Measurement of continuous damage parameter

The present paper introduces several measuring methods of continuous damage parameter derived by the classical definition D = 1 − (A_e/A_a): (1) The measuring method on the basis of D = 1 − (E'/ E); (2) The measuring method on the basis of D = 1 − (ε₁/ε₂); (3) The measuring method on the basis of D = −Δρ_o/ρ_o, (4) The measuring method on the basis of D = A_d/A_a, and comments on these measuring methods.     

Epitaxial growth of AB type compounds under quasi-equilibrium conditions

Single-crystal films of CdS, CdSe and CdTe have been grown in vacuum on mica (fluophlogopite and muscovite) under isothermal conditions, i.e. with T_ev ≈ T_ep ≈ T_gr where T_ev and T_ep are the evaporation and epitaxial temperatures respectively and T_gr is the growth temperature. The synthesis was carried out in the temperature range 430°–800°C in the case of CdS, 300°–650°C for CdSe and 270°–550°C for CdTe. It is shown that the growth rate of single crystal layers (V_gr) depends exponentially on the growth temperature: V_gr (Å/sec) = D exp (−E/RT_gr) Perfect epitaxial CdS, CdSe and CdTe films have a wide range of electrophysical properties. Co-evaporation of CdS and sulphur and of CdSe and selenium allowed high-resistance films of cadmium sulphide and cadmium selenide of both n- and p-types to be obtained.     

Spectroscopic ellipsometry analysis of GaAs1 − xNx layers grown by molecular beam epitaxy

In this work, we present the effect of nitrogen incorporation on the dielectric function of GaAsN samples, grown by molecular beam epitaxy (MBE) followed by a rapid thermal annealing (for 90 s at 680 °C). The GaAs_1 − xN_x samples with N content up to 1.5% (x = 0.0%, 0.1%, 0.5%, 1.5%), are investigated using room temperature spectroscopic ellipsometry (SE). The optical transitions in the spectral region around 3 eV are analyzed by fitting analytical critical point line shapes to the second derivative of the dielectric function. It was found that the features associated with E₁ and E₁ + Δ₁ transitions are blue-shifted and become less sharp with increasing nitrogen incorporation, in contrast to the case of E₀ transition energy in GaAs_1 − xN_x. An increase of the split-off Δ₁ energy with nitrogen content was also obtained, in agreement to results found with MOVPE GaAs_1 − xN_x grown samples.     

Optical transitions near the band edge in bulk CuInxGa1−xSe2 from ellipsometric measurements

From the analysis of the variation of optical absorption coefficient with incident photon energy between 0.8 and 2.6 eV, obtained from ellipsometric data, the energy E_G of the fundamental absorption edge and E_G′ of the forbidden direct transition for CuIn_xGa_1−xSe₂ alloys are estimated. The change in E_G and the spin-orbit splitting Δ_SO=E_G′−E_G with the composition x can be represented by parabolic expression of the form E_G(x)=E_G(0)+ax+bx² and Δ_SO(x)=Δ_SO(0)+a′x+b′x², respectively. b and b′ are called “bowing parameters”. Theoretical fit gives a=0.875 eV, b=0.198 eV, a′=0.341 eV and b′=−0.431 eV. The positive sign of b and negative sign of b′ are in agreement with the theoretical prediction of Wei and Zunger [Phys. Rev. B 39 (1989) 6279].     

Experimental investigation of the dynamic response of graphite-epoxy composite laminates under compression

In this study, the dynamic stress–strain response of graphite-epoxy composite laminates is investigated. The laminates are interposed in a section of a split Hopkinson apparatus. A quasi-rectangular wave is generated at one end of the incident bar by striking it with another bar of known length. This bar is accelerated using a compressed air gun. Approximate average stresses and strains can be obtained by measuring the incident, reflected and transmitted waves in the split bar. The dynamic behavior is evaluated for a range of impact velocities. The dependence of the response on impact velocity is analyzed and discussed. Three different specimen thicknesses have been used. These are obtained by increasing the repetition factor of a base stacking sequence: (+45°, −45°, 0°, 90°). This process is called sublaminate scaling; it is preferred to ply scaling since it has been shown that the accumulation of layers of the same orientation decreases the failure load to such an extent that residual stresses may crack the specimen before any external load is applied. The laminates considered are: (+45°, −45°, 0°, 90°)_ns, n=2,3,4. The scale effects observed in the experimental response are analyzed and discussed.     

