Effect of strain rate on the compressive mechanical behavior. Typically much lower than compressive strength 10% of compressive strength typical table 7. Numerical evaluation of the influence of aggregates on. It has been found that the salt strength increases with the applied stress and strain rates. However, even though the yield and tensile strengths for all samples were different with increasing strain rate, the ultimate tensile strengths of individual az31 sample under. The effect of strain rate on rock strength springerlink.
Variation of compressive strength with size c o 35 x l0. Effect of strain rate on the yield stress of structural. The reservoir rock for many geothermal projects in the upper rhine graben, such as those at soultzsousforets and rittershoffen both france, is porphyritic granite. In order to study this effect of strain rate on strength, a computer model of failure process of rocks was developed with finite element method f. The results showed an increase in compressive deformation with increasing strain and stressing rate, although the rate effect was very small. Technical note the effect of strain rate on rock strength. Quasistatic tests at strain rates of 10 7sec to 10 3sec were conducted using a standard material test machine. Study on dynamic mechanical properties of limestone under. It is observed that the peak stress decreases with temperature.
The results of true strain rate effect are reliable. It is observed that elastic modulus and yield strength increased with increasing strain rate both materials. Pdf effects of strain rate and confining pressure on the. Strain rate effects on steel strength physics forums. They are usually obtained by conducting laboratory tests such as split hopkinson pressure bar shpb test or dropweight test. Because of this, the effect of strain rate on the mechanical behaviour of rock has.
Typically much lower than compressive strength 10 % of compressive strength typical table 7. The strainrate effects on the numerical simulation of. A volume deformation model for brittle rock based on. Strainrate effects on the strength and fragmentation size of rocks. A third degree polynomial has been found to give the best fit to the plot between ultimate strength and strain rate, and youngs modulus and strain rate of rock samples. Effects of strain rate and confining pressure on the deformation. Carter 1 departments of 1civil and 2geological engineering, the university of manitoba, winnipeg, manitoba, canada summary the effect of the strain rate on strength has been evaluated for two widely different. This strain rate hardening effect is particularly pronounced with brittle materials such as rocks.
Uniaxial compressive strength c o x psi 0 50 100 150 specimen length l in. Rock strength decreases with decreasing strain rate apply same amount of strain over a very long period of time 29 compressive strength tensile strength resistance to failure under tensile stress. To practically remove the size effect, strain controlled loading rate s. Results of static and dynamic fatigue tests on tyndallstone, a dolomitic limestone, show an increase in strength with increasing strain or stressing rate although the. Figures 4a and 4b show comparisons of stress strain curves of unfilled polypropylene and talcfilled polypropylene at a strain rate of 5 mir and temper atures of. Based on the understanding of the crack evolution under the effect of the strain rates. In particular, at high strain rates it is necessary to generate a stress wave pulse well.
Strength and fatigue properties of sandstone under dynamic. This minimum value of fn is, by definition, the impact rock strength coefficient fn, as representing the optimum specific crushing energy minimum impact energy per unit volume of 0. Flgures 2 and 3 also show the effect of strain rate on the stressstrain curves of unfilled polypropylene and talcfilled polypropylene parallel to the flow l direc tion. In the ucs tests of rock materials, the loading rate is many times load. The rock strength coefficient fn is graphically determined from the curve f. Jul 28, 2005 the effect of increasing yield and tensile strength with increasing strain strain rate is observed in many, if not most, metals, and even polymers. Strainrate effects on the strength and fragmentation size of. In metals, this would have to do with the rate of dislocationdefect generation and dislocation pileup.
To better understand the effects of size and strain rate on measured rocks, rock specimens with six different sizes were tested at six different strain rates under uniaxial compression using the mts 815 rock mechanics test system. Rock material behavior under dynamic loading depends on the strain rate such that with the increase of strain rate, rock peak strength, strain, and elastic modulus rise. For instance, in case of increase in rock core specimen length from 64 mm to 108 mm, strain rate should be increased 10864 times in comparison to the rate in test of the small specimen. The effects of loading rate on the compressive strength and deformability of intact rocks have long been recognized 14. The effect of strain rate on rock strength nasaads. Strain rate exhibited insignificant effect on fracture strain for the tested materials.
