Decrease In Shear Strength Research Articles

Development and Analysis of Long-Term Measurement Systems for Groundwater Level Using Electric Capacity

In soil dams and embankments made of soil, deterioration and stress release owing to internal and external influences occur, and the instability of the body increases as the shear strength decreases. In particular, understanding the location and flow of underground water is very important for securing the long-term stability of waterfront structures in contact with water. However, the physical limitations of measuring equipment cause many difficulties in understanding the existence and location of groundwater over a long period of time. In this study, measuring equipment using electric capacity was developed for the long-term measurement of groundwater, and contactless measuring sensors were manufactured to eliminate the possibility of corrosion by water. In addition, the precision of the measurement data was improved by applying waterproof and water-repellent coatings to the measurement sensor. Laboratory tests conducted using the developed equipment demonstrate the high precision of the measurement data according to the groundwater level change and enhanced durability of the sensor, which facilitate long-term measurements in the field.

Numerical and theoretical studies on shear behavior of steel-UHPC composite beams with waffle slab

UHPC waffle slab was proposed to utilize the excellent material properties of UHPC and improve the rigidity of bridge deck. The flexural behavior of steel-UHPC composite beams with waffle slabs (SUCBWS) has been studied recently while the shear behavior of SUCBWS is still limited. This paper aims to supply the gap in the research system of mechanical properties of the novel bridge deck system. Based on the experimental study of four SUCBWS, a three-dimensional finite element model (FEM) was developed to investigate the shear behavior of SUCBWS. Extensive validations of the numerical analyses against the reported tests proved that FEM is reasonable. Meanwhile, the shear working mechanism of SUCBWS was analyzed. A subsequent parametric study was conducted to investigate the effects of shear span ratio, yield strength of steel, degree of shear connection, the ratio of rib height to top flat plate thickness and adding haunch at the rib-to-plate interface on the shear behavior of SUCBWS. Results show that shear span ratio and degree of shear connection present an obvious influence on ultimate bearing capacity, stiffness, ultimate deflection and failure mode of the composite beam. The shear span-to-depth ratio increased 1.34 to 3.14 resulted in a decrease in stiffness and shear strength while an increase in ultimate deflection. The increase of the degree of shear connection (from 0.5 to 1) improved the stiffness and ultimate bearing capacity but reduced the ultimate deflection. Adding the haunch at the rib-to-plate interface can significantly improve the integrity and decrease the risk of longitudinal splitting failure of the UHPC waffle slab. The high-strength steel can match well with the UHPC waffle deck so as to improve the ultimate bearing capacity of SUCBWS. The increase of the ratio of rib height to top flat plate thickness showed a limited influence on shear behavior of composite beams and the value of 3 is recommended for the design of SUCBWS. Meanwhile, the shear composite action coefficient, shear contribution coefficient of top flat plate and ribs were proposed to develop the theoretical models for predicting the shear capacity of SUCBWS and providing a reference for the design of SUCBWS. Besides, the effect of the haunch size at the rib-to-plate interface on the mechanical performance of SUCBWS should be further quantitatively analyzed.

Effect of Bentonite Content and Hydration Time on Mechanical Properties of Sand–Bentonite Mixture

The bentonite is commonly used mixed with soils for groundwater retention and waste contaminant facilities. The incorporation of bentonite could significantly reduce hydraulic conductivity. In this study, the effects of bentonite content, hydration time and effective confining pressure on the static properties of a sand–bentonite mixture were studied using experimental and numerical methods. Firstly, a large number of drainage static triaxial tests on the sand–bentonite mixture with various bentonite contents were conducted. The test results show that the increase in bentonite content and hydration time leads to a slight decrease in shear strength and initial tangent modulus of the sand–bentonite mixture. The presence of bentonite reduces the shear shrinkage and dilatancy trend of the mixture. The cohesion of the mixture increases with the increase in bentonite content and hydration time, but the internal friction angle decreases correspondingly. The hydration of bentonite on the surface of sand particles changes the contact form between particles. The bentonite slurry between pores of the sand skeleton also affects the mechanical behavior of the sand–bentonite mixture. Then, a series of 3D discrete element models were established for numerical simulations of drainage static triaxial tests. The numerical model parameters were calibrated by experimental results. The meso-mechanism of bentonite content affecting the mechanical behavior was revealed according to the contact force distribution between particles. The research results are helpful to understand further the mechanism of bentonite on the mechanical properties of the sand–bentonite mixture.

