Effect of heat pretreatment and strain rate on tensile properties of polycarbonate sheet

The effects of heat pretreatment and ambient gas (air and vacuum) on selected properties of the polycarbonate sheet have been studied. Changes in tensile properties as functions of heat pretreatment temperature (up to 160°C) and strain rate (wide range of 1.7 × 10^?4 ? 13.1 m/sec = 0.29 ? 2.3 × 10⁴ %/sec) were determined and these are discussed in relation to changes in differential scanning calorimetry (DSC) and gel permeation chromatography (GPC) data. The performance characteristics of the present tensile testing are obtained over a wide range of extension rates without changing the mode of deformation and the shape of the test pieces. It was suggested from the experimental results that heat pretreatment below the glass transition temperature (T_g) causes ordered molecular domains to grow on the free surfaces of the sheet, consisting of thermally deteriorated macromolecules and possessing lower crazing stresses (exhibiting more brittle mechanical responses, leading to the decrease in breaking strain and energy). The effect of annealing above T_g on the tensile properties, and on the results of DSC and GPC, could not be precisely understood.     

The effect of thermal pretreatment on the strength of polycarbonate

The effect of preheat treatment at temperatures below the glass transition for various periods of time on selected properties of molded polycarbonate has been studied. Changes in tensile and flexural strength as functions of time and preheat temperature (80–140°C.) were determined and these are discussed in relation to changes in the nature of the β-transition region and the influence of the glass transition region. It is suggested that the preheat treatment produces a greater degree of order within the amorphous region of the polymer, resulting in an increase in strength at temperatures up to 132°C. The strength of the polycarbonate before and after heat treatment appears to be independent of the presence of the equilibrium water content.     

Effect of thermal history on the tensile yield stress of polycarbonate in the β transition range

The tensile yield behaviour of three forms of polycarbonate differing in their thermal history is investigated, at constant strain rate, over a wide range of temperatures (?140° to + 80°C). The plot of the yield stress versus temperature exhibits a thermal history dependence over the whole range explored and reveals the β transition which is located at the same temperature T_β for the three forms. The yield behaviour is described assuming that two activated processes α and β requiring additive stresses are involved. The β component of the yield stress is found to be insensitive to thermal history as well as the related loss peak. Only the α process is affected; details concerning this dependence are discussed.     

Effect of strain rate on the tensile properties of mini-SiC/SiC composites

SiC/SiC composites are the ideal candidates for hot-end components in aerospace and other high-tech fields. In recent years, as one type of material with simple structures, mini-composites have been widely used to study or initially verify the properties of ceramic matrix composites (CMC). Nevertheless, attentions were rarely paid on the influence of strain rate on the mechanical properties of mini-composites. In this study, based on mini-SiC/SiC composites, we investigated the effect of the strain rate on their tensile strength, initial tensile modulus, Weibull modulus, and fracture work. Furthermore, the underlying mechanisms were discussed and the exact constitutive model of the as-prepared mini-SiC/SiC composites was constructed according to the Michaelis-Menten and generalized linear models. This work can fill the gaps in the CMC research in some degree and provide a preliminary theoretical basis for the formulation of tensile properties test standards of mini-composites.     

Effect of temperature and strain rate on the tensile deformation of polyamide 6

The effects of the draw temperature and the strain rate on the tensile deformation of polyamide 6 (PA6) were investigated using three PA6 samples with different initial shapes and physical dimensions. It is observed that the special double yielding phenomenon is indeed present in PA6, provided that certain temperature and strain rate are given, as well as the appropriate initial structure. The results also show that the dependence of the first yield stress on temperature is nearly linear while on strain-rate is logarithmic. The temperature and strain-rate sensitivity change at the draw temperature in the vicinity of the glass transition temperature of PA6. The double yielding of PA6 is not only the combination of two thermally activated rate processes depending on temperature and strain rate, but also associated with the initial structure of samples. The yielding manner for PA6 seems to be determined by the synergetic effect of both the deformation of amorphous and crystalline phases. Thus some special structure involving the crystalline and amorphous phases should come into being in PA6 exhibiting double yielding. Especially the important role of inter- and intra-link should be taken into account. The theory of partial melting-recrystallization cannot account fully for the double yielding of PA6.     

Effect of the strain rate on the tensile strength of a copper shaped-charge jet

The data on the penetration depth of a rotating shaped-charge jet were used to estimate the strength of the material of a copper jet formed from a “low” conical linear with an apex angle of120° under the action of centrifugal forces. The estimates0.07–0.15 GPa obtained are close to the static yield point of deformed copper. The jet strength, which is estimated using the length of the fragments formed upon breakup of a rotation-free jet owing to the axial velocity gradient, attains1–1.5 GPa at a strain rate of ≌2·10⁴ sec⁻¹. Lavrent’ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 1, pp. 111–118, January–February, 1997.     

