An ultrasonic testing method for gas pressure welded joints of reinforcing steel bars

Gas pressure welding for jointing of reinforcing steel bars is most commonly used in Japan and the Far Eastern regions, where there are frequent earthquakes. An ultrasonic testing method has been developed for gas pressure welded joints. An intrinsic feature of the ultrasonic testing method is that there is a correlation between the ultrasonic testing results and the mechanical property (tensile strength) of joints. This feature enables non-destructive detection of gas pressure welded joints with tensile strength below a reference value. The theoretical justification for the correlation between the ultrasonic testing results and the tensile strength of the joints is discussed.     

Processing of ultra-high molecular weight polyethylene/graphite composites by ultrasonic injection moulding: Taguchi optimization

Ultrasonic injection moulding was confirmed as an efficient processing technique for manufacturing ultra-high molecular weight polyethylene (UHMWPE)/graphite composites. Graphite contents of 1 wt%, 5 wt%, and 7 wt% were mechanically pre-mixed with UHMWPE powder, and each mixture was pressed at 135 °C. A precise quantity of the pre-composites mixtures cut into irregularly shaped small pieces were subjected to ultrasonic injection moulding to fabricate small tensile specimens. The Taguchi method was applied to achieve the optimal level of ultrasonic moulding parameters and to maximize the tensile strength of the composites; the results showed that mould temperature was the most significant parameter, followed by the graphite content and the plunger profile. The observed improvement in tensile strength in the specimen with 1 wt% graphite was of 8.8% and all composites showed an increase in the tensile modulus. Even though the presence of graphite produced a decrease in the crystallinity of all the samples, their thermal stability was considerably higher than that of pure UHMWPE. X-ray diffraction and scanning electron microscopy confirmed the exfoliation and dispersion of the graphite as a function of the ultrasonic processing. Fourier transform infrared spectra showed that the addition of graphite did not influence the molecular structure of the polymer matrix. Further, the ultrasonic energy led oxidative degradation and chain scission in the polymer.     

Fatigue strength of structural materials at sonic and ultrasonic loading frequencies

Experimental data on the influence of sonic and ultrasonic frequency loading on the fatigue strength of steels, and titanium, aluminium, and nickel-based alloys tested with longitudinal and transverse vibrations at room temperatures are discussed. Results of fatigue tests in liquid nitrogen at low (16 Hz) and high (3 kHz) loading frequencies are also given for a number of materials. The influence of the loading-cycle asymmetry on fatigue strength is studied for structural materials tested at 10 kHz frequency loading with a mean tensile and compressive stress. Limiting amplitude curves are plotted. Measurements of the energy dissipation in materials were carried out during fatigue tests with symmetrical and asymmetrical loading cycles at high-frequency with large amplitude longitudinal vibrations of the specimen. Measurements of the amplitude dependency of the energy dissipation and dependency of the energy dissipation obtained during continuous loading by fatigue tests were also made.     

Ecofriendly laccase–hydrogen peroxide/ultrasound-assisted bleaching of linen fabrics and its influence on dyeing efficiency

This study evaluates the bleaching efficiency of enzymatically scoured linen fabrics using a combined laccase–hydrogen peroxide bleaching process with and without ultrasonic energy, with the goal of obtaining fabrics with high whiteness levels, well preserved tensile strength and higher dye uptake. The effect of the laccase enzyme and the combined laccase–hydrogen peroxide bleaching process with and without ultrasound has been investigated with regard to whiteness value, tensile strength, dyeing efficiency and dyeing kinetics using both reactive and cationic dyes. The bleached linen fabrics were characterized using X-ray diffraction and by measuring tensile strength and lightness. The dyeing efficiency and kinetics were characterized by measuring dye uptake and colour fastness. The results indicated that ultrasound was an effective technique in the combined laccase–hydrogen peroxide bleaching process of linen fabrics. The whiteness values expressed as lightness of linen fabrics is enhanced by using ultrasonic energy. The measured colour strength values were found to be slightly better for combined laccase–hydrogen peroxide/ultrasound-assisted bleached fabrics than for combined laccase–hydrogen peroxide for both reactive and cationic dyes. The fastness properties of the fabrics dyed with reactive dye were better than those obtained when using cationic dye. The time/dye uptake isotherms were also enhanced when using combined laccase–hydrogen peroxide/ultrasound-assisted bleached fabric, which confirms the efficiency of ultrasound in the combined oxidative bleaching process. The dyeing rate constant, half-time of dyeing and dyeing efficiency have been calculated and discussed.     

