Band 28, Heft 1

Understanding the origin of quark confinement in hadrons remains one of the most challenging problems in modern physics. Recently, the pressure distribution inside the proton was measured via deeply virtual Compton scattering. Surprisingly, strong repulsive pressure up to 10 35 pascals, the highest so far measured in our universe, was obtained near the center of the proton up to 0.6 fm, combined with strong binding energy at larger distances. We show here that this profile can be derived semiquantitatively without any adjustable parameters using the rotating lepton model of composite particles (RLM), i.e. a proton structure comprising a ring of three gravitationally attracting rotating ultrarelativistic quarks. The RLM synthesizes Newton’s gravitational law, Einstein’s special relativity, and the de Broglie’s wavelength expression, thereby conforming with quantum mechanics, and also yields a simple analytical formula for the proton radius and for the maximum measured pressure which are in excellent agreement with the experimental values.

Concrete behaves as a brittle material due to its low inherent tensile strength, but it can also exhibit a markedly ductile behavior when coupled with transverse reinforcement like steel stirrups. The role of stirrups is to enhance confinement effect, to restrain the lateral expansion of concrete, thus modifying the concrete stress-strain constitutive law and enabling higher compression strains and higher ductility. This paper focuses on the confinement effect induced by different arrangements of transverse reinforcement on axially loaded concrete columns. An experimental campaign has been carried out, comprising 18 concrete columns with two different mechanical strengths and reinforced with three different layouts of stirrups, namely typical closed square hoops, closed stirrups with additional cross ties, and a novel type of stirrups involving rectangular hoops with additional restraint plates, the latter offering an enhanced diffused confinement action and limiting extensive spalling of the cover concrete. Formation and propagation of longitudinal micro-cracks are reduced with the novel type of diffused stirrups and a moderate-to-high increase of ductility is observed. However, the beneficial effects induced by diffused stirrups are more pronounced in medium-strength concrete and almost negligible in low-strength concrete that collapses due to a brittle cracking failure without involving the confinement action of the transverse reinforcement.

In the present investigation, rice husk waste from rice mill was utilized in the development of aluminum based green metal matrix composite. Response surface methodology (RSM) was employed to develop green metal matrix composite by considering tensile strength as a response. Rice husk ash (RHA) was used as primary reinforcement material and B 4 C was used as a secondary reinforcement material in the development of composite. Microstructure results showed a uniform distribution of RHA and B 4 C in aluminum based matrix material. The optimum combination of reinforcement parameters was found to be RHA weight percentage of 7.8%, RHA preheats temperature of 231.12 ∘ C, B 4 C preheats temperature of 435.24 ∘ C and B 4 C wt.% of 6.67% respectively to achieve a tensile strength of 249.867 MPa.

Natural fibers from agricultural waste have received more attraction than traditional synthetic fibers in recent years. In present investigation epoxy/rice husk composite has been fabricated to utilize the agricultural waste which can be recycled easily and overcome the pollution problems due to smoke and fine silica ash. Study of interfacial bonding and dispersion of rice husk in epoxy resin has been studied through scanning electron microscope image. Characterization of fabricated composites has been done by mechanical properties. Ultimate tensile strength, Young’s Modulus and hardness are highest at 10 wt.% of rice husk particle and their values are 66.5 MPa, 616.46 MPa and 16.8 HV respectively. Machinability of epoxy/rice husk composites has been determined through drilling operation. Effect of feed rate (0.1, 0.2 and 0.3 mm/rev), speed (300, 600 and 900 rpm) and wt.% of reinforcement (10, 15 & 20) have been studied on machinability of epoxy/rice husk composites. Taguchi L 27 orthogonal array has been applied to conduct the experiments to evaluate the performance characteristics viz thrust force and torque. Weight percentage was found the most significant factor for machinability followed by feed rate and speed.

