Shear Strain Research Articles

Molecular dynamics study on tribological properties of AlCrFeCoNi HEA at different temperatures

The microscopically wear mechanism of AlCrFeCoNi HEA effected by high temperatures still remains unclear. In this work, the tribological properties of AlCrFeCoNi HEA and tungsten carbide (WC) at temperatures ranging from 250, 400, 550, 700, 850 °C was investigated using molecular dynamics methods. Additionally, the shear strain, contact stress, and energy change at different temperatures were analyzed to explore the atomic wear mechanism. The simulated results indicated that the coefficient of friction and wear rate decrease with the increasing temperature, since the dislocation types decrease and the kinetic energy and total system energy increase. And high temperature can inhibit the synergistic effect of strain accumulation and atomic wear on the surface of AlCrFeCoNi HEAs.

Microstructural and material property changes in severely deformed Eurofer-97

Severe plastic deformation changes the microstructure and properties of steels, which may be favourable for their use in structural components of nuclear reactors. In this study, high-pressure torsion (HPT) was used to refine the grain structure of Eurofer-97, a ferritic/martensitic steel. Electron microscopy and X-ray diffraction were used to characterise the microstructural changes. Following HPT at room temperature to a maximum shear strain of 230, the average grain size reduced by a factor of ∼30, with a marked increase in high-angle grain boundaries. Dislocation density also increased by more than one order of magnitude. The thermal stability of the deformed material was investigated via in-situ annealing during synchrotron X-ray diffraction. This revealed substantial recovery between 450 K – 800 K. Irradiation with 20 MeV Fe-ions to ∼0.1 dpa caused a 20% reduction in dislocation density compared to the as-deformed material. However, HPT deformation prior to irradiation only had a minor effect in mitigating the irradiation-induced reductions in thermal diffusivity and surface acoustic wave velocity of the material. Microstructural and material property changes are dominated by deformation compared to irradiation. In light of this, the benefits of using HPT to improve the irradiation resistance of Eurofer-97 are limited. These results provide a multi-faceted view of the changes in ferritic/martensitic steels due to severe plastic deformation, and how these changes can be used to alter material properties.

Shear behavior on PBL shear connector with a relatively thin perforated steel plate in steel-UHPC composite bridge deck system

Recently, a new steel-UHPC composite deck system is used for long-span bridges, which uses the perfobond rib (PBL) shear connectors with a thinner steel perforated plate. Because the steel perforated plate is thinner, its failure mode may be different from that of thicker steel perforated plate. To explore the shear behavior of PBL shear connectors in this new composite deck system, five sets of ten specimens are tested in this study. The parameters of the hole diameter, D, the traverse rebar diameter, ds, and the perforated steel plate thickness, ts are considered. The failure modes, strain development versus loading, and some mechanical indexes are discussed. The experiments show that the PBL shear connector with a thinner perforated steel plate causes a shear failure, while the thicker one results in bending or bending-shear failure. According to FE (finite element) analysis, the orthogonal analysis is conducted to investigate the effect of each parameter and their interaction on the mechanical behavior. It is found that the ultimate capacity and stiffness are the most sensitive to the diameter of the traverse rebar, ds, and the perforated steel plate thickness, ts. In addition, a theoretical formula is proposed to predict the bearing capacity of PBL shear connectors. The proposed formula considers the relationship between shear strain and the dilation angle for the first time. The results show a good agreement with the experiments. The study in this paper provides a good reference for the application and optimization of PBLs with a thinner steel perforated plate in new steel-UHPC composite deck system.

