Deformation Path Research Articles

Deformation path and springback behavior in double-curved bending at high temperature

In this work, integrated double-curved bending-sizing-unloading is simulated for a Ti6Al4V titanium alloy sheet. Bending radii R30 mm × R30 mm and R30 mm × R15 mm are used in the bending tests at 700 °C and 750 °C, respectively. A holding time of 0–600 s is applied to explore the effect of sizing time on forming accuracy. Similar experimental tests are performed for comparison with the finite element analysis results. Results show that bending behavior varies remarkably with the bidirectional radii. As for equal bidirectional curvature, bending along each direction occurs simultaneously. Given that bidirectional radii are different, the sheet consecutively experiences single small-, single large-, and double-curved bending. The deformation path results in nonuniform plastic strain distribution. The springback amount increases from the center to the marginal middle zone. Sizing at 700 °C or 750 °C in 600 s or 180–600 s can remarkably reduce the springback amount, respectively. The springback prediction via finite element method is consistent with that of the experiment.

Equal channel angular bending as a new severe plastic deformation process: Application to thin Mg-3Al-1Zn sheet

Abstract A novel severe plastic deformation process (SPD), namely an equal channel angular bending (ECAB), was proposed and successfully applied to thin Mg-3Al-1Zn sheets. Results of microstructure characterization indicate that simultaneous activation of multiple types of twins can be introduced by ECAB, which can refine the grain and efficiently weaken the basal texture. Moreover, the dominant twin types in ECAB are found to be closely related to the imposed deformation paths of ECAB, and profuse extension twinning can be activated under cross shear deformation. After appropriate annealing, the tensile ductility under cross shear deformation is improved with a relative increase of 60.5% to original sheets.

Microstructural evolution, mechanical properties and fracture toughness of near β titanium alloy during different solution plus aging heat treatments

Ti-55531 (Ti-5Al-5Mo-5V-3Cr-1Zr) is near β titanium alloy, which plays a significant role in manufacturing landing gears and flap tracks in the aerospace industry. This study aims to find out an optimal heat treatment to obtain an excellent balance of strength, ductility and fracture toughness. For this purpose, the Ti-55531 alloy was subjected to solution plus aging treatments and mechanical properties tests. Optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM) were adopted to observe the microstructural evolution including morphology, distribution and size. Standard tensile and compact tension (CT) tests were carried out to obtain the yielding/tensile strength (YS, TS), elongation (EL) and fracture toughness (KIC) of Ti-55531 alloy. The effects of solution temperature, aging temperature and time on the microstructural evolution and fractography were analyzed. The relationships between the mechanical properties and microstructures were qualitatively described. The influencing mechanism of plastic deformation and crack propagation path on the KIC were discussed. Simultaneously, the values of YS and KIC were predicted based on mechanical property models, the predicted values were compared with tested data. Finally, an optimal heat treatment was proposed for the Ti-55531 alloy, to obtain a good balance of strength, ductility and fracture toughness.

Effect of punch geometry on hole expansion ratio

Stretch-flangeability of sheet metal is normally quantified by hole expansion ratio. Researchers have determined hole expansion ratio with various punch geometries such as conical, flat-bottom and hemispherical, and reported different hole expansion ratio values for identical test condition. Finite element investigation confirms that alteration of deformation path with punch geometries consequence different hole expansion ratio values. Necking and failure take place slightly away from the central hole edge for flat-bottom and hemispherical punches, while at the central hole edge for conical punch. Approximately plane strain tensile deformation prevails at the failure location for flat-bottom and hemispherical punches, while pure uniaxial tensile deformation prevails for conical punch.

Tuning deformation behavior of Cu0.5CoNiCrAl high-entropy alloy via cooling rate gradient: An atomistic study

The deformation behaviors of body-centered cubic Cu0.5CoNiCrAl high-entropy alloys processed by the cooling rate gradient are investigated by the molecular dynamics simulations. The plastic deformation ability of the high-entropy alloy is significantly improved by triggering multiple-type dislocation slips along different deformation paths. The cooling rate gradient introduces abundant atomic vacancies, proliferating the nucleation sites of dislocations. Additionally, the nucleation barriers of dislocations are reduced by the resultant structural disorder, high potential energy and chemical segregation. Consequently, the cooling rate gradient enhances the structural heterogeneity, promoting the formation of multiple deformation paths and preventing strain localization.