Influence of in-plane fibre orientation on mode I interlaminar fracture toughness of stitched glass/polyester composites

The influence of in-plane fibre orientation on the mode I interlaminar fracture toughness, G_Ic of unstitched and stitched glass/polyester composites is investigated in this paper. The G_Ic of planar specimens depends on the fibre orientation, θ in the layers adjacent to the fracture plane, in addition to the property of matrix material. The mode I fracture toughness and fracture behavior of unstitched and stitched 0/0, 30/−30, 45/−45, 60/−60, 90/90 and 0/90 interfaces of unidirectional fibre mats (UD) and 30/−30, 45/−45 and 90/90 interfaces of woven roving mats (WRM) are studied. WRM layer orientation is represented by the direction of warp fibres. Stitching is done by untwisted Kevlar fibre roving of Tex 175 g/km at the stitch densities (number of stitches per unit area) of 10.24 and 20.48 stitches/inch². The specimens having same stitch density, but different stitch distributions are prepared, and the influence of stitch distribution on G_Ic is studied. Double cantilever beam (DCB) tests are carried out and the G_Ic is determined using modified beam theory. The G_Ic of both unstitched and stitched specimens increases with increase in orientation angle, θ upto 45° above which it decreases. The G_Ic values of unstitched 45/−45 delamination interface is around 2.4 times that of the unstitched 0/0 interfaces. The influence of fibre orientation on G_Ic is clearly observed in unstitched specimens, whereas in the stitched specimens, stitching plays an important role in improving the G_Ic and suppresses the influence of fibre orientation; degree of suppression increases with increasing stitch density. When the value of θ is above 45°, transverse cracks are observed in the delamination interface surrounded by UD layers; while in the delamination interface surrounded by WRM layers, transverse cracks are not initiated irrespective of the fibre orientation angle.     

Influence of thermal treatments on the elastic parameters in iron rich metallic glasses

The change of magnetoelastic properties after thermal treatments has been investigated for two groups of metallic glasses. (Fe₇₉Co₂₁)_75+xSi_15−1.4xB_10+0.4x (x (at.%)=0, 2, 4, 6, 8, 10) has been studied both in the as-prepared state and after thermal annealing in an applied magnetic field, to achieve a particular domain structure, at temperatures well below the crystallization temperatures. Changes in the ΔE effect, magnetomechanical coupling (k) and internal friction coefficient (Q⁻¹) are reported, reaching values of about 60% of the saturation value E_S. Fe₆₄Ni₁₀Nb₃Cu₁Si₁₃B₉ alloys annealed in vacuum for 1 h in the temperature range 350–550 °C showed maximum values of the ΔE effect and k of 61% and 0.85, respectively, accompanied by a minimum value of Q of around 2 for the sample annealed at 460 °C. These variations are related to the progress of nanocrystalization. The properties achieved are among the best reported for magnetomechanical applications.     

Some physical properties of ZnO sputtered films

The secondary electron emission (SEE) yield δ of ZnO films was investigated. The films were deposited in an r.f. sputtering system using the r.f. power W, the argon pressure p, the O₂ partial pressure p_O2 and the substrate temperature T_s as parameters. Complementary measurements of the electrical resistivity and the optical absorption were performed. The ratio x of oxygen to zinc is an essential factor which determines the values of δ, and for the ZnO films.