Effects of high power ultrasonic vibration on the cold compaction of titanium

Titanium has widely been used in chemical and aerospace industries. In order to overcome the drawbacks of cold compaction of titanium, the process was assisted by an ultrasonic vibration system. For this purpose, a uniaxial ultrasonic assisted cold powder compaction system was designed and fabricated. The process variables were powder size, compaction pressure and initial powder compact thickness. Density, friction force, ejection force and spring back of the fabricated samples were measured and studied. The density was observed to improve under the action of ultrasonic vibration. Fine size powders showed better results of consolidation while using ultrasonic vibration. Under the ultrasonic action, it is thought that the friction forces between the die walls and the particles and those friction forces among the powder particles are reduced. Spring back and ejection force didn’t considerably change when using ultrasonic vibration.     

Elasticity and inelasticity of biomorphic carbon,silicon carbide,and SiC/Si composite produced on the basis of medium density fiberboard

The amplitude and temperature dependences of the Young’s modulus and the internal friction (ultrasonic absorption) of biomorphic carbon, silicon carbide, and SiC/Si composite produced from medium density fiberboard (MDF) by pyrolysis (carbonization), followed by infiltration of molten silicon into the prepared carbon preform have been studied in the temperature range 100–293 K in air and under vacuum. The measurements have been performed by the acoustic resonance method with the use of a composite vibrator for longitudinal vibrations at frequencies of approximately 100 kHz. The data obtained by acoustic measurements of the amplitude dependences of the elastic modulus have been used for evaluating the microplastic properties of samples under study. It has been shown that the Young’s modulus, the decrement of elastic vibrations, and the conventional microyield strength of the MDF samples differ from the corresponding data for previously studied similar materials produced from natural eucalyptus, beech, sapele, and pine woods. In particular, the desorption of environmental molecules at small amplitudes of vibrations, which is typical of biomorphic materials based on natural wood, is almost absent for the MDF samples. The results obtained have been explained by different structures and the influence of pores and other defects, which, to a large extent, determine the mechanical characteristics of the biomaterials under investigation.     

金属基复合结构粘接强度的非线性超声混频检测

采用非线性超声混频方法对金属基复合结构的粘接强度进行表征研究。以不同固化剂含量的铝合金丙烯酸酯粘接结构作为检测对象,基于非线性超声混频的共振条件及其作用机制,并结合粘接固化机理,开展了非线性超声混频实验。非线性超声混频模式选取两列横波生成和频纵波的方式,实验测量并计算不同基频周期数下的超声非线性参量。通过拉伸实验标定粘接结构的粘接强度,并采用扫描电镜分析拉伸断面微观结构,进而分析超声非线性参量与粘接强度的关系。从实验结果可以看出在不同周期的基频信号激励下,超声非线性参量随着粘接强度的增大均呈现出减小的趋势。研究表明非线性超声混频信号对金属基复合结构粘接强度的变化比较敏感,可以适用于类似结构件粘接强度状态弱化的表征。     

Multi-purpose explosion chamber with sound muffling and vibration cutting means

Abstract

An explosion chamber is operating for more than 13 years successfully. The chamber is used for procucing wBN powder and various dynamic high pressure experiments. The capacity of the chamber is 200 cubic meter by volume and 10 kg by the quantity of the explosives to be exploded. Safety means are equipped sequentially, transmitted sound level is less than 65 db at 60 m point from the chamber and earth vibrations cannot be detected at its periphery. The strength of the chamber was designed by simple static gas pressure model.     

Quantum Leap: From Dirac and Feynman,Across the Universe to Human Body and Mind,by V. Ivancevic and T. Ivancevic

Liquids can, under certain conditions, sustain quite large tensions. In this paper an account is given of experiments which have been performed to subject liquids to various rates of stressing, namely, static experiments, dynamic experiments and ultrasonic stressing. This is followed by a discussion of the theoretical work which has been done on the tensile strength of liquids. The paper ends with an account of recent work and an assessment of the present state of the subject.     

Preparation,structure and property research of nano-Mg/PP composites

The powder phases and structures of nano-magnesium powder prepared by high-energy ball milling and gas condensation method, i. e. resistance-heating evaporation, are characterized by means of XRD and TEM. Nano-Mg/PP composites are prepared by melt milling polypropylene, in which process the surface of nano-magnesium powder is modified first and then put into the melted PP. The results show that nano-magnesium powder prepared by the milling method improves the tensile strength of the polypropylene matrix and the powder prepared by gas condensation improves the toughness of the polypropylene matrix notably and maintains or improves the strength to some extent at the same time. The SEM observation of the cross-section of the composites shows that magnesium powder disperses in the matrix at nanometer size. The toughening mechanisms of nano-magnesium powder prepared by the condensation method can be compared to the cool tensile mechanism of rigid toughening.     

