Comparison study of spherical and multi-spherical particles under cyclic uniaxial compression

Numerical simulation of cyclic compression of granular material by performing oedometric test has been performed. Discrete Element Method (DEM) has been employed for simulation. A comparison study has aimed to examine the differences in macroscopic behaviour of material discretized by spherical (S) and non-spherical shape models of a particle. During the study, microscopic data of sand from Klaipėda were used for modelling the shape of particles. The nonspherical particles were described by multi-spherical (MS) models retaining distributions for size and aspect ratios. Two DE models of tested specimens were developed and the deformation behaviour under cyclic uniaxial compression was simulated numerically by applying the commercial EDEM code. The variation of the oedometric elasticity modulus was investigated and influence of particle shape on void ratio changes was demonstrated. It was clearly shown that application of S particles is much more sensitive to rearrangement of particles during densification DEM. Simulations illustrated that the elasticity modulus of material corresponding to MS particles is approximately 1.9 times larger comparing with material corresponding to S particles. Therefore, one must improve the magnitude of elasticity modulus by introducing a respective correction factor

Experimental and numerical investigation of sand compression peculiarities

Investigation of the compression properties of Klaipėda sand by oedometric testing and numerical modeling is presented. Klaipėda sand is characteristic of the Baltic seashore region sand. Experimental investigation was performed with fraction corresponding to diameter variation bounds of 0.6 and 0.425 mm. Compression test was realized with initial maximal void ratio (e 0 = 0.800) of sand. Employed vertical stress ramp value is 800.0 kPa/min, maximum loading σmax = 400.0 kPa. Applying loading within the range of 50.0 to 120.0, two vertical stress jumps have been identified. A rubber sample compression test has been performed aiming to deny an assumption, that vertical stress jumps are influenced by device construction. Experiment viewed that not any vertical stress jumps have been recognized. Numerical simulation yielded exactly the same two vertical stress jumps found by compression with oedometer. It proves that the nature of rearrangement of sand grains has been properly reflected by modeling compaction process by DEM. Sand compaction velocity is higher versus applied vertical stress ramp. This is the reason for appearing of the vertical stress jumps. Numerical simulation viewed that location of the largest compression in oedometer is at the top of the sample

Evaluation of friction due to deformed behaviour of rail in the electromagnetic railgun: numerical investigation

The dynamic behaviour and evaluation of friction due to deformed behaviour of rail in the electromagnetic rail gun under accelerating loading are investigated by us-ing the finite element method. The simplified uncoupled rail-projectile contact model is applied, where action of the projectile is described as given moving loading. The di-mension-less friction ratio is suggested to evaluate the in-crease of the friction during motion of the load

Bėgio deformacija sukeltos trinties vertinimas elektromagnetinėje šaudyklėje: skaitiniai tyrimai

The dynamic behaviour and evaluation of friction due to deformed behaviour of rail in the electromagnetic rail gun under accelerating loading are investigated by us-ing the finite element method. The simplified uncoupled rail-projectile contact model is applied, where action of the projectile is described as given moving loading. The di-mension-less friction ratio is suggested to evaluate the in-crease of the friction during motion of the load.Lietuviška santrauka. Baigtinių elementų metodu tirta elektromagnetinės šaudyklės, veikiamos tolygiai greitėjančia apkrova, bėgio dinamika ir trintį lemiantys rodikliai. Sviedinio ir bėgio kontaktas nagrinėjamas supaprastintai, pakeičiant sviedinio poveikį žinoma judančia apkrova. Judančios apkrovos sukeltam trinties padidėjimui vertinti pasiūlytas bematis trinties rodiklis, kurį lemia kontaktinio paviršiaus normaliniai poslinkiai

Simulation of the normal impact of randomly shaped quasi-spherical particles

The paper reports the modelling of randomly shaped partieles. An emphasis is placed on the illustration of random properties of particles, using simulations with a controlled probability distribution for the depth of the surface profile. The randornly-shaped quasi-spherical particles were described by applying a multi-sphere approximation and a statistical evaluation technique, and the surface of the partieles was approximated using randornly located overlapping subspheres. The concept of statistically similar particles, i.e., partieles characterised by having a similar probability distribution for the depth of the surface profile, was employed for these purposes, and an original method involving the application of a stochastic optimisation was developed. The optimization method was demonstrated by generating statistically similar particles. The contact behaviour was investigated by simulating a random particle impact against a wall, using the discrete element method. It was observed that statistically similar particles did not show statistically similar contact characteristies. The results of this study suggested that the refinement of the multi-sphere model (achieved by increasing the number of subspheres) was non-unique, not only in a deterministic context but also in statistical context, and that this subject requires further investigation

Investigation of the Sand Porosity via Oedometric Testing

Investigation of the porosity of Klaipėda sand by oedometric test is presented. The Klaipėda sand is typical Baltic see-shore sand consisting of grains the average diameter of which varies from 1.18 mm to 0.3 mm. Variation of the porosity during oedometric compression of the whole mixture of the sand and of three separate fractions were investigated experimentally. Porosity was characterised by the maximal (initial) and minimal (after compression) values of the void ratio. It was proved experimentally that porosity of the sand mixture is practically predicted by the coarse-grained fraction with grain diameters ranging between 1.18 mm and 0.6 mm. The role of microstucture in the densification mechanism is explained by employing the discrete element method simulations. The spherical particles and commercial EDEM code were used for modelling purposes. Discrete element method simulations confirmed generally the macroscopic experimental results and yielded additional data on microscopic behaviour. The non-smooth deformation behaviour was observed during detailed numerical time-history analysis. The detected instabilities are explained by rearrangement of the sand grains

Comparison of dynamic behaviour of EMA-3 railgun under differently induced loadings

Comparison of dynamic behaviour of EMA-3 railgun of the French-German Research institute of Saint-Louis (ISL) under differently. induced loadings is presented. Both magnetic pressure loads are generated by two current injections and lead to identical projectile velocities reaching up to 1200 m/s. The main difference between the loads lays in different locations of the injection points. FE simulation results presented in terms of deflections of the sliding rail surface illustrate, that loading differences result into different dynamic behaviours of the railgun. The breech-feed loading, where both injections are induced in the start position of the rail, leads to higher oscillation amplitudes of rail deflections. It was found, that the railgun structure is dynamically less sensitive to the distributed (DES) loading, induced in two different points

Application of technogenic-raw material and burning out additive in composite ceramic system

The investigation of the composite ceramic system containing easily fusible hydro-micous clay, technogenic finely dispersed raw material, and burning out waste additive is presented in the article. The properties of the raw materials used are described in the paper. The obtained ceramic bodies were burned at 1000°C and 1050°C temperatures, keeping at the highest burning temperature for 4 h. The analysis of physical-mechanical properties of composite ceramics (density, compressive strength, water absorption), its structural parameters (effective and total open porosity, reserve of pore volume, relative wall thickness of the pores and capillaries), and X-ray diffraction analysis was performed. The interdependencies between some structural parameters are described by empirical equations