Development Of Shear Strain Research Articles

Evaluation, sampling and testing methods for offshore disturbed sands with plastic fines: A case study

Sandy seabed, prevalent near continental shelves, often contains fines that obviously affect their apparent behaviour. The variation in the physical properties of sands and fines, the difference between seismic and marine wave loads, and the challenges in obtaining accurate geotechnical parameters and undisturbed samples for analysis make it difficult to effectively evaluate the properties of sands with plastic fines in offshore engineering. To address this issue, a method for discriminating and re-sampling sands with plastic fines is suggested, along with a case study to assess the static and dynamic behaviours of such sands from an offshore site in the South China Sea. In this study, evaluation processes for detecting the presence of fines in sands and classifying them as plastic or non-plastic are first recommended to gain a better understanding of such sands. Then, a reconstitution approach of re-sampling for disturbed sand samples from site and compactness assessment guided by the optimum moisture content, is suggested to restore their in-situ characteristics, addressing the difficulty in obtaining undisturbed sand samples. Subsequently, the failure behavior and shear strain development under cyclic loading are analyzed via a cyclic contour diagram to evaluate their mechanical properties under marine environmental loads. The obtained contour diagrams can be further integrated into the constitutive model in subsequent research and used in finite element analysis to simplify the computation for marine foundation design. These results can provide valuable insights for improving understandings and engineering practices related to sandy seabed with plastic fines in offshore environments.

Liquefaction behavior and shear strain-based pore pressure model of fiber reinforced calcareous sand

The generation mechanism of pore pressure plays an essential role in understanding the liquefaction behavior of sand under cyclic loading. Extensive undrained simple shear tests were undertaken to study the pore pressure and shear strain development characteristics of calcareous sand reinforced by fibers. The results show that the deformation patterns of the tested calcareous sand gradually shift from brittle to ductile failure as fiber content increases. The mechanism of pore pressure generation in calcareous sand subjected to cyclic loading is quite distinct from that of siliceous sand, exhibiting more pronounced accumulation in the initial stage of cyclic loading. Fiber reinforced calcareous sand exhibits reverse shear contraction behavior when liquefaction is imminent. A remarkable finding is the establishment of a unique correlation between pore pressure ratio and shear strain, irrespective of the fiber reinforcement. Consequently, a shear strain-based pore pressure generation model of reinforced calcareous sand is then developed to predict the pore pressure built-up trend under varying fiber content and length conditions. This model is also applicable to various testing conditions and soil types.

Undrained cyclic behavior of underconsolidated marine clay in multidirectional simple shear tests

In the field of marine reclamation engineering, underconsolidated marine clay often presents challenges owing to its susceptibility to multidirectional cyclic stresses and potential for excessive deformation. This research examined the undrained cyclic behavior of underconsolidated marine clay through multidirectional cyclic simple shear tests. It explored shear strain evolution, the cyclic shear stress–strain relationship, and stiffness degradation by analyzing the impacts of clay consolidation levels and phase differences in the cyclic stress. The findings indicated that as the degree of consolidation increased, the rate of cyclic shear strain development in marine clay gradually diminished. Conversely, an enhanced phase difference led to a quicker evolution of shear strain. Additionally, as loading continued, the tested clay exhibited notable softening behavior, leading to stiffness degradation. A larger phase difference resulted in more pronounced stiffness degradation, although a higher degree of consolidation effectively delayed this degradation. These findings provide new insights on the cyclic behavior of underconsolidated marine clay under multidirectional loading, offering crucial information for marine reclamation engineering.

