Tensile mechanical properties of basalt fiber reinforced polymer composite under varying strain rates and temperatures

High-strength woven fabrics and polymers are ideal materials for use in structural and aerospace systems. It is very important to characterize their mechanical properties under extreme conditions such as varying temperatures, impact and ballistic loadings. In this present work, the effects of strain rate and temperature on the tensile properties of basalt fiber reinforced polymer (BFRP) were investigated. These composites were fabricated using vacuum assisted resin infusion (VARI). Dynamic tensile tests of BFRP coupons were conducted at strain rates ranging from 19 to 133 s⁻¹ using a servo-hydraulic high-rate testing system. Additionally, effect of temperature ranging from −25 to 100 °C was studied at the strain rate of 19 s⁻¹. The failure behaviors of BFRP were recorded by a Phantom v7.3 high speed camera and analyzed using digital image correlation (DIC). The results showed that tensile strength, toughness and maximum strain increased 45.5%, 17.3% and 12.9%, respectively, as strain rate increased from 19 to 133 s⁻¹. Moreover, tensile strength was independent of varying temperature up to 50 °C but decreased at 100 °C, which may be caused by the softening of epoxy matrix and weakening of interfaces between fibers and matrix when the glass transition temperature was exceeded.     

Fractographic relation between progressive failure and strain measurement techniques for recently developed configuration of carbon fiber/epoxy laminate

In this work, fracture mechanisms of a newly developed carbon fiber/epoxy laminate [+75/0/-75]_s were assessed by scanning electron microscopy (SEM). The composite strain-stress curves were plotted with the displacement information simultaneously acquired from both a tensile testing machine crosshead and an extensometer. The strain-stress curve plotted with the displacement data from the machine test showed an average slope change from E_1m = 22.783 GPa to E_2m = 13.170 GPa on about 65% of the total strain before global failure, while strain-stress curves plotted with displacement data from the extensometer showed one single slope. While results reported in literature related to composite failure mechanisms, where some authors reported a slope change in strain-stress curves associated to progressive failure, experimental evidence in this work for strain-stress curves showed one single slope, indicating that such slope change is related to the strain measuring technique, and not to a progressive failure. The fracture surface was studied, and four main features were observed, which were related to failure mechanisms during the uniaxial test. The identified failure mechanisms occurred on a stage above 93% of the total strain before global failure.     

Influence of strain rate on the compressive yield stress of CMDB propellant at low,intermediate and high strain rates

The mechanical properties of composite modified double base (CMDB) propellant significantly depend on the strain rate. In particular, the yield stress increases dramatically at higher strain rates. To study this behaviour, low, intermediate and high strain rate compression testing (1.7 × 10⁻⁴ to 4 × 10³ s⁻¹) of CMDB propellant at room temperature was conducted by using a universal testing machine, a hydraulic testing machine and a split Hopkinson pressure bar (SHPB) system, respectively. The yield stress was observed to increase bilinearly with the logarithm of strain rate, with a sharp increase in slope at a strain rate of 5 × 10¹ s⁻¹, which was supported by dynamic mechanical analysis (DMA) testing. The Ree-Eyring model, involving two rate-activated processes, was employed to predict the yield behaviour of CMDB propellant over a wide range of strain rates. The predictions are in excellent agreement with the experimental data.     

Mechanical properties of fluorinated ethylene propylene (FEP) foils in use for neutrino detector project

The use of fluorinated ethylene propylene (FEP) foils as engineering materials for aerospace, solar thermal collector and neutrino detector applications has attracted considerable attention in recent decades. Mechanical properties are indispensable for analyzing corresponding structural behavior to meet the demands of safety and serviceability. In this paper, uniaxial tensile tests taking into account loading speeds, uniaxial tensile cyclic tests in terms of stress amplitude and loading cycles and creep tests considering loading stress and time were carried out to characterize mechanical properties. For uniaxial tensile properties, elastic modulus, yield stress, breaking strength and elongation were analyzed in detail. It is found that these mechanical properties except breaking elongation increased with loading speeds and that mechanical properties obtained in transverse direction were more sensitive than those obtained in machine direction. For cyclic properties, elastic modulus and ratcheting strain tended to be stable after certain cycles, demonstrating that cyclic elastic moduli were more suitable for analyzing structural behavior than those obtained in uniaxial tensile experiments. For creep properties, apparent strain at 6 MPa suggested that special attention was necessary for analyzing structural behavior if maximum stress was larger than 6 MPa. In general, this study could provide useful observations and values for understanding mechanical properties of FEP foils.     