Effects of temperature and strain rate on the tensile behavior of short fiber reinforced polyamide-6

Tensile behavior of extruded short E-glass fiber reinforced polyamide-6 composite sheet has been determined at different temperatures (21.5°C, 50°C, 75°C, 100°C) and different strain rates (0.05/min, 0.5/min, 5/min). Experimental results show that this composite is a strain rate and temperature dependent material. Both elastic modulus and tensile strength of the composite increased with strain rate and decreased with temperature. Experimental results also show that strain rate sensitivity and temperature sensitivity of this composite change at a temperature between 25°C and 50°C as a result of the glass transition of the polyamide-6 matrix. Based on the experimental stress-strain curves, a two-parameter strain rate and temperature dependent constitutive model has been established to describe the tensile behavior of short fiber reinforced polyamide-6 composite. The parameters in this model are a stress exponent n and a stress coefficient σ*. It is shown that the stress exponent n, which controls the strain rate strengthening effect and the strain hardening effect of the composite, is not only strain rate independent but also temperature independent. The stress exponent σ*, on the other hand, varies with both strain rate and temperature.     

Effect of tensile strain rate on the mechanical properties of polystyrene and high-impact polystryene

The dependency of the mechanical properties (Young's modulus, maximum load, breaking strain, and breaking energy) of polystyrene (PS) and high-impact polystyrene (HIPS) on the tensile deformation speeds was examined without changing the mode of deformation or the shape of the test specimen. It was found that HIPS has an excellent mechanical balance compared with PS for both low (1.7 × 10^?4 to 2.9 × 10^?2 m/sec) and high (1.3–16m/sec) speeds. This is due to the following two mechanisms ( which have different time responses) originating from the dispersed rubber particles: (1) at low speeds, the generation of large numbers of microcrazes, and (2) at high speeds, tensile-orientation hardening of the rubber and cold-drawing of the PS matrix resulting from the rise in temperature accompanied by the abrupt eleongation of the rubber phases.     

Thermal and strain rate sensitive compressive behavior of polycarbonate polymer - experimental and constitutive analysis

The mechanical behavior of polycarbonate (PC) polymer was investigated under the effect of various temperatures and strain rates. Characterization of polymer was carried out through uniaxial compression tests and split Hopkinson pressure bar (SHPB) dynamic tests for low and high strain rates respectively. The experiments were performed for strain rates varying from 10 ^?3 to 10³ and temperature range of 213 to 393 K. By conducting these experiments, the true stress–strain (SS) curves were obtained at different temperatures and strain rates. The results from experiments reveal that the stress–strain behavior of polycarbonates is different at lower and higher strain rates. At higher strain rate, the polymer yields at higher yield stress compared to that at low strain rate. At lower strain rate, the yield stress of the polymer increases with the increase in strain rate while it decreases significantly with the increase of temperature. Likewise, initial elastic modulus, yield and flow stress increase with the increase in strain rate while decreases with the increase in temperature. The yield stress increases significantly for low temperature and higher strain rates. On the basis of experimental findings, a phenomenological constitutive model was employed to capture the mechanical behavior of polymer under temperature and loading rate variations. The model predicted the yield stress of polymer at varying strain rate and temperature also it successfully predicted the compressive behavior of polymer under entire range of deformation.     

Effect of thermal treatments on the yielding of polycarbonate

Two different thermal treatments were applied to polycarbonate (PC) in terms of slow cooling (annealed samples) after a thermal treatment at a temperature above the glass‐transition temperature or abrupt cooling in a liquid‐nitrogen environment (quenched samples). Tensile and compression experiments were performed on the two types of samples at three different effective strain rates. A viscoplastic model based on the fundamental assumptions of the Eyring model and on a kinematic formulation, which separated the viscoelastic and plastic strain, developed in previous works, was used to describe the yield and postyield behavior of thermally treated PC. The different thermal treatments affected the parameters of the material microstructure. A satisfactory agreement between the experimental data and calculated results was found. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 796–805, 2005     

Effect of fiber reinforcement on the tensile, fracture and thermal properties of syntactic foam

This paper examines the effect of the fiber content and fiber length on tensile, fracture and thermal properties of syntactic foam. Results showed that a hybrid structure demonstrates a significant increase in the ultimate tensile strength, σ_uts, and Young's modulus, E, with increasing fiber loading. Interestingly, the fracture toughness, K_Ic, and energy release rate, G_Ic, increased by 95% and 90%, respectively, upon introduction of 3 wt% short carbon fibers in syntactic foam, indicating the potent toughening potential for short carbon fibers in syntactic foam systems. SEM and OM studies identified the presence of several toughening mechanisms. An estimate of the contribution from each toughening mechanism by composite theory and fractography revealed that the specific energy required to create new surfaces was enhanced by the presence of fibers and was the main contributor to the toughness of the short fiber reinforced syntactic foam.     