LVI analysis on the beams with nonuniform cross-sectional area using exponential shear–strain function

Purpose The study aims to investigate the low-velocity impact (LVI) on the surface of a beam with a changeable cross-sectional area. In the study “LVI on a beam with a changeable cross-sectional area and clamped-free boundary conditions”, the effect of changes in the cross-section are on the contact force, the beam displacement, the impactor displacement and the impactor velocity are investigated. Design/methodology/approach To obtain the motion equations, first, a field of displacements of the beam is written using third-order shear deformation of beams, including the exponential shear–strain function, and then the energy method is used. By combining Hamilton’s approaches and Ritz’s method, finally, the equations of motion are extracted. Using ABAQUS finite element code, validation of the theoretical approach is carried out. In this study, the beam with changeable cross-sectional area is considered in such a way that the height of the beam is constant, but the width of the beam changes linearly. Findings The results show that assuming the width of the beam in the clamped support is constant, an increase in the width of the beam in the free support leads to an increase in the peak contact force and the residual velocity of the impactor, also, the peak displacement of the beam and the impactor are decreased. Originality/value It can be shown from the analysis of LVI on beams with nonuniform cross-sectional area that the important influence on the contact force, impactor residual velocity, beam displacement and impactor displacement is achieved.

Smart Cushions with Machine Learning-Enhanced Force Sensors for Pressure Injury Risk Assessment.

Prolonged sitting can easily result in pressure injury (PI) for certain people who have had strokes or spinal cord injuries. There are not many methods available for tracking contact surface pressure and shear force to evaluate the PI risk. Here, we propose a smart cushion that uses two-dimensional force sensors (2D-FSs) to measure the pressure and shear force in the buttocks. A machine learning algorithm is then used to compute the shear stresses in the gluteal muscles, which helps to determine the PI risk. The 2D-FS consists of a ferroelectret coaxial sensor (FCS) unit placed atop a ferroelectret film sensor (FFS) unit, allowing it to detect both vertical and horizontal forces simultaneously. To characterize and calibrate, two experimental approaches are applied: one involves simultaneously applying two perpendicular forces, and one involves applying a single force. To separate the two forces, the 2D-FS is decoupled using a deep neural network technique. Multiple FCSs are embedded to form a smart cushion, and a genetic algorithm-optimized backpropagation neural network is proposed and trained to predict the shear strain in the buttocks to prevent PI. By tracking the danger of PI, the smart cushion based on 2D-FSs may be further connected with home-based intelligent care platforms to increase patient equality for spinal cord injury patients and lower the expense of nursing or rehabilitation care.

Multi-lane vehicle load measurement using bending and shear strains

Abstract Many load identification methods have been proposed, but most are affected by the basic axle parameters and lateral distribution of vehicles. To effectively measure traffic flow with lateral distribution information, this article presents an innovative method that employs a strain decoupling model (SDM) and a vehicle information identification model (VIDM) to measure multi-lane vehicle load depending on the bending strain and shear strain from long-gauge fiber bragg grating (FBG) sensors. The SDM decouples the measured coupling strain into the strain for a single lane load, thereby simplifying the complex structural response resulting from lateral distributed vehicles. By exploiting the distinct characteristics of different strain types that reflect various aspects of the structure, the VIDM establishes a sophisticated mapping relationship between bending, shear strain and axle parameters, which enables the accurate determination of axle parameters including axle speed and spacing. The real-time estimation of the multi-lane vehicle load is achieved by combining the obtained axle information with the decoupled bending strain. This method effectively solves the problem of large load estimation error caused by inaccurate identification of axle parameters, and enables accurate acquisition of vehicle load in lateral distribution using bending and shear strains near the bridge entrance. Both numerical studies and laboratory tests are carried out on a simply supported beam for conceptual verification. The results demonstrate that the proposed method successfully improves the measurement of multi-lane vehicle load.

New discoveries of stress fluctuations at the tool-chip interface and sticking tool tendency in metal cutting processes

