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The thermal response in paper has been studied by thermography. It was observed that an inhomogeneous deformation pattern arose in the paper samples during tensile testing. In the plastic regime a pattern of warmer streaks could be observed in the samples. On the same samples digital image correlation (DIC) was used to study local strain fields. It was concluded that the heat patterns observed by thermography coincided with the deformation patterns observed by DIC. Because of its fibrous network structure, paper has an inhomogeneous micro-structure, which is called formation. It could be shown that the formation was the cause of the inhomogeneous deformations in paper. Finite element simulations was used to show how papers with different degrees of heterogeneity would deform. Creped papers, where the strain at break has been increased, were analysed. For these paper it was seen that an overlaid compaction of the paper was created during the creping process. During tensile testing this was recovered as the paper network structure was strained. [ABSTRACT FROM AUTHOR]

Context: In this paper, the optimum coverage of 4.44% and the optimum adsorption sites were determined for the Be3N2 adsorption system of O atoms at different coverages based on density functional theory. The electronic and optical properties of the model were investigated by applying bending deformation to the model at these coverage and adsorption sites. Adsorption of O atoms disrupts the geometrical symmetry of Be3N2, resulting in orbital rehybridization and lowering its band gap. Bending deformation causes the band gap of the adsorbed O atom structure of Be3N2 to first increase and then decrease, resulting in the modulation of its band gap. With increasing bending deformation, the adsorbed system is redshifts, and the degree of redshift increases with increasing bending deformation. Methods: All calculations in this paper were performed using the first-principles-based CASTEP module of Materials Studio (MS). The generalized gradient approximation (GGA) plane-wave pseudopotential method and the Perdew-Burke-Ernzerhof (PBE) Perdew et al. Phys Rev Lett 77:3865, 1996 generalized functional were used in the geometry optimization and calculation process to calculate the exchange–correlation potential between electrons. The effect of coverage on the electronic and optical properties of the Be3N2-adsorbed O atom system was investigated by adsorbing different numbers of O atoms on a monolayer of Be3N2. The Be3N2 protocell contains two N atoms and three Be atoms with a space community of P6/MMM (No.191). The original cell was expanded 3 times along the direction of the base vectors a and b in the Be3N2 plane to create a 3 × 3 × 1 monolayer Be3N2 supercell system. A vacuum layer of 15 Å is set in the direction of the crystal plane of the vertical monolayer Be3N2 supercell to eliminate interactions between adjacent layers. In the overall energy convergence test of the Be3N2 supercell, the plane wave truncation energy was set to 500 eV, and the energy difference between the calculations given in the literature Reyes-Serrato et al. J Phys Chem Solids 59:743-6, 1998 using 550 eV was less than 0.01 eV, verifying the reliability of the data at a truncation energy of 500 eV. The Monkhorst–Pack special k-point sampling method Monkhorst et al. Phys Rev B 13:5188, 1976 was used in the structural calculations, and the grid was set to 3 × 3 × 1. The geometric optimization parameters are set as follows: the self-consistent field iteration convergence criterion is 2.0 × 10−6 eV, and the iterative accuracy convergence value is not less than 1.0 × 10−5 eV/atom for the total force of each atom and less than 0.03 eV/Å for all atomic forces. In addition the high-symmetry k-point path is taken as Γ(0,0,0) → M(0,0.5,0) → K(− 1/3,2/3,0) → Γ(0,0,0) Chen et al, AIP Adv 8:105105, 2018. [ABSTRACT FROM AUTHOR]

Evaluates an apparatus developed to measure uniaxial tensile and compressive creep for paper. Measurement of creep deformation; Difference from a traditional tensile creep tester; Advantages of the apparatus.

Layered rock slope exists widely. Because of its special slope structure, it is prone to bending deformation and toppling failure, which is a serious threat to engineering construction and safety operation. At present, the research of layered rock slope still has great innovation potential. During the construction of Wudongde Hydropower Station on Jinsha River, safety and stability problems such as slope geological structure development, face rock unloading and relaxation, and even slip and large deformation were encountered. Through field exploration, it is found that the rock and soil stratification of the slope on both sides of Wudongde Hydropower Station is highly obvious. At present, there is a lack of research on-site long-term displacement monitoring of layered rock high-steep slope, especially for layered slope in complex hydrogeology and construction environment. In order to strengthen the research on the deformation and stability of layered rock slope, this paper analyzes the measured displacement data of Wudongde hydropower station slope, and establishes three-dimensional geological finite element model with the help of numerical simulation software. The stability of the slope is calculated by combining the finite difference method and the strength reduction method. Finally, the evolution mechanism of the deformation of the layered rock slope is explained according to the geological structure characteristics. The main conclusions of this paper are as follows: the layered slope in the dam reservoir area is prone to deformation under the combined action of long-term construction disturbance and fissure water seepage, and the construction disturbance has a strong influence on the artificial excavation area below 1070 m, and the maximum rock mass deformation and surface displacement in the artificial excavation area of the slope reach 92.2 mm and 312.5 mm, respectively. However, the influence of construction disturbance on the natural mountain above 1070 m is limited, the valley deformation of the natural mountain on the left bank of the reservoir area is higher than that on the right bank, and the cumulative deformation is still less than 20 mm. The influence of seepage on the displacement of the area with higher elevation at the top of the slope is more obvious, and the influence of excavation and other disturbances on the displacement of the artificial excavation area with lower elevation is more obvious. The deformation of the river valley in the water cushion pond behind the dam increases slowly, and the change trend of the field deformation data is mostly consistent with that of the numerical calculation. The horizontal shrinkage of the mountains on both sides shows a contraction trend on the whole, and the maximum horizontal shrinkage calculated by numerical simulation is close to 20 mm, which is located at the elevation of 990 m. [ABSTRACT FROM AUTHOR]

Fracturing horizontal well casing deformation has become very prominent, particularly in tectonic stress-concentrated shale gas fields, limiting the efficient development progress of shale gas. The main failure mode of casing shearing deformation had been attributed to fault slip caused by multi-fracturing. The current research did not provide a clear picture of the dynamic evolution relationship between hydraulic fracturing, fault slip, and casing deformation. In this paper, the dynamic model of fault slip induced by formation pressure change is established, incorporating the effects of stress drop, physical change of friction, and casing and cement-sheath resistance loads. The discontinuous displacement approach and explicit/implicit coupling iteration methods are used to reveal the relationships between the effective normal stress, shear stress, friction coefficient, and sliding velocity during the fault slip process. Furthermore, the microscopic process of casing deformation sheared by fault slip is investigated using static equilibrium theory, and a characterization method for determining the amount casing deformation caused by real-scale fault slip is proposed. The results show that three stages exist in the process of casing deformation sheared by fault slip, including trigger activation stage, accelerated slip stage, and deceleration slip stage. Fault slip is clearly influenced by fault strike. To reduce the amount of fault slip, the fault direction with the maximum in-situ stress should be avoided as much as possible. Serious casing deformation still occurs for large-scale activated faults even though the optimization measure of wellbore structure has been well taken. To fundamentally reduce the possibility of casing shear deformation, it is necessary to prevent fault slip through optimizing the design of hydraulic fracturing. This study lays the theoretical groundwork for the casing deformation control method in shale gas wells. [ABSTRACT FROM AUTHOR]

