Strength Decay Research Articles

Flyweight 3D Graphene Scaffolds with Microinterface Barrier-Derived Tunable Thermal Insulation and Flame Retardancy.

In this article, flyweight three-dimensional (3D) graphene scaffolds (GSs) have been demonstrated with a microinterface barrier-derived thermal insulation and flame retardancy characteristics. Such 3D GSs were fabricated by a modified hydrothermal method and a unidirectional freeze-casting process with hierarchical porous microstructures. Because of high porosity (99.9%), significant phonon scattering, and strong π-π interaction at the interface barriers of multilayer graphene cellular walls, the GSs demonstrate a sequence of multifunctional properties simultaneously, such as lightweight density, thermal insulating characteristics, and outstanding mechanical robustness. At 100 °C, oxidized GSs exhibit a thermal conductivity of 0.0126 ± 0.0010 W/(m K) in vacuum. The thermal conductivity of oxidized GSs remains relatively unaffected despite large-scale deformation-induced densification of the microstructures, as compared to the behavior of reduced GSs (rGSs) whose thermal conductivity increases dramatically under compression. The contrasting behavior of oxidized GSs and rGSs appears to derive from large differences in the intersheet contact resistance and varying intrinsic thermal conductivity between reduced and oxidized graphene sheets. The oxidized GSs also exhibit excellent flame retardant behavior and mechanical robustness, with only 2% strength decay after flame treatment. In a broader context, this work demonstrates a useful strategy to design porous nanomaterials with a tunable heat conduction behavior through interface engineering at the nanoscale.

Influence of adhesion area, applied voltage, and adherend materials on residual strength of joints bonded with electrically dismantlable adhesive

ABSTRACTThe separation characteristics of an electrically dismantlable adhesive, ElectRelease, were experimentally investigated. The adhesive has a strength that decreases by applying voltage. The residual strengths of cylindrical butt joints bonded with the adhesive were measured after voltage application. Various experiments were carried out in order to investigate the influences of the bonding area and the type of adherend materials on the residual strength by changing the dimensions and material of the adherends. The influence of constant voltage and current applications was also examined. As a result, it was confirmed that the residual strength of a joint does not depend significantly on the bonding area but on the type of adherend material. The residual strength was able to be determined and predicted by using an areal density of the total charge passing through the bonding area. Higher applied voltage was able to accelerate the decay of the residual strength and shorten the time for a given decrease in strength. The constant current application also induced a decrease in joint strength, which also corresponded to the total charge that could easily be calculated from a duration for current application.

Role of Brittle Behaviour of Soft Calcarenites Under Low Confinement: Laboratory Observations and Numerical Investigation

The strength decay that occurs in the post-peak stage, under low confinement stress, represents a key factor of the stress–strain behaviour of rocks. However, for soft rocks this issue is generally underestimated or even neglected in the solution of boundary value problems, as for example those concerning the stability of underground cavities or rocky cliffs. In these cases, the constitutive models frequently used in limit equilibrium analyses or more sophisticated numerical calculations are, respectively, rigid-plastic or elastic–perfectly plastic. In particular, most of commercial continuum-based numerical codes propose a variety of constitutive models, including elasticity, elasto-plasticity, strain-softening and elasto-viscoplasticity, which are not exhaustive in simulating the progressive failure mechanisms affecting brittle rock materials, these being characterized by material detachment and crack opening and propagation. As a consequence, a numerical coupling with mechanical joint propagation is needed to cope with fracture mechanics. Therefore, continuum-based applications that treat the simulation of the failure processes of intact rock masses at low stress levels may need the adoption of numerical techniques capable of implementing fracture mechanics and rock brittleness concepts, as it is shown in this paper. This work is aimed at highlighting, for some applications of rock mechanics, the essential role of post-peak brittleness of soft rocks by means of the application of a hybrid finite–discrete element method. This method allows for a proper simulation of the brittle rock behaviour and the related mechanism of fracture propagation. In particular, the paper presents two ideal problems, represented by a shallow underground cave and a vertical cliff, for which the evolution of the stability conditions is investigated by comparing the solutions obtained implementing different brittle material responses with those resulting from the assumption of perfectly plastic behaviour. To this purpose, a series of petrophysical and mechanical tests were conducted on samples of soft calcarenite belonging to the Calcarenite di Gravina Fm. (Apulia, Southern Italy), focusing specific attention on the post-peak behaviour of the material under three types of loading (compression, indirect tension and shear). Typical geometrical features representative of real rock engineering problems observed in Southern Italy were assumed in the problems examined. The numerical results indicate the impact of soft rock brittleness in the assessment of stability and highlight the need for the adoption of innovative numerical techniques to analyse these types of problems properly.

