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The expansion of the oil palm industry has affected the environment and the poor handling of oil palm waste has greatly endangered the habitat surrounds it. The oil palm natural fibre waste can be put to good use and used as a sound absorber for its amazing acoustic properties. At the same time, the demand for natural fibre sound-absorbing panels is increasing due to its low-cost fabrication and its healthier than synthetic fibre. This research has studied the acoustic properties of mixing Empty Fruit Bunch (EFB) and Oil Palm Frond (OPF) in a thickness of 12 mm, 14 mm, 16 mm, and 18 mm. The fibreboard has been fabricated at a density of 120 kg/m3. The Sound Absorption Coefficient, SAC, and morphologies of all the samples were examined using the Impedance Tube Method (ITM) and Scanning Electron Microscope, (SEM). The sample’s SAC value increased with thickness. It is noteworthy that this combination percentage of natural fibres of EFB and OPF show good acoustic performance where the SAC values above 0.8 at wide frequency 3000 - 6400 Hz. Sample thickness 14 mm, 18 mm achieved unity (1.0) at frequency 4000 - 5500 Hz. In addition, all the samples were found to exceed 90 % of the absorption rate in the range of 4500 - 6400 Hz. The morphology content of EFB and OPF helps in enhancing the absorption rate.

Silicon electrodes with the columnar macroporous structure were investigated to determine the effect of variations in the columnar pore morphology on lithiation and energy storage capacity in Li-ion cells. Several variants of macroporous Si columnar electrodes were electrochemically cycled against the Li reference electrode. The changes in macro-pore size and Si wall thickness of the columnar architecture greatly affected the cyclic Li storage and discharge capacities. A strong correlation of the Li-storage capacity with the ratio of Si wall thickness to pore diameter is found to exist. Specifically, one columnar Si electrode with an optimum macroporous structure exhibited a very high reversible specific capacity of ~1250 mAh/g (total capacity 1.2 mAh/cm2) for over 200 cycles. Electron microscopy revealed that the high reversible Li-storage capacity is due to the macropores accommodating the change in volume of lithiation and providing nearly complete reconstruction of Si walls upon delithiation. The present observations can lead to practical, high-capacity, and damage-resistant Si electrodes for Li-ion batteries.

A rigorous analysis of yield strength of pure iron over a wide grain size scale, using an extensive compilation of experimental data, indicates that the common Hall–Petch relationship is not obeyed with large deviations at the extremes of grain size. The author proposes here a phenomenological exponential function to represent the grain size effect on strength over multiple length scales. It is shown that the exponential function describes the grain size dependence of strength remarkably well, on the basis of a large set of experimental data for pure Fe. A nonlinear regression analysis indicated that the function provided a very high degree of correlation of data. The validity of the function is also supported by its conformation to physical boundary conditions at the extremes of grain size, that is, by asymptotically reaching the limiting stress for dislocation nucleation at infinitesimal grain size, and, the strength of single crystal at infinite grain size. The exponential form is a significant improvement over the Hall–Petch relationship and may be used as a guide to develop a reliable theory of grain size strengthening of iron.

A new approach is demonstrated here for the correlation of fatigue crack growth (FCG) data, generated using compact tension (CT) specimens, for various mean stress levels or stress ratios (R) of testing. The approach uses the change in the cyclic strain energy of the net-section as a parameter to correlate fatigue crack growth rates. The derivation of the change in net-section strain energy, for the CT specimen, is demonstrated here on the basis of energy principles of solid mechanics. The total change in net-section strain energy is determined as the sum of the changes in the tension and the bending strain energy components, arising from the tensile stress and the bending moment acting on the net-section of the CT specimen. This leads to a compact physical equation for the change in cyclic strain energy, which is expressed as a direct function of applied cyclic load level, crack length, stress ratio, and specimen dimensions. Extensive experimental evaluations, using the data for steels, copper and titanium alloys, were conducted and are presented here to show that the change in net-section strain energy can successfully correlate the fatigue crack growth for various stress ratios or mean stress levels. The present work provides a new direction for physically-based characterizations of fatigue crack growth data generated using CT specimens.

