Strength Of Micro Research Articles

Improved tribological performance and enhanced tensile adhesive strength of micro- to near-nanocrystalline WC-17 wt. %Co coatings sprayed using HVOF

This study investigated the performances of micro- and near-nanocrystalline coatings of WC-17 wt.% Co applied to a steel substrate using the high-velocity oxy-fuel (HVOF) spraying method. The near-nanocrystalline coatings exhibited reduced decarburization, as shown by the XRD and Rietveld refinement analyses. SEM analysis revealed small grain size, low porosity, and uniform surface texture in the near-nanocrystalline coatings. These coatings exhibited superior properties, including a high hardness (∼1298 HV), high tensile adhesive strength (≈9890 PSI), low wear rate (∼0.0011 mm3/m), and minimal wear volume loss (∼0.022 mm3), surpassing microcrystalline coatings. Near-nanocrystalline coatings exhibited 52.17 % less wear volume loss, attributed to factors such as smaller particle size, denser coating structure, reduced porosity, limited decarburization, and the high hardness of near-nanocrystalline coatings. Triboscopic analysis further confirmed their exceptional wear resistance, low wear volume loss, and low coefficient of friction, suggesting that near-nanocrystalline coatings could be effective for protecting substrates in demanding critical conditions, align with the Boeing Standard BSS 7072 requirements, and hold promise as robust surface protection solutions.

Transverse Direction Loading Effect on the Elasticity and Strength of Micro and Nano Silica Oxide Composites

Using three-point bending experiments, the effect of the particle size of SiO2 on the flexural properties of epoxy composites was investigated. Young modulus and flexural strength were studied for different weight percentage of filler (2,4,6,8 and 10) wt%.The size of SiO2 particles varied from micro (100um) to nano (12nm) . Flexural strength and Young modul were found to increase with the filler content, but when the particle size decreased to the nanoscale, the Young module increased. Flexural strength was higher for microcomposites than nanocomposites.

On the application of Weibull statistics for describing strength of micro and nanostructures

Although the Weibull distribution has been used to describe strength data at the micro/nanoscale, its general applicability for micro/nanostructures has yet not been established. Most results are inconclusive due to insufficient data (an unavoidable challenge in micro/nanomechanical testing), and because they do not reveal the characteristics of the representative volume element. Macroscale structures are assumed to contain thousands of elements or more—the mathematical form of the Weibull distribution arises from this assumption. Micro/nanostructures, on the other hand, may contain much fewer elements. Another macroscale assumption is that the stress is far smaller than the strength of the representative element, i.e. the theoretical strength, but the strength of nanostructures approaches this value. The traditional mathematical form of the distribution also precludes calculation of the representative volume from strength data, preventing comparisons to defects or microstructural features that control failure (their size should be similar). Here, it is demonstrated that the Weibull distribution can mathematically describe the probability of failure with <5% error for a structure containing as few as 6 elements, provided the Weibull modulus m > 2. Furthermore, using the exact form of the distribution, without the assumptions that lead to its traditional exponential form, equations are derived that allow the representative volume to be calculated from strength data, provided sufficient specimens and sizes are tested. Data for graphene and polysilicon are analyzed with the newly-derived equations, obtaining representative elements that agree well with the observed defects.

Mechanical Behaviour of Micro and Nano Scaled Silicon Carbide Reinforced Al 6063 Metal Matrix Composite