A study on the influence of surface laser texturing on the adhesive strength of bonded joints in aluminium alloys

The influence of ns-pulsed laser ablation on the adhesive strength of bonded joints was studied under conservative conditions by tensile stress tests on cylindrical specimens of aluminium alloy. Surface textures were produced by hatching the cross section with concentric grooves and varying the average laser power at fixed repetition rate, the scan speed and the radial hatch distance.Despite a range of surface activation in which the adhesive strength increases step-wise of about 25% with respect to the non-treated material, the effect of too high roughness values resulted in a decay of the joint strength. Air entrapment into the ablated grooves fixed a limit to the energy density that could be delivered to the surface, establishing an optimal technology range.

Numerical Investigation of Shock Wave Decay Phenomenon in Free Atmosphere

A numerical investigation of shock wave propagation in open atmosphere is presented to observe the shock wave decaying phenomena due to expansion in the free space. By examining different parameters (Pressure, velocity and density) of the upstream and downstream flow of the wave, it is possible to estimate the decaying phenomena of the wave strength. The governing equations described for compressible inviscid flow are discretized by the finite volume method. The three-dimensional Euler equations are solved by shock capturing method. Shock wave of Mach number 1.5 is allowed to flow through a shock tube and at different time intervals (35 μsec, 96 μsec, 121 μsec and 190 μsec), velocity, pressure and density variations along the center line of shock tube are investigated to observe the decay phenomenon across the shock front in open atmosphere.. The results have been compared with the Navier-Stokes Simulation (NS) results to establish the absence of viscous effects in the present flow. Due to absence of the solid boundary of the selected numerical domain in the free space, the fluid flow will act as non-viscous flow. The wave propagation in free space changes its propagation characteristics due to rapid expansion in all directions and at the same time the decay of the wave strength is observed.

Effect of radial plasma transport at the magnetic throat on axial ion beam formation

Correlation between radial plasma transport and formation of an axial ion beam has been investigated in a helicon plasma reactor implemented with a convergent-divergent magnetic nozzle. The plasma discharge is sustained under a high magnetic field mode and a low magnetic field mode for which the electron energy probability function, the plasma density, the plasma potential, and the electron temperature are measured at the magnetic throat, and the two field modes show different radial parametric behaviors. Although an axial potential drop occurs in the plasma source for both field modes, an ion beam is only observed in the high field mode while not in the low field mode. The transport of energetic ions is characterized downstream of the plasma source using the delimited ion current and nonlocal ion current. A decay of ion beam strength is also observed in the diffusion chamber.

Controls on phase composition and ice water content in a convection-permitting model simulation of a tropical mesoscale convective system

Abstract. Simulations of tropical convection from an operational numerical weather prediction model are evaluated with the focus on the model's ability to simulate the observed high ice water contents associated with the outflow of deep convection and to investigate the modelled processes that control the phase composition of tropical convective clouds. The 1 km horizontal grid length model that uses a single-moment microphysics scheme simulates the intensification and decay of convective strength across the mesoscale convective system. However, deep convection is produced too early, the OLR (outgoing longwave radiation) is underestimated and the areas with reflectivities > 30 dBZ are overestimated due to too much rain above the freezing level, stronger updraughts and larger particle sizes in the model. The inclusion of a heterogeneous rain-freezing parameterisation and the use of different ice size distributions show better agreement with the observed reflectivity distributions; however, this simulation still produces a broader profile with many high-reflectivity outliers demonstrating the greater occurrence of convective cells in the simulations. Examining the phase composition shows that the amount of liquid and ice in the modelled convective updraughts is controlled by the following: the size of the ice particles, with larger particles growing more efficiently through riming and producing larger IWC (ice water content); the efficiency of the warm rain process, with greater cloud water contents being available to support larger ice growth rates; and exclusion or limitation of graupel growth, with more mass contained in slower falling snow particles resulting in an increase of in-cloud residence times and more efficient removal of LWC (liquid water content). In this simulated case using a 1 km grid length model, horizontal mass divergence in the mixed-phase regions of convective updraughts is most sensitive to the turbulence formulation. Greater mixing of environmental air into cloudy updraughts in the region of −30 to 0 °C produces more mass divergence indicative of greater entrainment, which generates a larger stratiform rain area. Above these levels in the purely ice region of the simulated updraughts, the convective updraught buoyancy is controlled by the ice particle sizes, demonstrating the importance of the microphysical processes on the convective dynamics in this simulated case study using a single-moment microphysics scheme. The single-moment microphysics scheme in the model is unable to simulate the observed reduction of mean mass-weighted ice diameter as the ice water content increases. The inability of the model to represent the observed variability of the ice size distribution would be improved with the use of a double-moment microphysics scheme.