A CALPHAD-guided alloy design strategy is used here to design and process fully dense titanium boride (TiB) ceramic alloys containing a ductile phase for toughening. This involved the construction of high temperature phase fields of the Ti-B-Fe-Mo quaternary alloy system using the CALPAHD approach. To design the compositions, ternary phase diagrams of Ti-B-Fe, Ti-B-Mo, and Fe-Mo-B systems were first constructed using the thermodynamic databases that were verified to predict well the binary phase diagrams of components. Using this as a basis, the pseudo-ternary diagrams of the Ti-B-Fe-Mo system were constructed to map the high temperature phase fields over a wide range of composition. This made it possible to identify relatively lower reaction sintering temperatures for various alloy compositions. Two compositions of TiB ceramic alloys with the ductile beta-phase (both having ∼85% TiB and ∼15% β-Ti phase), were considered for the demonstration of the present approach. Based on the pseudo-ternary phase fields, these two compositions could be processed using electric-field-activated sintering (EFAS), in a relatively short time, at their respective liquid-phase-forming temperatures. The processing temperature was as low as 1423 K for a Fe/Mo-rich ceramic alloy composition, but the formation of brittle intermetallic phase FeTi here was found to be detrimental to mechanical properties. The second TiB ceramic alloy composition, which was Fe/Mo-lean, could be processed at 1623 K. This composition is shown here to possess a very good combination of high flexural strength (∼850 MPa) and high fracture toughness (∼7.7 MPa√m), making it attractive for potential applications. The identification of the liquid phase reaction sintering regions in the ternary phase diagrams, and the eventual finding of one composition giving a relatively high strength and toughness, demonstrate that this is an effective approach for alloy design. The microstructural factors that control the strength and toughness have been identified and the ways to increase these properties further, in this class of materials, are suggested.

Rapid sintering at the beta-transus temperature (1010 °C) of a titanium alloy (Ti-6Al-4V), by exploiting the accelerated self-diffusion, is shown here to yield a high density (~98%), and a refined microstructure, relative to that obtained at a higher sintering temperature in powder-metallurgical processing. While saving energy and cost, this approach is shown to produce a nearly equivalent tensile stress-strain behavior, and, strikingly, a significant improvement in overall S N (stress-life) fatigue resistance, relative to that of the alloys sintered at a relatively higher temperature. This new approach may be broadly applicable to all titanium alloys exhibiting alpha-to-beta phase transformation.

The effect of a change in iron and boron contents on the Spark Plasma Sintering behaviour in the Ti-B-Fe alloys has been investigated through dilatometric sintering study using various samples having Ti-rich compositions. These samples are adequately chosen to study the sintering behaviour on the addition of boron and iron on the Ti-rich corner. The rate of sintering of Ti-B-Fe alloys was found to increase with an increase in iron content. The sintering enhancement can be attributed to the high diffusivity of iron in α-Ti and β-Ti phases and due to the formation of the intermetallic phase which results in greater overall shrinkage. The shrinkage was found to decrease with increase in boron content due to a greater amount of TiB2 which doesn’t participate in sintering in the observed range.

The major challenge in the mechanics of elastic-plastic fatigue crack growth is to find a physically based driving force parameter to correlate the crack growth rates under different loading conditions. Specifically, a parameter that can provide single-valued correlation of crack growth rates, in stress-controlled and strain-controlled fatigue, is needed. Approaches of the past used either cyclic strain (strain intensity factor) or nonlinear-fracture-mechanics based (cyclic J-integral, ΔJ) parameter, to correlate fatigue crack growth. The validity of these approaches, however, has not been established. Further, the J-integral based approach requires experimental load-deflection curves, recorded after every crack length increment, and geometry-correction factors, which are numerically determined and complicated. In the present work, a physically based approach, based on thecumulative change in the cyclic strain energy of the net-section, is used to develop new parameters that can successfully correlate fatigue crack growth behavior in a variety of loading situations. The driving force parameter, capturing the change in the net-section cyclic strain energy, is determined analytically from elastic-plastic behavior of material and from the relative sizes of cracked and uncracked sections in the crack plane. Load-deflection measurements, geometric correction factors, or numerical methods are not needed in the present approach. Remarkably, excellent correlations of fatigue crack growth, in a variety of specimen geometries and for various stress/strain levels, have been found in both stress- or strain-controlled fatigue conditions. This work, extending the author’s earlier works for elastic fatigue crack growth, validates that the change in net-section strain energy is a fundamental quantity in the mechanics of fatigue crack growth.