In this research study Al 6063 is used as the base matrix element, due to less weight, high specific strength, impact strength and good mechanical properties. Further, SiC are reinforced in Al 6063 matrix for enhancing its properties. Stir casting process has been accomplished for fabricating the (Al 6063-SiC) composites. In this experiment two various size of reinforcement particle are utilized, one of them is micro sized and another one is nano sized. Micro sized reinforcement particle has dimensions of (25-40µ), while nano sized particle consists dimensions of 500nm. The weight fraction of the micro and nano sized SiC particle taken in this experiment are in order of 0%, 2%, 4%, 6%, 8%, and 10% respectively. Various mechanical tests such as hardness, tensile tests and impact tests were conducted for determining the effect of micro and nano sized SiC reinforced aluminum matrix composites. The comparative study related with impact strength, hardness and tensile strength of micro and nano sized silicon carbide reinforced with aluminum matrix composites were shown in this work. There is an enhancement of mechanical properties has been observed with enhancement in weight percentage of micro sized silicon carbide, on other hand there is also a decrease in mechanical properties has been found while increasing the weight percentage of nano sized silicon carbide. The main objective of this paper is to enhance the mechanical properties of the Al 6063 metal matrix with reinforcing silicon carbide particle.

In vitro Mass Propagation of Cymbidium aloifolium (L.) Sw.

Cymbidium aloifolium (L.) Sw. is an epiphytic orchid distributed locally in Bangladesh. Natural populations of this orchid are under threat due to its high commercial value in the floriculture industry by over exploitation. Mass propagation provides an alternative means of satisfying the demand. In this study, half strength of MS supplemented with BAP or different combinations with NAA was evaluated for seed germination and early protocorm development of C. aloifolium (L.) Sw. The maximum percentage of seed germination (98) was obtained on modified MS (half strength of micro and macro nutrients and full strength of vitamin) supplemented with 0.5 mg/l BAP and 0.5 mg/l NAA after three weeks of culture. Maximum number of shoots (9.6 shoots per single shoot) were developed from shoot tip explants on half strength of MS supplemented with 1.0 mg/l BAP and 0.5 mg/l NAA. The most effective auxin source promoting root production (3.2 roots per shoot) was 1.0 mg/l IBA in combination with 0.5 mg/l BAP. The seedlings were successfully acclimatized (survival percentage 99) in a nethouse using a rooting medium of crushed sterile brick, cocopit and charcoal (1 : 1 : 1 v/v).&#x0D; Plant Tissue Cult. &amp; Biotech. 29(1): 73-79, 2019 (June)

Response of Al-Based Micro- and Nanocomposites to Rapid Fluctuations in Thermal Environments

The focus of this work is to highlight the relative response of Al-based micro- and nanocomposites in the form of enhancement in flexural strength via induced thermal stresses at high and cryogenic temperatures in ex situ and in situ atmospheres. In this investigation, we have tried to explore the reliability, matrix-reinforcement interaction and microstructural integrity of these materials in their service period by designing appropriate heat treatment regimes. Al-Al2O3 micro- and nanocomposites had been fabricated by powder processing method. The micro- and nanocomposites were subjected to down-thermal shock (from positive to negative temperature) and up-thermal shock (from negative to positive temperature) with varying thermal gradients. For isothermal conditioning, the composites were exposed to + 80 and − 80 °C for 1 h separately. High-temperature three-point flexural tests were performed at 100 and 250 °C on the composites. All the composites subjected to thermal shock and isothermal conditioning was tested in three-point flexural mode post-treatments. Al-1 vol.% Al2O3 nanocomposite’s flexural strength improved to 118 MPa post-thermal shock treatment of gradient of 160 °C. The Al-5 and 10 vol.% Al2O3 microcomposites possessed flexural strength of 200 and 99.8 MPa after thermal shock treatment of gradient of 160 and 80 °C, respectively. The observed improvement in flexural strength of micro- and nanocomposites post-thermal excursions were compared and have been discussed with the support of fractography. The microcomposites showed a higher positive scale of response to the thermal excursions as compared to that of the nanocomposites.

