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Two-phase γ-TiAl/α 2-Ti3Al lamellar intermetallics have attracted considerable attention because of their excellent strength and plasticity. However, the exact deformation mechanisms remain to be investigated. In this paper, a solidified lamellar Ti–Al alloy with lamellar orientation at 0°, 17°, and 73° with respect to the loading direction was stretched by utilizing molecular dynamics (MD) simulations. The results show that the mechanical properties of the sample are considerably influenced by solidified defects and tensile directions. The structure deformation and fracture were primarily attributed to an intrinsic stacking fault (ISF) accompanied by the nucleated Shockley dislocation, and the adjacent extrinsic stacking fault (ESF) and ISF formed by solidification tend to form large HCP structures during the tensile process loading at 73°. Moreover, cleavage cracking easily occurs on the γ/α 2 interface under tensile deformation. The fracture loading mechanism at 17° is grain boundary slide whereas, at 73° and 0°, the dislocation piles up to form a dislocation junction.

High-rate strength behavior plays an important role in the shock initiation of high explosives, with plastic deformation serving to localize heat into hot spots and as a mechanochemical means to enhance reactivity. Recent simulations predict that detonation-like shocks produce highly reactive nanoscale shear bands in the layered crystalline explosive TATB (1,3,5-triamino-2,4,6-trinitrobenzene), but the thresholds leading to this response are poorly understood. We utilize molecular dynamics to simulate the high-rate compressive stress–strain response of TATB, with a focus on understanding flow behavior. The dependence of strength on pressure and loading axis (crystal orientation) is explored. The deformation mechanisms fall broadly into two categories, with compression along crystal layers activating a buckling/twinning mode and compression normal to the layers producing nanoscale shear bands. Despite the complexity of the underlying mechanisms, the crystal exhibits relatively straightforward stress–strain curves. Most of the crystal orientations studied show rapid strain softening following the onset of yielding, which settles to a steady flow state. Trajectories are analyzed using five metrics for local states and structural order, but most of these metrics yield similar distributions for these deformation mechanisms. On the other hand, a recently proposed measure of intramolecular strain energy is found to most cleanly distinguish between these mechanisms, while also providing a plausible connection with mechanochemically accelerated decomposition kinetics. Localization of intramolecular strain energy is found to depend strongly on crystal orientation and pressure.

Despite the excellent improvement of high field by adopting REBa2Cu3Ox (REBCO) coated conductors (CCs), the resulting stress and strain due to winding tension, cooling stress and screening current-induced Lorentz force may lead to severe plastic deformation and degradation of superconductivity. Therefore, it is essential to understand the comprehensive electromechanical behavior and deformation mechanism of high-field REBCO magnets. In this paper, the multi-step finite element analysis is designed to simulate the electromechanical behaviors of REBCO coils after winding, cooling-down, and charging processes. All major constituent materials including mandrel, CCs, co-wind reinforcement and over-banding are considered in mechanical models to emulate contact-separation behavior between them. In addition to the contact nonlinearity, the intrinsic elastoplastic property is introduced to predict the plastic deformation observed by experiments. To reveal the screening current effect, the distributions of screening current and magnetic field are analyzed by solving T-A formulation of Maxwell's equations with homogenous technique. Then, with the electromagnetic load acting as body force, the electromagnetic stress and strain are computed and experimentally validated for pancake coil involving transport current and external field. Finally, the electromechanical behavior under Lorentz load is investigated by considering the accumulation of stress and strain due to winding tension and cooling down. Simulation results reveal that the winding tension and thermal stress affect the final stress-states at fully charged state and therefore the electromechanical properties. Both plastic deformation and possible degradation are more likely to occur in the outermost tape of several pancakes due to the influence of screening current-induced stress and strain. Besides, this work further analyzes the effect of current sweep reversal method, which could be favorable on reducing the screening current-induced high stress and strain at stable state.