Elasto-viscoplastic behaviour of a polyvinylidene fluoride (PVDF) in tension

The present paper is concerned with the plasticity of a polyvinylidene fluoride (PVDF) in tension. Strain rate strongly influences the plastic behaviour, but the variation of the elastic properties is almost negligible within the range of strain rates considered in the study (from 1.6 × 10⁻⁴ s⁻¹ up to 1.6 × 10⁻¹ s⁻¹). In particular, the yield stress and the ultimate tensile strength are strongly rate-dependent. A one-dimensional elasto-viscoplastic phenomenological model is proposed and analysed. Despite the nonlinearity of the model equations, only one tensile test performed with variable strain rate is sufficient to identify all material parameters. Model predictions are compared with experiments showing good agreement.     

Rapid solidification of cobalt melt by molecular dynamics simulation

Molecular dynamics simulation was applied to investigating the evolvement rule of cobalt melt microstructure during solidification at different cooling rates. The cooling rate for the formation of amorphous phase is determined by analyzing the radial distribution function, the H–A bond-type index and the mean square displacement. The simulation results showed that the nucleation undercooling increases with the initial temperature, and in the undercooling versus temperature curve, there are two inflection points. Besides, when the initial temperature reaches 2450 K, the undercooling will be stabilized at 1061 K. As the cooling rate is less than 1.0?×?10^11.0 K s^?1, the FCC and HCP crystal structures will be obtained. Amorphous structure will be obtained if the cooling rate is more than 1.0?×?10^13.0 K s^?1. If the cooling rate of the Co melt is between 1.0?×?10^11.0 and 1.0?×?10^13.0 K s^?1, the crystal and amorphous structures will be coexistent, which indicates that the critical cooling rate of crystal–amorphous transition is 1.0?×?10^11.0 K s^?1.

     

Quantitative assessment of deformation-induced damage in polyethylene pressure pipe

This paper presents results from a study that quantifies the influence of excessive deformation on the damage development in polyethylene (PE) pressure pipe. The experimental investigation is through the application of a novel two-stage approach to the D-split test of notched pipe ring (NPR) specimens. The first test is to introduce damage by subjecting the specimens to different levels of tensile strain at crosshead speeds of 0.01, 1, 10 or 100 mm/min. The second test is to apply monotonic tensile loading at a crosshead speed of 0.01 mm/min to characterize the mechanical properties for specimens that have had damage generated in the first test. Experimental results suggest that elastic modulus and yield stress decrease and yield strain increases with increase of the strain introduced in the first test. Variation of experimentally measured elastic modulus is used to establish influence of crosshead speed on the damage evolution in the PE pressure pipe.     

Slow-brittle-fracture transition in polymethylmethacrylate

A slow crack growth was achieved in initially edge-cracked specimens made of a high-molecular weight PMMA by regulating the cross-head speed of loading by a computer-driven testing machine. The strain rate \(\dot \varepsilon \) used during the tests varied between \(\dot \varepsilon \) =1× l0^?6 s^?1 and 1×10^?4 s^?1. It was shown that, in this zone of slow quasi-static loading of brittle polymethylmethacrylate specimens under conditions of plane stress, the crack initiated for a critical value of loading, at some characteristic zone of strain-rate variation at the crack tip. It was established that for strain rate between \(\dot \varepsilon \) =0.18×10^?5 s^?1 and \(\dot \varepsilon \) =0.45×10^?4 s^?1 brittle cracks were propagating always slowly with velocities in the range ofc=3 to 5×10^?2 m/s. For values ofv _s outside this transition zone fracture was typically brittle with high crack-propagation velocities. As the strain rate was varying beyond the stable low-velocity region, a two-step crack velocity pattern was operative, where the one step took always low values, and the other step corresponded to crack-propagation velocities significantly higher than these limits, tending to typical brittle-fracture velocities of the material. Oscillations of the velocityc at the transition zones, or, in many cases all over the zone of slow propagation of the crack, indicated the unstable character of crack propagation, influenced by different stress raisers and especially by the opposite longitudinal boundary of the specimen. Stress intensity factor values during crack propagation, evaluated from the front (cuspoid) and the rear (external) caustic, which remained alwaysk _g-dominant, were following similar trends as the variation of the crack propagation velocity.     

