparatus can apply axial force and internal pressure to a tubular specimen. A noncontact strain measurement system was also developed, and the biaxial strain components and the radius of curvature in the axial direction of the bulging specimen are continuously measured to control the stress path applied to the specimen. Polyethylene tube with an outer diameter of 17 mm and a thickness of 2 mm are used as a test sample. The tubular specimens were subjected to linear stress paths with stress ratios of σΦ:σθ =1:0, 4:1, 2:1, 4:3, 1:1, 3:4, 1:2, 1:4, and 0:1, where σΦ and σθ are the axial and circumferential stress components, respectively, applied to the central area of the bulging specimen. Loading and unloading tests were performed to determine the biaxial true stress-logarithmic plastic strain curves. The strain rate was 1×10-3s-1. From these test results, contours of plastic work and the directions of the plastic strain rates were measured to identify a proper material model for the test sample using the Yld2000-2d yield function (Barlat et al., 2003).

Numerical Analysis of Unidirectional GFRP Composite Mechanical Response Subjected to Tension Load using Finite Element Method

Composite material is a well-known structural material which is increasingly adopted as an engineering structure material. Glass fiber reinforced polymer offers the lightweight and high strength characteristics that is required for the modern industry, such as aviation, automotive, wind power, and marine technology. One of the important mechanical characteristics of the composite materials are the tensile properties, because it is well known as the material strength. Therefore, the investigation of mechanical response on the glass fiber reinforced polymer (GFRP) tensile test using numerical analysis is important for the estimation of structural response of the GFRP complex structure, such as boat construction. The objective of this research is to assess and estimate the mechanical response of the GFRP composite material subjected to tension load using finite element method. The linear transversely isotropic model is developed to estimate the unidirectional glass fiber GFRP with the configuration of fiber orientation angles of 0°, 30°, 45°, 60° and 90°. The results show that FE simulation are capable to detect the specimen response during the tensile test. The maximum discrepancy of the estimated stress strain diagram is about 16.5% to 32% compared to experimental data. The larger orientation angle has shown the larger discrepancy value. It is found that the increment of discrepancy value is generated by the nonlinearity behavior of the material due to the domination of polymer material behavior on the large orientation angle. Otherwise, the FE models have estimated accurately the ultimate strength, maximum displacement and fracture load. It can be concluded that the linear transversely isotropic model is adequately accepted as the estimation method of the GFRP composite structure response.

New method for accelerated testing of the aging behavior of polymeric materials as a function of radiation and temperature

A new method is described for accelerated testing of the aging behavior of polymeric materials depending on simulated solar radiation in UV and sample temperature. A flat sample is exposed to a matrix of many pairs of values of UV irradiance (initiates photochemical reactions without temperature increase) and IR irradiance (defined heating of the sample without photochemical effects). Thus, in one and the same experiment, a matrix of property changes is obtained depending on a variety of defined value pairs of UV irradiance and sample temperature. The forced coupling of photochemical primary reactions and sample temperature in both practical use and in existing accelerated weathering is eliminated. This is a considerable economic advantage compared to the existing test methods, in which only one combination of irradiance and sample temperature is realized in one and the same weathering device.

Elongation Behavior of Polymeric Materials for Membrane Applications Using Molecular Dynamics

Elongation Behavior of Polymeric Materials for Membrane Applications Using Molecular Dynamics

Effect of Build Parameters on the Mechanical Behavior of Polymeric Materials Produced by Multijet Fusion

Multijet fusion (MJF) is a novel additive manufacturing (AM) process for the powder bed fusion of thermoplastic polymers. In recent years, MJF has been established as a promising manufacturing technique for the rapid prototyping and production of fully functional, large‐scale components at high resolution. Like other powder bed fusion techniques, MJF permits the printing of parts without support material, and does not require chemical postprocessing steps, making it especially suitable for fabricating parts with complex and intricate internal features. However, the effects of common build volume parameters (such as part orientation, location, and interpart spacing) on mechanical properties are currently not well understood. This study aims to provide a thorough and comprehensive description of the trends in mechanical properties observed in polyamide (PA)‐11 and PA‐12 samples printed using the MJF process. Tensile, flexural, and impact specimens are printed using varying build volume packing parameters and tested according to the corresponding ASTM standards. The fracture surfaces of tested specimens are studied and characterized to further understand the method of failure propagation through MJF‐printed PA‐11 and PA‐12. As this work demonstrates, determining an optimal bed packing algorithm will be instrumental for optimizing desired mechanical properties of printed parts.

