Static Mechanical Parameters Research Articles

Study of Impact Dynamic Characteristics and Damage Morphology of Layered Rock Mass

To explore the dynamic mechanical properties and damage evolution law of the more common layered rock masses in geotechnical engineering, this paper determined the Holmquist–Johnson–Cook (HJC) constitutive model parameters of dolomite, gray sandstone, and limestone according to the static mechanical parameters of the rock mass. We used Hypermesh/ANSYS software to establish the numerical analysis model, carried out the dynamic impact numerical simulation of the layered rock mass, and analyzed the stress wave propagation characteristics, dynamic stress–strain relationship, energy dissipation, and damage evolution laws of layered rock masses under different combinations. At the same time, this paper analyzed the stress characteristics of the layered rock mass and studied its failure characteristics. The research results show that the wave impedance matching relationship alters the dynamic characteristics of the layered rock mass; however, with the increase in impact velocity, the difference gradually weakens. The difference in elastic modulus leads to different initial failure modes of layered rock masses, and the quality of the wave impedance matching relationship leads to differences in the law of damage evolution of layered rock masses. Under different combination forms, the failure degree and failure modes of the two parts of the layered rock mass are different.

Acoustic tomography outputs in comparison to the properties of degraded wood in beech trees

The interpretation of the outputs of acoustic tomography is often altered by different physical and mechanical parameters. Detailed information on the relationships between static mechanical properties and dynamic parameters of intact and degraded green wood can improve the results of this device-supported method used for tree stability assessment. This research presents a graphic and statistic comparison of acoustic tomography outputs with the laboratory assessed material parameters. The analysis was based on the relationship between the dynamic and static mechanical parameters of four cross-sections from two living tree stems. The occurrence of seven white and soft rot fungi was taken into consideration. The influence of density (uprho) on stress-wave propagation (v) was proved. A strong correlation between the dynamic moduli of elasticity ({E}_{dyn}) and compressive strength (upsigma) is reported. A higher heterogeneity of wood degradation among the cross-section can lead to an underestimation of the defect during AT assessment. The dynamic modulus of elasticity {E}_{dyn} was less influenced than v by the heterogeneity of degraded wood. Therefore, {E}_{dyn} can be used to form a better interpretation of acoustic tomography assessment of standing beech trees. Due to the complexity of the topic, further investigation of previously mentioned relationships is still needed.

Dynamic Mechanical Properties of Slag Mortar with Alkali-Resistant Glass Fiber

To investigate the influence of alkali-resistant glass fiber on the dynamic mechanical properties and microstructure of slag cement mortar (SCM), five SCM blocks with different volumes of alkali-resistant glass fiber (0%, 0.25%, 0.5%, 0.75%, and 1%) were prepared. A split Hopkinson pressure bar (SHPB) test device with a diameter of Φ50 mm was used to test the impact compression under different loading pressures. In this way, the stress–strain curve of SCM under average strain rates corresponding to different loading air pressures is obtained, and the relationship between the ultimate toughness, the dynamic increase factor (DIF), and the fiber content of SCM can be comprehensively analyzed in combination with the dynamic and static mechanical parameters. Research results showed that, with the increase in fiber content, the static compressive strength of the SCM showed a trend of first increasing and then decreasing, where 0.75% can be the optimal one with the maximum compressive strength. Under the impact load, the dynamic compressive strength of the SCM had a positive correlation with the average strain rate. Within the strain rate range of 75.03 s−1~141.47 s−1, When the fiber volume content is 0.75%, the dynamic compressive strength, ultimate toughness and DIF of SCM are higher than those of other groups, showing good impact resistance. According to the analysis of SEM images, the bonding performance between alkali-resistant glass fiber and cement matrix was strong, and the fibers were interlaced in the mortar to form a network structure, which has a good effect on toughening and strengthening the SCM.

