Extra Deformation Research Articles

TWIP and Fracture Behavior in the Superalloy 625 at Room and Cryogenic Temperatures

In this study an austenitic nickel base alloy (Alloy 625) with medium to high stacking fault energy was tensile tested at room temperature and at cryogenic temperature, -196°C, to investigate if twinning was involved in the fracture process. Fracture surfaces and microstructure were characterized using scanning electron microscopy and texture was evaluated with scanning electron microscopy-electron backscatter diffraction at three positions along the tensile test specimens. Features where investigated with electron channelling contrast imaging. At room temperature the predominant deformation mechanism is slip and at cryogenic temperature slip is followed by deformation twinning. At room temperature deformation twinning will make an extra deformation contribution in the localized necking region compared to the cryogenic temperature case where deformation twins already are distributed in the microstructure and in this case will hinder the dislocations to move freely and instead cause stress field build up at the twin boundaries and subsequent microcrack and void formation.

Microstructure Development and Related Mechanical Behavior of the ZEW200 Mg Alloy Processed by Differential Speed Rolling and Equal Channel Angular Pressing

The present work investigates the influence of shear deformation on microstructural-texture and mechanical behavior of ZEW200 Mg alloy sheets. For the introduction of extra shear deformation during thermomechanical processing, the separate effect of differential speed rolling (DSR) and equal channel angular pressing (ECAP) were analyzed. The results were compared with the microstructure and mechanical behavior of equal speed rolled (ESR) ZEW200 sheets. No significant texture changes were observed after the utilization of DSR, while ECAP processing was effective in changing the character of the texture and reducing the texture intensity. The large yield stress asymmetry observed in the rolled sheet is strongly reduced in the ECAP processed sheets. Results showed the potential to use shear deformation to modify the crystallographic texture via the profuse activation of {10-12}<10-11> extension twins. The presence of a large twin fraction of the microstructure modified the work hardening behavior of the processed sheets due to the further activation of basal <a> slip. The application of extra shear deformation to tailor the texture during processing is, therefore, an alternative to optimize the deformation behavior of already formable Mg alloys.

Selected spherical photon orbits around a deformed Kerr black hole

In this paper, we investigate the so-called spherical photon orbits around a deformed Kerr black hole with an extra deformation parameter. The change in the azimuth Δφ and the angle of dragging of nodes per revolution ΔΩ of a complete latitudinal oscillated orbit is calculated analytically. Finally, representative six examples orbits are plotted out to illustrate how spherical photon orbits look like and exhibit some interesting behavior. Especially, these spherical photon orbits are absent in circular orbits and different from the Kerr case.

Investigation on ultrasonic volume effects: Stress superposition, acoustic softening and dynamic impact

Conventional high power ultrasonic vibration has been widely used to improve manufacturing processes like surface treatment and metal forming. Ultrasonic vibration affects material properties, leading to a flow stress reduction, which is called ultrasonic volume effect. The volume effect contains multi-mechanisms such as stress superposition due to oscillatory stress, acoustic softening by easier dislocation motion and dynamic impact leading to extra surface plastic deformation. However, most researches ignored the stress superposition for the convenience of measurement, and few studies considered ultrasonic dynamic impact since the relatively low ultrasonic energy in macro scale. The purpose of this study is to investigate the characteristics and mechanisms of different ultrasonic volume effects in micro-forming. A 60 kHz longitudinal ultrasonic-assisted compression test system was developed and a series of ultrasonic-assisted compression tests at different amplitudes on commercially pure aluminum A1100 in micro-scale were carried out combining the surface analysis by SEM, EDX and micro-hardness test. Three different ultrasonic volume effects, stress superposition, acoustic softening and dynamic impact, were confirmed in the ultrasonic-assisted compression tests. In order to quantitatively predict stress superposition, a hybrid model for stress superposition is developed considering the elastic deformation of experimental apparatus in practice, the evolution of the modeling results fitted well with the experimental results. With low ultrasonic amplitude, stress superposition and acoustic softening occurred because vibrated punch contacted with the specimen all the time during compression. However, with higher amplitude, due to the extra surface plastic deformation by larger ultrasonic energy, forming stress was further reduced by the ultrasonic dynamic impact. A possible method to distinguish the effects of dynamic impact and acoustic softening is to analyze the waveform of the oscillatory stress in the process. In the case of ultrasonic dynamic impact effect, a higher amount of oxidation was observed on the specimen surface, which could be the result of local heating by surface plastic deformation and surface friction when the vibrated punch detached from the specimen. The findings of this study provide an instructive understanding of the underlying mechanisms of volume effects in ultrasonic-assisted micro-forming.

