Nanoparticle-induced enhancement in fracture toughness of highly loaded epoxy composites over a wide temperature range

The fracture toughness of an epoxy molding compound (EMC) has been enhanced over a wide temperature range by the addition of a very low volume fraction of silica nanoparticles to the EMC filled with micro-silica particles, which induces macroscopic crack deflection and plastic deformation in front of the crack tip. To evaluate the fracture toughness (G _IC) of these materials, the single edge notched bending (SENB) test was performed for a wide range of temperatures (from ambient temperature to 230°C). The fracture toughness of the nano-silica filled EMCs was found to be improved in this temperature range by as much as a factor of two. Investigation of the fracture surfaces revealed that the micro-silica particles are covered with deformed matrix materials, which implies that the silica nanoparticles induced the crack to move into the interface between the micro-silica particles. Fractography results suggest that the silica nanoparticles act as surface modifiers of the micro-silica particles, which results in crack deflection and plastic deformation.     

Creep deformation behaviour of AZ31 magnesium alloy over wide range of temperature and stress

Abstract

The creep deformation behaviour of coarse grained AZ31 magnesium alloy was examined in the temperature range from 423 to 673 K (0·46–0·73T_m) under various constant stresses covering low strain rate range from 4×10^?9 to 2×10^?2 s^?1. Most shape of the creep curve was typical of class II behaviour. However, only at low stress and low temperature, the shape of the creep curve was typical of class I behaviour. At very low stress at 673 K, the stress exponent for the secondary creep rate was ～2. At low stress level, the stress exponent was ～3 and the present results were in good agreement with the prediction of Takeuchi and Argon model. At high stress level, the stress exponent was ～5 and the present results were in good agreement with the prediction of Weertman model. The transition of deformation mechanism from solute drag creep to dislocation climb creep could be explained in terms of solute atmosphere breakaway concept.     

High temperature compressive properties over a wide range of strain rates in an AZ31 magnesium alloy

High temperature compressive properties in AZ31 magnesium alloy were examined over a wide strain rate range from 10^–3 to 10³ s^–1. It was suggested that the dominant deformation mechanism in the low strain rate range below 10^–1 s^–1 was dislocation creep controlled by pipe diffusion at low temperatures, and by lattice diffusion at high temperatures. On the other hand, analysis of the flow behavior and microstructural observations indicated that the deformation at high strain rates of 10³ s^–1 proceeds by conventional plastic flow of dislocation glide and twinning even at elevated temperatures.     

Thermal diffusivity of resin-bonded refractories over a wide temperature range

Results are shown of thermal diffusivity measurements made on resin-bonded refractories of various compositions and structures.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 24, No. 4, pp. 608–617, April, 1973.     

Thermal conductivity of inert gases over a wide temperature range

We present the results of correcting and correlating experimental data on the thermal conductivity of inert gases in the temperature range 90–6000°K.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 43, No. 5, pp, 788–795, November, 1982.     

Constitutive descriptions for hot compressed 2124-T851 aluminum alloy over a wide range of temperature and strain rate

The compressive deformation behaviors of 2124-T851 aluminum alloy were investigated over a wide range of temperature and strain rate on Gleeble-1500 thermo-simulation machine. The results show that the true stress–true strain curves exhibit a peak stress at a very small strain, after which the flow stresses decrease until high strains, showing a dynamic flow softening. The measured flow stress was modified by friction correction, and the corrected flow stresses are lower than the measured ones, which nicely reflect negative effects of the interfacial friction on the flow stress. A revised model is proposed to describe the relationships of the flow stress, strain rate and temperature of 2124-T851 aluminum alloy at elevated temperatures. The stress–strain values of 2124-T851 aluminum alloy predicted by the proposed model well agree with experimental results, which confirmed that the revised deformation constitutive equation gives an accurate and precise estimate for the flow stress of 2124-T851 aluminum alloy.     

The dielectric relaxation time of collagen over a wide temperature range

The dielectric properties of collagen were measured at two hydration levels over a frequency range of 10¹–10⁵ Hz and at temperatures from 298–470 K. In the low-frequency range, dielectric dispersion was observed which results from Maxwell-Wagner-Sillars polarization. The relaxation times for a collagen sample containing loosely bound water were shorter than for a collagen sample containing only structural water in the temperature range 298–390 K. Above 390 K, continuous decrease in the relaxation times was observed for both samples.     