The design and the processing of a new class of titanium boride (TiB)-based bulk cermets containing a metallic phase (β-Ti phase) for toughening is presented. The general approach is rapid reaction and densification, using starting powders of Ti, TiB2, Fe, and Mo, by electric-field-activated sintering. The cermets consist of two-phase microstructures in which the boride phase formed as a networked structure of TiB whiskers that were created in situ upon the reaction between the powders. Hardness, flexural strength, and fracture toughness measurements of these materials revealed that they possess an interesting set of properties up to: hardness values of 1090 kg/mm2, flexural strength values of 953 MPa, and fracture toughness values of 18 MPa m1/2. A remarkable finding is that although the metallic phase fractured by microscopic cleavage, the cermets showed good fracture toughness values. The present study not only illustrates the process details and microstructure leading to these properties but also provides a broad powder metallurgical approach to design and synthesize cermets that may yield further improved properties.

The continuous miniaturization of microelectronic devices places an ever increasing demand on energy-storage capacities of on-chip Li-ion batteries. The search for positive electrodes for such batteries inevitably leads to Si because of its very high mass specific capacity (∼4200 mAh/g for Li4.4Si). Although Si thin films and nanowires can provide very high specific capacities, their storage capacities (measured as coulombs per unit area) are, however, very limited. We report here a new Si electrode architecture, having columnar micropores, which provides a very high mass specific Li-storage capacity (∼1212 mAh/g), and the highest total Li-storage capacity (∼1.21 mAh/cm2) relative to other Si electrodes. These capacities are sustainable for over 200 cycles. It is shown that columnar microporous Si architecture can store a greater amount of charge (∼250%) than solid-Si, due to the increased surface area provided by the columnar pores. Further, the most exciting finding of this study is that the pore walls ...

Since the last decade, the collective intelligent behavior of groups of animals, birds or insects have attracted the attention of researchers. Swarm intelligence is the branch of artificial intelligence that deals with the implementation of intelligent systems by taking inspiration from the collective behavior of social insects and other societies of animals. Many meta-heuristic algorithms based on aggregative conduct of swarms through complex interactions with no supervision have been used to solve complex optimization problems. Data clustering organizes data into groups called clusters, such that each cluster has similar data. It also produces clusters that could be disjoint. Accuracy and efficiency are the important measures in data clustering. Several recent studies describe bio-inspired systems as information processing systems capable of some cognitive ability. However, existing popular bio-inspired algorithms for data clustering ignored good balance between exploration and exploitation for producing better clustering results. In this article, we propose a bio-inspired algorithm, namely social spider optimization (SSO), for clustering that maintains a good balance between exploration and exploitation using female and male spiders, respectively. We compare results of the proposed algorithm SSO with K means and other nature-inspired algorithms such as particle swarm optimization (PSO), ant colony optimization (ACO) and improved bee colony optimization (IBCO). We find it to be more robust as it produces better clustering results. Although SSO solves the problem of getting stuck in the local optimum, it needs to be modified for locating the best solution in the proximity of the generated global solution. Hence, we hybridize SSO with K means, which produces good results in local searches. We compare proposed hybrid algorithms SSO+K means (SSOKC), integrated SSOKC (ISSOKC), and interleaved SSOKC (ILSSOKC) with K means+PSO (KPSO), K means+genetic algorithm (KGA), K means+artificial bee colony (KABC) and interleaved K means+IBCO (IKIBCO) and find better clustering results. We use sum of intra-cluster distances (SICD), average cosine similarity, accuracy and inter-cluster distance to measure and validate the performance and efficiency of the proposed clustering techniques.

An understanding of Lithium (Li) spatial distribution within the electrodes of a Li-ion cell, during charge and discharge cycles, is essential to optimize the electrode parameters for increased performance under cycling. In this work, it is demonstrated that the spatial distribution of Li within Vanadium Pentoxide (V2O5) electrodes of a small coin cell can be imaged by neutron computed tomography. The neutron attenuation data has been used to construct the three-dimensional Li spatial images. Specifically, it is shown that there is sufficient neutron imaging contrast between lithiated and delithiated regions of V2O5 electrode making it possible to map Li distributions even in small electrodes with thicknesses

A physically based universal functional is shown to uniquely correlate the fatigue crack growth data of metals in high-cycle fatigue, generated at various stress ratios, extremely well. The functional is proposed based on the hypothesis that at any stage during fatigue, the remaining fraction of fatigue cycles required for final fracture is proportional to the fractional uncracked section size that remains to be severed by the fatigue crack. The basis for such a hypothesis is that the microscopic mechanism of fracture, such as striation formation in fatigue, is largely independent of the details (e.g. mean stress or stress ratio) of high-cycle fatigue loading. Experimentally, the functional is found to be a simple power law relating the fractional remaining uncracked section (net-section) size to the fractional (normalization by total fatigue life) remaining fatigue life. It is also shown that the surrogate form of the functional provides excellent descriptions of the raw crack-length-versus-cycles data generated in high-cycle fatigue experiments. The functional seems to provide a new physical basis, which is different from fracture mechanics, to characterize the effect of stress ratio on fatigue crack growth in materials.