Increasing demand of aerospace industry for more heat resistant and tough material have open up the possibility of the use of Inconel 825 for making of combustor casing and turbine blades. Because of its robust nature, Inconel 825 is a difficult-to-cut material with conventional methods. Wire-cut electrical discharge machining (WEDM), a non traditional method uses thermoelectric erosion principle to produce intricate shape and profiles of such difficult-to-cut material. In this study, various operating parameters of WEDM are optimized using desirability approach and microstructural behavior at optimum combinations was studied. Input parameters viz . pulse-on time, pulse-off time, peak current, spark gap voltage, wire tension, wire feed and performance has been measured in term of material removal rate, surface roughness and wire wear ratio. It has been observed that at 110 machine unit pulse-on time (T on ), 35 machine unit pulse-off time (T off ), 46 volt gap voltage (SV), 120 ampere peak current (IP), 11 machine unit wire tension (WT) and 5 m/min wire feed (WF), the values obtained for material removal rate (MRR), surface roughness (SR) and wire wear ratio (WWR) were 27.691mm 2 /min, 2.721 μmand 0.117 respectively. Scanning electron microscopy, energy dispersive spectrograph and X-ray diffraction analysis has also been carried out to study the surface characterization. Comparatively less numbers of cracks, pockmarks, craters, and pulled out material were found on work specimen surface and wire electrode surface under standardized conditions, thus maintaining the surface integrity of the machined surface.

Main objective of this paper is to present ananalysis of necessity of providing expansion joints in the plain cement concrete pavement considering the climate and weather conditions of Vietnam. This study would help in the proper designing of expansion joints of highways and airport roads and thus can improve life span of cement concrete pavements to be constructed in Vietnam.

In this paper, we consider a straight screw dis-location near a flat interface between two elastic media in the framework of strain gradient elasticity (as studied by Gutkin et. al. [1]) by now taking care of some incomplete calculations). Closed form solutions for stress components and the Peach-Koehler force on the dislocation have been derived. It is shown that the singularities of the stress components at the dislocation line are eliminated and both components are continuous and smooth across the interface. The effect of the distance of the dislocation position from the interface on the maximum value of stress is investigated. Unlike in the case of classical solution, the image force remains finite when the dislocation approaches the interface. It is shown that the dislocation is attracted by the medium with smaller shear modulus or smaller gradient coefficient.

The term gradient nano-chemo-mechanics was introduced to encompass models incorporating higher order couplings between deformation and chemistry at the nanoscale. Along these lines, the article first reviews the basics of a robust theoretical framework developed for such processes focusing on elasticity and diffusion. The classical laws for Hookean deformation and Fickean transport are modified to include extra Laplacian terms and corresponding internal lengths modeling nonlocal interactions. Then, special cases are considered to describe deformation and fracture aspects of new energy materials; namely Li-ion battery (LIB) nanostructured anodes and disclinated metallic microcrystals (DMC). Both of these material systems are characterized by a high degree of spatial gradient structures (SGS) with extended surface for energy storage and catalysis applications.

Historically known for being one of the major pollutants in the world, the construction industry, always in constant advancement and development, is currently evolving towards more environmentally friendly technologies and methods. Scientists and engineers seek to develop and implement green alternatives to conventional construction materials. One of these alternatives is to introduce an abundant, hard to recycle, material that could serve as a partial aggregate replacement in masonry bricks or even in a more conventional concrete mixture. The present work studied the use of 3 different types of repurposed plastics with different constitutions and particle size distribution. Accordingly, several brick and concrete mix designs were developed to determine the practicality of using these plastics as partial aggregate replacements. After establishing proper working material ratios for each brick and concrete mix, compression tests as well as tensile tests for the concrete mixes helped determine the structural capacity of both applications. Presented results proved that structural strength can indeed be reached in a masonry unit, using up to a 43% in volume of plastic. Furthermore, a workable structural strength for concrete can be achieved at fourteen days of curing, using up to a 50% aggregate replacement. A straightforward cost assessment for brick production was produced as well as various empirical observations and recommendations concerning the feasibility of each repurposed plastic type examined.

It is shown that the crack driving force for a fundamental antiplane crack problem is analogous to the limiting case of the force acting on an ideal fluid on free streamlines that form at the ends of flow around two parallel plates.

Mathematical models developed within the material mechanics and material physics communities have been routinely adapted to interpret and further understand physiological and biological processes. The field of biomechanics, in particular, has emerged from a direct application of elasticity and fluid mechanics theories to model cell and tissue behavior, as well as bone fracture and blood flow. On the other hand, Turing’s reaction-diffusion model of morphogenesis for biochemical systems has been adapted to interpret pattern formation in deforming materials. An important aspect, however, that has not been sufficiently examined is to investigate the role of an externally applied or internally developed stress. Another, equally interesting issue that has not been adequately explored, concerns the development of a common effective methodology to analyze signals and images for both humanmade and naturemade systems, especially when differential equations are not available to use for this purpose. The article is an initial modest effort to discuss such common features between nonliving and living materials. It focuses, in particular, to modeling analogies between pattern formation of defects in deforming engineering materials under application of external stress and morphogenesis of cellular structures in ageing brain tissue under development of internal stress.

