An investigation of some matrix protein components critical to the extensible properties of insect cuticle

Extensible abdominal cuticles from both nymphalRhodnius and nymphalTriatoma are very similar in mechanical properties: ultimate tensile strength ∼ 10MNm⁻², stiffness ∼ 100 MNm⁻² and ultimate strain ∼ 15%. The cuticles are also similar in composition, minor differences found do not appear to be sufficient to allow different mechanical properties. Some proteins can be identified, tentatively, as having a contribution to the extensible properties of the cuticles. There appears to be no contribution to the change in extensibility by stress-softening.     

Synthesis and equilibrium studies of titanium vanadate and its use in the removal of some hazardous elements

Titanium vanadate was synthesized and characterized by X-ray diffraction, thermal analysis (TGA and DTA), X-ray fluorescence, and IR spectroscopy. The empirical formula of titanium vanadate is Ti₂V₂O₉·2.5H₂O. Titanium vanadate was tested as sorbent for removing some harmful ions such as Cs, Co, Cu, and Cd. The distribution coefficients (K _d) were determined. They decrease in the order Cs⁺ ? Cu²⁺ > Co²⁺ > Cd²⁺. The distribution coefficients increase with increasing pH and reaction temperature. The thermodynamic functions of sorption (ΔH ⁰, ΔS ⁰, ΔG ⁰) were calculated. Negative values of ΔG ⁰ and positive values of ΔH ⁰ show that the sorption is a spontaneous endothermic reaction.     

A critical appraisal of reliability estimation procedures for high dimensions

A critical appraisal of reliability procedures for high dimensions is presented. Available approximate methods and methods based on Monte Carlo simulation are discussed. It is shown that procedures which perform well in low dimensions may become impractical if the dimension increases considerably or tends to infinity. It is observed that some types of Monte Carlo based simulation procedures in fact are capable of treating high dimensional problems.     

A critical investigation of the use of a mandrel peel method for the determination of adhesive fracture toughness of metal-polymer laminates

The application of peel tests for the measurement of adhesive fracture toughness of metal-polymer laminates is reviewed and the merits of a mandrel peel method are highlighted. The mandrel method enables a direct experimental determination of both adhesive fracture toughness (G_A) and the plastic bending energy (G_P) during peel, whilst other approaches require a complex calculation for G_P. In this method, the peel arm is bent around a circular roller in order to develop a peel crack and an alignment load attempts to ensure that the peel arm conforms to the roller.The conditions for peel arm conformance are thoroughly investigated and the theoretical basis for conformation are established. Experimental investigations involve the study of the roller size (radii in the range 5-20 mm are used), the peel arm thickness (varied from 0.635 to 2.0 mm) and the magnitude of the alignment load. In addition, the plane of fracture is studied since fractures can vary from cohesive to interfacial and this has a profound influence on the value of G_A and on interpretation of results.A test protocol for conducting mandrel peel is developed such that the roller size for peel arm conformance can be established from preliminary fixed arm peel tests.The work is conducted on two epoxy/aluminium alloy laminates suitable for aerospace applications. Comparative results of adhesive fracture toughness from mandrel peel and multi-angle fixed arm peel are made with cohesive fracture toughness from a tapered double cantilever beam test.     

Theoretical modelling of experimental diagnostic procedures employed during pre-dose dosimetry of quartz

The pre-dose technique in thermoluminescence (TL) is used for dating archaeological ceramics and for accident dosimetry. During routine applications of this technique, the sensitisation of the quartz samples is measured as a function of the annealing temperature, yielding the so-called thermal activation characteristic (TAC). The measurement of multiple TACs and the study of the effect of UV-radiation on the TL sensitivity of quartz are important analytical and diagnostic tools. In this paper, it is shown that a modified Zimmerman model for quartz can successfully model the experimental steps undertaken during a measurement of multiple TACs.     