To investigate the dynamic recrystallization (DRX) behavior of forged 42CrMoA steel during hot deformation, the hot deformation experiments of forged 42CrMoA steel under different deformation conditions (strain rate, temperature, and strain) were carried out in this paper. The hot deformation activation energy of forged 42CrMoA steel was determined to be 413627.2 J · mol - 1 . The constitutive model and DRX kinetic model of the steel were established. Analyzing the reconstructed parent phase grains reveals that when the strain is constant, as the deformation temperature increases and the strain rate decreases, the average size and DRX volume fraction of the parent phase grains gradually increase, and the peak stress gradually decreases. When the deformation temperature and strain rate are constant, as the strain increases, the average size of the parent phase grains gradually decreases, and the volume fraction of DRX gradually increases. Based on the cellular automaton theory model and considering the influence of grain deformation on the DRX process, a cellular automaton dynamic recrystallization (T-DRX-CA) model for forged 42CrMoA steel based on topological deformation technology was established, and the microstructure evolution under different deformation conditions was simulated. The microstructure evolution under different deformation conditions was simulated, which was compared with experimental results. The results showed that the average errors between the simulated and experimental values of the average grain size of the parent phase, the volume fraction of DRX, and peak stress were all less than 8%, and the simulated results were in good agreement with the experimental values, which indicates that the established model can accurately predict the DRX behavior of the forged 42CrMoA steel in the process of hot deformation. The hot deformation behavior of forged 42CrMoA steel under different deformation conditions was investigated by a cellular automaton dynamic recrystallization (T-DRX-CA) model based on topological deformation technique. The results showed that the average errors between the simulated and experimental values of the average grain size of the parent phase, the volume fraction of DRX, and peak stress were all less than 8%, and the simulated results were in good agreement with the experimental values, which indicates that the established model can accurately predict the DRX behavior of the forged 42CrMoA steel in the process of hot deformation. [ABSTRACT FROM AUTHOR]

Abstract  In this study, a simplified Acoustic Emission (AE) equipment, in essence an AE signal conditioner and a USB (Universal Serial Bus) data acquisition system, is used to study what happens in paper structures during mechanical loading. By the use of such equipment, some parameters that can be extracted are e.g. the stress and strain at onset of AE, the stress and strain at the onset of rapid AE defined as some numerical factor (larger then one) times the initial emission rate, the emission rate at the first stage of loading and the stress and strain at final failure i.e. when the specimen loses its load carrying ability.In this study however, the interest is focused on one particular parameter i.e. the elastic strain energy density W c at onset of AE. This is a parameter with a clear physical meaning and in this study, the correlation between this parameter and a fracture toughness measure, is investigated.The conclusion is that when nine different paper materials (with a large span regarding properties) are considered, there is a correlation (however not linear) between these two parameters. [ABSTRACT FROM AUTHOR]

Integral blisk blades are typical complex curved structures with small thickness, low stiffness, and complex boundaries. Due to the high material removal rate during the machining process, they are prone to force-induced deformation, resulting in significant machining errors. This seriously contradicts the requirements for high design accuracy and surface accuracy in the aerospace industry. Therefore, accurately predicting the distribution pattern of deformation caused by dynamic milling forces during the machining process and proposing reasonable error compensation strategies are urgent issues to be solved in the manufacturing of integral blisk blade. Firstly, this paper establishes a prediction model for the deformation distribution during the milling process of the integral blisk blade. Secondly, based on the finite element deformation prediction model of blades, the selection of blade milling processing methods and parameters was completed with the goal of minimizing machining deformation. Finally, a reverse reconstruction geometric modeling compensation strategy is proposed, and the tool path program containing the deformation error compensation amount is regenerated. The prediction model and compensation strategy proposed in this paper were validated through milling experiments and profile accuracy measurement experiments on a certain aeroengine integral blisk blade. The results showed that the prediction model has high reliability, with an average error of 7.96%; the new compensation strategy can reduce the tool-yielding error to within the tolerance range. This study will provide technical support for improving the machining accuracy and efficiency of integral blisk blade. [ABSTRACT FROM AUTHOR]

Free-standing paper-like or foil-like materials are an integral part of our technological society. Their uses include protective layers, chemical filters, components of electrical batteries or supercapacitors, adhesive layers, electronic or optoelectronic components, and molecular storage. Inorganic ‘paper-like’ materials based on nanoscale components such as exfoliated vermiculite or mica platelets have been intensively studied and commercialized as protective coatings, high-temperature binders, dielectric barriers and gas-impermeable membranes4,5. Carbon-based flexible graphite foils composed of stacked platelets of expanded graphite have long been used in packing and gasketing applications because of their chemical resistivity against most media, superior sealability over a wide temperature range, and impermeability to fluids. The discovery of carbon nanotubes brought about bucky paper, which displays excellent mechanical and electrical properties that make it potentially suitable for fuel cell and structural composite applications. Here we report the preparation and characterization of graphene oxide paper, a free-standing carbon-based membrane material made by flow-directed assembly of individual graphene oxide sheets. This new material outperforms many other paper-like materials in stiffness and strength. Its combination of macroscopic flexibility and stiffness is a result of a unique interlocking-tile arrangement of the nanoscale graphene oxide sheets. [ABSTRACT FROM AUTHOR]

Cutting toolholders, with designed in-built compliant mechanisms, are frequently used for machining microfeatures. In this paper, compliant structures are designed using trusses as they exhibit a superior strength-to-weight ratio. Systematically stacked two-stage truss structures along with flexure hinges are designed to yield the desired precise cutting motion. The materially reduced efficient design amplifies the output force and greatly assists in overcoming cutting resistance during machining. The characteristics of the designed compliant tool holder are analysed by considering the output force and displacement for a given input. Both mathematical modelling to determine the force and finite element analysis to identify the critical stress regions when subjected to a prescribed input displacement are presented. As part of dynamic analysis, modal analysis and harmonic response studies were performed to determine how the trussed compliant structure deforms when subjected to dynamic loadings. The designed tool holder was additively manufactured using functionally rigid polyamide-12-glass-bead (PA12-GB) material. The performance of the developed cutting tool holder is then verified by machining radially graded surfaces following which, the machining results are presented in this paper. [ABSTRACT FROM AUTHOR]

