Ultimate Shear Stress Research Articles

Research of rheological characteristics of the mixture as a way to create a new backfill material with specified characteristics

The transportation of a backfill mixture prepared on the basis of enrichment waste of water-soluble ores and an emergency stop of its movement were modeled in laboratory conditions. The rheological characteristics of the backfill mixture were obtained experimentally: viscosity; ultimate shear stress. It was found that the deterioration of the rheological characteristics of the backfill mixture occurs with an increase in the time of movement of the mixture. After 14 min the characteristics do not satisfy the criterion that allows the use of gravity delivery, which corresponds to a delivery length of 1.35 km, at a movement speed of 1.8 m / s. It was revealed that the critical time for gravity transportation is 10–11 min, which corresponds to the ultimate delivery length of up to 1.1 km. It has been established that stopping the transportation at this level for more than 25–30 min is critical and causes the backfill mixture to harden and block the pipeline. The use of lingosulfonate as an activating additive in an amount of 1% of the total dry mass improves the rheological properties, which increases the length of transportation by 25–30%.

Magnetorheological elastomers characterization under shear loading up to failure: A magneto-mechanical multivariate analysis

This work analyses the shear behavior of magnetorheological elastomers (MRE), a class of smart materials which presents interesting magneto-mechanical properties. In order to determine the effect of several variables at a time, a design of experiment approach is adopted. A set of several samples of MRE was manufactured, by varying the weight fraction of ferromagnetic material inside the viscoelastic matrix and the isotropicity of the material, by adding an external magnetic field while the elastomeric matrix was still liquid. The mechanical behavior of each sample was analyzed by conducting cyclic tests at several shear rates, both with and without an external magnetic field. Moreover, in order to estimate the maximum shear stress, the specimens were loaded monotonically up to failure. Shear stiffness, maximum shear stress and specific dissipated energy were calculated on the basis of the experimental data. The results were analyzed using an Analysis of Variance (ANOVA) to assess the statistical influence of each variable. The experimental results highlighted a strong correlation between the weight fraction of ferromagnetic material in each sample and its mechanical behavior. Moreover, the dissipated energy of the MRE drops down when the magnetic field stiffens the behavior or the shear rate increases. The ultimate failure shear stress is strongly affected by the external magnetic field, increasing it by nearly 50%. The ANOVA on the results provides a simple phenomenological model is built for each output variable and it is compared with the experimental tests. These models produce a fast and fairly accurate prediction of each analyzed response of the MRE under various shear rates and applied magnetic fields.

Methodology for brick/mortar interface strength characterization at high temperature

The interface between bricks and mortar is often the weakest part of masonry structures. For refractory linings, the interface strength must be measured at high temperature. Adapted slant shear tests and a new dedicated tensile test set up are proposed here for this purpose. To test the ability of the proposed method, it was applied on two representative brick/mortar couples from room temperature up to 1450 °C. Slant shear tests were conducted to measure ultimate compression and shear stresses and to identify temperature dependent parameters of the Mohr-Coulomb failure criterion. Tensile tests were performed to identify the tensile cut-off. Depending on the brick/mortar couples, the failure can appear at the interface or in the mortar. Cohesion and tensile strength decrease sharply over 900 °C.

Testing methods for shear strength of bond line between concrete and different types of engineered wood

This paper identified a reliable testing method for determining the shear strength of bond lines between concrete and engineered wood. The identification was carried out based on analytical derivations and experimental tests on concrete (compressive strength of 24.8 MPa) and engineered wood composite connections glued by two types of epoxy. Forty specimens were tested under two commonly used test setups, i.e. 20 double-shear tests on timber-concrete composite specimens with a bond length of 50 mm and another 20 compression-shear tests on specimens with a bond length of 300 mm. The result analysis showed that there was no significant statistical difference between the shear strength of the bond lines (around 2.3 MPa) as well as between the failure modes obtained (dominated by concrete failure), regardless of the considered bond lengths and adhesive types investigated. The analysis used a quasi-non-linear fracture mechanics model, considering the boundary conditions of the tests. The analytical model revealed that the ultimate shear stress is approximately uniformly distributed both in the double-shear and in the compression-shear tests, so the spatially averaged shear stress value can approximate the critical shear stress of the bond line with sufficient accuracy. However, if the failure occurred in the wood or the strength of the concrete was higher, the shear stress distribution at ultimate load in the compression-shear tests with a bond length of 300 mm would not be uniform. The maximum shear stress value, which is significantly larger than the average one, occurred at the fixed (or supporting) end of the bond line. Even so, in the shear tests with a bond length of 50 mm, the average ultimate shear stress value was still close to the shear strength with a difference smaller than 5%. Hence, a bond length of 50 mm is recommended for determining the shear strength of a bond line between normal strength concrete and engineered wood when using a push-out shear test setup.

