Main Deformation Mode Research Articles

Deformation behavior at fatigue crack tip in nickel-based alloy

The microstructure and deformation behavior around the fatigue crack tip can significantly affect the early stage of the fatigue crack propagation, but currently, the evolution and deformation mode of the microstructure in the fatigue crack tip at the nanoscale are still unclear. Therefore, it is important to study the microstructure and deformation behavior at the fatigue crack tip in nanoscale to further reveal the fatigue failure mode of metal materials. In this study, the microstructure evolution and deformation mode of the fatigue crack tip of nickel-based alloy are studied by HRTEM technique. The results show that a large number of dislocation, stacking fault and micro/nano-twin are formed around the fatigue crack tip. The formation of these microstructures can promote the release of strain in the matrix during cyclic deformation. The main deformation mode of the fatigue crack tip includes slip, twinning, and dislocation shearing micro/nano-twin.

Failure Mechanisms in Stainless Steel/Carbon Steel Clad Plate Under Shear Tensile Loading: Experimental and Modeling Methods

The deformation behavior of a stainless steel/carbon steel (SS/CS) clad plate under interface shear loading is characterized in this work. A 2D digital image correlation method is applied to track the strain field variation near the interface during shear tensile tests. Then, a cohesive zone model (CZM) finite‐element method is developed to clarify the delamination behavior of the tested clad plate. Finally, the interfacial failure characteristics of the SS/CS clad plate are further presented through the comparison between the finite‐element method and fractography analysis at the interface. In the experimental and simulation results, it is shown that the mixed‐mode CZM, which couples the constitutive equations of three fracture modes, demonstrates excellent capabilities in capturing SS/CS interfacial deformation behavior. The main deformation mode in shear tensile tests is variable according to locations. The central region at the bonded surface is dominated by the shear delamination mode, and the region near the notches shows shifted crack propagation toward normal mode. These abrupt interfacial failures can be clarified via stress state and local damage analysis of the well‐reproduced finite‐element model of cladding material.

Non-uniform microstructure evolution rules and mechanisms of Ti55 alloy with initial basket-weave structure during electrically-assisted V bending

Electrically assisted V-bending (EAVB) experiments of Ti55 alloy sheets with initial basketweave structure were carried out at effective current densities of 3–5A/mm2. The history of temperature field, microstructure patterns and mechanical properties were characterized by IR imaging, OM, EBSD and hardness tests. The results show that α lamellae continuously decrease in thickness (from 2.38 μm to 0.64 μm) with increasing current density. The microstructure patterns of the three deformation zones are significantly different due to different deformation mode and electro-thermo-mechanical routes. Due to limited plastic strain, the orientation rotation and shear fracture of the α lamellae are restricted in the neutral layer, while the ones in the inner and outer layers are refined and become more uniform at mild current density. With increasing current density, the main deformation mode of α grains in the inner layer is {1010} prismatic slip and dynamic spheroidization/recrystallization tends to occur at α lamellae with <0110>α//TD orientation. In the neural and outer layer, intense local Joule heat effect induces α→β→α′ phase transformation in “hot spots”, leading to massive growth of 3 variant needle-like α′, intensified heterogeneous micro-deformation and significant strengthening effect. The combined effects of local Joule heat, residual α phase and deformation-induced defect nucleation break the strict Burgers orientation relationship between α/α’ lamellae and β matrix during EAVB and subsequent cooling process.