This paper presents a data-driven solver (DDS) for the growth-induced deformation problems of soft materials. Contrary to the over-reliance of traditional numerical methods on material constitutive models, the DDS requires only a discrete material dataset of stress–strain pairs to describe the stress–strain relationship. With the multiplicative decomposition of the gradient tensor, the growth effects are introduced. The growth-induced deformation problems are then solved as the pre-strain problems. To overcome the difficulty in determining the growth-induced pre-stress without an explicit constitutive model, a strain-driven searching scheme is thus proposed. Several numerical examples demonstrate the robustness and its good performance of the proposed DDS. In particular, the reason for choosing the strain-driven searching scheme is also illustrated according to the numerical example results. [ABSTRACT FROM AUTHOR]

This paper describes a study of deformation of an ideal elastoplastic adhesive layer of a sample in the form of an elastic double-cantilever beam. The integral values are determined for a number of adhesives with account for all diagonal stress tensor components in the layer. It is shown that the integral value is significantly affected by the plane problem type in the case where an elastic-plastic model of layer deformation is applied. As demonstrated in the study, compressive stresses may be present during normal fracture in the irreversible deformation region of the adhesive in a plane stressed state. [ABSTRACT FROM AUTHOR]

Context: Molecular dynamics (MD) was carried out to simulate the friction behavior of Ni-Cr alloy coating containing pores. The mechanical properties, displacement, abrasion depth, and defect change patterns of the coating under nano-friction were studied. It was found that the stacking fault would extend to the pores, and both tangential and normal forces decreased when the grinding ball was above the pores. Meanwhile, the pores changed the extension direction of shear strain inside the coating, and stress concentrations were generated at the pores. In addition, the deformation behavior inside the coating was influenced by the processing depth, the smaller the relative height of the grinding ball and the pore, the greater the atomic deformation around the pore. The pores changed the path of atomic movement, resulting in less deformation of the coating below the pores. The presence of pores promoted the generation of surface steps and increased the amount of wear on the coating. It was also found that pores facilitated energy release and provided space for dislocation extension, and the large accumulation of dislocations led to frictional strengthening near the pores, which enhanced the properties of the material below the pores. It was found that the increase of the pore size caused the normal force decrease and the wear performance of the coating decrease, but the thermal insulation performance would be improved. Methods: In this paper, nanoscale modeling was performed in the large-scale atomic/molecular parallel simulator (LAMMPS) simulation environment. The model was visualized and analyzed in three dimensions by Open Visualization Tool (OVITO), the common neighbor analysis (CNA) method was used to obtain the atomic structure information, and the dislocation analysis (DXA) method was applied to obtain the dislocations. [ABSTRACT FROM AUTHOR]

In dissimilar friction stir welding (FSW), the influence of tool position with respect to the weld interface (tool-offset) on the microstructural evolution and its effect on joint formation, particularly considering the difference in deformation behavior of the two joining materials, has not been fully explored. This investigation highlights the influence of tool position in friction stir welding of titanium to aluminum and the mechanisms of microstructural evolution that leads to joint formation. It was observed that the tool position controls the deformation behavior and the mixing mechanism of the two metals in the weld nugget. In titanium, the deformation mechanism changed from the formation of "continuous flakes" to "finely distributed particles" when the tool offset was more toward the aluminum side. The deformation and fracture mechanism in titanium is mediated through the formation of adiabatic shear bands (ASBs). Furthermore, the amount of intermetallic phases formed is affected by tool offset. At the optimum tool offset the presence of Ti particles, intercalated particles, interfaces without defects, and controlled diffusion gives rise to improved tensile properties. The mechanisms involved in the joint formation process, such as deformation and distribution, are also discussed in this paper. [ABSTRACT FROM AUTHOR]

Electromagnetic punching (EMP) is a dynamic, high-energy and high-speed hole-processing method. In this paper, the EMP specimens under different discharge energies (11–19 kJ) was prepared. By numerical and experimental methods, the deformation characteristic was analyzed, and hole-quality assessments (including morphology observation, dimensional measurements and microhardness test) were implemented. Results showed that the deformation process of sheet consisted of electromagnetic induction, elastic deformation, plastic deformation and separation stage, and the duration of the entire process was within 100 μs. For 11–15 kJ, the sheet had not completed the entire EMP process (no separation stage), and the deformation degree was aggravated with the increase of discharge energy. For 16 kJ, the incomplete punching occurred owing to the insufficient of electromagnetic force and uneven force. As discharge energy continued to increased, the dimensional accuracy of punching improved, the proportion of rollover zone (η) decreased, the slant angle of fracture zone (β) increased (gradually perpendicular to the sheet plane), the surface morphology of hole wall was more regular, and the micro hardness value of cross section increased, indicating that the punching quality of punched hole was improved. In addition, this work can provide a scientific guidance for the engineering application of EMP technology in automobile industry. [ABSTRACT FROM AUTHOR]

Hot gas forming (HGF) is an advanced technique for fabricating complex-shaped hollow tubular parts. Practically, multi-step pre-forming involving pre-deformation is often necessary prior to HGF. This paper performs an experimental investigation to simulate the pre-forming operation evaluating the effect of pre-strain on the subsequent HGF. Firstly, the dislocation density was accumulated with uniaxial pre-stretching with different strains (5%, 10%, and 15%) at room temperature, simulating the pre-forming operations. Secondly, the sub-sized specimen from the pre-stretched sample was characterized at different temperatures (350, 400, and 450 °C) to evaluate the effect of pre-strain on successive hot deformation for simulating practical HGF. The experimental results proves the coupled influence of pre-strain and temperature on the flow stress and stress-strain variations. To thoroughly understand the micro-mechanisms, EBSD analysis of grains and grain boundary angles was carried out under different pre-deformation levels and temperatures, which shows the recrystallization phenomenon at 15% pre-strain and 450 °C temperature. Finally, a physical mechanism constitutive model is established based on the determined macro and micro results where the pre-strain effect shows the accurate modeling of stress flow behavior of the material. [ABSTRACT FROM AUTHOR]

It has been well established that the internal length scale related to the cell size plays a critical role in the response of architected structures. It this paper, a Volterra derivative-based approach for deriving nonlocal continuum laws directly from an energy expression without involving spatial derivatives of the displacement is proposed. A major aspect of the work is the introduction of a nonlocal derivative-free directionality term, which recovers the classical deformation gradient in the infinitesimal limit. The proposed directionality term avoids issues with correspondences under nonsymmetric conditions (such a unequal distribution of points that cause trouble with conventional correspondence-based approaches in peridynamics). Using this approach, we derive a nonlocal version of a shear deformable beam model in the form of integro-differential equations. As an application, buckling analysis of architected beams with different core shapes is performed. In this context, we also provide a physical basis for the consideration of energy for nonaffine (local bending) deformation. This removes the need for additional energy in an ad hoc manner towards suppressing zero-energy modes. The numerical results demonstrate that the proposed framework can accurately estimate the critical buckling load for a beam in comparison to 3-D simulations at a small fraction of the cost and computational time. Efficacy of the framework is demonstrated by analysing the responses of a deformable beam under different loads and boundary conditions. [ABSTRACT FROM AUTHOR]

Presents a quantitative description of the shape, response and stability of conical dislocation in crumpling of paper. Results of deformation; Scaling laws for the size of the core; Characteristics of the geometry of the dislocation away from the core; Interaction between conical dislocations in a simple geometry.