Viscoelastic properties of Nafion at elevated temperature and humidity

Tensile stress–strain and stress relaxation properties of 1100 equivalent weight Nafion have been measured from 23 to 120 °C at 0–100% relative humidity. At room temperature, the elastic modulus of Nafion decreases with water activity. At 90 °C, the elastic modulus goes through a maximum at a water activity of ～ 0.3. At temperatures ≥90 °C, hydrated membranes are stiffer than dry membranes. Stress‐relaxation was found to have two very different rates depending on strain, temperature, and water content. At high temperature, low water activity, and small strain, the stress relaxation displays a maximum relaxation time with stress approaching zero after 10³–10⁴ s. Water absorption slows down stress‐relaxation rates. At high water activity, the maximum stress relaxation time was >10⁵ s at all temperatures. No maximum relaxation time was seen at T ≤ 50 °C. Increasing the applied strain also resulted in no observed upper limit to the stress relaxation time. The results suggest that temperature, absorbed water, and imposed strain alter the microstructure of Nafion inducing ordering transitions; ordered microstructure increases the elastic modulus and results in a stress relaxation time of >10⁵ s. Loss of microphase order reduces the elastic modulus and results in a maximum stress relaxation time of 10³–10⁴ s. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 11–24, 2009.     

Experimental investigation and modeling of the mechanical behavior of PC/ABS during monotonic and cyclic loading

The purpose of this work is to characterize the mechanical behavior of blends of polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) during monotonic and cyclic loading. Compression experiments were performed using a SHIMADZU universal testing machine (10⁻⁴ to 10⁻² s⁻¹) and a split Hopkinson pressure bar (1600–5000 s⁻¹), with, the test temperatures ranging from 293 to 353 K. The influence of the rate and temperature on the deformation of PC/ABS is discussed in detail. Based on the investigation of numerous constitutive models, a phenomenological model called DSGZ was chosen to describe the compression behavior of PC/ABS. This model could not accurately reproduce the deformation of polymers at high strain rates when utilizing the same material coefficients for the low and high strain–rate deformations. In addition, this model was unable to capture the deformation features during unloading and subsequent reloading when adopting the original stress–strain updating algorithm. Hence, some improvements to the model have been implemented to better predict the deformation. Finally, the model predictions are shown to be consistent with the experimental results.     

Molecular origin for rheological characteristics of native gellan gum

The ¹H-nuclear magnetic resonance spectrum showed that the l-rhamnosyl residues of native gellan gum were coinvolved in both a small number of ⁴C₁-pyranose conformations and a large number of ¹C₄-pyranose conformations, whereas for deacylated polymer, almost of the residues were involved in ⁴C₁-pyranose conformation. The flow curves of native gellan gum showed plastic behavior above 0.2%. The elastic modulus stayed at a constant value with increase in temperature up to 40 °C, then decreased rapidly. The elastic modulus increased with addition of CaCl₂ (6.8 mM) and stayed constant value with increase in temperature up to 65 °C, then decreased rapidly. The stronger elastic modulus was observed in deacylated gellan gum with addition of CaCl₂. The elastic modulus of native gellan gum showed larger value than that in aqueous solution in the presence of urea (4.0 M). Intra- and intermolecular associations of native gellan gum molecules in the presence of Ca⁺² were proposed.     

