Contribution To Shear Strength Research Articles

AN ENGINEERING APPROACH TO THE STUDY OF THE PROCESSES OF DOUGH FLOW IN THE PRODUCTION OF PASTA AT AGRO-INDUSTRIAL ENTERPRISES

Background. In modern conditions, the provision of domestic pasta produced from durum wheat varieties on modern technological equipment is becoming important. At the same time, the quality of the finished pasta is also determined by the rheological properties of the pasta dough when passing through the pasta press matrix, which determined the purpose of the study to develop a method of computational evaluation for calculating the relationship between the speed parameters of the flow of pasta dough in the cylindrical sections of the channels of the molding matrix with pressure drops to overcome viscous resistance, the dimensions of the structural elements of the channel, as well as with indicators of the rheological properties of pasta dough. Materials and methods. To study the flow of pasta dough, baking flour of the highest grade M-54 28 was chosen as a raw material in stepped cylindrical channels. The applied rheological model is described and a technique for mathematical modeling of the flow parameters of pasta dough in cylindrical channels is given. Due to the small contribution of the pasta dough shear strength to the total pressure loss, a rheological model of a nonlinear-viscous medium is used, which is described by a power equation containing physically determined constants. Neglecting the elastic deformations of the dough due to their smallness, we assumed the condition of constancy of the volumetric productivity for each cross section of the channel. Results. Analytical dependencies are presented that relate the change in velocity over the channel cross section to the pressure developed necessary to overcome the viscous resistance, as well as to the radii and length of the channel, and to the rheological properties of the pasta dough. These dependences formed the theoretical basis of the method for calculating the parameters of pasta dough flow in cylindrical channels. Conclusion. On the example of an industrial matrix of a pasta press, made in the form of a system of cylindrical channels of a stepped-variable diameter in the preforming zone, calculations were made to determine the average and maximum flow rates of pasta dough in each section of the channel and the developed pressure. The results of the research can be used in engineering practice when designing new matrices for forming pasta dough and in the production processes of enterprises to calculate their production capacities.

Effects of carbonation modification on shear performance of recycled aggregate concrete beams: Test and mechanism analysis

The effective use of recycled aggregates (RAs) in construction significantly contributes to environmental preservation and the conservation of non-renewable natural resources. However, RAs typically exhibit inferior performance relative to natural aggregates (NAs). To improve the quality of RAs, carbonation modification has been introduced as an eco-friendly and practical method. This study explores the shear performance of concrete beams that incorporate various replacement ratios (30 %, 50 %, 70 %, and 100 %) of carbonated recycled aggregates (CRAs). The experiment employed Digital image correlation (DIC) system to evaluate the stress distribution on the concrete surface within the shear span section. The evaluation of shear performance was conducted through comprehensive analysis includes load-deflection curve, steel strain, the width of the primary diagonal crack, average principal tensile strain, orientation of principal directions, average shear strain, and shear deflection. A practical approach was adopted to separate the shear strength contributions of transverse steel (Vs) and concrete (Vc), based on transverse steel strains along the primary diagonal crack. Results indicate that carbonated recycled aggregate concrete (CRAC) beams demonstrate enhanced shear performance in comparison to recycled aggregate concrete beams. Shear strength significantly decreases with replacement rates exceeding 70 %. Furthermore, the experimental results were compared against shear strength with the design codes, and shear deflection with existing models.

Predicting the shear strength of rectangular RC beams strengthened with externally-bonded FRP composites using constrained monotonic neural networks