Auger analyses showed that excess (overstoichiometric, x =1) oxygen is present in ZnO films obtained at room temperature. For x =1 the values of , the maximum SEE yield δ_m and the energy band gap E_g (determined from ) were found to be higher than those for stoichiometric ZnO (obtained at T_s200 °C). The highest values of (10⁴ Ω m), δ_m (4.4) and E_g (3.44 eV) were obtained for films with x = 1.7.     

Matrix cracking behavior of K3B/IM7 composite laminates subject to static and fatigue loading

The matrix cracking behavior of a new high-performance thermoplastic composite material, K3B/IM7, was systematically investigated. Laminates in various grouped thickness and ply stacking sequences, [0₂/90₂/0₂], [0₂/90₄/0₂], and a quasi-isotropic laminate [+45/0/−45/90]_s were tested under static and tension–tension fatigue loading. Depending on the stacking sequence of the laminates and the type of loading, various matrix cracking behavior were found. Under static loading, the matrix cracks were mainly close to the specimen edges. A few cracks were found to penetrate the specimen width, even when the load was large enough to break the specimen. However, under fatigue cyclic load, the edge initiated cracks propagated fully across the specimen width. Combined with the fatigue Paris Rule and considering the ply thickness and stacking sequence, the energy release rate method was applied to predict the relations between the loading strain amplitude and fatigue cycles for matrix cracking failure.     

An investigation of graphite PEEK composite under compression with a centrally located circular discontinuity

The failure characteristic of graphite polyetheretherketone (Gr/PEEK) under compression with a centrally located circular discontinuity was investigated through experimentation and a nonlinear ply-by-ply finite element technique. The stacking sequence of the laminates investigated were: [0 °₁₆], [90 °₁₆], [±45 °]_4S [0 °/90 °]_4S, and [0 °/ ± 45 0°/90 °]_2S. In the experimentation, [90 °]₁₆, [0 °/90 °]_4S, and [0 °/ ±45 °/90 °]_2S laminates, as well as three of the [0 °]₁₆, failed due to a crack that was normal to the loading direction and initiated from the edge of the hole progressing to the outer edges of the specimen. The [±45 °]_4S specimens failed to support the load due to an internal crack that originated from the hole's edge and then traveled at an angle of about 42% to the direction of loading. The finite element method used to analytically model the failure of Gr/PEEK accurately modeled the response of the specimens tested experimentally.     

Contact analysis of mechanically fastened joints in composite laminates by linear complementarity problem formulation

The contact phenomena and stress distributions in the vicinity of the hole on mechanically fastened joints are investigated in composite laminates exhibiting nonlinear elastic behavior. The effects of fastener stiffness, friction force between the fastener and the composite laminates, geometrical nonlinearities due to concentrated fastener load around the hole edge for the snug and clearance-fit in the [0 °]_S, [± 45 °]_S, [0°/± 45 °]_S and laminates are also considered. An efficient numerical procedure is developed for the solution of the contact problems with Coulomb friction between the fastener and the hole based on a linear complementarity problem (LCP) formulation in an incremental form. A nonlinear finite element code for stress analysis of laminated composites using Lemke's complementary pivoting algorithm is developed for solving the LCP. The nonlinear analysis is composed of the combination of updated Lagrangian formulation of the frictional contact problem and the nonlinear shear stress-strain relation in each ply. The accuracy, applicability and computational efficiency of the proposed method are confirmed by comparison with previous researches.     

Equilibrium, kinetic and thermodynamic study of the biosorption of uranium onto Cystoseria indica algae