Addressing the issue of sticking tools during the metal cutting process is crucial for enhancing cutting efficiency and ensuring industrial safety. This study employs molecular dynamics (MD) simulations to investigate single-crystal SiC tools and 27 different grain orientations of single-crystal pure metal workpieces (Ni, Cu, Co, and Fe). MD models were established to simulate the nanocutting and tool retraction processes. This study revealed a new phenomenon of stress fluctuations at tool-chip interfaces and proposed a new theory on the relationship between stress fluctuations and metal sticking tool tendencies. Research indicates that during nanocutting, the normal stress distribution at the tool-chip interface of different materials exhibits the same periodic fluctuation (T=0.5a, where a is the tool lattice constant). The greater the stress fluctuation is, the greater the sticking tool tendency. By fitting the results for 27 workpieces, an approximate relationship was established. For metals with the same lattice type, such as FCC-structured Ni and Cu, the stress fluctuation and sticking tool tendency are both greater when the cutting orientation is 11111¯0, and the chip morphology and temperature distribution are similar. Through the analysis of lattice transformation, atomic shear strain, and temperature field, this study explored the microscopic mechanisms and thermomechanical theories underlying the new findings of stress fluctuations and sticking tool tendencies. The stress fluctuation distribution at the tool-chip interface is a new discovery that differentiates nanocutting from traditional processing models. Future research can further investigate the cutting behavior of complex materials under complex conditions, which will help to further elucidate the mechanism of sticking tools during processing.

Dynamic deformation characteristics of lightweight soil based on Davidenkov model

The dynamic deformation characteristics of lightweight soil were studied using consolidated-undrained dynamic triaxial tests to predict its non-linear stress and strain behaviour under a traffic load. The results showed that the influence of confining pressure on the attenuation of the dynamic shear modulus ratio became significant with increasing expanded polystyrene (EPS) particle content or cement content. The attenuation curve of the dynamic shear modulus ratio was evaluated using Davidenkov model parameters, A, B and γ 0. It was proved that the parameter A was mostly affected by EPS particle content and confining pressure, with its value ranging between 1.1 and 1.85. The parameter γ 0 was affected by cement content and confining pressure, and its value ranged between 0.0007 and 0.0016. The parameter B was found to range between 0.38 and 0.55, in general. The relationship curves between damping ratio and dynamic shear strain revealed two forms, S shaped and bell shaped. The verification tests showed that the Davidenkov model could predict accurately the dynamic deformation characteristics of lightweight soil both under a changing stress state and under constant gradient loading conditions. These results provide a theoretical basis for determining the deformation of a lightweight soil subgrade under a traffic load.

Study on microstructure evolution mechanism and inhomogeneous characteristic of 2219 aluminum alloy in hot flow forming

In order to reveal the evolution mechanism of the deformation microstructure of 2219 aluminum alloy tube under compression-shear stress, in this paper, flow forming tests and their numerical simulations were carried out, respectively, at temperatures from 250 °C to 400 °C. Meanwhile, a midrange layer index was proposed to analyze the gradient of deformation microstructure. The results show that multiple recrystallization mechanisms of the 2219 aluminum alloy are presented simultaneously during hot flow forming. The shear stress during forming is the main factor that generated the microstructure gradient along the thickness direction, and the recrystallization level is higher with higher shear strain. In addition, it is beneficial to improve microstructure homogeneity and mechanical properties by increasing thickness reduction or decreasing the temperature. This study provides guidance for microstructure control of the 2219 aluminum alloy tube flow forming process.

A Standard Penetration Test-Based Step-by-Step Inverse Method for the Constitutive Model Parameters of the Numerical Simulation of Braced Excavation

Numerical simulation is an essential method for predicting soil deformation caused by foundation pit excavation. Its accuracy relies on the constitutive model and its parameters. However, obtaining these parameters through lab tests has limitations like long durations, high costs, and potential errors. To improve the simplicity and accuracy of the selection of constitutive model parameters, this study proposes a step-by-step inverse analytical method. Using the braced excavation project in Hangzhou City, China as a case study, the proposed method firstly determines the ratio of the important constitutive parameters then the values of the key constitutive parameters. The results show that the reference secant stiffness (E50ref) and shear strain (γ0.7) of the hardening soil (HS) and hardening soil–small soil (HSS) models are the key constitutive parameters. The step-by-step inverse method not only reduces the number of parameters, but also improves the predicting accuracy. The established empirical relationship between the E50ref and standard penetration test (SPT) blow counts exhibits a good linear correlation. The parameter selection method proposed in this study is an accurate, practical, and efficient method, which can effectively predict the horizontal displacement and surface settlement of the retaining structure in multiple excavation stages.

