The calcuLatoR—software for evaluation of evidence value of continuous type data

The role of the forensic chemist can be to evaluate physicochemical data (evidence—E) in the context of the prosecution proposition H_p and the defence proposition H_d. From a forensic point of view, the most suitable form of evaluating the evidence value of physicochemical data is by calculation of the likelihood ratio (LR).There are many LR models which could be used for measuring the evidence value of results of analysis of glass samples. A disadvantage of these models is that there is a lack of commercially available software that is suitable for use by forensic experts, who may lack experience in programming. Therefore such users are required to write their own case specific routines, e.g. in R software (www.r-project.org).The Graphical User Interface software named “calcuLatoR” for the calculation of the LR value for univariate data (such as refractive index data) has been developed. The LR model assumes two sources of variation, i.e. between replicates within the same object (within object variability) and between replicates between various objects (between object variability). It was assumed that the within object distribution is normal with constant variance. The between object distribution was modelled by a univariate kernel density estimator, i.e. using Gaussian kernels. The calcuLatoR could also be used for evaluating the evidential value of multivariate data but it must be assumed that the considered variables are independent. In this situation, LR should be calculated for each variable separately and a final value of LR is equal to their product.Validation of the calculations performed by the calcuLatoR was carried out by comparing results obtained by routines written in R.     

Transformations for compositional data with zeros with an application to forensic evidence evaluation

In forensic science likelihood ratios provide a natural way of computing the value of evidence under competing propositions such as “the compared samples have originated from the same object” (prosecution) and “the compared samples have originated from different objects” (defence). We use a two-level multivariate likelihood ratio model for comparison of forensic glass evidence in the form of elemental composition data under three data transformations: the logratio transformation, a complementary log-log type transformation and a hyperspherical transformation. The performances of the three transformations in the evaluation of evidence are assessed in simulation experiments through use of the proportions of false negatives and false positives.     

Effect of stress relief groove on fretting fatigue strength and index for the selection of optimal groove shape

The applicability of small stress relief groove for the improvement of fretting fatigue strength was studied. Fretting fatigue tests were done using several kinds of grooved specimens. The shape of groove was systematically changed with parameters of groove radius R and tangential angle θ. The improvement of fatigue limit by a stress relief groove depended on both R and θ. The fretting fatigue limit with stress relief groove was increased with the increase of R and θ. The parameter θd (d: groove depth) was selected for the unified evaluation of the improvement. FEM stress analyses were done to investigate the stress condition. In a simple elastic FEM analysis assuming that the contact edge is ideally shaped, a highly compressive stress field was generated near the contact edge, where small cracks could never propagate. This suggested that such a simple analysis was not enough to solve this problem. Thus, an assumption to relieve the highly compressive contact pressure near the contact edge was introduced to explain the experimental fact that a crack could propagate. The profile change was simulated by the local plastic deformation at the contact edge calculated by elasto-plastic FEM deformation analysis. This deformation reduced the highly compressive contact pressure and enabled the crack propagation. As a result, it was found that fretting fatigue limit of grooved specimen could be evaluated on the basis of the maximum axial stress near the contact edge. The estimation of fretting fatigue limit using a relationship between K_t/K_t0 and θd provided a good estimation with the experimental results and it would be a useful method to select the optimal groove shape.     

Evaluation of elastic/mechanical properties of some glasses and nanocrystallized glass by cube resonance and nanoindentation methods

Elastic and mechanical properties of 10La₂O₃·30Bi₂O₃·60B₂O₃ (LaBiB) glass, 15K₂O·15Nb₂O₅·68TeO₂·2MoO₃ (KNbTeMo) glass and a transparent KNbTeMo nanocrystallized (particle size: ∼40 nm) glass were examined using cube resonance and nanoindentation methods. The values of Poisson’s ratio, Young’s modulus (E), Debye temperature (θ_D), fractal bond connectivity, Martens hardness, indentation hardness, indentation Young’s modulus, elastic recovery, Vickers hardness, fracture toughness (K_c) and brittleness for the samples were evaluated, and the relation with the structure and nanocrystallization were clarified. LaBiB glass containing high oxygen-coordinated La³⁺ ions and two-dimensional BO₃ structural units shows excellent properties of E=90.6 GPa, θ_D=404 K and K_c=0.72 MPa m^1/2 and a high resistance against deformation during Vickers indentation. KNbTeMo glass with the three-dimensional network structure and consisting of weak Te-O bonds has small values of E=51.4 GPa and K_c=0.29 MPa m^1/2. It was demonstrated that the elastic and mechanical properties of KNbTeMo precursor glass are largely improved by nanocrystallization, e.g., E=69.7 GPa and K_c=0.32 MPa m^1/2. The nanocrystallization also induces a high resistance against deformation during Vickers indentation.     

