Uniaxial Tensile Strength Research Articles

Determination of strength variation in jointed anisotropic rocks behavior using UCS and Brazilian Tensile test

Abstract The objective of this study is to determine the variations of strength on anisotropic rock using Uniaxial Compressive Strength (UCS) and Brazilian Tensile Strength (BTS) tests. The variability and distribution of UCS and BTS values were statistically estimated using measured strength of rock. The strength obtained was later to correlate with the quality of rock mass zones. The location of study is at the Ulu Jelai Hydroelectric Dam project, Cameroon Highland, the NW corner of Pahang on the upper reaches of the Sg. Bertam downstream of the existing Sultan Abu Bakar Dam and east of the township of Ringlet. The study is essentially required due to the exposure of sheared bedrock in the mylonite zones beneath the proposed dam. Six (6) boreholes were drilled at different depths along the dam foundation and 23 cores were collected and tested using the UCS and BTS tests. Simple regression analysis was conducted and a wide range of data on uniaxial compression strength and tensile strength of the rock were tabulated. The correlation between UCS and BTS obtained in this experiment is moderately correlated with R2 = 0.8066. Based on the UCS and BTS results, the overall range of UCS was in between 0.9 and 96.0 MPa and tensile strength range is between 0.5 and 14.31 MPa. For further correlation, UCS and Young’s Modulus were studied to shows good reliability (R2 = 0.818). The distribution of UCS data of each borehole is affected by the anisotropic rock behaviour that controls the quality of rock mass zoning.

New empirical failure criterion for shale

A new failure criterion was presented to predict the ultimate strength of shale under the triaxial and polyaxial state of stress. A database containing 93 datasets was obtained from the results of the uniaxial, triaxial, polyaxial compressive tests, an indirect tensile test was collected from reliable references, and this test was carried out on the shale samples taken from the southwestern oilfields in Iran. The database was used to evaluate the proposed criterion, and its accuracy was compared against the popular failure criteria in rock mechanics, particularly those used for stability analysis such as the Hoek-Brown, Mohr-Coulomb, Drucker-Prager, and Mogi-Coulomb failure criteria. In order to evaluate the model, seven important statistical indices were selected. Subsequently, curves from various failure criteria were fitted to the triaxial and polyaxial data, and the corresponding coefficients and statistical indices were determined. The results obtained indicated that, in all cases, compared to the other failure criteria, the proposed criterion succeeded to predict the ultimate strength at a higher accuracy. Also the proposed criterion was used calculate the uniaxial compressive and tensile strengths with a minimum error. For a further examination of the proposed criterion, a series of results from the triaxial test including the ductile failure data were utilized for evaluation of the applicability of the proposed criterion to the ductile zone. It showed that the criterion could predict the ultimate strength of shale over a wide range of stresses.

Determination of Drilling Rate Index Based on Rock Strength Using Regression Analysis.

Drillability is influenced by many factors, including machine parameters and rock properties. The main machine parameters for drilling include rotational speed, thrust force, torque and flush pressure. The specific rock characteristics that affect penetration rate comprise uniaxial compressive strength (UCS), tensile strength, Young's modulus, hardness and brittleness. In this study, drilling rate index (DRI) is attempted to predict based on UCS and Brazilian tensile strength (BTS) of rocks. Simple and multiple regression analyses have been carried out to determine the best measure of the relation between DRI and two geomechanical properties. The DRI value is strongly related to the uniaxial compressive strength and indirect tensile strength. However, when the uniaxial compressive strength and tensile strength of rock are jointly considered, the correlation coefficient increases. The relationship between the geomechanical properties (UCS, BTS) and the DRI were determined using multiple regression analysis. Strong relationships were obtained from these analyses for the rock strength (UCS) above and below 100 MPa with the correlation coefficients 0.81 and 0.88 respectively.The results of the regression analyses show that for more precise prediction of DRI, rocks should be classified according to their strength.