A continuum theoretical model for describing nanotube formation from a self-bending (self-curling) nanofilm driven by surface stress was established in this paper. Surface stress, surface elasticity and anisotropic deformation were considered. A nanofilm was cured along tangential direction to form a nanotube. The other in-plane direction (cylindrical direction) maintains straight state. Isotropic surface stress no longer induces an isotropic bent under this condition. Therefore, isotropic Stoney theory should be modified and the anisotropic deformation should be reckoned in. Curling structure affects radius as well as elongation strain of nanotubes obviously. Film stiffness instead of biaxial modulus in the curling equation means the difference between our theory and Stoney formula (as well as its modified form). If surface elasticity is balance, elongation strain holds isotropic despite the anisotropic curling structure of nanotubes. Since residual strain and stress influence the physical properties within nanotube wall, the residual strain and stress were also analyzed in this paper. [ABSTRACT FROM AUTHOR]

It is vital to reveal the effect of microstructure features on the corrosion behavior of pure aluminum anode in alkaline electrolyte for Al-air batteries. In this paper, we extensively studied the influence of mechanical deformation on the corrosion microstructure and then corrosion features of pure aluminum anode. The results demonstrate that the cold-rolling deformation could facilitate the grain size refinement of pure aluminum. Surprisingly, the aluminum anodes with smaller grain sizes and larger grain boundary areas could effectively improve the corrosion resistance. The further characterization of the microstructure indicates that the deformation is capable of causing the fracture of the cathodic secondary phase precipitate clusters thus weakening the galvanic corrosion effects. The results of this paper could gain insights into the design and processing of pure aluminum for Al-air battery. [ABSTRACT FROM AUTHOR]

Spherulite is the main microstructure feature of semicrystalline polymers, exhibiting a non-axisymmetric geometry with a sheaf structure in the center. In the initial stage of growth, spherulite is manifested initiation from the sheaf structure with a certain orientation. The size and orientation of sheaf structure are affected by various processing parameters. Previous research considered spherulite as completely radially symmetric structures, ignoring the effects of anisotropic sheaf on mechanical properties. In this paper, an anisotropic micromechanical model for evaluating the mechanical properties of semicrystalline polymers was proposed. The microstructure of single spherulite was modeled with different sheaf sizes, orientations, and crystallinities. The viscoplastic constitutive model together with the Arruda–Boyce model was used to describe the micromechanical behaviors of the crystalline lamellae and amorphous lamellae, respectively. The evolution of inhomogeneous plastic deformation, interlayer deformation and slip activities in spherulite was observed under tension. The results shown in this work enhance the understanding of the microstructure–property relationship of semicrystalline polymers, which, in turn, guides the development of advanced manufacturing techniques for tailoring mechanical properties. [ABSTRACT FROM AUTHOR]

In this paper, the deformation mechanisms of a Fe–2.25%Cr–1%Mo (P22) steel are studied after tensile tests at room temperature (RT) and 550 °C (HT), creep-fatigue tests at 550 °C and stress relaxation test at 550 °C (HTSR). The RT, HT and HTSR tests produced permanent strain of about 2.5% by different processes. Deformation features such as the orientation of the grains, local misorientation, grain boundary type and distribution, etc., were characterized using electron backscatter diffraction. Transmission electron microscopy was done subsequently to obtain greater insight into the dislocation substructures. The as-received sample had a ferritic–bainitic microstructure, and a large amount of local misorientation was found in the bainite, indicating plastic strain due to phase transformation. After tensile strain to 2.5% at room temperature, the dislocations formed very small substructures (~100–200 nm) in the ferrite grains, and most of the retained plastic strain seemed to be concentrated in the bainite after deformation. Both the ferrite and bainite showed much lower local misorientation and dislocation wall content after a tensile test to 2.5% strain at 550 °C. Compared to the RT tensile sample, after creep-fatigue at 550 °C, the substructures in ferrite opened up considerably and formed small-angle grain boundaries, with clean areas as large as 20–25 μm. After stress relaxation at 550 °C, the ferrite displayed even less substructure, while the bainite seemed to have greater amounts of local misorientation than in the creep-fatigue case. However, the degree of misorientation was less pronounced than in the room temperature tensile case. These results have been discussed with respect to the causes behind the phenomena observed herein and their possible effects on mechanical behaviour. [ABSTRACT FROM AUTHOR]

In this paper, the deformation behavior of a nickel-based single-crystal superalloy with [ 1 ¯ 40] and [ 3 ¯ 40] orientations was studied at room temperature by in situ electron backscattered diffraction (EBSD) tensile equipment. The mechanical properties, slip behavior and the corresponding Schmidt factor were analyzed. The deformation bands generated during the plastic deformation stage were found and characterized by using the electron backscattered diffraction (EBSD) technique. Furthermore, the formation and propagation of deformation bands played a softening effect on stress–strain curves; however, the secondary slip bands occurring after the propagation of deformation bands played a hardening effect. Finally, the formation of deformation band and its propagation on the mechanical properties are discussed. [ABSTRACT FROM AUTHOR]

This paper addresses the problems of easy deformation, difficult dimensional control and difficult accuracy assurance during the production of thin-walled gears for helicopter spoke cutting. It uses finite element simulation technology, metal cutting principles, process optimization and other design and manufacturing technologies to reveal the causes of cutting deformation, effectively predict the deformation of parts during cutting, and develop reasonable deformation control strategies. This study explores the effects of cutting force, residual stress and clamping method on gear machining deformation. The deformation of the spoke plate is analysed by finite element simulation. Abaqus software is adopted to establish a finite element model for 2D turning simulation to predict the machining residual stresses and cutting forces during gear turning machining with different cutting parameters. The simulated cutting forces are compared with the residual stresses and experimentally measured values to verify the accuracy of the finite element model and provide a theoretical basis for model construction in the next simulation study. With Abaqus software, the effect of different cutting forces on the deformation of the spoke plate is simulated, and the effect of the superposition of cutting and clamping forces on the deformation of the spoke plate is simulated using life and death cell technology to simulate the machining of the workpiece. Then, a corresponding fixture is designed to realise the corresponding clamping position for machining experiments, and the deformation of the spoke plate is measured by CMM (coordinate measuring machine) to verify the realism of the simulation. This research provides scientific theoretical guidance and process support for aerospace thin-walled gear spoke plate turning. [ABSTRACT FROM AUTHOR]