Comparisons of distributed and lumped rainfall-runoff model for soil moisture estimation

Soil moisture is an important parameter in landslides because of increased pore pressure and decreased shear strength. This research aims to derive soil moisture indicators from two hydrological models: the physically-based distributed hydrological model and the lumped model. Rainfall-Runoff-Inundation (RRI) Model is used to simulate the hydrological response of catchments to the rainfall-induced landslide in a distributed manner. Tank Model as a lumped hydrological model is also used in this study to simulate the dynamic of soil moisture. The study area is the upper Brantas River Basin, prone to landslides due to heavy rainfall and steep slope. Calibration of the model is conducted by tuning the model according to the river discharge data. The simulation indicates that acceptable performance is confirmed. Tank Model can provide the dynamic of the soil moisture. However, by using this approach, the spatial variation of the soil moisture cannot be presented. Regarding the quantitative amount of soil water content, RRI Model could make a reasonable simulation though the temporal variation is not adequately reproduced. Validation of this method with satellite soil moisture as well as ground measurement is also presented. The challenges of using these approaches to develop landslide hazard assessment are discussed.

The short-term and creep mechanical behaviour of clayey soil-geocomposite drainage layer interfaces subjected to environmental loadings

In this paper, to investigate the impact of environmental loadings on the short-term and creep mechanical characteristics of different types of clayey soil-Geocomposite Drainage Layers (GDL) interfaces, a series of rapid loading and creep shear tests were conducted on Mercia Mudstone Clay-GDL interfaces and Kaolin Clay-GDL interfaces subjected to drying-wetting cycles, thermal cycles and elevated temperature, etc, using a bespoke temperature and stress-controlled large direct shear apparatus. The experimental results indicate that, compared with the original specimens, the interfaces subjected to drying-wetting cycles, thermal cycles and elevated temperature, have lower peak shear strength and creep shear resistance. For example, under 25 kPa normal stress, the peak shear strength of original Mercia Mudstone Clay-GDL interfaces and Kaolin Clay-GDL interfaces falls by 11.91% and 10.11%, respectively, when subjected to 1 drying-wetting cycle. This can be ascribed to the weakening of interlocking effects and skin friction between soil and GDL caused by the softening of drainage core and geotextile fibres of GDL. The peak shear strength of clayey soil-GDL interfaces subjected to one drying-wetting cycle is lower than that subjected to one thermal cycle because of the reduction in the peak shear strength of clayey soil above GDL during drying-wetting cycles. The impact of drying alone on the decrease in the peak shear strength of clayey soil-GDL interfaces during drying cycles with heating is small, and the main influence factor is the elevated temperature.

Investigation of Liquid Metal Embrittlement during Resistance Spot Welding of Martensitic Steel with Zn Jet Vapor-Deposited Coating

Advanced high-strength steels protected by zinc coatings have contributed to a reduction in CO2 emissions in the automotive industry. However, the liquid metal embrittlement (LME) of the Fe/Zn couple induced by simultaneously acting stresses and high temperatures during resistance spot welding could be the cause of unexpected failure. We investigated the possible risk of LME in spot-welded martensitic steel with Zn jet vapor-deposited coating and its influence on weld strength. The weld nugget cross-sections were analyzed (optical microscopy, SEM-EDS), and their tensile shear strengths were compared with their uncoated counterparts. LME cracks were observed in all samples meeting the process window (6, 6.5, 7 kA) located at the edge of the sheet/electrode indentation area. The frequency and length of cracks increased with current, and the occurrence of Zn within cracks indicated the LME mechanism. The shear tests showed the Zn-coated sample underwent a decrease in tensile shear strength that was most evident at a welding current of 7 kA (13.2%). However, LME was excluded as a cause of lower strength. The decrease was attributed to the smaller nugget diameter and the thin slit of Zn coating remaining in the weld notch.