Fiber-reinforced polymer (FRP) composites bonded externally to reinforced concrete beams have shown promise for increasing shear load-carrying capacity. However, accurately predicting the shear strength contribution of FRP remains challenging due to the complexity of the shear failure mechanisms and interactions between the contributing components. Existing design provisions have limitations in modeling this behavior. Recently, machine learning has shown promise for addressing such complex problems but lacks transparency. Therefore, this study developed a data-driven Constrained Monotonic Neural Network (CMNN) approach implemented using Python libraries Keras and Tensorflow, which integrates domain knowledge to provide reliable FRP shear-strength predictions. This framework directly encodes expected monotonic input-output relationships through constraints, harnessing both predictive power and monotonicity guarantees. A comprehensive database of 273 beam tests was used to train and evaluate the model. Bayesian optimization through the Optuna framework and 4-fold cross-validation were used to tune the hyperparameters of the CMNN model. Extensive evaluation demonstrated the CMNN model's superior accuracy, yielding an R² value over 0.9, a CI above 0.93 and a low MAE under 16 kN on both training and unseen test data. The model also outperformed existing design code provisions, achieving significantly optimal performance metrics across various strengthening configurations. The analysis of the predictions revealed logical sensitivity trends aligned with the principles of shear mechanics. Such physics-informed machine learning presents a next-generation technique for performance-based structural design, contributing an effective and interpretable tool to advance knowledge on quantifying the shear capacity contribution of externally bonded FRP reinforcement in concrete beams.

Study on the double-sided shear test and three-dimensional numerical simulation of anchor cable with C-shaped tube

Using an indoor pipe-cable-rod double-sided shear test system, tests for double-sided shear are carried out on three types of prestressed anchor cables and anchor cables with C-shaped tubes that eliminate the joint surface's resistance to movement. The shear failure characteristics and shear strength contribution of the anchor cable with C-shaped tube were compared and analyzed. For the anchor cable with C-shaped tube, the C-shaped tubes' geometrical specifications were altered and the effects of the C-shaped tubes' thickness and diameter on the anchor cables with C-shaped tubes' shear strength were investigated. The research results showed that the thickness of the C-shaped tube had a substantial impact on improving the ultimate shear capacity of the anchor cable with C-shaped tube. With the increase in the thickness of the C-shaped tube, the increment of the ultimate shear capacity showed an exponential growth trend. However, under the same thickness, the ultimate shear capacity had a negative correlation with the diameter of the C-shaped tube. In addition, the anchor cable with C-shaped tube was the subject of numerical simulation research using the three-dimensional numerical simulation program ABAQUS. The stress distribution and the development trend with increasing shear load were obtained. The simulation findings revealed that the numerical model and the outcomes of the laboratory tests were in good agreement, which might serve as a guide for future research.

Overcoming the brittleness of shear failure: A new FRP-RSC strengthening philosophy

Due to the linear elastic stress–strain behavior of carbon fiber reinforced polymer (CFRP), the ductility of CFRP shear-strengthened reinforced concrete (RC) beams will be significantly reduced. Compared with shear capacity enhancement, increasing the ductility of CFRP shear-strengthened RC members is a much more challenging task, and a satisfactory solution has yet to be found. This paper introduces a new methodology that combines the brittle fiber reinforced polymer (FRP) with ductile rubber support composite (RSC) to form the FRP-RSC strengthening system. The variable stiffness RSC can adjust the stiffness of the strengthening system, which is achieved by the changed shear transfer actions in FRP, transverse reinforcement and concrete. Eight specimens were tested to evaluate the effectiveness of the FRP-RSC strengthening method. Experimental tests demonstrated that the displacement ductility with this FRP-RSC technique was 2.15 times that of the conventional externally bonded (EB) FRP strengthening, reaching remarkably 5.24. The mechanisms for enhancements in ductility, deformability and shear capacity were revealed. Poor matches were observed between the predicted FRP shear strength contribution (Vf) per existing models and test data. A new model that can predict Vf of FRP-RSC strengthened RC beams was developed, and better agreements between predictions and experimental results were obtained.