Research Regarding Uniaxial Tensile Strength of Nylon Woven Fabrics, Coated and Uncoated with Silicone

Properties of woven fabrics used to make airbag cushions are influenced by a lot of factors: the nature of raw materials, woven fabric geometry and density, technological parameters of the weaving operation and finishing. The main purpose of this research paper is to find the values of three mechanical parameters – tensile strain, tensile stress and specific modulus – according to the type of samples and test direction on the testing stand. To obtain woven fabric samples were used polyamide 6-6 polyfilament yarns (nylon), silicone coated and uncoated fabric. Testing procedure and samples preparation were done following the standard EN ISO 13934-1:1999. Test results and graphs show that, we have a good uniformity of the geometry for the analyzed fabrics.

Evaluation of the single compressive strength test in estimating uniaxial compressive and Brazilian tensile strengths and elastic modulus of marlstone

Uniaxial strength (UCS), tensile strength (BTS), and elastic modulus (E) are important rock strength parameters used in many engineering projects such as dam, bridge, and tunnel constructions. Several direct and indirect methods have been proposed to measure these parameters. For direct methods, standard samples should be prepared and loaded. Indirect methods are used to estimate these parameters when there is no access to the standard core for various reasons. In this regard, the single compressive strength test (SCS) is one of the indirect methods for estimating these parameters using small specimens. In the present study, the possibility of using SCS test for predicting strength parameters of marlstones is investigated. For this purpose, a total of 10 marlstone blocks were collected from different geological formations of Iran. After preparation of the standard samples, an attempt was made to determine uniaxial strength (UCS), Brazilian tensile (BTS), and elastic modulus (E) of each sample. Next, the samples were crushed and 50 small spherical particles with diameters of 3, 5, 8, 9, and 10 mm were prepared from each sample. A total of 500 particles were used for SCS testing. Then, the single compressive strength index (SCSI) was determined for each particle by plotting load-displacement diagrams; the SCSI of each sample was the average SCSI of 10 same size particles. Subsequently, UCS-SCSI, E-SCSI, and BTS-UCS correlations for specific particle sizes were proposed using the regression analysis. The mean values for the correlation coefficients were obtained as 0.93, 0.89, and 0.91, respectively. The empirical relationships were verified by conducting 100 tests on the control samples, which revealed the reliable validity of the outcomes. The results of this regression modeling, compared with the data obtained from SCS experiments on limestone and sandstone particles mentioned in the literature, demonstrated that the empirical relationships were affected by rock types. Therefore, rock-specific diagrams have to be drawn for particles with different lithologies.

Failure mechanisms of geocell walls and junctions

Geocell panels are honeycomb-like systems used to provide earth reinforcement. Strips of perforated high-density polyethylene sheets, also known as cell-walls, are welded together at locations known as junctions. The cell-wall and junctions are designed to support and transfer tensile and shear loads and the integrity of these is essential for the appropriate performance of geocells in practice. Nevertheless, there is no standardized test procedure to assess the strength of the cell-wall or junction, and limited research has been undertaken regarding the failure mechanisms of geocell panels when subjected to various loading scenarios. This paper aims to examine the responses of geocell junctions and cell-walls under various loading conditions. An extensive testing program was undertaken to assess the geocell junctions, which included uniaxial tensile, shear, peeling and splitting strength tests. The uniaxial tensile strength, trapezoidal tearing strength, and creep tests were carried out on the geocell walls. A ductility ratio was developed to measure the rapidness of failure under different short-term loading scenarios for both the cell-wall and junction. This paper presents the observed failure patterns and an evaluation of the implications of the practical uses of geocells.