The restriction effect increases with the increasing of strain rate, the stress state of rock sample is not onedimensional stress but approximately. Influence of strain rate on dilatancy and strength of oshima granite. In other words, if the rock is allowed to deform quickly, its yield stress is high and the elastic range is large. Lecture 9 introduction to rock strength david hart. The strength of rock materials is largely affected by water, and the static properties have been widely studied before, while there is virtually no data for dynamic compressive strength of saturated rock at different strain rates. This paper demonstrates that the rock mass strength sensitivity to strain rate may be regarded as the result of competition between the coexisting thermally activated and macroviscous mechanisms, which dominate at different ranges of strain. Effects of strain rate and confining pressure on the. The effect of strain rate on compressive strength of water. Loading rate conditions and specimen size effect on strength and. This paper carries out progressive collapse analysis to research the influence of strain rate effects on collapseresistant capacity, collapse mode, and collapse path of the rc frame structure. Universities and colleges under beijing municipalitynoidht20512, the 973 key state research program. However, the soft components absorbed more energy and deformed more. Size and strain rate are two key factors that dramatically influence the estimation of rock mechanical behaviors. The increase in yield strength at high strain rate as compared with quasistatic strain rate was found to be higher in the alloy than pure magnesium.
The size effect on the strength of geomedia is closely related to the structural hierarchy of rock mass. Effects of size and strain rate on the mechanical behaviors. However, a method fot obtaining the stress corresponding to zero strain rate will be described in section 2. If the pore pressure in the shale is high, increasing the strain rate beyond about 0. The strainrate effects on the numerical simulation of steel beams under blast loads s. Peak strength, mechanical behavior, and shear band sb of anisotropic jointed rock jr were modeled by fast lagrangian analysis of continua flac. The stressstrain curve figure 1 above is a good way of graphically demonstrating this. Extension tests with confining pressure greater than the compressive stress show that the intermediate principal stress as well as the strain rate has an effect on the strength. Effect of strain rate on ultimate tensile strength. The evolution of microcracks in rocks under different strain rates is of great. The experimental data describing the effect of strain rate on strength and stiffness of the.
Changes in the stress strain behaviour were discovered indicating the importance of strain rate on breakage characteristics. The effects of strain rate on the tensile and compressive properties of plain concrete specimens 51 mm in diameter were studied both experimentally and numerically. Smiglewicz et al the effect of strain rate on the impact strength of the highmn steel metalurgija 54 2015 4, 631634 conclusions the studied carried out proved an influence of the deformation rates on the ability to transfer dynamic loads of the studied fe 30 wt. Mechanism underlying dynamic size effect on rock mass strength. This includes detailed understanding of the combined effects of strain rate, confinement, and temperature on the rock behavior. The effect of strain rate on the mechanical behavior of various rocks has been widely studied in compression, tension,,, and bending. It is impossible to test a coupon at zero strain rate andob tain a stressstraindiagram. Effect of strain rate on mechanical behaviour of rocks. We conduct meterscale rock friction experiments loaded at different rates. Effect of strain rate on the yield stress of structural steel. Knowledge of the strength and elastic modulus of a reservoir rock is important for the optimisation of a particular geothermal resource. This paper demonstrates that the rock mass strength sensitivity to strain rate may be regarded as the result of competition between the coexisting thermally activated and macroviscous mechanisms, which dominate at different ranges of strain rates. It is commonly agreed now that the dynamic increase factor dif obtained from impact test is affected by lateral inertia confinement, friction confinement between the specimen and. A disc of soft and deformable copper with a thickness of 0.
It is observed from figure 27 that the true strain rate effect obtained from shpb experimental data of samples with different diameters agrees well, which indicates that the determined true strain rate effect is independent of specimen diameter, thus the inertial effect is indeed eliminated. The effect of temperature on rock plasticity has been explored by several teams of researchers. For each rock type high speed uniaxial compression tests were carried out at six different strain rates over the range 2. Moreover, strength decreases with decreasing strain rate in rock deforming by intracrystalline gliding may be. In this computer model, inhomogeneity of rock specimens can be easily taken into account by changing elastic constants for each element. Lajtai et al 5 investigated the effect of strain rate on deformation for brittle limestone ductile salt rock. Effect of strain rate on the dynamic compressive mechanical. The cs equation has been used extensively in situations where an estimate of the increase of the flow stress due to material strainrate sensitivity is necessary. Horizontal rock beams can be dangerous because of the weak tensile strength rock unit must be. Effect of the strain rate and water saturation for the dynamic tensile strength of rocks p.