Machine learning-based models for predicting the shear strength of synthetic fiber reinforced concrete beams without stirrups

Stirrups can be added to reinforced concrete (RC) beams made of plain concrete to increase the shear strength providing better performance against embrittlement. If the need for shear stress is less than the strength of RC beams, reinforced with the minimum number of stirrups, then this choice might not be the most cost-effective. Synthetic Fiber Reinforced Concrete (SyFRC) in Reinforced Concrete (RC) structures is limited due to the lack of predicting models for this emerging material in current literature. However, recent advances in concrete technology have revealed more significant benefits of SyFRC, including high deformation capacity and less corrosive concrete. This study predicts shear strength of SyFRC beams without stirrups using the ACI 318-19 equation in addition to Machine Learning (ML) methods such as LightGBM, XGBoost, and Gene Expression (GEP). A database of 102 tested SyFRC specimens were compiled, processed, and evaluated. With R2 values of 98.91% and 97.22%, respectively, the LightGBM and XGBoost outperformed the other examined algorithms by having the least predictions discrepancy and highest accuracy values. As the ACI 318-19 equation does not account for the fibers volume ratio and shear span-to-depth ratio effects on the shear strength contribution, it projected shear strength with the lowest degree of accuracy, with R2 = 75.5%. The feature importance analysis revealed that these two factors, in addition to the effective beam depth, beam width, longitudinal steel reinforcement ratio, and concrete compressive strength should not be negligible in shear strength prediction. For forecasting the shear strength, a closed-form GEP-based model was suggested. The proposed GEP model has a little lower prediction accuracy with R2 = 88.4%. The performance of the four examined models was evaluated from various perspectives. The analysis shows that, apart from the ACI equation, all considered models effectively predict the effects of shear span-to-depth ratio. This is critical for investigating deep and slender beams, and size effect, which are critical for beams with high effective depths. The current study's findings should give practitioners a solid platform for making precise and straightforward assessments of shear strength.

Contribution of geosynthetic to the shear strength of geosynthetic encased stone columns

This paper presents a numerical study to evaluate the contribution of geosynthetic to the shear strength of geosynthetic encased stone column (GESC) under direct shear loading conditions. The backfill soil was characterised using the linearly elastic–plastic Mohr–Coulomb model. The geosynthetic encasement was simulated using linearly elastic liner elements. The interaction between the geosynthetic encasement and soils on both sides was modelled through two interfaces. The three-dimensional numerical model was validated using experimental data from direct shear tests of GESC models. The shear stress–strain response and the development of longitudinal and circumferential strains of GESC during the shear process were first discussed, and then a parametric study was conducted to investigate the effects of various design parameters on the shear strength of GESC and the contribution of geosynthetic. Results indicate that the shear resistance provided by the geosynthetic encasement develops slowly, which depends on the mobilisation of tensile strains. At the failure condition, the longitudinal strains are larger than the circumferential strains, which indicates that the longitudinal tensile rupture is more critical for GESC under shear loading. The vertical stress, geosynthetic encasement stiffness and stone column diameter and spacing have the most important influences on the shear strength contribution of geosynthetic encasement.

Investigation of Newtonian and non-Newtonian Bingham fluid models for lateral flow simulation of liquefied soil

This study applies a Newtonian model and non-Newtonian Bingham model to simulate the lateral flow of liquefied soil and investigates the models’ parameters. First, the study derives analytical solutions for the lateral flow velocity under free-field conditions in both the transient and steady states for both models. The study determines that the solution derived for the Newtonian model can be applied to derive that for the Bingham model through a simple transformation considering the contribution of undrained residual shear strength of liquefied soil. Second, three-dimensional numerical analyses are executed using COMSOL to investigate the boundary conditions of experimental models, which significantly affect the fluid behavior of liquefied soil. The results reveal that the model length and sidewall effects can be ignored at a length-to-thickness ratio of >30 and width-to-thickness ratio of >6, respectively. The Bingham model can describe the behavior of liquefied soil under different boundary conditions using a single set of parameters. Through normalization, the Bingham and Newtonian models can share the same normalized velocity–time curve. Additionally, the Bingham model with boundary conditions can have a similar curve to that under the free-field condition through the replacement of the original viscosity coefficient with an apparent viscosity coefficient.