Melt elongation flow behaviour of LDPE/LLDPE blends

The extensional rheological properties of low density polyethylene (LDPE)/linear low density polyethylene (LLDPE) blend melts were measured using a melt spinning technique under temperatures ranging from 160 to 200 °C and die extrusion velocities varying from 9 to 36 mm/s. The results showed that the melt elongation stress decreased with a rise of temperature while it increased with increasing extensional strain rate and the LDPE weight fraction. The dependence of the melt elongation viscosity on temperature roughly obeyed the Arrhenius equation, it increased with increasing extensional strain rate and the LDPE weight fraction when the extensional strain rate was lower than 0.5 s⁻¹, and it reached a maximum when the extensional strain rate was about 0.5 s⁻¹, which can be attributed to the stress hardening effect.     

Nonlinear viscoelasticity of polystyrene solutions. III. Stress development at the start of steady shear flow and an experimental check of some constitutive models

The development of the shear stress at the start of shear flow at constant rate of shear κ was measured for polystyrene solutions in diethyl phthalate with a cone-and-plate rheometer. Ranges of molecular weight M and concentration c were 3.10 × 10⁶?7.62 × 10⁶ and 0.112?0.329 g/cm³, respectively. The shear stress as a function of time t exhibited a marked maximum at large κ when either M or c was relatively low. When M and c were high, the maximum was broad and low. In a few extreme cases no maximum was observed in the range of κ studied. The constitutive model of Bernstein, Kearsley, and Zapas could describe approximately the shear stresses at a sudden start and on cessation of steady shear flow with a memory function evaluated from the strain-dependent relaxation modulus. The strain dependence of the memory function for solutions of low M or c was approximately expressed as exp{?α|s|} where α is a constant (ca. 0.37) and |s| is the absolute value of shear strain. When M and c were high, the strain dependence was found to be more diffuse and to require several terms if approximated by exponential functions of |s|. The Lodge model based on a strain-rate dependent relaxation spectrum was not able to describe the strain-dependent relaxation modulus as well as the interrelation between shear stresses at a sudden start and a cessation of steady shear flow.     

Comparative studies of oxygenated fuel synthesis with diesel from the measurements of density,speed of sound and refractive index

An experimental investigation on the feasibility and relevance of the tri fuel blends of ethanol and dibutyl ether with diesel was studied to replace pure diesel. The solubility of the ethanol and dibutyl ether with a percentage of 25% and 75% resulted with no phase separation, found miscible and stable with diesel at any percentage. However, the properties such as densities and refractive index experimentally verified for different blend ratios. A density of test samples with various compositions was tested. High precise equipment is engaged to analyze the density, speed of sound, refractive index for various fuel compositions. The temperature ranges between 298 K and 343 K show a greater impact on variation in the fuel properties. Density, speed of sound, refractive indices measured as a function of the temperature with an accuracy of?±?0.001 and?±?0.0001. Further, the validation of experimental method has been tested using Lorentz–Lorenz (L–L) analysis with a deviation of 0.4%. The uncertainty for fluid velocity is?±?0.3 m s^?1, and the experimental estimated excess molar volume uncertainty is 2?×?10^?3 cm³ mol^?1. The substantiation of intermolecular interactions between the liquids is found to be significant in both experimental and prediction analysis of each sample. The exergy destruction specifies with 46% which includes the air flow and chemical heat energy transfer losses.

     

Polyurethanes for potential use in transparent armour investigated using DSC and DMA

A material combination that may be applied as transparent armour is glass-clad polyurethane. These are comprised of a relatively thin glass strike face and a relatively thick (transparent) polyurethane backing layer. Three transparent polyurethane samples were investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The DSC results identified the glass transitions and in some cases the melting and crystallisation processes. The DMA experiments were only performed on heating around the glass transition region to further investigate this transition. The experiments were performed at three different frequencies (1, 10 and 100 Hz); the shift of the glass transition with the frequency was clearly observed. The method of time–temperature superposition was used to extrapolate the results to higher frequencies as the magnitude of the strain-rate occurring within ballistic applications is in the order of 1000 s⁻¹ or higher. Polyurethane with a rubbery behaviour at normal (low) strain rates can be stiff and brittle when used as an armour component (temperature below its dynamic T _g value).     