A combination of advanced in-situ and ex-situ methods providing complementary information was employed in order to reveal the active deformation mechanisms during deformation of a heavily textured commercial magnesium alloy AZ31. Three sets of samples for both compression and tension testing were prepared from the rolled sheet with respect to its identified strong basal texture – normal direction (ND), rolling direction (RD) and 45° between RD and ND. During both compressive and tensile deformation of these samples, the signal of acoustic emission (AE) was concurrently measured. Afterwards, electron backscattered diffraction (EBSD) was used to study the microstructure after the selected stages of deformation. The EBSD analysis revealed that in the samples favourably oriented for extension twinning it played an important role during the plastic deformation, whereas its role in the unfavourably oriented samples was minor. This orientation and deformation mode dependency of extension twinning activation resulted in considerable differences in the deformation behaviour, which also influenced the AE response. A consistent link between the AE signal and the microstructural changes investigated by EBSD was established. Furthermore, to study the dynamics of plastic deformation and twin growth, high-speed camera footage of the sample surface was captured during compressive deformation. The obtained results were in complete accordance with the predicted behaviour, thus providing direct proof of the theory and extending the understanding of the deformation mechanisms.

In recent years, new metamaterials emerge one after another in various fields with various functions, showing a bright future for the development of metamaterials. Negative Poisson’s ratio material is one of the promising materials. It has a wide range of applications in mechanical engineering, acoustics and architecture science. This paper attempts to explore the different deformation mechanisms and possible applications of perforated plate materials with negative Poisson’s ratio. Finite element analysis is used to simulate a typical perforated plate structure, which shows negative Poisson’s ratio effect and abundant deformation forms in vibration condition. In addition to the existing applications in vehicle buffering and building noise reduction, this paper proposes that the perforated plate can be used as a filter screen for water treatment, as well as the filter screen of air purifier. In addition, it can also be used to cultivate precious herb seedlings. Intersects with the medical field, it can even manufacture the vascular embolization treatment device, which can ensure that the longitudinal does not contract and scratch the blood vessel when the blood vessel is opened. On the basis of this study, we can further study the special properties of metamaterials and solve the specific problems in various applications.

The greywacke sandstone in the Bulukuning area, Banjarnegara where was previously proposed as the Bulukuning Formation is part of the Luk Ulo Mélange Complex. In general, these molassic deposits show alternation between siltstone and siltstone with thin bedding deposited in the foreland basin. The Eocene sandstones are in some parts associated with the boudin structure, folded and cut by faults in the contractional regime. This study aims to determination of boudin type, structural orientation is highly correlated with deformation mechanism. This mechanism of deformation can be formed in different deformation periods. The correlation between the orientation of the systematic fault P-foliation, Y-shear, and R shows that the formation of boudinage is thought to be affected by the presence of a right movement (dextral), which follows the principle of the riedel shear. The deformation mechanism in the formation of sandstone boudin structures embedded in the scaly clay matrix is thought to be affected by plastic (ductile) by following the simple shear principle.

The mechanical property and deformation mechanism of twinned gold nanowire with non-uniform distribution of twinned boundaries (TBs) are studied by the molecular dynamics (MD) method. It is found that the twin boundary spacing (TBS) has a great effect on the strength and plasticity of the nanowires with uniform distribution of TBs. And the strength enhances with the decrease of TBS, while its plasticity declines. For the nanowires with non-uniform distribution of TBs, the differences in distribution among different TBSs have little effect on the Young’s modulus or strength, and the compromise in strength appears. But the differences have a remarkable effect on the plasticity of twinned gold nanowire. The twinned gold nanowire with higher local symmetry ratio has better plasticity. The initial dislocations always form in the largest TBS and the fracture always appears at or near the twin boundaries adjacent to the smallest TBS. Some simulation results are consistent with the experimental results.