Dependence of mechanical and surface characteristics on twin boundaries of CoCrFeNiAl high-entropy alloy

The mechanical and surface properties of non-equiatomic CoCrFeNiAl high-entropy alloy (HEA) in the scratching process are explored through molecular dynamics simulation in the current work. The result reveals that the loading force decreases with the reduction of the twin thickness because the presence of excessive twinning in the structure is obviously related to the material softening. The average coefficient of friction (COF) is not proportional to the increment of twin thickness, and the COF in the scratching of monocrystal HEA is greater than in the scratching of twinning-containing workpieces. The plastic deformation behavior shows that the development of shear strain and residual stress into the workpiece in-depth decreases with rising the twin boundary distance. In addition, the pile-up height is larger with the increment of twin thickness, showing the ease of material removal in the machining for the large twin boundary sample. The number of wear atoms of a monocrystal sample is significantly larger than that of the twinning-containing specimens. The microstructure evolution shows that the dislocation and the stacking fault grow along the {111} primary sliding system for the monocrystal specimen, while the defects develop along the twin boundary for twinning-containing specimens.

Quantification of Shear Strain Development in the Through-Thickness Direction During Sliding Wear

Quantification of Shear Strain Development in the Through-Thickness Direction During Sliding Wear

Characterization of shear deformations in reinforced concrete members without shear reinforcement

The load-carrying capacity of many reinforced concrete structures is governed by shear failures, occurring before reaching the flexural capacity of the member. For redundant systems, such as slabs subjected to concentrated loads, local shear failures (typically initiated at locations with highest shear forces) can however occur after redistributions of internal forces due to the propagation of the shear cracks. Such process can depend upon the development of shear strains and the softening response of the member and can be stable or unstable. A suitable understanding and modelling of the complete shear response of reinforced concrete, including its deformations both for its pre- and post-peak branches, is thus instrumental for a consistent and comprehensive analysis of the shear response and strength of redundant elements.Such topic has received little attention in the past and analyses of redistributions of internal forces in concrete structures are often performed on the basis of refined flexural models, but coarse considerations for shear strains (typically elastic laws). This situation is a consequence of the lack of consistent experimental measurements on the shear deformations of reinforced members both before and after reaching the maximum shear capacity. Currently, however, the advent of refined measurements techniques such as Digital Image Correlation allows for an accurate tracking of the shear strains and for a fundamental understanding of its development. In this paper, taking advantage of such techniques, a comprehensive approach for determining the shear strains and their distribution across the depth of a section is presented. This approach allows reproducing accurately the development of shear strains and to predict the load-carrying capacity of redundant systems. The model is validated with selected test data and is considered as an effort to contribute to future numerical implementations of reinforced concrete shell models with realistic out-of-plane responses.

Effect of principal stress rotation on deformation behavior of dense sand–clay mixtures

This paper investigated the deformation behaviour of K-consolidated sand–clay mixtures through cyclic triaxial (CT) and hollow cylinder (CHC) tests. The sand–clay mixtures contained 0%, 5%, 10% and 20% clay by weight and were prepared at a relative density of 75%. Clay inclusion caused an increase in the permanent axial strain of mixtures (0.075% to 5% in CT and 0.186% to 5% in CHC), while a relatively insignificant increase in permanent axial strain was observed in the CT specimens containing 5% and 10% clay (0.075% to 1.299%). However, all CHC specimens with clay failed (εz ≥ 5%). It was also observed that shear strain development of sand is significantly influenced by clay inclusion (0.096–2.241%) in CHC tests. Test results clearly show that the effect of a principal stress rotation should be taken into account to better estimate the deformation behaviour of sand–clay mixtures under repetitive traffic loads.

Deformation mechanisms and kinematics of a soft sedimentary bed beneath the Scandinavian Ice Sheet, north-central Poland, revealed by magnetic fabrics