On matrix crack saturation in composite laminates

This paper presents a comparative experimental investigation on matrix crack saturation in the constrained laminae of glass–fibre resin composite laminates. Fatigue tests under load and strain control were conducted on [±θ/90₃]_s and [0/±θ₄/0]_T laminates, respectively. The crack density was periodically measured by using digital image method and optical microscope examination during fatigue tests, to determine crack saturation. It is found that matrix crack saturation occurs in all laminates of different lay-ups under both stress and strain control cyclic loading. The crack density at saturation in the constrained plies is dependent on the cyclic loading type, the off-axis angle of the laminates, as well as the constraining ply. Based on the strain energy release rate, a crack saturation criterion is developed and the experimental findings are qualitatively analysed.     

Damage characterization in non-isothermal stretching of acrylics. Part I: Theory

An improved version of dual-mechanism constitutive model was proposed to describe thermo-mechanical response of amorphous polymers below and above glass transition temperature (θ_g). Material property definitions and plastic flow rules were revisited to provide a smooth and continuous transition in material response around θ_g. The elastic-viscoplastic constitutive model was developed based on thermodynamics framework and was implemented in a fully coupled thermo-mechanical simulation of non-isothermal testing of PMMA in Part II [Gunel, E. M., Basaran, C., 2010. Damage characterization in non-isothermal stretching of acrylics. Part II: Experimental validation. Mechanics of Materials]. For damage evolution in complex thermo-mechanical problems such as polymer processing operation, irreversible entropy production was considered as the measure of damage.     

Creep characterization of a Ni-based Hastelloy-X alloy by using theta projection method

The θ projection method was applied to characterize the creep behavior of the Hastelloy-X alloy at 950 °C. Four θ parameters were established by a nonlinear least square fitting (NLSF) to the creep curves. In the NLSF of the full creep curves, the θ₁ and θ₂ parameters were not defined with a large error, but the θ₃ and θ₄ parameters were defined well without an error. An optimum cutoff strain range for defining the four θ parameters was found to be a 3% strain. Four θ parameters revealed a good linearity as a function of stress. The predicted minimum creep rate showed a good agreement with the experimental data. At 950 °C of the Hastelloy-X alloy, the creep curves, the creep rate, and the time to reach a limiting strain were estimated with a wide range of stresses.     

Dependence of mixed-mode crack propagation on the variation of σr and τrθ

The variation of the direction θ_p of crack propagation in mixed mode with the angle β of the inclined crack is shown to fit very well to the variation of θ_r, of the bisector of the angle of directions θ_r1 and θ_r2 of max σ_r and sufficiently well to that of θ_rθ, bisector of the angle of directions θ_rθ1 and θ_rθ2 of min τ_rθ < 0 and max τ_rθ > 0. The variation of σ^cr/σ^cr_I, causing initiation of propagation, with β as predicted by the max σ_θ criterion, fits very well to that of a critical loading evaluated by considering the combined “opening” effect of σ and τ_rθ along the circumference of a small circle centered at the crack tip. The above results may be used as criteria of mixed-mode fracture based on σ_r and τ_rθ.     

Thermoelectric power of superionic conductor Ag7I4VO4

Thermoelectric power studies on Ag₇I₄VO₄. superionic conductor have been carried out in the temperature range 25 to 60°C. Thermo-electric power is found to vary linearly with the inverse of the absolute temperature, and can be expressed by the equation −θ = [(0.182 × 10³/T) + 0.276] mV/K. The heat of transport is nearly equal to the activation energy of Ag⁺ ion migration calculated from the conductivity plots indicating that the material has an average structure.     

Forced Wetting Dynamics of Sodium Dodecyl Sulfate Glycerol Solution on Solid Substrates

The forced wetting dynamics of a sodium dodecyl sulfate glycerol solution on both intermediate hydrophilic and hydrophilic solid substrates was studied by using the Wilhelmy plate method. The dynamic contact angle θ _D at different contact line velocities U (θ _D–U relationship) was measured. The influences of the macroscopic properties including the surfactant solution concentration, the substrate surface free energy, and the surface tension on the θ _D–U relationship were investigated, and all three properties are important. An interesting phenomenon that θ _D initially increases then decreases with U was found in the experiment, which could not be explained by modern theoretical models. The microscopic effect of the surfactant adsorption on the solid–vapor interface near the three-phase contact line was used to explain this phenomenon. A modified molecular-kinetic model was proposed, and the model can well describe the experimental results.     

