Mode mixity for tubular K-joints with weld toe cracks

This paper examines the mode-mixity of stress-intensity factors for surface cracks located near weld toes of the crown point at the toe of the tension brace in circular hollow section K-joints under different chord/brace end constraints. The remote loading applies a uniform stress at the end of the brace along its axis. The 3-D finite element models employ mesh-tieing between a topologically continuous, global mesh and a separate, local crack-front mesh. The linear-elastic analyses compute the mixed-mode stress-intensity factors along the crack front using an interaction-integral approach. The analyses for three different crack locations along the brace-chord intersection demonstrate that the critical location for the surface flaw lies at the crown point of the brace toe. The numerical investigation of six different boundary conditions indicate that the unbalanced loading conditions cause significant bending stresses in the chord and generate a considerably larger mode I stress-intensity factor than found for the balanced loading case. The mixed-mode stress-intensity factors indicate that the crack front experiences predominantly mode I loading, with K_III → 0 near the deepest point on the front (? = π/2). The non-dimensional, mode I crack driving force, described by , reaches a maximum value at the deepest point of the crack for the crack aspect ratio a/c = 0.25 considered here. The mode-mixity angle, ψ = tan⁻¹(K_II/K_I), at ? = π/2 is compared for a range of practical K-joint configurations. The present study demonstrates that the mode-mixity angle ψ becomes significantly larger in the balanced loading conditions than in the unbalanced loading condition. Values of the non-dimensional stress-intensity factors ( and ), however, decrease for the balanced loading condition. Variations in the brace-to-chord diameter ratio (β) and chord radius to wall thickness ratio (γ) generate significant changes in the mode mixity. Thin-walled joints (γ = 20) generally experience a larger crack driving force with a higher mode-mixity angle.     

Nondestructive investigation of β-FeSi2/Si interface by photoluminescence measurements

Ion-beam-synthesized β-FeSi₂/Si interfaces were investigated by carrier-injection photoluminescence (CPL) measurements. The CPL intensity of Al-doped β-FeSi₂/Si sample was larger than that of non-doped one. We obtained a carrier injection efficiency (γ) of γ = 0.41 in the Al-doped sample and γ = 0.19 in the non-doped one. These results revealed that Al-doping into β-FeSi₂ is an effective technique for the improvement of β-FeSi₂/Si interface which is defective due to ion implantation damages.     

Synthesis of cubic niobium nitride by reactive diffusion under nitrogen pressure

The synthesis of niobium nitride by reactive diffusion in a furnace at 1395-1475 °C and under nitrogen pressure in the range 2-25 MPa was investigated. In experiments, we used compacted Nb powder with a mean particle size of 43 μm. Phase transformations in the product as studied by electron probe microanalysis (EPMA) were found to proceed in the following order: Nb → α-Nb(N) → β-Nb₂N_1±x → γ-Nb₄N_3±x → δ-NbN_1±x. The size of niobium particles which could react with nitrogen to yield cubic niobium nitride was estimated (SEM analysis) from the dependence of the thickness Δ of the δ-NbN_1±x outer layer formed on the surface of Nb particles on the dwell time t_dw at 1460-1473 °C. It was shown that Δ grew nearly proportional to t_dw. At t_dw = 30 min and P(N₂) = 2 MPa, Δ was found to attain a value of about 15.5 μm. Prolonged heating (t_dw ≈ 60 min) was found to result in decomposition of the single-phase cubic niobium nitride into a two-phase (multiphase) product. This was confirmed by XRD data and magnetic measurements which showed the occurrence of two different critical temperatures T_c in the same sample. The maximum critical temperature T_c was found to attain a value of 15.6 K.     