Effect of clustering on the emission of light charged particles

Energy spectra of light charged particles emitted in the reaction $p + {}^{27}\mathrm{Al} \rightarrow {}^{28}\mathrm{Si}^{\ast}$ have been studied and compared with statistical model calculation. Unlike 16O + 12C where a large deformation was observed in 28Si*, the energy spectra of $\alpha$ -particles were well explained by the statistical model calculation with standard “deformability parameters” obtained using the rotating liquid drop model. It seems that the $\alpha$ -clustering in the entrance channel causes extra deformation in 28Si* in the case of 16O + 12C, but the reanalysis of other published data shows that there are several cases where extra deformation was observed for composites produced via non- $\alpha$ -cluster entrance channels also. An empirical relation was found between mass-asymmetry in the entrance channel and deformation, which indicates that along with $\alpha$ -clustering, mass-asymmetry may also affect the emission of a light charged particle.

Shadow casted by a Konoplya-Zhidenko rotating non-Kerr black hole

We have investigated the shadow of a Konoplya-Zhidenko rotating non-Kerr black hole with an extra deformation parameter. The spacetime structure arising from the deformed parameter affects sharply the black hole shadow. With the increase of the deformation parameter, the size of the shadow of black hole increase and its shape becomes more rounded for arbitrary rotation parameter. The D-shape shadow of black hole emerges only in the case a<2√3/3\\,M with the proper deformation parameter. Especially, the black hole shadow possesses a cusp shape with small eye lashes in the cases with a>M, and the shadow becomes less cuspidal with the increase of the deformation parameter. Our result show that the presence of the deformation parameter yields a series of significant patterns for the shadow casted by a Konoplya-Zhidenko rotating non-Kerr black hole.

Fracture behavior of high-entropy alloy coating by in-situ TEM tensile testing

The fracture behavior of high-profile high-entropy alloy coating was characterized by in-situ TEM tensile testing. The samples for in-situ TEM tensile testing were obtained by FIB technology. The results show that irrelevant to phase constitution, the Young's module, fracture strength and ultimate elongation are measured as ∼107 GPa, ∼2.70 GPa and ∼2.6%, respectively. Transcrystalline fracture and cleavage fracture with the cleavage plane of {112} are observed evidentially and the evolution of the dislocation motion in the material could be directly connected with the fracture behavior from the recorded movies obtained by a Gatan CCD camera. The engineering stress-strain curve is nearly linearity, however, a slight deviation away from linearity could be noted in the end of engineering stress-strain curve, which is attributed that the extra elastic deformation results in part of continued deformation.

Excavation-caused extra deformation of existing masonry residence in soft soil region

Growing need for construction of infrastructures and buildings in fast urbanization process creates challenges of interaction between buildings under construction and adjacent existing buildings. This paper presents the mitigation of contradiction between two parties who are involved the interaction using civil engineering techniques. Through the in-depth analysis of the results of monitoring surveys and enhanced accuracy and reliability of surveys, a better understanding of the behavior of deformable buildings is achieved. Combination with the original construction documents, the two parties agree that both of them are responsible for building damages and a better understanding for the rehabilitation of the existing buildings is focused on. Two cases studies are used to demonstrate and describe the importance of better understanding of the behavior of existing buildings and their rehabilitations. The objective of this study is to insight into mechanisms of soil-structure interaction for buildings adjacent to deep excavations, which can result in a damage in existing masonry residence, and to take the optimized measures to make deep excavations safety and economic and adjacent buildings keep good serviceability in urban areas with soft soil conditions.