Experimental and numerical investigation of debris flow interception using multiple stepped flexible barriers

Flexible barriers are a type of environmentally friendly and easily constructed retaining structure. Owing to the deformability and limited strength of the flexible barrier material, these barriers can only be used in small- or medium-sized debris-flow gullies. In this study, we proposed an improved layout, namely the multiple stepped flexible barriers, to address the limitations of traditional flexible barriers in the application of debris-flow control. We used experimental and numerical methods to investigate the separation effect of the multiple stepped flexible barriers and their stress and strain distributions in solid aggradation after reaching its maximum storage capacity. The results demonstrated that the ability of the multiple stepped flexible barriers to separate large particles gradually decreases with increasing debris-flow density, which implies that the debris-flow regulation ability of the multiple stepped flexible barriers decreases with increasing debris-flow density. When the debris-flow density exceeds 2200 kg/m3, the multiple stepped flexible barriers will completely lose their ability to reduce the density of debris flows. In addition, the thickness of the solid aggradation initially increases and then subsequently decreases upstream; the thickness of the solid aggradation increases with increasing debris-flow density. The results obtained from numerical simulation demonstrated that there would be relatively large shear stress and shear strain near the bottom of each flexible barrier. When the longitudinal spacing of the flexible barriers increases to 1.6 times their height, the internal stress of the upper aggradation layer that was transferred to the lower layer gradually weakens or disappears. Under this condition, the soil pressure of the flexible barrier is relatively small. The results of this study provide guidance for the design and construction of multiple stepped flexible barriers in wide debris-flow gullies.

In Situ Synchrotron Diffraction Assessment of Reversibility of the Martensitic Transformation in Single-Crystalline Co–Ni–Ga Shape Memory Alloy Under Torsion

AbstractHeusler-type Co–Ni–Ga shape memory alloys attracted significant attention due to their excellent functional properties in single-crystalline state under both compressive and tensile loading. The present study investigates the superelastic deformation behavior under torsion. Using a newly installed torsion testing setup, in situ synchrotron diffraction was carried out on single-crystalline material in order to investigate the martensitic phase transformation. Incremental deformation experiments reveal a fully reversible martensitic transformation under torsional loading at room temperature, leading to excellent strain recovery after deformation to 6.5% shear strain. Furthermore, relevant aspects towards the analysis of powder diffraction data obtained for single-crystalline material in transmission mode under torsional loading are presented and critically discussed.

Fault system dynamics of the Kashmir, NW Himalaya, India using continuous GPS observations and geomorphic evidences

We collected data from the continuous Global Positioning System (cGPS) sites across the Kashmir Valley, situated at latitude 34◦N, spanning from 2008 to 2021. Inter-site velocities define a region of approximately 15,000 km2 with broadly distributed strain accumulation at −7.22×10−8 nano strain/year (compression component) and the maximum shear strain γmax of 1.9051×10−7 nano strain/year. The estimated site velocity in the ITRF14 ranges between 30.5±1–42.85±3 mm/yr. It was observed that the average deformation rate of the GPS sites in the Kashmir region ranges between 2.86±1–15.47±3 mm/yr relative to the India fixed reference frame, suggesting a predominant N-S directed compressional tectonic regime. The focal mechanism solutions of the earthquakes in and around the Kashmir Valley suggest dominant thrust faulting followed by normal faulting. Analysis of the vertical component of the GPS time series shows that the northwest segment of the valley subsides at the rate of −1.71± 0.70 mm/yr, while the southeast segment uplifts at the rate of 5.4 ± 0.5 mm/yr. In addition to vertical component, we observed differential movement of the sites relative to IISC site on the northwest and southeast segments. The rate of baseline change of the GPS sites indicates 7.30 ± 0.75 mm/yr extension in SE-NW direction and −5.32 ± 0.75 mm/yr NE-SW compression across and along the Kashmir Valley. Geodetic observations reveal a transition that aligns with the Magam lineament/fault previously identified by Ganju and Khar (1984) using gravity and magnetic data. The observation was supported by the field investigations and remote sensing techniques, confirming the existence of Magam Fault. During the field investigations, various geomorphic expressions of fault were observed, including fault ruptures, fault scarps, offset ridges, deflected drainages/rivers, linear alignment of springs, linear drainage lines, triangular facets and offset Recent sedimentary deposits (Karewas) were observed. The field evidence suggests exposure of normal faults at Kondabal, Nasrullapora, Biru and Radbugh. These exposed extensional structures, trends in NE-SW direction and dip in NW direction with varying offset and dip amount. GPS observations supplemented by geomorphic evidences infer the presence of normal fault ̴ 80 Km extending from northeast to southwest.

