Shear Strength Research Articles

Effects of joint persistence and testing conditions on cyclic shear behavior of en-echelon joints under CNS conditions

Cyclic shear tests on rock joints serve as a practical strategy for understanding the shear behavior of jointed rock masses under seismic conditions. We explored the cyclic shear behavior of en-echelon and how joint persistence and test conditions (initial normal stress, normal stiffness, shear velocity, and cyclic distance) influence it through cyclic shear tests under CNS conditions. The results revealed a through-going shear zone induced by cyclic loads, characterized by abrasive rupture surfaces and brecciated material. Key findings included that increased joint persistence enlarged and smoothened the shear zone, while increased initial normal stress and cyclic distance, and decreased normal stiffness and shear velocity, diminished and roughened the brecciated material. Shear strength decreased across shear cycles, with the most significant reduction in the initial shear cycle. After ten cycles, the shear strength damage factor D varied from 0.785 to 0.909. Shear strength degradation was particularly sensitive to normal stiffness and cyclic distance. Low joint persistence, high initial normal stress, high normal stiffness, slow shear velocity, and large cyclic distance were the most destabilizing combinations. Cyclic loads significantly compressed en-echelon joints, with compressibility highly dependent on normal stress and stiffness. The frictional coefficient initially declined and then increased under a rising cycle number. This work provides crucial insights for understanding and predicting the mechanical response of en-echelon joints under seismic conditions.

Improved thermal shock reliability of Ag paste sintered joint by adjusted coefficient of thermal expansion with Ag-Si atomized particles addition

In this study, two kinds of atomized Ag-20 wt%Si and Ag-50 wt%Si particles are fabricated and added to Ag paste to fabricate composite pastes to achieve a low coefficient of thermal expansion (CTE), and their performance stability in SiC power module is evaluated under thermal shock from −50 to 250 °C. Four kinds of composite Ag pastes using the two kinds of atomized Ag-Si addition with 10 % and 30 % were obtained, AS20-10, AS50-10, AS20-30 and AS50-30, respectively. The results show that the CTE reduction intensifies with increasing Ag-Si atomized particle content. The retention ratio of shear strength of AS20-30 sintered joint after 1000 cycles was 102.3 %, which means the shear strength did not decrease during so harsh thermal shock test. The mechanism was discussed in detail. In addition, the properties such as thermal conductivity and electrical conductivity for the composite pastes were also evaluated to gain a more comprehensive understanding for the new materials especially for the design of SiC power modules with a long-time life. Comprehensively considering the material parameters of the composite pastes and the reliability of the sintered joints under thermal shock, the optimized composite pastes as die attach material in power electronics are obtained. The findings should be inspiring in developing novel die attach materials for high reliable interconnections in SiC power modules.

Investigation into the strength of β-Sn/α-CoSn3 and Co/α-CoSn3 interfaces with Ni-doped α-CoSn3 using first-principles calculations

The strength of Pb-free solder/Co-Ni alloy joints was investigated using first-principles calculations. The adhesion work was computed, revealing that the inclusion of Ni in the α-CoSn3 phase reduced the adhesion work for both β-Sn/α-CoSn3 and Co/α-CoSn3 systems. Tensile and shear simulations further demonstrated distinct differences in the mechanical properties between β-Sn/α-(Co,Ni)Sn3 and Co/α-(Co,Ni)Sn3 systems. The results demonstrate that Co/α-(Co,Ni)Sn3 exhibited superior tensile and shear strength. The analysis suggests that failure in β-Sn/α-(Co,Ni)Sn3 structures was more likely to originate either at the interface or near the β-Sn region, as opposed to within the α-(Co,Ni)Sn3 phase for the Co/α-(Co,Ni)Sn3 structures. This observation is consistent with predictions made by Griffith’s fracture theory. Additionally, the valence electron density map illustrates the electron transfer under varying tensile strains.