Fibre orientation of novel dynamically sheet formed discontinuous natural fibre PLA composites

This paper describes work carried out to fabricate and to assess the fibre orientation in PLA reinforced by aligned discontinuous harakeke and hemp fibre mats produced using a dynamic sheet former (DSF). These mats were combined with PLA sheets to make composites with fibre contents of 5–40 wt% using a hot press. It was found that the fibre orientation factors (K_θ) for both harakeke and hemp fibre composites were higher than those values seen in the literature for composites prepared using injection moulding and hot pressed using randomly oriented fibre mats, but slightly lower than the highest values obtained with aligned fibre nonwoven preform composites utilising more processing stages. The highest K_θ values for harakeke and hemp fibres in this work were found to be 0.58 and 0.44 respectively. K_θ decreased, reflecting increased fibre misalignment as fibre content increased, believed to be due to fibre agglomeration and the higher pressure required during processing.     

Strained coherent interface energy of the Guinier–Preston II phase in Al–Cu during stress aging

θ″-phase, with a formal stoichiometry of Al₃Cu, is a coherent, metastable precipitate (GP-II) phase commonly found in Al-based aerospace alloys. In this paper, we employed a first-principles based method to study the energetics of the Al/θ″ interface as response to external strains. The potential effects of temperature, Cu activity, and different strain modes on interface energy (γ _Al/θ″) were systematically investigated. Calculations show that (i) an unstrained γ _Al/θ″ always increases with temperature: as temperature increases from T = 298 to 498 K, γ _Al/θ″ increases by ~9.0 %; (ii) γ _Al/θ″ is more sensitive to compressive strains than to tensile strains of the same magnitude. In particular, for a parallel compressive strain increasing from 0 to 2 % at a typical aging temperature, γ _Al/θ″ decreases by ~6.6 %, while a vertical compressive strain of 2 % has a slightly stronger impact by decreasing γ _Al/θ″ by ~9.6 %. Different influences of applied strain/stress on the formation energies of different orientated interfaces can be further exaggerated by the Poisson effect, and eventually affect the preferential precipitation orientation of θ″ in the matrix.     

Resonant heat transfer between He4 and metal surfaces

A calculation is made of the heat transferred from a metal surface to liquid He⁴ by resonant states sitting on the metal surface, which radiate acoustic energy into the liquid. The results are compared with experimental evidence and satisfactory agreement is obtained. It is argued that the experimentally observed Kapitza conductance varies as θ_D^?3 and not as θ_D^?0.8 as is generally assumed.     

Finite element analysis for surface diffusion-controlled shape instabilities of plate-like grains

Based on classical theory of surface diffusion and evaporation–condensation, a finite element program is developed to simulate the unstable shape evolution of plate-like grains. The program is used to analyze thermal grooving on a polycrystalline surface and compared with a non-linear solution and finite difference analysis. It shows that the finite element method used is robust, accurate and efficient. Then, the shape evolution kinetics of the plate-like grains are simulated as a function of the thermal grooving angle θ at the grain boundary–surface junctions and the initial aspect ratio of the plate β (plate width to thickness). When θ=0 (without internal boundary), the plate-like grain will evolve into cylinders directly. When an internal boundary exists, there is a critical thermal grooving angle θ_min for given β. If θ<θ_min, the plate cannot split, otherwise, the plate will split along the internal boundary of the plate-like grain. An approximate formulation of θ_min as a function of β is given based on a number of finite element analyses. The effect of initial termination shape of the plate on θ_min is also examined, and a weak effect was found. When β>10, its effect can be neglected.     

Damage characterization in non-isothermal stretching of acrylics. Part II: Experimental validation

Influence of temperature and strain rate on damage accumulation and large deformation behavior of acrylics was investigated under conditions similar to actual polymer processing. Poly(methyl methacrylate) (PMMA) samples were stretched to large strains at different rates under transient thermal conditions. During testing, specimens were cooled down from temperatures above glass transition temperature (θ_g) to temperatures well-below θ_g inducing a transition from rubbery state to solid state. Contrary to common practice of studying thermo-mechanical coupling in terms of adiabatic heating; in proposed experimental study, temperature effect on mechanical response of material was emphasized by externally intervening temperature variation within specimen. An improved version of dual-mechanism constitutive model presented in Part I [Gunel, E.M., Basaran, C., 2010. Damage characterization in non-isothermal stretching of acrylics. Part I: Theory. Mechanics of Materials] was proposed to predict thermo-mechanical response of amorphous polymer below and above θ_g. Applicability of proposed constitutive model for the specific case of non-isothermal stretching of PMMA at different test conditions was demonstrated by incorporating it into a finite element scheme. Constitutive model was reasonably accurate to capture observed temperature-displacement-force history in experimental study. Damage evolution under different testing conditions was studied in terms of irreversible thermal and mechanical entropy production.     

