Scaling properties of slow fracture in glass: from deterministic to irregular topography

In this work we discuss the morphology and self-affine properties of the slow-fracture surfaces of soda-lime glass obtained by a bending process under the effect of applied water vapor. The fractographic analysis showed the presence of secondary cracks in the mirror zone, whereas in the mist–hackle region step-like morphologies were observed and over them we found fine undulations. The self-affine analysis, performed by two methods, showed the existence of two different statistical distributions for the roughness exponent, ζ. At the beginning of the mirror zone ζ = 0.5, in the mist–hackle region we detected the same value for fine length scales, whereas at large length scales we observed ζ = 0.8. This scenario may be described by a qualitative model in which the deterministic mirror–mist–hackle pattern coexists with an irregular topography, the two observed regimes are thus characterized by two different roughness exponents, with the 0.5 value dominating at low-speed/fine-scales and the 0.8 value governing the high-speed/large-scales regimes.     

Texture evolution in an Al–Cu alloy during equal channel angular pressing: the effect of starting microstructure

In this article, the effect of initial microstructure on the texture evolution in 2014 Al alloy during equal channel angular pressing (ECAP) through route A has been reported. Three heat treatment conditions were chosen to generate the initial microstructures, namely (i) the recrystallization anneal (as-received), (ii) solution treatment at 768 K for 1 h, and (iii) solution treatment (768 K for 1 h) plus aging at 468 K for 5 h. Texture analyses were performed using orientation distribution function (ODF) method. The texture strength after ECAP processing was different for the three samples in the order, solutionised > solutionised plus aged condition > as-received. The prominent texture components were A _E /[`(A)]<sub>E</sub> \bar{A}_{E} and B <sub>E</sub> /[`(B)]_E \bar{B}_{E} in addition to several weaker components for the three materials. The strong texture evolution in solutionised condition has been attributed to higher strain hardening of the matrix due to higher amount of solute. In case of the as-received as well as solutionised plus aged alloy, the weaker texture could be due to the strain scattering from extensive precipitate fragmentation and dissolution during ECAP.     

Sputtering of ice films by the bombardment of Ar ions

The process of sputtering ice films covered on Au(1 1 1) surface at normal incidence by Ar ions with an initial energy of E₀ = 300 eV and 700 eV has been investigated by the molecular dynamic simulation. The mass spectrum and kinetic energy distributions have been calculated. Our simulations clearly show that the mass spectrum contains peaks of the water molecules, water clusters and Au atoms. These results are of interest for the study of mass spectrometry in films and surfaces.     

Energy-based prediction of low-cycle fatigue life of BS 460B and BS B500B steel bars

This paper develops energy-based models for predicting low-cycle fatigue life of BS 460B and BS B500B steel reinforcing bars. The models are based on energy dissipated in the first cycle, in average cycles and in total energy dissipated to failure for strain ratios R = −1, −0.5, and 0. Upon prediction of the low-cycle fatigue life, the total energy dissipated during the entire fatigue life of steel reinforcing bars can also be predicted based on the predicted fatigue life. The results indicated that the hysteresis plastic strain energy dissipated during fatigue loading is an important and accurate parameter for predicting the fatigue life of steel reinforcing bars and that the predictions based on energy dissipated on average cycles are more accurate than those based on energy dissipated in the first cycle. It is concluded that the strain ratio R has a clear effect on the energy dissipation for both materials where BS B500B dissipated more energy than BS 460B for R = −0.5 and 0 and about the same energy for R = −1 for certain range of fatigue life. Other conclusions and observations were also drawn based on the experimental results.     

Influence of Y on the phase composition and mechanical properties of as-extruded Mg–Zn–Y–Zr magnesium alloys

The influence of Y on the microstructure, phase composition and mechanical properties of the extruded Mg–6Zn–xY–0.6Zr (x = 0, 1, 2, 3 and 4, in wt%) alloys has been investigated and compared by optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometer and tensile testing. The increase in Y content has shown grain refinement effects on the microstructure morphologies of the extruded alloys. However, when the content of Y exceeds 2.2 wt%, the grain refinement effect of the Y is not obvious any more with the increase of the Y content. The quasicrystal I-phase (Mg₃YZn₆), face-centred cubic structure W-phase (Mg₃Y₂Zn₃) and a long period stacking ordered (LPSO) X-phase (Mg₁₂YZn) can precipitate in different ranges of Y/Zn ratio (in at.%) when the Y content in the Mg–Zn–Y–Zr alloys is varied. Comparison of the mechanical properties of the alloys showed that the different ternary Mg–Zn–Y phases have different strengthening and toughening effects on the Mg–Zn–Y–Zr alloys in the following order: X-phase > I-phase > W-phase > MgZn₂.     

