Study of Dry and Wet Cement Mortar Dynamic Properties

We performed the dynamic tests and studied the dynamic properties under compression of dry and wet cement mortar specimens using the Hopkinson split pressure bar method. As a result, we determined the fracture stresses and their dependence on the applied loading growth rate. It is noteworthy that the strength characteristic of wet material under study is less by 10-15% as compared to the dry one.С использованием метода разрезного стержня Гопкинсона проведены динамические испытания на сжатие образцов цементного раствора в сухом и увлажненном состоянии. Экспериментально определены разрушающие напряжения и их зависимость от роста скорости приложенной нагрузки. Отмечено, что прочность сухого материала на 10...15% превышает прочность материала в увлажненном состоянии.За допомогою методу розрізного стрижня Гопкінсона проведено динамічні випробування на стиск зразків цементного розчину в сухому і зволоженому стані. Експериментально визначено руйнівні напруження й їхню залежність від росту швидкості навантаження, що прикладається. Відмічено, що міцність сухого матеріалу на 10...15% перевищує міцність матеріалу у зволоженому стані

Structural-temporal approach for dynamic strength characterization of gabbro-diabase

This paper presents some of the results of dynamic compression, splitting and direct-tensile tests of gabbro-diabase using two split Hopkinson bar apparatus. The results of laboratory experiments on specimens without and with notch for a wide range of loading parameters are given. Strength and deformation characteristics of gabbro-diabase were determined experimentally at high strain rates up to 103 s-1. Mechanical characteristics were found to be strongly depended on the strain rate. A uniform interpretation of the rate effects of fracture of the tested gabbro-diabase is given on the basis of structural-temporal approach based on a set of fixed material constants. It is shown that temporal dependences of both the compressive and tensile strengths of the tested material can be effectively calculated using the incubation time fracture criterion

Experimental analysis of wear resistance of compacts of fine-dispersed iron powder and tungsten monocarbide nanopowder produced by impulse pressing

The paper presents the results of studying the structure and wear resistance of compacts produced from fine dispersed reduced iron powder (average particle size 3–5μm) with the addition of tungsten carbide (WC) nanopowder with the average particle size of 25–30 nm. The mass fraction of tungsten carbide (wolfram carbide) in the powder composition was 5% and 10% of the total mass. Impulse pressing was conducted using the modified Kolsky method at compacting temperatures of 20 °C to 300 °C. The produced compacts had relative density of over 90%. Metallographic studies using the scanning electronic microscopy method on a TESCAN VEGA II electronic microscope have shown that the produced compacts have a fairly homogeneous fine-grained structure, with a uniform pattern of pore distribution, the form of the pores being close to spherical. X-ray microanalysis using an INCA Energy 250 energy-dispersion spectrometer with scanning along the surface line and transversal laps testifies to the fact that, in the considered temperature range, dynamic compaction does not lead to any noticeable changes in the distribution of the Fe, W and C elements over the bulk of the specimens. The conducted measurements of micro-hardness of the compacts have shown that it increases considerably with the pressing temperature. The produced compacts were tested for wear resistance in a dry friction regime, using the ‘rotating disk – stationary specimen’ configuration. Mass loss of the compacts as a function of testing time is presented. Wear resistance of compacts depends on pressing temperature and concentration of the WC powder in the matrix of reduced iron. It has been experimentally determined that maximal wear resistance is observed in the compacts with the mass fraction of WC equal to 10%, produced at a pressing temperature of 300 °C

Mechanical Response Change in Fine Grain Concrete Under High Strain and Stress Rates

International audienceExperimental results on assessing the effects of strain and stress rates on the behavior of fine-grain concretes are presented. Specimens of fine-grain and fiberreinforced concretes were dynamically tested using the Kolsky method and its modification, the “Brazilian test”. As a result of the experiments, values of the Dynamic Increase Factor (DIF) were determined for both the materials studied. Their curves as a function of strain and stress rates were constructed. The experimental data is compared with the theoretically obtained values of DIF as a function of strain rate available in the literatur

Strain-Rate Dependency of a Unidirectional Filament Wound Composite under Compression