A strain components-based Mohr–Coulomb fracture criterion for proportional loading

Ductile fracture criteria are crucial in the application of elastoplastic materials like advanced high-strength steels, particularly due to their tendency to fail without significant localized necking. It is aimed to figure out the unified mechanism for ductile fracture and accurately describe it with phenomenological criteria. In this study, the effect of the stress triaxiality and the Lode parameter is analyzed mathematically. The maximum shear strain and the normal strain to fracture are emphasized in the proposed strain components-based Mohr–Coulomb fracture criterion particularly designed for plane stress states, and it is assumed that fracture occurs when the combination of the maximum shear strain and the normal strain reaches the critical value. It is then extended to describe fracture with the equivalent plastic strain and the normal strain to fracture. The experimental fracture data of AA 2024-T351 and the additively manufactured Ti-6Al-4V titanium alloy are used to verify the proposed models. A fracture forming limit diagram comprising forming limit curves calibrated from stress states under different stress triaxialities is proposed based on the proposed fracture criteria for plane stress states. This study shows that a strong correlation between the maximum shear strain and the normal strain to fracture has been observed, and it can be described piecewise-linearly. Besides, the orientation of the fracture surface under both tension (including plane strain tension) and compression (including plane strain compression) can be qualitatively explained by the Mohr’s strain circles. The results provide a new insight into the intrinsic deformation and fracture mechanism of materials that fail without severe localized necking.

Comparison of thermal, rheological properties of Finnish Pinus sp. and Brazilian Eucalyptus sp. black liquors and their impact on recovery units

Black liquor (BL) is the major bioproduct and biomass fuel in pulp mill processes. However, the high viscosity of BL makes it a challenging material to work with, resulting in issues with evaporators and heat exchangers during its transport and processing. The thermal and rheological properties of BLs from Pinus sp. (PBL) and Eucalyptus sp. (EBL) were studied. FTIR spectra revealed the presence of the characteristic functional groups and the chemical composition in liquors. TGA/DTG curves showed three characteristic degradation stages related to evaporation of water, pyrolysis of organic groups, and condensation of char. Rheologically, liquors are classified as non-Newtonian and with comportment pseudoplastic. Their rheological dynamic shear properties included a linear viscoelastic region up to 1% shear strain, while frequency sweeps showed that storage modulus (Gʹ) > loss modulus (Gʹʹ), thus confirming the solid-like behavior of both BLs. The rheological study demonstrated that increasing the temperature and oscillatory deformations of PBL and EBL decreased their degree of viscoelasticity, which could favor their pumping and handling within the pulp mill, as well as the droplet formation and swelling characteristics in the recovery furnace.

On the Conservation Laws and Traveling Wave Solutions of a Nonlinear Evolution Equation that Accounts for Shear Strain Waves in the Growth Plate of a Long Bone

On the Conservation Laws and Traveling Wave Solutions of a Nonlinear Evolution Equation that Accounts for Shear Strain Waves in the Growth Plate of a Long Bone

Ultrasound Imaging of Thoracolumbar Fascia: A Systematic Review.