A through interface crack between a transversely isotropic pair of materials (+30°/−60°, −30°/+60°)

This study focuses on a delamination between two layers of a fiber-reinforced composite material oriented in the directions θ/(θ − 90°). Two specific interfaces are examined: the +30°/−60° interface and −30°/+60° interface. The delamination in these cases is treated effectively as a crack between two monoclinic materials. The behavior of the stress and displacement fields near the crack tip is studied. The first term of the asymptotic expansion for the stress and displacement fields are found by means of the Stroh and Lekhnitskii formalisms. A general solution is obtained for an interface crack in the x₂ = 0 plane. The crack is between two monoclinic materials with x₂ = 0 a symmetry plane.In order to calculate the stress intensity factors, a three-dimensional interaction energy or conservative M-integral is extended and implemented in conjunction with the finite element method. For the M-integral, the auxiliary fields used are particular cases of the stress and displacement fields obtained earlier. The displacement extrapolation method is also extended for this case. The crack surface displacements obtained from a finite element analysis are employed. The methods are independent of each other; hence, they may be used for validation of the results determined.Three test cases are analyzed to examine the accuracy of the results obtained by means of the M-integral method. In addition, two problems of a central crack in a symmetric composite under different loadings are solved. Those loadings are tension and in-plane shear. Stress intensity factors and the interface energy release rate are obtained along the crack front for all cases.     

Luminescence of rare earth borosilicates with the stillwellite and related structures

By hydrothermal reactions it was possible to prepare well-crystallized borosilicates of composition La_{1 − x − y}Ln_xLn′_yBSiO₅ with the trigonal stillwellite structure. Ln = Eu³⁺ and Tb³⁺ produce compounds with only weak luminescence. Compounds with Ln = Ce³⁺ are strong UV phosphors with peak intensity at x = 0.08 and abrupt concentration quenching at x = 0.10. Compounds with Ln = Ce³⁺ and Ln′ = Tb³⁺ exhibit effective Ce³⁺ → Tb³⁺ coactivation and strong green luminescence. This family of borosilicates appears to be useful phosphor hosts, aside from the necessity of non-traditional synthesis.     

The magnetoelectric perovskite Sr2CoMoO6: An insight from neutron powder diffraction

A study of the crystallographic and magnetic structure of the double perovskite Sr₂CoMoO₆ (SCMO) has been carried out on a polycrystalline sample using neutron powder diffraction (NPD) data between 10 and 700 K. An analysis of the NPD patterns at room temperature has shown that this compound crystallises in the tetragonal space group I4/m with a = 5.5616(1) Å and c = 7.9470(2) Å and has a 1:1 ordered arrangement of Co and Mo at the B-sites. This compound undergoes a I4/m → Fm3m improper ferroelectric phase transition near 560 K. A low-temperature antiferromagnetic ordering (below T_N = 36 K) has been followed from sequential NPD data analysis. The antiferromagnetic structure is defined by the propagation vector k = (1/2, 0, 1/2). In addition to the obtained experimental results on magnetic and electric properties some aspects of magnetoelectricity in this perovskite are also discussed.     

Synthesis and luminescence properties of color-tunable Ba1−ySryLa4−xTbx(WO4)7 (x = 0.02-1.2, y = 0-0.4) phosphors

Ba_1−ySr_yLa_4−xTb_x(WO₄)₇ (x = 0.02-1.2, y = 0-0.4) phosphors were prepared via a solid-state reaction and their photoluminescence properties were investigated. An analysis of the decay behavior indicates that the energy migration between Tb³⁺ ions is conspicuous in the ⁵D₃ → ⁷F₄ transition due to the cross-relaxation in BaLa₄(WO₄)₇. A partial substitution of Ba²⁺ by Sr²⁺ can not only enhance the emission intensity but also increase the solid solubility of Tb³⁺ in Ba_1−ySr_yLa_4−xTb_x(WO₄)₇. The emission intensity of the ⁵D₄ → ⁷F_J (J = 4, 5, 6) transitions can be enhanced by increasing Sr²⁺ and Tb³⁺ concentrations, with the optimal conditions being x = 1.2, y = 0.4 (Ba_0.6Sr_0.4La_2.8Tb_1.2(WO₄)₇). Under near-UV excitation at 379 nm, the CIE color coordinates of Ba_1−ySr_yLa_4−xTb_x(WO₄)₇ vary from blue (0.212, 0.181) at x = 0.04, y = 0, to green (0.245, 0.607) at x = 1.2, y = 0.4.     