Curvature-Bounded Lengthening and Shortening for Restricted Vehicle Path Planning

In this paper, the traditional shortest path planning problem for vehicle is advanced to length-targeted path planning problem, i.e., to plan path with its length being as close to a specified value as possible. Lengthening and shortening of given initial paths are used to solve this problem. Based on an operation set consisting of three basic path homotopies, we build a comprehensive and systematic framework to plan paths with target length, which is a generalization of the existing related studies. Thereby, the expected paths can be independently searched through such deformation processes within topological classes. The proposed framework can produce the largest length coverage in different scenarios and under different conditions, and it can also generate expected paths with arbitrary topological classification in terms of the curvature constraint and the obstacle constraint. Examples show that our lengthening and shortening method can effectively solve the length-targeted path planning problem in environment without or with obstacles. Note to Practitioners —This paper presents a curvature-bounded lengthening and shortening approach for path planning of vehicles. The curvature and obstacle constraints in the path planning problem are handled using the topological technique. In addition, a rigorous classification system is presented to systematically categorize the potential paths. Within a path class, any path can be deformed to other paths while keeping the curvature bounded. Then, the path deformation process is conducted via a series of basic homotopy operations to approach the target length. The length coverage range of this process is reduced when some endpoint conditions are meet or the vehicle is trapped into a closed region.

Integrated robot planning, path following, and obstacle avoidance in two and three dimensions: Wheeled robots, underwater vehicles, and multicopters

We propose an innovative, integrated solution to path planning, path following, and obstacle avoidance that is suitable both for 2D and 3D navigation. The proposed method takes as input a generic curve connecting a start and a goal position, and is able to find a corresponding path from start to goal in a maze-like environment even in the absence of global information, it guarantees convergence to the path with kinematic control, and finally avoids locally sensed obstacles without becoming trapped in deadlocks. This is achieved by computing a closed-form expression in which the control variables are a continuous function of the input curve, the robot’s state, and the distance of all the locally sensed obstacles. Specifically, we introduce a novel formalism for describing the path in two and three dimensions, as well as a computationally efficient method for path deformation (based only on local sensor readings) that is able to find a path to the goal even when such path cannot be produced through continuous deformations of the original. The article provides formal proofs of all the properties above, as well as simulated results in a simulated environment with a wheeled robot, an underwater vehicle, and a multicopter.

FINITE STRAIN MEASUREMENT USING IMAGE ANALYSIS UNDER REVERSE SHEAR AFTER FORWARD SHEAR

The purpose of this research is to investigate the progress of local deformation under finite deformation by using image analysis based on the Natural Strain theory. Since Natural Strain used in the image analysis can satisfy the addition law of strain on an identical line element and can remove the rigid body rotation from shearing strain component, it is an effective strain for representing stress and strain behavior under large deformation. Therefore, in this research, these features of Natural Strain theory will be incorporated into the method of image analysis. In the present study, using the test pieces made of high purity tough pitch copper, the local deformation occurring under large simple shear is investigated by comparing the strains in each element from the upper position to the middle position with the average strain in the gauge length. In order to investigate the progress of local deformation caused by differences of strain hardening in the material, the experiments are conducted under different deformation histories which are given by applying reverse shear after applying forward shear with different sizes. Consequently, it is revealed that if the value of plastic strain obtained by integrating over the whole deformation path is almost the same, the progress of local deformation is approximately the same even if the deformation path is different.

Petroleum tectonic comparison of fold and thrust belts: the Zagros of Iraq and Iran, the Pyrenees of Spain, the Sevier of Western USA and the Beni Sub-Andean of Bolivia