The physical meaning of the finite-width-correction factors (FWCF), which commonly appear in stress intensity factor solutions of fracture mechanics, is mysterious. The present work is an attempt to resolve this mystery. Specifically, it is shown that for the middle-crack-tension (M(T)) specimen and for the embedded-circular-crack in a specimen of round cross-section, the FWCF factor is related to the average net-section stress for a given crack size. An increase in K at the crack tip means an increase in the average net-section stress ahead of the crack, in addition to the increase in the level of normal stress in the near-tip (or singularity-dominated) zone of fracture mechanics. It is also shown that this increase in net-section stress can be determined, in a straightforward manner, using a simple approach based on strength of materials (SOM). The agreement between the net-section stress determined from the strength of materials approach and that from fracture mechanics is surprisingly good. This connection between the finite-width-correction factor and the net-section stress has not been demonstrated before, and, hence it provides a new point of view to analyze fracture mechanics problems. More importantly, the connection validates the correlation of fatigue crack growth on the basis of the change in the net-section cyclic strain energy, which has recently been demonstrated by the author elsewhere.

A critical review and assessment of 3D columnar Si electrode architectures, as negative electrodes for Li-ion cells, has been undertaken to provide insight on the structure parameters that enable high specific and total Li-storage capacities and high cycling performance. The selected set represents a sufficiently wide variety of columnar architectures, covering most of the possible routes of fabrication, including etching, patterning, photolithography and micromachining. The outcome of this evaluation identifies the structural factors that determine the best performing 3D electrode architecture. Specifically, electrodes with a high mass loading have been shown to correlate very well with high total capacities for Li-storage. Thus, the preferred 3D electrode structures are identified as those with columns of Si with an optimum porosity giving high enough mass loading, but with a balanced column depth and spacing providing effective volume accommodation during cell cycling. The review also provides details of experimental validations of the optimum electrode architecture, which effectively accommodates the volume change, and enables cycling for a larger number of cycles.

A simple universal functional is shown here to correlate fatigue crack growth data of a wide variety of materials (metals, polymers), test conditions (high-cycle and low-cycle fatigue), and specimen configurations (tension and bending). The proposed functional is a power law that relates the normalized remaining ligament size to the normalized remaining fatigue life in a cyclically loaded specimen. The functional evolved from the idea that at any stage during fatigue, the remaining fraction of cycles required to fracture the specimen, completely, depends on the remaining fraction of section to be broken by the fatigue crack before that final fracture. More importantly, the surrogate form of the functional is shown to provide excellent descriptions of the raw crack-length-versus-cycles data in fatigue crack growth. The functional provides a new physical basis to characterize fatigue crack growth in materials and is promising for extensions in to more complicated fatigue loading conditions.

In this work, fatigue failure mode, crack initiation, and early stage crack growth mechanism in Ti-6Al-4V alloys with different levels of microstructural inhomogeneity were investigated. The quantitative correlations between fatigue life, crack origin size, and early stage short crack growth, were analyzed and discussed. The interior early stage short crack growth rate was determined to be 10−12–10−10 m/cycle. The high and very high cycle fatigue lives predicted based on crack initiation site size and early stage short crack growth rate agree well with real fatigue data.

Powder metallurgy (PM) of titanium is a potentially cost-effective alternative to conventional wrought titanium. This article examines both traditional and emerging technologies, including the prod...