Adhesively bonded CFRP/Al joints: Influence of the surface pretreatment on corrosion during salt spray test

AbstractThe objective of this study was to investigate the influence of different surface pretreatments on the aging behavior of adhesively bonded carbon fiber reinforced polymers/Al joints in a standardized salt spray environment. Therefore, the bonding surfaces were acetone‐cleaned or laser‐pretreated by near‐infrared laser radiation. The pretreated surfaces were examined using optical microscopes, roughness measurements, and infiltration tests. Mechanical testing of the joints was performed in the unaged state and after five aging durations from 120 to 1440 h. The acetone‐cleaned specimens lose a maximum 20% of their initial average shear strength of 22 MPa after aging up to 1440 h. In contrast, the fracture patterns of the laser‐pretreated samples show corrosive degradation after 720 h, indicating galvanic coupling and crevice corrosion. This leads to a significant decrease in shear strength up to 50% after 1440 h of aging. Therefore, some strategies to avoid contact corrosion via the pretreatment and joining process are presented additionally.

Size Effect in FRP Shear-Strengthened RC Beams: Design Models versus Experimental Data

Numerous studies on the size effect have been devoted to reinforced concrete (RC) beams. They have shown that increasing the beam size leads to a decrease in ultimate shear strength (stress) at failure. This is reflected in the design model of most current international codes and guidelines, where the size effect is taken into consideration by reducing concrete contribution to the shear resistance (force). In contrast, the size effect of RC beams strengthened with externally bonded (EB) fibre-reinforced polymer (FRP) is not fully documented, and very few experimental studies have been devoted to the phenomenon. The objective of this study was to evaluate the accuracy of the current code and guideline models in terms of the size effect on the EB-FRP contribution to shear resistance. To this end, a database of experimental findings on the size effect in EB-FRP-strengthened beams was built based on the reported literature, as well as our own experimental tests. The data were analysed and compared with the predictions of six current codes and design guidelines to assess their accuracy. Experimental results clearly revealed the presence of a size effect related to EB-FRP as well as the existence of interaction between internal stirrups and EB-CFRP. Based on analysis of the collected experimental test results, the study clearly revealed that the predictions of current codes and guidelines overestimate the contribution of EB-FRP systems to shear resistance. The size effect tends to exacerbate this overestimation as the effective depth (d) of the beams increases. Therefore, until the size effect for RC beams strengthened in shear with EB-FRP is captured by the prediction models, current codes and design guidelines are to be used with caution.

Experimental and Numerical Modeling of Overhanging Riverbank Stability

AbstractOverhanging riverbank stability is a key feature of bank retreat. Although different mechanisms of bank collapse have been studied by many researchers, prediction of cantilever failure patterns and understanding of three‐dimensional failure surfaces continue to puzzle scientists. To address this problem, we conducted laboratory experiments and numerical simulations to investigate the stability of overhanging riverbank. In the laboratory experiments, we analyzed the characteristics of failure surface using a three‐dimensional laser scanner. Results show that with decreased ratio between bank height and near‐bank water depth, there is a transition from a ‘tensile failures followed by toppling failure’ pattern to a ‘shear failure’ pattern. Flow infiltration in our experiments leads to a sharp decrease in soil shear strength and consequently the occurrence of shear failure. For toppling failure, the observed upper retreat distance is much greater than the lower undermining depth, thus challenging the widely adopted assumption of a constant failure surface along the endpoint of the cantilever. Also, we found that failure surface distance can be characterized by twice the width of the overhanging block. As for the failure surface angle, a negative linear correlation is proposed with respect to bank retreat distance, implying a distinct distribution of bank stability along the arched‐shape bank line induced by bank collapse events. Overall, our study deepens understanding of overhanging stability, providing a new perspective on bank retreat process, critical for the morphodynamics of rivers and estuaries.