Moisture dynamics in the masonry fabric of historic buildings subjected to wind-driven rain and flooding

Current climatic projections show clearly that increasingly more extreme weather events are to be expected in the future. Historic buildings are considered to be the most vulnerable to this adverse climatic impact, via moisture induced deterioration and resulting strength decay in their construction materials. Therefore, the identification of these climatic effects is important to be able to develop suitable tools to mitigate them, both for individual buildings and on a regional scale. This paper presents the analysis of a comprehensive environmental monitoring of two historic buildings in Tewkesbury, Gloucestershire, UK, to provide thorough insight on their performances under environmental loading on a comparative basis. Firstly, the effect of wind-driven rain (WDR) and flooding is assessed by correlation with relative humidity (RH) measurements. The WDR measurements are then compared against values calculated using well established semi-empirical models and reasons behind the limited correlation are discussed. The dynamic hygrothermal response of two different historic fabrics is studied in greater detail by monitoring in-wall temperature and RH. The conclusions drawn from the analysis of the monitoring outputs are then further elaborated on by using hygrothermal characterization obtained by dynamic vapour sorption (DVS) testing of material samples extracted from the fabric of these buildings. The study concludes that the current environmental conditions pose a threat on the building envelopes unless routine maintenance is provided, and that monitoring methodology devised is clearly successful in quantifying the exposure of the two historic buildings to environmental conditions, onsetting deterioration phenomena in the envelop materials.

Strength decay of RC sections for chloride attack

Purpose Corrosion of reinforcement, and mainly the one induced by chloride attack, is one of the leading causes of deterioration in reinforced concrete structures. Then, it is very important to develop a simplified analytical tool, able to simulate the corrosion processes and the consequences for the structural safety. Design/methodology/approach Aim of this paper is the definition of a simplified integrated procedure, able to predict the decay with the time of the bending moment and axial force resistance of a reinforced concrete section, exposed to a chloride attack. Starting from various literature findings, the rebar mass loss in time is evaluated and related to the chloride distribution and content in time. Then the mechanical properties of the corroded rebars are evaluated by means of strength decay laws developed by the authors. Finally, moment curvature relationships and bending moment – axial force (M-N) interaction envelopes are defined. Findings The strength variation with the time can be easily evaluated and then the life cycle and the timing of repair or rehabilitation strategies can be estimated. Originality/value The proposed methodology can be considered a very simple, but useful tool for a first analysis of the strength reduction in time, due to chloride pitting corrosion, before performing more complex and time-spending analyses.

Behaviour of clay bricks from small-scale production units after high temperature exposure

The mechanical and thermal behaviour of traditional clay bricks were investigated after one hour exposure at three different temperatures (200, 400, 600 °C). Specimens collected from small-scale production units in Cameroon were used. It has been shown that the mechanical behaviour of traditional clay bricks after exposure depends on their quality of firing, which is most of the time affected by the limits of the traditional technologies used for their production. Among the samples collected, bricks of good quality and low quality of firing were identified. Bricks of good quality of firing have shown a progressive decay of mechanical strength from 200 °C after an increase from the room temperature to 200 °C. Those of low quality have shown an increase in mechanical strength from 400 °C after a stability observed between the room temperature and 400 °C. Both bricks have shown a phenomenon of embrittlement with the increase of the exposure temperature, which was much accentuated in the case of less fired bricks. Thermal conductivity of both bricks has shown a quasi-stability with exposure temperature due to their high porosity from the beginning.

Naphthyl-functionalized oligophenyls: Photophysical properties, film morphology, and amplified spontaneous emission

Herein, we reported a series of deep-blue-emitting naphthyl-functionalized oligophenyls as new organic laser active materials with tunable wavelength from 385 to 410nm in solid state. Introduction of peripheral naphthyl into the oligophenyls enabled the great sterical dimensions due to the prominent steric hindrance but not destroyed the molecular conjugation. We assumed that it would suppress the π-π stacking efficiently, driving by intermolecular interaction, to hinder crystallization in solid films. Finally, the neat films of naphthyl-functionalized oligophenyls demonstrated amorphous state compared to the polycrystalline state of oligophenyls. Thus, naphthyl-functionalized oligophenyls displayed high emission quantum yield (22–35%) in solid state neat films. In addition, these molecules possessed large oscillator strength and radiative decay rate, as predicted by the theoretical analysis. The outstanding photophysical properties and amorphous films render naphthyl-functionalized oligophenyls a new class of optical gain media in solid state.