A numerical investigation of porous titanium as orthopedic implant material

Porous titanium is being developed as an alternative orthopedic implant material to alleviate the inherent problems of bulk metallic implants by reducing the stiffness to be comparable to bone stiffness and allowing complete bone ingrowth. However, a porous microstructure is susceptible to local permanent plastic strain and residual stress under cyclic loading which reduces damage tolerance and therefore limits their application as orthopedic implants. The mechanical properties of porous titanium are governed by the microstructural configurations such as pore morphology, porosity, and bone ingrowth. To understand the influence of these features on performance, the macroscopic and microscopic responses of porous Ti are studied using three-dimensional finite element models. The models are generated based on simulated microstructures of experimental materials at porosities of 15%, 32% and 50%. The results show the effect of porosity and bone ingrowth on Young’s modulus, yield stress, and microscopic stress and strain distribution. Importantly, simulations predict that the bone ingrowth reduces the stress and strain localization under cyclic loading so significantly that it counteracts the concentration condition caused by the increased porosity of the structure.     

A preliminary investigation into the microscopic depassivation of passive titanium implant materials in vitro

A sensitive electrochemical technique has been used to examine the passive state of titanium-based materials in Ringer's physiological solution. At ambient temperature, the alloy Ti-6Al-4V shows transient microscopic breakdown of the passive state induced by the presence of chloride ions, and enhanced by increased acidity. These breakdown events involve highly localized depassivation of the passive surface followed by repassivation. Under similar experimental conditions no breakdown of passive titanium was detected.     

A numerical and experimental investigation on the use of J-integral

Finite element analysis was used to determine numerically Rice's J-integral values in centrally notched plates of 4340 steel. These numerical values were compared with corresponding J-integral values using Dugdale model and antiplane strain model with a power law hardening of n = 0.3. J-integral was also computed for a crack extending into its own plastic yield region under constant loading. For increasing level of loading, σ, the rate of increase in J-integral decreases and J-integral remains almost constant at $\text{σ}\text{σ}{}_{\mathrm{YS}}\text{= 1}$ under such crack extension.A limited number of fracture tests were conducted with centrally notched 4340 steel specimens heat treated to yield strength levels of 150,180, 210 and 240 ksi. Fracture data showed that the critical J-integral, calculated and measured, is insensitive to crack tip sharpness for the lower strength 4340 material and thus the J_c fracture criteria appears suited in correlating fracture data.     

A preliminary investigation into preparation and characterisation of a Raney titanium catalyst

A preliminary investigation is carried out into the preparation and characterisation of a Raney-type titanium catalyst. Titanium-40 wt % aluminium powder is used as the precursor alloy and caustic leaching as the preparation method. Leaching in 25 wt % NaOH solutions at both 50°C and 80°C results in preferential removal of aluminium and formation of a highly porous layer containing almost complete titanium. The thickness and the surface roughness of the leached layer increases with leaching time and to a less degree with higher solution temperature. The combined morphological and kinetic measurements suggest that a diffusion barrier built up in the solution/metal interphas plays a key role in the leaching process. Electrochemical tests performed with the leached powder show a significantly reduced overpotential towards cathodic hydrogen evolution reaction, thus a potentially promising catalyst. Further work is needed to establish optimal leaching parameters to increase its electrochemical activity.     

A spectroscopic investigation into the setting and mechanical properties of titanium containing glass polyalkenoate cements

Titanium (Ti) implants are extensively used in a number of biomedical and dental applications. This work introduces Ti into the glass phase of a zinc based glass polyalkenoate cement (GPC) and investigates changes in handling and mechanical properties considering two molecular weight polyacrylic acids (PAA), E9 and E11. Considering the handling properties, the working time (T _w) increased from 50 s_E9, 32 s_E11 (BT 101, Ti-free) to 169 s_E9, 74 s_E11 with TW-Z (highest Ti content), respectively. The setting time (T _s) increased from 76 s_E9, 47 s_E11 (BT 101) to 303 s_E9, 232 s_E11 with TW-Z, respectively. Ti was also found to have a significant increase on both compressive (σ _c) and biaxial flexural strength (σ _f), where σ _c increased from 36 MPa_E9, 56 MPa_E11 (BT 101) to 56 MPa_E9 and 70 MPa_E11 with TW-Z respectfully. σ _f also increased from 11 MPa_E9, 22 MPa_E11 (BT 101) to 22 MPa_E9 and 77 MPa_E11 with TW-Z, respectively. No increase in mechanical properties was evident with respect to maturation. Raman Spectroscopy was employed to investigate changes in glass structure and the setting of the cements with. This revealed increased glass network disruption with increasing TiO₂ content and matured cement setting with TW-Z as compared to the control BT 101. FT-IR was then employed to investigate any additional setting mechanism and changes with time. Spectroscopy determined that Ca²⁺/Sr²⁺PAA complexes are primarily responsible for the setting and mechanical strength with no changes occurring over time.     

