Effect of growth rate on microstructure parameters and microhardness in directionally solidified Ti–49Al alloy

Intermetallics Ti–49Al (at.%) alloy was directionally solidified with different growth rates (V = 5 μm/s–30 μm/s) at a constant temperature gradient (G = 12.1 K/mm) by using a Bridgman type directional solidification furnace. The primary dendritic spacing (λ), interlamellar spacing (λ_L), and microhardness (HV) were measured. Effect of V on HV, λ and λ_L was experimental investigated. The dependencies of λ, λ_L and HV on the growth rate were determined by using linear regressing analysis. According to the result, the values of λ and λ_L decrease with the increasing of V, and the values of HV increase with the increasing of V and with the decreasing of λ and λ_L. The results were compared with previous similar experimental results for TiAl-based alloys.     

Crack growth behavior of 7075-T6 under biaxial tension–tension fatigue

Crack growth behavior of aluminum alloy 7075-T6 was investigated under in-plane biaxial tension–tension fatigue with stress ratio of 0.5. Two biaxiality ratios, λ (=1 and 1.5) were used. Cruciform specimens with a center hole, having a notch at 45° to the specimen’s arms, were tested in a biaxial fatigue test machine. Crack initiated and propagated coplanar with the notch for λ = 1 in L–T orientation, while it was non-coplanar for λ = 1.5 between L–T and T–L orientations. Uniaxial fatigue crack growth tests in L–T and T–L orientations were also conducted. Crack growth rate in region II was practically the same for biaxial fatigue with λ = 1 in L–T orientation and for the uniaxial fatigue in L–T or T–L orientations, while it was faster for biaxial fatigue with λ = 1.5 at a given crack driving force. However, fatigue damage mechanisms were quite different in each case. In region I, crack driving force at a given crack growth rate was smallest for biaxial fatigue with λ = 1.5 and for uniaxial fatigue in T–L orientation, followed by biaxial fatigue with λ = 1 and uniaxial fatigue in L–T orientation in ascending order at a given crack growth rate.     

On the microstructure and physical properties of untreated raffia textilis fiber

We report on the first measurements of the physico-mechanical properties of the raffia textilis fiber. This fiber is the epidermis of the leaflet and is used to fabricate many ethnographical items. Scanning electron microscopy reveals a layered structure: a top layer with a tile-like structure, and a bottom layer with a honeycomb-like structure. X-ray diffraction and FTIR-ATR show the presence of cellulose I_β with a crystallinity index of 64%. Tensile tests give a Young’s modulus of 30 GPa, a tensile strength of 500 ± 97 MPa, and a total elongation between 2% and 4%. The fiber density is 0.75 ± 0.07, conferring to it the highest known specific mechanical properties among all studied raw vegetable fibers.     

Electrochemical sensor for ranitidine determination based on carbon paste electrode modified with oxovanadium (IV) salen complex

The preparation and electrochemical characterization of a carbon paste electrode modified with the N,N-ethylene-bis(salicyllideneiminato)oxovanadium (IV) complex ([VO(salen)]) as well as its application for ranitidine determination are described. The electrochemical behavior of the modified electrode for the electroreduction of ranitidine was investigated using cyclic voltammetry, and analytical curves were obtained for ranitidine using linear sweep voltammetry (LSV) under optimized conditions. The best voltammetric response was obtained for an electrode composition of 20% (m/m) [VO(salen)] in the paste, 0.10 mol L^? 1 of KCl solution (pH 5.5 adjusted with HCl) as supporting electrolyte and scan rate of 25 mV s^? 1. A sensitive linear voltammetric response for ranitidine was obtained in the concentration range from 9.9 × 10^? 5 to 1.0 × 10^? 3 mol L^? 1, with a detection limit of 6.6 × 10^? 5 mol L^? 1 using linear sweep voltammetry. These results demonstrated the viability of this modified electrode as a sensor for determination, quality control and routine analysis of ranitidine in pharmaceutical formulations.     