Proposal for characterisation of direct shear strength of steel-fibre-reinforced concrete

A proposal for the direct pure shear characterisation of steel-fibre-reinforced concrete specimens with two grooved shear planes is presented. In the first stage of work, crimped steel fibres (CSF) were used at volume fractions (Vf) of 0, 0.5, 1.0 and 1.5%, the concrete compressive strength was 35 MPa and the maximum coarse aggregate size (Dmax) was 9.5 mm. With these specifications, eight block specimens were subjected to the direct shear tests. A significant gain in shear strength was observed with an increase in fibre dosage – an increase of 90% when Vf = 1.5%. Based on this, three analytical expressions to compute the shear stress were formulated. The models were assessed by testing 15 blocks of smaller size and additional variables – hooked-end steel fibres (HSF), concrete compressive strength of 25 MPa and coarse aggregates with Dmax = 9.5, 19.0 and 25.0 mm. Better performance was obtained with the CSF rather than the HSF, with a strength gain of around 100% for Vf = 1.5% with the maximum coarse aggregate particle size of 25 mm and variability between the proposed analytical models of 2–7%.

Variation of Shear Strength of Cohesive Soils Subjected to Cyclic Loading at Different Rates of Loading

Variation of Shear Strength of Cohesive Soils Subjected to Cyclic Loading at Different Rates of Loading

The Behavior of Post-installed Rebar Connectors in Steel Frame Retrofitted Concrete Structures Under Combined Shear and Tension

To investigate the response of post-installed rebar connectors in steel frame retrofitted concrete structures under combined shear and tension, seven shear-and-tensile tests were conducted. The bearing capacity, stiffness, and hysteresis behavior of the connectors were investigated during the tests. Both Monotonic and cyclic load regimes were applied in the loading process. The results show that with the increase of the loading angle, the deformation capacity, the yield force, ultimate tensile force, and tensile stiffness of the specimen decrease, while the maximum shear force and shear stiffness of the specimen increase. The bearing capacity, stiffness, and energy dissipation performance of the specimen under a monotonic load is greater than that under the coupled shear-and-pull load. The bearing capacity, stiffness, hysteresis curve, and failure status of the specimens are not affected by different loading regimes. At the end, the design formula of anchor bolt for this type of connectors from the design code of China, United States, and Japan were compared. Formulas to calculate the shear strength under combined shear and tension is developed.

Eucalyptus-Based Glued Laminated Timber: Evaluation and Prediction of Its Properties by Non-Destructive Techniques

Eucalyptus-based glued laminated timber (glulam) was produced to determine the feasibility of a non-destructive method (drilling resistance) to predict the properties of structural elements and add value to lower-quality hardwood species. Glulam was manufactured with formaldehyde (Resorcinol), reference condition, and bio-based (Castor oil-based) adhesives in two assembly schemes, the core composed either of two continuous lamellae each 105 cm long, or of two formed by the juxtaposition of shorter boards (35 and 55 cm). The shear strength of the glue line (fv0), modulus of elasticity (Ec90), and strength (fc90) in compression perpendicular to the grain; delamination (DL); and main and extended glue line thicknesses were evaluated. The Resistograph equipment was used to perform the perforation perpendicular to the glue line (samples extracted from the glulam elements) to correlate the properties. The results of this research demonstrate that the scheme of the boards had little effect on the physical and mechanical properties evaluated (except the main glue line and delamination), and the drilling resistance (DR) presents a significant correlation with practically all properties evaluated (variations in density values and other properties are explained by variations in DR values), making it possible to estimate Ec90 and fc90 with desired precision (R2adj ≈ 80%). This highlights the feasibility of using this methodology in the quality control of glulam elements. It is concluded that regardless of the adhesive, elements comprising a 105 cm-length core and external lamellae (T1 and control) are indicated for external use, presenting low delamination. Short-length central lamellae adhesively glued with PUR (T2) are not recommended for external applications due to their susceptibility to delamination. However, T2 is indicated for internal environments due to its low production cost. This study also proved the efficiency of using models based on drilling resistance to estimate wood density and its resistance to compression perpendicular to the fiber.