Mechanical Properties of Rubber Sheets Produced by Direct Molding of Ground Rubber Tire Powder

The so called “direct powder molding” is a compressions molding process which can be directly applied to ground rubber tire (GRT). This study shows that the GRT can be re-used to produce medium-size parts with good mechanical properties without any addition of virgin rubber. For rubber sheets prepared from the mechanically ground rubber tire (MGRT) and the cryogenically ground rubber tire (CGRT), the densities and crosslink densities of the rubber sheets increased with a decrease of the particle size of the waste tire powder. The tensile strength of the rubber sheets increased with the decreasing of the particle size for the two types of waste tire powder to 250 μm and 120 μm, respectively, and then became level. The moulding pressure had no effect on the densities, tensile strength or elongation at break of the rubber sheets. These results suggested that the effect of the particle size is important and is correlated with the mechanical properties of the rubber sheets produced by direct powder moulding technology. In general, the best mechanical properties were obtained with waste tire rubber with a size of about 250 μm for the rubber particles obtained from the mechanical grinding method of waste tire powdering.     

Investigation of Ti-6Al-4V alloy acoustic softening

High power ultrasonic vibration is widely used for improving manufacturing processes such as machining and metal forming. High frequency mechanical vibration affects material properties and friction forces in contacting surfaces. Flow stress reduction under superimposed ultrasonic vibration is called as acoustic softening. The amount of this parameter should be determined for ultrasonic assisted metal forming processes. For determination of this parameter for workhorse Ti-6Al-4V alloy, experimental setup was designed and fabricated. Then tensile test under longitudinal ultrasonic vibration was performed for different ultrasonic powers. Results show that ultrasonic vibration has considerable effect on plastic behavior of the alloy and decreases flow stress. Also, increasing ultrasonic power leads to higher acoustic softening. Yield stress reduction up to 9.52%, ultimate stress reduction up to 4.55% and elongation up to 13% were obtained at 340 W ultrasonic power. After applying ultrasonic vibrations and its termination, hardness of specimens were measured in which increase up to 9% was observed.     

Influence of ultrasound on nanostructural iron formed by electrochemical reduction

A method for control of particle dimensions of nanostructural amorphous iron powder obtained by electrochemical reduction under the effect of ultrasonic oscillations in reaction medium is described in this paper. Depending on the character of ultrasonic oscillations nanostructural powders were obtained differing both in average dimension and distribution of particle dimensions. In the case of simultaneous sonocation using ultrasonic vibrations with frequencies differing from each other by a factor of ten (20 and 200 kHz), the effect is complex, but includes narrowing of the average particle dimension.     

Study on preparation and properties of molybdenum alloys reinforced by nano-sized ZrO<Subscript>2</Subscript> particles

The nano-sized ZrO₂-reinforced Mo alloy was prepared by a hydrothermal method and a subsequent powder metallurgy process. During the hydrothermal process, the nano-sized ZrO₂ particles were added into the Mo powder via the hydrothermal synthesis. The grain size of Mo powder decreases obviously with the addition of ZrO₂ particles, and the fine-grain sintered structure is obtained correspondingly due to hereditation. In addition to a few of nano-sized ZrO₂ particles in grain boundaries or sub-boundaries, most are dispersed in grains. The tensile strength and yield strength have been increased by 32.33 and 53.76 %.     

Ultrasonic actuators for nanometre positioning

This paper deals with ultrasonic motors based on bimodal plate vibrations and their application to nanometre resolution stepper positioning systems. The concept of a linear ultrasonic motor drive capable of nanometric steps, long-range travel and reversible controlled motion is presented. The motor concept developed is based on the superposition of a longitudinal and bending vibrations of a rectangular resonator. The ultrasonic motor model based on system identification via discrete observations and prediction has been developed for control applications. The control algorithm for ultrasonic motors has been developed and theoretical investigations have been made. The open loop positioning system with designed stepper ultrasonic drive produced 10 nm resolution and 5% displacement repeatability. The system with computer controlled position feedback has shown 0.3 micron positioning accuracy over the 100 mm positioning range.     