Rock Mechanical Properties and Breakdown Pressure of High-Temperature and High-Pressure Reservoirs in the Southern Margin of Junggar Basin

The mechanical properties of the high-temperature and high-pressure reservoirs in the southern margin of Junggar Basin have not been clearly understood, which correspondingly results in uncertainties when predicting the breakdown pressure. To address this issue, firstly, rock mechanical experiments under high temperature, high confining pressure, and high pore pressure were carried out. Secondly, empirical formulas related to the transformation of dynamic and static mechanical parameters in the regional strata were proposed. Finally, the existing prediction model for the formation breakdown pressure was improved by taking the wellbore seepage and thermal stress into consideration. Results show that under the reservoir condition of high temperature and high pressure, the rock sample tends to form closed shear cracks. High temperature causes thermal damages and the reduction of the compressive strength and elastic modulus, while the combined effects of high confining pressure and pore pressure enhance the compressive strength and plasticity of the rock sample simultaneously. Based on the correlation analysis, it is found that the static elastic modulus is linearly related to the dynamic value, while static Poisson’s ratio is a quadratic function of the dynamic value. These fitting functions can be used to obtain the profiles of static elastic modulus and Poisson’s ratio based on their dynamic values from the logging interpretation. Besides, the improved prediction model for the rock breakdown pressure can yield more accurate results indicated by the error less than 2%. Therefore, the proposed breakdown pressure prediction model in this study can provide theoretical guidance in the selection of fracturing truck groups and the design of the pumping schedule for high-temperature and high-pressure reservoirs.

Anisotropic dynamic and static mechanical properties of organic-rich shale: The influence of stress

Understanding the relationship between dynamic and static mechanical properties of organic-rich shales is crucial for successful in situ stress profile prediction and hydraulic fracturing stimulation in unconventional reservoirs. However, the relationship between dynamic and static properties remains ambiguous, considering the complex rock microstructure and subsurface stress environment. We have reported pseudotriaxial tests on a pair of outcrop Eagle Ford shale plugs, with the axial load applied perpendicular and parallel to bedding planes, to investigate the effects of intrinsic anisotropy and anisotropic stress on dynamic-static relationships. The bedding-parallel Young’s modulus is larger than the bedding-normal one dynamically and statically, whereas there exist complex relations among three static Poisson’s ratios, which are attributed to the intrinsic anisotropy induced by the lenticular texture and finely laminated alignment of kerogen. Along with a stress increment, static tests respond to superpositions of the elastic, viscoelastic, and nonelastic properties, whereas dynamic tests, with more than two orders of magnitude smaller strain amplitude, only reflect the elastic properties of rocks. As a result, the static properties characteristically exhibit more stress dependence than the dynamic properties. Moreover, the evolutions of static properties, especially two static Poisson’s ratios in the horizontal plug, are significantly influenced by the applied stress orientation with respect to the bedding plane. Lastly, we calculate four independent stiffnesses using the five static mechanical parameters with the assumption of transverse isotropy to compare with those calculated from ultrasonic velocities at different stress levels. Finally, when the deviatoric stress is approximately 20 MPa, static parameters derived from stress loading, unloading, and reloading almost intersect together. At this stress level, dynamic and static stiffnesses demonstrate a reasonable correlation with the fitting coefficient of approximately 1.4.

Dynamic tests and mechanical model for water-saturated soft coal with various particle gradations

Particle gradations significantly affects the dynamic response of water-saturated soft coal. To obtain the dynamic response of soft coal to various particle gradations, static and dynamic mechanical properties of water-saturated soft coal with different particle gradations were tested and compared. During these processes, the enhancement coefficient of the dynamic mechanical parameters to the corresponding static mechanical parameters was set as an index to describe the effect of non-uniformity coefficient Cu and median diameter d50. The results demonstrate that both the static and dynamic mechanical parameters of the water-saturated soft coal were affected by particle gradations. The enhancement coefficient was affected by both the d50 and Cu, which was microscopically attributed to effect of the d50 and Cu on the average dynamic liquid bridge force and scale dynamic rupture energy among the particles based on the microstructure and dynamic fracture evolution processes. In addition, the dimensionless scale rupture energy model among the water-bearing particles varied with the d50 and Cu were further established and applied to discuss the effect mechanism of particle gradations on the dynamic response of water-saturated soft coal. On this basis, the support measures of roadways in coal seam with different particle gradations were further discussed.