Self-compacting concrete with TPP fly ash

The prospects and problems of multilevel optimization of the dispersed composition of self-compacting concrete are considered with the aim of significantly increasing its construction and technical properties, with a minimum content of binder. Theoretical and practical principles have been developed for the design of disperse-particle size distribution of self-compacting concrete mixtures for high-strength concrete, in which various types of dispersed mineral modifiers (MM) are used, including fly ash of thermal power plants (TPPs). Effective MMs for self-compacting concrete mixtures are varied granular blast furnace slag and fly ash of thermal power plants, which create a dense packing structure of particles of a multicomponent binder with a low degree of disorder and ensure a decrease in the consumption of Portland cement in concrete by 43-48%. With such a choice of the type and parameters of MM, self-compacting concrete mixtures are characterized by lower water content, high viscosity and a low level of ultimate shear stress, ensuring its high-quality compaction. To study the properties and structure of concrete, quartz sand with Mk −2.58 and granite crushed stone were used as a fine aggregate. 5-10 and 10-20mm, Portland cement of class CEM I 52.5N, finely dispersed blast furnace granulated slag, fly ash of thermal power plants. and Glenium 430 superplasticizer. Research methods: the shape and size of the dispersed particles of the components were determined by a laser analyzer, the mobility of the concrete mix according to GOST 10181-2014, the compressive strength of concrete according to GOST 10180-2012. The structure of the cement stone was studied by thermographic and x-ray phase analysis methods. The strength of concrete only from the use of fly ash from TPPs instead of the equivalent part of fine aggregate increases by 4.1−9.2%.

Экспериментальные исследования сопротивления мерзлого грунта продольным перемещениям трубопровода при изменении температуры и влажности

The significant part of the frozen soils, common of the northeastern regions of the laying of pipelines, loses its bearing capacity when the temperature rises to the values of melting ice. In turn, the loss of the design position of the pipeline section located in the thawed soil area causes unacceptable deformations, which can lead to incidents and accidents. The most dangerous places arise at the boundaries of sites with different soils properties, and primarily at the border of frozen and thawed soils. Currently, to evaluate the thermal interaction of pipelines with frozen thawing soils, data are used for ordinary thawed soils, however standard methods are not suitable in these cases, since they do not take into account a sharp change in the properties of frozen soils during thawing. The authors conducted studies of soil resistance (coefficient of soil reaction) to the longitudinal displacements of the pipeline depending on the temperature and humidity of the soil. For this purpose, an experimental model of a pipeline in frozen ground was developed. The main characteristics of the model and the experimental technique are described in detail. The results of studies of the coefficient of soil reaction in the longitudinal direction, as well as the ultimate shear stresses depending on the temperature and humidity of the soil, the type of soil and the depth of the pipeline are presented. The dependence of the coefficient of soil reaction on the ratio of the depth of the pipeline to its diameter is shown. It was established that at a temperature t = –8... –10 °С and humidity w = 10...15 %, the highest value of the coefficient of soil reaction is achieved. In the absence of moisture, the temperature does not affect the coefficient of soil reaction. The lowest coefficient of soil reaction for frozen soils is achieved at a positive soil temperature.

Biomechanical properties and thermal characteristics of frozen versus thawed whole bone.