This study systematically investigates the cyclic behavior and deformation mechanism of superelastic shape memory alloy U-shaped dampers (SMA-UDs) that are intended for seismic resilient applications. The study first summarized the experimental investigations of a series of SMA-UD component tests under loadings in two directions (i.e. in-plane and out-of-plane directions). Test results demonstrated that SMA-UDs exhibit excellent self-centering (SC) capability and stable energy dissipation under both loadings. Subsequently, two detailed finite element models were validated through the comparisons with experimental results in terms of global hysteresis loops and deformation shapes. The insights into the SMA-UD behavior under different directional loadings were presented. The influences of different geometric parameters of the SMA-UDs on the deformation mechanism were further highlighted. Parametric studies were carried out to investigate the effects of the existence of adjacent plates and the perpendicular compression on the SMA-UD’s mechanical properties of practical interest in earthquake engineering. Results show that the adjacent plate has a positive role in the deformation mechanism of the SMA-UD under in-plane loading, whereas it has a slight effect on the SMA-UD under out-of-plane loading. The perpendicular compressive deformation undertaken by the SMA-UD itself can deteriorate its SC capability under in-plane loading. The results attained from this research are conducive to the design and applications of the SMA-UDs in engineering practice.

The TRIP effect and tensile behaviour of a TRIP steel were studied at temperatures ranging from -120 to 200°C. The initial microstructure comprises of austenite and martensite (50:50). Excellent combination of UTS (∼2395 MPa) and elongation (28 %) was observed at -100°C and is attributed to the TRIP effect, that found absent above 100°C and below -120°C. Transformation temperatures were studied by DSC and DMA. Analysis of the tensile behaviour, phase changes and fracture surface suggest possible changes in the deformation mechanisms at different temperatures.

In this study, laser melting deposited TA15 alloy was examined by in-situ SEM tensile deformation at a range of temperatures; RT, 300℃ and 500℃. The as-fabricated microstructure consists of prior β grains boundaries and fine basketweave microstructure. Due to LMD fabricated alloys’ anisotropic behavior, the tested samples were collected from the same region and direction. The XRD and SEM results showed that the temperature up to 500℃ has no impact on the phase constituent and structure morphology, revealing a stable microstructure. The tensile deformation at room temperature (RT) revealed that slip lines were the primary deformation mechanism generated in the parallel and larger alpha grain. An increase in temperature triggered grain boundary sliding during deformation, which enhanced the elongation in the material at the cost of tensile strength reduction. The grain boundary resistance to dislocation slip was affected by the sliding phenomenon due to increased temperature. Overall, the material showed stable tensile characteristics related linearly to the temperature variation.

During the construction of the pumped-storage power station, problems such as the stability of the surrounding rock of the underground chamber of the powerhouse appeared, which put forward higher requirements for the safety of the construction of the project. How to reasonably analyze and evaluate the stability of the surrounding rock of the underground chamber became a constraint to the smooth construction of the project Obstacles to progress. In response to this problem, a typical underground powerhouse chamber of a pumped storage power station was selected, and for the problems caused by the stress unloading of the surrounding rock during the excavation of the powerhouse chamber, field sampling, indoor triaxial unloading test, and numerical analysis were adopted. The stress path test results are applied to the numerical simulation analysis of different types of surrounding rock and different excavation conditions. The calculation analysis shows that the types of surrounding rock and the excavation conditions affect the arches, arch abutments and spans of underground chambers. Key positions such as the intersection of the arch bottom and the side wall have a significant impact. When the surrounding rock grade is the same, the displacement field distribution characteristics and maximum displacement of the two step-by-step excavation schemes are not much different; when the surrounding rock grade changes from type II to type III, the maximum displacements of the arch top and the bottom of the surrounding rock increase doubled.