Railroad ballast structure layer may experience a decline in mechanical and geometrical performance due to heavy train and environmental loads. In order to improve the quality of ballast structure, the addition of asphalt to ballast layer can be considered as a solution. Therefore, this research utilizes 60/70 penetration grade asphalt for ballast layer binding and stabilization. The objective of this study was to evaluate and analyze the mechanical behavior of clean-ballast and fouled-ballast layers with 2% and 4% penetration grade 60/70 asphalt poured in one (ballast surface layer) and three ballast surface layers. Compressive strength test was performed to analyze the weight of specimen, vertical deformation, and ballast material abrasion. The most prominent finding to emerge from this research was that the use of 60/70 penetration grade asphalt on ballast surface layer is crucial in retaining the load applied by UTM, in order to produce preferable load distribution to the entire ballast structure. It is found that, the higher the 60/70 penetration grade asphalt proportion and the more layers poured with asphalt, the stronger asphalt in reducing ballast abrasion percentage.

The present study aimed to investigate the influence of a number of fiber parameters including fiber type, content and hybridization on strength and ductility of polymer fiber reinforced concrete (PFRC) and steel fiber reinforced concrete (SFRC) used mostly in tunneling practices as the primary shotcrete lining. Numerous cylindrical and prismatic beams were casted and undergone various tests in which main previously mentioned fiber traits varied. It was understood that SFRC excels at every mechanical feature in comparison to PFRC; however, such transcendence found predominant in compressive strength but marginal in flexural and tensile strength. Despite being classified under different compressive strength classes (SFRC in the upper and PFRC in the lower class) according to EFNARC, both FRC types fell under a similar flexural class (at 4% of fiber fraction); a result possibly in debt to excellent bonding properties and more slender polymer fibers. Tensile strength of PFRC was measured lower than SFRC. Augmentation of fiber content positively affected mechanical characteristics of FRC at most cases. Hybridization of different fibers at a specific range of fiber mixing proportions was observed to have advantageous impacts on ductility and strength of a more corrosive resistant and cost efficient hybrid fiber reinforced concrete (HFRC).

Aluminium alloys of 6xxx series are widely used in the fabrication of light weight structures especially, where high strength to weight ratio and excellent weld-ability characteristics are desirable. Gas metal arc welding (GMAW) is the most predominantly used welding process in many industries due to the ease of automation. In this investigation, an attempt has been made to identify the best variant of GMAW process to overcome the problems like alloy segregation, precipitate dissolution and heat affected zone (HAZ) softening. Thin sheets of AA6061-T6 alloy were welded by cold metal transfer (CMT) and Pulsed CMT (PCMT). Among the two joints, the joint made by PCMT technique exhibited superior tensile properties due to the mechanical stirring action in the weld pool caused by forward and rearward movement of the wire along with the controllable diffusion rate at the interface caused by shorter solidification time. However, softening still exists in the welded joints. Further to increase the joint efficiency and to minimize HAZ softening, the joints were subjected to post weld heat treatment (PWHT). Approximately 10% improvement in the tensile properties had been observed in the PWHT joints due to the nucleation of strengthening precipitates in the weld metal and HAZ.

In the present study, turning of two grades of composites such as ZA43 silicon carbide and ZA43 silicon carbide and graphite was carried out. The fabrication of both categories of composites were done using stir casting technique. The silicon carbide of grit size 60μm with concentration of 5% was reinforced for one category of the composite and for the other grade of composite, 5% silicon carbide and graphite were added. Thus fabricated materials were turned on a conventional lathe using coated carbide tools (SNMG). Dry turning of the fabricated composite was carried out with varying cutting parameters. Measurement of cutting force was done for the both compositions of fabricated materials using lathe tool dynamometer. It was observed that, while machining composite containing silicon carbide and graphite, tool experience more cutting force than composite containing silicon carbide alone.