Modeling of Fiber Optic Strain Responses to Shear Deformation of Fractures

Identifying distributed strain sensing (DSS) patterns (or signatures), particularly those arising from different hydraulic fracture geometries, has gained significant attention and research effort. Recent works have generated a catalogue of signatures for planar hydraulic fractures in an elastic rock formation. Yet, in numerous cases (e.g., fault motion and some geothermal reservoir stimulation), the main mode of deformation is a shear on a fracture or a network of natural fractures (particularly during low pressure injection/circulation). However, the specific fiber signatures that result from such shear deformation have not been studied. In this study, we use a three-dimensional poroelastic hydraulic fracture simulator to capture the strain signatures resulting from the shear deformation of fractures in various orientations with respect to the monitoring well. Five key cases are examined: one where the fracture strike is perpendicular to the fiber, another with the strike running parallel to the fiber, a third case where the fracture strike is at 45 degrees to the fiber, a fourth case with a strike slip fault perpendicular to the fiber, and a fifth case where fiber is intersecting the fracture. Theoretically and physically meaningful results were obtained in all five cases, which completely differ from the heart-shaped signature of tensile fracture propagation. It was discovered that the strain pattern changes with the shear deformation direction with respect to the fiber. The model is then used to simulate the response of a fracture network at Utah FORGE to injection to assess whether a signature might be expected in response to the planned injection and circulation rates, and, if so, what strain pattern might be expected. The simulation confirms that a strain response can indeed be observed. More importantly, the fiber response that would be detected in the monitoring well would be a combination of strain signatures from dilation and shear deformation of differently oriented natural fractures. The results in this study provide useful insights on the application of fiber to other stimulation and/or circulation scenarios where shear deformation of a fracture or fracture network plays a major role.

Dislocation structure evolution during room temperature dwell loading of a Ti-6Al-4 V alloy

The current work examines the evolution of the dislocation structure, within both the α and β phases, of a Ti-6Al-4 V alloy subjected to room temperature dwell loading performed at about 96% of the macroscopic yield stress level for several durations, as part of a synchrotron in-situ deformation experiment. The obtained findings represent a vital contribution to creating a scientific basis for improving lifing predictions for aero-propulsion components. The dislocation configuration, type and density were examined post-mortem using transmission electron microscopy (TEM). Despite the relatively low applied stress level, well-developed dislocation structures were already formed within the α phase at a dwell duration of 10 min and changed only modestly up to 60 min. The plastic deformation of the above phase took place solely via dislocation slip. To facilitate a comparison between different dwell durations, the TEM investigation focused on the regions oriented for the prismatic glide that represented the main deformation mode due to the starting crystallographic texture. After deformation, the regions oriented for the prismatic slip contained planar slip bands largely consisting of dislocations of a screw type. There was rather limited interaction between different bands, as the dislocation arrays passed through the slip band intersections with only minor difficulty. The screw-type dislocations seemed to preferentially form during straining. Dislocation Burgers vectors experimentally determined within the β phase occasionally departed from the Schmid rule and such dislocations typically showed a prevalent screw component. Some deformation banding and {112} 〈111〉 − type mechanical twin formation were locally detected within the β phase.

High-speed perforation of high-entropy alloy CrMnFeCoNi plates: Experiments and modeling

The perforation behavior of 2-mm thick CrMnFeCoNi high-entropy alloy plates is investigated via ballistic impact experiments using spherical stainless steel 304 projectiles with high-speed photography at impact velocities ranging from 500 ms−1 to 2213 ms−1. Postmortem target samples are characterized with macro photography, three-dimensional laser scanning, optical metallography, scanning electron microscopy, electron backscatter diffraction and microhardness tests. The absorbed energy and aperture area show a nearly linear increase with increasing the initial kinetic and absorbed energy, respectively. Dislocations, twins and kink bands are the main microstructural deformation modes. As the distance away from the bullet hole sidewall, both the deformation degree and hardness decrease. Besides, shear-dominated and tensile/shear-dominated fracture are found in the middle part and near the rear side of the bullet hole sidewall, respectively. Parameters of the Johnson–Cook(JC) constitutive model are obtained via the split Hopkinson pressure bar system. A finite element method (FEM) model comprised of the JC constitutive and JC progressive damage model is established and reproduces experimental observations.

The hardness and electrical conduction in TiB2 and MgB2: Computational insights

Achieving the coexistence of hardness and electrical conduction in materials is of great interest for fundamental scientific understanding and practical technological applications. Here, we investigated the hardness and electrical conduction of isostructural TiB2 and MgB2 based on the dislocation theory and first-principles calculations. The calculated hardness values obtained by the Sachs deformation texture model (20.20 GPa for TiB2 and 12.96 GPa for MgB2 at 300 K) are in good agreement with the measured ones (21.2 ± 1.1 GPa for TiB2 and 12.65 ± 1.39 GPa for MgB2). The analysis of hardness indicates that the dislocations on the {0001} and {10 1¯ 0} planes have the lower activation energy, and their movements are the main plastic deformation modes of TiB2 and MgB2. But, the hardness of TiB2 is larger than that of MgB2. From the perspective of the bonding mechanism, the strong Ti-B bonds associated with the hybridization of Ti 3d and B 2p states play a crucial role in the hardness of TiB2. Electrical conduction in TiB2 mainly results from the contribution of Ti 3d electrons, while it is from the partially occupied B σ- and π-bonding orbitals in MgB2.