Degradation model of the dynamic mechanical properties and damage failure law of sandstone under freeze-thaw action

In the construction process of alpine regions, the construction zone is often subjected to blasting vibrations, heavy truck transportation vibrations, earthquakes and other dynamic loads. It is of great significance to analyse the dynamic mechanical properties of a rock mass under the coupling action of freeze-thaw cycles and dynamic loading. In this paper, the degradation laws of the static mechanical parameters and dynamic mechanical parameters and the failure modes of the sandstone are studied by static mechanical tests, electron microscopic tests and uniaxial impact compression tests on sandstone samples with different numbers of freeze-thaw cycles under impact loading. The test results show that the dynamic increase factor (DIF) is affected by the number of freeze-thaw cycles and the strain rate, and the strain rate is the dominant factor. For the dynamic increase factor of the elastic modulus DIFE, the effect of the strain rate on the DIFE is much smaller than that on the DIF, and the variation in the DIFE decreases with the increase in the number of freeze-thaw cycles. When the strain rate is constant, the dynamic compressive strength of the sandstone samples decreases exponentially with an increase in the number of freeze-thaw cycles. When the number of freeze-thaw cycles is constant, the dynamic compressive strength of the sandstone samples increases linearly with increasing strain rate. The dynamic compressive strength degradation model of sandstone considering the number of freeze-thaw cycles and strain rate is obtained by fitting the experimental data. In the early stage of the freeze-thaw cycle, the main dynamic failure mode of sandstone under the action of freeze-thaw cycles and a lower impact load is the axial splitting failure mode, while the dynamic failure mode of sandstone under freeze-thaw action and a higher impact load is the crushing failure mode. The research results can be used to predict the dynamic compressive strength of rock under different strain rates and varying numbers of freeze-thaw cycles and provide a theoretical basis for similar engineering construction.

Modified method for fracability evaluation of tight sandstones based on interval transit time

Fracability is a property that indicates how easy reservoir rocks can be fractured in hydraulic fracturing operations. It is a key parameter for fracturing design and evaluation. In order to utilize continuous logging data to predict fracability, synchronous tests of dynamic and static mechanical parameters of rocks under different confining pressures were conducted on 13 tight sandstone samples derived from the central Junggar Basin, China. A modified formula between dynamic and static mechanical parameters was established. Fracability of the tight reservoir in the Junggar Basin was then evaluated based on brittleness index, fracture toughness, and fracability index. The effectiveness of fracturing was analyzed combined with the oil testing curve after hydraulic fracturing. The results show that: (1) The distribution of oil-bearing formations in the studied area coincides well with stratum of higher fracability index. (2) The critical fracability index is determined to be 0.3, three formations are selected as fracturing candidates, and a thin mudstone interbed is identified in the oil-bearing formation. (3) Well testing curve verifies the reliability of the fracability evaluation method and the accuracy of the modified formula between dynamic and static mechanical parameters. This study provides useful information for improving fracturing operations of tight oil and gas reservoirs.

Brittleness Logging Evaluation of Shihezi Formation in Yanchang Gas Field in Ordos Basin Based on Rock Mechanical Characteristics

Brittleness determines the effect of reservoir fracturing and is important for increasing the production of unconventional oil and gas. The reservoir of Yanchang gas field is characterized by low porosity, low permeability and strong heterogeneity, which make it difficult to produce industrial gas flow under natural conditions. Triaxial compression tests in sandstone samples of Shihezi formation in Yanchang gas field show that the main fracturing mode is multiple horizontal splitting, the main cracks are completely fractured, and the brittleness index ranges from 46.1% to 51.4%. After S-wave velocity model in the study area is established, the conversion relation of dynamic and static mechanical parameters could be obtained, that is,Es=0.4142Ed+10.769(R2=0.8387),and μs=1.1076 μd-0.068(R2=0.7366), according to which, the dynamic mechanics parameters calculated by well logging can be adjusted, and then the reservoir brittleness could be quantitatively evaluated. Combining with the brittleness index calculated by mineral component method, it can be concluded that the brittleness calculated by well logging is reliable and the brittleness of Shihezi formation in Yanchang gas field is high, which is beneficial for reservoir fracturing.