Borehole contraction and depth analysis based on Extended SMP criterion

The excavation of vertical boreholes is involved in several geotechnical engineering constructions. Earth pressure in the soil is released during the drilling process, resulting in soil stress redistribution and borehole contraction along the excavation surface. The stress and displacement responses tend to increase with soil depth, which may degrade the quality of hole formation and cause collapse. Therefore, the concerns of three-dimensional (3-D) stress and displacement states of the soil around the borehole should be addressed during the design and construction of associated engineering. This study proposes exact and simplified analytical solutions based on the Extended Spatially Mobilized Plane criterion to obtain a more accurate borehole contraction law and depth in drained soil. The 3-D stress and displacement values along the borehole depth are obtained by combining the derived plane solution of cylindrical cavity contraction with the classical earth pressure formula. The proposed solution can reasonably consider the influence of the intermediate principal stress and explicitly state its value. The contraction degree of the proposed solution is 7.76% less than the Mohr–Coulomb solution at a depth of 80 m with the specified soil parameters. A parametric analysis shows that the contraction will be reduced by 21.4% and 36.8% if the unloading ratio increases from 0.4 to 0.5 and 0.6, respectively. The borehole can be supported by a high unit weight of slurry in an elastic state. A decrease in soil shear strength impairs borehole stress state and hole formation quality, and internal friction angle affects more than cohesion in deep soil. The effect of dilatancy on borehole contraction is insignificant. Further, the proposed approximate solution, which ignores the elastic strain in the plastic zone, has a slight error in borehole displacement but is convenient for engineering calculation.

The clays involved in the 1963 Vajont landslide: Genesis and geomechanical implications

The catastrophic Vajont landslide that occurred on 9 October 1963 caused about 2000 deaths when 270–300 Mm3 of rock and debris slid from the northern slope of Mt. Toc into the newly created artificial reservoir, displacing some huge water waves that flooded the nearby villages. The 1963 slide was an en-block remobilisation of a prehistoric rockslide lying on the southern reservoir bank. Basal sliding took place within a complex lithostratigraphic sequence of cherty–marly limestones and clay interbeds belonging to the Fonzaso Formation of Upper Jurassic age. In this work, we investigate the geological origin and provenance of the Vajont clays according to the results of mineralogical and geochemical analyses performed on several clay samples which were collected from the landslide failure surface and the same limestone sequence in the surrounding area. The sampled clayey materials contained variable amounts of clay minerals (36–96%), calcite (4–64%) and quartz (0–6%). The dominant clay minerals were illite/smectite (I/S) mixed layers with a high illite content (85–50%), which was consistent with the high percentage of K2O (1.17–5.77%). The Vajont clays included in the Fonzaso Fm. can be referred to as K-bentonites and can be interpreted as distinct deposits of volcanoclastic materials (tephra), representing the sedimentary inputs of volcanic ashes that interrupted the “normal” calcareous sedimentation during the late Oxfordian–upper Tithonian (158–145 Ma). The soft clay interbeds played a different mechanical role in the occurrence of the prehistoric rockslide and the 1963 en-block remobilisation. When referring to the ancient slope failures, distinct clay-rich layers that were concentrated within some specific lithostratigraphic intervals of the Jurassic cherty limestone sequence caused a localised decrease in the available shear strength, allowing for relative shear displacements along the dip-slope bedding planes. This caused additional shear/tensile fracturing of limestone beds and the formation of a stepped basal failure surface. During the 1963 remobilisation, the clay layers contributed to the average shear strength decrease of the debris material forming the basal shear zone of the slide, but the main triggering factor was the increase in pore pressures caused by the reservoir-induced groundwater inflow.