Ferroelectric properties of Mn-Doped Bi3.15Nd0.85Ti3O12 thin films prepared under different annealing conditions

Mn-doped Bi_3.15Nd_0.85Ti₃O₁₂ (BNTM) thin films were fabricated on Pt/Ti/SiO₂/Si(100) substrates by a chemical solution deposition technique and annealed at different temperatures from 650 to 800 °C. The structures of the films were analyzed using X-ray diffraction, which showed that the BNTM films exhibit polycrystalline structures and random orientations. The surface morphologies of the samples were investigated using scanning electron microscopy. The average grain size of the films increases with increasing annealing temperature. Electrical properties such as remanent polarization (2P_r) are quite dependent on the annealing temperature of BNTM films. It is found that the film annealed at 750 °C exhibits excellent ferroelectricity with a remanent polarization of 2P_r = 89.3 μC/cm² and a coercive field of E_c = 99.2 kV/cm respectively.     

Optical properties of metal phthalocyanines

In this study, optical properties of phthalocyanines of five metals, i.e., cobalt, nickel, iron, copper, and manganese, have been discussed in the energy (E) range of 1.5–4.1 eV. Utilizing the available data of refractive index (n) and extinction coefficient (k) of these materials in the literature, the related optical properties such as the real (ε₁), imaginary (ε₂) parts of the complex dielectric constant (ε), and reflectivity (R) are calculated. Interpretations for the energies corresponding to the peaks in ε₂ are explained in terms of the Penn gap (E _P). High-frequency dielectric constant (ε_∞) values corresponding to four models, i.e., the conventional Lorentz model, modified Lorentz model, relaxed Lorentz model, and the dual Lorentz model are used to determine E _P. It is found that the E _P values corresponding to the conventional and dual Lorentz models are in good agreement with the average of energy peaks in the R-E and the ε₂-E spectra. The oscillator energy (E ₀) and the dispersion energy (E _d) of these materials have been determined utilizing the Wemple–DiDomenico model. The calculated values of (a) E ₀ are generally in good agreement with the Penn gap E _P, the average of the energy peaks in the R-E and the ε₂-E spectra and (b) E _d are comparable to those in the literature for CoPc and NiPc.     

Electrochemical,surface analytical and quantum chemical studies on Schiff bases of 4-amino-4H-1, 2, 4-triazole-3,5-dimethanol (ATD) in corrosion protection of aluminium in 1N HNO<Subscript>3</Subscript>

The present study describes the inhibition of aluminium in 1N HNO₃ with different concentrations of 1,2,4-triazole precursors ATD, BATD and DBATD using gravimetric method, potentiodynamic polarization studies (Tafel), electrochemical impedance spectroscopy (EIS), adsorption studies, surface morphological studies and quantum chemical calculations at 298 K. Polarization studies clearly showed that ATD, BATD and DBATD act as mixed type inhibitors. As the electron density around the inhibitor molecule increases due to substitution, the inhibition efficiency also increases correspondingly. Quantum chemical approach was used to calculate some electronic properties of the molecule to ascertain the correlation between inhibitive effect and molecular structure of the inhibitor. The corrosion inhibition efficiencies of these molecules and the global chemical reactivity relate to some parameters, such as E _HOMO , E _LUMO , gap energy (ΔE), electronegativity (χ), global hardness (η) and the fraction of electrons transferred from the inhibitor molecule to the metallic atom (DN\Delta \emph{N}). In addition, the local reactivity has been analysed through the Fukui function and condensed softness indices. Both the experimental and theoretical studies agree well in this regard and confirm that DBATD is a better inhibitor than BATD and ATD. The adsorption behaviours of molecules on the copper surface have been studied using molecular dynamics method and density functional theory. The order of inhibitory action is DBATD > BATD > ATD.     