Abstract The genetic analysis of fold and thrust belts is facilitated by tracking the evolution of their organic endowment (petroleum tectonics). Petroleum tectonic analysis of convergent orogenic systems provides an audit of the processes that control the deformation and kinematics of orogenic belts. The distribution and deformation paths of the organic endowment intervals are key factors in determining the petroleum system evolution of fold and thrust belts. This comparison of orogenic systems illustrates the importance of flexural v. dynamic processes, orogenic wedge taper, mechanical stratigraphy and inherited architecture on the creation, preservation and destruction of petroleum accumulations. The Zagros, Pyrenees, Sevier and Beni Sub-Andean convergent systems share key characteristics of fold and thrust belts, with major differences in scale, degree of incorporation of organic endowment in evolution of the fold and thrust belt and its foreland, and preservation of fold and thrust belt wedge-top deposits. The Zagros is an orogen dominated by flexural processes that is a perfect storm for hydrocarbon generation and preservation. Its multiple stacked sources ensure continuous hydrocarbon generation while stacked detachments foster a low taper and thick wedge-top basins. The Pyrenees is also a flexurally dominated orogen, but the early consumption of its source rocks led to minimal survival of hydrocarbon accumulations during exhumation in a long lasting, high-taper orogenic wedge. The Sevier was initially a flexural orogen that was later dominated by dynamic uplift of the fold and thrust belt and distal foreland subsidence with foreland deformation. The consumption of its pre-orogenic sources during the early low-taper phase indicates a probable robust petroleum system at that time. However, the late high-taper phase exhumed and destroyed much of the early petroleum system. The addition of syntectonic foreland sources to be matured by both local and dynamic subsidence created an additional later set of petroleum systems. Post-orogenic events have left only remnants of world-class petroleum systems. The Beni segment of the Sub-Andean Orogen is a flexural system with probable dynamic overprints. Its most robust petroleum system probably occurred during its early low-taper flexural phase, with dynamic subsidence enhancement. Its late high-taper phase with possible dynamic uplift shuts down and stresses the petroleum systems. Comparison of these orogenic systems illustrates the importance of flexural v. dynamic processes, orogenic wedge taper kinematics, mechanical stratigraphy, distribution of source rocks relative to shortening and inherited architecture on the creation, preservation and destruction of petroleum accumulations in fold and thrust belts.

A post-buckling compressive failure analysis framework for composite stiffened panels considering intra-, inter-laminar damage and stiffener debonding

A post-buckling failure analysis framework was established to accurately and thoroughly capture the post-buckling deformation paths and failure processes as well as bearing capacities of composite stiffened panels under uniaxial compression. In this framework, the progressive damage method to thoroughly track the intra- and inter-laminar damage in laminates, the cohesive zone method to accurately examine the stiffener debonding damage, and the arc-length iteration algorithm to tracking the geometrical nonlinear post-buckling path, were all introduced. Post-buckling failure processes of a blade-stiffened panel and a large-scale hat-stiffened panel under uniaxial compression were systematically investigated. Computation cases with various damage models were designed and implemented, and the effects of intra- and inter-laminar damage, stiffener debonding, and their potential interactions on the post-buckling failure process of the stiffened panel were clarified. The predicted post-buckling failure processes of both panels were highly consistent with their experimental outcomes, thus giving evidence of the effectiveness of the failure analysis framework. It follows that a comprehensive failure mode characterization including intra- and inter-laminar damage, stiffener debonding should be all considered in a failure analysis framework for accurately predicting the failure of composite stiffened panels in engineering applications.

Numerical investigating the effect of nonuniform proppant distribution and unpropped fractures on well performance in a tight reservoir

Distribution of the propped and unpropped fracture is an important factor affecting well performance that is necessary to study. This paper presents new numerical proppant and rock fracture conductivity models. The models are based on the results of physical experiments conducted for this study and the models consider proppant deformation, embedding, and loading paths. The models were implemented in a 3D hydromechanical coupled numerical simulator to model well production. A 3D hydraulic fracturing simulator was used to generate an artificial fracture with nonuniform proppant distribution using reservoir and operational parameters from a tight oil reservoir in northwestern China. The fracture generated by the model was further used to investigate the influence of the nonuniform propped fracture on well performance. According to the study, proppant distribution can significantly affect well performance, a decreased aperture distribution from the well to the fracture front is preferred when using certain amounts of proppant. A parameter sensitivity study was carried out during which the influence of proppant deformation, proppant embedment, proppant permeability, proppant volume, reservoir damage, in-situ stress, and the loading path effect were investigated. Based on the results, suggestions were given to improve the well performance.