Tensile behaviour and durability aspects of sustainable ultra-high performance concrete incorporated with GGBS as cementitious material

The supplementary cementitious materials (SCMs) are used as a substitute for the cement to reduce the environmental issues backed by concrete industry for the past three decades. Additionally, the use of industrial waste as SCMs can mitigate the wastes dumped in lagoons and landfills sites. Ground granulated blast furnace slag (GGBS) is one of the potential candidates as it possesses strength, durability, economic, and environmental benefits. In this study, GGBS is used in Ultra high performance concrete (UHPC) up to 80% replacement level of cement. Various properties such as flowability, compressive strength, tensile strength, fracture, and durability of UHPC with a high volume GGBS are experimentally evaluated under two curing conditions (Standard water and elevated temperature curing). Uniaxial tensile (UAT) strength test is conducted to determine the tensile strength for UHPC. The test results inferred that the hardened properties of GGBS based UHPC are significant upto 40% cement replacement level under standard water curing. Elevated temperature curing, improves its performance upto 60% replacement level. Finally, microstructure properties are studied using scanning electron microscopy which confirms the dense microstructure of UHPC with a high volume GGBS.

Strength evaluation of utilizing recycled plastic waste and recycled crushed glass in concrete footpaths

The increasing rate of waste generation and the consequent environmental penalties of landfilling waste glass and waste plastic need global attention to pursue innovative sustainable industrial applications that can divert these wastes from landfills for useful construction activities. This study entails incorporating recycled plastic waste (RPW) and recycled crushed glass (RCG) as coarse aggregate replacement in concrete mixture and to evaluate its feasibility as concrete footpath construction. The coarse aggregates in concrete were replaced by RPW and RCG aggregates in proportions of 0%, 10%, 20%, 30%, 40%, and 50% was investigated. The properties of concrete evaluated in this study include uniaxial strength, tensile strength and capillary water uptake. Results from this investigation showed that incorporation of RPW and RCG in concrete can be a viable solution for the recycling of plastic waste and crushed glass in industrial applications. Although, the compressive and splitting tensile strength values of the concrete samples containing RPW and RCG aggregate were found to be reduced due to low adhesion between the recycled aggregates and the cement gel matrix as well as low aggregate crushing resistance, coarse aggregate replacement were found to be still viable up to 20% by volume for RPW and up to 30% by volume for RCG for use in footpath construction.

Size effect in unnotched concrete specimens in bending: An analytical approach

The size effect in unnotched concrete specimens in bending causes a higher modulus of rupture compared with its axial tensile strength. To determine the axial tensile strength of concrete from flexural tensile tests, size effect coefficients are, therefore, required. Analytical equations have been derived in the past by the application of nonlinear fracture mechanics and finite element parametric studies. However, the well‐known equations from the Model Codes do not represent the correct asymptotic behavior of the size effect which is problematic for high values of fracture energy, for example, for fiber‐reinforced concrete. Other equations known to the authors require knowledge of the characteristic length of the specimen, that is, their uniaxial tensile strength has to be known a priori. Therefore, this paper presents an analytical approach for the size effect in unnotched concrete specimens in bending that features correct asymptotic behavior and does not require a priori knowledge of the axial tensile strength. The comparison with finite element parametric studies and test results from the literature shows a very good agreement of the proposed equation from brittle to plastic behavior.

Classified prediction model of rockburst using rough sets-normal cloud

In view of complexity and uncertainty of problems in the prediction of rockburst, a classified prediction model of rockburst using rough sets-normal cloud is established. Seven main influencing factors including uniaxial compressive strength of rock σc, uniaxial tensile strength of rock σt, maximum tangential stress of surrounding rock σθ, rock integrality coefficient kv, ratio between uniaxial compressive strength of rock and uniaxial tensile strength of rock σc/σt, ratio between maximum tangential stress of surrounding rock and uniaxial compressive strength of rock σθ/σc and rock elastic deformation energy index wet are selected as the evaluation index of rockburst. Sixteen groups of rockburst examples at home and abroad are used as model construction samples. Then, the weight value of evaluation index of rockburst is obtained by rough sets and fuzzy sets. According to normal cloud theory and classification standard of rockburst, the cloud maps of evaluation index of rockburst are generated. Based on the normal cloud generator and sample data, the evaluation index of the classified sample is determined, and the comprehensive determination of evaluation index of the classified sample is obtained by combining the weight of the evaluation index of rockburst. Finally, the rockburst level is identified according to the principle of maximum membership degree. The classified prediction model of rockburst is used to predict five groups of rockburst samples at home and abroad, and the rockburst classification is coincident with the actual situation. The results show that the classified prediction model of rockburst using rough sets-normal cloud has great practicability.