Over the past decade, there has been a notable increase in research focused on ultrasound imaging of thoracolumbar fascia (TLF). Nevertheless, published papers' results about the application of US imaging in TLF examination are still sparse. Background and Objevtives: Hence, this systematic review was performed aiming to firstly investigate the use and the methodology of ultrasound imaging to assess pathologic and healthy TLF. Secondarily, we aim to assess intra- and inter-observer reproducibility of US imaging in TLF assessment. Materials and Methods: The search was done on PubMed and Web of Science database from inception to April 2024. Furthermore, the references of included papers were thoroughly checked to find eligible publications. The MeSH keywords used were: "Thoracolumbar fascia", "Ultrasound Imaging", "Ultrasound", "Ultrasonography", and "Ultrasound examination". Results: Studies were aimed primarily at TLF diagnosis, treatment monitoring, or evaluating movement-related changes, underscoring the diverse clinical applications. The US parameters assessed included TLF thickness, echogenicity, stiffness, deformation, shear strain, and displacement, providing comprehensive insights into TLF features. Conclusions: Advanced US imaging holds promise as a reliable tool in musculoskeletal assessment, offering insights into TLF pathology/disfunction, treatment outcomes, and movement dynamics.

Mechanism of a rainfall-induced landslide in a large-scale flume experiment on a weathered granite sand

IntroductionsA large-scale flume experiment was performed to evaluate the mechanism of landslide occurrence due to rainfall using weathered granite sand. The dimensions of the flume were 9 m (length), 1 m (width), and 1 m (depth). The weathered granite sand from the actual landslide site at Da Nang City, Vietnam was used. The pore water pressure was measured by a pore-water pressure transducer at two depths (middle and bottom) to determine the process of rainwater infiltration into the soil. The surface deformation was measured with extensometers at three positions of the slope. The deformation of the entire slope was determined by the 160 cylindrical-shaped makers evenly spaced in the slope and three cameras.ResultsThe results showed that the rainfall infiltrated into the slope process, increasing from negative pore water pressure to approximately 0. The maximum shear strain contour has been plotted in total and in time increments. The shear band was detected from the time increments maximum shear strain contour. The localization in the shear band formed just before failure.ConclusionsTo the best of our knowledge, this is the largest scale laboratory test ever conducted to calculate the shear band. Moreover, it was found that the failure occurred when the sand was in an unsaturated phase. Failure does not seem to depend on the increase in pore water pressure but on the maximum shear strain. This feature can be used to explain the phenomenon of landslides that occur even when the groundwater level does not increase but large deformation occurs.

New design charts for evaluating the damage potential to RC frame buildings adjacent to deep excavations

PurposeUrban excavations are a cause for concern in terms of the probability of damage to nearby structures. In this study, various structural and excavation parameters were investigated to determine the probability of building damage during excavations.Design/methodology/approachFinite-element analysis software was used to develop a set of valid three-dimensional models. Models were developed to assess the effects of structural parameters (building height and position relative to the excavation site) and excavation parameters (depth and support system type) on the responses of the adjacent buildings.FindingsThe new design charts estimated the damage to reinforced concrete frame buildings during excavation by focusing on the angular distortion of the building, additional shear strain on the masonry walls and additional strain and stress on columns. This study showed that the probability of damage decreased as the distance between the building and the excavation increased. By contrast, it increased when the building was located at a distance equal to the excavation depth at its edge. According to this study, the axial stress caused by the excavation of building columns does not exceed 10.9% of the compressive strength of the concrete.Originality/valueThe proposed design charts can replace comparable charts and provide a deeper understanding of damage potential based on key parameters. These charts are more practical than previous charts with limited parameters.

Development of Tools for the Direct Measurement of Shear Stress and Shear Strain within a Soil Mass

Abstract This article describes the development of sensing tools designed and applied to the direct measurement of shear stresses and shear strain within a soil mass. The importance in the development of these tools is in their ability to measure shear stresses and shear distortions within soil without any a priori information of the stress and strains applied at the boundaries of the system. These tools may be applied to element testing, testing of physical models, and field applications. The sensors were used in the testing of a sand in a large simple shear apparatus, under both constant height and constant vertical pressure conditions. Testing demonstrated that shear stresses smaller than 0.1 kPa are easily resolved. Shear strains smaller than 10−5 (abs) were reliably measured. Measurement of shear stress and shear distortion within the soil mass allows for direct determination of the shear stiffness of the soil. Shear stiffness measured in this fashion is significantly greater than that determined from the globally measured shear stress and shear strain. The stiffness degradation curve illustrates a constant shear stiffness over the range of 10−5 through 5·10−4.