The excellent mechanical properties of Graphdiyne (GDY) family has enabled it as an appealing candidate in the field of impact protection. In this in silico study, Monolayer GDY nanosheets of different morphology including GDY, GY-3, GY-4, GY-5 and GY-6 are assessed under hypervelocity impacts (from 1 to 6 km s−1). Tracking the deformation mechanisms under impacts as well as the Probability density function based on atomic Von Mises stress distribution, the length of acetylenic chain clearly alters ductile behavior as well as the energy dissipation/delocalization rate of GDY family during the impact. Results also suggest the penetration energy is not only determined by the energy delocalization rate but also sensitive to impact velocity for nanosheet with various acetylenic chain length. GY-5 with a much lower energy delocalization rate presents a close penetration energy comparing with GDY at a low impact at ∼2.0 km s−1, its superior ductility granted by long acetylenic chain not only dissipates kinetic energy of projectile via deformation, but also extends time for acceleration during the contact with projectile. Considering the impact resist performance of GDY family in terms of Specific penetration energy, GY-5 with the perfect balance between material density, ductility and Young’s modulus makes it the superior anti-ballistic material for impact velocity at −1. For impact velocity >5 km s−1, it induces severer local deformation, and leaves no time for a well-developed distributed pattern as observed in a lower impact velocity scenario. As such, extensive elastic deformation of the nanosheet is not captured under impact, nanosheets with shorter acetylenic chains and hence greater material strength demonstrates superior impact resist. This study provides a fundamental understanding of the deformation and penetration mechanisms of monolayer GDY nanosheets under impact, which is crucial in order to facilitate their emerging applications for impact protection.

The deformation of abutment slope during impoundment poses great challenges to the working behavior and long-term safety of the arch dam. According to the monitoring data of impoundment and slope, slope deformation, valley width change, and arch dam chord length change are systematically analyzed and studied. It is pointed out that the deformation of the dam body and foundation is an irreversible plastic deformation and is evidently correlated with impoundment. Based on the unsaturated effective stress principle of fractured rock mass and the action mode of the reservoir basin pressure, the deformation mechanism of abutment slope has been discussed. The large-scale 3D nonlinear finite element model is established based on numerical analysis, and the deformation mechanism during impoundment and the effect of the effective stress change on the displacement and stress of the dam body are analyzed. The results indicate that effective stress can elucidate the valley contraction to some extent and that the contribution of the reservoir basin pressure is small. Slope deformation is beneficial to the dam displacement to some extent. Moreover, it has a negligible influence on the dam surface stress. However, the junction of the dam and foundation needs to be given special attention.

Micro-disturbance grouting has been widely used in the control of transversal deformation of shield tunnel. It is proved that the grouting not only effectively controls the further deformation in the future but also reduces the existing large deformations. However, the study on grouting mechanism is relatively limited. By using the analytical model with the soil expressed by the Mohr-Coulomb yield criterion, the nonlinear relationship between soil stress and displacement in elastic-plastic zone of the grouting area are derived based on cavity expansion theory. The grouting pressure and required volume for different grouting distance between grouting holes and tunnel linings, and the grouting depth are given. The analytical results are compared with the monitoring data to validate the proposed model. According to the comparison results, the construction sequence of grouting hole can be optimized which can avoid short-time stress superposition to squeeze the tunnel segments and produce structural diseases. Moreover, the optimal grouting volume can effectively keep the effect of the reduction of the tunnel deformation by micro-disturbance grouting technology. The proposed micro-disturbance grouting and its associated optimized construction scheme can be quite helpful to the practical control of the large deformation.