Changes in tensile strength and microstructure of loess due to vibration

Loess soils typically have an open and metastable structure. Humidification and vibration can modify their microstructure and thus influence their mechanical behavior. In the present study, to investigate the influence of train vibration on the tensile strength behavior of loess, the tensile tests were performed on loess specimens that had been vibrated at a low amplitude for a long period using a modified horizontal extensograph. In addition, the microstructures of vibrated and non-vibrated loess specimens before and after the tensile tests were characterized, changes in the loess microstructure due to vibration and that in the tensile test were analyzed. The results show that the relationship between uniaxial tensile strength and water content in soil specimen could be represented using a power function. The axial displacement at failure varies at the same manner as tensile strength with respect to water content. In comparison to intact loess, occurrence of less clay bridges and clay buttresses between aggregates or coarse particles is identified in the disturbed specimens. While aggregates are seen to be a very little more loose in vibrated specimens after the tensile tests than that before the tensile tests. This indicates that vibration reduces the tension-resistance and ductility of loess soil structure, which could be attributed to loss of bonding strength as a result of breakage of clay cementations and disintegration of aggregates. In the tensile test, the soil structure goes through two distinct phases of change, i.e., stretching phase and cracking phase. In the stretching phase, the tensile deformations take place throughout the specimen without altering the contacts between soil particles significantly. In the cracking phase, weak cementations fail to resist tensile deformation and suffer from breakage; once a through-crack is developed, the specimen breaks in two, leading to a catastrophic drop of tensile stress.

Epoxy nanocomposites simultaneously strengthened and toughened by hybridization with graphene oxide and block ionomer

Epoxies are widely used in many engineering applications, however, their fracture energy remains less than desired and conventional toughening agents usually lead to compromised tensile strength. In this study, a simple one-pot blending method was used, in which both graphene oxide and a block ionomer were blended with epoxy resin. Herein, we reported that increases of ∼200% in fracture energy (GIC), 48% in uniaxial tensile strength (σt) and 340% in tensile strain could be achieved by incorporating 1.0 wt% graphene oxide into an epoxy matrix with 20 wt% sulfonated polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene (SSEBS). In addition, the glass transition temperature (Tg) of the nanocomposite increased with increasing graphene oxide (GO) content and the storage modulus (E′) decreased when the GO content was less than 0.50 wt% owing to the introduction of the block ionomer SSEBS. Careful examination of the nano-morphology of SSEBS revealed that it improved the dispersion of the graphene oxide in and enhanced its interaction with the epoxy matrix, hence simultaneously strengthening and toughening the epoxy resin.

Modeling and interpreting large deformation behavior of rubber nanocomposites containing carbon nanotubes and nanoplatelets

The principles of large deformation rubber viscoelasticity are not new, but there is a need to make explicit certain theories or modify the available models for deeper understanding of behavior of rubber nanocomposites. The difficulties are chiefly due to the assumptions under which a given theoretical model fails to predict large deformation behavior of elastomer nanocomposites, as models are basically proposed for neat rubbers, and more critically they can hardly be supposed to remain valid for systems in which two or more nanofillers having different nature, shape, and size are used. This work attempts to apply nonlinear hyperelastic theoretical models proposed for hyperelastic behavior of rubbers for nanocomposites containing multi‐walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GnPs), and to explore the interplay between morphology, viscoelastic properties, and large deformation behavior of typical hydrogenated acrylonitrile butadiene rubber (HNBR)‐based rubber nanocomposites. Morphological observations used for knowing the localization of nanofillers, where dynamic mechanical and uniaxial tensile strength analyses exhibited a rise in both Young's modulus and tensile strength of composites by MWCNTs and GNPs content up to 200 and 160%, respectively. We applied Arruda‐Boyce model and appropriately predicted nonlinear hyperelastic behavior of HNBR model nanocomposites and interfacial interactions between phases, as recognized by comparing model parameters for nanocomposites containing only MWCNTs, or only GNPs, and their combinations varying filler content. POLYM. COMPOS., 40:E1548–E1558, 2019. © 2018 Society of Plastics Engineers