This article presents the results of experimental studies concerning the dynamic deformation and failure of a unidirectional carbon fiber reinforced plastic (T700/LY113) under compression. The test samples were manufactured through the filament winding of flat plates. To establish the strain rate dependencies of the strength and elastic modulus of the material, dynamic tests were carried out using a drop tower, the Split Hopkinson Pressure Bar method, and standard static tests. The samples were loaded both along and perpendicular to the direction of the reinforcing fiber. The applicability of the obtained samples for static and dynamic tests was confirmed through finite element modeling and the high-speed imaging of the deformation and failure of samples during testing. As a result of the conducted experimental studies, static and dynamic stress-strain curves, time dependencies of deformation and the stress and strain rates of the samples during compression were obtained. Based on these results, the strain rate dependencies of the strength and elasticity modulus in the strain rate range of 0.001–600 1/s are constructed. It is shown that the strain rate significantly affects the strength and deformation characteristics of the unidirectional carbon fiber composites under compression. An increase in the strain rate by 5 orders of magnitude increased the strength and elastic modulus along the fiber direction by 42% and 50%, respectively. Perpendicular loading resulted in a strength and elastic modulus increase by 58% and 50%, respectively. The average strength along the fibers at the largest studied strain rate was about 1000 MPa. The obtained results can be used to design structural elements made of polymer composite materials operating under dynamic shock loads, as well as to build models of mechanical behavior and failure criteria of such materials, taking into account the strain rate effects

Investigation of the effect of the grain sizes on the dynamic strength of the fine-grained alumina ceramics obtained by Spark Plasma Sintering

The results of dynamic strength tests of the alumina ceramics with various grain sizes are presented. The ceramics were obtained by Spark Plasma Sintering (SPS) of industrial submicron and fine Al2O3 powders. The heating up was performed with the rate of 10 oC/min; the grain sizes in the ceramics was controlled by varying the SPS temperature and the heating rate as well as by varying the initial sizes of the Al2O3 particles in the powders. The ceramics had a high density (over 98%) and a uniform fine-grained microstructure (the mean grain sizes varied from 0.8 to 13.4 mkm). The dynamic compressing tests were carried out by modified Kolsky method with using split Hopkinson pressure bar. The tests were performed at room temperature using a 20-mm PG-20 gas gun with the strain rate of ~10^3 s-1. The dependence of the dynamic ultimate strength of alumina on the grain size was found for the first time to have a non-monotonous character (with a maximum). The maximum value of the dynamic ultimate compression strength (SY = 1060 MPa) was provided at the mean grain size of ~2.9-3 mkm. The reduction of SY for alumina in the range of submicron grain sizes was shown to originate from the reduction of the relative density of the ceramics sintered at lower SPS temperatures.Comment: 16 pages, 1 table, 6 figures, 28 reference

Dynamic properties of Some Wood Species

The report presents the dynamic test results for wood. Compression tests were done according to Kolsky method, using a 20-mm dia split Hopkinson pressure bar (SHPB). The samples were loaded both along and across the fibers. Obtained are dynamic deformation diagrams for pine, birch and lime. Direction of cutting is noted to affect the mechanical properties of the woods tested. The obtained deformation diagrams are nonlinear and differ in their loading and unloading brunches. For the wood species tested, the stress values resulting in different forms of fracture, such as cracking and spallation, were obtained. Alongside with the SHPB tests, plane-wawe experiments were conducted and shock adiabates for the wood samples were obtained.Cette communication représente les résultats des épreuves dynamiques sur la lignine. Les épreuves sur la compression sont exécutés à la méthode de Kolsky en utilisant le tige de coupe a 20 mm de Hopkinson. La charge des modèles est exécutée de long en large des fibres. Des diagrammes dynamiques sur la déformation de pin, de bouleau, de tilleul sont obtenues grâce aux épreuves. On a marqué l'influence de la direction de la découpure d'un modèle sur les propriétés mécaniques des variétés de lignine épreuvées. Les diagrammes obtenues sur la déformation sont non-linéaires et se diffèrent par la chargement et la déchargement. Pour les variétés de lignine épreuvées on a obtenu des significations des tensions qui détruient la lignine p.ex. fendille, casse. On a exécuté des expériences sur des ondes plats et on a obtenu des adiabates de choc de la lignine