Dielectric relaxations and conduction mechanism in Aurivillius-type Bi4Ti3O12–Bi5Fe0.5Co0.5Ti3O15 solid solution

The structural, multiferroic, dielectric and conductivity properties of Aurivillius-type Bi₄Ti₃O₁₂–Bi₅Fe_0.5Co_0.5Ti₃O₁₅ solid solutions prepared by a modified pechini method are investigated. The magnetic measurements indicate that the double remnant magnetization 2M_ris 2.6 memu/g and the ferromagnetic Curie temperature is 599 K. The optical band gap E_g is obtained as 2.31 eV. Meanwhile, four different dielectric relaxations are observed in the temperature ranging from 300 to 1050 K. The corresponding relaxation mechanisms are systematically studied by the measurements of complex dielectric, impedance, electrical modulus and ac conductivity spectra. The low-frequency relaxation with E_a?=?0.752 eV is ascribed to the thermal migration of oxygen vacancy, the medium-frequency one with E_a?=?0.294 eV is assigned to the localized hole transfer behavior, whereas the high-frequency one with E_a?=?0.327 eV is associate with the hopping process of electron. In addition, the dielectric loss relaxation above?~?800 K exhibits a rather large activation energy of E_a?=?2.00 eV. The dc conductivity can be ascribed to the ionic-p-type mixed conduction mechanism.

     

On the validity condition of the chi-squared test in 2×2 tables

A 2×2 contingency table is usually analyzed by using the chi-squared asymptotic test, with Yates' continuity correction (c=n/2, wheren is the total size of sample). This correction is the correct one when the chi-squared test is an approximation to Fisher's exact (conditional) test. When the chi-squared test is used as an approximation to Barnard's exact (unconditional) test for comparing two independent proportions (two samples of sizen ₁ andn ₂) or for contrasting independence (one sample with a size ofn), the correctionc is different (c=1 ifn ₁≠n ₂ orc=2 ifn ₁=n ₂ in the first case;c=0.5 in the second). Whatever the case, it is traditional to affirm that the asymptotic test is valid whenE>5, whereE is the minimum expected quantity. Today it is recognized that this condition is too general and may not be appropriate. In the case of Yates' correction. Martín Andrés and Herranz Tejedor (2000) proved that the validity condition must be of the typeE>E ^* —whereE ^* is a known function depending on the marginals of the table—and that checking the validity of the asymptotic test is equivalent to checking the asymmetry of the base statistic (a hypergeometric random variable). In the present article the authors prove that this argument is valid for the other two continuity corrections, and moreover, that the valueE ^* is obtained for all three cases. Given that the functionE ^* reaches an absolute maximum, it can be affirmed that the three chisquared tests referred to are valid whenE<19.2, 14.9 or 6.2 (orE>8.1, 7.7 or 3.9 ifn≤500) respectively for the three previous models (although for the first model and the two-tailed testE>0 is sufficient). This research was supported by the Dirección General de Investigación (Spain). Grant BFM2000-1472.     

A study of the effect of the electro-mechanical loading history on the fracture strength of piezoelectric material

Many studies to grasp and describe the fracture behavior of piezoelectric materials under electro-mechanical loading have been done. Although the crack energy density (CED) theory predicts that the mechanical and electrical CEDs can depend on the loading history, the effect of electro-mechanical loading history on the fracture strength of piezoelectric materials has not been studied. Therefore, in this paper, a fracture criterion based on the mechanical contribution of CED (CEDM) is introduced. Its applicability is studied by analyzing the results of three-point bending test regarding the loading path dependence of the fracture strength of piezoelectric ceramic. From the results of (E → M) and (M → E) tests for a C-21 piezoelectric ceramic specimen, it was found that the fracture behavior of piezoelectric ceramics depend on the loading history. The results further showed that the effect of the electric field on the fracture strength of piezoelectric ceramic in the (M → E) test was larger than that in the (E → M) test. Results from linear FE analyses, which assumed that the fracture-initiating load was the same, indicated that the CEDM values increased linearly from negative to positive, and the slopes of CEDM in descending order were: linear (M → E) analysis > linear (M, E) analysis > linear (E → M) analysis.     

