Experimental Investigation on Influence of Molding Methods on Properties of Pervious Concrete

Despite the common use of pervious concrete (PC), there is no standard way of producing the test specimens, which undergo testing to infer the behaviour of PC in the field. Vibrating table is the most common method but greatly reduced in vibration time compare with normal concrete in the laboratory. Marshall compaction and superpave gyratory compactor (SGC) are recommended standard molding methods for porous asphalt mixtures manufactured in the laboratory environment. Three kinds of pervious concrete samples with three target porosities were prepared by the above three methods, and the effects of the molding method on the physical properties, mechanical properties and durability of the samples were investigated in the study. Experimental results showed, with different molding methods adopting, pervious concrete with the same mixture design exhibits slightly different physical and mechanical properties. After analysis and comparison, SGC is the best choice to obtain concrete with high permeability, good freeze-thaw resistance and high strength, followed by Marshall compaction molding, and vibration molding is the last one. As a result, a win-win situation of the hydraulic characteristics and mechanical properties of pervious concrete can be achieved due to both optimized mix-design and appropriate molding method.

Effects of the Vibration Amplitude in Vibratory Stress Relief on the Fatigue Life of Structures

This research aims to investigate the effects of vibration amplitude in vibratory stress relief (VSR) on the fatigue strength of structures with residual stress. Experiments are carried out on specimens with residual stress generated by local heating. Flat specimens made of A36 steel are prepared to be suitable for setting up fatigue bending tests on a vibrating table. Several groups of samples are subjected to VSR at resonant frequencies with different acceleration amplitudes. The results show that VSR has an important influence on the residual stress and fatigue limit of steel specimens. The maximum residual stress in the samples is reduced about 73% when the amplitude of vibration acceleration is 57 m/s2. The VSR method can also improve the fatigue limit by up to 14% for steel samples with residual stress.

Approximate Calculation of the Natural Oscillation Frequency of the Vibrating Table in Inter-Resonance Operation Mode

The first natural frequency of oscillations of the vibrations of a discrete-continuous interresonant vibrating table plate was found using the functions of the Krylov-Duncan. The continuous member, presented in a plate hinged at four points, is used as a reactive mass with distributed parameters to create an inter-resonance vibrating table with an electromagnetic drive. For this purpose, the plate was considered as a rod on hinged supports. The justification of this approach is confirmed by simulation in the Ansys software. The results were confirmed using the approximate Rayleigh-Ritz method. The geometric shape of the plate is reduced to a section of a hyperboloidal surface. The results of simulation of the first natural frequency were verified experimentally.

Correction of the static characteristic of a frequency converter to reduce the amplitudes of resonance vibrations of the vibrating table

It is known that vibration systems of directional vibrations based on asynchronous vibration motors are currently widely used in practice, but at the same time they have a significant drawback - a sharp increase in vibration amplitudes when passing through the resonance zone at the time of acceleration and deceleration of vibration motors, which negatively affects their operation. The article discusses a vibration table with two unbalanced asynchronous vibration motors. The calculation scheme and equations of motion of such a vibration system are presented. It is shown that the vibration table as a control object is an oscillatory link with a pronounced resonant frequency. The equations of motion of asynchronous vibration motors with scalar frequency control are given. A structural diagram of a vibration table with unbalanced exciters has been developed, the modeling of which made it possible to determine the amplitudes of resonant oscillations. It is proposed to apply correction of the static characteristics of the frequency converter, which connects the effective value of the output voltage with the frequency, to reduce the resonance amplitudes. Equations of the desired static characteristics of the inverter and analytical dependences for calculating the necessary coefficients for its implementation are given. A computational model has been developed that makes it possible to take into account the effect of the corrected static characteristic of the frequency converter on the operation of the vibrating table at the stages of acceleration and deceleration. The results of computer simulation are given, convincingly showing that the correction of the static characteristics of the inverter is an effective means of reducing the amplitudes of resonant oscillations. It is shown that modern frequency converters have functionality that makes it easy to correct the dependence of the effective value of the output voltage on the frequency. The need to adjust the static characteristics of the inverter for a specific type of product tested on the vibration table is noted.