Characterising deformable substrates of modern and past ice sheets is a key factor in understanding ice mass behaviour and dynamics. This is challenging when field-scale signatures of deformation in soft sedimentary beds are weakly developed or absent. To overcome these difficulties, in this study, we combine micro- and macroscale studies and quantitative analyses to decipher the nature of subglacial sediment deformation under a Pleistocene fast-flowing (streaming) ice sheet. We investigated a complex sedimentary succession at Nieszawa in north-central Poland. A multi-proxy approach involving till micromorphology in thin sections, ripple-cross lamination orientation, till fabric, clast microfabric and the anisotropy of magnetic susceptibility (AMS) data in a closely sampled vertical profile throughout the fluvial sand and till was used to reveal subglacial bed deformation mechanisms and kinematics. This records subglacial deformation of the sedimentary succession at Nieszawa under low basal shear stresses, where simple shear was the dominant bed deformation mechanism. Intergranular advection, decoupling at the ice-bed interface related to high subglacial water pressure, clast ploughing, and basal sliding also took place. The main finding of this study is that AMS reveals the shear strain development and ice flow direction in the structurally and texturally complex deposits under weak coupling conditions at the ice-bed interface beneath a fast flowing/streaming ice sheet, where strain and kinematic indicators other than AMS fabrics are vague or absent.

SANISAND-MSf: a sand plasticity model with memory surface and semifluidised state

A new constitutive model for sand is formulated by incorporating two new constitutive ingredients into the platform of a reference critical state compatible bounding surface plasticity model with kinematic hardening, in order to address primarily the undrained cyclic response. The first ingredient is a memory surface for more precisely controlling stiffness affecting the plastic deviatoric and volumetric strains and ensuing excess pore pressure development in the pre-liquefaction stage. The second ingredient is the concept of a semifluidised state and the related formulation of stiffness and dilatancy degradation, aiming at modelling large shear strain development in the post-liquefaction stage. In parallel, a modified flow rule aimed at providing a better description of non-proportional monotonic and cyclic loading is introduced. With a single set of constants, for which a detailed calibration procedure is provided, this new model successfully simulates undrained cyclic torsional and triaxial tests with different cyclic stress ratios, separately for the pre- and post-liquefaction stages, as well as liquefaction strength curves based on [Formula: see text] and shear strain criteria for initial liquefaction. The successful reproduction of the sand element response under undrained cyclic shearing contributes to future applications in realistic and thorough seismic site response analysis.

Cyclic shear characteristics of marine cement soil under stress path with bidirectional shear stress

Under seismic loading, marine soil experiences horizontal shearing in two directions with different shear directions and amplitudes. It is therefore of considerable practical relevance to study the deformation behavior of marine cement soil under bidirectional shear loading. In this study, a series of cyclic simple shear tests were carried out to investigate the undrained deformation behavior of marine cement soil. The cyclic strain, stiffness softening, and cyclic strength were found to be significantly related to the phase difference and cement content. Cyclic shear strain accumulation increases as the number of cycles increases, and the emergence of inflection on the shear strain curve can be considered a suitable failure criterion for cement soil. The turning strain decreases as the cement content increases, and the phase difference decreases. With a decrease in cement content and an increase in phase difference, the rate of cyclic degradation and development of shear strain significantly increased. It was observed that the cyclic strength of cement soil increases with the cement content and decreases as the phase difference decreases.

The effects of initial deviatoric stress on anisotropy of marine clay and strain components

This study investigated effects of initial deviatoric stress state and the orientation of their major principal stresses on the strain components and shear strength of soft marine clay. Hollow cylinder test results demonstrated that the axial and circumferential strain component magnitudes substantially depended on the initial deviatoric stress and the principal stress direction. The octahedral shear indicated the highly anisotropic microstructure of the clay, and the initial deviatoric stress significantly affected the octahedral shear strain development and influenced the anisotropic microstructure. The results can provide an experimental basis for constitutive modeling of marine clay and provide guidance for ocean engineering.

Experimental study on Shear behaviors of RC beams strengthened with ECC layers

The experimental study on shear behaviors of reinforced concrete (RC) beams externally strengthened with Engineered Cementitious Composite (ECC) layers were conducted and analyzed. The RC beams were designed and fabricated without stirrups. ECC was sprayed onto the sides of the beams to the designed thicknesses which were 20 mm, and 40 mm. A series of four-point bending experiments were performed to study and analyze the shear behavior of the specimens. The thickness of ECC layers and shear span-to-depth ratios were considered and analyzed. It is an effective way for the shear strengthening of RC beams with ECC layers. The ECC layers’ thickness should be restricted to override the debonding between ECC layers and RC beam or to strengthen an RC beam into an under reinforced one. Fibre Bragg Grating sensors can be used to measure the development of shear strain of the strengthened specimens.