Vacuum-ultraviolet ellipsometry spectra and structural properties of Pb(Zr,Ti)O3 films

Optical properties of PbZr_xTi_1 − xO₃ material have been actively studied in the visible and near band-gap region, but data in the vacuum-ultraviolet spectral region is rather scarce. In this work we focus on well known interband transitions for the perovskite materials, 2p → dγ, located in VUV spectral region. Dielectric functions of chemical solution deposited and sputtered PZT were obtained in the spectral range 1-8.8 eV. Differences between the absorption maxima for chemical solution deposited and sputtered PbZr_xTi_1 − xO₃ samples near Kahn-Leyendecker 2p → dγ interband transition were found and are interpreted by change of interatomic distances. This is confirmed by different lattice constants. In the case of PbZr_xTi_1 − xO₃ film with microcracks, the void fraction was estimated from the effective medium approximation. Direct band-gap energies appear to be nearly the same for all reactive sputtered samples weakly depending of Zr/Ti concentration.     

Synthesis and crystal structure of [3,5-(CH3O)2C6H3NH3]4P4O12·4H2O

The chemical preparation and crystal structure are given for a new organic-cation cyclotetraphosphate. This compound is triclinic P-1 with the following unit cell parameters: a=7.857(1) Å, b=8.877(2) Å, c=17.271(3) Å, α=93.94(1)°, β=101.75(2)°, γ=103.72(1)° V=1137.0(4) Å³, Z=1 and ρ_cal=1.467 g cm⁻³. The crystal structure has been determined and refined to R=0.037, using 6291 independent reflections. The atomic arrangement can be described by inorganic layers parallel to the (0 0 1) planes, between which the organic entities are located.     

A general weight function approach to compute mode-II stress intensity factors and crack paths for slightly curved or kinked cracks in finite bodies

A simple procedure is proposed that allows computing the stress intensity factors for slightly curved and kinked cracks in finite bodies. Basis of the method is the computation of the stress field around a straight crack under externally applied tractions. Then, this auxiliary crack is replaced by the crack of interest. The stress intensity factors are computed from the stresses caused by the auxiliary crack using the weight function technique. In a practical application of the method, mode-II stress intensity factors are computed for the edge-cracked half-space. From the usual crack path condition, K_II = 0, the paths of propagating cracks under biaxial loading and the critical biaxiality ratio for global directional instability are computed. The results are in very good agreement with finite element computations.     

A novel compound with the formula Cd2InVO6

As a result of a solid-state reaction, a compound with the formula Cd₂InVO₆ has been obtained for the first time. This compound melts congruently at 1050 ± 10 °C. It crystallises in the monoclinic system and the unit cell parameters are: a = 0.7964(2) nm, b = 1.1311(3) nm, c = 0.6001(1) nm, γ = 104.1°, Z = 4.     

Stress intensity factors for a wide range of long-deep semi-elliptical surface cracks, partly through-wall cracks and fully through-wall cracks in tubular members

To calculate the rate of fatigue crack growth in tubular members, one approach is to make use of the fracture mechanics based Paris law. Stress intensity factors (SIF) of the cracked tubular members are prerequisite for such calculations. In this paper, stress intensity factors for circumferential deep semi-elliptical surface crack (a/t > 0.8), semi-elliptical partly through-wall crack and fully through-wall crack cracks in tubular members subjected to axial tension are presented. The work has produced a comprehensive set of equations for stress intensity factors as a function of a/T, c/πR and R/T for deep surface cracks. For the partly through-wall cracks and fully through-wall cracks, two sets of bounding stress intensity factor equations were produced based on which all stress intensity factors within the range of parameters can be obtained by interpolation.     

Absorption and emission properties of Ho doped lead-zinc-borate glasses

This paper reports on the affect of lead content on the absorption and emission spectra of the Ho³⁺ ion doped lead-zinc-borate glasses in the composition (mol%) of (20 − x)PbO-20ZnO-(59 + x)B₂O₃-1.0Ho₂O₃ where x = 0, 5,10,15 of PbO content with λ_exc = 405 nm. The experimental absorption band energies have satisfactorily been correlated with the theoretical results with an r.m.s deviation of zero with the following correction factors obtained by a least square fit analysis: ΔE¹ = 348.495936 cm^− 1, ΔE² = 1.436043 cm^− 1, ΔE³ =  46.481575 cm^− 1, Δξ_4f = − 28.512979 cm^− 1, Δα = 55.508936 cm^− 1, Δβ = − 1394.339908 cm^− 1 and Δγ = 1208.424336 cm^− 1. By applying the Judd-Ofelt intensity parameter Ω₂ has been found to be linearly decreasing with the PbO content from 5 to 10 mol% and then increasing. And also radiative (A, A_T, β, τ_r) characteristic factors of the luminescent transitions (⁵I₈ ← ⁵F_3,4,5 and ⁵S₂) of the glasses have been evaluated. Stimulated emission cross-sections (σ_p^E) of the measured emission transitions of holmium glasses have also been computed.     

