Indirect Strengthening Research Articles

Static and seismic strengthening of RC frame joints by using CFRP sheets with various anchoring methods

This study proposes an indirect strengthening method using carbon fiber-reinforced polymer (CFRP) and hybrid bolt-plate locking anchored CFRP hoops, which is more suitable than direct externally bonding strengthening on the reinforced concrete frame joints due to the orthogonal beam and slabs and debonding problem, especially for improving seismic performance. To understand the structural behavior of the joint using the proposed strengthening method, static and quasi-static cyclic tests were carried out on 8 joint specimens in a scale of 1:2. Three different anchoring systems were compared including through-slab CFRP closed hoops, border-beam-slab U-shaped CFRP anchored hoops, and the newly proposed hybrid bolt-plate locking anchored CFRP hoops. Results show that the hybrid bolt-plate locking anchored CFRP hoops has the least damage to the original structure and can be the most effective method in delaying the slip of the longitudinal rebars and the debonding of the CFRP on the beam, which can significantly enhance the seismic performance of the joint. Compared with the unstrengthened case, the yield load, ultimate load and ductility coefficient improved 25%, 19.7% and 55.7%, respectively. Under the cyclic loading, the utilization ratio of longitudinal CFRP sheet can be further improved with respect to the other two methods, up to 1.5 and 1.75 times respectively. Additionally, theoretical calculations were performed to predict the bearing capacity of the joints, which shows good agreement with the experimental values. The findings are significant in the engineering application to improve the structural behavior and performance of the joint using the proposed strengthening method.

Characterization, corrosion and failure strength analysis of Al7075 influenced with B4C and Nano-Al2O3 composite using online acoustic emission

This paper aims to establish the mechanical, corrosion and failure analysis using online acoustic emission of Al7075 alloy, Al7075-B4C composite and Al7075- B4C-Al2O3 hybrid composite with different Boron Carbide (B4C) content of 5, 10, 15 & 20% and Nano Aluminium Oxide (Al2O3) content of 2% on a weight basis with the high energy stir casting method. The casted samples have been characterized by x-ray Diffraction (XRD), Thermo gravimetric analysis (TGA/DSC), Energy Dispersive Spectrum (EDS), and Scanning Electron Microscope (SEM). In case of hybrid composite, the hardness and the tensile strength decrease when the content of Al2O3 increases. However, in the present research, the addition of B4C with nano Al2O3 particles in certain proportions has increased the hardness and tensile strength. In addition, the tensile fractographs of the specimens were analysed using SEM. Acoustic Emission (AE) method was used for monitoring the acoustic energy that are released at the time of deformation process and early crack detection. The influence of the volume fraction of the B4C particulates on the microstructural and corrosion characteristics of Al7075- B4C with nano Al2O3 metal matrix composites (MMCs) was also studied. It has been observed from the literature that the direct strengthening of composites occurs due to the presence of hard ceramic phase, while the indirect strengthening arises from the thermal mismatch between the matrix alloy and reinforcing phase during solidification. Based on the database for material properties, the application area of HAMCs has been proposed in the present review. The effects of nanomaterial dispersion in the metal matrix and the formation of interfacial precipitates on these properties are also addressed. Particular attention is paid to the fundamentals and the structure–property relationships of such novel Nano composites.

Microstructural evolution and load transfer in a nickel-based alloy: An in situ high-energy X-ray diffraction study

The microstructural evolution and matrix–carbide load transfer in a nickel-based alloy (GH3535) under tension were investigated by in situ high-energy X-ray diffraction. The sample containing smaller carbides (1–3 μm) shows obvious load transfer from the matrix to the carbides during the initial elastic deformation. However, the sample with larger carbides (10–20 μm) shows no remarkable load-transfer behavior. The sample with smaller carbides possesses slightly higher yield strength and lower ultimate tensile strength than the sample with larger carbides. These results are attributed to indirect strengthening by dislocation obstruction in the sample with larger carbides and direct strengthening via load transfer for that with smaller carbides.