To reveal the deformation law and mechanism of bedding slopes under excavation unloading, an unloading rebound model of slope deformation is established on the basis of Mindlin’s strain solution, and a bedding-slip model of slope deformation is deduced on the basis of the Kalhaway constitutive model. Combining the two models, this study presents a computational model for the deformation response of bedding slope excavation. This model can reflect the mechanism of excavation unloading and the characteristics of rock mass structure. The reliability of the model is verified by comparing the calculated results of the analytical model with the experimental results in the laboratory. On this basis, the influences of excavation angle, excavation depth, and stratum thickness are analyzed by using several calculation examples. The calculation results show that the deformation induced by excavation increases with the increase in excavation angle or depth and decreases with the increase in stratum thickness. The excavation response of bedding slopes is mainly affected by the effect of unloading and the slip of the structural plane. Moreover, the unloading effect is controlled by the amount of excavation, and the rebound deformation of slopes is approximately linearly correlated with excavation volume. Bedding slip is affected by many factors because the increase in excavation angle or the amount of rock stratum leads to the increase in slip deformation. The proposed model can provide a basis for the deformation mechanism of bedding slopes under excavation.

The macro-scale mechanical behaviors of materials under impact can be dominated by the meso and micro-scale deformation mechanisms and cracking patterns. In combination with the X-ray imaging and diffraction techniques, impact tests are performed on boron carbide (B4C) ceramic bulks with two different porosities by a miniature split Hopkinson pressure bar (SHPB). After a transient quasi-elastic deformation process, catastrophic failure occurs in the high-porosity bulk, with a weak failure strength. Abundant tensile and shear cracks nucleate in the low porosity bulk, but cannot connect into a cracks network due to the high adhesive force, and finally the dissociative failure occurs with several main cracks penetrating. By analyzing the diffraction peak splitting phenomenon, the extent of shear deformation is quantitatively characterized to be 60-70% of the compression deformation. The damage extent is expressed by the voids volume induced by cracks. The macroscopic stress increment of B4C bulk under impact can be expressed by a function of the damage extent evolution.

Considering the influence of flattening of casing cross-section on collapse, the stress equivalence principle was applied to conclude the triaxial stress and collapse strength. The method to determine casing collapse strength considering flattening of casing cross-section was established. The diameter-to-thickness ratio had a major influence on the flattening of the casing cross-section compared with curvature. For the 5 1/2”×7.72mm P110 casing, the flattening coursed by the 0.01/m curvature decreased the collapse strength concluded by API 5C3 by approximately 7.5%.

When subjecting cast irons to mechanical loading the deformation and damage mechanisms occur on a microstructural level and are dependent on the inherent microstructure. A deeper understanding of the relation between the different microstructural constituents and the macroscopic mechanical behaviour would be beneficial in material development efforts and for the ability to design and cast components with tailored properties. Traditionally, microscopy examinations on sectioned cast iron samples have been used when analysing the microstructure in cast irons. Since all microstructural heterogeneity is in three-dimensions (3D), methods that provide a three-dimensional characterisation are essential for a deeper understanding of, both the microstructural features as well as the deformation and damage of cast irons. Therefore, different cast iron grades have been studied using synchrotron X-ray tomography and 3D x-ray diffraction (3DXRD) at ESRF in Grenoble, France. The samples were stepwise loaded and unloaded in-situ at in the tomography/3DXRD set-up to study the deformation with regard to microstructural constituents and the microstructural evolution in 3D. Based on the 3D tomography image sequences, digital volume correlation (DVC) was used for full strain field analysis and for the analysis of damage and deformation mechanisms. In addition, 3DXRD data were analysed to provide details on the lattice parameters and lattice strain of individual ferrite grains. This work shows the possibilities of such synchrotron experiments for advanced study of the mechanical behaviour of cast iron.

The mechanical properties and bending deformation behaviors of homogenization treated (HT), solution treated (ST), natural aging (NA) treated and T6 6061 aluminum alloy sheets were investigated by tensile tests and three-point bending tests, respectively. The results showed that the heat treatment conditions have a significant impact on mechanical properties and bending characteristic. Bending radius and thickness of the HT alloy is the highest, and its springback angle is the lowest. However, the deformation mechanism of T6-8h alloy is just the opposite. The bending characteristics are attributed to the combined effects of yield strength, strain-hardening exponent and coefficient of the neutral layer. The simulation results are in good agreement with the experiment.