Preparation,characterization and photocatalytic properties of nanoplate Bi<Subscript>2</Subscript>MoO<Subscript>6</Subscript> catalysts

Bismuth molybdate (Bi₂MoO₆) nanoplates have been successfully synthesized by a simple hydrothermal process. The nanoplates were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and IR spectroscopy. The effects of hydrothermal temperature and reaction time on the structures and morphologies of the nanoplates were investigated. On the basis of TEM observation of time series samples, a possible formation mechanism of the nanoplates was proposed. Optical absorption experiments revealed that Bi₂MoO₆ nanoplates had absorption in visible-light region, but a blue shift appeared compared with the corresponding bulk materials. Photocatalytic experiments showed that the nanoplates exhibited good photocatalytic activities for degradation of N,N,N′,N′-tetraethylated rhodamine (RhB) under visible-light irradiation (λ > 420 nm).     

Lead-Free Relaxor Ferroelectric Ceramics with Ultrahigh Energy Storage Densities via Polymorphic Polar Nanoregions Design

One of the long-standing challenges of current lead-free energy storage ceramics for capacitors is how to improve their comprehensive energy storage properties effectively, that is, to achieve a synergistic improvement in the breakdown strength (E_b) and the difference between maximum polarization (P_max) and remnant polarization (P_r), making them comparable to those of lead-based capacitor materials. Here, a polymorphic polar nanoregions (PNRs) structural design by first introducing 0.06 mol BaTiO₃ into Bi_0.5Na_0.5TiO₃ is proposed to construct the morphotropic phase boundary with coexisting structures of micrometer-size domains and polymorphic nanodomains, enhance the electric field-induced polarization response (increase P_max). Then Sr(Al_0.5Ta_0.5)O₃ (SAT)-doped 0.94 Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ (BNBT) energy storage ceramics with polymorphic PNRs structures are synthesized following the guidance of phase-field simulation and rational composition design (decrease P_r). Finally, a large recoverable energy density (W_rec) of 8.33 J cm⁻³ and a high energy efficiency (η) of 90.8% under 555 kV cm⁻¹ are obtained in the 0.85BNBT-0.15SAT ceramic prepared by repeated rolling process method (enhance E_b), superior to most practical lead-free competitors increased consideration of the stability of temperature (a variation <±6.2%) and frequency (W_rec > 5.0  cm⁻³, η > 90%) at 400 kV cm⁻¹. This strategy provides a new conception for the design of other-based multifunctional energy storage dielectrics.     

Porosity dependence of elastic moduli in LAST (Lead–antimony–silver–tellurium) thermoelectric materials

Porosity in thermoelectric materials affects the thermal, electrical and mechanical properties of the materials. In this study, the resonant ultrasound spectroscopy technique was used to determine the Young's modulus, E, shear modulus, G, and Poisson's ratio, ν, of 12 hot pressed and five cast polycrystalline specimens of the thermoelectric material LAST (lead–antimony–silver–tellurium) as a function of volume fraction porosity, P, for P ranging from 0.01 to 0.14. A least-squares fit of the Young's and shear moduli data to the relationships E = E_D(1 − b_PEP) and G = G_D(1 − b_PGP), respectively yielded E_D = 58.4 ± 0.6 GPa and G_D = 23.0 ± 0.2 GPa, where E_D and G_D are the estimated Young's modulus and shear modulus at room temperature for theoretically dense specimens, respectively. The unitless, material-dependent constants b_PE and b_PG were b_PE = 3.5 ± 0.2 and b_PG = 3.5 ± 0.2.     

Thermal buckling behavior of composite laminated plates

Thermal buckling behavior of composite laminated plates was studied by making the use of finite element method. The thermal buckling mode shapes of cross-ply and angle-ply laminates with various E₁/E₂ ratios, aspect ratios, fiber angle, stacking sequence and boundary condition were studied in detail. The results indicate that the high E₁/E₂ and α₂/α₁ ratios of AS4/3501-6 and T 300/5208 laminates produce higher bending rigidity along the fiber direction and higher in-plane compressive force in a direction perpendicular to the fiber direction. Therefore, the higher thermal buckling mode shapes are formed. The thermal buckling mode that composite laminated plate will buckle into is mainly dependent on the E₁/E₂ ratio, α₂/α₁ ratio, fiber orientation and aspect ratio of the plate.     