In this paper, materials with nonlocal properties are considered as a continuum model composed of micro-elements with certain volumes. Based on this hypothesis, the deformation and corresponding energy of micro-structure system are studied in detail, and the equivalent governing equations in simplified form are given. In the framework of micro-structure system, a simplified deformation gradient theory (SDG) with two length-scale parameters is obtained by defining the micro-strain and micro-rotation of elements specifically from the perspective of deformation, which has definite physical significance. The generalized strain energy is introduced in the SDG, which gives a new explanation of elastic moduli, and the nonlocal effect parameter is defined to capture nonlocal properties of materials quantitatively. Under certain micro-deformation assumptions, the SDG can be degenerated into couple stress theory, strain gradient theory and classical continuum theory. The nonlocal deformation consists of two branches: one is the macro-deformation of non-uniform materials and the other is the micro-deformation of materials with micro-structures. For the macro-tension of particle reinforced composites, the SDG successfully verifies and predicts the approximatively linear relationship between elastic moduli and particle sizes on the micron scale. Moreover, the theoretical solution to nonlocal micro-torsion based on the SDG agrees well with the experiment results and also predicts the torsion stiffness of cylinder at smaller diameters. [ABSTRACT FROM AUTHOR]

High-strength DP980 steel has been used on the automobile to improve the crash safety and lightweight, but serious springback is unavoidable during stamping. In this paper, complicated deformation behaviors during cold stamping of DP980 steel are investigated by combining experiment and simulation in order to promote the accuracy of springback prediction. Deformation behaviors including varied elasticity, anisotropic yield, and cyclic hardening are studied by testing, modelling, and model-programming. Firstly, uniaxial tension, biaxial tension, and in-plane cyclic tension–compression tests are carried out by a self-developed platform to test the mechanical behaviors of DP980 steel in the complicated deformation process. Secondly, elastic, yield, and hardening behaviors are modelled and evaluated. A modified elastic attenuation model by establishing a relation between chord elastic modulus and plastic strain is proposed to describe the elastic behavior. Three yield models, such as BBC2005, Hill-1948, and von-Mises, are presented to compare the description ability to the yield locus and anisotropy. A coupled isotropic and nonlinear kinematic (CINK) hardening model is proposed to accurately describe the hardening behaviors (Bauschinger effect, transient effect and permanent softening) by cyclic tension and compression loads. Finally, U-shaped part is stamped and simulated by using models that can describe actual deformation behaviors. The springback prediction with modified elastic attenuation, anisotropic yield, and CINK hardening models obtains an optimal result, and the overall relative error is only 1.803%. Among three factors, the effect of elastic attenuation on springback is the greatest. The results show that the accurate testing, modelling, and implementing of complicated deformation behaviors of DP980 steel contribute to high-precision simulation results. [ABSTRACT FROM AUTHOR]

One factor that plays an important role in the aerodynamic performance of aeroengines is the shape of the blades, which is vulnerable to change resulting from the plastic deformation and the residual stresses induced by the complex manufacturing processes, especially the shot peening. However, few studies were focused on the detailed strategies of shot peening on the complex profile and the superposition effects of residual stresses during the entire manufacturing processes. In this paper, based on the concept of eigenstrains, we investigated the effect of shot peening on residual stresses and deformation of the blade by combining the experimental measurement and the local-global simulation. The results show that the initial residual stresses induced by the previous milling process could be neglected. After the shot peening, the blade has the largest deformation if considering the initial residual stresses during milling with large amount of material removal, compared with the case without considering initial residual stresses and the case considering initial residual stresses after dynamic milling of blades. Furthermore, the in-out sequence of shot peening results in the smallest deformation and the pre-deformation of the blade can effectively offset this deformation. Finally, the shot peening intensity should not be too high in practical blade manufacturing for small thickness in order to avoid compromising the reliability and safety of blades. [ABSTRACT FROM AUTHOR]

In this paper, the development law of residual deformation of coal gangue subgrade filler is analyzed through large scale triaxial test, and the residual deformation model of coal gangue mainly sandstone and limestone is established. The purpose is to provide research basis for the applicability of coal gangue as subgrade filler. The results show that the deformation of coal gangue filler increases first and then tends to be constant under cyclic load of multiple vibration times. It is found that the Shenzhujiang residual deformation model cannot accurately predict the deformation law, and the corresponding modification is made to the residual deformation model of coal gangue filling body. Finally, according to the calculation of grey correlation degree, the influence degree of main factors of coal gangue filler on its residual deformation is sorted. Combined with the actual engineering situation represented by these main factors, it can be analyzed that the effect of packing particle density on residual deformation is greater than that of packing particle size composition. [ABSTRACT FROM AUTHOR]

In the process of machining aircraft monolithic components, the initial stress in the blank will cause machining deformation. Based on the energy method, an analytical mathematical model of machining deformation is presented in this paper. The key point is to transform the energy in the removed material into the deformation energy of the part after machining. The initial residual stress of 7050-T7451 aluminum alloy blank and single frame part are used as investigated cases in the analytical model. For layer by layer machining, the deformation evolution is closely related to the tensile or compressive properties of the initial stress of removed material. Combined with the change of neutral axis position, the machining deformation is calculated by a theoretical model. Then, utilizing the semi-analytical model of equivalent bending stiffness, FEM simulation is carried out to analyze the influence of stiffening ribs on machining deformation. Furthermore, experiments are set up to verify the validity of the theory and FEM data. The results indicate that the deformation results of the experiment are consistent with that of theory and FEM model. Deformation is determined by energy of removed material. This paper provides a novel theoretical approaches for the further investigation of this issue. [ABSTRACT FROM AUTHOR]

With the changes in joint torque and driving state caused by robot postures, the stiffness properties behave differently. However, constant joint stiffness parameters cannot accurately reflect the deformation of different robot postures. To solve this problem, based on the hypothesis of flexible joints, this paper proposes a pose-dependent identification method for joint stiffness. By changing the load at the end of the robot, the laser tracker is used to monitor the slight change of the measuring point on the link near the joint, and the joint deformation monitoring is realized with the analysis of micro displacements. Combined with the external loads monitored by the dynamometer, the change of joint torque is obtained through structural analysis, and then the joint stiffness at a given joint position is identified. Based on the joint stiffness identification results of different joint positions, the joint stiffness is fitted by a polynomial function, and then the varied robot joint stiffness model is obtained. Jacobean transformation and conservative congruence transformation are combined to predict the Cartesian stiffness of the robot. The effectiveness of the stiffness model proposed in this paper is verified by the loading experiments at the end of the robot and robot deformation measurement for milling long aluminum strip. [ABSTRACT FROM AUTHOR]