Dynamic fracture and spall in aluminum with helium bubbles

Investigation of the dynamic properties of aluminum targets with helium bubbles is presented. The targets were obtained by melting pure aluminum with 0.15% wt.¹⁰B powder. The solid targets were neutron irradiated to get homogeneous helium atoms inside the aluminum boron 10 matrix according to the reaction ¹⁰B + n → ⁷Li+⁴He. Helium atoms further accumulated into bubbles by diffusion in the bulk aluminum. Shock wave experiments were performed by accelerating the aluminum impactor into different targets: (1) pure aluminum, (2) Al-¹⁰B, and (3)Al-¹⁰B with different radii and concentrations of helium bubbles. The spall strength was calculated and analyzed from the free surface velocity measurements. It was found that the addition of ¹⁰B in pure aluminum reduces the spall strength of the material by 25–32%. However, irradiated sample with helium bubbles was found to have higher spall strength compared to samples without bubbles. This finding was reconstructed by numerical simulations. The impacted targets were collected after the impact experiments and examined by TEM. These targets were compared to TEM pictures before the impact. The number of helium atoms in the bubbles was calculated from the electron energy loss spectrum (EELS). TEM comparison between the pre-impacted and the impacted targets shows bubbles coalescence and EELS measurements demonstrate a reduction of the helium atoms concentration in the bubbles from ~10²⁸ m^?3 before the impact to ~10²⁷ m^?3 after the impact.     

Speed of ultrasound in water over a wide range of pressure and temperature

Experimental data are used to derive a formula for determination of the speed of sound in water over a wide range of state parameters.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 36, No. 1, pp. 156–160, January, 1979.     

Determination of the reflectivity of liquid semiconductors over a wide temperature range

A new method for the determination of the reflectivity of liquid semiconductors in the temperature range from the melting point to the boiling point is presented in the paper, The method is based on the pulsed laser irradiation of the semiconductor surface. the time-resolved reflectivity (TRR) measurement technique, and the numerical simulation of the process using a nonequilibrium thermal model, Matching the experimental and computed values of the maximum reflectivity of the cw probe laser and the surface melt duration in the dependence on energy density of the laser pulse and a least-squares-based fitting procedure lead to the determination of the reflectivity of the liquid at the wavelength of the primary laser beam, The method is illustrated by experimental data on XeCl (308-nm) and ArF (193-nm) excimer laser irradiation of Si(100 ), giving the results B,=0.67±0.01-(8±I) x10^–5 (T-1687) at 308 nm and R,= 0.755 ±0.010 - (7 ± I ) x 10^–5( T-1687) at 193 rim, where R, is the reflectivity of the liquid and T is temperature in K,Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Laser-target technique for determination of elastic constants of glass over a wide temperature range

Optical methods have been developed for high temperature application in the determination of the basic quantities, E, Young's modulus and , Poisson's ratio. The methods are simple and the techniques are inexpensive. The methods presented have been tried on commercially available soda-lime-silica glass and consistent results were obtained.     

Analysis of the device characteristics of AlGaN/GaN HEMTs over a wide temperature range

In this study, we investigate the behavior of the current–voltage (I–V) characteristics of AlGaN/GaN HEMT in the temperature range of 223–398 K. Temperature dependent device characteristics and the current transport mechanism are reported. It is observed that the Schottky barrier height Φ increases and the ideality factor n decreases with temperature. There is a linear relationship between the barrier height and the ideality factor, which is attributed to barrier height inhomogeneities of AlGaN/GaN HEMT. The estimated values of the series resistances (R_s) are in the range of 144.2 Ω at 223 K to 74.3 Ω at 398 K. The Φ, n, R_s, G_m and Schottky leakage current values are seen to be strongly temperature dependent.     

Automatic complex for determining static and dynamic characteristics of pressure transducers over a wide temperature range

The possibility of using the electrohydraulic effect for dynamic calibration of pressure transducers over a wide range of temperatures, including cryogenic, is examined along with a series of related questions pertaining to theory, instrumentation, and software.Translated from Izmeritel'naya Tekhnika, No. 6, pp. 40–43, June, 1993.     

Dynamic shear properties of polysulphide and ethylene propylene rubbers over a wide range of frequency and temperature

Methods for measuring dynamic shear properties of viscoelastic solids are discussed and a new method for direct measurement at high frequencies (1500 Hz) is outlined. The variation of complex shear modulus, dynamic in-phase shear modulus and the loss, out-of-phase shear modulus for polysulphide and ethylene propylene rubbers is shown as a function of temperature (–40 to 100° C) and frequency (50 to 1500 Hz). The Mooney theory of deformation of cross-linked polymer networks is used to define the molecular structure of the elastomers more fully. Recommendations are made for producing high-damping elastomers in the audiofrequency range.