Using molecular dynamics simulations, the plastic deformation behavior of nanocrytalline Ti has been investigated under tension and compression normal to the {0001}, { 1 ¯ 010 } , and { 1 ¯ 2 1 ¯ 0 } planes. The results indicate that the plastic deformation strongly depends on crystal orientation and loading directions. Under tension normal to basal plane, the deformation mechanism is mainly the grain reorientation and the subsequent deformation twinning. Under compression, the transformation of hexagonal-close packed (HCP)-Ti to face-centered cubic (FCC)-Ti dominates the deformation. When loading is normal to the prismatic planes (both { 1 ¯ 010 } and { 1 ¯ 2 1 ¯ 0 } ), the deformation mechanism is primarily the phase transformation among HCP, body-centered cubic (BCC), and FCC structures, regardless of loading mode. The orientation relations (OR) of {0001}HCP║{111}FCC and 〈 1 ¯ 210 〉 HCP | | 〈 110 〉 FCC , and { 10 1 ¯ 0 } HCP | | { 1 1 ¯ 0 } FCC and 〈 0001 〉 HCP | | 〈 010 〉 FCC between the HCP and FCC phases have been observed in the present work. For the transformation of HCP → BCC → HCP, the OR is 0001 α 1 | | { 110 } β | | { 10 1 ¯ 0 } α 2 (HCP phase before the critical strain is defined as α 1-Ti, BCC phase is defined as β-Ti, and the HCP phase after the critical strain is defined as α 2-Ti). Energy evolution during the various loading processes further shows the plastic anisotropy of nanocrystalline Ti is determined by the stacking order of the atoms. The results in the present work will promote the in-depth study of the plastic deformation mechanism of HCP materials.

In this work, surface mechanical attrition treatment (SMAT) was carried out on 316L stainless steel in order to study the effects of treatment parameters on the deformed depth and deformation mechanisms. results showed that the residual stresses caused by collision of shots led to formation of martensite. Increase in treatment duration and shot size led to more martensite formation because of higher strains. An increasing hardness profile was also observed from the depth towards the surface in SMATed samples which was due to grain refinement, martensite formation and twinning. Strength of samples also improved by SMAT so that the yield strength in the sample treated for 2h by 6mm shots was increased by 58 percent. In addition, Crussard-Jaoul diagrams for samples treated under various conditions and untreated samples were compared. It was observed that slope variation occurred earlier in SMATed samples. In other words, mechanisms were activated at lower strains.

In contrast to classical materials, auxetic materials (from the Greek word αὐξητικόσ / auxetikos) possess negative Poisson’s ratios, thereby exhibit reverse deformation mechanism. Under a tensile force applied in the longitudinal direction, auxetics expand in the perpendicular transverse direction. Consequently, auxetic materials possess various useful properties for potential applications. This review contains the classification of auxetic materials according to different criteria: the type of structure, cell geometry and scale, mechanical characteristics, methods of their production, and engineering applications. The aim of this work is to sum up structural information on auxetics.

This paper presents a novel tri-directional negative stiffness (NS) mechanical metamaterial, consisting of disk structure elements arranged in three-dimensions. The NS behavior was achieved through the elastic instability of the disk structure. Through the combination of numerical simulations and experiments, the NS property, the deformation mechanisms, and the basic mechanical performance of the disk structure and the novel NS mechanical metamaterial were systematically investigated. The influence of the geometric parameters on the snap-through behaviors of the NS metamaterial was investigated through the experimentally verified numerical method, and further designs were conducted on the disk structure to tailor its mechanical responses. Also based on the instability of the disk structure, several novel multidirectional NS structures, which can achieve NS behavior along five and seven loading directions, were firstly proposed. This innovation improves the homogeneity of the NS metamaterials, and is expected to expand the application scope of such metamaterial, considering that the previous reported NS metamaterial can exhibit NS behavior along three-dimensions at most. Moreover, the mechanical performance of the proposed NS metamaterial is tunable, benefited from the special structure form of itself. To our knowledge, this work is first to design NS metamaterial using the disk structures, and report the multidirectional (more than tri-directions) NS metamaterials.