Wybrane zagadnienia dotyczące pozycji prawnej duchownego w orzecznictwie Europejskiego Trybunału Praw Człowieka

Celem niniejszego artykułu jest zrekonstruowanie wybranych aspektów pozycji prawnej duchownego na gruncie orzecznictwa Europejskiego Trybunału Praw Człowieka. Analizie poddano 33 wyroki i decyzje w przedmiocie dopuszczalności skargi podjęte przez organy Europejskiej Konwencji Praw Człowieka w latach 1976-2017. Na ich podstawie można stwierdzić, że orzecznictwo ETPCz jest w tym zakresie ugruntowane wieloletnią praktyką.
 Duchowny jako taki nie posiada gwarancji innych niż przysługujące każdej innej osobie wyznającej przekonania religijne, ale korzysta z pośredniego wzmocnienia tej ochrony dzięki gwarancjom korporacyjnej wolności sumienia i wyznania. To właśnie autonomia związku wyznaniowego dokonuje różnicowania jego pozycji tak pozytywnie, jak i negatywnie dla niego samego. Autonomia związku wyznaniowego jest bowiem w świetle orzecznictwa ETPCz istotnym komponentem pluralizmu w społeczeństwach demokratycznych, a należy do niej także określanie wymagań względem duchownych. Z tego powodu duchowny uzyskuje silną ochronę przed ingerencją władzy państwowej w sprawy dotyczące jego powołania i usunięcia z urzędu. Kosztem uzyskania tej ochrony jest istotne ograniczenie jego osobistej wolności sumienia i wyznania, a pośrednio także innych praw w czasie pełnienia urzędu duchownego, w stosunku do związku wyznaniowego. Należy jednak pamiętać, że ocena spraw związanych z pełnieniem urzędu duchownego jest zależna od relacji ustrojowych między związkiem wyznaniowym i państwem. W przypadku kościołów państwowych możliwe jest np. poddanie pewnych spraw kościelnych orzecznictwu państwowemu, a związek wyznaniowy może dokonać swojego samoograniczenia kształtując relacje z duchownym na podstawie zwykłej umowy o pracę. Co do zasady jednak ETPCz w sposób jasny wskazywał, że sprawy duchownych leżą poza jurysdykcją państwa i jego organów. Niemniej kontrowersje związane z orzekaniem w sprawie Károly Nagy v. Hungary wskazują, że status duchownego może ulegać pewnym zmianom w przyszłości.

Effects of reheating duration on the microstructure and tensile properties of in situ core–shell-structured particle-reinforced A356 composites fabricated via powder thixoforming

A novel in situ core–shell-structured Ti@(Al–Si–Ti) particulate-reinforced A356 composite was synthesized via powder thixoforming. It is noted that there is a significant improvement in toughness of the particulate-reinforced Al matrix composites, and the problems related to fabrication techniques were also solved. The effects of reheating duration at a semisolid temperature of 600 °C on the microstructure and tensile properties of the resulting composites were investigated. The results indicated that a thick, compact Al–Si–Ti intermetallic shell formed around the Ti powders when the reheating time was at 50 min. A composite containing these reinforcing particles exhibited good tensile properties. Its ultimate tensile strength and yield strength (YS) were decreased by only 2.1 and 3.5%, respectively, while its elongation was increased by 167.8% and up to 8.3%, compared to the (Al, Si)3Tip/A356 composite that was thixoformed after the Ti powders had completely reacted. This occurred because the core–shell-structured particles with hard, compact shells exhibited strengthening role comparable to that provided by the monolithic (Al, Si)3Ti intermetallic particles, and the Ti core effectively inhibited or delayed crack propagation by blunting crack tips and severe plastic deformation. In addition, a modified shear lag model that incorporated the indirect strengthening mechanisms and varying shell thicknesses of Al–Si–Ti intermetallics was proposed to successfully predict the YS of the composites.

NONLINEAR MODEL OF OVERFISHING FOR THE VOLGA STURGEON BASED ON COGNITIVE GRAPH OF INTERACTION OF ENVIRONMENTAL FACTORS

We have discussed the development of models of dynamics of formation of reserves juveniles from natural spawning sturgeon Acipenser gueldenstaedtii of theCaspian Seaon historical data. Working hypotheses are based on the graph conceptual scheme aimed chain links. Structuring multivariate analytical conclusions about the quality of the interaction of 12 natural and anthropogenic factors in the ecosystem of the Caspian Sea have allowed us to recharge from the general ideas of the theory on to describe the specific situation of the tragic consequences of overfishing of anadromous fish with a long lifecycle. Reducing the word was swiftly enough and not consistent with the expectations of the replenishment of stocks by artificial reproduction. Dedicated contact circuit pulse propagation cognitive digraph where arcs contains the power of influence, says an indirect strengthening of action depends on the density of mortality. Interestingly, the relationship did not have a permanent independent sign + or . Recessions manifested dramatically on both boundaries of the range of optimum number of spawning manufacturers. Perhaps the decline in the efficiency of the reproduction right of the balance associated with the migration routes overlap. It is more intense withdrawal of fish more prolific race hibernating until spring in the river. The model takes into account the additional effect of increasing variations in the pace of development of the size on the survival of migrating hatchery. The system of differential equations is investigated in an iterative discrete continuous hybrid form with alternative position of equilibrium trajectory. One of the equilibrium is unstable, and is the starting point for the degradation of reproductive activity. The proposed model of reproduction under supercritical level seizures shows subtle transition from the brink of fading fluctuation to the permanent historical perspective depletion, the way into the Red Book.