Local use of ECC to simultaneously enhance the shear strength and deformability of RC beams

• A new method that can simultaneously enhance the shear strength and deformability of RC beams was proposed. • The effects of compression-zone material on the variation of V c and v s were evaluated. • Shear deflection and flexural deflection were decoupled. • The mechanisms of how compression-zone material affects the shear strength and deformability were investigated. Existing studies have substantiated that the stress (or strain) states of compression-zone concrete exert significant influence on the performance of shear-critical reinforced concrete (RC) beams. Based on this understanding, the current paper presents a tentative work by replacing the compression-zone concrete with engineered cementitious composite (ECC) to simultaneously enhance the shear strength and deformability of a RC beam. To uncover the reasons behind the enhancements due to the inclusion of ECC, the shear strength contributions from concrete ( V c ) and stirrups ( V s ) were obtained with reasonable accuracy using an innovative methodology. Shear and flexural deformations were decoupled utilizing two methods with the help of the imaging technique. The cracking process, crack width, strain fields, and principal direction evolutions were monitored by a digital image correlation (DIC) system. The test results clearly show that the inclusion of ECC in the compression zone significantly increased both the shear strength and deformability of RC beams. More specifically, the inclusion of ECC changed the crack width and pattern, the variation trends of V c and v s and the deformation proportion. Finally, existing shear deformation models were evaluated, and none of them could predict the shear deformation of beams incorporating ECC due to the high nonlinear feature.

Methodology for calculating the pasta dough flow parameters in stepped cylindrical channels

The introduction provides information about the state of the problem and substantiates the relevance of the research. The purpose of the work is to develop a methodology for calculating the relationship between pressure losses during the flow of pasta dough in channels with a stepped-variable cross section with the dimensions of the channel structural, as well as with the pasta dough rheological properties and the performance of device. In the methodological part of the work, the applied rheological model is described and a technique for mathematical modeling of power and kinematic parameters of pasta dough flow in stepped cylindrical channels is given. Due to the small contribution of the pasta dough shear strength to the total pressure loss, a rheological model of a non-linear-viscous medium is used, which is described by the power – law rheological Ostwald–de Waele equation. Neglecting the elastic deformations of the dough and the elastic change in volume, we assumed the condition of constancy of the volume and mass flow (productivity) for any cross section of the channel in each of its sections. In the main part of the work, analytical dependencies are presented that relate the magnitude of the pressure drop to overcome viscous resistance during the flow of pasta dough in channels with a stepped-variable cross section with the dimensions of the structural elements of the channel, as well as with the rheological properties of the pasta dough and the performance of the device. These dependences formed the theoretical basis for calculating method of the pasta dough flow parameters in stepped cylindrical channels. The technique was tested on the example of an industrial macaroni press matrix equipped with a system of stepped-variable channels in the pre-forming zone. The results of the research can be used in the design of new sizes of matrices for pasta dough molding as well as in the educational process in the training of food production process engineers.

Seismic shear behavior of new high-strength reinforced concrete column and steel beam (New RCS) joints

New high-strength reinforced concrete column and steel beam (New RCS) joints were developed in this research. Two-way, through-beam New RCS joint details with beams concentrically or eccentrically connected to the joint were proposed. The beam in one direction was continuous through the joint (continuous beam). The beam in the other direction was connected to the continuous beam by complete joint penetration (CJP) groove welds. Five-spiral reinforcement was used for joint transverse reinforcement. A method to calculate the amount of five-spiral reinforcement was proposed considering the confinement effect from the face-bearing plates (FBPs). Doubler plates were used to strengthen the eccentric beam flanges with predrilled holes to allow the passage of column longitudinal reinforcement. A method was proposed for the design of the doubler plates. Large-scale New RCS joint specimens designed to fail in joint shear were tested. Test results showed that the proposed joint details and design methods effectively avoided failure in undesirable locations. All the specimens failed in joint shear but still reached high drift ratios. The eccentric joint specimens (IDEHS and ISEHS) exhibited peak joint shears higher than the concentric beam specimen (IHS). The 1994 ASCE and 2015 ASCE shear strength models produced conservative predictions of the peak joint shear and the joint shear at 0.5% joint shear deformation for all the specimens. The predictions by the 2015 ASCE method were more reasonable with less scatter than the 1994 ASCE method because the former recognizes the shear strength contribution from the outer joint panel even without the use of shear keys and allows a longer steel web in shear strength calculation.