Impact fracture behavior of molecularly orientated polycarbonate sheets

The impact fracture behavior of molecularly orientated polycarbonate (PC) sheets was investigated. The molecular orientation was achieved via a newly developed equal channel angular extrusion (ECAE) process. Improvement in impact fracture propagation resistance was observed in the ECAE processed PC sheets. The improved impact resistance was found to be directly related to the changes in molecular orientation because of ECAE. The unique characteristics of the ECAE process for polymer extrusion are described. The potential benefits of ECAE in enhancing physical and mechanical properties of the extruded PC sheets are discussed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2060–2066, 2001     

Constitutive modeling of polycarbonate during high strain rate deformation

A constitutive model is presented for large strain deformation of polycarbonate (PC) at high strain rates (above 10² s^?1). The proposed model considers the primary process (α) and the two secondary rate‐activated processes (β and γ). It is shown that the secondary transitions in the material affect the yield and post yield behavior of the material at high strain rates. The constitutive model has been implemented numerically into a commercial finite element code through a user material subroutine. The experimental results, obtained using a split Hopkinson pressure bar, are supported by dynamic mechanical thermal analysis (DMTA) and DSR (Decompose/Shift/Reconstruct) method. These are employed to gain understanding of the material transitions, and to further the linkages between material viscoelastic, yield, and stress–strain behavior. Comparison of model predictions with experimental data demonstrates the ability of model to capture the characteristic features of stress–strain curve of the material such as initial linear elasticity, global yield, strain softening, and strain hardening at very high strain rates (up to 10,000 s^?1). POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers     

Mechanical behaviour at large strain of polycarbonate nanocomposites during uniaxial tensile test

The present study focuses on the mechanical behaviour of polycarbonate nanocomposites reinforced by alumina or silica nanoparticles at low levels of incorporation. More particularly, we present an experimental approach, specific to large strain measurements by using a Digital Image Correlation (DIC) technique. The mechanical mechanisms involved during uniaxial tensile test of polycarbonate nanocomposites were studied at two-dimensional scales. First, elastic properties of the nanocomposites were determined at macro-homogeneous scale and compared to values obtained by continuum-based elastic micromechanical models. Then the in-plane kinematics measurements at the central part of a double-edge notched sample is analysed locally. The evolution during the test of the volumetric strain and axial strain profiles were studied before and after the yield stress: this analysis revealed the existence of several damage processes during the test up to rupture and put in relief the influence of fillers. Finally, the necking phenomenon was statistically studied and the shape of the neck in terms of strain intensity and localisation was analysed.     

Effects of molecular weight and strain rate on the flexural properties of polycarbonate

The effects of changes in molecular weight (7000 to 22,000) and strain rate (0.0001 to 4 min.^?1) on the flexural properties of polycarbonate have been examined in detail with the use of speciments of different molecular weight prepared by high-energy electron irradiation. The results have been plotted as surfaces which show the dependence of both stress and strain on molecular weight and strain rate, and these surfaces have been described in terms of brittle, transitional, and ductile regions. The relationships between stress or strain and molecular weight in the brittle region have been shown to be hyperbolic. A single failure locus has been found to include all the corresponding stress and strain data obtained at the various molecular weights and strain rates. In the low strength region this locus exhibits a proportionality between stress and strain, while at high strength values, strain becomes a logarithmic function of stress. Stress–molecular weight data obtained at the various rates have been superimposed to form a single composite curve, and the corresponding crossplots of stress–log rate have been treated similarly. It is concluded from these superpositions that an equivalence exists between changes in both molecular weight and strain rate such that a tenfold change in strain rate corresponds approximately to a change of 1000 in molecular weight. Strain-strain rate data obtained at the various molecular weights have also been superimposed in a similar manner. Modulus is shown to increase slowly with decrease in molecular weight and appears to be relatively insensitive to changes in strain rate.     

An experimental investigation of the large-strain tensile behavior of neat and rubber-toughened polycarbonate

The large-strain tensile behavior of polycarbonate and polycarbonate filled with several volume fractions (f) of rubber particles is studied via an optical technique. Digital image correlation is used to determine, in two dimensions, the local displacement gradients and full-field displacements during a uniaxial tension test. Full-field strain contours, macroscopic true stress-strain behavior, and local volumetric strain are reduced from the raw test data. Full-field strain contours exhibit a decreasing degree of localization with increasing f. The true stress-strain results show a decrease in modulus, yield stress, post-yield strain softening, and subsequent strain hardening with increasing f. The volumetric strain decreases with increasing f as well. In the case of the neat polymer, comparisons are made to a three-dimensional finite element simulation.     