Experimental study on shear mechanical properties of concrete joints under different unloading stress paths

In order to study the shear mechanical properties of rock joint under different unloading stress paths, the RDS-200 rock joint shear test system was used to carry out direct shear tests on concrete joint specimens with five different morphologies under the CNL path and different unloading stress paths. The unloading stress paths include unloading normal load and maintaining constant shear load (UNLCSL), unloading normal load and unloading shear load (UNLUSL), unloading normal load and increasing shear load (UNLISL). The results show that the peak shear strength, cohesion, internal friction angle, pre-peak shear stiffness and residual shear strength of concrete joints under CNL path increases with the increasing JRC and normal stress. Under the UNLCSL path, under the same initial shear stress τ1, instability normal stress σi decreases with the increasing JRC, and normal stress unloading amount Δσn increases with the increasing JRC. Under the same JRC, σi increases with the increase of τ1, and Δσn decreases with the increasing τ1. Under the same JRC and σi, τi is significantly smaller under the UNLCSL path than the CNL path. Under the same JRC, the cohesion under the UNLCSL path is less than the CNL path, and the internal friction angle is higher than that the CNL path. Under the same JRC and σi, τi is the largest under the path of CNL and UNLISL, followed by the UNLCSL path, and τi under the UNLUSL path is the smallest. Compared with the CNL path, the variation range of the specimen internal friction angle is within 3% while the average decrease percentage of the specimen cohesion reaches 37.6% under the UNLCSL path, UNLISL, and UNLUSL. Therefore, it can be inferred that the decrease in cohesion caused by normal unloading is the main reason for the decrease in joint instability shear strength. After introducing the correction coefficient k of cohesion to modify the Mohr-Coulomb criterion, the maximum average relative error after correction is only 3.5%, which is significantly improved compared with the maximum average relative error of 56.9% before correction. The research conclusions can provide some reference for the accurate estimation of shear bearing capacity of rock joints under different unloading stress paths, which is of great significance to the stability evaluation and disaster prevention of rock mass engineering.

Modulating Carbon Fiber Surfaces with Vinyltriethoxysilane Grafting to Enhance Interface Properties of Carbon Fiber/Norbornene–Polyimide Composites

In this study, vinyltriethoxysilane (TEVS) was introduced onto the surface of carbon fiber using liquid-phase oxidation and impregnation methods to incorporate vinyl groups onto the carbon fiber, thereby enhancing the chemical bonding between the carbon fiber and norbornene–polyimide (PI-NA). Through a systematic study of the hydrolysis conditions and concentration of the TEVS solution, the optimal modification conditions were determined. These conditions were used to graft TEVS onto the surface of oxidized carbon fiber to prepare carbon-fiber-reinforced PI-NA composites (CF/PI-NA). The results show that when carbon fiber was treated with a 0.4 wt% TEVS solution, the interlaminar shear strength (ILSS) of the composites reached 65.12 MPa, and the interfacial shear strength (IFSS) reached 88.58 MPa, representing increases of 27.58% and 35.62%, respectively, compared to the CF/PI-NA composite materials prepared from untreated carbon fiber. It is worth noting that the modification method described in the study is simple and easy to implement, and it has the potential for large-scale continuous production applications.

THE EFFECT OF SUPPORT LAYER MATERIAL AND ADHESIVE TYPE ON COMPRESSIVE DYNAMIC BENDING AND SHEAR STRENGTH IN LAMINATED WOOD

In this study, strength properties of wood material reinforced with carbon fiber fabric, steel wire mesh and bamboo veneer were determined. Polyvinylacetate (PVAc) and polyurethane (PUR) glues (D4)were used for the lamellas obtained from Scotch pine (Pinus sylvestris L.) and eastern beech (Fagus orientalis L.). Compressive strength according to TS EN 408+A1; dynamic bending (shock) strength according toTS ISO 13061-10 and shear strength according to ASTM D 3110 were determined on 3 and 5-layers samples. According to the results, the highest compressive strength (62.8 N/mm2) was found in 5-layerseastern beech samples reinforced with carbon fiber fabric and bonded with PUR glue. The highest dynamic bending strength value (110.8 kJ/m2) was found in 5-layerseastern beech samples reinforced with carbon fiber fabric and bonded with PUR glue and the highest shear strength value (12.3 N/mm2) in 3-layered eastern beech samples reinforced with steel wire mesh and bonded with PUR glue.