Characterization of hybrid aluminum matrix composites for advanced applications – A review

Hybrid aluminum matrix composites (HAMCs) are the second generation of composites that have potential to substitute single reinforced composites due to improved properties. This paper investigates the feasibility and viability of developing low cost-high performance hybrid composites for automotive and aerospace applications. Further, the fabrication characteristics and mechanical behavior of HAMCs fabricated by stir casting route have also been reviewed. The optical micrographs of the HAMCs indicate that the reinforcing particles are fairly distributed in the matrix alloy and the porosity levels have been found to be acceptable for the casted composites. The density, hardness, tensile behavior and fracture toughness of these composites have been found to be either comparable or superior to the ceramic reinforced composites. It has been observed from the literature that the direct strengthening of composites occurs due to the presence of hard ceramic phase, while the indirect strengthening arises from the thermal mismatch between the matrix alloy and reinforcing phase during solidification. Based on the database for material properties, the application area of HAMCs has been proposed in the present review. It has been concluded that the hybrid composites offer more flexibility and reliability in the design of possible components depending upon the reinforcement's combination and composition.

Hall–Petch Breakdown at Elevated Temperatures

The Hall­Petch effect responsible for the strength of fine-grained and ultrafine-grained (UFG) metals is almost exclusively measured at room temperature. One reason for this is that at elevated temperatures grains tend to coarsen, and this negates the strengthening. The grains may, however, be stabilized by small volume fractions of fine dispersoids. These dispersoids cause direct Orowan strengthening and, by stabilizing the so-called Zener grain size, indirect strengthening due to Hall­Petch. We show that for most metals the critical Zener grain size above which Hall­Petch strengthening is more important than Orowan strengthening is lower than, and sometimes even considerably lower than 1μm, i.e., in the range of UFG metals. Breakdown of the Hall­Petch relationship, which occurs at elevated temperatures once mechanisms weaker than Hall­ Petch start to control the strength, is best studied for grain sizes well above this critical grain size. The Hall­Petch breakdown due to either Coble creep or grain size-dependent dislocation creep is modeled. We present model calculations for copper and verify our approach by comparing with experimental results for ferritic steels containing nanoscale dispersions. [doi:10.2320/matertrans.MA201309]

Temperature dependence of the strength of fine- and ultrafine-grained materials

The yield stress of oxide dispersion-strengthened (ODS) PM2000 steel and nanocluster-strengthened (NCS) 14YWT steel was measured as a function of temperature for grain sizes from 0.2 μm to ∞. In combination with data from the literature, it was found that the indirect strengthening (i.e., the Hall–Petch strengthening) for small grain sizes was often greater than the direct strengthening (i.e., the Orowan strengthening due to the dispersoids). The yield stress dropped significantly at a transition temperature near 500 °C even though the grain size remained constant. For small grain sizes, a large fraction of this drop was attributed to a decrease in grain size strengthening. Three published models describing this effect were compared with the experimental data. The observed transition temperatures were consistent with two of them. The strength–temperature curves for PM2000 with different grain sizes tended to intersect, whereas those for 14YWT did not. Because of this feature, the description of the strength–temperature dependence of 14YWT could be narrowed down to a single model. It is concluded that ODS and NCS materials are well suited to examining the temperature dependence of grain size strengthening.

Creep resistance in magnesium alloys and their composites

A considerable improvement in the creep properties of magnesium alloys can be potentially achieved by non-metallic reinforcement (metal matrix composites - MMCs). This paper provides a comparative report on experiments which were conducted on the two representative magnesium alloys (AZ91 and QE22) and their composites in order to evaluate the creep properties and to clarify the direct and indirect strengthening effects of reinforcement in creep. A comparison between the creep characteristics of squeeze-cast AZ91 and QE22 magnesium alloys reinforced with 20 vol.% Al2O3 short fibres and unreinforced matrix alloys shows that the creep resistance of the reinforced materials is considerably improved compared to the monolithic alloys. By contrast, the investigations of the creep behaviour of a particulate QE22-15 vol.% SiC composite prepared by powder metallurgy and the squeeze-cast hybrid QE22 matrix composites have revealed no substantial increase in the creep strength of the composite compared to the matrix alloy and AZ91 matrix composites. These results indicate a paramount importance of the choice of the composite matrix alloy and the reinforcement used.