Effect of ethylamine pretreatment on the tensile strength of periodate oxycelluloses

A study has been made of the effect of ethylamine pretreatment on the changes in strength suffered by cotton fibres and viscose rayon filaments on oxidation with periodate and on subsequent reduction with borohydride. The extent of chain scission during periodate oxidation has been estimated roughly from intrinsic viscosity measurements in cadoxen on the borohydride-reduced materials and has proved to be small. The variation of strength with the degree of oxidation of the oxycelluloses themselves has been interpreted in terms of Bueche's model for rubbery polymers. It appears to be a combination of the effects of chain scission, chain flexibility, swelling and the formation of hemi-acetal crosslinks. By assuming that the first two are the same in both the original and the reduced oxycelluloses, the effects on the strength of the oxycelluloses of the destruction of intermolecular hydrogen bonds by swelling and the formation of intermolecular hemi-acetals have been estimated. In the early stages of the oxidation of cotton, hemi-acetal formation causes a fall in strength, which is much smaller in ethylamine-treated than in untreated cotton. This is because of the more uniform distribution of reactive sites in the former material. As oxidation proceeds the destruction of hydrogen bonds through swelling more than offsets the number of hemi-acetals formed, and an increase in strength occurs. In viscose rayon, no initial fall of strength occurs because this material is far less effectively crosslinked than cotton.     

Effects of temperature and strain rate on the tensile behavior of polypropylene composites insulator coatings used in offshore deepwater pipelines

Polypropylene (PP) composites are being increasingly used as thermal insulation coatings in both onshore and offshore pipelines. In this study, the direct tensile behavior of pure PP, PP with glass microsphere filler, and PP with 65% glass filler were investigated at 22, 60, and 90 °C temperatures at various strain rates from 0.003/min to 0.300/min. Fourier transform infrared spectroscopy and scanning electron microscope studies were used to characterize the materials. Stress–strain relationships of the materials were nonlinear in the elastic and inelastic domains. Addition of glass fiber to the PP increased the elastic modulus, but the yield strength and yield strain were reduced along with the ductility. Based on the experimental results, constitutive models coupling the strain rate and temperature have been developed to predict the yield strength, the initial elastic modulus and secant modulus at yield for the PP composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45209.     

Effect of strain rate on tensile properties of polyurethane/(multiwalled carbon nanotube) nanocomposite

In this research, polyurethane (PU)/(carbon nanotube) (CNT) samples, with two different contents of multiwalled carbon nanotubes (MWCNTs; i.e., 0.5 and 1.0 wt%) were fabricated through a solution casting method. To investigate the effect of strain rate on tensile properties, tensile tests were done on standard samples at constant temperature and different strain rates (2 × 10^?5 to 2 × 10^?2 s^?1). Eyring's model was performed to clarify the role of both strain rate and CNTs content on activation volume and activation enthalpy of PU. To elucidate the role of strain rate and CNTs content on fracture behavior of PU, fracture surfaces of some samples were also investigated by scanning electron microscopy. The results of tensile tests show the intense effect of strain rate on tensile properties of PU/MWCNTs nanocomposites. Also, it was proved that the dependency of tensile properties of PU nanocomposites on strain rate decreases as CNTs content increases. The microscopic observations of the samples also demonstrate that increasing the strain rate changes the behavior of the fracture surface to less a ductile fracture, and increasing CNTs content causes much surface roughness. Finally, by investigation of the activation enthalpies, it is confirmed that much higher enthalpy is needed to fracture the samples with increased MWCNTs content, as the activation enthalpy changes from 45 for neat PU to 131 kJ/mol for PU/(1% MWCNTs) samples. J. VINYL ADDIT. TECHNOL., 22:356–361, 2016. © 2014 Society of Plastics Engineers     

The tensile behavior of polycarbonate and polycarbonate–glass bead composites

The tensile behavior at 20°C of unfilled polycarbonate and polycarbonate–glass bead composites (90/10 vol %) has been investigated by tensile testing with simultaneous volume change measurements. Both the effect of the bead size and the degree of interfacial adhesion on the tensile behavior of the composites has been studied. A simple model has been applied to obtain quantitative information on the separate contributions of several possible deformation mechanisms to the total deformation. For unfilled polycarbonate and the polycarbonate–glass bead composites with excellent interfacial adhesion, shear deformation is found to be the only significant non-Hookean deformation mechanism. By means of strain recovery experiments it is shown that the shear deformation is highly elastic in character. For the composites with poor interfacial adhesion, besides shear deformation also dewetting cavitation contributes to the non-Hookean deformation. The differences in tensile behavior between the composites with excellent and poor interfacial adhesion are explained by the different mechanisms for shear band formation at excellently and poorly adhering glass beads.