Aiming at the problems of complex processing technology, uneven deformation, and poor forming accuracy of multi-curvature positive Gaussian slewing egg-shaped shells, it is proposed to use unidirectional loading rubber flexible medium bulging technology to improve the tube deformation distribution and enhance the processing accuracy of plastic forming of bionic egg-shaped shells. By analyzing the structure and manufacturing method of egg-shaped shells, this paper explores the optimization problems in the rubber bulging technology of non-homogeneous deformation egg-shaped shells. The simulation analysis and experimental verification methods are used to study the different technological parameters and forming accuracy of rubber bulging of egg-shaped shells under unidirectional loading and to master the deformation mechanism of rubber bulging of egg-shaped shell structural components under unidirectional loading. The study shows that optimizing technological parameters in unidirectional loading mode can effectively improve the uniformity of strain distribution and thickness distribution during the forming of egg-shaped shells, thus improving the processing accuracy of plastic deformation of bionic egg-shaped thin-walled parts. Furthermore, the simulation of the rubber bulging technology of the egg-shaped shell after the optimization of technological parameters is in good agreement with the experiment. [ABSTRACT FROM AUTHOR]

Bend tubes have been widely used in aerospace equipment due to their excellent mechanical properties and chemical properties. However, elliptic deformation will occur in the process of bending, which will reduce the pressure bearing capacity and service life of the bend tube. In order to ensure the production quality of the bend tube, a method of detecting elliptic deformation based on the spine line of the tube is proposed in this article. Firstly, the spine line reconstruction method, which employs scanning points of the tube is proposed. Specifically, a voting points inspired spine line initialization method, and a bend part identification preferred spine line shape analysis method are designed. Secondly, the contour extraction method based on the natural coordinate system of the spine line is studied. Thirdly, the contour integrity assessment method based on the maximum center angle of the missing contour line is proposed. Contours satisfying the integrity will be used for ellipse fitting to determine the ovality of the tube. Finally, various bend tubes and standard elliptical cylinders are used to illustrate the effectiveness of the proposed method. Extensive experimental results show that our proposed method can extract the contour of the bend tube and analyze its deformation in only 7 s, and the ovality error is about 0.039%. Therefore, the method proposed in this paper can quickly and effectively analyze the elliptic deformation of the bend tube and can be used for online detection. [ABSTRACT FROM AUTHOR]

This paper proposes a model of static transverse elastic deformations of a magnetic gel sample shaped as a strongly elongated cylinder, which is under the action of a transverse uniform magnetic field and the force of gravity. Theoretical results obtained within the framework of the proposed model are in qualitative agreement with the results of laboratory experiments. [ABSTRACT FROM AUTHOR]

The rock mass around deep roadways has obvious creep characteristics in high-stress environments. Meanwhile, the cyclic impact load induced by roof fracturing also causes dynamic damage to the surrounding rock, leading to long-term large deformation. This paper examined the rock mass deformation mechanism around deep roadways based on the theory of rock creep perturbation effect considering perturbation sensitive zone. This study proposed a long-term stability control guideline for deep roadways under dynamic load. An innovative support system was developed for deep roadways, with concrete-filled steel tubular support being recommended as the main supporting body. A case study was conducted to validate the proposed supporting system. Monitoring over one year in the case study mine showed that the overall convergence deformation of the roadway was 35 mm, indicating that the roadway's long-term large deformation induced by creep perturbation was effectively controlled by using the proposed bearing circle support system. [ABSTRACT FROM AUTHOR]

Strain gradient plasticity has been the subject of extensive research in the past 40 years in order to model size effects in metal plasticity, on the one hand, and provide finite width shear bands in the simulation of localization phenomena, on the other hand. However, the use of the emerging models is still limited to academic applications and has not yet been adopted by industry practitioners. The present paper systematically reviews the pros and the cons of gradient plasticity at finite strains based on the gradient of scalar plastic variables, in particular the gradient of the cumulative plastic strain. It proposes benchmark tests addressing both size effect modeling and plastic strain localization simulation. It includes new analytical solutions for validation of FE implementation. It focuses on the micromorphic approach to gradient plasticity, as a convenient method for implementation in FE codes. New features of the analysis include the comparison of three distinct formulations of rate-independent gradient plasticity at finite deformations, based on the multiplicative decomposition of the deformation gradient and on quadratic potentials with respect to gradient terms. The performance of micromorphic and Lagrange-multiplier-based strain gradient plasticity models is evaluated for various monotonic and cyclic loading conditions including confined plasticity in simple glide and tension, bending and torsion at large deformations. Limitations are pointed out in the case of bending and torsion, which can be overcome for instance by the use of the gradient of equivalent plastic strain model. [ABSTRACT FROM AUTHOR]

The impact of crushing on the macroscopic mechanical characteristics of granular materials from a microscopic perspective has recently been revealed using the discrete element method (DEM). The influence of the self-organized, mass conservation and volume conservation of daughter particles in the fragment replacement method (FRM) on particle breakage is complex and crucial. In this paper, 14-ball Apollo directly filling method (DFM) and expansion method are combined to keep balance among particles before and after crushing, considered to establish DEM to simulate granular material. By considering the influence of volume loss on the micro-fracture condition of the samples, the macro-responses of mechanical and deformation characteristics, the gradation change and the critical state are studied. The effect of inter-particle interaction on macroscopic properties is also analyzed from the microscopic perspective. The rationality of the volume expansion method is verified. The comparisons of samples with volume conservation and volume loss show that the stress development process and the volumetric strain are affected. The existence of the balance point of volume effect is related to the stress level which lead to the difference in stress and strain. Through analysis of relative breakage index (Br) and the statistical number of microscopic particles, it can be seen that the gradation deviation comes from the two-way influence of the volume loss on the crushing of particles. The volume loss has no effect on stress ratio in the critical state, but has a significant effect on stress change during shearing process, and results in the critical state void ratio to decrease with increasing confining pressure. The rationality of daughter particles' volume conservation are analyzed from the motion, displacement development and force chain evolution. [ABSTRACT FROM AUTHOR]

The convergence-confinement method (CCM) is a simplified widely utilised tool for assessing the interplay between the rock mass behaviour and the support effect, so it is quite helpful for tunnel support design purposes. However, the direct application of this technique has shown some limitations, many of which are directly related to the three-dimensionality issue. Indeed, the CCM tries to solve the three-dimensional (3D) problem of tunnel advance deformation and support response, by means of a series of two-dimensional (2D) plane strain analyses. So, regardless purely elastic cases, certain deviation is observed when comparing CCM and 3D numerical modelling results. The reasons behind this deviation have been studied from different points of views, but they seem to be still not well understood. With the aim of advancing towards a better knowledge of this issue, this paper discusses the limitation of CCM to correctly reflect the 3D tunnelling effect by comparing CCM and 3D numerical deformation, support pressure and liner load results in a typical tunnel case for various geological conditions. The reasons for CCM results in different rock deformation and support pressure in comparing to the 3D numerical modelling are explained. Some guidelines are eventually given recommending when the use of CCM can be acceptable according to the rock mass strength and tunnel depth, and when a more rigorous 3D approach is convenient. [ABSTRACT FROM AUTHOR]