Slope Stability Analysis of Open-Pit Mine Considering Weathering Effects

Weathering processes gradually alter the physical and mechanical attributes of slope materials, weakening the structural integrity and stability of slopes. This paper presents an in-depth analysis of slope stability in an open-pit mine, emphasizing the pivotal role of weathering effects in determining slope stability. To accurately capture the impact of weathering on slope stability, a comprehensive analysis model was developed, incorporating field observations, laboratory testing, and numerical simulations. The effects of weathering on the mechanical properties of black shale were studied through extensive laboratory tests. The uniaxial compressive strength, shear strength, and modulus of elasticity significantly decreased with increasing weathering, indicating a heightened vulnerability to slope failure. The correlation function between mechanical parameters and weathering time was obtained, providing the basis for evaluating the stability of mine slopes. It was found that more severe weathering conditions were strongly correlated with elevated risks of slope failure, including landslides and collapses. Based on these findings, practical recommendations are provided for slope reinforcement and management strategies, aimed at mitigating slope failure risks and ensuring the safe and efficient operation of the mine. By incorporating weathering effects into slope stability analysis, mine operators can make informed decisions that account for the dynamic nature of slope materials and their susceptibility to weathering, thereby improving overall mine performance and safety.

Bonding Characteristics of CLT Made from Silver Birch (Betula pendula Roth.), European Aspen (Populus tremula L.) and Norway Spruce (Picea abies (L.) H. Karst.) Wood

This paper deals with the bonding characteristics of cross-laminated timber (CLT) panels made of Silver birch (Betula pendula Roth.), European aspen (Populus tremula L.), and Norway spruce (Picea abies (L.) H. Karst.) wood. Three-layered single-species CLT panels were manufactured using birch, aspen, and spruce lamellae bonded with a one-component polyurethane (PUR) adhesive. Spruce CLT panels were used as reference. The bonding characteristics of CLT were assessed based on bond shear strength, total and maximum delamination, and wood failure percentage. The reference spruce CLT met both criteria (Delamtot ≤ 10%, Delammax ≤ 40%) for passing the delamination test, where up to 80% of the test samples passed. The aspen and birch CLTs met the criterion for maximum delamination (26.5% and 33.2%, respectively), but exceeded the maximum allowed value for total delamination (12.7% and 13.2%, respectively). However, the minimum requirement of 70% wood failure percentage (WFP) was met for all CLT types, with aspen CLTs achieving 83.7% and birch CLTs 76.9%. The spruce CLTs achieved an average bond shear strength of 1.9 N/mm2, while both hardwood CLTs had significantly higher values, with the aspen CLT at 3.3 N/mm2 and the birch CLT at up to 3.9 N/mm2. Based on the results obtained, it can be concluded that cross-laminated timber (CLT) made from hardwoods like aspen and birch is suitable for environments with low humidity fluctuations.

Investigating the impact of corrosion on behavior and failure modes of reinforced concrete slabs: An experimental and analytical study

Corrosion of steel reinforcement significantly reduces the load-carrying capacity of reinforced concrete (RC) flat slabs, making them more vulnerable to punching shear failure. This type of failure can lead to sudden and catastrophic collapse of the structure. Despite its critical implications, research on this topic remains limited, and a mechanical model to estimate the load-displacement behavior of RC flat slabs with corroded reinforcements is currently lacking. In this paper, experimental work on corroded RC slabs under punching shear loading was conducted. To investigate the impact of corrosion on the structural behavior of reinforced concrete (RC) flat slabs, eight specimens, including both corroded and uncorroded controls, were subjected to load testing. The study focused on key performance indicators including punching shear strength, stiffness, crack patterns, failure modes, and energy dissipation capacity. Additionally, an analytical study based on the newly developed Critical Shear Crack Theory (CSCT) was conducted to understand the behavior of corroded RC slabs. Experimental results indicated a significant reduction in the punching shear strength of corroded slabs. Moreover, as corrosion progressed, a notable shift in failure mode from punching shear to flexural failure was observed. The proposed CSCT model demonstrated good agreement between the experimentally obtained and analytically predicted load-displacement curves.

Performance of channel shear connectors in steel frame with reinforced concrete infill walls

To examine the mechanical properties of channel shear connectors employed in steel frame with reinforced concrete infill wall (SRCW) structures, the improved push-out tests were performed on three specimens of channel shear connectors subjected to the monotonic and cyclic loading. This study investigated the influences of loading protocol and concrete strength on the mechanical behavior of channel shear connectors. After the refined finite element (EF) models of channel shear connectors were validated based on the push-out tests, a systematical parametric analysis was conducted to evaluate the effects of RC infill wall thickness, concrete strength, and channel dimensions on its shear strength of the channel shear connectors. In addition, this study also compared the accuracy of the CSA S16, AISC 360 and GB50017 design code in predicting the shear capacity of channel shear connectors in SRCW structures. The experimental results and parametric studies indicated that the current design equations inaccurately evaluate the shear capacity of channel shear connectors used in SRCW structures. Consequently, an alternative equation was developed to estimate the shear-resistant capacity of channel shear connectors in SRCW structures, which provided the desirable calculation precision for engineering design.