Seismic performance of reinforced concrete columns after freeze–thaw cycles

The purpose of this study is to investigate the seismic performance of reinforced concrete columns after freeze–thaw cycles. Based on low cyclic loading tests of eight column specimens, the failure patterns, hysteresis loops, load carrying capacity, displacement and ductility factor, skeleton curves, stiffness degradation and energy dissipation capacity of frost-damaged concrete columns were analyzed. The effect of freeze–thaw cycles and axial compression ratios were investigated in detail. Test results show that for the column specimens under the same level of axial compression, with the number of freeze–thaw cycles increasing from 0 to 300, the plastic deformation capacity decreased whereas the rate of stiffness degeneration and strength decay increased continuously. The coupling effect of the deterioration of material and loosening of bond induced the value of equivalent viscous damping coefficients to decrease at first then increase, however, the cumulative energy dissipation decreased continuously. Test results also indicate that for the column specimens with the same level of frost damage, with the increase of axial compression ratio, the load carrying capacity and initial stiffness increased, whereas the deformability capacity, the equivalent viscous damping coefficients and the cumulative energy dissipation decreased obviously, respectively.

On the decay of strength in Guilin red clay with cracks

In order to research the effect of cracks in red clay on shear strength through dry-wet cycle test, the experimenters used imaging software and a mathematical model to determine fractal dimension and crack ratio of surface cracks in red clay in Guilin, China. After each dry-wet cycle, direct shear tests were carried out on the sample, and such variables as matrix suction on the crack propagation process of red clay were analyzed. The mechanics model was established and obtained the critical condition of soil cracks. The results show that with the increase in the number of dry-wet cycles the shear strength of the samples would decrease. But the rule of shear strength of sample 3 is slightly different from samples 1 and 2. The shear strength of red clay has a good correlation with fractal dimension and crack ratio, which could be an identification index of the strength of red clay.

Theoretical analysis of direct CP violation and differential decay width in $$D^\pm \rightarrow \pi ^\pm \pi ^+\pi ^-$$ D ± → π ± π + π - in phase space around the resonances $$\rho ^0(770)$$ ρ 0 ( 770 ) and $$f_0(500)$$ f 0 ( 500 )

We perform a theoretical study on direct $CP$ violation in $D^\pm\to \pi^\pm \pi^+\pi^-$ in phase space around the intermediate states $\rho^0(770)$ and $f_0(500)$. The possible interference between the amplitudes corresponding to the two resonances is taken into account, and the relative strong phase of the two amplitudes is treated as a free parameter. Our analysis shows that by properly chosen the strong phase, both the $CP$ violation strength and differential decay width accommodate to the experimental results.

Comparison and preparation of multilayered polylactic acid fabric strengthen calcium phosphate-based bone substitutes for orthopedic applications.

An attempt to maintain the three-dimensional space into restorative sites through the conveniently pack porous fillers are general used strategy. Advancement in the manufacturing protective shells in the scaffolds, which would be filled with brittle ceramic grafts for the development of highly connective pores provides the approach to solve crack problem for generating the tissues. Therefore, multilayered braided and alkalized poly(lactic acid) (PLA) composites with calcium phosphate bone cement (CPC) were synthesized and compared. The PLA/CPC composites were divided into various groups according to a series of heat-treatment temperatures (100-190°C) and periods (1-3h) and then characterized. The effects of 24-h immersion on the strength decay resistance of the samples were compared. Results showed that the residual oil capped on the surfaces of alkalized PLA braid was removed, and the structure was unaltered. However, the reduced tensile stress of alkalized PLA braids was due to ester-group formation by hydrolysis. Mechanical test results of PLA/CPC composites showed that the strength significantly increased after heat treatment, except when the heating temperature was higher than the PLA melting point at approximately 160-170°C. The degree of PLA after recrystallization became higher than that of unheated composites, thereby leading to reduced strength and toughness of the specimen. Braiding fibers of biodegradable PLA reinforced and toughened the structure particularly of the extra-brittle material of thin-sheet CPC after implantation.