Microstructure and microtexture evolution of shear bands in Al–Cu single crystal during asymmetric rolling

Asymmetric rolling process (ASR) introduces extra shear deformation compared with conventional symmetric rolling (SR), and induces shear bands in microstructures. ASR technique has been applied to manufacture thick aluminum plate with improved mechanical properties due to the fine grains or even ultrafine-grains obtained in shear bands. Single crystal specimens of Al–Cu alloys were prepared in this work to study the microstructure and texture evolution in asymmetric rolled sheet. Microstructures of deformation bands were observed and the microtexture was analyzed through electron backscatter diffraction (EBSD). Compared with the SR process, ASR induced more homogeneous deformation and shear bands were observed in deformation area. Microstructure of shear bands depends on the initial orientations of single crystals. After single crystal with (3, −1, 9) plane orientation is processed in ASR, shear bands consist of S-type grains were formed, which have uniform size and almost the same twisting degree. But for single crystal with (−3, 0, 7) plane orientation, shear bands have various twisting degrees and grains distributed inhomogeneously. Texture of the shear bands in ASR processed specimens always rotated towards Copper component for single crystals with different orientations.

Strong gravitational lensing by a Konoplya-Zhidenko rotating non-Kerr compact object

Konoplya and Zhidenko have proposed recently a rotating non-Kerr black hole metric beyond General Relativity and make an estimate for the possible deviations from the Kerr solution with the data of GW 150914. We here study the strong gravitational lensing in such a rotating non-Kerr spacetime with an extra deformation parameter. We find that the condition of existence of horizons is not inconsistent with that of the marginally circular photon orbit. Moreover, the deflection angle of the light ray near the weakly naked singularity covered by the marginally circular orbit diverges logarithmically in the strong-field limit. In the case of the completely naked singularity, the deflection angle near the singularity tends to a certain finite value, whose sign depends on the rotation parameter and the deformation parameter. These properties of strong gravitational lensing are different from those in the Johannsen-Psaltis rotating non-Kerr spacetime and in the Janis-Newman-Winicour spacetime. Modeling the supermassive central object of the Milk Way Galaxy as a Konoplya-Zhidenko rotating non-Kerr compact object, we estimated the numerical values of observables for the strong gravitational lensing including the time delay between two relativistic images.

Maximally extended as a quantum double

We derive the universal R-matrix of the quantum-deformed enveloping algebra of centrally extended using Drinfeld's quantum double construction. We are led to enlarging the algebra by additional generators corresponding to an automorphism. For this maximally extended algebra we construct a consistent Hopf algebra structure where the extensions exhibit several uncommon features. We determine the corresponding universal R-matrix containing some non-standard functions. Curiously, this Hopf algebra has one extra deformation parameter for which the R-matrix does not factorize into products of exponentials.

Influence of asymmetric hot rolling on through-thickness microstructure gradient of Fe–20Mn–4Al–0.3C non-magnetic steel

Through-thickness microstructure gradient as a function of asymmetric hot rolling (ASHR) process parameters was investigated for a high manganese non-magnetic steel. Shear strain distribution was calculated using a two-dimensional finite element method. According to the simulation results, the surface layer of ASHR plate undergoes the highest total shear deformation which leads to the formation of a fine-grained surface layer under conditions of large rolling reduction and relatively high temperature. In the central layer is still the partially recrystallized microstructure. With velocity ratio increasing, the depth of fine-grained surface layer approaches 1/4 plate thickness, while the recrystallization proportion for the central layer is also enhanced due to the reinforced extra shear deformation. By appropriate parameter optimization, the austenitic grain size is finally refined to ~5µm for the surface layer and ~9µm for the center, such that the tensile property is improved.