Study of solute–solvent interaction in the solutions of PVA with PEG at 338 K by ultrasonic technique

The implementation of low Intensity ultrasound in polymer system acts as a dynamic mechanical deformation. It can be widely used to observe the variations in chemical and physical phenomenon related to change in the visco-elastic behavior. The velocity of ultrasound is related to the density and polymer storage modulus whereas the absorption of ultrasonic wave is connected with energy dissipation in the polymers. Frequently the technique is used in association with rheological methods as a medium of proffer a better understanding about the visco-elastic behavior of polymer materials. The aim of this paper is to study of solute–solvent interaction in the solution of polymer polyvinyl alcohol(PVA) andpolyethylene glycol(PEG) mixed with double distilled water have been done. The mixtures of samples such as Poly Vinyl Alcohol (PVA), Poly ethylene glycol (PEG) and DD water have been prepared at different concentrations. The solution has been magnetically stirred to find homogeneous solution. The Ultrasonic velocities, densities and viscosities are measured at 338 K by using the ultrasonic Interferometer, specific gravity bottle and Oswald viscometer respectively. The ultrasonic waves of two different frequencies such as 2 MHz and 5 MHz have been used. Depending upon the various data obtained, the different acoustical parameters such as adiabatic compressibility, intermolecular free length, acoustic impedance, relaxation time, ultrasonic attenuation coefficient (α/f2) have been evaluated. The obtained results have been discussed in detail and it has been observed that these results are very much helpful in describing the complete molecular interaction in the present sample. The observed variations in acoustical parameters show that all these parameters increase by increasing of the polymer concentration except of adiabatic compressibility and intermolecular free length.

Experimental Elucidation of volume change and local behavior of deformation of Nylon 66 and PC Materials by DIC Method and Micro-Vickers Hardness Test

It is a well-known fact that there is significant difference in magnitude of flow stresses and work hardening rates of polymeric materials between in tension and compression. There is a possibility that hydrostatic pressure is involved in this asymmetry to the loading axis, in which case volume change occurs in plastic deformation. And also, the propagation of localized deformations is often observed as a deformation behavior of polymeric materials. In such cases, it has been confirmed that the propagating portion of the crack must be hardened, but the deformed portion is softened. The aim of this study is to measure the variation of plastic Poisson’s ratio by means of Digital Image Correlation method to clarify the existence of the plastic compressibility of Naylon66 and Polycarbonate. Another aim is to elucidate the mechanism of softening at the neck. The authors conducted tensile tests of thin strip specimens and measured the axial and lateral strains by DIC method, then, plastic Poisson's ratio was derived. The result showed that plastic Poisson’s ratio of Naylon66 and Polycarbonate was smaller than the value of 0.5, that result in the existence of plastic compressibility in these materials. The Micro-Vickers hardness measurement for a gauge length was also performed to clarify the strength distribution of a specimen, and the results showed that the necking part of the materials was softened.

Rheological aspects of polysaccharides

The material structure which is formed in the manufacturing process of products with tailored properties governs the viscoelastic behavior of polymeric materials, and consequently determines the functionality of products made of polysaccharides. The mechanical (rheological) properties of these biopolymers reflect their time- and frequency-dependent behavior, and therefore, its determination represents the reliable instrument to study correlation between structure formation and rheological properties of polysaccharides. Three microbial extracellular polysaccharides, i.e., gellan, welan and xanthan, and two water-soluble cellulose derivatives, i.e., carboxymethylcellulose (CMC) and hydroxypropylmethylcellulose (HPMC) were examined by using frequency and creep-recovery tests. The resulted shear dynamic moduli demonstrated differences in viscoelastic behavior of the examined polysaccharides. For gellan samples differences in response at different stages of aging were observed, indicating that aging considerably influences the structure changes of water-based gellan systems.