Investigation on seismic performance of inclined Dou-Gong bracket between columns of ancient timber structures

To investigate the seismic behavior of the inclined Dou-Gong (DG) brackets, three full-scaled Dou-Gong bracket between columns with different inclinations along the width direction were tested under the pseudo-static test. The failure mode, hysteretic characteristic, stiffness degradation, deformation and energy dissipation capacity as well as the deformation modes of DG were discussed. Besides, numerical analysis of DG’s stress distribution and seismic behavior of DG brackets inclined in the overhanging direction was also studied. Parameter analysis was conducted to study the effect of frictional coefficient, vertical load and wood properties on the bearing capacity of DG. The results demonstrated that the DG bracket rotates as a whole and the relative slip of Da-Dou and Pingban-Fang leads to the shear damage of Mantou-tenon when DG failed. As the inclination in width and overhanging direction increases, the positive bearing capacity and lateral stiffness decrease, while the negative direction increases. The DG’s negative deformation ability is better than the positive direction and the larger the inclination, the stronger the deformation capacity. However, inclination reduces the energy dissipation capacity of DG. Rotation deformation is the main deformation mode of the DG bracket. Increasing the frictional coefficient, vertical load and compressive strength along the grain improves the bearing capacity of the DG, but the bearing capacity is slightly affected by the elastic modules along the grain. The research results can provide a scientific basis for the performance evaluation and repair protection of inclined DG brackets.

High strain rate plastic deformation driven microstructure evolution in AlCoCrFeNi dual-phase high entropy alloy

High strain rate plastic deformation under laser shock processing (LSP) has been applied to the AlCoCrFeNi dual-phase high entropy alloy (HEA) for optimizing the microstructure and properties. Phase constituents, microstructure evolution of the HEA before and after LSP were investigated. Microstructures of the HEA samples were examined using scanning electron microscopy and transmission electron microscopy. Results showed that the microstructure in the LSPed region was obviously refined. High density dislocations were produced in the alloy and dislocation slip was the main plastic deformation mode during LSP treatment. When the laser energy increased to 5 J and 7 J, nano-precipitates, twins and stacking faults appeared, and the plastic deformation mode was a mixture of deformation twinning and dislocation slip. The refined grains, dislocation structures, deformation-induced twins and stacking faults were analyzed and associated with the microhardness. The microhardness of the HEA was significantly improved after LSP, which can be attributed to the synergistic strengthening of grain refining strengthening, precipitation strengthening and dislocation strengthening.

High-speed projectile perforation of nickel-based Inconel 718 superalloy plates: Experiments and modeling

Understanding ballistic behavior of structural materials is important for their applications in aeronautical and astronautical industries. We investigate perforation of 2-mm thick Inconel 718 superalloy plates by spherical stainless steel 304 projectiles with high-speed photography at impact velocities ranging from 548 ms−1 to 1360 ms−1. Postmortem target samples are characterized with optical metallography, scanning electron microscopy and electron backscatter diffraction as regards bullet hole morphology and deformation. Grain refinement and shear banding are the main microstructural deformation modes near the bullet holes. Shear dominated deformation and tension–shear dominated deformation of target material occur sequentially in bullet hole along the impact direction. The morphologies of bullet holes and postmortem projectiles are obtained from the experiments and simulations. The effect of projectile deformation on ballistic behavior of the target is investigated. On the basis of dimensional analysis, a quadratic relation is derived between the energy absorption ratio of target and the dimensionless postmortem projectile diameter, along with a phenomenological model that can well predict projectile residual velocities.