Influence of Water Content on the Mechanical Parameters of the Intact Rock and Rock Mass

The goal of this paper is to present the influence of the water saturation of the intact rock on different mechanical parameters, such as internal friction angle, cohesion, Hoek-Brown constant (mi ). Analyzing the previously published results, it was found that due to water saturation both the uniaxial compressive strength and tensile strength decrease similarly, i.e. the ratio of these two values is constant, thus the internal friction angle does not change but only the cohesion. Likewise, Hoek-Brown constant (mi ) remains constant; it is independent on the moisture content.The ratio of the elastic modulus and the uniaxial compressive strength of the intact rock is also calculated. According to the laboratory results, this ratio (namely modulus ratio) is also independent on the water content.It is shown that the mechanical parameters of the rock mass (such as compressive strength, tensile strength, deformation modulus) similarly depend on the water content than the intact rock.

Drilled Core Specimen Testing Method for Determination of Tensile Strength Values of Rock Materials

In this study, a new direct tensile strength determination method of drilled core specimen testing was investigated with numerical and experimental studies. Effect of different drill diameters of holes of the rock specimens was analysed to assess the ideal drill-hole design. The aim of drilling process is decreasing the failure load and stress concentration at the adhesive part to prevent invalid failures. Drilled specimens were determined to fail due to the start of cracking under the condition of uniaxial tensile stress distribution at sidewalls of holes. It was found that drill bits with the diameter of 11 mm is usable for a practical specimen drilling process to make a significant decrease in the failure load of the core specimens with the NX size (@54 mm) diameter. According to the results obtained from numerical and experimental analyses, an equation was suggested to determine uniaxial tensile strength values of drilled core specimens with the hole diameter of 11 mm.

Successfully estimating tensile strength by small punch testing

The Small Punch (SP) test is a relatively simple test well suited for material ranking and material property estimation in situations where standard testing is not possible or considered too material consuming. The material tensile properties, e.g. the ultimate tensile strength (UTS) and the proof strength are usually linearly correlated to the force-deflection behaviour of a SP test. However, if the test samples and test set-up dimensions are not according to standardized dimensions or the material ductility does not allow the SP sample to deform to the pre-defined displacements used in these correlations, the standard formulations can naturally not be used. Also, in cases where no supporting UTS data is available the applied correlation factors cannot be verified. In this paper a formulation is proposed that enables the estimation of UTS without supporting uniaxial tensile strength data for a range of materials, both for standard type and for curved (tube section) samples. The proposed equation was originally developed for estimating the equivalent stress in small punch creep but is also found to robustly estimate the UTS of several ductile ferritic, ferritic/martensitic and austenitic steels. It is also shown that the methodology can be further applied on non-standard test samples and test set-ups and to estimate the properties of less ductile materials such as 46% cold worked 15-15Ti cladding steel tubes. In the case of curved samples the UTS estimates have to be corrected for curvature to match the corresponding flat specimen behaviour. The geometrical correction factors are dependent on tube diameters and wall thicknesses and were determined by finite element simulations. The outcome of the testing and simulation work shows that the UTS can be robustly estimated both for flat samples as well as for thin walled tube samples. The usability of the SP testing and assessment method for estimating tensile strength of engineering steels in general and for nuclear claddings in specific has been verified.