Indices De Minéralisations En Or Dans La Province Panafricaine Du Sud Maradi (Sud Niger)

Le socle du Sud Maradi (Sud Niger) correspond à l’extrémité Nord du bouclier Bénino-Nigérian, appartenant à la zone mobile panafricaine à l’Est du Craton Ouest-Africain. Cette étude apporte une modeste contribution dans la caractérisation géochimique des minéralisations aurifères de cette province métallogénique panafricaine. A cet effet, l’approche méthodologique mise en oeuvre associe le dosage géochimique de l’or par absorption atomique (Au Fire Assay/AA) pour les roches saines, et la séparation des pépites d’or par l’utilisation de la table à secousse pour les altérites du socle et les sédiments (placers et paléoplacers). Les analyses géochimiques ont mis en évidence l’existence de deux types de minéralisations: primaires et secondaires. Les minéralisations primaires de l’or sont à l’état disséminé (faibles teneurs de 0.005 à 0.017 g/t) mais des teneurs relativement plus élevées (0.006 à 0.017 g/t) ont été enregistrées au voisinage des zones de cisaillement du socle. Tandis que la minéralisation secondaire, mise en évidence dans les altérites du socle, dans les alluvions (placers) et dans les grès du Crétacé (paléoplacers) présentent des teneurs en or plus élevées (5 à 30 g/t), dépassant largement les teneurs des minéralisations primaires observées dans les roches saines du socle. Ce grand écart de teneurs s’explique par un fort lessivage du socle, qui aurait permis une reconcentration de l’or dans les sédiments. The South Maradi (South Niger) basement corresponds to the northeastern part of the Benin-Nigerian Shield, belonging to the Pan-African mobile zone, which is located to the east of the West African Craton. This study brings a modest contribution to the geochemical characterization of gold mineralization in this Pan-African metallogenic province. For this purpose, the methodological approach implemented combines the geochemical determination of gold contents by atomic absorption (Au Fire Assay/AA) for basement rocks and physical separation of gold specks by using the vibrating table process for basement alterites and sediments (placers and paleoplacers). The obtained results showed two types of gold mineralization: primary and secondary. Primary gold mineralization is in a disseminated state (low contents of 0.005 to 0.017 g / t) but relatively the higher values (0.006 to 0.017 g / t) were recorded near the basement shear zones. While the secondary gold mineralization, highlighted in basement alterites, alluvium (placers) and Cretaceous sandstones (paleoplacers) present higher gold contents (5 to 30 g / t) than primary gold contents observed in basement rocks. This large difference in values can be explained by a strong alteration of the basement, which would have allowed a reconcentration of the gold in the sediments.

Wideband fractal-inspired piezoelectric energy harvesters

Harvesting kinetic ambient energy from vibrations or impact loads to obtain electrical energy useful to supply electronic sensors is still a challenging issue, with a huge number of potential applications, from the industrial field to consumer goods. This work investigates four simple piezoelectric energy harvesters developed from fractal-inspired structures: these structures are square laminas with inner divisions that originate a fractal geometry, since it is obtained by the repetition of a base configuration. Starting from the description of the fractal-inspired structures, the work presents a computational modal analysis highlighting the peculiar wideband frequency response of these structures and thus their applicability as energy converters. Using commercial piezoelectric transducers, we built four energy harvesters and assessed their output voltage and output power performing dynamic tests on a vibrating table. The proposed structures exhibit a wideband frequency response and a good energy conversion, specifically at the fundamental eigenfrequency.