Effects of Crumb Rubber on the Shear Strength of Sand: An Experimental Study

The application of waste rubber tires for ground improvement helps to improve the environment by recycling and reusing it as admixtures. This research aims to investigate the shear strength parameters of rubber-sand mixtures. By using crumb rubber with a constant size (425μm), the sand is replaced by different percentages (0, 2.5, 5.0, 7.5, and 10%) of crumb rubber by weight. A direct shear box test is used to determine the shear strength parameters of rubber-sand mixtures with two different controlled densities. The samples were loaded with normal stresses of 20, 40 and 80kPa and were sheared at a rate of 1mm/min. Although, this experiment discovered that crumb rubbers improve the shear strength parameters in loose sand, however, a reduction in shear strength parameters was found in dense sand. Moreover, it was observed that the inclusion of crumb rubbers into sand greatly improve the strain energy of both loose and dense sand. Likewise, rubber has a low unit weight which makes it suitable for lightweight backfill materials. The surface properties of rubber should be further studied to understand the contribution of shear strength in the rubber-sand mixture.

Technological and rheological bases for molding pasta in press houses with preliminary two-stage compaction, plasticization and warming of dough

One of efficient directions for pasta press designs modernization is installation of special conical-andcylindrical inserts in the pre-matrix space and matrix wells in front of the dies having, like Venturi tubes, narrowing zones (convergent), expansion (divergent) and a cylindrical path located between them. However, rheological aspects of such method of forming tool modernizing in relation to pasta presses have not been studied, recommendations for structural elements calculation and design have not been developed. All this is a significant obstacle for using the method in engineering and industrial practice. The research purpose is to develop rheological models the pasta dough flow in the conical-cylindrical channels of convergent-divergent inserts and to evaluate with their help the impact of structural dimensions and rheological properties on resistance to pasta dough flow. Pasta dough was considered as a rheological complex nonlinearly viscous plastic material. In technical calculations contribution of shear strength was neglected and a rheological analysis was performed using the Oswald-de-Ville power law equation. Analytical dependences obtained make it possible to calculate the pressure drops in the convergent-divergent insert and its elements. Numerical modeling was performed and calculated data were obtained regarding the impact of dimensions of structural elements of the insert and rheological parameters of pasta dough on its resistance to viscous flow. The results obtained can form the basis of engineering and technological calculations in design of convergent-divergent inserts for laboratory and industrial pasta presses.

Shear Resistance Contribution of Constituent Elements Consisting RCS Joint

In this study, constituent elements affecting the shear strength of RCS joints were investigated through experiment and analysis study. A series of five interior RCS beam-column joint specimens, which were classified as JH-type and CP-type, was tested to investigate the contribution of each shear resisting element such as JH (Joint Hoop), CP (Cover Plate), FBP (Face Bearing Plate), E-FBP (Extended Face Bearing Plate), TB (Transverse Beam), and BP (Band Plate). Comparison between experiment and analysis results showed that the stiffness and strength of the RCS joint were reasonably assessed from the analysis. As a result of the analysis, it was found that TB, E-FBP, and CP increased the shear strength by about 15%, 14%, and 26%, respectively. For the JH-type specimen, 70% of the shear strength of the RCS joint is supported by the inner element and 30% of the shear strength is supported by the outer element. Shear strength contribution ratio of the outer element of CP-type specimen is larger than that of the JH-type specimen. For all specimens except for SNI-1, around 10% of total shear strength is supported by FBP. The shear strength equation of the RCS joint proposed by ASCE underestimates the contribution of the outer element, while that of M-Kanno tends to overestimate it.