The present work is focused on optimization of Fe-Mo content, which is essential for transient liquid phase formation and densification, during in-situ reaction sintering of nanostructured titanium boride (TiB) in the bulk form. The principle objective is to develop a systematic understanding of how the Fe-Mo additions affect the densification, microstructure, and hardness of the TiB nano-ceramic. Various TiB ceramic compositions, with varying Fe-Mo content and retaining a high-volume fraction of TiB in the final microstructure, were made by the electric field activated sintering (EFAS) technique. An increase in Fe-Mo content is found to decrease the beginning point of densification temperature/time during the consolidation process through transient liquid phase formation. It is shown that at the optimum level of Fe-Mo, which is around 1.5 wt.%, the density and hardness reach maximum levels with a least amount of spatial segregation of Fe within the ceramic. Interestingly, it has been found that Mo is uniformly incorporated within the orthorhombic lattice of the boride, while Fe is largely segregated to β-Ti phase. At the optimal Fe-Mo content (1.5 wt.%), a relative density of 99.7% and a Vickers hardness of 2050±40 kg/mm2 were achieved. From microstructural and X-ray diffraction analyses, it is found that a high proportion of TiB (>99 Vol.%), with a least amount of metallic ductile phase, is formed in this composition. This article is protected by copyright. All rights reserved.

An unsolved problem in the mechanics of fatigue crack growth is why mean stress or stress ratio in a fatigue cycle has a profound effect on growth rate when compared in terms of stress intensity factor range (ΔK). Specifically, there has not been any fracture-mechanically-consistent theory to explain the effects of mean stress on fatigue crack growth. In this work, a new and generalized driving force parameter for fatigue crack growth, which effectively incorporates the mean stress or stress ratio effect, is developed from energy principles of solid mechanics. A successful explanation of the effect of mean stress on the growth rate is provided. The driving force is the accumulated change in net-section strain energy , which develops as a function of increasing crack length and decreasing net-section size in fatigue. A generalized mechanics analysis, showing how to account for the stress amplitude and the maximum stress of a fatigue cycle in the change in net-section strain energy, is presented. Equivalently, the new crack growth parameter can also be interpreted as the cumulative work done by cyclic loading at the crack length at which the crack growth data is determined. Several experimental data, including some historically significant fatigue crack growth data, generated on aluminum, steel and titanium alloys, are used to demonstrate the success of the correlation. As a further validation of the proposed concept, it is shown that the empirical Walker parameter (ΔK 0.5 Kmax 0.5 ), which had some success in correlating stress ratio effect, is in fact related to the change in net-section strain energy.

A new approach to correlate fatigue crack growth data of metals on the basis of the change in net-section strain energy is presented. Extensive experimental data, including some historically significant fatigue crack growth data, generated using center-cracked (CCT) and single-edge notched (SENT) tension specimens, are used to demonstrate this correlation. It is shown that this correlation, quite remarkably, is as strong as that based on the stress intensity factor range (ΔK) in fracture mechanics. The reason for this surprising similarity is explored using the analysis of the net-section stress increase in fracture mechanics specimens. It is found that the actual role of the finite-width-correction factor in fracture mechanics is to create the stress amplification effect on the finite specimen, having a given crack length, to produce the same K as that of an infinite specimen. The present work demonstrates that the phenomenon of fatigue crack growth can be easily understood on the basis of the accumulated change in net-section strain energy which directly relates to the accumulated work done at the loading ends, which determines the rate of fatigue crack growth. It is a simpler and a physical approach for the accurate description of fatigue crack growth behavior of metals. The approach simultaneously validates the use of fracture mechanics parameters (∆K) for fatigue crack growth, by providing the insight that the physical meaning of stress intensity factor is embedded in the change in the net-section strain energy.

It is demonstrated that high density powder metallurgy (PM) Ti-6Al-4V alloy, with a finer prior-β grain size, can be achieved by vacuum sintering of TiH2 compacts at the β-transus (1010 °C) temperature, taking advantage of the accelerated self-diffusion. The subsequent refinement of the coarse lamellar microstructure by hydrogenation-dehydrogenation treatment produces a high tensile strength (~ 1130 MPa) and ductile (~ 10%) alloy. The superior tensile strength and ductility result from the nanoscale Widmanstatten structure and the finer prior-β grain size, respectively, created by the two treatments. The results show a promising pathway to make high strength and ductile PM titanium alloys.

A comprehensive assessment of tensile properties of powder metallurgical (PM) processed Ti-6Al-4V alloy, through the mapping of strength–ductility property domains, is performed in this review. Tensile property data of PM Ti-6Al-4V alloys made from blended element (BE) and pre-alloyed powders including that additive manufactured (AM) from powders, as well as that made using titanium hydride powders, have been mapped in the form of strength–ductility domains. Based on this, porosity and microstructure have been identified as the dominant variables controlling both the strength and the tensile ductility of the final consolidated materials. The major finding is that tensile ductility of the PM titanium is most sensitive to the presence of pores. The significance of extreme-sized pores or defects in inducing large variations in ductility is emphasized. The tensile strength, however, has been found to depend only weakly on the porosity. The effect of microstructure on properties is masked by the variations in porosity and to some extent by the oxygen level. It is shown that any meaningful comparison of the microstructure can only be made under a constant porosity or density level. The beneficial effect of a refined microstructure is also brought out by logically organizing the data in terms of microstructure groups. The advantages of new processes, using titanium hydride powder to produce PM titanium alloys, in simultaneously increasing strength and ductility, are also highlighted. The tensile properties of AM Ti-6Al-4V alloys are also brought to light, in comparison with the other PM and wrought alloys, through the strength–ductility maps.