Development and implementation of some BEM variants—A critical review

Due to rapid development of boundary element method (BEM), this article explores the evolution of BEM over the past half century. We here summarize the overall development and implementation of several well-known BEM variants that includes collocation BEM, galerkin BEM, dual reciprocity BEM, complex variable BEM and analog equation method. Their theoretical and mathematical backgrounds are carefully described and a generalized Laplace’s equation (and Poisson’s equation) is utilized in demonstrating the different approaches involved. An up-to-date review on characteristics and implementation for each of the five variants is presented and also highlighted their significant contributions in boundary element research. In addition, this article tries to cover whole aspect of interests including efficiency, applicability and accuracy in order to give better understanding of BEM evolution. Comparisons and techniques of improvement for these variants are also discussed.     

Development of high critical current densities in niobium 46.5 wt% titanium

A systematic investigation of the effects of varying the heat treatment time and temperature over a wide range in a series of composites made from high homogeneity Nb 46.5 wt% Ti has been made. The study has been confined to processes involving two or three heat treatments since these are most compatible with industrial scale fabrication. Very high J_c values have been obtained using process variables significantly different from those normally used. In particular, we find that increasing the heat treatment temperature and the final drawing strain are very helpful in raising J_c. The maximum J_c values (at a sensitivity of 10⁻¹⁴ Ωm) of 3680 Amm⁻² (5 T, 4.2 K) and 1560 Amm⁻² (8 T, 4.2 K) were obtained for heat treatments at 420°C and for final drawing strains > 5.     

A first-principles investigation on mechanical and metallic properties of titanium carbides under pressure

The titanium carbides are potential candidates to achieve both high hardness and refractory property. We carried out a structural search for titanium carbides at three pressures of 0 GPa, 30 GPa and 50 GPa. A phase diagram of the Ti-C system at 0 K was obtained by elucidating formation enthalpies as a function of compositions, and their mechanical and metallic properties of titanium carbides were investigated systematically. We also discussed the relation of titanium concentration to the both mechanical and metallic properties of titanium carbides. It has been found that the average valence electron density and tractility improved at higher concentrations of titanium, while the degree of covalent bonding directionality decreased. To this effect, the hardness of titanium carbide decreases as the content of titanium increases. Our results indicated that the titanium content significantly affected the metallic properties of the Ti-C system.     

Ellipsometric investigation of the mechanism of the formation of titanium oxynitride nanolayers

The formation mechanism of insulating titanium oxynitride nanolayers was studied by means of spectroscopic ellipsometry. The parameters of the model for solving the inverse problem of ellipsometry were chosen on the basis of experimental data obtained with the help of high-resolution transmission electron microscopy, atomic force microscopy, UV and X-ray photoemission spectroscopy. The layers were obtained using the plasmachemical nitridation of thin titanium layers on silicon substrate. The features of nanolayer preparation procedure (low temperature and short process time), as well as good masking characteristics (the minimal density of pores and defects, and the perfect smoothness of the surface) allow one to use these layers for chemical and electron passivation and stabilization of the surface of semiconductor nano-objects (quantum dots, quantum wires, nanowhiskers etc.) for electron and photon nanodevices.     

A cost-effective P/M titanium matrix composite for automobile use

The aim of the present study is to obtain a new high-performance titanium matrix composite appropriate for automobile parts using a new low-cost powder metallurgy process. The results can be summarized as follows:

1. A production process was developed for a sintered titanium alloy from cheap, low-purity titanium powder (sponge fines) which in its as-sintered form (without expensive hot isostatic pressing or heat treatment) achieves superior fatigue properties to hot-isostatic-pressed titanium alloy made from expensive high purity hydride-dehydride titanium powder.
2. TiB was found to be a superior reinforcing compound for blended elemental titanium matrix composites than SiC, B₄C, TiAl, TiB₂, TiN and TiC tested previously and it was used in the above low-cost production process to make the new disperse-particle titanium matrix composites.
3. The developed titanium matrix composite allows considerably cheaper production of parts from titanium alloy than by conventional ingot forging methods and was confirmed to be far superior to conventional titatium alloys in tensile strength, fatigue properties, rigidity, heat resistance, and wear resistance.