STUDY OF OVERBURDEN TUFF ROCKS AND DEVELOPMENT ON ITS BASIS OF LIGHTWEIGHT STRUCTURAL CONCRETE

Introduction. The work presents the research results on the development of technology for lightweight structural concrete based on overburden tuff rocks. To develop the technology of lightweight structural concrete, overburden tuff rock (Almaty region of the Republic of Kazakhstan) is used, which is formed during the extraction of volcanic tuff for the manufacture of facing tiles. Aim. Study of the basic physical, mechanical and chemical properties of tuff, development of lightweight structural concrete compositions. Methods. The overburden tuff rock is crushed in a jaw crusher and screened through a set of standard screens. As a result, aggregates from tuff of fractions were obtained: 0.16-5 mm, 5-10 mm, and 10-20 mm. The composition of tuff concrete was selected by calculation according to the standard procedure. After calculating the composition of tuff concrete, all raw materials: cement, aggregates, additives, and water are dosed and mixed. The concrete mixture is placed in a mold and compacted by vibro-compression on a vibrating table. Hardening of concrete samples is carried out in humid conditions for 7, 14, and 28 days and steaming in a steaming chamber for 12-16 hours. Results and Discussion. After hardening, the properties were determined: compressive strength, average density, and heat transfer coefficient of concrete samples according to standard methods. The tuff concrete grade is in the range of 15.0-20.0 MPa. The average density of tuff concrete is 1822-1910 kg/m3. The thermal conductivity coefficient (λ) is in the range of 0.66-0.75 W/m∙K. The possibility of manufacturing finishing tiles from tuff concrete by grinding and polishing its surface has been established. Based on tuff sand, with a grain size of 3-5 mm, concrete stones with dimensions of 390x190x188 mm with 2 technological voids were made by vibration pressing. The hollowness of the stone is 51% of its total volume, and the compressive strength grade is 2.5-3.5 MPa. Conclusions. As a research result, the main physical, mechanical and chemical properties of overburden tuff rocks as a filler for lightweight structural concrete were studied. The possibilities of manufacturing wall blocks and facing slabs have been established.

SIMULASI TRANSPORTASI TOMAT DAN PERUBAHAN MUTU TOMAT SELAMA PENYIMPANAN

Chemical, physical, and microbiological damage of fruits and vegetables can occur during the transportation process. The percentage of damage can reach 30-50% if the treatment during transportation is not carried out properly. The research objective was to determine the quality changes in tomatoes after transportation simulation based on the arrangement of the fruit in cardboard packaging. The treatment in this research is tomato arrangement patterns: the face centered cubic (FCC) arrangement, the traditional arrangement and the jumble (farmer) arrangement. The research begins with a transportation simulation using a vibrating table in a vertical direction, using a frequency range of 3.9 Hz and an amplitude of 5.2 cm. The simulation is carried out in 1 hour. After the simulation at the 1st hour, amount of mechanical damage (bruising) on ​​every package was carried out. The results showed that the pattern of arranging tomatoes in cardboard packaging that gave the least damage was the FCC arrangement pattern. The FCC pattern only causes shrinkage of 0.11% and the smallest amount of mechanical damage (bruising) is 0.64%.

Digital Twin For Fatigue Analysis

The main design parameters that impact the fatigue of components are geometry, material and loading. Simulation with Finite Element Analysis (FEA) and tests on a vibrating table are often used to understand the dynamic behaviour of components and thus validate those items. Accelerated tests are used for the mission profile and test definition, as described in GAM-EG-13, MIL-STD-810F and RTCA DO-160E. The shock response spectrum (SRS) and the extreme response spectrum (ERS) allow for a comparison of the power spectrum density (PSD) and the acceleration factor applied in terms of fatigue severity through the fatigue damage spectrum (FDS). In addition, the hypothesis of linear damage accumulation enables the combination of several events for specifying a mission profile. Ultimately, the mission profile, which represents a usage that might span over several years, can be reduced to a shorter duration with a damage extraction technique. This is particularly useful for the definition of vibrating table specifications. An advantage of the virtual vibrating table is the reduction of the number of prototypes and the understanding of failure modes. To achieve this objective, finite element analysis in the frequency domain (harmonic analysis) is used and the structural stress response is evaluated with a PSD loading. A statistical model of rainflow allows assessing the damage on the components. The presentation also shows the effects of the damping factor on damage results. To achieve accurate results and define a Digital Twin, the correlation between test results and the finite element analysis is fundamental. Experimental modal analysis, based on the measured acceleration responses, helps to validate calculated modal frequencies and to assess the damping for each mode. This study shows the importance and the sensitivity on damping of the structural response, and in turn on fatigue.