In order to reduce the machining deformation of thin-walled parts during milling, a non-uniform allowance planning method for thin-walled parts based on the workpiece deformation constraint with the idea of adding materials in reverse material removal sequence is proposed in this paper. This method does not require accurate deformation prediction and extensive experiments compared to traditional error compensation methods. It strives to maximize the allowance to enhance the stiffness of the in-process workpiece. First, a cutting force threshold calculation method is proposed according to the finite element method. The cutting force threshold at different positions is calculated by obtaining the local stiffness characteristics at the cutter-contact point under the constraint of allowable deformation. And then, the maximum machining allowance at the cutter-contact point is calculated depending on the cutting force model. Considering that the stiffness of the workpiece is position-dependent and affected by material removal, the stiffness of the workpiece is updated by adding elements in the reverse cutting direction, and the finishing stock is obtained by surface fitting. Experimental results show that compared with the traditional uniform allowance method, the error of the proposed method is reduced by about 83%, which can effectively reduce the deformation and improve the machining accuracy. [ABSTRACT FROM AUTHOR]

Due to the low rigidity, the milling process of cantilever thin-walled structure (CTWS) inevitably generates machining-induced deformation, ultimately resulting in poor surface quality and thickness accuracy. In this paper, to avoid these issues, a novel and green ice-based fixture (IBF) is innovatively proposed to hold CTWS firmly to suppress machining deformation during the whole processing. Firstly, a stair-step model is established to express machining-induced deformation of CTWS with/without IBF. Next, IBF is designed to clamp CTWS steadily. Secondly, finite element model (FEM) for CTWS is utilized to simulate milling deformation with/without IBF to reflect the effect of IBF on eliminating CTWS deformation. Finally, the experiment of CTWS milling is carried out, and the experiment results show that IBF can achieve a reliable and stable holding for CTWS, and hence suppress machining-induced deformation and improve thickness accuracy. In this paper, research on IBF for CTWS processing provides reference and guidance for the application and promotion of IBF in industry. [ABSTRACT FROM AUTHOR]

As the first study in the field regarding CB, this paper investigates the implications of interchanging between RDB and CB through manufacturing bends with various angles and investigates the difference between the two methods in form of springback, cross section compression and widening, cross section shape and wall thinning/thickening. The experiments conducted consists of aluminum alloy 6060-T4 round tubes of 60 mm diameter and 3 mm wall thickness, bent around 222 mm radius tooling with various bend angles. In this case, we have found that CB is capable of manufacturing bends with quality near those manufactured by RDB with less springback, however with a dimensional penalty regarding increased deformation of the cross section. [ABSTRACT FROM AUTHOR]

During the actual operation of subways, high-speed railway, and other infrastructure, subgrade soil will be subjected to periodic vibration and intermittent loading, i.e., intermittent cyclic load. To study the deformation characteristics of subgrade soil under intermittent cyclic loading, the Newtonian dashpot in the generalized Kelvin model is replaced by the fractional Abel dashpot, a fractional generalized Kelvin model is established. Then, a nonlinear viscoplastic body model considering damage is proposed, which is connected in series with the improved fractional generalized Kelvin model, and the deformation constitutive model of soil under intermittent cyclic loading is obtained. Finally, the effectiveness and applicability of the model are analyzed, and the model is compared with other constitutive models. The results show that the constitutive model established in the paper can reflect the combined effect of confining pressure, frequency, dynamic stress amplitude and other factors on the cumulative plastic strain of soil, and can well characterize the development law of three types of cumulative plastic strain curves of soil: stable, critical, and failure. The fitting parameters α and η tend to decay and rise, respectively, with the increase in loading stage N, which reflects the rationality and accuracy of the model. [ABSTRACT FROM AUTHOR]

Small specimen test techniques (SSTTs), developed for scarce materials, industrial products, in-service equipment, etc., could be challenging to obtain sufficient materials for routine testing. This review focuses on the research on millimeter- and micron-scale SSTTs of metallic materials in the past decade. Mainstream small specimens are divided into similarity, penetration, and semi-penetration. Representative tests of the above three categories are analyzed in detail, including the small tensile test, small punch test, and indentation test. The macro- or micro-correlation methods of deformation and failure parameters between the SSTTs and conventional tests are discussed, including Young's modulus, yield strength, ultimate tensile strength, damage evolution, fracture strain, and the stress–strain full-history relationships. Meanwhile, the extensive requirements for material testing are also considered, such as anisotropy and strain rate, temperature, and stress triaxiality sensitivities. The characteristics and modification strategies of the SSTTs are described from the aspects of size effects, inhomogeneous structures, and manufacturing defects. Finally, this paper discusses the application of SSTTs in forging, stamping, welding, and additive manufacturing and highlights the potential development directions of SSTTs. [ABSTRACT FROM AUTHOR]

The design of pressure hull structures plays an essential role in the research and development of underwater operation equipment such as deep-sea submersibles. As a bionic structure, an egg-shaped shell has apparent advantages in the application of an underwater pressure hull. Still, the egg-shaped shell is a positive Gauss surface, so it is difficult to control the manufacturing accuracy and quality. In this paper, the technology of solid particle flexible medium forming and the principle of high-pressure bulging in tubes is proposed to manufacture high-precision egg-shaped shell parts. By optimizing the shape of the punch structure, optimizing the process parameters, improving the stress and strain distribution of the egg-shaped shell, and analyzing the deformation mechanism in the bulging process, we have mastered the deformation and quality control methods of the granular medium flexible bulging of non-equal curvature tubular structures in some aspects. [ABSTRACT FROM AUTHOR]

This paper presents a pump using polyvinyl chloride (PVC) gel. PVC gels are compliant, have a simple structure, and exhibit large deformation at voltages in the range of 100–1000 V, which make them suitable for micropumps. In this study, a PVC gel sheet with a surface pattern that enhances active deformation in the thickness direction was employed for the fabrication of a pump. To this end, the PVC gel sheet was sandwiched between three sets of anode and cathode electrodes, after which voltages were sequentially applied to these electrodes to generate a peristaltic deformation of the gel sheet, thus pushing the liquid and creating a one-directional flow. Various pumps were fabricated using PVC gel sheets with different surface patterns, and the pumps were characterized. The pumps exhibited an outline dimension of 35 mm × 25 mm with a thickness of 4 mm, corresponding to a total volume of 3.5 × 103 mm3. The results revealed that the pump fabricated using a 174-μm-high pyramid-patterned gel sheet generated a flow rate of 224.1 µL/min at an applied voltage of 800 V and a driving frequency of 3 Hz. This observed value is comparable to or better than those of existing pumps based on smart materials. [ABSTRACT FROM AUTHOR]