Numerical modeling of site response at large strains with simplified nonlinear models: Application to Lotung seismic array

Abstract Site response analyses at large strains are routinely carried out neglecting the shear strength of soil and the stiffness degradation due to the increase in pore pressures, leading to unrealistic predictions of the seismic response of soil deposits. The study investigates the performance of a simplified nonlinear (NL) approach, implemented in the Deepsoil code, constituted by coupling a hyperbolic model incorporating shear strength with a strain-based semi-empirical pore pressure generation model. The first part of the study, based on a large one-dimensional parametric study, shows that above a shear strain of 0.1%, it is necessary to include shear strength in the site response modelling to get more realistic results. Then, the approach has been evaluated with reference to the well-known downhole Large-Scale Seismic Test array located in Lotung (Taiwan): numerical results have been compared with recordings in terms of acceleration response spectra and pore water pressure time histories at different depths along the soil profiles. The comparison shows that the NL simplified model is characterized by an accuracy comparable with more sophisticated advanced elasto-plastic NL analyses adopting essentially the same input data of the traditional equivalent linear approaches(shear modulus and damping curves) and simple physical-mechanical properties routinely determined during geotechnical surveys (i.e., shear strength, relative density, fine content). This approach is therefore recommended for site response analyses reaching large strains (i.e., soft soil deposits and moderate-to-high input motions).

Performance Evaluation of Carbon Fiber Fabric-Reinforced Formaldehyde-Free High-Strength Plywood

Plywood is lightweight, strong, and durable, making it a widely used material in building decoration and furniture areas. In this study, formaldehyde-free, high-strength plywood was prepared through the incorporation of carbon fiber fabrics (CFFs) as reinforcement layers and their bonding with maleic anhydride polyethylene (MAPE) films. Various tests were performed to assess the impact of the carbon fiber fabric positioning on the physical and mechanical properties of plywood, including tensile shear strength, flexural strength, water absorption, thickness swelling, and electro-thermal properties. The results revealed that the plywood with CFFs exhibited significantly higher mechanical properties than plywood without CFFs. Particularly, the addition of CFFs increased the tensile strength of the plywood by nearly 54.43%, regardless of the CFFs’ position. The symmetric placement of CFFs near the bottom and upper layers of the plywood resulted in a maximum modulus of rupture of 85.6 MPa. These findings were validated by numerical simulations. Scanning electron microscopy analysis of the plywood microstructures revealed that MAPE penetrated both the vessels and xylem of the wood veneers and the pores of the CFFs, thereby improving the mechanical properties of the plywood. Plywood reinforced with CFFs exhibited increased water absorption and thickness swelling after immersion. Additionally, the placement of CFFs influenced the electro-thermal properties of the plywood. Plywood with CFFs positioned near the bottom and upper surfaces exhibited superior thermal conductivity. Overall, this study presents a feasible method for developing high-performance, formaldehyde-free plywood and sustainable wood-based structural materials with potential applications in geothermal flooring.

Numerical Simulation of Effects of Previous PVD Treatment on Second Vacuum-PVD Improvement

The influence of the initial improvement through prefabricated vertical drains (PVD) and surcharge embankment on the second improvement by vacuum PVD has not been comprehensively explored in the existing literature. The expansion of the Second Bangkok International Airport (Suvarnabhumi Airport) underwent initial treatment with PVD and surcharge, followed by further soft ground improvement with vacuum PVD, which serves as a valuable case study for understanding the impact of the initial PVD improvement. This study highlights the effects of the initial PVD improvement through a comparison of two case studies: the first improvement by vacuum PVD on Taxiway Extension D at Zone 27 and the second vacuum PVD improvement on the Third Extension North at Zone 7. Extensive back analysis results reveal significantly higher flow parameters and reduced settlements for the second improvement at Zone 7 compared to the first improvement at Zone 27. The water contents, void ratios, and compression indices decreased while the undrained shear strengths and maximum past pressures increased. These results demonstrated the effectiveness of the vacuum PVD improvement with a modified field-distributed air-water separation system. Numerical studies further corroborated these findings and confirmed the observed crack patterns at the surface resulting from inward lateral movement.