Effect of Deformation Path on the Microstructure and Mechanical Behavior of TWIP980 Steel

Recent technological advances have made it possible to manufacture steels with both high strength and high ductility. This is the case for Twinning-Induced Plasticity (TWIP) steels which are characterized by a twinning deformation mechanism, which is responsible for its excellent properties. In this work, TWIP980 steel was tested under tensile loading along the rolling direction until pre-deformations of 10%, 20%, and 30% were reached. In order to assess the effect of the deformation path, the pre-deformed samples were reloaded in directions of 0°, 45° and 90° against the rolling direction. Microstructural analysis was performed by means of optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The yield stress increased with the imposed deformation for all the tested directions. As the strain path changed from 0° to 90°, the yield stress for reload decreased, and the Bauschinger effect and permanent softening was observed. The yield plateau was observed as being directly influenced by deformation path without influence by strain rate and temperature.

Effect of {10−12} twinning on the deformation behavior of AZ31 magnesium alloy

Twinning process and dislocation characteristics were determined by means of quasi in-situ electron backscatter diffraction and high-resolution transmission electron microscopy techniques in a rolled AZ31 magnesium alloy under different strain paths (compression along rolling direction and tension along normal direction). It is demonstrated that the activation of different twin variants depends on the strain path, and thus these twin variants can further induce different texture characteristics. In addition, two independent slip systems were activated during deformation of both strain paths. However, the dislocation slip modes of the two kinds of deformation are different, resulting in different stress-strain response.

Accounting Bauschinger effect in the numerical simulation of constrained groove pressing process

Constrained groove pressing (CGP) is one of the severe plastic deformation techniques to achieve ultrafine grains in bulk sheet metals. The CGP process induces large plastic strain through incremental steps of shear and reverse shear using grooved and flat dies. The equivalent plastic strain distribution during CGP process can be correlated to the extent of grain refinement and the uniformity of ultrafine grains. The numerical analysis in the past have assumed isotropic hardening to model CGP process that does not consider the Bauschinger effect due to continuous change in deformation path between subsequent stages. In the present work, the effect of Bauschinger effect is considered using a combined isotropic-kinematic hardening model in simulation. The finite element model assuming isotropic hardening is validated with the results available in literature. Experiments on CGP were performed using three different materials and were modelled using both isotropic and combined hardening models. The maximum strain and the strain inhomogeneity predicted using combined hardening models were consistently greater than the isotropic hardening assumption.

Forming limit of 1GPa-class high-strength steel sheet under various deformation paths

Forming limit of 1GPa-class high-strength steel sheet under various deformation paths

Деформовність маловуглецевого дроту в процесі його багатоступінчастого холодного волочіння

The aim of the work is to analyze the distribution of deformations over the cross section, features of the deformation paths, also is carried out the assessment of wire deformability from low carbon steels typical for the modern market G3Si1 and Sv-08G2S during its multistage cold drawing. For the analysis, one of the typical technological processes of drawing with 16 transitions was selected, which is aimed at the production of wire with a diameter of 0.8 mm from a rod of diameter 5,5 mm. This process is implemented in real production in the PJSC «PlasmaTek» environment. The mechanics of cold drawing process are carried out using the finite element method. The evaluation of deformability was performed using the V. Ogorodnikov criterion, which takes into account the nonlinear nature of damage accumulation, the features of deformation paths in the form of derivatives, as well as the stress state indicator, taking into account the third invariant of the stress tensor (volume of the stress state). The analysis of the distribution of deformations in the section through their representation in relative units carried out. It is shown that the graphs of the distribution of strains over the cross section practically coincide for different transitions and diameters of the workpieces. The coefficient of non-uniformity of deformations practically does not depend on the number of transitions and the degree of stretching and reaches 0, 87. The deformation paths in the hazardous area — on the axis of the wire — are analyzed — they are characterized by a significant change in the derivative and curvature of the deformation territory. It is established that the indicators of the stress state, taking into account the volume of the stress state (in particular, the parameter Nadai–Lode) practically do not change during cold drawing. Сonsidering at third invariant of the stress tensor with the appropriate deformability criterion makes it possible to correctly evaluate the deformability of low-carbon welding wire in its drawing process in existing drawing practices and to further implement on this basis the assessment of technological heredity in the form of residual plasticity, hardness, and ect.