Experimental analysis of dynamic and static mechanical properties of deep thick anhydrite cap rocks under high-stress conditions

Across the globe, the formation of large oil and gas fields is always associated with a wide range of anhydrite cap rocks. Thus, an accurate analysis of the dynamic and static mechanical properties of anhydrite rocks is required. A deep thick anhydrite cap rock is developed in the Paleogene formation of the southwestern Tarim Basin, NW China. In this paper, we designed mechanical and acoustic synchronization tests and acquired the corresponding parameters. The effects of stress and mineral composition on the dynamic and static mechanical properties of the anhydrite rock were analyzed systematically. The results indicate that under uniaxial conditions, the anhydrite rock showed obvious brittle rupture characteristics, while under triaxial conditions, the shear rupture characteristics were obvious. The stress–strain curves of the anhydrite rocks under triaxial conditions can be divided into five stages: initial compression stage, linear elasticity stage, nonlinear steady extension stage, nonlinear unsteady extension and failure stage and post-peak stress stage. An increase in the anhydrite content can delay the weakening time of the anhydrite rocks, greatly improving the rock strength. Under high-stress conditions, the anhydrite mineral particles can accumulate large amounts of energy, exhibit a long period of creep behavior and produce significant additional stresses. The anhydrite composition can improve the strength and rigidity of the anhydrite rocks. However, anhydrite rock with a high anhydrite content will also have strong plasticity. The greater the stress environment that the anhydrite rock bears, the stronger its plasticity will be. The anhydrite component can improve the ability of the anhydrite rocks to resist shear rupture. Compared to the anhydrite mudrocks (AMR), argillaceous anhydrite rocks (AR) have higher VP, VS and VP/VS values. There is a very good positive correlation between VP/VS and the anhydrite content. A regression model of the longitudinal and shear wave time differences of the anhydrite rocks is obtained, which can be used for the prediction of the shear wave time difference. The dynamic Young’s modulus, Poisson’s ratio and shear modulus of the AR are higher than those of the AMR. The regression models of dynamic and static mechanical parameters of the anhydrite rocks are also obtained. These models will be valuable in the evaluation of mechanical characteristics for similar types of anhydrite rocks worldwide.

Experimental Study on Rock Mechanics Parameters-A Case of the Sand Conglomerate Reservoir in M2 Well Area

This paper presents the acoustic characteristics tested on 20 groups of cores (20 vertical samples and 60 horizontal samples) from the sand conglomerate reservoir in Baikouquan and lower Wuerhe Formation (two wells in the M2 well area). The average values of dynamic modulus of elasticity and Poisson's ratio of rocks from Baikouquan Formation are 32.1 GPa and 0.2055 respectively, and those of lower Wuerhe Formation are 28.4 GPa and 0.2425 respectively. The three axis rock mechanics test device is used to test the stress-strain curves of the corresponding rock samples. The sand-conglomerate samples in this area generally have good brittleness characteristics; the static modulus of elasticity and Poisson's ratio of the corresponding rock samples are 13.7GPa and 0.2858 respectively, and those of rocks from lower Wuerhe Formation are 14.9GPa and 0.2565, respectively. In general, there is a good correlation between P&S wave velocity, and poor correlation in the dynamic and static mechanical parameters.

On the Temperature-Related Mechanical Properties of UV-LIGA Nickel Material

MEMS nickel material is commonly used for structural material in micro devices. In order to study the effect of environmental temperature on its mechanical properties,this paper has built up a experimental system which can measure the temperature-related static mechanical parameters of the UV-LIGA nickel material. By using the system for uniaxial tensile experiments of the micro specimen under different temperature, the stress-strain curves of the micro specimen under different temperature were obtained; the mechanical parameters of the micro specimen such as elastic modulus, yield stress and failure stress under different temperature were also calculated out;Finally, the relationship between temperature and mechanical parameters including elastic modulus, yield stress and failure stress was analyzed.

The effect of sterilization on the dynamic mechanical properties of paired rabbit cortical bone

The optimal sterilization method for load bearing allografts remains a clinical concern. Recently, supercritical carbon dioxide (SCCO2) treatments have been shown to be capable of terminally sterilizing a range of bacteria and viruses, while preserving the static mechanical properties of cortical bone. This study evaluated the effect of SCCO2 treatment compared with two doses of gamma irradiation, on clinically relevant dynamic mechanical properties of cortical bone. Quasi-static testing was also performed to compare the impairment of treatment. Whole paired adult rabbit humeri were dissected and randomly assigned into either SCCO2 Control, SCCO2 Additive or gamma irradiation at 10 or 25kGy treatment groups. The bones were treated and mechanically tested in three-point bending, with the lefts acting as controls for the treated rights. Maximum load, energy to failure and stiffness were evaluated from static tests. The number of cycles to failure was determined for fatigue at 6–60% of the ultimate load. This study found that SCCO2 treatment with or without additive did not alter static or dynamic mechanical properties. Gamma irradiation had a deleterious dose dependent effect, with statistically significant (p<0.05) reductions in all static mechanical parameters at 25kGy. This effect was increased in fatigue with statistically significant decreases in both the 10 and 25kGy dose groups. This study highlights the expediency of SCCO2 treatment for load bearing bone allograft processing as terminal sterilization can be achieved while maintaining both the quasi-static and dynamic mechanical properties of the graft.