In this paper, the N back-migration and restoration behavior of duplex stainless steels (DSSs) 2101 and 2205 (DSS2205) were studied. Experimental findings indicated that the Cr2N in the ferrite (α) persistently decreased for both steels during the cooling process from 1200 °C to 1000 °C, and the disappearance rate of Cr2N in DSS2205 was significantly faster than that of lean duplex stainless steel 2101 (LDX2101). On the one hand, due to the severe partitioning behavior of N atoms in α migrating back to austenite (γ), on the other hand, the enriched Mn in LDX2101 and the enriched Ni in DSS2205 exerted an impact on N migration. Also, the cumulative thermal deformation at 1200 °C contributed to the N migration back into γ with the assistance of high-density dislocations and thermal deformation energy. Furthermore, the softening mechanism of constituent phases was dominated by discontinuous dynamic recrystallization (DDRX) mechanism in both steels at a strain rate of 10 s−1, which was characterized by strain-induced boundaries migration from low-density dislocations to high ones. [ABSTRACT FROM AUTHOR]

In this paper, we present the results of computational and experimental studies of changes in patterns of resistance to deformation and damage accumulation under conditions of irregular low-cycle loading, which are compared with similar data of a regular cyclic elastoplastic deformation upon equal loading. An irregular mode of low-cycle loading implemented in research is adopted as a uniform distribution of the change in the stress amplitude between specified maximum and minimum levels at the symmetric shape of the cycle. This mode was reproduced on test equipment by introducing into the control program of the corresponding functional dependence of changes in the stress amplitude in the cycles. Obtained in the irregular loading mode, the data on a cycle-by-cycle kinetics of both cyclic and unilaterally accumulated strains were recorded in a database and then compared with the data for a regular loading. This made possible their analytical description by the corresponding state equations with the correction of the diagram parameters of cyclic elastoplastic deformation, accounting for the irregularity conditions of loading modes. The experimental results are presented as test mode diagrams, curves of a low-cycle fatigue of the studied material in the soft and hard loading modes, diagrams of a cycle-by-cycle kinetics of the cyclic and accumulated strains in the regular and irregular modes, and kinetic diagrams of damage accumulation under these conditions. The summation criteria that include the deformation characteristics of accumulated damage are used. It is shown that, with allowance for change in the nature of the strain development during irregular low-cycle loading, the criterion dependences when accepting the condition of reaching the limiting state can be used to estimate the durability and compare it with the similar data in regular modes. [ABSTRACT FROM AUTHOR]

In this paper, the strain-induced martensite transformation (SIMT) process of 304 stainless steel tubes under the action of a high shear stress state (HSSS) in the deformation zone of a new spinning process is studied and analyzes the changes in the microstructure and mechanical properties of each tubular workpiece obtained after continuous cold spinning under HSSS. Firstly, the contact equations and stress–strain state equations for the external cold extrusion spinning (ECES) were established and combined with the stress state criterion to find that ECES has a higher softening coefficient than conventional spinning (CS) in the deformation zone. To study the performance of the workpiece at each stage of processing, a longitudinal unidirectional tensile test was carried out on 304 stainless steel tubes. The material was obtained by cold spinning 5 times in succession for each pass of the tube, while X-ray diffraction (XRD) analysis was performed to measure the phase volume fraction of the workpiece at each stage, which provides a reference for subsequent transmission electron microscope (TEM) observation of the microstructure. The results show that the martensitic phase changes gradually after the volume fraction of martensite grows to a peak of 35% and gradually refines and fractures in tension, forming ultra-fine grain size laths of martensitic phase, while the tensile limit increases by 2.1 times, at which time the elongation at break is less than 5%. [ABSTRACT FROM AUTHOR]

Titanium alloy extruded profiles with complex cross-section are usually used to manufacture special-shaped structural parts in the aviation industry. In this paper, a Ti-6Al-4 V profile with asymmetric Y shape was manufactured by a direct extrusion process. A comparative study was conducted at the different lubrication conditions, in which the different process deformation mechanisms, resulting microstructures, and mechanical properties of profiles have been investigated by finite element simulation and a series of experiments, i.e., scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). It was revealed that the metal flow is blocked at the narrow die orifice due to the deterioration of lubrication, resulting in the continuous shrinkage defect. The metal deformation coordination mechanism becomes gradually significant due to poor friction contact, which promotes the internal stress in the cross-sectional center to transfer outward to balance the friction at the edge of the orifice, resulting in the reduction of the effective strain in the center. The heat generated by friction weakens the heat exchange behavior between the metal and the die, which helps the profile retain a more uniform temperature field. In the sectional center of the profiles made from the two different lubrications, extrusion with good lubrication results in greater grain/colony refinement due to greater effective strains, and a slightly greater dislocation density was found due to the uniform deformation. The tensile tests revealed that compared with poor lubrication, due to the improvement of Hall–Petch strengthening and dislocation strengthening in the cross-sectional center with good lubrication, the variation range of yield strength and tensile strength is reduced to 11 MPa and 7 MPa, respectively, and the variation range of microhardness is reduced to 44 HV and 32 HV, respectively. The improvement of lubrication not only helps to reduce forming defects but also can obtain uniform mechanical properties. [ABSTRACT FROM AUTHOR]

A new numerical approach is presented to compute the large deformations of shell-type structures made of the Saint Venant-Kirchhoff and Neo-Hookean materials based on the seven-parameter shell theory. A work conjugate pair of the first Piola Kirchhoff stress tensor and deformation gradient tensor is considered for the stress and strain measures in the paper. Through introducing the displacement vector, the deformation gradient, and the stress tensor in the Cartesian coordinate system and by means of the chain rule for taking derivative of tensors, the difficulties in using the curvilinear coordinate system are bypassed. The variational differential quadrature (VDQ) method as a pointwise numerical method is also used to discretize the weak form of the governing equations. Being locking-free, the simple implementation, computational efficiency, and fast convergence rate are the main features of the proposed numerical approach. Some well-known benchmark problems are solved to assess the approach. The results indicate that it is capable of addressing the large deformation problems of elastic and hyperelastic shell-type structures efficiently. [ABSTRACT FROM AUTHOR]

Filament-wound flexible pipes are widely used to transport fluid in pipeline systems, proved extremely useful in marine engineering. The hyperbolic flexible pipes have good vibration suppression performance, but they are easily deformed under internal pressure. This paper focuses on the stability of hyperbolic flexible pipes based on the composite Reissner shell theory and the transfer-matrix method. The nonlinear stretch of the reinforced filament and the fiber bridge effect are considered in the model. The calculation results show that a large winding angle reduces the deformation and the meridional stress. The available initial winding angle is limited by the geometry and the slippage coefficient of flexible pipe. The reinforced filament of high tensile modulus will reduce the deformation of the pipe. Compared with the geodesic winding trajectory, non-geodesic winding trajectories improves the stability of the pipe. The theoretical result is verified by the finite element analysis. The investigation method and results present in this paper will guide the design and optimization of more novel flexible pipes in the future. [ABSTRACT FROM AUTHOR]