Rheological modeling of pasta dough flow processes in channels of convergent-divergent inserts of molding matrix

One of efficient directions for pasta press designs modernization is installation of special conical-and-cylindrical inserts in the matrix wells in front of the dies having, like Venturi tubes, narrowing zones (convergent), expansion (divergent) and a cylindrical path located between them. However, rheological aspects of such method of forming tool modernizing in relation to pasta presses have not been studied, recommendations for structural elements calculation and design have not been developed. All this is a significant obstacle for using the method in engineering and industrial practice. The research purpose is to develop rheological models the pasta dough flow in the conical-cylindrical channels of convergent-divergent inserts and to evaluate with their help the impact of structural dimensions and rheological properties on resistance to pasta dough flow. Pasta dough was considered as a rheological complex nonlinearly viscous plastic material. In technical calculations contribution of shear strength was neglected and a rheological analysis was performed using the Oswald-de-Vila power law equation. Analytical dependences obtained make it possible to calculate the pressure drops in the convergent-divergent insert and its elements. Numerical modeling was performed and calculated data were obtained regarding the impact of dimensions of structural elements of the insert and rheological parameters of pasta dough on its resistance to viscous flow. The results obtained can form the basis of engineering and technological calculations in design of convergent-divergent inserts for laboratory and industrial matrices of pasta presses.

Assessment of the existing models to evaluate the shear strength contribution of externally bonded frp shear reinforcements

This paper presents an analysis of the performance of different existing formulations to quantify the FRP contribution to the shear strength of RC elements strengthened in shear by externally bonded FRP sheets. A large database of 555 tests has been assembled distinguishing between the shape of the section, the existence of internal transverse reinforcement and the FRP configurations. In general, predictions are more conservative for beams without transverse reinforcement. In addition, in some cases predictions are unsafe for beams with transverse reinforcement, showing a possible interaction with the internal transverse reinforcement which is not considered in the experimental FRP contribution to the shear strength. For wrapped FRP configurations, models generally assumed failure at the bottom corner of the section and results are very conservative in some cases where failure was experimentally observed along the web. For U-shaped and side-bonded configuration, results depend mainly on the assumed bond model and are more accurate than in the previous case, showing for some models unsafe predictions for the continuous FRP system applied in beams with transverse reinforcement.

Quasi-static cyclic performance of RC exterior beam-column joint assemblages strengthened with geosynthetic materials

The beam-column joints are the most critical and vulnerable part of the RC framed structures when subjected to earthquake load. The objective of the present study is to investigate the cyclic behaviour of seismic and non-seismic exterior reinforced concrete (RC) beam-column joints strengthened with innovative polymeric based geosynthetic materials. Two variants of geosynthetic material named geogrid and geotextile were used for strengthening the beam-column joints in the experimental program. In this strengthening protocol, two different types of strengthening patterns were used in which one was horizontal U-shaped pattern, and the other one was the diagonal cross (X-shaped) pattern. All the beam-column specimens were tested under the quasi-static cyclic loading with controlled amplitude to explore the cyclic performance on the parameters such as failure modes, hysteresis loops, load-deformation envelope curves, ductility, energy dissipation capacity, stiffness and strength degradation behaviour, pinching width ratio, damage index and joint distortion. The test results showed that the adopted strengthening schemes with geotextile and geogrid materials could successfully alter the failure of beam-column joints from shear to flexural and improved the ductile behaviour of the strengthened specimens. The load-carrying capacity and ductility-factor of the geosynthetic strengthened specimens significantly increased up to 48.4% and 37.8%, respectively when compared to the non-seismic control specimen, and it was highest in geogrid strengthened BCJs, especially in diagonal X-shape bonded specimen. The significant increment of energy dissipation capacity was also observed as 2.08 to 3.73 times for the strengthened specimens. Furthermore, the post-elastic performance and the joint shear strength of strengthened RC beam-column joints was also improved in comparison to the non-seismic control specimen. In addition, an analytical study was carried out to predict the shear strength contributions of externally bonded strengthening materials in the RC beam-column joint, which was compared with experimental findings. A good agreement was observed between the analytical and experimental results. Hence, the experimental and analytical study of the strengthened beam-column joints using geotextile and geogrid have confirmed that the appropriate bonding of these materials to the concrete can improve the seismic performance of the non-seismic exterior RC beam-column joints.

Experimental and Analytical Investigations of the Use of Groove-Epoxy Anchorage System for Shear Strengthening of RC Beams Using CFRP Laminates.