Taking the construction of a certain section of Guiyang rail transit as an example, the theoretical analysis of the stress conditions and constraints of the pipe shed during tunnel excavation is carried out for the support parameters of the large pipe shed. By analyzing the force of the micro-segment of the pipe shed, bringing the Bernoulli-Euler beam theory formula into the equilibrium equation of the micro-segment, the governing differential equations of the pipe shed at the vault and the non-arch is obtained. Two types of pipe sheds are designed, and the numerical simulation of the tunnel with two structural forms of tunnel with advanced support of large pipe shed is carried out by using MIDAS/GTS NX finite element software, and the displacement and stress of the pipe shed are obtained and the theoretical verification is carried out. By comparing the displacement and vertical stress of the large tubular awning in plan 1 and plan 2, it is concluded that plan 2 is more reasonable and has better bearing capacity.

Accurately understanding of the strata behaviors law and stability characteristics of the mining roadway is the basics of effective surrounding rock control, and the structural characteristics of the surrounding rock is the decisive factor for large deformation of that in mining roadways. In this paper, the surrounding rock structure characteristics of mining roadway in different conditions were discussed and mechanical model was established accordingly. And the deformation characteristics of the material were simulated by the combined model of deformation elements, and the theory of the surrounding rock deformation in the mining roadway with time was obtained.

Deformation of metallic glasses is closely related to their microstructures which depend on the composition, processing method, and the size of the materials. This subtle structure-property relation is fairly complex and remains to be explored. Here, we scrutinize the microstructural evolution in relation to the mechanical properties in metallic glass nanowires with the same composition and size but subtle microstructural differences by controlling the preparing process using molecular dynamics simulations. The results suggest that a structural threshold exists for the transformation of deformation mechanisms in metallic glasses: when the structural feature exceeds the threshold, the deformation changes from homogeneous flow to shear localized deformation.

Mg-3Gd (wt. %) samples were prepared by accumulative roll-bonding (ARB) and subsequent annealing to produce samples with average grain sizes in a wide range from 3.3 μm to 45.1 μm. These samples were tensile tested at room temperature. Dislocation structures and deformation twins in the tested tensile samples were characterized by transmission electron microscopy. Dislocations with different types of Burgers vector were identified based on two-beam diffraction contrast experiments. The results revealed that deformation twins and dislocations are dominant in coarse-grained samples while and dislocations characterize the fine grain deformation structure. The transition of deformation mechanisms and its implications for microstructural design and property optimization are discussed.

The mechanical indexes of the geotextile and filling sand were obtained by laboratory test based on geotextile bag with sand cofferdam of Zhoutouzui immersed tunnel in Guangzhou, and a fine calculation model was established. The deformation development law of geotextile bag with sand cofferdam was explored by refined numerical calculation. Combining with the existing research results, the deformation mechanism was determined. Numerical results were verified by theoretical analysis and the control index of design and construction was proposed. The results show that cofferdam moves to the side of dry dock under the action of unbalanced pressure, and the displacement decreases from the top to the bottom. Cofferdam appears settlement under gravity and pumping action as well as the displacement increases with the pumping water level decline. The main reason of cofferdam’s large deformation is density increase caused by dewatering, which increases overlying pressure from upper geotextile bag to lower one and makes geotextile flattening deformation. Foundation soil experiences vertical pressure consolidation, lateral extrusion and local sliding, which causes the maximum and minimum deformation present to the top and toe of geotextile bag. The cofferdam has no sliding failure and is in overall stability as well as the numerical results are consistent with results deduced by theoretical analysis, so the cofferdam should take the height as the control index.