Assessing the Compressive and Impact Behavior of Plastic Safety Toe Caps through Computational Modelling

Toe caps are one of the most important components in safety footwear, but have a significant contribution to the weight of the shoe. Efforts have been made to replace steel toe caps by polymeric ones, since they are lighter, insulated and insensitive to magnetic fields. Nevertheless, polymeric solutions require larger volumes, which has a negative impact on the shoe’s aesthetics. Therefore, safety footwear manufacturers are pursuing the development of an easy, low-cost and reliable solution to optimize this component. In this work, a solid mechanics toolbox built in the open-source computational library, OpenFOAM®, was used to simulate two laboratory standard tests (15 kN compression and 200 J impact tests). To model the polymeric material behavior, a neo-Hookean hyper-elasto-plastic material law with J2 plastic criteria was employed. A commercially available plastic toe cap was characterized, and the collected data was used for assessment purposes. Close agreements, between experimental and simulated values, were achieved for both tests, with an approximate error of 5.4% and 6.8% for the displacement value in compression and impact test simulations, respectively. The results clearly demonstrate that the employed open-source finite volume computational models offer reliable results and can support the design of toe caps for the R&D footwear industry.

Shock Wave Behaviour of Polymeric Materials for Detonation Waveshapers

This paper discusses the experimental determination of explosive shock attenuation parameters of four different polymers viz., Teflon, Phenol formaldehyde, Polyethylene foam and Polypropylene foam. These polymers are candidate materials for waveshapers in shaped charge warheads. Cylindrical specimens of the polymer materials were subjected to explosive shock loading by the detonation of RDX:Wax (95:5). Shock arrival time was measured using piezo-wafers positioned at known spatial intervals in the specimens. Initial shock velocity, stabilised shock velocity and attenuation constant were determined. These parameters are essential for the design of waveshapers. Foams have better shock attenuating properties compared to solids due to their cellular structure. Polypropylene foam has the highest shock attenuating characteristic among the four materials studied.

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.

Wear behaviour of polymeric materials reinforced with man-made fibres: A comprehensive review about fibre volume fraction influence on wear performance

In the mineral processing, mining, oil and gas industries, it is not uncommon to find mechanical components exposed to degradation and wear from slurries. Polymeric matrix composites (PMCs) are considered as potential alternatives to replace metallic materials in such severe environments because of their high strength to weight ratio, ease of production, high wear resistance and good corrosion/chemical resistance. Often, seemingly erratic wear behaviour is observed making preventive maintenance and time-to-failure difficult to manage. A major culprit is the complex physical and chemical interaction with the slurry, such as exposure to high temperatures, high alkalinity, high slurry density, insoluble inorganic contents, high hardness of suspended particles and humidity. It is well understood that the addition of reinforcing fibres greatly improves the stiffness and strength of polymeric matrix composites. However, the effect the reinforcement has on the wear performance is far less established and a framework to analyse the effect of fibre volume fraction is yet to be established. The difficulties in establishing such a framework lay in the multi-factorial contributions and the potential trade-offs with mechanical performance. This makes it much more difficult to isolate clear trends. The objective of the present work is to present a comprehensive review on the influence reinforcing fibres play on wear behaviour of PMCs. The influence of fibre volume fraction on wear performance of polymeric composites reinforced with man-made fibres is presented. The applied load, fibre length, coefficient of friction and chemical treatment of fibres are analysed with respect to wear performance of PMCs. Future trends in the use of fibre-reinforced polymeric composites in wear critical applications are identified. Research gaps in designing composites for wear applications are explained, aiming at motivating future research to address these gaps.

Dynamic mechanical analysis performance of pure 3D printed polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS)

Dynamic mechanical analysis (DMA) is a technique that is used to study the viscoelastic behaviour of polymeric materials. 3D printing is one of the well-known applications of additive manufacturing techniques which has wide areas of application. In that, Fusion Deposition modelling (FDM) has very fine outcomes with better printing qualities to execute good products. In this research work, the 3D printed samples of pure ABS and PLA were examined under dynamic mechanical analysis to study the various temperature heat, absorbing, storing, and dissipating behaviour of these samples. The results show, both ABS and PLA performed well under the heat flow categories. While comparing to conventional manufacturing technologies, these 3D printed DMA results are showing some excellent results. These polymeric samples may prepare as composites and used for various applications, for better outcomes and capabilities. Storage modulus, while taking the temperature values of ABS to 90 °C maximum and for PLA about 48 °C. This will happen, but this pure form of materials printed through FDM also has such a very good energy storing capacity. Considering the loss modulus energy dissipation in the form of heat started from 110 °C, this is one of the good signs on the fabricated technique and build quality of ABS. The continues decrease in the degree of crystallinity of the PLA and ABS increases the meshing strength noted in the damping factor.