A method for improving the simulation efficiency of trawl based on simulation stability criterion

The lumped-mass method is one of the most fundamental methods to simulate the dynamic behavior of submerged flexible nets. However, the low calculation efficiency limits its applications. In order to improve the calculation efficiency, the numerical stability of lumped-mass method based on explicated Euler integral algorithm was investigated. The simulation stability criterion was derived as a function of simulation step size and the physical parameters of netting materials. A physical parameter optimization (PPO) method was put forward to calculate the desired values of the lumped-mass model’s physical parameters based on stability criterion; length compensation was implemented to compensate the extra deformation of mesh bars caused by the changes of their stiffness. The PPO method can ensure the stability of the lumped-mass model with a desired simulation step size while minimizing the change to the physical parameters. A lumped-mass model of trawl gear was established with the PPO method, the simulation results were compared with those of the conventional lumped-mass method (without PPO) to validate the improvements. By using the PPO method, the calculation efficiency can be accelerated by 40 times while only inducing less than 2% error to the simulation results.

Increasing the capability of laser peen forming to bend titanium alloy sheets with laser-assisted local heating

The present work proposes a new process to bend high-strength titanium alloy by laser peen forming (LPF) with laser-assisted local heating. In experiments, a nanosecond pulsed laser and a CW fiber laser for laser peening and heating, respectively, were arranged to irradiate the top and bottom sample surfaces coaxially. Laser heating beam moved along with the laser-shock loading in a synchronized way to cover a specified area. Different powers of fiber laser output were used in experiments to investigate heating effect on the bending deformation and microstructure change of Ti6Al4V alloy. It is proved that the proposed process is an effective way to improve the bending capability of LPF through increasing the plastically-deformed layer induced by the dynamic loading. And the radius of bending curvature is found to decrease greatly by increasing laser heating power. Although laser heating would provide an extra plastic deformation on the opposite side of laser peening to increase the convex bending simultaneously, the generated alpha-case and small cracks close to heating surface are detrimental to fatigue strength and ductility. Therefore, only the temperature effect to decrease the material strength is acceptable in LPF with laser-assisted local heating to increase the bending deformation & of titanium alloy.

Modeling heterogeneous materials with multiple inclusions under mixed lubrication contact

A numerical solution for heterogeneous materials with multiple inclusions under mixed elastohydrodynamic lubrication contact is presented in this study. The pressure generated within the fluid area as well as that caused by asperity contact is obtained through solving a unified Reynolds equation system. The inclusions are modeled as homogeneous inclusions (which are assumed to have same material with matrix) with initial eigenstrains plus unknown equivalent eigenstrains by employing Eshelby׳s equivalent inclusion method. A modified conjugate gradient method is implemented to determine these unknowns within the governing equations. Extra deformations due to the inclusions are iteratively introduced into lubricant film thickness. The computational process is performed until the convergence of the half-space surface displacements caused by the embedded inclusions and the pressure obtained within the computational domain. This solution takes into account the interactions among the loading body, the fluid lubricant and the half-space matrix with embedded inclusions.

Foam behavior of solid glass spheres – Zn22Al2Cu composites under compression stresses

Solid glass spheres – Zn22Al2Cu composites, having different densities and microstructures, were elaborated and studied under compression. Their elaboration process involves alloy melting, spheres submersion into the liquid alloy and finally air cooling. The achieved composites with densities 2.6884, 2.7936 and 3.1219g/cm3 were studied in casting and thermally induced, fine-grain matrix microstructures. Test samples of the composites were compressed at a 10−3s−1 strain rate, and their microstructure characterized before and after compression by using optical and scanning electron microscopes. Although they exhibit different compression behavior depending on their density and microstructure, all of them show an elastic region at low strains, reach their maximum stress (σmax) at hundreds of MPa before the stress fall or collapse up to a lowest yield point (LYP), followed by an important plastic deformation at nearly constant stress (σp): beyond this plateau, an extra deformation can be limitedly reached only by a significant stress increase. This behavior under compression stresses is similar to that reported for metal foams, being the composites with fine microstructure which nearest behave to metal foams under this pattern. Nevertheless, the relative values of the elastic modulus, and maximum and plateau stresses do not follow the Ashby equations by changing the relative density. Generally, the studied composites behave as foams under compression, except for their peculiar parameters values (σmax, LYP, and σp).