Biosorption equilibrium, kinetics and thermodynamics of binding of uranium ions to Cystoseria indica were studied in a batch system with respect to temperature and initial metal ion concentration. Algae biomass exhibited the highest uranium uptake capacity at 15 °C at an initial uranium ion concentration of 500 mg l⁻¹ and an initial pH of 4. Biosorption capacity increased from 198 to 233 mg g⁻¹ with an decrease in temperature from 45 to 15 °C at this initial uranium concentration. The Langmuir isotherm model were applied to experimental equilibrium data of uranium biosorption depending on temperature. Equilibrium data fitted very well to the Langmuir model C. indica algae in the studied concentration range of Uranium ions at all the temperatures studied. The saturation type kinetic model was applied to experimental data at different temperatures changing from 15 to 45 °C to describe the batch biosorption kinetics assuming that the external mass transfer limitations in the system can be neglected and biosorption is chemical sorption controlled. The activation energy of biosorption (E_A) was determined as −6.15 using the Arrhenius equation. Using the thermodynamic equilibrium coefficients obtained at different temperatures, the thermodynamic constants of biosorption (ΔG°, ΔH° and ΔS°) were also evaluated.     

Calculation of the ferrite volume in some dual phase steels

The relation between the γ/γ + boundary temperature, T, and the equivalent values of [Cr] and [Ni], as well as the variation of the ferrite volume, V_f, with the temperature in + γ dual-phase steels have been studied. With the aid of a computer, the regressive expressions derived from the experimental results are: T (°C) = T₃ + 21.2 [Cr] − 15.8 [Ni] + 223; V_f (%) = 0.715 exp [0.015(T − T_δ)] − exp[0.015(T_c − T_δ)] + 1.85 exp [0.0083(T − T_c]).     

Inference of critical cod from Charpy V test result

Correlation between the Charpy absorbed energy and critical COD is investigated to obtain a useful method for estimating critical COD from Charpy V data. The round bar tension test, Charpy V-notch test and static 3-point bend test with fatigue notched specimen are carried out using mild steel, 785 MPa grade high strength steel and A5083 aluminum alloy. Correlation is found between W'_c/σ_Y and δ_c as well as between EW'_c/σ_Y² and Eδ_c/σ_Y, where W'_c is the Charpy absorbed energy obtained by considering temperature difference between the Charpy transition temperature and COD transition temperature. The symbols σ_Y, δ_c and E are yield strength, critical COD and Young's modulus, respectively. The correlations are established for various kinds of metals and over a wide temperature range including not only upper shelf range but also the transition range.     

A damping analysis of composite laminates using the closed form expression for the basic damping of Poisson's ratio

Various methods have been presented to obtain the effective damping of a symmetric laminated composite. In this paper, modified classical lamination theory based upon the elastic–viscoelastic correspondence principle was utilized by developing the basic damping of Poisson's ratio for accurately predicting the damping of laminated composite beams. The analysis involves an extension of the elastic–viscoelastic approach. Futhermore, Ni and Adams' theory was used for verifying the modified classical lamination theory. Six typical laminated composites with [±θ]_s,[0/θ]_s,[0/±θ/90]_s,[90/±θ/0]_s,[0/90/±θ]_s and [90/0/±θ]_s, stacking sequences were employed for this study. Numerical results have shown that damping values were in some difference among prediction methods over the particular range of fiber orientation.     

High strain rate compressional behavior of stitched and unstitched composite laminates with radial constraint

This paper is concerned with the high strain rate compressional behaviour of glass/epoxy (Hy-E 9134B, Fiberite, USA) composite laminates with or without stitching reinforcement by untwisted Kevlar-49 threads (1140 denier). The split Hopkinson pressure bar (SHPB) apparatus is used in performing the high strain rate tests. Test data are analyzed in a manner similar to that reported by Hauser Exp. Mech., 6 (1966) 395. Specimens are tested at strain rates up to 10⁴ s⁻¹. Unidirectional laminated parallelepiped samples are impacted along their fiber direction. Their high velocity compressive ductility is observed. Both [0°]₂₄ and [(0°/90°)₆]_S glass/epoxy circular specimens with disc diameters of 10 and 50·8 mm are transversely impacted by an input bar in order to study their high strain rate behavior. Moreover, two sets of stitched circular specimens with disc diameters of 10 and 50·8 mm are also examined. The effect of strain rate and radial constraint on the dynamic properties of stitched and unstitched GFRP laminated specimens and their associated damage patterns are described.     