DYNAMIC THREE-POINTS-BENDING TEST MODE OF TWO AMORPHOUS POLYMER MATERIALS (PMMA, PC) FOR THEIR VISCOELASTIC AND MECHANICAL CHARACTERIZATION

This paper presents an approach to classifying amorphous polymer materials. Temperature is This classification involves the determination of mechanical and viscoelastic characteristics considered a descriptive variable to clarify the specific field of practical applications of amorphous polymers. according to the reference temperature characterizing the behaviour of polymer materials. The mechanical and viscoelastic characteristics of amorphous polymers such as methyl poly-methacrylate (PMMA), polycarbonate (PC) and imide poly ether (PEI) are determined through the three-point dynamically embedded test carried out in an adiabatic close enclosure. The complex dissipative or conservative modules according to the temperature are represented. The results obtained show that the fluidity index of these materials is linked to their viscosity, which is a determining property which is decisive for the choice of the technique of the application of the material. Our method of measuring properties is therefore, in principle, comparable to the techniques used in industrial development.

Comprehending the role of process parameters and filament color on the structure and tribological performance of 3D printed PLA

The recent growth of 3D printing has prompted researchers to investigate the reliability of its products in numerous implementations. However, 3D printed object tribology has not been extensively reviewed so far. The present study is the first to explore how the tribological qualities of 3D printed PLA polymer are affected by the existence of different colors. To this end, fused deposition modeling (FDM) technology is used to produce tribological testing specimens. The impact of print orientation and the color is assessed by producing the samples in different directions (Horizontal, 45° angle, and Vertical) and filament colors (white, black, and grey), while the performance of tribological tests is undertaken in reciprocating sliding at two various applied loads (150 and 200 N). Attention is also paid to surface roughness and product hardness because they are important aspects for understanding the tribological behavior. Furthermore, to improve insight into the pre- and post-test surface morphology of parts produced through 3D printing, microscopy is used for capture of multiple images. According to the results, tribological behavior differs due to the diversity of print orientations and filament colors. Of the examined parameters, the white filament color is associated with maximum friction tendency, while maximum wear depth is associated with test pieces of 45° angle orientation and black filament color. Moreover, the sliding under high loads reduces wear, but the stick-slip phenomenon is more likely to occur at low load. The results indicate the demand for tribological testing to grasp the 3D printed polymer material behavior fully.

Can Accelerated Aging Procedures Predict the Long Term Behavior of Polymers Exposed to Different Environments?

During their useful life, polymers are subject to degradation processes due to exposure to specific environmental conditions over long times. These processes generally lead to changes, almost always irreversible, of properties and performances of polymers, changes which would be useful to be able to predict in advance. To meet this need, numerous investigations have been focused on the possibility to predict the long-term performance of polymers, if exposed to specific environments, by the so called “accelerated aging” tests. In such procedures, the long-term behavior of polymeric materials is typically predicted by subjecting them to cycles of radiations, temperatures, vapor condensation, and other external agents, at levels well above those found in true conditions in order to accelerate the degradation of polymers: this can produce effects that substantially deviate from those observable under natural exposure. Even following the standard codes, different environmental parameters are often used in the diverse studies, making it difficult to compare different investigations. The correlation of results from accelerated procedures with data collected after natural exposure is still a debated matter. Furthermore, since the environmental conditions are a function of the season and the geographical position, and are also characteristic of the type of exposure area, the environmental parameters to be used in accelerated aging tests should also consider these variables. These and other issues concerning accelerated aging tests applied to polymers are analyzed in the present work. However, bearing in mind the limitations of these practices, they can find useful applications for rating the durability of polymeric materials.

Parameter Determination and Model Modification of Sherwood-Frost Constitutive Model

The Sherwood-Frost constitutive model is widely used to predict the mechanical behavior of polymer materials, and it is a very important material model. In this study, the stress-strain curve of high-density polyethylene (HDPE) with a strain rate ranging from 935 to 5450 s−1 was obtained through the split Hopkinson bar test device. Based on the HDPE dynamic mechanical performance test, the method for determining the strain-rate parameters of the Sherwood-Frost constitutive model was analysed and the strain-rate term in the constitutive model revised. Using the experimental results of Sherwood and Frost, the method to determine the parameters of the density and temperature terms in the model was introduced. This study provides a reference for parameter determination and model modification of the Sherwood-Frost constitutive model.