Effect of CuO nanostructure morphology on the mechanical properties of CuO/woven carbon fiber/vinyl ester composites

The effect of CuO nanostructure morphology on the mechanical properties of CuO/woven carbon fiber (WCF)/vinyl ester composites was investigated. The growth of CuO nanostructures embedded in the surface of woven carbon fibers (WCFs) was carried out by a two-step seed-mediated hydrothermal method; i.e., seeding and growth treatments with controlled chemical precursors. CuO nanostructural morphologies ranging from petal-like to cuboid-like nanorods (NRs) were obtained by controlling the thermal growth temperature in the hydrothermal process over a growth time of 12 h. The Cu²⁺/O⁻ ratio and the rate of reaction greatly influenced the formation of CuO nanostructures as self-assembled shapes on the crystal planes in the order L[0 1 0] > L[1 0 0] > L[0 0 1]. Morphological variations were analyzed by scanning electron microscopy, X-ray diffraction, and Brunauer–Emmett–Teller surface area analysis. The impact behavior, in-plane shear strength, and tensile properties of the CuO/WCF/vinyl ester composites were analyzed for different CuO NR morphologies at various growth temperatures and molar concentrations. The CuO/WCF/vinyl ester composites had improved impact energy absorption and mechanical properties because the higher specific surface area of CuO NRs grown as secondary reinforced nanomaterials on WCFs enhanced load transfer and load-bearing capacity.     

High-speed deposition of dense,dendritic and porous SiO2 films by Nd: YAG laser chemical vapor deposition

Dense, dendritic and porous SiO₂ films were prepared by laser chemical vapor deposition (LCVD) using a high-power continuous-wave mode Nd: YAG laser (206 W) and a TEOS (tetraethyl orthosilicate) precursor. The effects of laser power (P_L) and total chamber pressure (P_tot) on the microstructure and deposition rate (R_dep) were investigated. Amorphous SiO₂ films were obtained independent of P_L and P_tot. Flame formation was observed between the nozzle and the substrate at P_L > 160 W and P_tot > 15 kPa. At P_L = 206 W, dense, dendritic and porous SiO₂ films were obtained at P_tot < 20 kPa, P_tot = 23 kPa and P_tot > 25 kPa, respectively. The R_dep increased thousands of times under flame formation conditions, the highest R_dep being reached at 1200 μm h^?1, 22,000 μm h^?1 and 28,000 μm h^?1 for the dense, dendritic and porous SiO₂ films, respectively.     

Neutral N,N′-bis(2-pyridinecarboxamide)-1,2-ethane as sensing material for determination of lutetium(III) ions in biological and environmental samples

The biological properties of the lutetium as well as other lanthanide ions, primarily based on their similarity to calcium, have been the bases for research into potential therapeutic applications of lanthanide series since the early part of the twentieth century. In this research, a Lu(III) potentiometric membrane sensor based on N,N′-bis(2-pyridinecarboxamide)-1,2-ethane (PCAE) is described. The sensor exhibits a Nernstian response over a concentration range of 1.0 × 10^? 6 mol L^? 1–1.0 × 10^? 1 mol L^? 1, with a detection limit of 6.0 × 10^? 7 mol L^? 1. The best performance was achieved with a membrane composition, consisting of 30% PVC, 63% o-nitrophenyl octyl ether (NPOE), 5% PCAE and 2% sodium tetraphenylborate (NaTPB). It was found that at the pH range of 4.0–9.0, the potential response of the sensor was not affected by the pH. Furthermore, the electrode presents satisfactory reproducibility, very fast response time (5 s) and relatively good discriminating ability for Lu(III) ions with respect to many common cations and other lanthanide ions. The sensor has been applied to the determination of Lu(III) in human serum and in some soil samples where domestic devices were stored.     