Effects of mechanical properties of concrete constituents including active mineral admixtures on fatigue behaviours of high performance concrete

ABSTRACTIn order to explore the links between the macroscopic and microstructural characteristics of concrete with admixtures of active mineral additions, four series of concrete prisms, of mortar matrix prisms and mortar‐aggregate Interfacial Transition Zone (ITZ) are prepared and tested under monotonic and cyclic loads. Five static mechanical parameters (compressive and bending strength, fracture energy, elastic modulus, Poisson ratio) and bending fatigue performance (fatigue life, critical maximum displacement and strain, fatigue damage) of such materials are experimentally evaluated. The results show that degradation laws of concrete properties under both monotonic and cyclic loads vary with the different cohesive strength ratio and elastic modulus ratio of ITZ and mortar matrix. The single or double additions of ground slag and fly ash with optimized mass fractions remarkably enhance the static and bending fatigue properties as well as change the failure mechanisms of concrete.

Tensile and fatigue behavior of thin-walled cylindrical specimens under temperature gradient condition

In the present study, a temperature gradient system was designed with the aim of carrying out the tensile and fatigue test of thin-walled cylindrical alloyed steel (30CrMnSi). The tensile test under different temperatures was first carried out to obtain the static mechanical parameters. And then a three-dimensional (3D) finite element model was constructed to further study the deformation behavior under temperature gradient by the finite element analysis (FEA). The FE result was in good agreement with that of the experiment. Following this, the tensile fatigue test was performed under cooled air and no-cooled air to investigate the influence of the temperature gradient on fatigue life-time, respectively. The influence of cooled air under the lower nominal stress on fatigue life was not obvious than that of higher nominal stress. Finally, the scanning electron microscopy (SEM) was employed to investigate the fracture mechanism. The microstructure revealed that the fracture first occurred at the zone where there was a lower temperature.

Relationship Between Physical and Mechanical Parameters of Coal Measures Rocks and Acoustic Wave Velocity

AbstractThe longitudinal and transverse wave velocity of sedimentary rock of coal measures is systematically analyzed by ultrasonic‐time dynamic testing. The parameters of dynamic elasticity are calculated. Static mechanical parameters of the rocks are synchronously tested. The qualitative and quantitative relationships between the dynamic and static elasticity parameters, and between the physical and mechanical parameters and acoustic wave velocity of the rocks are established. The research results show that there is a good positive correlativity between dynamic modulus of elasticity and the longitudinal or transverse wave velocity, but there is no such positive correlativity between dynamic Poisson's ratio of the rocks and its longitudinal or transverse wave velocity. The dynamic elastic modulus of the rocks is higher than its static elastic modulus, while the dynamic Poisson's ratio is lower than its static Poisson's ratio, and there is a linear correlativity between them. The relationships between density of the rock, uniaxial compressive strength, tensile strength and the longitudinal or transverse wave velocity are also the positive correlativity, which are best fitted by quadratic function, exponential function and linear function, respectively.

Polyolefins ‐ poly(ethylene oxide) blends: Structure and properties

AbstractStructure and properties of polyolefins‐poly(ethylene oxide) (PEO) blends were studied by combination of thermal analysis, light microscopy and fluorescence probe technique. Mixing and preparation conditions influence the calorimetric behavior, changing heat and temperature of melting and crystallinity degree of blended polymers. Values of the static mechanical parameters as well as flow characteristic parameters of the blends are lower for the higher PEO fraction in the samples. Fluorescence investigation of pyrene (changes in the vibrational fine structure) showed a nonhomogeneous distribution of the probe molecules between polyolefin and PEO environment. From these data the partition coefficient between polyolefin and PEO phase can be calculated and correlated with the crystallinity changes of the mixture composition.