Microstructure, properties and reaction kinetics of a Cu–Al2O3–TiB2 alloy prepared by a new liquid phase in-situ reaction technology

Cu–Al2O3–TiB2 is an important high-performance dual-phase dispersion strengthened copper alloy. The problem of serious coarseness and agglomeration of TiB2 and Al2O3 particles is a bottleneck that restricts the preparation of high-performance Cu–Al2O3–TiB2 alloys by traditional liquid-phase in-situ reaction method. In this paper, an idea of combining the split cavity melting of complex reactants and efficient solidification of melt was proposed, and a new liquid phase in-situ reaction technology for dual-phase strengthened metal matrix composites was invented. Compared with the traditional liquid phase in-situ reaction method, the strengthening particles in the Cu-0.75Al2O3-0.75TiB2 (wt.%, nominal composition) prepared by the new liquid phase in-situ reaction technology were more uniform, and the tensile strength and hardness were significantly improved. Large-deformation cold rolling can improve distribution of particles. With the increase of deformation, the main deformation mode of the composite changed from matrix plastic deformation to matrix-particle shear deformation, with the main fracture mechanism changing from particle-matrix interface fracture to particle shear fracture. The new liquid phase in-situ reaction technology effectively solved the problem of particle coarsening and agglomeration in Cu–Al2O3–TiB2 composites. The new liquid phase in-situ reaction technology combined with large deformation is a new process with high efficiency and short flow for preparing dual-phase dispersion strengthened copper alloys.

Localization of Deformation in a Non‐Collisional Subduction Orogen: The Roles of Dip Geometry and Plate Strength on the Evolution of the Broken Andean Foreland, Sierras Pampeanas, Argentina

AbstractThe southern Central Andes (SCA, 27°–40°S) exhibit a complex deformation pattern that is influenced by multiple factors, including the present‐day dip angle of the subducting oceanic Nazca plate and the influence of inherited heterogeneities in the continental South American plate. This study employs a data‐driven geodynamic workflow to assess the role of various forcing factors in determining upper‐plate strain localization, both above the flat slab and the steeper segment to the south. These include the dip angle of the Nazca plate, the mechanically weak sedimentary basins, the thickness and composition of the continental crust, the strength of the subduction interface, and the plate velocities. Our modeling results predict two main deformation modes: (a) pure‐shear shortening in the broken foreland above the flat‐slab segment and eastward propagation of deformation, and (b) simple‐shear shortening restricted to the eastern margin of the Andean fold‐and‐thrust belt above the steep‐slab segment. While the convergence velocity and the frictional strength of the subduction interface primarily control the intensity of the deformation, inherited heterogeneities tend to localize deformation, and weak sediments leads to intensified surface deformation. Thicker crust and surface topography also influences strain localization by transferring stress to the eastern orogenic front. Above the flat‐slab segment deformation migrates eastward, which is facilitated by enhanced interface coupling. The transition between the steep and sub‐horizontal subduction segments is characterized by a diffuse transpressional shear zone, likely controlled by the change in dip geometry of the Nazca plate, and the presence of inherited faults and weak sedimentary basins.

Analytical and Numerical Investigations of Circular Metal Foam Sandwich Tube Under Free Inversion

Abstract The foam sandwich tube contains inner and outer tubes and filling foam. The foam sandwich tube is widely used in engineering, due to its lightweight, high specific strength, energy absorption, and other excellent characteristics. In this paper, the free inversion of the circular metal foam sandwich tube (CMFST) under axial loading is studied analytically and numerically. The plastic deformation occurs in the CMFST, and its main deformation modes include circumferential expansion, radial bending of the CMFST, and compression of the metal sandwich foam. An analytical model for the free inversion of the CMFST under axial loading is established, considering metal tube expansion, the radial bending of metal circular tube wall, and metal foam compression. The commercial abaqus software is adopted to numerically study the free inversion behavior of the CMFST. The analytical predictions agree well with the numerical ones. It is shown that the specific energy absorption (SEA) of the CMFST under free inversion is significantly better than the empty tube. When the non-dimensional foam strength is 0.05, the SEA of the CMFST under free inversion is 107.68% higher than the empty tube. Thus, the metal foam sandwich tube under free inversion is an excellent energy-absorbing device.