Biomechanics research often requires cadaveric whole bones to be stored in a freezer and then thawed prior to use; however, the literature shows a variety of practices for thawing. Consequently, this is the first study to report the mechanical properties of fully frozen versus fully thawed whole bone as 'proof of principle'. Two groups of 10 porcine ribs each were statistically equivalent at baseline in length, cross-sectional area, and bone mineral density. The two groups were stored in a freezer for at least 24 h, thawed in air at 23 °C for 4 h while temperature readings were taken to establish the time needed for thawing, and once again returned to the freezer for at least 24 h. Mechanical tests to failure using three-point bending were then done on the 'frozen' group immediately after removal from the freezer and the 'thawed' group when steady-state ambient air temperature was reached. Temperature readings over the entire thawing period were described by the line-of-best-fit formula T = (28.34t - 6.69)/(t + 0.38), where T = temperature in degree Celsius and t = time in hours, such that frozen specimens at t = 0 h had a temperature of -17 °C and thawed specimens at t = 1.75 h reached a steady-state temperature of 20 °C-23 °C. Mechanical tests showed that frozen versus thawed specimens had an average of 32% higher stiffness k, 34% higher ultimate force Fu, 28% lower ultimate displacement δu, 40% lower ultimate work Wu, 43% higher elastic modulus E, 37% higher ultimate normal stress σu, and 33% higher ultimate shear stress τu. Whole ribs failed at midspan primarily by transverse cracking (16 of 20 cases), oblique cracking (three of 20 cases), or surface denting (one of 20 cases), each having unique shapes for force versus displacement graphs differentiated mainly by ultimate force location.

Formation of Organic Deposits in Model Petroleum Systems

The formation of organic deposits in model petroleum-containing systems of various compositions has been studied. Introduction of asphaltene–resin substances into a model paraffin system reduces the amount of precipitated wax deposit to 40 wt %; significantly changes the ratio of liquid and solid hydrocarbons in the n-alkane composition of the deposits, shifting the distribution maximum towards a lower molecular weight; and substantially reduces the mechanical strength. In the model paraffin system in the presence of resins and asphaltenes, which contain a greater amount of condensed aromatic structures and a smaller amount of paraffin structures, a precipitate is formed with an increased proportion of the liquid phase. The deposits are characterized by lower strength of the crystal lattice and, hence, a decreased value of ultimate shear stress.

Optimisation of Shear and Lateral–Torsional Buckling of Steel Plate Girders Using Meta-Heuristic Algorithms

The shear buckling of web plates and lateral–torsional buckling are among the major failure modes of plate girders. The importance of the lateral–torsional buckling capacity of plate girders was further evidenced when several plate girders of a bridge in Edmonton, Alberta, Canada failed in 2015, because insufficient bracing led to the lateral buckling of the plate girders. In this study, we focus on the optimisation of the cross-sections of plate girders using a well-known and extremely efficient meta-heuristic optimisation algorithm called the harmony search algorithm. The objective of this optimisation is to design the cross-sections of the plate girders with the minimum area that satisfies requirements, such as the lateral–torsional buckling load and ultimate shear stress. The base geometry, material properties, applied load and boundary conditions were taken from an experimental study and optimised. It was revealed that the same amount of load-carrying capacity demonstrated by this model can be achieved with a cross-sectional area 16% smaller than that of the original specimen. Furthermore, the slenderness of the web plate was found to have a decisive effect on the cost-efficiency of the plate girder design.

Characterization and modeling the flow behavior and compression strength of the cement paste modified with silica nano-size at different temperature conditions