On the variation of mechanical properties of saturated sand during liquefaction observed in shaking table tests

Soil liquefaction induced by earthquakes not only causes settlement and lateral spreading of the ground, but also lowers the stiffness and strength of soil. In this paper, the variation of soil mechanical properties during liquefaction was investigated by revisiting the data of the physical model shaking table tests on saturated sand using a large laminar shear box conducted in National Center for Research on Earthquake Engineering with sinusoidal waves and the record of 1999 Chi-Chi Earthquake as input motions. The excited responses of the ground specimen during liquefaction were firstly characterized through spectrum analysis. One-dimensional shear beam idealization of the ground for wave propagation was further introduced to deduce the stress-strain relationship of the soil body. Thus, the variation of mechanical properties of saturated sand with respect to the development of shear strain and excess pore water pressure can be examined, which is beneficial to estimate appropriate soil parameters for the seismic design of foundations and to reasonably assess the seismic response of liquefied ground.

Shear Behaviors of RC Beams Externally Strengthened with Engineered Cementitious Composite Layers.

The shear behaviors of reinforced concrete (RC) beams externally strengthened with engineered cementitious composite (ECC) layers were studied and the strengthening effect was evaluated based on a truss and arch model. The beams were designed without web reinforcement in the middle part and ECC was sprayed onto both sides of the beams to the designed thicknesses, which were 20 mm and 40 mm. A series of four-point bending experiments were conducted and analyzed. The development of the shear strain in each side of the beams was recorded by strain rosettes formed with three fiber Bragg grating (FBG) sensors. The thickness of ECC layers, reinforcement ratios, and shear span-to-depth ratios were considered and analyzed. This is an effective way to shear strengthen RC beams with ECC layers. The ultimate load of the strengthened specimen can be improved by 89% over the control specimen. Strengthening an RC beam into an under-reinforced beam should be avoided. The FBG sensors are suitable to measure and monitor the development of shear strain in the side of the strengthened specimen. Based on the truss and arch model, an evaluation of the shear strengthening effect was established and the results agree well with the experimental results.

Effect of liquefaction on nonlinear seismic response in layered soils: a case study of Babol, North of Iran

Soft soil layer can significantly increase destruction during ground motions. Although, earthquake waves pass through mainly rocky media to reach ground surface, they often transit through a thin layer of surficial soil which can dramatically affect ground surface motions. This study thoroughly investigates the effect of liquefaction on the seismic response of soft soil layers using the finite difference method in specific areas of Babol City, north of Iran. Nonlinear effective stress analysis was carried out using FLAC 2 D, a finite difference based software. Liquefaction potential was evaluated based on both pore pressure ratio (R u) and shear strain amplitude criteria. The logical agreement of these two criteria was observed. Based on the results, near the river of this city, strong site effect observed due to the presence of soft soil layers and liquefaction, effectively altered the amplitude and frequency content of ground motions. Seismic analyses proved that spectral acceleration responses were attenuated for low periods due to the shear strain development and energy dissipation of motion but they increased for longer periods, which could strongly affect the seismic design of structures.

Effects of the principal stress rotation in numerical simulations of geotechnical laboratory cyclic tests

Cyclic stress paths in geotechnical experiments can generate considerable principal stress rotation (PSR) in the saturated soil. The PSR without changes of principal stress magnitudes can generate additional excess pore water pressures and plastic strains, thus accelerating liquefactions in undrained conditions. This paper simulates a series of laboratory tests considering the PSR using two types of sand. The impact of PSR is taken into account by using an elastoplastic soil model developed on the basis of a kinematic hardening soil model with the bounding surface concept. The soil model considers the PSR by treating the stress rate generating the PSR independently. The capability of this soil model is verified by comparing the numerical predictions with and without PSR, as well as experimental results. The comparative results indicate that the simulation with the soil model considering the PSR can better reproduce the test results on the development of shear strain, reduction of effective confining pressure and liquefaction than the soil model without PSR. Therefore, it is important to consider PSR effects in simulations of geotechnical experiments under cyclic loadings.