Exact solutions for plane stress problems of piezoelectric semiconductors: Tuning free-carrier motions by various mechanical loadings

Certain crystalline solids can be used for semiconducting devices, while mechanical forces have a great impact on their electrical behaviors. Especially, piezoelectric semiconductors (PSs) are one of the deformation-sensitive crystals. Mechanical forces can be utilized to tune the electronic transports in PSs. To illustrate these effects quantitatively, this paper provides exact solutions for free-carrier motions in different deformation modes of PSs. Two-dimensional (2D) governing equations for a rectangular domain are first presented based on the three-dimensional (3D) phenomenological theory. Then, exact solutions for plane stress problems with the c-axis along two perpendicular directions are formulated. By applying the analytical solutions, we study the distributions of free carriers when mechanical forces are applied. Four main deformation modes are investigated including extension, bending, thickness-shear, and thickness-stretch. Numerical results reveal that the poling direction of PSs can effectively change the coupling mechanism between the electric and mechanical fields. The electrons redistribute themselves to shield the piezoelectric polarization, resulting in a reduction of the electric potential. These findings shed light on the impact of mechanical loadings on charge redistribution and can serve as benchmarks for designing piezotronic devices.

Three-dimensional study of grain scale tensile twinning activity in magnesium: A combination of microstructure characterization and mechanical modeling

Tensile twinning is a main deformation mode in hexagonal close packed structure metals, so it is important to comprehensively understand twinning mechanisms which are not fully disclosed using 2D or small volume 3D characterization techniques. A large area 3D electron backscatter diffraction (EBSD) measurement and crystal plasticity modeling were carried out to investigate the tensile twinning behaviors in a magnesium (Mg) alloy. The results showed that tensile twinning activity was underestimated using conventional 2D EBSD scans. When compressed to yield point, the examined twin frequency with 2D was lower than that using 3D EBSD. The effects of Schmid factor (SF) on twinning were investigated. Almost all high Schmid factor (SF>0.35) grains were twinned. A surprising high twin frequency of 82% in middle SF (0.35>=SF>=0.15) grains was observed, which was unexpected since the middle SF grains were believed to be unfavorable for twinning. The twin frequency in low SF (SF<0.15) grains was slightly increased from 2D to 3D EBSD due to the small volume of twins. The shear stress maintained a high level and was homogeneously distributed in high SF grains, facilitating twin nucleation and growth. The shear stress was distributed heterogeneously within the middle SF grains, and twins were nucleated within areas with positive shear stress. The shear stress in low SF grains was not favorable for twinning and twins occurred in the vicinity of stress accumulation. Twinning activities in the same grain varied on different layers. It was attributed to the stress fluctuation derived from grain environment changes.

Multiscale crystal plasticity finite element simulations of the deformation inhomogeneity of TiBw/TA15 composites with network-structured during hot rolling

Understanding the micromechanical responses during hot forming between TiB whiskers (TiBw) and matrix titanium alloy as well as grains is essential to effectively control the properties of the final products. In this work, a method to study the deformation inhomogeneity of network-structured TiBw/TA15 composites during rolling in high temperature single-phase regions at macro and micro scales was proposed. A crystal plastic finite element model with dislocation slip and grain boundary (GB) sliding as the deformation mechanism was established. Results showed that the discontinuous distribution of TiBw reinforcements along the GB reduced the strain difference between the network boundary region and the matrix region during high temperature deformation. Therefore, the plasticity of the composites was improved. For the high temperature β-phase, the {110}<111> with higher activity was the main deformation mode. The difference in stress distribution between the grains was caused by the different combinations of the “soft” and “hard” states of adjacent grains, which was determined by whether the value of Schmid factors was greater than 0.45. The local stress concentrations tended to spread at the interface of “soft-hard” grains. The TiBw reinforcements increased the GB strength and reduced the deformation difference between the GB and intragranular.

A hybrid inter-module connection for steel modular building systems with SMA and high-damping rubber components