Qualitative analysis of rivers sand sources (silica sand, ravi river sand, indus river sand, and jhelum river sand) for metal casting: a comparative study

Abstract Recent geological investigations revealed extensive use of Silica sand in Pakistan resulting in depletion of tectonic resources. Hence, it is important to explore cost-effective and alternative sources of sand for its applications. Also, Pakistan has a river network that provides river sand as a potential substitute for Silica sand. However, it is essential to systematically study and assess the potential applicability of river sand as an alternative to Silica sand. In this context, this study examined sand samples collected from various rivers in Pakistan to investigate their suitability for metal-casting molds. For that purpose, random samples were selected from major rivers in Pakistan for characterization by utilizing chemical composition analysis, microscopy, XRD, TGA-DSC (thermogravimetric analysis), clay content analysis, grain size distribution analysis, pH measurement, green and dry compression strength testing, shear strength testing, permeability analysis, shatter index analysis, compactibility testing, and Specific gravity measurement. The chemical composition analysis revealed that all types of sands contained over 90% SiO2 content. The mechanical tests demonstrated that river sand exhibited acceptable mechanical properties, with a moisture content ranging from 4.5-5%. The pH value of all the sands exceeded 7, making them suitable for casting purposes. These investigations suggest that river sand can be effectively utilized in casting applications by implementing pre-processing techniques and incorporating additives.

Interfacial properties and mechanical performance of hybrid graphene/carbon fibre composites

The interaction zone between the matrix and the reinforcing component within carbon fibre (CF) composites plays a crucial role in influencing their performance characteristics, as extensively documented in scientific literature. Building on this fundamental knowledge, this research focuses to the investigation of the interface of fibrous composites and the effect of the incorporation of graphene nanoplatelets (GNPs) into the epoxy matrix. Through the utilization of laser Raman spectroscopy, a significant increase of over 60 % in interfacial strength with just a 2 % weight fraction of GNPs, as expressed by the enhanced shear-lag parameter observed in single fibre model composites, has been observed on model composites indicating a stronger interfacial interaction between the matrix and fibres. The effect of the incorporation of GNPs on CF-graphene interaction has been also investigated on a macroscopic level. Hybrid carbon fibre epoxy resin composite produced, by the introduction of GNPs into the polymer matrix. A series of mechanical tests were conducted, including extensive tensile testing of epoxy/graphene nanocomposite films, thorough examination of bending characteristics, and meticulous measurement of interlaminar shear strength for hybrid GNP/carbon fibre composites. These evaluations provided a clearer understanding of how the GNP integration affects the interface parameters that govern the mechanical behaviour of both the resin and carbon fibre composites.

Experimental Investigation on Shear Strength at the Permeable Concrete–Fine-Grained Soil Interface for Slope Stabilization Using Deep Socket Counterfort Drains

In slopes where high pore water pressure exists, deep counterfort drains (also called drainage trenches or trench drains) represent one of the most effective methods for improving stability or mitigating landslide risks. In the cases of deep or very deep slip surfaces, this method represents the only possible intervention. Trench drains can be realized by using panels or secant piles filled with coarse granular material or permeable concrete. If the trenches are adequately “socket” into the stable ground (for example sufficiently below the sliding surface of a landslide or below the critical slip surface of marginally stable slopes) and the filling material has sufficient shear strength and stiffness, like porous concrete, there is a further increase in shear strength due to the “shear keys” effect. The increase in shear strength is due both to the intrinsic resistance of the concrete on the sliding surface and the resistance at the concrete–soil interface (on the lateral surface of the trench). The latter can be very significant in relation to the thickness of the sliding mass, the “socket depth”, and the spacing between the trenches. The increase in shear strength linked to the “shear keys effect” depends on the state of the porous concrete–soil interface. For silty–clayey base soils, it is very significant and is of the same order of magnitude as the increase in shear resistance linked to the permanent reduction on the slip surface in pore water pressure (draining effect). This paper presents the results of an experimental investigation on the shear strength at the porous interface of concrete and fine-grained soils and demonstrates the high significance and effectiveness of the “shear keys” effect.