Magnetic, magnetocapacitance and dielectric properties of Cr doped bismuth ferrite nanoceramics

BiFe_1−xCr_xO₃ (x = 0, 0.04, 0.06 and 0.08) nanoceramics were prepared by sol-gel method. Nanoceramics were calcined at 450 °C. Calcined powders were leached in diluted nitric acid to get single phase. TEM analysis shows the particle size to be ∼80 nm. Thermogravimetric analysis of as prepared powder indicates that the single phase is formed at around 450 °C. Magnetization was found to increase as the concentration of Cr was increased. Dielectric constant and dielectric loss were found to decrease with increase in frequency for all the compositions. Magnetocapacitance was found to increase with magnetic field. For BiFe_1−xCr_xO₃ (x = 0.04, 0.06 and 0.08) nanoceramics, the change of dielectric constant induced by magnetic field may be well approximated by Δ?/? = γM², here, γ (magnetoelectric interaction) is small and positive. A linear fit gave the value of γ of ∼18.4 × 10⁻², 12.3 × 10⁻² and 3.3 × 10⁻² for BiFe_1−xCr_xO₃ (x = 0.04, 0.06 and 0.08) nanoceramics, respectively.     

Influence of mixed alkalis on spectroscopic parameters of Sm, Dy doped chloroborate glasses

This article reports the effect of mixed alkalis on the optical absorption and emission spectra of Sm³⁺ and Dy³⁺ doped chloroborate glass matrices of the compositions 69.5B₂O₃xLiCl(30 − x)NaCl0.5R₂O₃ and 69.5B₂O₃xLiCl(30 − x)KCl0.5R₂O₃ (where R = Sm and Dy and x = 5, 10, 15, 20 and 25). Using Judd-Ofelt theory, the spectral intensities and Judd-Ofelt intensity parameters (Ω_2,Ω₄ and Ω₆) were obtained from the measured absorption bands of the spectra. Using these intensity parameters, total radiative transition probabilities (A_T), radiative lifetimes (τ_R), branching ratios (β) and peak emission cross-sections (σ_P) were obtained for the two rare earth ions in these two glass matrices. Variation of these parameters with x in the glass matrix has been discussed. It is found that for Sm³⁺ ion, the transition, ⁴G_5/2 → ⁶H_9/2 shows highest emission cross-section and is maximum at x = 10 mol% in lithium-sodium and at x = 20 mol% in lithium-potassium glass matrices. For Dy³⁺ ion, the transition, ⁴F_9/2 → ⁶H_13/2 shows highest emission cross-section and is maximum at x = 20 mol% in lithium-sodium and at x = 10 mol% in lithium-potassium glass matrix.     

Effect of isoelectronic substitution of Bi on the photoelectrical properties in amorphous Sn-Sb-Se films

Amorphous thin films of Sn₁₀Sb_20 − xBi_xSe₇₀ (0 ≤ x ≤ 6) system have been prepared by thermal evaporation technique. The optical gap and dc activation energy first increases with the addition of Bi (x = 2) and then decreases sharply with further addition. The photocurrent initially increases with time and then saturates to a constant value for all the samples. The decay portion of photocurrent has two components, fast one followed by a slow decay. Photocurrent (I_ph) versus light intensity (F) follows the power law I_ph ∝ F^γ and the value of the exponent (γ) decreases from 0.76 to 0.53 as the Bi concentration varied from x = 0 to 6 in the present system. The photosensitivity of these samples varies from 1.27 to 1.13 as Bi content increases.     

Non-equilibrium phases in the Fe-Rh system studied by ion beam mixing and ab initio calculation

In the Fe-Rh system, the Fe_100 − xRh_x (x = 40, 50, 65, 70, and 90) multilayered films were prepared and then subjected to ion beam mixing using 200 keV Xe ions. Upon ion beam mixing, amorphous alloy was obtained in the Fe₇₀Rh₃₀ sample, in which an interesting phase transition path was observed as Fe + Rh → fcc → fcc + a →? fcc + bcc → fcc. In addition, a new metastable crystalline fcc phase was observed in the Fe₅₀Rh₅₀ sample together with the solid solutions, and the lattice constants of the ion mixed phases were consistent with those from ab initio calculations. Possible mechanisms for the formation of both amorphous and metastable crystalline phases are discussed in terms of the atomic collision theory.     