Building-Up Process of Cold-Sprayed Al5056/In718 Composite Coating

A composite model was established to demonstrate the building-up process of the Al5056/In718 composite coating and to reveal a strengthened deformation of the Al5056 particle from the In718 particle. Results show that the building-up process of the Al5056/In718 composite coating is combined with the intercollision between the Al5056 particles and the In718 particle’s impact on the Al5056 particles. The addition of In718 particle induced an extra deformation of the Al5056 particles, induced by the kinetic energy of the In718 particles.

Tailoring texture and refining grain of magnesium alloy by differential speed extrusion process

Magnesium alloy sheets were processed by conventional extrusion (CE) and differential speed extrusion (DSE). The velocity evolutions of DSE sheets at near-surface and mid-layer region are different due to the extra asymmetric shear deformation. This simple shear enforces the near-surface microstructure to exhibit more dynamically recrystallized grains having the c-axis tilted about ±12° toward the extrusion direction. Grain refinement and tilted weak basal texture obtained by DSE process dramatically enhance the room temperature strength and plasticity of the extruded Mg alloy sheets.

Prediction of temperature difference effect in the buckling of a bi-material column with interface crack using ANN and FE

Article history: Received September 20, 2013 Received in Revised form October, 14, 2013 Accepted 20 December 2013 Available online 28 December 2013 Buckling is one of the most complicated concepts in mechanical engineering. Buckling often happens by compressive loads on thin structures. Thermal gradient between two ends of a column may cause a deflection in it. This will add an extra deformation to the one provided by compressive loads on the column. This phenomenon occurs when two ends of the column are at different temperatures, which can be seen at various structures. Because of the considered temperature gradients, the critical load of the column will decrease. In the current paper, various columns are modeled and the effect of thermal gradient and compressive load and other parameters on the Bi-material columns are studied. In other words, influences of compressive load and temperature gradient on critical load of Bi-material columns with interface crack are investigated. Effect of change in each parameter on critical load of column and crack opening was investigated. First, the thermal gradient was only applied to the model and in the next step; only the effect of mechanical loading was studied. Furthermore, artificial neural network (ANN) was used to extend the results to a bigger range of temperature conditions through the columns. Based on the results, ANN and finite element results are in a good agreement and the thermal effects may have a significant role in buckling of the column. © 2014 Growing Science Ltd. All rights reserved.

Axial strength of concrete-filled double skin steel tubular (CFDST) columns with preload on steel tubes

Concrete filled double skin steel tubular (CFDST) columns have some advantages when compared to conventional concrete filled steel tubular (CFST) columns, such as lighter self-weight and better cyclic performance. CFDST columns have the potential to be used in structures such as bridges, high-rise buildings, viaducts and electricity transmission towers. The inner and outer steel tubes will be subjected to preloads from upper structures and wet filled concrete. The initial stresses and extra deformations on steel tubes caused by these preloads would affect the capacity of the CFDST members. This paper thus discusses the behaviour of axially loaded CFDST columns with preload either on the outer tube alone or on both tubes. A general purpose finite element analysis (FEA) model is developed to predict the behaviour of CFDST columns with the steel tubes subjected to preload. The FEA model is verified using test results of CFDST columns without preload and those of CFST columns with preload. The influences of preload ratio, slenderness ratio, hollow ratio and material strength on axial strength are discussed. Finally, formulas are proposed for calculating the ultimate strength of CFDST columns with preload on steel tubes.