Microstrain investigation of polyethylene

The small-strain mechanical behavior of crystalline polyethylene has been studied by using a microstrain technique with strain resolution on the order of 10^?6. The strain rate was varied from 10^?6 to 10^?4 sec.^?1, and a temperature range of 17–28°C. was investigated. A strong dependence on strain rate and temperature has been observed for the following parameters which characterize the mechanical response of polyethylene in the microstrain region: the initial modulus of the stress–strain curve, the deviation in strain from ideal linear elastic behavior at a given stress amplitude, and the energy dissipated in a deformation cycle. The Young's moduli that were observed by means of tensile tests in the microstrain region were only about 20% lower than the values reported in other investigations at kilocycle and megacycle frequencies. The experimental method made it possible to isolate a deformation process which was attributed to a crystallographic shear mechanism corresponding to a yield point of 27 psi. This shear mechanism is discussed in terms of the various shear processes, such as slip, twinning, and the orthorhombic–monoclinic phase change.     

The use of nano- and micro-instrumented indentation tests to evaluate viscoelastic behavior of poly(vinylidene fluoride) (PVDF)

Nano-load (n-IIT) and micro-load (μ-IIT) instrumented indentation tests (IITs) were used to characterize elastic modulus and hardness in a semicrystalline polymer. The tests were conducted with loading rates ranging from 4.9 to 317 mN.min⁻¹ for n-IIT and from 300 to 10000 mN.min⁻¹ for μ-IIT. A decrease in the elastic modulus was observed as the load rate increased for the n-IIT process, and the elastic modulus increased as the load rate increased for the μ-IIT process. This behavior was explained by two-flow volume control under the indenter and the corresponding shear stress, which can influence the state of stress. The effect of holding time on the elastic modulus and hardness was also investigated for μ-IIT. E decreased with increasing holding time up to 30 s and became constant from there on. Hardness, however, decreased for all holding times evaluated. The steady state creep was only reached after 90 s, which is significantly higher than the time for elastic modulus stabilization.     

Comparison of the transient stress–strain response of rubber to its linear dynamic behavior

Master curves of the small strain and dynamic shear modulus are compared with the transient mechanical response of rubbers stretched at ambient temperature over a seven‐decade range of strain rates (10^?4 to 10³ s^?1). The experiments were carried out on 1,4‐ and 1,2‐polybutadienes and a styrene–butadiene copolymer. These rubbers have respective glass transition temperatures, T_g, equal to ?93.0, 0.5, and 4.1 °C, so that the room temperature measurements probed the rubbery plateau, the glass transition zone, and the onset of the glassy state. For the 1,4‐polybutadiene, in accord with previous results, strain and strain rate effects were decoupled (additive). For the other two materials, encroachment of the segmental dynamics precluded separation of the effects of strain and rate. These results show that for rubbery polymers near T_g the use of linear dynamic data to predict stresses, strain energies, and other mechanical properties at higher strain rates entails large error. For example, the strain rate associated with an upturn in the modulus due to onset of the glass transition was three orders of magnitude higher for large tensile strains than for linear oscillatory shear strains. © 2011 Wiley Periodicals, Inc.* J Polym Sci Part B: Polym Phys, 2011     

Effects of humidity on Young's modulus in poly(methyl methacrylate)

Tensile tests on poly (methyl methacrylate) (PMMA) were conducted to clarify the effects of humidity and strain rate on tensile properties, particularly Young's modulus. Prior to the tensile tests, specimens were kept under various humidity conditions at 293 K, which were the same as the test conditions, for a few months to adjust the sorbed water content in the specimens. The tensile tests were performed under each humidity condition at three different strain rates (approximately 1.4 × 10^?3, 1.4 × 10^?4, and 1.4 × 10^?5 s^?1). Stress‐strain curves changed with humidity and strain rate. Young's moduli were also measured at small applied stresses (below 6.7 MPa) under various humidity conditions at 293 K. Young's modulus decreases linearly with increasing humidity and a decreasing logarithm of strain rate. These results suggest that Young's modulus of PMMA can be expressed as a function of two independent parameters that are humidity and strain rate. A constitutive equation for Young's modulus of PMMA was proposed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 460–465, 2002; DOI 10.1002/polb.10107