In this study, the effect of nano-silica (NS) as an additive to the Ordinary Portland Cement was evaluated and quantified. Scanning Electronic Microscope (SEM), X-ray diffraction (XRD), Thermogravimetric Analysis (TGA), Fourier-Transform Infrared Spectroscopy (FTIR), and Raman Spectroscopy analysis were used to identify the cement and NS content. Experimental tests and modeling were conducted to quantify and predict the rheological properties of the modified cement in the liquid phase such as yield stress, maximum shear strength, plastic viscosity, and mechanical properties such as compressive strength of cement after hardening. The cement modified with NS was tested at water-to-cement ratios (w/c) of 0.35 and 0.45 and temperatures ranging from 25 °C to 75 °C. Non-linear regression (NLR) based model was used to evaluate the effect of nano-silica on the rheological properties and compressive strength of cement. Modifying the cement with nano-silica substantially reduced the volume of Ca (OH)₂. TGA tests showed that the 1% nano-silica additive leads to a decrease in the total weight loss of the cement at 800 °C by 82% due to the de-carbonation of CaCO3 in the hydrated compound and due to interacting the NS with the cement. The addition of NS increased the ultimate shear stress (τmax) and the yield stress (τo) by 15% to 53% and 23% to 186% respectively based on the NS content, w/c, and temperature. An additional 1% of NS to the cement paste the compressive strength increased by 14%–66% based on the curing time, and w/c. The unprecedented conclusions can be drawn in this study, which is the effect of the nano-silica content, water-cement-ratio and temperature effect on the plastic viscosity, yield stress and shear stress limit in the fresh stage (slurry) of the cement paste and also, the impact of the nano-silica content, water-cement-ratio and curing time on the compressive strength in the hardened stages of the cement modified with nano-silica were modeled. The experimental and the modeling results illustrated that the SiO2 nanostructure, which was mixed with the cement paste was highly beneficial in improving the rheological properties of cement paste and compressive strength after hardening.

Characteristic of baltic cod mince Gadus Morhua Callarias washed with electrochemical activated water with different concentration of active chlorine ions

The relevance of the above technological process makes it possible to reduce intensity of fish smell and taste, to improve color, to form a more dense structure and to increase shelf life of minced cod. For the first time minced cod was washed by Electrolyzed – water (EW-water) containing various concentrations of active chlorine, as well as free radicals. The influence of different concentration of active chlorine ions on physical and chemical characteristics of washed minced cod was determined. The optimum concentration of active chlorine ions was determined. The amount of removed water-soluble proteins depends on the type of water and the concentration of active chlorine in it. Pure and electrolyzed - water was characterized before and after washing minced cod. The rheological characteristics of minced cod washed by EW - water with different concentrations of active chlorine ions do not change significantly at a concentration in the range from 25 to 150 mg/l. With a concentration of active chlorine ions more than 200 mg / l, the ultimate shear stress increases significantly, the texture of minced cod becomes too dense, which negatively affects the sensory characteristics. Dependence of ratio of protein coefficient and suitability level of minced cod for preparation of high-quality food product was determined. It was found that washing of the minced cod removes water-soluble proteins, which leads to a change in their ratio with salt-soluble proteins, as a result of which the protein coefficient increases by 1.5-2.4 times. The advantage of washing minced cod by electrolyzed – water, which differs in better rheological characteristics compared to minced cod washed with pure water, was justified.

Nonlinear Response Study and a Rotational Spring Model for Degrading Cyclic Behavior of Interior Reinforced Concrete Connections

ABSTRACT A parametric study is performed on the cyclic behavior of reinforced concrete connections. A number of 64 analytical cases are developed being different in the value of the axial force of column, volume of the transverse reinforcement in the connection, ratio of the bending capacity of column and beam, and the continuity index of the longitudinal bars of beam in the connection. The stiffness, dissipated energy, ductility, and ultimate shear stress and strain of the connections are calculated. Finally, a cyclic model for the nonlinear behavior of the connection is proposed that includes stiffness and strength degradation and longitudinal bar slip.

Experimental Study of Shear Behavior of Rock Joints under Two Types of Boundary Conditions: Constant Normal Load and Constant Normal Stiffness

Shear destruction of rock mass along weakened planes is one of the main reasons of the failure of career boards, underground workings and rock slopes. The paper deals with laboratory testing of rock joints under direct shear loading. Special test and measurement complex was created to study deformation and strength characteristics of rock joints. Test specimens were made from single slab of sandstone of homogeneous structure. Shear tests have been conducted under constant normal load (CNL) and constant normal stiffness (CNS) boundary conditions at three values of normal compressive stress: 0.5 MPa, 1.2 MPa and 1.8 MPa. The analysis of test results allowed to reveal patterns of changes of deformation-strength properties of rock joints depending on the level of normal load, boundary conditions and roughness values. The ultimate shear stress is always higher under CNS boundary condition than CNL for the same values of normal compressive stress. Shear stress practically retains constant value after reaching the ultimate stress under CNL boundary conditions and it decreases under CNS conditions. The values of ultimate shear stresses, shear modulus and the length of linear section on “shear stress–shear displacement” curve increases with increasing surface roughness at the equal levels of normal compressive stress.

