In this study, high performance magnesium-yttria nanocomposite’s room temperature, strength and ductility were significantly enhanced by the dispersion of nano-sized nickel particles using powder blending and a microwave sintering process. The strengthening effect of the dispersed nano-sized nickel particles was consistent up to 100°C and then it gradually diminished with further increases in the test temperature. The ductility of the magnesium-yttria nanocomposite remained unaffected by the dispersed nano-sized nickel particles up to 100°C. Impressively, it was enhanced at 150°C and above, leading to the possibility of the near net shape fabrication of the nanocomposite at a significantly low temperature.
The behaviour of concrete under quasi-static loadings for uniaxial compression, tension and planestress conditions is studied. The failure criteria of concrete are discussed as well as the methodsof constitutive parameters identification are elaborated. The attention is focus on an energeticinterpretation of selected failure criteria. The numerical example with concrete damage plasticitymaterial model is shown.
This study investigates the use of steel fibers and hybrid composite with a total fibers content of 2% on the high strength flowing concrete and determines the density, compressive strength, static modulus of elasticity, flexural strength and toughness indices for the mixes. The results show that the inclusion of more than 0.5% of palm fibers in hybrid fibers mixes reduces the compressive strength. The hybrid fibers can be considered as a promising concept and the replacement of a portion of steel fibers with palm fibers can significantly reduce the density, enhance the flexural strength and toughness. The results also indicates that the use of hybrid fibers (1.5 steel fibers + 0.5% palm fibers) in specimens increases significantly the toughness indices and thus the use of hybrid fibers combinations in reinforced concrete would enhance their flexural toughness & rigidity and enhance their overall performances.
Mechanical and technological properties of castings made from 3xx.x alloys depend mainly on properly performed process of melting and casting, structure of a casting and mould, as well as possible heat treatment. Precipitation processes occurring during the heat treatment of the silumins containing additives of Cu and/or Mg have effect on improvement of mechanical properties of the material, while choice of parameters of solutioning and ageing treatments belongs to objectives of research work performed by a number of authors. Shortened heat treatment, which is presented in the paper assures suitable mechanical properties (Rm), and simultaneously doesn’t cause any increase of production costs of a given component due to long lasting operations of the solutioning and ageing. Results of the research concern effects of the solutioning and ageing parameters on the Rm tensile strength presented in form of the second degree polynomial and illustrated in spatial diagrams. Performed shortened heat treatment results in considerable increase of the Rm tensile strength of the 320.0 alloy as early as after 1 hour of the solutioning and 2 hours of the ageing performed in suitable.
The paper presents results of compressive strength investigations of EN AC-44200 based aluminum alloy composite materials reinforced with aluminum oxide particles at ambient and at temperatures of 100, 200 and 250C. They were manufactured by squeeze casting of the porous preforms made of α-Al2O3 particles with liquid aluminum alloy EN AC-44200. The composite materials were reinforced with preforms characterized by the porosities of 90, 80, 70 and 60 vol. %, thus the alumina content in the composite materials was 10, 20, 30 and 40 vol.%. The results of the compressive strength of manufactured materials were presented and basing on the microscopic observations the effect of the volume content of strengthening alumina particles on the cracking mechanisms during compression at indicated temperatures were shown and discussed. The highest compressive strength of 470 MPa at ambient temperature showed composite materials strengthened with 40 vol.% of α-Al2O3 particles.
Describes how to obtain a soluble sodium silicate with a density of 1.40 g/cm3, 1.45 g/cm3, 1.50 g/cm3, and silica module M = 2.1 obtained from the silica- sodium glass with module M = 3.3 and M = 2.1. Residual (final) strength of molding samples made with these binders, were determined at temperatures corresponding to the characteristic temperatures of phase and temperature transitions of silica gel. Indicated the type of soluble sodium silicate capable of obtain the smallest value of the final strength of molding sand in the specified range of temperatures.
The results of testing of the selected group of wax mixtures used in the investment casting technology, are presented in the paper. The measurements of the kinetics of the mixtures shrinkage and changes of viscous-plastic properties as a temperature function were performed. The temperature influence on bending strength of wax mixtures was determined.