Structural, optical, and electrical properties of AZO films by tilted angle sputtering method

We investigate the structural, optical, and electrical properties of aluminum-doped zinc oxide (AZO) films on Si substrate by a tilted angle sputtering method. The substrate holder is tilted by varying the angle from θ_sh = 0° to θ_sh = 80° during the sputtering process. As the tilted angle is increased, the deposition rate is increased due to the decreased distance between the substrate and the target. Without substrate rotation, the deposited AZO films exhibit apparently the inclined nanocolumnar structures, depending on the tilted angle. The refractive index, which is related to the porosity within films, is reduced for the larger inclined nanocolumnar structure while the extinction coefficient remains almost the same in the visible wavelength range. The inclination of nanocolumns disappears when the substrate is rotated. On glass substrate, the electrical properties as well as optical transmittance of AZO films are also dependant on the tilted angle.     

Synthesis, structure and impedance spectroscopic analysis of [(Pb x Sr1?x )·OTiO2]–[(2SiO2·B2O3)]–7[BaO]–3[K2O] glass ceramic system doped with La2O3

Various compositions of glasses were prepared by melt quenching method in the glass ceramic 64[(Pb _x Sr_1?x )OTiO₂]–25[(2SiO₂·B₂O₃)]–7[BaO]–3[K₂O]–1[La₂O₃] (0.5?≤?x?≤?1) system doped with La₂O₃. Dielectric constant, ε_r versus temperature, T, plots revealed diffused peaks, while dielectric loss, D, versus T plots showed shifting in the peaks toward the higher temperature side similar to relaxor-like ceramics. Curie temperature was found to change systematically with changing the concentration of SrO. Impedance spectroscopy results indicated the contributions of polarization process relaxing in low frequency region attributed to polarizations at the crystal to glass interface and the glassy region.     

An advanced model for initiation and propagation of damage under fatigue loading – part II: Matrix cracking validation cases

A series of tests were conducted to act as validation cases for the numerical model developed in part I of this paper to predict the initiation and propagation of damage in composite materials. The onset of matrix cracking in [0₂/θ₄]_s specimens under tension–tension fatigue loading was studied using acoustic emission (AE) and dye-penetrant enhanced X-rays. The number of cracks identified by significant AE hits correlated well with the number of cracks identified by X-rays. Finite Element simulations of the [0₂/θ₄]_s specimens using the model from part I for cohesive interface elements fatigue loading showed a good correlation with the experimental results.     

Residual stresses and Raman shift relation in anatase TiO2 thin film

Anatase TiO₂ film (100-1000 nm thick) grown on glass, sapphire (0001), and Si (100) substrates by pulsed dc-magnetron reactive sputtering were evaluated for stress and strain analysis using Raman spectroscopy and curvature measurement techniques. The X-ray analysis revealed that films prepared for this study were purely anatase, and the measurements indicate that the film exhibit that (101) is the preferred growth orientation of the crystallites, especially for the film thicker than 100 nm. Curvature measurements and Raman spectroscopy, with 514.5 nm excitation wavelength, phonon line shift were used for stress analysis. A comparison between Raman lineshapes and peak shifts yields information on the strain distribution as a function of film thickness. The measurements of residual stresses for crystalline anatase TiO₂ thin film showed that all thin film were under compressive stress. A correlation between Raman shifts and the measured stress from the curvature measurements was established. The behavior of the anatase film on three different substrates shows that the strain in film on glass has a higher value compared to the strain on sapphire and on silicon substrates. The dominant 144 cm^− 1E_g mode in anatase TiO₂ clearly shifts to a higher value by 0.45-5.7 cm^− 1 depending on the type of substrate and film thickness. The measurement of the full width at half maximum values of 0.59-0.80 (2θ°) for the anatase (101) peaks revealed that these values are greater than anatase powder 0.119 (2θ°) and this exhibits strong crystal anisotropy with thermal expansion.