Anomalous elastic response of amorphous alloys suggesting collective motions of many atoms

The dynamic Young’s modulus, E, of amorphous (a-) Zr₆₀Cu₃₀Al₁₀ (numbers indicate at.%) alloy was measured as a function of frequency, f, with a strain amplitude, _t, of 10⁻⁶, E(10⁻⁶,f), and also as a function of _t for f near 10² Hz, E(_t,10² Hz), by means of the vibrating reed methods. The elasticity study under the passing of electric current (PEC) was carried out too. E(10⁻⁶,f) is lower than E₀ for f between 10 and 10⁴ Hz showing local minima near 5×10, 5×10² and 5×10³ Hz, which are indicative of the resonant collective motion of many atoms, where E₀ is the static Young’s modulus. E(_t,10² Hz) increases showing saturation with increasing _t. Qualitatively, the outlines of E(10⁻⁶,f) and E(_t,10² Hz) observed for a-Zr₆₀Cu₃₀Al₁₀ are similar to those reported for various a-alloys. Quantitatively, a change in E(_t,10² Hz) for a-Zr₆₀Cu₃₀Al₁₀ is smallest among that reported for various a-alloys, presumably reflecting that the crystallization volume, (ΔV/V)_x, is smallest for a-Zr₆₀Cu₃₀Al₁₀. The effective charge number, Z^*, estimated from the change in E(10⁻⁶,10² Hz) due to PEC is 3.0×10⁵, which is comparable with Z^* reported for various a-alloys. We surmise that the number of atoms in the collective motions excited near 10² Hz is similar among various a-alloys. The E(10⁻⁶,f) data suggest that the spatial sizes of the density fluctuations may show a distribution.     

CdSe band-splitting on thermal annealed films

Semiconducting polycrystalline CdSe thin films were prepared on glass substrates by chemical bath at 65 °C. As-deposited films grew in the metastable cubic sphalerite (S) crystalline structure with good stoichiometry. Upon thermal annealing (TA) in Ar+Se₂ atmosphere at different temperatures in the range 200–500 °C, the gradual phase transformation from cubic modification to hexagonal wurtzite (W) stable phase could be observed. From optical absorption measurements the fundamental energy band gap (E_g) and the second electronic transition (E_g+ΔE_g) were calculated for as-deposited and thermal annealed films. For TA350 °C, S-phase dominates the crystalline structure and only the spin orbit (ΔE_so) contribution to ΔE_g is present. Above 350 °C, the W-phase dominates and the energy splitting (ΔE_cf), owed to crystal field contribution and originated by the loss of lattice symmetry, should be added to ΔE_so in order to complete ΔE_g in the W-phase. The values ΔE_so=0.389±0.011 eV and ΔE_cf=0.048±0.018 eV were found from our analysis, and T_c=350 °C was here defined as the critical point of the phase transformation.     

Corrosion of tin in citric acid solution and the effect of some inorganic anions

The corrosion behaviour of tin in different concentrations of citric acid solutions (0.3–1.0 M, pH=1.8) was studied at 30 °C by potentiodynamic technique. The E/I profiles exhibit an active passive behaviour. The active dissolution involves one anodic peak A associated with a dissolution of the metals as Sn(II) species. The passivity is due to the formation of thin film of SnO₂ and or Sn(OH)₄ on the anode surface. The cathodic sweep shows a small peak C related to the reduction of the passive film. The peak current density I_p of peak A increases with increasing both acid concentration and sweep rate.

The effects of adding increasing concentrations of Na₂CrO₄, NaMoO₄, NaNO₃ and NaNO₂ on the corrosion of tin in 0.5 M citric acid at 30 °C were investigated. Both CrO₄²⁻ and MoO₄²⁻ ions inhibit the corrosion of tin and the extent of inhibition enhances with their concentrations. Addition of either NO₃⁻ or NO₂⁻ accelerates the corrosion of tin. NO₃⁻ ions are more aggressive than NO₂⁻ ions.