Numerical investigation of the dynamic compressive behaviour. Fault peak strength and strength drop can increase with increasing. Effects of temperature and strain rate on the tensile. Results of static and dynamic fatigue tests on tyndallstone, a dolomitic limestone, show an increase in strength with increasing strain or stressing rate although the rate effect is very small. Strain rate effect on the progressive collapse analysis of rc.
Loading rate conditions and specimen size effect on. Effects of stress rate on uniaxial compressive strength of. The tensile strengthstrain rates curves of the alloys at 225c are plotted in figure 2. The ratio of stress to strain is the elastic modulusstiffness, but the stress, and only the stress, defines the strength of the material. The strain rate effect can influence the seismic responses of reinforced concrete rc structures because the constitutive relationship of concrete and rebar is rate dependent. Jun 23, 2016 size and strain rate are two key factors that dramatically influence the estimation of rock mechanical behaviors. The strainrate effects on the numerical simulation of steel. The effect of strain rate on fracture toughness of bone was investigated via compact tension specimen models which were created using the finite element program, abaqus version 6. With the increase of strain rate and confining pressure, rock strength was increased significantly and material strength increased more quickly under high strain when theres a limit of below. The solid red curve in figure 2 illustrates the effects of strain rate on the tensile strength of the quasibrittle solids captured by the sigmoid transition 4. The effect of rate of deformation on dry spring gulch rock pile material was investigated with a compaction density of 1850 kgm 3 at four different rates, 0. The dislocations diffuse through the crystal structure from inside grains to grain boundaries.
However, the dynamic strength of the rock drops significantly faster than the. Effect of strain rate on strength in uniaxial compression. Microcrack evolution and associated deformation and strength. The results showed an increase in compressive strength with increasing strain and stressing rate, although the rate effect was very small. The failure criterion of rock was a composite mohrcoulomb criterion with tension cutoff and the postpeak constitutive relation was linear strain softening. Pdf effect of strain rate on the mechanical properties of salt rock. Enhanced strain rates resulted in an obvious increase in fracture strength. Effect of the strain rate and water saturation for the. Effects of strain rate and surface cracks on the mechanical. Effects of strain rate on tensile properties and fracture. A stressstrain curve showing the relationship between stiffness and yield strength yield point.
Bradford centre for infrastructure engineering and safety, school of civil and environmental engineering, the university of new south wales, australia abstract currently, there is significant interest amongst computational mechanics. An investigation, therefore, was carried out by the authors to study the effect of strain rate on mechanical behaviour of some indian rocks. The effect of the strain rate on strength has been evaluated for two widely different rock types, a brittle limestone tyndallstone and a ductile salt rock lanigan potash rock. For az31, the elongations of were approximately 15% which showed that there is no influence of strain rates on elongation. The dynamic compressive strength of rock materials increases with the strain rate. Request pdf strainrate effects on the strength and fragmentation size of rocks rock mass possesses a complex structural hierarchy. Summarythe effect of the strain rate on strength has been evaluated for two widely different rock types, a brittle limestone tyndallstone and a ductile salt rock. Natural deformations are very slow and to study the effect of strain rate on rock behaviour, the influence of strain rate shows that as the strain rate increases, so does the yield stress. The cs material model is a simple elastoplastic, strainrate hardening model. Strain rate effect on fault slip and rupture evolution. The effect of the strain rate on strength has been evaluated for two widely different rock types, a brittle limestone tyndallstone and a ductile salt roc results of static and dynamic fatigue tests on tyndallstone, a dolomitic limestone, show an increase in strength with increasing strain or stressing rate although the rate effect is very small. Strain rate has little effect on uniform elongation and total elongation for advanced high strength steels ahss such as dp590 and dp780. For rock salt such effects have been studied by various researchers 58. Strainrate effects on the strength and fragmentation size.
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