Direct shear behavior of cementitious mortar reinforced by carbon fiber textile

This study experimentally investigated the characteristics of carbon fiber textile-reinforced mortar (TRM) under direct shear. The main test parameters of this study include the fiber reinforcement ratio of carbon fiber textile, the surface treatment used between mortar matrix and the fiber textile, and the inclination angle of the fiber filaments. Three fiber reinforcement ratio of carbon fiber textile of (0.17, 0.35, and 0.53) % in the mortar matrix were investigated. Two different surface treatment methods were employed to improve the bond performance of carbon fiber textiles in the mortar matrix: epoxy impregnation only, and sand coating after epoxy impregnation. Two inclination angles of fiber filaments of 0°/90° and –45°/45° were investigated. The test results showed that the textile reinforcement within cementitious mortar matrix affected the failure modes and the shear performance of test specimens in terms of cracking and ultimate shear stress, crack deformation, and residual shear stress in the pre- and post-peak stages. Moreover, a crack-shear slip model for cementitious mortar reinforced by carbon fiber textile was developed considering the material characteristics of the mortar and the fiber textile, and its prediction showed good agreement with the experimental results.

Shear Strength of Sand–Clay Interfaces Through Large-Scale Direct Shear Tests

Shear failures of sand–clay interfaces are frequently encountered in engineering practice. It is of great concern to investigate the shear strength of the sand–clay interfaces. In this work, a series of large-scale direct shear tests have been conducted on the sand–clay interfaces. Considering the influences of the interface roughness, the preloading and the stiffness ratio, the interface shear stresses and the vertical displacements are evaluated and compared under different normal stresses. Results indicate that the interface shear stresses and the vertical displacement of the sand–clay samples are quasi-dependent of normal stresses. The shear stress curves feature hardening characteristics with no peak values followed by softening. Light dilation at the shear beginning followed by continuous contraction show in the vertical displacement curves. The interface shear strength is reduced, and the ultimate vertical displacement increases when the preloading is applied before shearing. Larger stiffness ratio leads to smaller ultimate shear stresses and larger ultimate vertical displacements. The values of the ultimate interface shear stresses and vertical displacements of sand–clay samples are between those of the sand–sand and clay–clay samples. Additionally, the movement pattern of the upper sand particles is observed by particle image velocimetry analysis.

The Influence of Nanotechnogenic Raw Materials on the Drying Properties and Physical and Mechanical Properties of Ceramic Bricks

When obtaining ceramic bricks only from low-melting clay with the number of plasticity less than 12 without the use of thinners, there is a sharp drop in the limiting shear stress in the temperature range of 20-80oC, which contributes to the appearance of cracks and deformation curvatures of products. The use of nanotechnogenic raw materials as a thinner does not contribute to a sharp drop in the ultimate shear stress of the semi-finished brick in the temperature range of 20-80oC, eliminates the appearance of cracks and increases the physical and mechanical performance of the finished product. Studies have shown that in order to improve the drying properties of the ceramic mass, the system «nanotechnogenic raw materials-fusible clay-water» is more homogeneous in relation to the system «clay-water». The analysis of the ultimate shear stress in hot forming conditions showed that the function of dependence of plastic strength on molding humidity PM =f (W,t) than the function of dependence of plastic strength on temperature PM =f(t) acquires special importance in this case.

Load transfer mechanism and critical length of anchorage zone for anchor bolt.