Mechanics of the reciprocal effects of bending and torsion during 3D bending of profiles

Profiles with circular cross-sections can be geometrically described by the shape of the bending line. To achieve 3D bending lines with kinematic bending processes, a continuous change of the bending plane is needed, resulting in bending force vectors that change direction accordingly. These force vectors generate a bending moment in the forming zone and, hence, longitudinal tensile and compressive stresses. For profiles with non-circular cross-sections the orientation of the cross-section along the bending line needs to be controlled additionally. This can be achieved by applying a specific torque to the bending process and, thus, introducing desired shear stresses into the forming zone. Until now, this fundamental aspect of 3D profile bending has not been studied in a coherent fashion. To take into account the reciprocal effects of the various stresses applied to the forming zone and their effect on the bending moment and, thus, on springback, a comprehensive analytical process model was set up. The model is validated by experimental investigations performed using the Torque Superposed Spatial (TSS) profile bending machine and by comprehensive numerical investigations. Analyses were performed during plane bending as well as during bending superposed with torsion. The investigations show that the applied bending force and torque not only result in stress superposition, but actually also affect the development of shear strains over the cross-section of the profile. Similar to the longitudinal strains, the shear strains decrease linearly from the intrados and extrados of the profile to the neutral axis. Considering this newly observed behavior in the analytical process model, the absolute bending force deviation was reduced by a factor of four down to 7.6%.

Effect of degree of cure on viscoplastic shear strain development in layers of [45/−45]s glass fibre/ epoxy resin composites

Effect of degree of cure on irreversible (viscoplastic) shear strain development in layers of glass fibre/ epoxy resin (LY5052 epoxy resin) [+45 °/−45 °]slaminate is studied performing a sequence of constant stress creep and viscoelastic strain recovery tests. For fixed values of degree of cure in range from 79.7% to 100%, the viscoplastic strains were measured as dependent on time and stress and Zapa's integral representation was used to characterize the observed behaviour. It is shown that at all degrees of cure the viscoplastic behaviour can be described by Zapa's model with parameters dependent on degree of cure. It is shown that for degree of cure lower than 80% the viscoplastic strains grow much faster and are much more sensitive to the increase of the applied shear stress. These irreversible strains developing in the final phase of the curing can significantly alter the residual stress state in the composite structure.

Effect of the middle lamella biochemical composition on the non-linear behaviour of technical fibres of hemp under tensile loading using strain mapping

This manuscript describes the effects of alterations in biochemical composition on structural morphology and the mechanical behaviour of technical fibres of hemp used for composite applications. First, the strength and apparent Young’s modulus distribution of technical fibres of hemp of 96 hemp samples, corresponding to 32 different hemp accessions cultivated in 3 locations, were analysed using Weibull distribution. From these, 2 samples (one with high and one with low fibre strength) were selected for further analysis. Next, full-field strain measurement at the micro-scale during tensile loading via digital image correlation analysis was used for evaluating both, the stress-strain behaviour at a global scale and the local mechanical behaviour heterogeneity at a micro-scale, along a technical fibre of hemp. The analysis reveals 2 typical types of tensile stress-strain curves, and a complex and very irregular pattern of strain concentrations, which are associated to the technical fibre strength. The non-linear behaviour of the stress-strain curve is explained by the development of shear strain at the elementary fibre (botanically defined as the individual cell) interphases. Micro tomography and biochemical analysis of the technical fibre microstructure showed that alterations in cell wall composition, in particular substitution of pectin, leads to changes in the non-linear behaviour of technical fibres of hemp under tensile loading.

Statement of Retraction

This article refers to:RETRACTED ARTICLE: Initial shear strain development during formation of nanostructured metal chips