Effect of Sizing Agents on Surface Properties of Carbon Fibers and Interfacial Adhesion of Carbon Fiber/Bismaleimide Composites.

Physicochemical, surface, and mechanical properties of three batches of T800 grade carbon fibers (CFs) treated with three kinds of sizing agents and Toray T800H CFs were characterized to study the effect of sizing agents on surface properties. Scanning electron microscopy for morphology, atomic force microscopy calculations, and results for the content of sizing agents showed that sizing agent B improved the surface roughness and CFs with high content of sizing agent always presented small surface roughness in a certain content range 1.2–1.6%. Surface energy of CFs was calculated by Young’s contact angle using the test results with water and glycol, and contact angles with LY-1 and modified-AC531 were also acquired. The results proved that CFs of sizing agent group B had the highest average surface energy and the lowest average contact angles with both LY-1 and modified-AC531. From both single-filament and tensile strength test results, the average strength of CFs of sizing agent group B was found to be the lowest, which indicated that sizing agent B had an influence on tensile strength decrease of T800 grade CFs. Comparing the results of interfacial shear strength both in a natural dry state and after hygrothermal treatment, high surface energy was found to be the key element to obtain high interfacial adhesion between T800 grade CFs and bismaleimide, and high surface roughness and low contact angle also played important roles. Among sizing agents A, B, and C, A had an effect on the interfacial shear strength decrease of CFs in the natural dry state, while C had that after hygrothermal treatment.

Effect of fiber hybridization types on the mechanical properties of carbon/glass fiber reinforced polymer composite rod

In order to balance the cost performance of carbon and glass fibers, the unidirectional carbon/glass hybrid fiber reinforced polymer composite rods were developed through the pultrusion technology in the present paper. Two kinds of fiber hybridization types were proposed including intra-yarn hybrid (uniform dispersed hybrid, UDH) and inter-layer hybrid (core-shell hybrid, CSH). Furthermore, the effects of fiber hybridization types on the mechanical properties (interface/short beam shear strength, three-point bending strength and tensile strength) were investigated experimentally. The full-field strain was obtained through the digital image correlation method to reveal the hybrid mechanism. It was found that the effects of fiber hybridization types on mechanical properties were remarkable. Through uniformly dispersing the carbon fiber into the glass fiber, the maximum increase percentages of available strength were up to 10.9% for short beam shear, 60.3% for three-point bending and 58.7% for tensile strength, respectively. The results of full-field strain analysis revealed that the mechanical failure of CSH rods was dominant by the interface debonding of shell/core, which significantly decreased the mechanical properties. In comparison, UDH rods had the intact interface bonding of carbon/glass fiber/resin, the mechanical failure was derived from the fracture of carbon fiber. The tensile strength of carbon fiber was fully utilized, which contributed to the higher mechanical properties. The larger scale carbon fiber tow may form the weaker interface layer of carbon/glass fiber/resin, which led to uneven interface stress distribution under the external loading and the decrease of interface shear strength.

Performance of snow density measurement systems in snow stratigraphies

Abstract Gravimetric and dielectric permittivity measurement systems (DMS) are applied to measure snow density, but few studies have addressed differences between the two measurement systems under complex snowpack conditions. A field experiment was conducted to measure the snow density using the two measurement systems in stratigraphical layers of different densities, liquid water content (LWC), hardness, and shear strength, and the performance of the two measurement systems was analyzed and compared. The results showed that the snow density from the DMS tended to underestimate by 9% in the dry snowpack and overestimate by 3% in the wet snowpack, expressed as the percentage of the mean density from the gravimetric measurement system (GMS). Compared with the GMS, the DMS has relatively low precision and accuracy in the dry snowpack and similar precision and accuracy in the wet snowpack. The accuracy and precision of the two measurement systems increased with the increase of hardness and shear strength of snow in the dry snowpack, but the accuracy and precision measured of the DMSs increased with the decrease of hardness and shear strength of snow in wet snowpack. The results will help field operators to choose a more reasonable measurement system based on snowpack characteristics to get reliable density data and optimize field measurements.