Combined effects of Ag content and cooling rate on microstructure and mechanical behavior of Sn–Ag–Cu solders

Sn–0.7 wt%Cu–1.0 wt%Ag and Sn–0.7 wt%Cu–2.0 wt%Ag alloys were directionally solidified under transient conditions undergoing cooling rates varying from 0.1 to 25 K/s. The microstructure was characterized along the castings lengths and the present experimental results include the secondary dendrite arm spacing (λ₂) and its correlation with: the tip cooling rate ($\dot{T}$) during solidification and microhardness (HV), yield tensile strength (σ_y), ultimate tensile strength (σ_u) and elongation to fracture (δ). The aim is to examine the effects of Ag content and tip cooling rate on both the microstructure and mechanical properties. The initiation of tertiary branches within the dendritic arrangement, as well as the distinct morphologies of the intermetallic compounds (IMC) related to the solidification cooling rate was also assessed for both examined alloys. While the Cu₆Sn₅ phase appeared as large faceted crystals along the entire casting length, very fine Ag₃Sn spheroids prevailed at higher cooling rates (>7.5 K/s and > 4.0 K/s for 1.0 wt%Ag and 2.0 wt%Ag alloying, respectively) with a mixture of Ag₃Sn coarser spheroids and fibers predominating at lower cooling rates. The Sn–0.7 wt%Cu–2.0 wt%Ag alloy exhibited smaller dendritic spacings and HV of about two times higher than the corresponding values of the Sn–0.7 wt%Cu–1.0 wt%Ag alloy. A single Hall–Petch equation is proposed relating δ to λ₂ for both alloys, which means that the increase in Ag content from 1.0 to 2.0 wt% does not affect the elongation. It is shown that δ decreases with the increase in λ₂.     

Bi1.5Y0.3Sm0.2O3–La0.8Sr0.2MnO3 − δ dual-phase composite hollow fiber membrane for oxygen separation

Dense Bi_1.5Y_0.3Sm_0.2O₃–La_0.8Sr_0.2MnO_3 ? δ hollow fiber membrane was fabricated by the combined phase inversion/sintering technique. The hollow fiber possessed an asymmetric structure. The oxygen permeability of the hollow fiber was measured by exposing its shell side to ambient air and sweeping the core side with helium to carry away the permeated oxygen. An oxygen permeation flux 3.9 × 10^? 7 mol cm^? 2 s^? 1 was obtained at 850 °C under a gradient of air/helium. The oxygen permeation flux was related to the helium sweeping rate, the length of the hollow fiber and the oxygen partial pressure on the feed side, and can be further increased by modifying the membrane surfaces.     

Investigation on structure optimization of crashworthiness of fiber reinforced polymers materials

Composite materials, in most cases fiber reinforced polymers, are nowadays used in the aerospace and transportation, in which high specific energy absorption (SEA) and strength are critical issues. Aimed at the improvement of SEA and the peak impact load (P), the structure optimization of composite tape sinusoidal specimen and corresponding experiments are investigated in this paper. Firstly, the finite element model of composite tape sinusoidal specimen is constructed and is validated by experiments. Then, both the single-objective and multi-objective optimizations are performed for composite tape sinusoidal specimen under axial impact loading. At last, the optimal results are validated by experiments. The optimal results show that the SAE increases 67.8% (from 51.3666 kJ/kg to 88.887 kJ/kg) and the P decreases 42.9% (from 34.9936 kN to 20.178 kN). This work lays a foundation for structural design of crashworthiness using fiber reinforced polymers materials.     

Compression properties at different loading directions of as-extruded Mg–9RY–4Zn (RY: Y-rich misch metal) alloy with long period stacking ordered phase

The compression properties at different loading directions of as-extruded Mg–9RY–4Zn alloy with long period stacking ordered (LPSO) phase were investigated. The compressive yield strength (σ_0.2), ultimate compressive strength (σ) and elongation to failure (ε) are 272 MPa, 520 MPa and 19% at ED, 172 MPa, 412 MPa and 17% at TD, and 150 MPa, 370 MPa and 16% at 45° orientation, respectively. The excellent compression properties result from the 14H LPSO strips and random oriented DRX grains with 14H LPSO lamellae. Meanwhile, the as-extruded Mg–9RY–4Zn alloy exhibits obvious mechanical anisotropy. The strength at ED is much higher than that at 45° orientation. Specific to the present alloy, besides the weak basal texture, it is considered that the LPSO long strips with characteristic orientation play an important role in influencing the mechanical anisotropy.     