The current study focuses on the parametric optimization of electroless Ni-Co-P coating considering surface roughness as a response using Box-Behnken Design (BBD) of experiment. The two bath parameters namely the concentration of cobalt sulphate and sodium hypophosphite were varied along with the bath temperature to predict the variation in surface roughness. Analysis of variance (ANOVA) method has been applied to determine the interactions of the substantial factors which dominate the surface roughness of the coating. The process parameters for surface roughness of the coating were optimized by successfully utilizing the statistical model of Box-Behnken Design (BBD) of experiment. From the BBD model, the optimum condition for the deposition of the coating has been evaluated. In that specific condition, the surface roughness of the as-deposited coating is found to be 0.913μm. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), and X-Ray Diffraction (XRD) study have been utilized to characterize the electroless Ni-Co-P coating deposited in optimized condition.

The effect of pouring temperatures of an ex situ (Al/SiCp) and in situ (Al/TiB 2 ) metal matrix composites (MMCs) synthesized using stir casting method were studied. The Al/SiCp composite were fabricated by mixing of 6wt.% of SiCp into cast A356 aluminium alloy melt and poured at diverse pouring temperatures (730 ∘ C, 750 ∘ C and 770 ∘ C). The Al/TiB 2 MMCs were obtained by melting A356 aluminium alloy and mixing of KBF 4 and K 2 TiF 6 precursor salts whose stoichiometric ratio composition corresponds to 6wt.% of TiB 2 reinforcement and other parameters were constant (stirring speed 300 RPM and holding time 30 minutes). The composite melt was poured into the permanent mould with varied pouring temperatures (800 ∘ C, 820 ∘ C and 840 ∘ C). Coarser and homogenous SiC particles were presented in the Al/SiCp MMCs, whereas, finer and uniformly distributed TiB 2 particles were appeared at the MMCs of Al/TiB 2 . The mechanical properties viz. tensile strength, fracture toughness and hardness of Al/SiCp and Al/TiB 2 MMCs were experimentally determined as per the ASTM standards and compared. Higher tensile and fracture strength were occurred at the MMCs of Al/TiB 2 as compared to Al/SiCp MMCs and base alloy of aluminium as well. Maximum hardness was attained at the pouring temperatures of 820 ∘ C and 750 ∘ C in the MMCs of Al/ TiB 2 and Al/SiCp, respectively.

The quality of friction stir welded joints depends upon the working parameters such as rotational speed, welding speed, shoulder diameter, tilt angle; etc. Each process parameter has a significant effect on the formation of joint strength. This investigation attempts to understand the effect of friction stir welding parameters on microstructural characteristics and tensile strength of AA2014-T6 aluminium alloy. This is performed by changing any one of the process parameters from minimum to maximum and keeping others constant. The joint fabricated from a rotational speed of 1500 rpm, welding speed of 40 mm/min, shoulder diameter of 6 mm and tilt angle of 1.5 ∘ yielded superior tensile properties compared to their counter joints. Due to the formation of defect-free weld, balanced material flow and uniform distribution of strengthening precipitates in the stir zone is achieved.

Inconel 718 is a nickel-based superalloy which finds major applications in lightweight welded frames and other parts in gas turbine engines. This alloy is frequently joined by gas tungsten arc welding (GTAW) process for clean and precise welds. However, the weldability of Inconel 718 alloy is limited by the high heat input and slower cooling rate in GTAW process. It leads to the segregation of alloying elements and detrimental laves phase formation in weld metal which significantly reduces the tensile properties of the welded joints. To overcome this problem, a newly developed gas tungsten constricted arc welding (GTCAW) process is used for joining Inconel 718 alloy. The main effect of Delta Current (DC) and Delta Current Frequency (DCF) on the tensile properties and microstructure of GTCA welded 2 mm thick Inconel 718 alloy sheets was investigated. Superior tensile properties were exhibited at Delta Current of 50 A and Delta Current Frequency of 4 kHz due to the refinement in fusion zone. Delta Current and Delta Current Frequency showed deleterious effect at higher levels due to the high heat input.

Adhesion between bodies is strongly influenced by surface roughness. In this note, we try to clarify how the statistical properties of the contacting surfaces affect the adhesion under the assumption of long-range adhesive interactions. Specifically, we show that the adhesive interactions are influenced only by the roughness amplitude h rms , while the rms surface gradient h0 rms only affects the non-adhesive contact force. This is a remarkable result if one takes into account the intrinsic difficulty in defining hrms′ . $h_{\mathrm{rms}}^{^{\prime }}.$ Results are also corroborated by a comparison with self-consistent numerical calculations.