Enhanced ability of magnesium silicate hydroxide in transforming base oil into amorphous carbon by annealing heat treatment

The morphology, thermal stability, phase composition, chemical groups of nanoparticles were characterized, and appropriate thermal process maintains layered structure and weakens the interlayer interaction of the MSH-AHT400. The tribological performances of MSH-AHT400 as lubricant additive are improved due to the decrease of interlaminar shear strength of nanoparticle. Usage of the as-synthesized nanoparticle leads the formation of a-C tribofilm with higher degree of graphitic structural order. Meanwhile, the degree of graphitic structural order of the a-C correlates with the tribological performances positively. The simulations of classical molecular dynamics (CMD) and Ab-initio molecular dynamics (AIMD) confirm the ability of hydroxyl (–OH) and magnesium ions (Mg2+) in transforming base oil into a-C. A tribological mechanism of MSH-AHT400 as lubricant additive is proposed based on the aspects of easier interlaminar cleavage, nano-polishing and filling and repairing of composite tribofilm containing a-C.

Identification of Landslide with Resistivity Method at Candi Industrial Area, Ngaliyan, Semarang

Landslides can be occurred in almost every natural slope or artificial slope slowly or suddenly with or without any prior signs. The main reason for slope collapse is the increase in shear stress in the landslide, the decrease in shear strength, or both. Landslide problems can result in loss of life and property, damage to the environment, infrastructure, public facilities, and disrupt livelihood generally. Landslides can be detected by exploration of the subsurface. The geoelectrical method is one of the geophysical methods to know the change of resistance of a type of rock layer below ground level. The research aims to interpret the lithology of the subsurface in the Candi Industrial Area, Ngaliyan, Semarang using Schlumberger configuration. The results of measurements are voltage and electric current to calculate the apparent resistivity value processed by IP2Win software to determine the lithology and the slip surface area. The results present that lithology in the research area consists of sand clay, clay, and sandstone. The results showed that the locations of landslide-prone areas lie at the contact between sand clay and clay with that area at a depth of between 19.95 – 31.62 m there is one difference in the resistivity value which can be assumed to be a slip surface.The result of the research can be used to make policy rules of landslide mitigation.

Effects of Trace Oxygen Content on Microstructure and Performances of Au-20Sn/Cu Solder Joints

The Au-20Sn solder is widely used in the packaging of high-end electronic products, and the requirement on the reliability of the solder joints is more and more strict with a continuous increase in the performance of the package products. As the oxygen content in the Au-Sn solder is a key factor dominating the quality of fluxless packaging, in this study, the wettability and spreading performance of the Au-20Sn solder with different oxygen contents and the interfacial microstructure, mechanical properties, gas tightness and ratio of soldering area of the Au-Sn/Cu solder joints prepared using these solders were comprehensively investigated to clarify the effects of trace oxygen content. The results reveal that the wetting and spreading performances of the solder decrease sharply with increasing oxygen conte[nt. When the oxygen content increased from 18 to 77 ppm, the spreading area of the solder on the Cu substrate decreased from 92.8 to 49.2 mm2, reducing by 47%. Meanwhile, pores and microcracks appear in the solder joint with relatively high oxygen content, making the shear strength decrease from 56.6 to 31.7 MPa. The oxygen also greatly affects the gas tightness and ratio of soldering area. For the optical window packaged using Au-Sn solder containing 40 ppm of oxygen, the leakage rate was higher than 5 × 10−11 mbar·m−3·s−1 and cannot fulfill the requirements. With increasing oxygen content in the Au-Sn solder, the cleanliness of the chip packaged with these solders deteriorated, and the solder surface was obviously oxidized. When the oxygen content was 18 ppm, the ratio of soldering area was 92%, but decreased sharply to 53% when the oxygen content increased to 77 ppm. It is demonstrated that an oxygen content lower than 27 ppm is required for the Au-20Sn solder used in fluxless packaging.