A correction to the analytical solution of the mixed-mode bending (MMB) problem

This paper addresses the analytical solution of the mixed-mode bending (MMB) problem. The first published solutions used a load separation in pure mode I and mode II and were applied for a crack length less than the beam half-span, a ⩽ L. In later publications, the same mode separation was used in deriving the analytical solution for crack lengths bigger than the beam half-span, a > L. In this paper it is shown that this mode separation is not valid when a > L and in some cases may lead to very erroneous results. The correct mode separation and the corresponding analytical solutions, when a > L, are presented. Results, of force vs. displacement and force vs. crack length graphs, obtained using the existing formulation and the corrected formulation are compared. A finite element solution, which does not use mode separation, is also presented.     

Determination of laminar and turbulent flow ranges through vertical packed beds in terms of particle friction factors

Despite the presence of a variety of studies dealing with the magnitude of particle Reynolds number, Re_p defining transition from laminar to turbulent regime for flow through packed beds, the manner is still one of the unknowns. An approach based on the experimental data concerning upward airflow through fixed cylindrical packed beds is presented in this paper. The utilized packed beds had the following ranges of; sphericity, Φ, 0.55 ? Φ ? 1.00, packing material diameter to bed length ratio, D_p/L, 0.04 ? D_p/L ? 0.72, and bed porosity, ε, 0.36 ? ε ? 0.56. The test cases covered the ranges of particle Reynolds number, Re_p 708 ? Re_p ? 7772 and particle Froude number; Fr_p 2.86 ? Fr_p ? 10.39. The measurements of pressure drop through packed bed; ΔP_Bed and superficial mean exit velocity; U are used to determine bed frictional effects in reference to the available literature on particle friction factors, f_p. The magnitude of Re_p defining transition is assumed to be 2000 with particular emphasis to the flow dynamics. The definitions of Bird et al. [R.B. Bird, W.E. Stewart, E.N. Lightfoot, Transport Phenomena, John Wiley and Sons, NY, 1960] are used to calculate f_p. The calculated f_p for the covered test cases are given as a function of pressure coefficient, ΔP* and Re_p, Fr_p, Φ, ε, D_p/L in the approximate ranges of laminar and turbulent flow for Re_p < 2000 and Re_p > 2000, respectively. The proposed separate equations of f_p = f_p(ΔP*, Re_p, Fr_p, Φ, ε, D_p/L) are satisfied for laminar and turbulent flows with corresponding average error margins of ±7.6% and ±18%. Furthermore ranges of transitional and fully rough flow through packed beds are estimated as 2000 ? Re_p ? 4000 and Re_p > 5000 with an analogy to the well-known Moody Chart in pipe flows.     

A simple and efficient electrochemical sensor for folic acid determination in human blood plasma based on gold nanoparticles–modified carbon paste electrode

Folic acid (FA) is a water soluble vitamin that exists in many natural species. The lack of FA causes some deficiencies in human body, so finding a simple and sensitive method for determining the FA is important. A new chemically modified electrode was fabricated for determination of FA in human blood plasma using gold nanoparticles (AuNPs) and carbon paste electrode (CPE). Gold nanoparticles–modified carbon paste electrode (AuNPs/CPE) was characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The experimental parameters such as pH, scan rate (ν) and amount of modifier were studied by cyclic voltammetry and the optimized values were chosen. The electrochemical parameters such as diffusion coefficient of FA (D_FA), electrode surface area (A) and electron transfer coefficient (α) were calculated. Square wave voltammetry as an accurate technique was used for quantitative calculations. A good linear relation was observed between anodic peak current (i_pa) and FA concentration (C_FA) in the range of 6 × 10^? 8 to 8 × 10^? 5 mol L^? 1, and the detection limit (LOD) achieved 2.7 × 10^? 8 mol L^? 1, that is comparable with recently studies. This paper demonstrated a novel, simple, selective and rapid sensor for determining the FA in the biological samples.     