Optimizing Compressive Strength of Micro- and Nano-silica Concrete by Statistical Method

In recent years, the use of nano-particles to improve the properties of concrete has created a new perspective on concrete technology. Studies in this field indicate improved concrete properties and higher strength by adding nano and micro silica particles to concrete mixes. In this regard, 12 mixing designs with different amounts of these admixtures with three types of cement strength classes (525,425,325) and 36 cubic samples (10 × 10 × 10) were designed and tested to measure compressive strength, of which we have only used 6 mixing plans in this research. The purpose of this research is to present a new method for concrete mix design by optimizing principles. Therefore, in this paper, the Taguchi statistical methods and the factorial design of the optimal mixing plan for this type of concrete are used to reduce the number of experiments to predict the optimal composition of the materials. The results obtained from the MINITAB software show that the effect of combined micro-silica and nano-silica on the compressive strength is in one direction and the effect of these two factors is more than cement strength grade of the cement and also the optimal value for micro-silica and nano-silica are estimated to have an optimum amount of micro-silica and nano-silica of 95 and 38 grams, respectively.

Regulation of early growth and antioxidant defense mechanism of sweet basil seedlings in response to nutrition

Basil cultivars are among most used crops worldwide, but high level of morpho-physiological variations is mainly due to the cultivation characteristics. The present study aimed to investigate the physiological changes and the accumulation of secondary metabolites as a response to prolonged nutrient deprivation in shoots and roots of sweet basil (Ocimum basilicum L. var. minimum). Sweet basil seedlings were grown in media with quarter, half and full strength of micro and macronutrients under different levels of KNO3 alone or in combination with different levels of NH4NO3. Evaluated parameters included characteristics of germination, development of leaves, content of photosynthetic pigments and responses of different parameters related to oxidative stress. While the early growth is influenced mainly due to NH4NO3 presence, all the levels of nutrient supply were found to trigger and maintain the antioxidant defence system of sweet basil seedlings. With the variations among seedling parts, the ammonium nutrition was notably enhanced levels of activity of SOD, CAT, A-POX, G-POX and P-POX, but had no effect on total antioxidant activity and total phenolic content, including flavonoids, which is mainly accumulated in nutrient deprived roots. In addition, phenylalanine ammonia-lyase activity was analysed and potential pathways of secondary metabolites synthesis were discussed. The enzymatic and non-enzymatic system in O. basilicum var. minimum seedlings was capable to reverse the stress conditions during growth under nutrient deprivation.

Effect of surface energy upon size-dependent yield strength of single-crystalline hollow micro- and nanopillars

The physical nature of the size-dependent yield strength of micro- and nanopillars is still an open issue, where the surface energy may be one factor that influences the size effect of these pillars, especially for hollow pillars. In this study, the influence of the surface energy and surface elasticity upon the size-dependent yield strength of single-crystalline hollow micro- and nanopillars is considered quantitatively. An analytical expression of the size-dependent yield strength is established that considers the surface energy and the inner defects by the principle of minimum potential energy. The predicted yield strength of our model as a function of the pillar size is more precise than that of the well-known single arm source model when comparing the predictions with the experimental results of pillars made of Al or Ni. According to the surface elasticity, the surface energy can be determined by the thickness of the hollow pillars, the surface modulus and the surface strain, where the latter two are related to the external damages.

A look at the strength of micro and macro EEG analysis for distinguishing insomnia within an HIV cohort.

HIV patients are often plagued by sleep disorders and suffer from sleep deprivation. However, there remains a wide gap in our understanding of the relationship between HIV status, poor sleep, overall function and future outcomes; particularly in the case of HIV patients otherwise well controlled on cART (combined anti-retroviral therapy). In this study, we compared two groups: 16 non-HIV subjects (seronegative controls) and 12 seropositive HIV patients with undetectable viral loads. We looked at sleep behavioral (macro-sleep) features and sleep spectral (micro-sleep) features obtained from human-scored overnight EEG recordings to study whether the scored EEG data can be used to distinguish between controls and HIV subjects. Specifically, the macro-sleep features were defined by sleep stages and included sleep transitions, percentage of time spent in each sleep stage, and duration of time spent in each sleep stage. The micro-sleep features were obtained from the power spectrum of the EEG signals by computing the total power across all channels and frequencies, as well as the average power in each sleep stage and across different frequency bands. While the macro features do not distinguish between the two groups, there is a significant difference and a high classification accuracy for the scoring-independent micro features. This spectral separation is interesting because evidence suggests a relationship between sleep complaints and cognitive dysfunction in HIV patients stable on cART. Furthermore, there are currently no biomarkers that predict the early development of cognitive decline in HIV patients. Thus, a micro-sleep architectural approach could serve as a biomarker to identify HIV patients vulnerable to cognitive decline, providing an avenue to explore the utility of early intervention.