A physical model and constitutive equations for metal fatigue, to characterize completely the S-N fatigue behavior of structural materials, have been developed on the basis of the macroscopic behavior of fatigue crack growth. The macroscopic behavior that forms the basis is that at any time during fatigue the fractional remaining fatigue life is proportional to the fractional remaining uncracked section size. A crack growth functional has been shown to describe this behavior accurately, and universally, for a wide range of materials, test conditions, and specimen geometries. By integrating this functional and with the introduction of physical boundary conditions, a surprisingly compact constitutive equation for the stress-life (S-N) fatigue behavior is derived. The constitutive equation represents accurately the sigmoidal shape of S-N high cycle fatigue behavior of single crystals and polycrystals, including the asymptotic approach of the fatigue data toward a physical endurance limit stress. Metallurgical fatigue strengthening effects due to pre-strain, alloying and grain refinement have also been shown to be accurately predictable. The equation is then expanded to include the mean-stress effects in various forms, which facilitated the complete prediction of stress-life behavior and fatigue limit, for any mean stress, solely from the S-N behavior of fully reversed fatigue data. A very interesting consequence of this is a new, master constitutive equation capturing the mean stress effect on fatigue behavior. Extensive experimental data, generated at various mean stresses, have been used to validate the present approach.

This research demonstrates a novel concept of surface hardening, termed “cyclic-phase-change-diffusion (CPCD),” where cyclic phase transitions were induced at the surface by thermal cycling across the phase transition temperature along with diffusion of surface hardening atoms. Specifically, boron was diffused through the surface of titanium during thermal cycling across the α-β phase transition temperature. The CPCD method is shown to result in an unusually deeper (~ 125 μm) and richer boride layer, on titanium, compared that obtained by isothermal diffusion either at the equivalent temperature or at a higher temperature. This concept is quite promising for superior surface hardening of titanium and its alloys.

This study focuses on the extraction of cellulose nano-whiskers (CNWs) from the leaves of Adansonia kilima (AK), usually known as African baobab, using a combination of a microwave-assisted alkali (KOH) pre-treatment with subsequent bleaching process prior to ultra-sonication. Ultra-sonication was carried out using the ionic liquid (IL) 1-butyl-3-methylimidazolium hydrogen sulfate (Bmim-HSO4). Process parameters for ultra-sonication were optimized using a two-level factorial Box&ndash, Behnken design (BBD). Process variables such as ultra-sonication power (x1), hydrolysing time (x2) and temperature (x3) were varied. Responses selected were percentage crystallinity index, CrI% (y1) and yield% (y1) for the finally procured CNWs sample. Regression analysis was carried out to develop quadratic model to analyze the effect of process variables on IL-assisted ultra-sonication process. Analysis of variance (ANOVA) showed that ultra-sonication power was the most influential aspect for hydrolyzing the amorphous segments of crude cellulose extracted from baobab leaves. A relative study of the physio-chemical properties of the starting lignocellulosic substrate (AK), KOH pre-treated, bleached and IL-assisted ultra-sonicated CNWs was conducted. The synthesized samples were characterized using Fourier transform infrared spectroscopy, Scanning electron microscopy, atomic force microscopy, high resolution transmission electron microscopy, X-ray diffraction and thermo-gravimetric and zeta potential analysis. Under optimum condition, the extracted CNWs showed an average width of 15&ndash, 20 nm, with high crystallinity index of 86.46%. This research provides an insight about the delignification of Adansonia kilima (AK) leaves and its effective conversion to CNWs having high crystallinity.