Some Aspects of Shear Behavior of Soft Soil-Concrete Interfaces and Its Consequences in Pile Shaft Friction Modeling.

This paper examines the stiffness degradation and interface failure load on soft soil–concrete interface. The friction behavior and its variability is investigated. The direct shear tests under constant normal load were used to establish parameters to hyperbolic interface model which provided a good approximation of the data from instrumented piles. Four instrumented piles were used to obtain reference soil–concrete interface behavior. It was found that the variability of the friction characteristics is the highest for organic clays and the lowest for organic silts. The intact samples exhibit lower shear strength than reconstituted ones. The adhesion varies significantly depending on interface and soil type, which can result in high scatter of the skin friction prediction. The analysis of parameters variability can be used to determine the upper and lower bound of friction behavior on the interface at constant normal load condition. The backward shearing results in decrease in shear strength up to 40% of the precedent forward phase but higher initial stiffness by a factor of between 2 and 3. Presented research provides basic shear and stiffness parameters for four soft soils (organic clay, organic silt, peat, and silty loam) and gives information about variability of interface characteristics.

Effects of Suction and Drying–Wetting Cycles on Shearing Response of Adobe

Adobe has been extensively used as a viable construction material in various hot and arid climatic regions throughout the world for several centuries. Adobe bricks, primarily made out of clay, remain in an unsaturated state for the majority of their life span. These unsaturated bricks are vulnerable to weathering, erosion, cracking, and strength degradation due to changes in moisture and drying–wetting cycles imposed by climatic events and seasonal changes. However, limited information exists in the literature regarding the effect of suction and degree of saturation on the mechanical response of unsaturated adobe. The main objective of this study was to experimentally examine the effect of suction on the shear strength and dilatancy of the adobe used for the repair of a 1,500-year-old adobe castle, the Izad Khast Castle, in Central Iran. We tested the index, physical, mineralogical, and microstructural characteristics of the adobe. After determining the drying and wetting paths of the soil water retention curve (SWRC), we built and employed an osmotic direct shear device to evaluate the shear strength extensively and dilatancy of the adobe under various matric suctions (0, 200, 400, and 800 kPa) and vertical stresses (39, 66, and 122 kPa) without and with the application of drying–wetting cycles. The tested adobe exhibited a significant suction hardening with a brittle behavior along with the shear-induced dilation. Increasing suction prompted a notable rise in the effective angle of friction and a linear increase in dilatancy of the adobe. Applying drying–wetting cycles led to a less brittle response accompanied by a decrease in the peak shear strength. The findings offer new insight into the mechanical behavior of unsaturated adobe, which can contribute toward the preservation and maintenance of historical and contemporary adobe structures.

Molecular Dynamics-Based Cohesive Law for Epoxy–Graphene Interfaces

Molecular dynamics simulations are used to obtain mode I and mode II fracture energies and cohesive laws for bulk epoxy and interfaces formed between epoxy and single-layer graphene (SLG), multilayer graphene (MLG), and multilayer graphene oxide (MLGO). The elastic moduli and ultimate tensile and shear strengths of epoxy–graphene interfaces are calculated from uniaxial tension and simple shear loadings. The results show that Young’s modulus and the ultimate tensile strength increase relative to bulk epoxy, whereas the shear modulus and ultimate shear strength are reduced. Failure of epoxy–graphene interfaces in tension occurs due to the formation of voids in the epoxy. Failure in shear is due to tangential slipping at the interface. Under mixed-mode conditions, the shear modulus and shear strength decrease with increasing tensile load. The critical energy release rate $$G_{\text{c}}$$ for the studied epoxy–SLG/MLG/MLGO systems is obtained using a continuum fracture mechanics approach and is found to be significantly lower than for bulk epoxy. All of the results are combined to define mode I and II cohesive laws for bulk epoxy and epoxy–SLG/MLG/MLGO interfaces that can be used in theoretical models and numerical methods, such as finite elements, that employ cohesive zones.