Fracture strength of micro- and nano-scale silicon components

Silicon devices are ubiquitous in many micro- and nano-scale technological applications, most notably microelectronics and microelectromechanical systems (MEMS). Despite their widespread usage, however, issues related to uncertain mechanical reliability remain a major factor inhibiting the further advancement of device commercialization. In particular, reliability issues related to the fracture of MEMS components have become increasingly important given continued reductions in critical feature sizes coupled with recent escalations in both MEMS device actuation forces and harsh usage conditions. In this review, the fracture strength of micro- and nano-scale silicon components in the context of MEMS is considered. An overview of the crystal structure and elastic and fracture properties of both single-crystal silicon (SCS) and polycrystalline silicon (polysilicon) is presented. Experimental methods for the deposition of SCS and polysilicon films, fabrication of fracture-strength test components, and analysis of strength data are also summarized. SCS and polysilicon fracture strength results as a function of processing conditions, component size and geometry, and test temperature, environment, and loading rate are then surveyed and analyzed to form overarching processing-structure-property-performance relationships. Future studies are suggested to advance our current view of these relationships and their impacts on the manufacturing yield, device performance, and operational reliability of micro- and nano-scale silicon devices.

Effect of deicing solutions on the tensile strength of micro- or nano-modified asphalt mixture

This paper reports on the potential benefits of micro- or nano-sized materials for asphalt mixtures used on pavements, specifically when they are exposed to water or deicing solutions. Asphalt mixtures were prepared with various amount of nanoclay and/or carbon microfiber, and compacted using the Superpave™ gyratory compactor. Moisture susceptibility and deicer impacts were assessed by exposing the samples to water or deicing chemicals (NaCl, MgCl 2 and CaCl 2), and seven freeze–thaw cycles, in a modified AASHTO T283 test. Comparisons of micro- or nano-modified asphalt mixtures exposed to deicers are made based on results of indirect tensile strength tests, which preliminarily demonstrate the great potential of using microfibers and nanoclays in asphalt mixture for improved performance. Based on the results, it was found that the addition of nanoclay and carbon microfiber would improve a mixture’s moisture susceptibility performance or decrease the moisture damage potential in most cases. The detailed effects of deicing solutions on the tensile strength of micro- or nano- modified asphalt mixture are discussed in this paper.

Plasticity and strength of micro- and nanocrystalline materials

This review is devoted to the effect of grain boundaries on the deformational and strength properties of poly-, micro-, and nanocrystalline materials (predominantly metals). The main experimental facts and mechanisms concerning the dislocation structure and mechanical behavior of these materials over wide ranges of temperatures and grain sizes are presented. The experimentally established regularities are analyzed theoretically in terms of equations of dislocation kinetics taking into account the properties of grain boundaries as barriers, sources, and sinks for dislocations and as places where dislocations annihilate. The origin of the Hall-Petch relations for the yield stress and the flow stress as functions of the grain size, as well as the deviations from these relations observed in nano- and microcrystalline materials, is discussed in detail in terms of the dislocation-kinetics approach. Embrittlement of micro- and nanocrystalline materials at low temperatures and superplasticity of these materials at elevated temperatures are also analyzed in terms of the dislocation-kinetics approach.