Flow-based method for epinephrine determination using a solid reactor based on molecularly imprinted poly(FePP–MAA–EGDMA)

A solid phase reactor based on molecularly imprinted poly(iron (III) protoporphyrin-methacrylic acid-ethylene glycol dimethacrylate) (MIP–MAA) has been synthesized by bulk method and applied as an selective material for the epinephrine determination in the presence of hydrogen peroxide. In order to prove the selective behaviour of MIP, two blank polymers named non-imprinted polymer (NIP1), non-imprinted polymer in the absence of hemin (NIP2) as well as a poly(iron (III) protoporphyrin-4-vynilpyridine-ethylene glycol dimethacrylate) (MIP–4VPy) were synthesized. The epinephrine-selective MIP–MAA reactor was used in a flow injection system, in which an epinephrine solution (120 μL) at pH 8.0 percolates in the presence of hydrogen peroxide (300 μmol L^? 1) through MIP–MAA. The oxidation of epinephrine by hydrogen peroxide is increased by using MIP–MAA, being the product formed monitored by amperometry at 0.0 V vs. Ag/AgCl. The MIP–MAA showed better selective behaviour than NIP1, NIP2 and MIP–4VPy, demonstrating the effectiveness of molecular imprinting effect. Highly improved response was observed for epinephrine in detriment of similar substances (phenol, ascorbic acid, methyl-l-DOPA, p-aminophenol, catechol, l-DOPA and guaiacol). The method provided a calibration curve ranging from 10 to 500 μmol L^? 1 and a limit of detection of 5.2 μmol L^? 1. Kinetic data indicated a value of maximum rate V_max (0.993 μA) and apparent Michaelis–Menten constant of K_m^app(725.6 μmol L^? 1). The feasibility of biomimetic solid reactor was attested by its successful application for epinephrine determination in pharmaceutical formulation.     

Grafting of nano-TiO2 onto flax fibers and the enhancement of the mechanical properties of the flax fiber and flax fiber/epoxy composite

In this article, a flax fiber yarn was grafted with nanometer sized TiO₂, and the effects on the tensile and bonding properties of the single fibers and unidirectional fiber reinforced epoxy plates were studied. The flax fiber yarn was grafted with nanometer sized TiO₂ through immersion in nano-TiO₂/KH560 suspensions under sonification. The measured grafting content of the nano-TiO₂ ranged from 0.89 wt.% to 7.14 wt.%, dependent on the suspension concentration. With the optimized nano-TiO₂ grafting content (∼2.34 wt.%), the tensile strength of the flax fibers and the interfacial shear strength to an epoxy resin were enhanced by 23.1% and 40.5%, respectively. The formation of Si–O–Ti and C–O–Si bonds and the presence of the nano-TiO₂ particles on the fiber surfaces contributed to the property enhancements. Unidirectional flax fiber reinforced epoxy composite (V_f = 35.4%) plates prepared manually showed significantly enhanced flexural properties with the grafting of nano-TiO₂.     

Characterization of hot-pressed short ZrO2 fiber toughened ZrB2-based ultra-high temperature ceramics

Two different ZrB₂-based ultra-high temperature ceramics were produced by hot pressing: ZrB₂ + 20 vol.% SiC particle + 15 vol.% ZrO₂ fiber and ZrB₂ + 20 vol.% SiC whisker + 15 vol.% ZrO₂ fiber. The microstructures were analyzed by using transmission electron microscopy and high-resolution transmission electron microscopy. It was shown that a clean interface without any impurities was identified in ZrB₂-based hybrid ceramics with SiC whiskers and ZrO₂ fibers, which would significantly improve the toughening mechanism. The results of high-resolution transmission electron microscopy showed that stacking faults in SiC whiskers resulted from an insertion of a (111) layer, which would be one of the main reasons for material anisotropy. However, the interface between the SiC particle and ZrO₂ fiber was found to be ambiguous in ZrB₂-based hybrid ceramics with SiC particles and ZrO₂ fibers due to the slight reaction. The orientation relationship between t-ZrO₂ and m-ZrO₂ phases obeyed the classical correspondence: (100)_m//{100}_t and [001]_m//〈001〉_t, which further verified the feasibility of phase transformation toughening mechanism.     