The effect of particle reinforcement on the creep behavior of single-phase aluminum

The effect of TiC particle reinforcement on the creep behavior of Al (99.8) and Al-1.5Mg is investigated in the temperature range of 150 °C to 250 °C. The dislocation structure developed during creep is characterized in these materials. The addition of TiC increases creep resistance in both alloys. In pure aluminum, the presence of 15 vol pct TiC leads to a factor of 400 to 40,000 increase in creep resistance. The creep strengthening observed in Al/TiC/15p is substantially greater than the direct strengthening predicted by continuum models. Traditional methods for explaining creep strengthening in particle-reinforced materials(e.g., threshold stress, constant structure, and dislocation density) are unable to account for the increase in creep resistance. The creep hardening rate(h) is found to be 100 times higher in Al/TiC/15p, than in unreinforced Al. When incorporated into a recovery creep model, this increase inh can explain the reduction in creep rate in Al/TiC/15p. Particle reinforcement affects creep hardening, and thus creep rate, by altering the equilibrium dislocation substructure that forms during steady-state creep. The nonequilibrium structure generates internal stresses which lower the rate of dislocation glide. The strengthening observed by adding TiC to Al-1.5Mg is much smaller than that found in the pure aluminum materials and is consistent with the amount of strengthening predicted by continuum models. These results show that while both direct (continuum) and indirect strengthening occur in particle-reinforced aluminum alloys, the ratio of indirect to direct strengthening is strongly influenced by the operative matrix strengthening mechanisms.

Additivity of Direct and Indirect Strengthening in TiB2-Reinforced Near-γ Titanium Aluminides

AbstractAn experimentally-based description of strengthening in a series of TiB2-reinforced near-y titanium aluminides is presented. The analysis provides a means to examine the strengthening contributions which are individually attributable to compositional variants, to indirect sources which are present due to the influence of the particulate on the underlying microstructure, and to those directly evolving from the presence of the reinforcement and its interaction with dislocations. Once the indirect strengthening contributions are isolated and arithmetically removed from the magnitude of the experimentally determined composite strength, the resulting direct strengthening increments are found to obey a linear relationship with the inverse-squareroot of the edge-to-edge interparticle spacing. The description of the dependence on spacing is found to be compatible with other studies where similar relationships have been reported.

Convolution and matrix systems as content addressible distributed brain processes in perception and memory

The curious theory of Bain and others that each idea is lodged in a separate ganglion cell [is] an hypothesis impossible both psychologically and physiologically ( Ebbinghaus 1964 : 63, footnote). The proper way in which to think of this causation [the indirect strengthening of associations] would become clear only by the introduction of physiological conceptions which must first be constructed or at least remodeled ( Ebbinghaus, 1964 , p. 122).

Creep of Dispersion-Strengthened Nickel–Chromium Alloys

Creep studies over the range 700–1100° C have been made on four Ni–1 vol.-% ThO2-base alloys, which contained 0, 13·5, 22·6, and 33·7 wt.-% Cr. The phenomenological creep expression that describes the stress- and temperature-dependence of the steady-state creep rate, έ s , is έ s = K(σ/E)n exp − (Qc /RT). The stress exponent was n ≃ 7 for each alloy, and the activation energy for creep, Qc , increased from 64 kcal/mole for the 0% Cr alloy to 78 kcal/mole for the 33·7% Cr alloy. The constant K was dependent on the matrix stacking-fault energy. At a given stress and temperature, increasing the Cr concentration reduced the steady-state creep rate. This is attributed to a combination of three possible effects: (a) decreasing the matrix stacking-fault energy, γ, by Cr additions; (b) short-range ordering (SRO), especially in the 22·6 and 33·7% Cr alloys; (c) a slightly lower volume self-diffusivity in Cr-containing alloys, assuming that the rate-determining creep process is diffusion-controlled. Using the Barrett–Sherby analysis it was possible to show that έ s ∝ γm, where m was 2·6–3·0. It was not possible to assess the magnitude of the SRO strengthening effect. The presence of 1% ThO2 reduced έ s by ∼ 102 by comparison with previous results on polycrystalline single-phase Ni and Ni–Cr alloys This “creep-strengthening” is attributed both to direct strengthening by particles blocking dislocation motion during creep and to indirect strengthening caused by ThO2 particles helping to develop and pin a fine, stable, pre-creep substructure during alloy fabrication.