Rapid in situ synthesis of bulk nanostructured titanium boride (TiB) ceramic, at the lowest possible processing temperature, is demonstrated. Using electric-field-activated-sintering (EFAS), nanoscale TiB whiskers were formed and densified uniformly throughout the volume, from a mixture of micron-sized Ti, TiB 2 and FeMo powders, at 1100 °C in 30 min and at a relatively low pressure. Microstructure and X-ray diffraction (XRD) analysis, revealing the formation of TiB whiskers in this rapid processing condition, are presented. The formation of a transitional quaternary liquid phase, facilitated by localized joule heating at particle contacts, are hypothesized as contributors to rapid and low-temperature synthesis.

A phenomenological constitutive equation for the stress–life (S–N) fatigue behavior of metal single crystals is presented and is validated on the basis of physical definition of fatigue endurance limit. The constitutive equation is developed here on the basis of probabilistic arguments for fatigue fracture in cyclic loading. The physical endurance limit for fatigue is taken as the stress amplitude corresponding to the critical resolved shear stress for dislocation slip initiation in ductile single crystals. It is shown that the constitutive equation is surprisingly compact and very flexible to accurately describe a wide range of S–N behaviors, as found in fatigue of nickel-based superalloy single crystals as well as in Fe and Zn single crystals. The S–N constitutive equation is also expanded by the superposition of the mean stress effect and the cyclic effect in fatigue. A remarkable outcome of this is a master S–N fatigue equation that yields S–N curves for any mean stress, on the basis of the S–N parameters for fully reversed fatigue behavior. The application of the presented equations to characterize the S–N behavior of polycrystalline materials is quite promising.

In fatigue crack growth experiments of miniature specimens of Ti-6Al-4V alloy, it is shown that the stress intensity factor range (∆K) cannot uniquely correlate the crack growth rates based on the standard stress intensity factor solution, but can only on the basis of the solution for uniformly displaced ends. It also is shown that, remarkably, a similar and strong correlation exists between the change in the net section strain energy amplitude and the rate of fatigue crack growth. The proposed approach is direct and simpler and it throws a new light on the nature of driving force for fatigue crack growth in structural materials.

This work demonstrates that a continuum-based characterization of mechanical fatigue fracture of polymers, in the absence of thermal effects, is possible on the basis of macroscopic crack growth mechanism. The macroscopic mechanism is that the fractional remaining fatigue life of a given polymer specimen is uniquely related to the fractional size of the remaining uncracked section, which includes the intact craze length, anytime during fatigue. A crack growth functional is proposed and is the used to represent the cyclic fatigue crack advance due to the increasing net-section stress amplitude in fatigue. A crack growth equation, which is consistent with Frost, Dugdale and Weibull's observations of macroscopic crack growth mechanics, is proposed as a base equation. A compact constitutive equation for the stress-life (S N) fatigue behavior of polymers is then derived. The constitutive equation accurately describes the mechanical S N fatigue behavior of a large number of polymers under test conditions in which the thermal effects were absent. The effect of temperature is rationalized on the basis of beta relaxation, glass transition and the variation of strength with temperature, depending on the polymer. The constitutive equation is then expanded to create a master equation to include the mean-stress effects, which allowed the prediction of stress-life behavior and endurance limit for any mean stress solely from the S N behavior of fully reversed fatigue data. It is demonstrated that the present the S N constitutive equations can quantitatively and accurately describe the polymer fatigue phenomenon.

Tensile properties of Ti-6Al-4V titanium alloy, sintered by a new process (sintering, phase transformation, and dehydrogenation of titanium hydride compacts, termed HSPT process), were investigated to determine how the sintering pores influence the tensile strength and ductility. It was found that the ductility in the sintered alloy is severely affected by the size of the largest pore, referred here as extreme-sized pore, even when the average volume fraction of porosity is nearly constant between a large number of samples. It is shown that the rapid decrease in ductility, with an increase in the extreme pore size, is caused by strain localization around the extreme-sized pore and early crack initiation. This crack initiation leads to fracture of the plane containing the pore thereby limiting the extent of uniform plastic strain that can be attained before fracture. Interestingly, the strength properties are, however, found to be independent of the size of the extreme-sized pore. The results are explained on the basis of stress concentration and strain localization around the extreme-sized pores. The work also reveals that if the extreme-sized pores are eliminated, PM Ti-6Al-4V alloy with high strength (~1100 MPa) and good ductility (~12 pct), which is easily comparable to a wrought Ti-6Al-4V alloy, can be achieved even at oxygen levels up to 0.4 wt pct.