Upper bound analysis of ultimate pullout capacity of shallow 3-D circular plate anchors based on nonlinear Mohr-Coulomb failure criterion

Based on the nonlinear Mohr-Coulomb failure criterion and the associated flow rules, the three-dimensional (3-D) axisymmetric failure mechanism of shallow horizontal circular plate anchors that are subjected to the ultimate pullout capacity (UPC) is determined. A derivative function of the projection function for projecting the 3-D axisymmetric failure surface on plane is deduced using the variation theory. By using difference principle, the primitive function of failure surface satisfying boundary condition and numerical solution to its corresponding ultimate pullout capacity function are obtained. The influences of nonlinear Mohr-Coulomb parameters on UPC and failure mechanism are studied. The result shows that UPC decreases with dimensionless parameter m and uniaxial tensile strength increases but increases when depth and radius of plate anchor, surface overload, initial cohesion, geomaterial density and friction angle increase. The failure surface is similar to a symmetrical spatial funnel, and its shape is mainly determined by dimensionless parameter m; the surface damage range expands with the increase of radius and depth of the plate anchor as well as initial cohesion but decreases with the increase of dimensionless parameter m and uniaxial tensile strength as well as geomaterial density. As the dimensionless parameter m=2.0, the numerical solution of UPC based on the difference principle is proved to be feasible and effective through the comparison with the exact solution. In addition, the comparison between solutions of UPC computed by variation method and those computed by upper bound method indicate that variation method outperforms upper bound method.

Identification of brittle and ductile zones in sandstone reservoir using well log analysis; a case study, Southern Indus Basin, Pakistan

Brittleness and ductility play a very important role in the stimulation design of unconventional reservoirs as it controls the fracture length and shape of hydraulic fractures. The estimation of mechanical properties of the reservoir rock is very important for the successful execution of reservoir drilling, production, and development operations. In this study, the mechanical properties are calculated using well log responses for selected reservoir section after a quality check of the data. Brittleness is estimated from empirical correlations based on mechanical properties estimated from well logs response, uniaxial compression strength and tensile strength. High values of young modulus and corresponding low values of Poison’s ratio were indicating the brittle zones in the reservoir. Brittle-ductile zone identification based on mechanical properties were giving consistent results. Brittle-ductile categorization is done for identification of brittle, less brittle, less ductile and ductile reservoir lithology in each studied well. It was found from the computer-assisted approach and graphical presentation that, there was a high brittleness in the lower part of the reservoir which is due to highly compressed shale formation. This part of the reservoir could be a good candidate for hydraulic fracturing if it satisfies all other constraints for a prospective reservoir.

Measurement of the Ideal Strength of Graphene Nanosheets

The uniaxial tensile strength of graphene nanosheets at 77 K was determined by the method of loading two-dimensional nano-objects with strong electric fields. It was shown that, for graphene sheets 0.5 to 2.8 nm thick, the maximum strength within the measurement error does not depend on the thickness of the sheets. The average strength, due to significant statistical dispersion, was 43% lower than its maximum value (92 GPa). The strength of graphene nanosheets is almost an order of magnitude greater than the strength of nanoneedle samples made from original carbon fibres. Evidence that graphene nanosheet strength does not depend upon sheet depth indicates the achievement of the ideal strength of these objects.

Effect of Alloy Composition on Microstructure and Tensile Properties of Net-Shaped Castings of Al–Zn–Mg–Cu Alloys

In this study, the effect of alloy composition on uniaxial tensile properties of Al–Zn–Mg–Cu alloys was investigated using seven distinctive alloy compositions. The sample alloys were manufactured as net-shaped components using the controlled diffusion solidification technology coupled with the tilt pour gravity casting process. The effect of T4 and T6 heat treatment on the castings was investigated using seven alloy compositions with the total alloying content (Zn + Mg + Cu) varying from 4.6 to 10.6 wt%. The uniaxial tensile yield strengths (0.2% proof stress) of the respective alloys were measured for T4 temper and varied between 125 and 316 MPa and for the T6 temper samples varied between 280 and 540 MPa. A quantitative image analysis was carried out to measure the eutectic phase fraction, which was compared with predictions from thermodynamic solidification simulations. The experimental phase characterization of various secondary phases/precipitates was conducted using an electron microscopy (STEM) methodology along with energy dispersive spectroscopy (EDS) results; other experimental method such as the Archimedes’ density measurements was also used to evaluate porosity content in the samples.