Notch stress concepts for the fatigue assessment of welded joints - Background and applications

Among modern fatigue design concepts for welded structures, the linear-elastic notch stress concept gains increasing industrial acceptance. There are two variants of this concept, one for thick walled (t ? 5 mm) welded joints with the reference radius r_ref = 1.00 mm, which is already included in the fatigue design recommendations of the IIW and applied for the assessment of big welded structures, and one for thin walled (t < 5 mm) welded joints with the reference radius r_ref = 0.05 mm, which is more and more used in the automotive industry.The concept with r_ref = 1.00 mm is based on the micro-support theory of Neuber with the fictitious radius r_ref = 1.00 mm, derived by Radaj. The background of the concept with r_ref = 0.05 mm is the relationship between the stress-intensity factor and the notch stress according to Creager and Paris as well as Irvin’s theory of crack blunting. Besides these two theories, the definition of both of these radii has also an experimental background; they are observed in many welded joints.In the present paper, first the background and then different applications of both concept variants are described: the application of the reference radius of r_ref = 1.00 mm for MAG-welded offshore K-nodes (t = 30 mm) and sandwich panels for ship decks (t = 5 mm), and the application of r_ref = 0.05 mm for spot-welded automotive doors (t = 1 mm) and MAG-welded automotive trailing links (t = 3-4 mm). The sandwich panels were evaluated additionally with r_ref = 0.05 mm. Calculations and experimental results are compared and the reliability of the notch stress concept variants underlined. Additionally, recommendations for the slope of design lines distinguishing between thin and thick dimensions are given, i.e. k = 3.0 and 5.0 (normal stress, shear stress) for thick and stiff structures, k = 5.0 and 7.0 for thin and flexible structures.     

Synthesis and characterization of 2-amino-3-methylpyridinium dihydrogenomonoarsenate

A new crystal of 2-amino-3-methylpyridinium dihydrogenomonoarsenate has been prepared and characterized by X-ray crystallography, thermal analysis and spectroscopic studies. This compound crystallizes in the triclinic space group with a = 7.2689 (2) Å, b = 8.0975 (2) Å, c = 8.3969 (4) Å, α = 77.09 (3)°, β = 79.20 (3)°, γ = 88.16 (2)°, V = 473.19 (3) Å³, Z = 2. The crystal structure was solved and refined to R = 0.027 with 3375 independent reflections. The atomic arrangement can be described as (H₂AsO₄⁻)_n polymeric chains anchoring the 2-amino-3-methylpyridinium cations through short hydrogen bonds. All the ring atoms of the organic entity are coplanar. The exocyclic N atom is an electron receiving center, which is consistent with features of imino resonance evidenced by bond lengths and angles. Solid-state ¹³C and ¹⁵N CP-MAS-NMR spectroscopies are in agreement with the X-ray structure. Ab initio calculations allow the attribution of carbons and nitrogen to the independent crystallographic sites.     

Crystal structure of a new organic condensed phosphate (C6H9N3O)H2P2O7

Crystals of a new organic compound, the isonicotinic acid hydrazide dihydrogendiphosphate, (C₆H₉N₃O)H₂P₂O₇ (denoted INHDP) were prepared and grown at room temperature. The INHDP crystallizes in the triclinic system with the space group. Its unit cell dimensions are: a = 7.316(3) Å, b = 7.783(3) Å, c = 10.802(4) Å, α = 82.41(3)°, β = 75.19(3)°, γ = 72.57(3)°, with V = 566.3(4) Å³ and Z = 2. Crystal structure has been determined and refined to a reliability R factor of 0.0389. The atomic arrangement can be described as inorganic infinite ribbons of H₂P₂O₇²⁻ anions spreading parallel to the b-axis. These ribbons are themselves interconnected by the organic (C₆H₉N₃O)⁺ cations so as to build a three dimensional arrangement. In the present work, we describe the crystal structure, thermal behaviour and IR analysis of this new compound.