In the paper, an attempt was made to evaluate the effect of preliminary wetting of high-silica base during preparation of moulding sands containing a selected grade of sodium water-glass, designed for hardening by traditional drying or by electromagnetic microwaves at 2.45 GHz. In the research, some water was dosed during stirring the sandmix before adding 1.5 wt% of the binder that was unmodified sodium water-glass grade 137, characterised by high molar module within 3.2 to 3.4. Scope of the examinations included determining the effect of wetting the base on mechanical parameters like compression, bending and tensile strength, as well as on technological parameters like permeability, abrasion resistance and apparent density. The research revealed a significant positive effect of adding water to wet surfaces of high-silica base grains on mechanical properties and quality of moulding sands hardened by physical methods, in particular by microwave heating
Metal pieces wear out due to variable loading, because cracks formed on their surface of them. In order to increase useful life of metal pieces with the help of different methods of welding, surface cracks are repaired. In this research, performance of the diffusion welding of pure iron powder through magnetic induction evaluated for repairing structural steel surface cracks. First, four specimens prepared including one control specimen and other three specimens grooved specimens in length of 6.25mm and in depth of 1mm and groove width in the sizes of 0.5, 0.75 and 1mm. Then by a coil, the induced current created in the piece surface. After crossing the current, the powder melted and the groove repaired due to diffusion welding. To prevent oxidation, the atmosphere inside the coil filled with argon gas. The results show that after repairing surface groove, tensile strength of the repaired specimens reached to the tensile strength of control specimen with the margin of 7.5%.
This paper presents the details of optimized mix design for normal strength and high performance concrete using particle packing method. A critical review of mix design methods have been carried out for normal strength concrete using American Concrete Institute (ACI) and Bureau of Indian Standards (BIS) methods highlighting the similarities and differences towards attaining a particular design compressive strength. Mix design for M30 and M40 grades of concrete have been carried out using ACI, BIS and particle packing methods. Optimization of concrete mix has been carried out by means of particle packing method using EMMA software, which employs modified Anderson curve to adjust the main proportions. Compressive strength is evaluated for the adjusted proportions and it is observed that the mixes designed by particle packing method estimates compressive strength closer to design compressive strength. Further, particle packing method has been employed to optimize the ingredients of high performance concrete and experiments have been carried out to check the design adequacy of the desired concrete compressive strength.
Nano technology is an emerging field of interest for civil engineering application. Among the nano materials presently used in concrete, nano-silica possess more pozzolanic nature. It has the capability to react with the free lime during the cement hydration and forms additional C-S-H gel giving strength, impermeability and durability to concrete. Present paper investigates the effects of addition of nano silica in normal strength concrete. Three types of nano-silica in the form of nano suspension having different amount of silica content have been investigated. Mix design has been carried out by using particle packing method. X-Ray diffraction (XRD) analysis has been carried out to find the chemical composition of control concrete and nano modified concrete. Further, experimental investigations have been carried out to characterize the mechanical behaviour in compression, tension and flexure. It has been observed that the addition of nano-silica in normal strength concrete increased the compressive strength and decreased the spilt tensile strength and flexural strength. Also, Rapid chloride permeability test (RCPT) has been conducted to know the chloride permeability of control concrete, nano modified concrete, and nano coated concrete. It has been observed that the chloride permeability is less for nano coated concrete.
Monitoring of the mechanical properties of fruit obtained from cucumber plants is extremely important because of their use in processing, since these properties are reflected by the finished products of processing. Mechanical defects produced at the time of harvesting, during transport and at the specific stages of processing may adversely affect the course of technological processing (brine and vinegar pickling), resulting in spoilt preserves no longer useful for commercial purposes. The study was designed to identify selected mechanical properties in fresh and pickled fruit obtained from field cucumbers during spontaneous fermentation and fermentation promoted by selected lactic bacteria cultures. Additionally, water contents were measured in fresh cucumbers. The findings show significant differences between the analysed parameters.
The paper presents a method of obtaining short-termpositioning accuracy based on micro electro-mechanical system (MEMS) sensors and analysis of the results. A high-accuracy and fast-positioning algorithm must be included due to the high risk of accidents in cities in the future, especially when autonomous objects are taken into account. High-level positioning systems should consider a number of sub-systems such as global positioning system (GPS), CCTV – video analysis, a system based on analysis of signal strength of access points (AP), etc. Short-term positioning means that there are other locating systems with a sufficiently high degree of accuracy based on, e.g. a video camera, but the located object can disappear when it is hidden by other objects, e.g. people, things, shelves etc. In such a case, MEMS sensors can be employed as a positioning system. The paper examines typical movement profiles of a radio-controlled (RC) model and fundamental filtering methods in respect of position accuracy. The authors evaluate the complexity and delay of the filter and the accuracy of the positioning in respect of the current speed and phase of movement (positive acceleration, constant) of the object. It is necessary to know whether and how the length of the filter changes the position accuracy. It has been shown that the use of fundamental filters, which provide solutions in a short time, enables to locate objects with a small error in a limited time.