Dynamic microstructure evolution and mechanism of Fe-38Mn alloy during hot shear-compression deformation

The dynamic microstructure evolution and mechanism were investigated for Fe-38Mn alloy during hot shear-compression deformation under wide ranges of deformation temperature and strain rate. It was found that increasing the strain rate or the deformation temperature can promote the dynamic recrystallization of Fe-38Mn alloy. In comparison, increased strain rate is more beneficial to obtain fine grains. However, when the deformation temperature reached 1100 °C the obvious growth of dynamic recrystallized grains occurred under all strain rates. Benefited from the strain path of the shear-compression deformation and low stacking fault energy of Fe-38Mn alloy, numerous micro-shear bands were introduced into deformed microstructures. The dynamic recrystallization is discontinuous in appearance but continuous in nature, which is actually caused by the micro-shear bands. Furthermore, the mechanism of twinning induced nucleation was confirmed. Particularly, the deformation twinning played a key role on grain refinement and exhibited strong dependence on the strain rate.

Analysis of Mechanical Characteristics of Foundation Pit Excavation of Super High-rise Building in Strong Weathered Sandstone Area

The foundation pit excavation of the natural foundation of the super high-rise building in the strong weathered sandstone area of Lanzhou is the first foundation excavation project of Gansu Province. Excavation method and soil condition affect the excavation of foundation pits to different extents. In order to obtain the excavation method of foundation pit excavation in the area, based on the local soil conditions, he ABAQUS finite element software was used to establish the 3D numerical simulation of foundation pit excavation, and the stress and deformation curves during foundation excavation were drawn. The simulation results were compared with the specifications to obtain a feasible scheme for foundation pit excavation. Then a typical soil layer was selected for excavation, and the effects of elastic modulus and cohesion on the deformation of the foundation pit during excavation were studied, the model damage cloud diagram during the foundation pit excavation process is obtained. By comparing the deformation of a certain path in the model and drawing the curve, the influence of elastic modulus and cohesion force on the excavation deformation of the foundation pit is obtained. At the same time, this article can also provide reference for similar projects in the future.

Phase Stability of Dynamically Disordered Solids from First Principles.

Theoretical studies of phase stability in solid materials with dynamic disorder are challenging due to the failure of the standard picture of atoms vibrating around fixed equilibrium positions. Dynamically disordered solid materials show immense potential in applications. In particular, superionic conductors, where the disorder results in exceptionally high ionic conductivity, are very promising as solid state electrolytes in batteries and fuel cells. The biggest obstacle in living up to this potential is the limited stability of the dynamically disordered phases. Here, we outline a method to obtain the free energy of a dynamically disordered solid. It is based on a stress-strain thermodynamic integration on a deformation path between a mechanically stable ordered variant of the disordered phase, and the dynamically disordered phase itself. We show that the large entropy contribution associated with the dynamic disorder is captured in the behavior of the stress along the deformation path. We apply the method to Bi_{2}O_{3}, whose superionic δ phase is the fastest known solid oxide ion conductor. We accurately reproduce the experimental transition enthalpy and the critical temperature of the phase transition from the low temperature ground state α phase to the superionic δ phase. The method can be used for a first-principles description of the phase stability of superionic conductors and other materials with dynamic disorder, when the disordered phase can be connected to a stable phase through a continuous deformation path.

Tectonometamorphic evolution of the tip of the Himalayan metamorphic core in the Jajarkot klippe, west Nepal

AbstractNew phase equilibrium modelling, combined with U–Th/Pb petrochronology on monazite and xenotime, and 40Ar/39Ar geochronology on white mica, reveal the style of deformation and metamorphism near the southern tip of the extruded Himalayan metamorphic core (HMC). In the Jajarkot klippe, west Nepal foreland, greenschist to lower amphibolite facies metamorphism is entirely constrained to the Cenozoic Himalayan orogeny, in contrast with findings from other foreland klippen in the central Himalaya. HMC rocks exposed in the Jajarkot klippe yield short‐lived, hairpin pressure–temperature–time–deformation paths that peaked at 550–600°C and 750–1,200 MPa at 25 Ma. The Main Central thrust (MCT) and the South Tibetan detachment (STD) bound the base and the top of the HMC, respectively, and were active simultaneously for at least part of their deformation history. The STD was active at c. 27–26 Ma and possibly as late as c. 19 Ma, while the MCT may have been active as early as 27 Ma and was still active at c. 22 Ma. The tectonometamorphic conditions in the Jajarkot klippe are characteristic of crustal thickening and footwall accretion of new material at the tip of the extruding metamorphic orogenic core. Our new results reveal that collisional processes active in the middle to late Miocene at the base of the HMC now exposed in the hinterland were also active earlier, during the Oligocene, at the tip of the southward‐extruding middle crust.