A comprehensive assessment of fatigue performance of powder metallurgy (PM) Ti-6Al-4V alloy, manufactured using various powder-based processing approaches to-date, is performed in this work. The focus is on PM processes that use either blended element (BE) or pre-alloyed (PA) powder as feedstock. Porosity and the microstructure condition have been found to be the two most dominant material variables that control the fatigue strength. The evaluation reveals that the fatigue performance of PM Ti-6Al-4V, in the as-sintered state, is far lower than that in the wrought condition. This is largely caused by residual porosity, even if it is present in small amounts, or, by the coarse lamellar colony microstructure. The fatigue strength is significantly improved by the closure of pores, and it approaches the levels of wrought Ti-6Al-4V alloys, after hot-isostatic-pressing (HIPing). Further thermo-mechanical and heat treatments lead to additional increases in fatigue strength–in one case, a high fatigue strength level, exceeding that of the mill-annealed condition, was achieved. The work identifies the powder, process and microstructure improvements that are necessary for achieving high fatigue strength in powder metallurgical Ti-6Al-4V alloys in order for them to effectively compete with wrought forms. The present findings, gathered from the traditional titanium powder metallurgy, are also directly applicable to additively manufactured titanium, because of the similarities in pores, defects, and microstructures between the two manufacturing processes.

The high temperature phase fields of a multicomponent titanium alloy system have been determined by the CALPHAD approach to assist in rapid processing of a titanium metal matrix composite by electric-field-assisted reaction sintering. The phase field calculations revealed the existence of a wide composition range (in terms of B, Fe, Mo and Al content) for the flexible synthesis of various β-Ti-TiB composites. After processing, the uniform dispersion of in-situ formed titanium boride (TiB) whiskers, in the ductile beta titanium (β-Ti) matrix, has resulted in a composite with a flexural strength of 1622 MPa and a fracture toughness of 23 MPa m , which are much greater than the levels achieved before in this class of materials.

Fracture mechanics analysis of a generalized compact tension specimen, on the basis of the mechanics of deformation of the net-section, is shown to provide a simple and a broadly useful expression for stress intensity factor calculations. A single analytical expression is found to be sufficient for the characterization of crack behavior in compact tension, extended compact tension and wedge splitting test specimens without any restriction on the specimen length (or height) and width. The analysis is enabled by the concept of the change in net-section energy, which is determined by summing the changes in strain energies of the net-section of the generalized specimen for tension and bending deformation modes, which result from the introduction of the crack. This is equivalent in concept to the increase in strain energy upon the introduction of the crack, as in the Griffith’s fracture theory. The square-root of the change in net-section strain energy parameter multiplied by the elastic modulus provides an expression that is equivalent to the conventional stress intensity factor expression. The application of the net-section based expression to the standard compact tension, the extended compact tension and the wedge-splitting test specimens shows very good agreements with the crack behaviors as expressed by the stress intensity factor expressions for the respective geometries. The proposed method enables easy analytical determination of stress intensity factors for any asymmetrically-loaded mode-I crack problem.

In this paper, we evaluate a nature inspired algorithm namely Social Spider Optimization (SSO) for data clustering that performs local and global searches in a balanced way. We compare CPU elapsed time of the proposed algorithm SSO with K-means and Particle Swarm Optimization (PSO). Though the convergence speed of K-Means clustering is very high when compared with other clustering algorithms, it has the weakness of getting stuck in the local optima in the solution space. Though SSO solves this problem to an extent, it has to be combined with K-means in order to speed up the convergence. Hence, we combine SSO with K-means that produces good results in local searches. We compare CPU elapsed time of proposed hybrid algorithm SSO + K-means (SSOKC) with K-means + Bat algorithm (KBat), K-means + Firefly algorithm (KFA) and K-means + Flower pollination algorithm (KPA). The study is carried out on real life datasets taken from UCI machine learning repository.

Since the last decade, researchers have been concentrating on high quality clustering methods for the effective analysis of the growing data. Algorithms inspired by nature have become part of a widely used class of computing methods, because of their ability to adjust to variety of conditions. These nature inspired algorithms have been frequently used for solving complex, real-world optimization problems. In recent years, they have emerged as powerful optimization techniques. These algorithms inspired by the cooperative behavior of social animals have the ability to provide better solutions for clustering problems. Social Spider Optimization (SSO) is a population based stochastic optimization algorithm. It has been used to solve many complicated optimization problems. It simulates the behavior of social spiders. In this paper, a new and more effective implementation of SSO (ESSOSC) for solving text document clustering problem is specified by using single cluster implementation for each spider.