Weak value amplification is a measurement technique where small quantum mechanical interactions are amplified and manifested macroscopically in the output of a measurement apparatus. It is shown here that the linear nature of weak value amplification provides a straightforward comparative methodology for using the value of a known small interaction to estimate the value of an unknown small interaction. The methodology is illustrated by applying it to quantify the unknown size of an optical Goos-Hänchen shift of a laser beam induced at a glass/gold interface using the known size of the shift at a glass/air interface.
The paper deals with the accuracy of measurements of strains (elongation and necking) and stresses (tensile strength) in static room-temperature tensile strength tests. We present methods for calculating measurement errors and uncertainties, and discuss the determination of the limiting errors of the quantities measured for circular and rectangular specimens, which is illustrated with examples.
The paper presents the new solution to a road acoustic screen consisting of elements which are highly diffusing and simultaneously resistant to weathering, but also characterised by a sound absorption. There is described the comprehensive research of such the road acoustic screen with absorbing and diffusing surface. The study includes screen’s resistance to wind load and snow removal, impact tests and mea- surements of some acoustic parameters
The paper reports on investigation and development of a flywheel device intended for an energy storage prototype. The goal was to design and experimentally verify the concept of self-integrated flywheel with smart control of energy flow and accumulation. The Flywheel Energy Storage System (FESS) must has high energy efficiency and structural robustness. Investigation on structural dynamics of the composite flywheel connected with outer type rotor was carried out using Finite Element Method. The FESS is designed to run in vacuum and is supported on low-energy, controlled, active magnetic bearings (AMBs). The flywheel device of 10 MJ energy density and a weight of 150 kg with two integrated rotors/generators of 50 kW power density each is intended to operate up to 40 000 rpm.
This paper presents the findings of fatigue strength tests of 15CrNi6 steel following low-pressure carburizing and oil quenching, subjected to cycles of one-sided three-point bending. The fatigue fractures were compared with the results of fatigue strength studies of 16MnCr5 steel following low-pressure carburizing and nitrogen quenching. The fatigue tests for 16MnCr5 steel were conducted as part of a high-cycle resonance test, with a pendular bending load. The study also involved an analysis of the effects on non-metallic inclusions in the structure on the mechanism of fatigue destruction. The inclusions were found to initiate fatigue cracks. In both cases, a similar method of a fatigue fissure initiation was observed, independent of the study method or specimen material.
Aluminium based metal matrix composite (Al-MMC’s) are much popular in the field like automobile and aerospace industries, because of its ease of fabrication process and excellent mechanical properties. In this study, Al-Zn-Mg alloy composite reinforced with 3, 6 and 9 v % of zircon sand was synthesised by stir casting technique. The microstructure of the composites revealed uniform distribution of reinforced particles. Hardness, tensile strength and wear resistance of Al-Zn-Mg alloy/zircon sand composite were found to increase with increase in v % percentage of zircon sand. Scanning Electron Microscope analysis of wear tested sample surface of composites revealed no evidence of plastic deformation of matrix phase. Particle pulls out and abrasive wear was the common feature observed from all the composites.
In this study, the effect of electroless Pd-P plating on the bonding strength of the Bi-Te thermoelectric elements was investigated. The bonding strength was approximately doubled by electroless Pd-P plating. Brittle Sn-Te intermetallic compounds were formed on the bonding interface of the thermoelectric elements without electroless Pd-P plating, and the fracture of the bond originated from these intermetallic compounds. A Pd-Sn solder reaction layer with a thickness of approximately 20 µm was formed under the Pd-P plating layer in the case of the electroless Pd-P plating, and prevented the diffusion of Bi and Te. In addition, the fracture did not occur on the bonding interface but in the thermoelectric elements for the electroless Pd-P plating because the bonding strength of the Pd-Sn reaction layer was higher than the shear strength of the thermoelectric elements.
Ag and Cu powders were mechanically alloyed using high-energy planetary milling to evaluate the sinter-bonding characteristics of a die-attach paste containing particles of these two representative conductive metals mixed at atomic scale. This resulted in the formation of completely alloyed Ag-40Cu particles of 9.5 µm average size after 3 h. The alloyed particles exhibited antioxidation properties during heating to 225°C in air; the combination of high pressure and long bonding time at 225°C enhanced the shear strength of the chip bonded using the particles. Consequently, the chips sinter-bonded at 225°C and 10 MPa for 10 min exhibited a sufficient strength of 15.3 MPa. However, an increase in bonding temperature to 250°C was detrimental to the strength, due to excessive oxidation of the alloyed particles. The mechanically alloyed phase in the particle began to decompose into nanoscale Ag and Cu phases above a bonding temperature of 225°C during heating.