The length of anchorage zone of an anchor bolt affects the distribution of axial force and shear stress therein. Based on a shear-displacement model, the load distribution of anchor bolts in the elastic deformation stage was analysed. Moreover, the mechanical response of threaded steel anchor bolts with different anchorage lengths was explored through pull-out test and numerical simulation. The results showed that axial force and shear stress were negatively exponentially distributed within the anchorage zone of anchor bolts in which there were the maximum axial force and shear stress at the beginning of the anchorage zone. In the elastic deformation stage of the anchorage, the longer the anchorage length, the more uniformly the shear stress was distributed within the anchorage zone and the larger the ultimate shear stress; however, there was a critical anchorage length, which, when exceeded, the ultimate shear stress remained unchanged. The calculation formula for the critical anchorage length was deduced and a reasonable anchorage length determined. The research result provides an important theoretical basis for rapid design of support parameters for anchor bolts.

Improvement of Strength Parameters of Foam Ceramics for Energy-Efficient Enclosing Structures

Studies of the influence of vibration impact on the strength of foam-ceramic raw material, produced on the basis of chemically modified natural silicites, are presented. The natural oscillation frequencies of mineral particles are established, taking into account their size, density and ultimate shear stress of raw suspensions. It is shown that the coincidence of the natural and forced oscillations of the particles leads to an increase in the thixotropic effect. Using the technology of a controlled «sol-gel» transition in the structure of raw material, swelling under the influence of vibration load, samples of the material were obtained with a higher-quality macrostructure without the use of binders. Indicators of compressive strength and average density of raw and ceramics are given.

Experimental Investigations on Impact Toughness and Shear Strength of Lead Free Solder Alloy Sn–0.5Cu–3Bi–xAg

Lead is banned in alloy making citing toxicity concerns and environmental legislations. Researchers around the world were in search of new lead free solder alloys which could replace the old Sn–Pb alloy. Solder alloys are important electronic material used in electronics package industries. In this study, shear strength and impact toughness tests were conducted on Sn–0.5Cu–3Bi when different amounts of Ag (0.25, 0.5, 0.75, 1 wt%) is added. Shear strength test is done using micro force test system. Impact toughness test is done using Charpy impact test set up by finding the energy difference before and after impact. Ultimate shear stress is found to be increased from 17.3 to 23 MPa. Yield strength is found to be increased from 23.4 to 28 MPa. Impact toughness of the alloys increased from 10.4 to 11.3 J. EDAX analysis and mapping of the Sn–0.5Cu–3Bi–1Ag is also obtained Sn–0.5Cu–3Bi–1Ag is found to be having good improved shear strength and impact toughness than Sn–0.5Cu–3Bi.

МНОГОКОМПОНЕНТНОСТЬ – ОСНОВНОЙ ФАКТОР ФОРМИРОВАНИЯ СТРУКТУРЫ И СВОЙСТВ ВЫСОКОПРОЧНЫХ БЕТОНОВ

The prospects and problems of multicomponent multilevel optimization of the dispersed composition of self-compacting concrete are considered with the aim of significantly increasing its construction and technical properties, with a minimum content of binder. Theoretical and practical principles have been developed for the design of disperse-particle size distribution of self-compacting concrete mixtures for high-strength concrete, in which various types of dispersed mineral modifiers (MM) are used, including fly ash of thermal power plants. Effective MMs for self-compacting concrete mixtures are differently dispersed granular blast furnace slag, fly ash of thermal power plants and silica fume, which create a dense packing structure of particles of a multicomponent binder with a low degree of disorder and ensure a decrease in the consumption of Portland cement in concrete up to 50% and higher. With such a choice of the type and parameters of MM, self-compacting concrete mixtures are characterized by lower water content, high viscosity and a low level of ultimate shear stress, ensuring its high-quality compaction. To study the properties and structure of concrete, quartz sand with Mk -2.58, granite crushed stone fr. 5-10 mm, Portland cement of class CEM I 52.5 N, finely dispersed granulated blast furnace slag, fly ash of thermal power plants, micro-silica and superplasticizer Glenium 430. For a uniform course of the pozzolanic reaction, a finely dispersed cement fraction was used in each micro-volume. Research methods: the shape and size of the dispersed particles of the components were determined by a laser analyzer, the mobility of the concrete mix in accordance with GOST 10181-2014, the compressive strength of concrete in accordance with GOST 10180-2012. The structure of the cement stone was studied by thermographic and X-ray phase analysis methods.