Reinforced concrete (RC) beams strengthened in shear with carbon fiber reinforced polymer (CFRP) laminates as externally bonded reinforcement (EBR) usually fail due to debonding. This paper presents an experimental and analytical investigation on the use of groove-epoxy as an anchorage system for CFRP plates and sheets bonded on both sides of shear deficient RC beams. The aim of this study is to assess the effectiveness of using groove-epoxy in enhancing the shear capacity of RC beams. Nine rectangular RC beams were strengthened with CFRP plates and sheets with groove-epoxy anchorage systems of different groove widths and tested under four point bending. It is observed that the RC beams strengthened with the groove-epoxy anchorage system showed an increase in the shear-strength over the unstrengthened control beam up to 112 and 141% for plates and sheets, respectively. Also, the increase of shear-strength contribution of the groove-epoxy system to that of CFRP without grooves ranged between 30–190% for CFRP plates and between 40–100% for CFRP sheets. Generally, the contributions of groove-epoxy on shear-strength decreased with the increase of groove width. Moreover, shear strength prediction models, based on modifications of the ACI440.2R-17 shear model, were developed by incorporating groove factors as a modifier to the FRP shear-strength contribution. The developed models predicted the experimental shear-strength of the tested RC beams with a good level of accuracy, with an average mean absolute percent error (MAPE) = 3.31% and 6.68%, normalized mean square error (NMSE) = 0.072, 0.523, and coefficient of determination R2 = 0.964, 0.691, for plates and sheets, respectively.

Effects of net normal stress on hydro-mechanical behaviour of a kaolinite clay soil under different suction paths

Hydro-mechanical behaviour of unsaturated soils has been extensively reported in the literature. However, the effects of net normal stress on soil behaviour under different suction paths have not been addressed. Therefore, in this study, the shear behaviour of a kaolinite clay soil subjected to drying or wetting prior to shearing was investigated by suction-controlled direct shear tests. It was found out that net normal stress suppresses both irreversible volume contraction and decrease in degree of saturation. The magnitude of irreversible volume contraction and the size of hydraulic hysteresis after drying–wetting decreased with the net normal stress. Soil specimens experiencing drying–wetting had lower degree of saturation, and thus generally exhibited lower residual shear strength due to the lower average skeleton stress as compared with those specimens experiencing only drying. It was also found out that, at (σv − σa) = 50 kPa, peak shear strength of specimens experiencing drying–wetting was generally higher than that experiencing only drying, since the contribution to peak shear strength made by lower void ratio might be dominant over the reduction of peak shear strength caused by lower degree of saturation. However, the contrary effect of suction path on peak shear strength was observed at (σv − σa) = 100 and 200 kPa. The peak shear strength of soil specimens experiencing drying–wetting was generally lower, because they had lower degree of saturation and hence lower average skeleton stress at the same net normal stress and the same suction as compared with those experiencing only drying. Furthermore, as compared with those experiencing only drying, soil specimens experiencing drying–wetting exhibited smaller stronger strain-softening and stiffer stress–strain relations, larger shear-induced volume dilation (or less contraction), and more obvious trend of water absorption during shearing at various net normal stresses. Regarding peak shear strength parameters, soil specimens experiencing drying–wetting showed higher cohesion, but lower friction angle than those experiencing only drying.

Characterization of interfacial shear strength and its effect on ploughing behaviour in single-asperity sliding

The shear strength at the interface contributes to the overall friction force experienced by the contacting bodies sliding against each other. In this article, an experimental technique to characterize the shear strength at the interface of metallic bodies in sliding contact has been developed. The boundary layers formed at interface in a lubricating contact have been varied by using two different types of lubricants in combination with both zinc coated and uncoated steel sheets. The empirical relations between the experimental parameters such as contact pressure and sliding velocity and the interfacial shear strength have been expressed by fitting the experimental results. These expressions have been incorporated in the Material Point Method (MPM) based ploughing model. The coefficient of friction and ploughing depth obtained from the numerical simulations have been validated relative to the experimental results with a good agreement for both lubricated and unlubricated substrates, different loads and spherical indenter sizes. Furthermore, the interfacial shear strength has been varied in the MPM-based ploughing model and ploughing experiments to study the contribution of interfacial shear strength to overall friction, deformation and wear.