Power ultrasound interaction with DC atmospheric pressure electrical discharge

The effect of power ultrasound application on DC hollow needle to plate atmospheric pressure electrical discharge enhanced by the flow of air through the needle electrode was studied experimentally. It was found that applying ultrasound increases discharge volume. In this volume take place plasmachemical processes, used in important ecological applications such as the production of ozone, VOC decomposition and de-NOx processes enhancement. In our experiments we used a negatively biased needle electrode as a cathode and a perpendicularly placed surface of the ultrasonic resonator--horn--as an anode. To demonstrate the effect of ultrasound waves on electrical discharge photographs of the discharge for the needle to the ultrasonic resonator at distances of 4, 6 and 8mm are shown. By varying the distance between needle and the surface of the transducer, we were able to create the node or the antinode at the region around the tip of the needle, where the ionization processes are effective. In our experimental arrangement the amplitude of acoustic pressure at antinode exceeded 10(4) Pa. The photographs reveal that the diameter of the discharge on the surface of the ultrasonic horn is increased when ultrasound is applied. The increase of discharge volume caused by the application of ultrasound can be explained as a combined effect of the change of the reduced electric field E/n (E is electric field strength and n is the neutral particles density), strong turbulence of the particles in the discharge region caused by quick changes of amplitudes of the standing ultrasonic wave and finally by the boundary layer near the ultrasonic transducer perturbations due to vibrations of the transducer surface.     

Elasticity of BaFCl single crystal under hydrostatic pressure

The sound velocities for longitudinal and transverse waves have been measured in single crystalline BaFCl at room temperature using ultrasonic pulse echo and Brillouin scattering techniques. The complete set of elastic constants is deduced and lead to the bulk moduli values of BaFCl at ambiant conditions (, , ) which are compared with those obtained by a shell model. Moreover, using the ultrasonic technique under pressure, the pressure derivatives of the second order elastic constants at 298 K have been determined up to 0.3 GPa. All moduli increase linearly with pressure in this pressure range, allowing to determine directly and separately the first derivative of the bulk modulus B'₀ = 5.8. These data are used to calculate a Murnaghan equation of state. A detailed comparison is given between our results with those recently obtained by X-ray diffraction on powder or calculated using the local density approximation method. Finally, the anisotropy of BaFCl under pressure is discussed. Received: 19 March 1998 / Revised: 15 May 1998 / Accepted: 19 May 1998     

The Relevance of Powder/Liquid Wettability to the Cohesiveness of Carbon Black Agglomerates

Particle size enlargement operations often involve the use of a liquid to improve powder cohesiveness. Capillary suction and surface tension forces acting through liquid menisci between particles are the primary source of the cohesive bonding. The strength of these forces, and consequently the strength of the wet agglomerate, is dependent upon the total liquid content, its distribution within the agglomerate, and the powder wettability (characterized by the liquid surface tension and powder/liquid contact angle). The tensile strength of powder compacts containing submicron carbon black particles has been measured as a function of saturation level for several liquids. It is found that the compact strength increases with increasing surface tension for liquids that exhibit a zero contact angle. Above the critical surface tension for wetting a more complicated situation exists where both the surface tension and contact angle are important.     

基于光纤光栅传感的模压腔内压强分布式测量

针对模压腔内压强分布式测量的需要,研制了等强度梁结构的光纤光栅压强传感器.该传感器的波长改变量与压强之间的线性度达到0.999 92.将六个研制的微型光纤光栅压强传感器镶嵌于模具内部,通过圆柱形刚性金属杆传递压力,实现了模压腔内部多点压强分布式测量,取得了很好的实验结果.实验研究了粉末状材料挤压成型过程中模压腔内压强的分布以及变化规律.     

Ultrasonic-assisted Dunlop method for natural rubber latex foam production: Effects of irradiation time on morphology and physico-mechanical properties of the foam

An ultrasonic-assisted technique was first introduced for the production of natural rubber latex foam (NRLF). The flexible elastomeric foam was formed by a liquid–solid state transformation in an aqueous media. The aim of the current research was to provide a novel strategy for fabricating NRLF using ultrasonication and the Dunlop method, as well as to simultaneously utilize irradiation events to achieve the desired foam properties. NRLFs were exposed to ultrasonication at 25 kHz at the beginning of the gelling process. The effects of irradiation times of 0, 1, 3, 5 and 7 min on the morphology, foaming behaviors, physical properties and mechanical performance of NRLFs were investigated. The results revealed that using ultrasonic irradiation, unfoamed regions and a bimodal structure, which seem to be microstructural defects in conventional NRLF, could be completely eliminated. However, excessive irradiation times of 5 min and longer appeared to affect the physico-mechanical properties of the foams in terms of transient cavitation and the unfavorable physicochemical effects of ultrasonic vibrations. As a result, the optimal ultrasonic irradiation time was found to be 3 min. Using this irradiation duration, a foam with the suitable microcellular structure achieved the most desirable properties, such as its expansion ratio (7-fold increase), foam porosity (85.7%), compression recoverability (98.7%), and tensile strength (307.3 kPa). Moreover, the foam still maintained its characteristic soft nature (hardness less than 100 N) with an indentation hardness of 71.9 N. Therefore, ultrasonic treatment introduced to the conventional Dunlop method is a potentially feasible technique since it improves the morphology and the physico-mechanical properties of NRLFs.