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.     

The ion energy distributions and ion flux composition from a high power impulse magnetron sputtering discharge

The energy distribution of sputtered and ionized metal atoms as well as ions from the sputtering gas is reported for a high power impulse magnetron sputtering (HIPIMS) discharge. High power pulses were applied to a conventional planar circular magnetron Ti target. The peak power on the target surface was 1-2 kW/cm² with a duty factor of about 0.5%. Time resolved, and time averaged ion energy distributions were recorded with an energy resolving quadrupole mass spectrometer. The ion energy distributions recorded for the HIPIMS discharge are broader with maximum detected energy of 100 eV and contain a larger fraction of highly energetic ions (about 50% with E_i > 20 eV) as compared to a conventional direct current magnetron sputtering discharge. The composition of the ion flux was also determined, and reveals a high metal fraction. During the most intense moment of the discharge, the ionic flux consisted of approximately 50% Ti¹⁺, 24% Ti²⁺, 23% Ar¹⁺, and 3% Ar²⁺ ions.     

AFM-Based Poroelastic@Membrane Analysis of Cells and its Opportunities for Translational Medicine

Cell mechanics is an emerging field of research for translational medicine. Here, the cell is modeled as poroelastic cytoplasm wrapped by tensile membrane (poroelastic@membrane model) and is characterized by the atomic force microscopy (AFM). The parameters of cytoskeleton network modulus E_C, cytoplasmic apparent viscosity η_C, and cytoplasmic diffusion coefficient D_C are used to describe the mechanical behavior of cytoplasm, and membrane tension γ is used to evaluate the cell membrane. Poroelastic@membrane analysis of breast cells and urothelial cells show that non-cancer cells and cancer cells have different distribution regions and distribution trends in the four-dimensional space composed of E_C, η_C. From non-cancer to cancer cells, there is often a trend of γ, E_C, η_C decreases and D_C increases. Patients with urothelial carcinoma at different malignant stages can be distinguished at high sensitivity and specificity by analyzing the urothelial cells from tissue or urine. However, sampling directly from tumor tissues is an invasive method, may lead to undesirable consequences. Thus, AFM-based poroelastic@membrane analysis of urothelial cells from urine may provide a non-invasive and no-bio-label method to detecting urothelial carcinoma.     

Transverse mechanical properties of collagen fibers from nanoindentation

The mechanical properties of collagenous tissues, such as tendon and ligaments, are of particular interest as they are found extensively in the human body. In the present study the transverse mechanical properties of collagen fibers are reported for the first time. The elastic modulus was found to be 63 ± 4 MPa, while the viscosity was estimated to be 14  \textGPa ￡ h ￡ 56  \textGPa  \texts 14\;{\text{GPa}} \le \eta \le 56\;{\text{GPa}}\;{\text{s}} . Comparison with similar data in the literature, for bulk tendon and collagen fibrils, suggests that the apparent modulus of a network of interconnected building blocks is reduced as compared to the modulus of the individual building blocks; in particular E _tendon < E _fiber < E _fibril; this is due to the fact that as the scale of the microstructure increases (i) slippage and sliding between the respective building blocks (fibrils or fibers) increases, (ii) the volume fraction of the stiff collagen proteins decreases.     

Cover Picture: Direction‐Dependent Homoepitaxial Growth of GaN Nanowires (Adv. Mater. 2/2006)

GaN nanowires with vastly different morphologies depending upon their growth direction can be produced by direct nitridation and vapor transport of Ga in disassociated ammonia, report Sunkara and co‐workers on p. 216. Nanowires grown along the c‐direction develop hexagonal‐prism island morphologies, while wires grown along the a‐direction form uniform, belt‐shaped morphologies. A “ballistic” phenomenon involving the 1D transport of adatoms on the non‐polar surfaces of <0001> GaN nanowires is proposed to explain the prismatic island morphologies.