パルスＹＡＧレーザによるマイクロ補修溶接の研究 １ 溶接部の硬さと強さに及ぼすパルスショット数の影響

In this study, the effect of laser pulse shot number on the hardness of weld metal and strength of welds was investigated. In the repair welding for such micro part as the cutter, laser welding was carried out to investigate the effects of pulse shot number for the hardness and strength of micro welded zone by the methods of changing pulse shot number under the condition that pulse output energy is constant. The following results were obtained in this study.In the case of laser welding under the condition that pulse output energy is 30 J/P and pulse shot number change from 10 to 60 pulse, the hardness of weld metal was increased with increasing pulse shot number. However, the hardness of weld metal is low against the hardness of base metal.The structure of martensite in the weld metal was decreased with increasing the pulse shot number, and pulse shot number is more than 30 pulse, the martensite in the weld metal disappeared from the weld metal.The strength of welds was increased with increasing the pulse shot number, but the rate of increasing at the strength of welded joint were moderated under the condition that pulse shot number is more than 30 pulse.

Betaine a novel candidate for rapid induction of somatic embryogenesis in tea (Camellia sinensis (L.) O. Kuntze)

Addition of betaine to the inductionmedium significantly enhanced the rapid formation ofsomatic embryos directly without callusing from maturefresh seeds of tea within two weeks of cultureinitiation. The induction response was furtherenhanced when ABA (7.5 mgl−1) was co-supplementedwith betaine in the induction medium. The rate ofinduction of somatic embryogenesis increased linearlywith external betaine concentration. Globular somaticembryo-like structures (embryoids) were observed in 4-week old cultures when inoculated on the inductionmedium without ABA and betaine. The positive effectof ABA on the induction process was found to bedependent on the presence of betaine in the medium. ABA alone in the medium could not bring the inductionstimulus in the explants; on the contrary, it provedinhibitory. The optimum response of ABA was observedwhen the medium was supplemented with 500 to1000 mgl−1 of betaine. Primary somatic embryosobtained in the presence of ABA and betaine were ableto produce secondary embryos. A conversion rate of15–20% was achieved upon transfer of somatic embryosof size 3–5 mm in diameter to the basal medium consistof half strength of macro nutrients, full strength ofmicro nutrients and vitamins of MS. Medium wasfurther supplemented with 100 mg l−1 each ofadenine hemisulfate sulphate and L-glutamine, 30 gl−1 sucrose, gelled with 7 gl−1 bitek agar. The plantlets regenerated by this procedure did notshow any visible abnormalities. This report for thefirst time details the potential use of betaine inplant tissue culture.

Influence of stress distribution on adhesion strength of sputtered hard coatings

Today’s research activities in improving the properties of cutting tools are concentrated on optimizing manufacturing technologies and tool geometry, on alloying of special cutting materials and on coating of tools. As a result of the poor machinability of new cutting tool materials, the surface properties are influenced by the grinding process used during tool manufacturing. In spite of optimized coating-parameters, deposited PVD-coatings fail because of insufficient surface properties of the substrates. In this contribution, influences of residual stress distribution in subsurface layers on interface strength of PVD-coated cemented carbides were investigated. Considered topics are the influence of grinding, micro blasting, and water peening of carbides on surface topography and surface integrity. Dependencies between stress distribution in subsurface layers and interface strength of (Ti,Al)N-coatings as well as effects on wear behavior in dry machining are highlighted. Surface properties of the tools are characterized by SEM and X-ray residual stress measurements (XRD). The X-ray measurement of the depth profile of the residual stress distribution is done by using different lattice planes which correspond to different penetration depths. Due to increased interface strength of micro blasted tools a superior wear behavior in dry machining is observed.