Functional brain network changes associated with clinical and biochemical measures of the severity of hepatic encephalopathy

Functional properties of the brain may be associated with changes in complex brain networks. However, little is known about how properties of large-scale functional brain networks may be altered stepwise in patients with disturbance of consciousness, e.g., an encephalopathy. We used resting-state fMRI data on patients suffering from various degrees of hepatic encephalopathy (HE) to explore how topological and spatial network properties of functional brain networks changed at different cognitive and consciousness states. Severity of HE was measured clinically and by neuropsychological tests. Fifty-eight non-alcoholic liver cirrhosis patients and 62 normal controls were studied. Patients were subdivided into liver cirrhosis with no outstanding HE (NoHE, n=23), minimal HE with cognitive impairment only detectable by neuropsychological tests (MHE, n=28), and clinically overt HE (OHE, n=7). From the earliest stage, the NoHE, functional brain networks were progressively more random, less clustered, and less modular. Since the intermediate stage (MHE), increased ammonia level was accompanied by concomitant exponential decay of mean connectivity strength, especially in the primary cortical areas and midline brain structures. Finally, at the OHE stage, there were radical reorganization of the topological centrality—i.e., the relative importance—of the hubs and reorientation of functional connections between nodes. In summary, this study illustrated progressively greater abnormalities in functional brain network organization in patients with clinical and biochemical evidence of more severe hepatic encephalopathy. The early-than-expected brain network dysfunction in cirrhotic patients suggests that brain functional connectivity and network analysis may provide useful and complementary biomarkers for more aggressive and earlier intervention of hepatic encephalopathy. Moreover, the stepwise deterioration of functional brain networks in HE patients may suggest that hierarchical network properties are necessary for normal brain function.

Vortex dynamics during blade-vortex interactions

Vortex dynamics during parallel blade-vortex interactions (BVIs) were investigated in a subsonic wind tunnel using particle image velocimetry (PIV). Vortices were generated by applying a rapid pitch-up motion to an airfoil through a pneumatic system, and the subsequent interactions with a downstream, unloaded target airfoil were studied. The blade-vortex interactions may be classified into three categories in terms of vortex behavior: close interaction, very close interaction, and collision. For each type of interaction, the vortex trajectory and strength variation were obtained from phase-averaged PIV data. The PIV results revealed the mechanisms of vortex decay and the effects of several key parameters on vortex dynamics, including separation distance (h/c), Reynolds number, and vortex sense. Generally, BVI has two main stages: interaction between vortex and leading edge (vortex-LE interaction) and interaction between vortex and boundary layer (vortex-BL interaction). Vortex-LE interaction, with its small separation distance, is dominated by inviscid decay of vortex strength due to pressure gradients near the leading edge. Therefore, the decay rate is determined by separation distance and vortex strength, but it is relatively insensitive to Reynolds number. Vortex-LE interaction will become a viscous-type interaction if there is enough separation distance. Vortex-BL interaction is inherently dominated by viscous effects, so the decay rate is dependent on Reynolds number. Vortex sense also has great impact on vortex-BL interaction because it changes the velocity field and shear stress near the surface.

Dual-mode-locking mechanism for an akinetic dispersive ring cavity swept source.

A fast dual-mode-locked akinetic optical swept source in the 1550-nm wavelength band is presented that is tested up to a sweep rate of 797 KHz. It comprises a voltage-controlled oscillator-driven wideband semiconductor optical amplifier (SOA) along with a dispersion compensation fiber, in a ring laser configuration. A Faraday rotating mirror is employed in the cavity as a reflective element in order to achieve better polarization control. By driving the SOA at a high-MHz-frequency value multiple of the resonant frequency f(R), equal to the inverse round trip time, a first-mode locking mechanism is imposed. A second locking mechanism consists in sweeping the radio frequency of the locking signal at a rate slightly detuned from f(R). A dynamic linewidth of 0.8 nm is assessed by measuring the decay of interference signal strength versus optical path difference in a Mach-Zehnder interferometer.

Experimental Investigations on Fatigue Damage and Residual Properties of Interacting Notched Woven E-Glass/Epoxy Composite

The interacting notched laminates of plain weave E-glass fiber reinforced with epoxy were fatigued at predetermined frequency in tension–tension to investigate the fatigue damage and residual properties. The results from stress-life curves summarize that damage growing around the notches due to stress concentration is the underlying cause for the variation in fatigue strengths among the geometrically different specimens considered. The residual strength and modulus decay with respect to cycle number at 50 % of the ultimate tensile strength were investigated. It is evident from the experimental data that the residual strength decreases with cycle number and increases due to redistribution of stress around the notches. The detailed study of the damage development under cyclic loads also explains the causes of modulus reduction for all the laminate geometries.

Research on the Attenuation Law of Metal Magnetic Memory Testing Signal

In order to clear the timeliness issues of metal magnetic memory signal value after unloading, we conduct some static tension experiments on some specimens in materials of KMN, which is commonly used in centrifugal compressors? Furthermore, we analyze the specimen, which is prefabricated artificial defects, on the surface normal magnetic field strength decay law with EMS-2003, the intelligent magnetic memory tester. The results show that: the surface magnetic field signal value is reduced by time after unloading, in other words it has certain timeliness.