The recent technological advancements achieved in modular construction have accelerated the trend of building taller self-standing steel modular building systems (MBSs), leading to a consensus among researchers regarding the vital role that inter-module connections (IMCs) play in the structural performance of MBSs subjected to extreme lateral loading. However, existing IMCs are typically designed such that the global structural system heavily relies on the hysteresis of the steel framing members, leading to severe sustained damage and costly, impractical retrofitting programmes. To unlock the full “disassembly and reuse” potential of steel MBSs, IMCs can be designed to contribute more effectively to the global damage distribution mechanism, by engaging specific “fuse” components which are easy to replace, improving the reuse prospects of volumetric modules. In this regard, the present study proposes a novel, hybrid IMC using custom corner fittings, a high-damping rubber (HDR) core and a shape-memory alloy (SMA) bolt. Calibrated and validated material models using data from experimental material characterisation tests have facilitated the full characterisation of the hybrid mechanical response, determining the deformation modes, stress states, hysteresis loops and mechanical parameters. The parametric FEA included the variation of bolt preload, endplate thickness, axial load magnitude and the vertical layout of the HDR core. The study represents a preliminary, proof-of-concept investigation, showcasing the favourable cyclic performance of the proposed IMC under the main deformation modes expected in tall self-standing MBSs during lateral loading. Due to the effective contribution of each component to the combined hybrid response, the connection succeeds in preventing the formation of significant plastic damage in the MBS’s corner fittings to facilitate reusability of modules.

Microstructure change characteristic and fracture mechanism of Ti-47.5Al-2.5V-1.0Cr-0.2Zr alloy during high temperature tensile deformation

Changes in the microstructure characteristics and fracture mechanism of Ti-47.5Al-2.5 V-1.0Cr-0.2Zr alloy during tensile deformation were studied by high temperature tensile tests at 750–900 °C and strain rate of 10−5–10−3 s−1. The experimental results indicate that when the tensile temperature increases or the strain rate decreases, the number of small dimples in the tensile fracture structure increases, the proportion of cross-layer fracture decreases, the dimples have torn edges, and the plastic deformation resistance increases. The higher tensile temperature corresponds to a higher dynamic recrystallization (DRX) ratio, and the number of dislocations near the DRX structure is reduced, which shows that the rheological softening effect is significantly enhanced. A lower strain rate corresponds to a higher proportion of DRX and a smaller proportion of lamellar microstructure. Dislocation slip is the main deformation mode; stacking faults can be observed in DRX grains. The changes in the hot deformation microstructure directly reflect decrease of high temperature tensile strength in macroscopic flow behavior. Under the action of tensile stress, holes usually form at the lamellar grain boundary, and the aggregation of multiple micro-holes will merge and connect to form micro-cracks. Cracks are generated and propagated between layers, and the tendency of holes or cracks generated at lower deformation temperatures or higher strain rates is greater. When the stress concentration reaches a certain critical value, the specimen will eventually fracture.

Shock compression and spall damage of dendritic high-entropy alloy CoCrFeNiCu

Plate impact experiments are conducted on a dendritic dual face-center cubic phase high-entropy alloy (HEA) CoCrFeNiCu, consisting of Cu-lean dendritic (DR) and Cu-rich interdendritic regions (ID). Free surface velocity histories are obtained along with microstructure characterizations. The Hugoniot equation of state and spall strength at different shock stresses are determined. Dislocation slip is the main deformation mode for CoCrFeNiCu HEA, and the dislocation density of the Cu-rich interdendritic regions increases more significantly during shock compression. Both ductile and brittle damage modes are observed. With increasing impact velocity, the Cu-rich interdendritic regions with severe strain localizations and more defects provide more damage nucleation sites. The spall strength increases firstly, reaches its maximum at a peak shock stress of 5.8 GPa, and then decreases. Molecular dynamics simulations reveal that the abnormal dependence of spall strength on peak shock stress is a result of strain localization and thermal softening in the Cu-rich regions.

Microstructure evolution and deformation mechanism of Mg−Zn−Gd sheet during Erichsen cupping test

AbstractAn Erichsen cupping test of GZ31 sheet at room temperature with different reductions was carried out, and four samples with IEs (Erichsen index) of 2.0, 4.1, 7.1, and 7.3 mm were obtained. The deformation and fracture mechanisms of the cupping deformation process were studied by OM, SEM and EBSD. The results show that the IE of the GZ31 rolled sheet with the non-basal texture can reach 7.3 mm. Basal and pyramidal dislocation slips and {10 1-2} extension twinning are the main deformation modes during the Erichsen cupping test. The dislocation slip is hindered by the second phase particles and grain boundaries and entangles with each other to form voids, which eventually leads to the fracture of the material. The reason for the GZ31 sheet showing high IE is that the weak non-basal texture and rare earth elements are favorable for dislocation slip and extension twining to coordinate deformation.