Surface treatment of cutting tool substrates

Today's research activities are concentrated on improving the properties of cutting tools by optimizing manufacturing technologies, by alloying of special cutting materials and by coating of tools. As a result of the poor machinability of new cutting materials, grinding processes get more difficult. Especially in grinding of new WC-carbide and cermet compositions, high mechanical and thermal loads influence the surface topography and surface integrity of the tool. In particular, the coating adhesion depends on the surface structure of the substrate. Variations of subsurface properties cause distinct differences to interface strength and tool life. Influences of surface properties on film adhesion of PVD-coated carbides were investigated. Considered topics are the influence of grinding, micro blasting and water peening of carbides on surface topography and surface integrity as well as effects on film adhesion of (Ti,AI)N-coatings. Residual stress measurements and SEM-pictures were used for characterization of surface properties. Film adhesion was analysed by scratch and indentation tests. Due to increasing interface strength of micro blasted tools a superior wear behaviour in dry machining was observed.

微小複合負荷試験機による微小接合部の強度評価

This paper presents the strength of micro bonding with adhesive resin and solder under combined loads. The combined loading tests of micro butt joints between steel and piano wire bonded with resin or solder were carried out using a new testing machine of micro combined loads. The machine is available to measure the strength of microbonded parts under combined loads. In case of micro-bonded parts, the torsional failure stress of the specimen is stronger than the tensile stress. For adhesive bonding the tensile failure stress of the specimen as well as the torsional failure stress decreased with increasing the bonded area. For solder bonding, the tensile failure stress decreased with increasing the bonded area. But the torsional failure stress was not dependent on the bonded area in the experiments.

Effect of grain size on ductility and anomalous yield strength of micro- and submicrocrystalline TiAl

Results obtained recently indicate that the TiAl intermetallic compound brittleness at room temperature (RT) and its limited ductility at elevated temperatures is caused by extremely fast localization of deformation. This is primarily due to the limited character of its slip systems, impeded cross-slip, and sequential transition of deformation from one grain to another, as well as formation of dislocation barriers typical of ordered alloys. One of the ways for improving the intermetallic compound ductility is to refine its microstructure, because it can provide for a more uniform straining. On the other hand, the growth of the grain boundary area hinders rack propagation, thus stimulating plastic flow. This is why it was supposed that there must be a certain critical value of grain size under which intermetallics can become ductile. This supposition was supported by results reported for NiAl where, at 400C, a brittle to ductile transition was observed as the grain size decreased. However, recent attempts to improve the RT ductility of some intermetallics by refining their microstructure had no noticeable effect. Even if a certain critical grain size truly exists, it is probably smaller than that described in those papers. In this connection, the authors suggested that intermetallics couldmore » probably be made ductile by converting then into a nanocrystalline state. The present paper contains new data on the mechanical behaviour of submicrocrystalline TiAl as well as a detailed discussion of the grain size effect on the relative elongation to rupture and yield strength of the intermetallic compound under study over a broad range of temperatures.« less

Effects of grain size and grain boundary structure on yield strength of micro- and submicrocrystalline TiAl

Mechanical properties of polycrystalline intermetallics strongly depend on their type of grain boundaries. An interesting example of the structure and properties being affected by grain boundaries is related to TiAl. By processing TiAl in certain special modes, it is possible to obtain structural states with practically the same grain size, but different content of random and special boundaries. Comparing the mechanical properties of the intermetallic compound in the above states has indicated that, with one and the same grain size, the growth of the fraction of special boundaries and, hence, the reduction of the fraction of random ones result in a considerable deterioration of the TiAl ductility above 600C and in an abrupt reduction of its strength below 750C. The latter effect is rather interesting, for it implies a question of whether TiAl obeys to the Hall-Petch equation, which is known to related yield strength to grain size. At the same time, the TiAl yield strength largely depends on the slip character which, in its turn, is determined by the grain size and grain boundary structure. As the grain size grows up to d[approximately]10 [mu]m and the number of special boundaries increases, a transition from very fine and homogeneous slipmore » to planar slip can be observed, which dramatically reduces the yield strength. This experimentally confirmed fact also causes doubt about the validity of the Hall-Petch relationship for TiAl.« less