Effect of Zn addition,strain rate and deformation temperature on the tensile properties of Sn–3.3 wt.% Ag solder alloy

Stress–strain characteristics of the binary Sn–3.3 wt.% Ag and the tertiary Sn–3.3 wt.% Ag–1 wt.% Zn solder alloys were investigated at various strain rates (SR, ε^·) from 2.6 × 10^− 4 to 1.0 × 10^− 2 s^− 1 and deformation temperatures from 300 to 373 K. Addition of 1 wt.% Zn to the binary alloy increased the yield stress σ_y and the ultimate tensile stress σ_UTS while a decrease of ductility (total elongation ε_T) was observed. Increasing the strain rate (ε^·) increased both σ_y and σ_UTS according to the power law σ = C ε^·m. A normal decrease of ε_T with strain rate was observed according to an empirical equation of the form ε_T = A exp (− λε^·); A and λ are constants. Increasing the deformation temperature decreased both σ_y and σ_UTS in both alloys, and decreased the total elongation ε_T in the Zn-free binary alloy, whereas ε_T was increased in the Zn-containing alloy. The activation energy was determined as 41 and 20 kJ mol^− 1 for these alloys, respectively. The results obtained were interpreted in terms of the variation of the internal microstructure in both alloys. The internal microstructural variations in the present study were evaluated by optical microscopy, electron microscopy and X-ray diffraction. The results show the importance of Zn addition in enhancing the mechanical strength of the Sn–3.3 wt.% Ag base alloy.     

Fatigue behavior and failure mechanism of basalt FRP composites under long-term cyclic loads

This paper studies the fatigue behavior of basalt fiber reinforced epoxy polymer (BFRP) composites and reveals the degradation mechanism of BFRP under different stress levels of cyclic loadings. The BFRP composites were tested under tension–tension fatigue load with different stress levels by an advanced fatigue loading equipment combined with in-situ scanning electron microscopy (SEM). The specimens were under long-term cyclic loads up to 1 × 10⁷ cycles. The stiffness degradation, S–N curves and the residual strength of run-out specimens were recorded during the test. The fatigue strength was predicted with the testing results using reliability methods. Meanwhile, the damage propagation and fracture surface of all specimens were observed and tracked during fatigue loading by an in-situ SEM, based on which damage mechanism under different stress levels was studied. The results show the prediction of fatigue strength by fitting S–N data up to 2 × 10⁶ cycles is lower than that of the data by 1 × 10⁷ cycles. It reveals the fatigue strength perdition is highly associated with the long-term run-out cycles and traditional two million run-out cycles cannot accurately predict fatigue behavior. The SEM images reveal that under high level of stress, the critical fiber breaking failure is the dominant damage, while the matrix cracking and interfacial debonding are main damage patterns at the low and middle fatigue stress level for BFRP. Based on the above fatigue behavior and damage pattern, a three stage fracture mechanism model under fatigue loading is developed.     

Nanoscale characterization of natural fibers and their composites using contact-resonance force microscopy

Contact-resonance force microscopy (CR-FM) has been used for the first time to evaluate the mechanical properties of the interphase in natural fiber-reinforced composites and of cell wall layers of natural fibers. With CR-FM, quantitative images of the spatial distribution in nanoscale elastic properties were acquired. The images were calibrated with nanoindentation values. From the modulus images, the average interphase width was found to be (49 ± 5) nm for composite without any treatment, and (139 ± 21) nm for one with a maleic anhydride polypropylene treatment. There was a gradient of modulus across the interphase that ranged between the values of fiber and the polymer. The average values of indentation modulus obtained for different cell wall layers within a fiber were 22.5–28.0 GPa, 17.9–20.2 GPa, and 15.0–15.5 GPa for the S₂ and S₁ layers and the compound middle lamellae, respectively.