Deformation Of Bulk Material Research Articles

Infrared Thermographic Testing of Steel Structures by Using the Phenomenon of Heat Release Caused by Deformation

Deformation of steel parts is accompanied by either heating or cooling of particular zones depending on deformation mechanism. The use of infrared thermographic equipment allows analyzing spatial/temporal temperature distributions on the surface of steel parts thus allowing the evaluation of heat release caused by deformation in bulk material. Determination of stressed state in critical parts by analyzing infrared thermograms can be most simply conducted for components subjected to uniaxial tension–compression. The paper describes some potentials and problems of nondestructive testing of steel parts and constructions based on the analysis of heat release caused by deformation. By analyzing this methodology, it is possible to better evaluate the life expectancy of critical parts in steel structures (components of offshore oil platforms, seismic-resistant buildings, frames of large mining trucks, etc.).

Rotordynamic Analysis of Rotor–Stator Rub Using Rough Surface Contact

Undesirable rotor–stator rub is frequently observed in rotordynamic systems, and has been the subject of many investigations. Most of these studies employ a simple piecewise-smooth linear-elastic contact model (LECM), where the rotor switches between noncontacting and contacting operation once the clearance is exceeded (various complications have been incorporated, though the essential model premises endure). Though useful as a first step, the LECM relies on an arcane contact stiffness estimate, and therefore does not emulate the actual contacting surfaces. Consequentially, the LECM fails to elucidate how real surface parameters influence contact severity and surface durability. This work develops a novel model for rotor–stator rub which is commensurate with reality by treating the surfaces as a collection of stochastically distributed asperities. Specifically, the elastoplastic Jackson–Green (JG) rough surface contact model is used to calculate the quasistatic contact force as a function of rotor displacement, where bulk material deformation and surface cumulative damage are ignored. A simple exponential fit of the contact force is proposed to reduce computational burden associated with evaluating the JG rough surface contact model at each simulation time step. The rotor's response using the LECM and JG rough surface contact model is compared via shaft speed bifurcations and orbit analysis. Significant differences are observed between the models, though some similarities exist for responses with few contacts per rotor revolution.

Redox-induced actuation in macromolecular and self-assembled systems

Because of their dynamic nature, stimuli-responsive molecules that undergo conformational changes have attracted much research interest for applications in the field of actuators and sensors. In particular, redox-active molecules that undergo redox state switching have many advantages, including electrical control and drastic conformational change that involves electrostatic interactions. In this review, we focus on the conformational changes for macromolecularly and molecularly assembled systems and evaluated their potential for use as building blocks of redox-driven soft actuators. Moreover, the current review provides insights for the design and fabrication of actuating materials by considering changes in redox state. This review focuses on redox-induced molecular actuation in macromolecular and self-assembled systems. Effective amplifications of conformational changes of unit molecular part are explored on the basis of three categories: polymeric system; molecular interactions; and self-assembled system. The importance of highly ordered structures is suggested to effectively amplify conformational change of small molecular unit into macroscopic deformation of bulk materials. Finally, future outlook toward electrochemical soft actuators and tips to prepare stimuli-responsive molecular assemblies, which undergo amplification in conformational change of constituent molecules, are provided.

Effect of Plastic Deformation of Bulk Material on Frictional Behavior in Dry Metal Forming

The friction behavior in dry metal forming is studied with a new tribometer. From the microscopic observation, it is found that the ratio of the flattened area starts to increase sharply when plastic deformation extends in the whole bulk. But, the nominal frictional stress increases linearly with the nominal contact pressure irrespective of the ratio of the flattened area. The surface texture of the flattened area is measured by using electron probe surface roughness analyzer. Before the start of bulk plastic deformation, the flattened area is smooth and almost the whole area seems to be real area of contact. After plastic deformation in the bulk material, the flattened area is roughened. A new friction law for dry metal forming, Coulomb's friction with constant friction coefficient μ holds up to the critical pressure and the law of constant frictional stress τ holds for the higher pressures, is proposed based on the experimental results.

On the processing of hetero-nanostructured metals for improved strength/ductility balance by ECAE and SPS techniques

This paper has examined some recent findings concerning the processing of fully dense hetero-nanostructured materials (i.e. consisting of nano, ultrafine and micrometric grains) which can be produced by using the interplay between heavy deformation and recrystallization. By plastic deformation of bulk materials, an improved strength/ductility balance can be obtained directly by imparting high strain deformation (by equal channel angular extrusion) until the occurrence of recrystallization. Using a powder metallurgy route, the strong potential of electric field assisted sintering (ECAS) techniques for producing multi-scale microstructures when a conducting milled powder is used is demonstrated. In this case, in addition to modify the classic processing parameters (time/temperature of spark plasma sintering), altering the nature of the milled powder – by Y 2O 3 addition during the milling stage – is also a good way to delay the onset of recrystallization and, thereby, increase the fraction of ultrafine grains.

Simple geometrical explanation of Gurtin-Murdoch model of surface elasticity with clarification of its related versions

It is showed that all equations of the linearized Gurtin-Murdoch model of surface elasticity can be derived, in a straightforward way, from a simple second-order expression for the ratio of deformed surface area to initial surface area. This elementary derivation offers a simple explanation for all unique features of the model and its simplified/modified versions, and helps to clarify some misunderstandings of the model already occurring in the literature. Finally, it is demonstrated that, because the Gurtin-Murdoch model is based on a hybrid formulation combining linearized deformation of bulk material with 2nd-order finite deformation of the surface, caution is needed when the original form of this model is applied to bending deformation of thin-walled elastic structures with surface stress.

Processing Dense Hetero-Nanostructured Metallic Materials for Improved Strength/Ductility Balance through High Strain Deformation and Electrical Current Assisted Sintering (ECAS)

This paper has examined some recent findings concerning the processing of fully dense hetero-nanostructured materials (i.e. consisting of nano, ultrafine and micrometric grains) which can be produced by using the interplay between heavy deformation and recrystallization. By plastic deformation of bulk materials, an improved strength/ductility balance can be obtained directly by imparting high strain deformation (by ECAE) until the occurrence of recrystallization. Using a powder metallurgy route, the strong potential of electric field assisted sintering (ECAS) for producing multi-scale microstructures when a milled powder is used is also demonstrated. In this case, in addition to modify the classic processing parameters (time/temperature of ECAS), altering the nature of the milled powder - by Y2O3 addition during the milling stage - is also a good way to delay the onset of recrystallization and, thereby, increase the fraction of ultrafine grains.

Microdeformation of soft particles in metal matrix composites

In this study, microdeformation of soft particles in metal matrix composites was investigated. For that purpose, two different types of ductile iron having different metal matrix microstructures were tensile stressed and compressed. It was found that graphite nodules do not change their shape during tensile stressing, only decohesion occurs on the graphite and metal matrix interface. However, compression testing at room temperature resulted in a significant change in graphite shape. A relationship between average aspect ratio of graphite after various degrees of compression and bulk material deformation was devised. Furthermore, graphite nodule and metal matrix microdeformation was compared to bulk material deformation. This implies that deformation process is not homogenous. It strongly depends on metal matrix microstructure and can be represented with deformation ratio ( K). Deformed or deformed and cracked graphite nodules were found on the fractured surface of compressed specimens, indicating that the graphite does not turn into powder during compression at room temperature, as other previous researches found.

Multiscale friction mechanisms and hierarchical surfaces in nano- and bio-tribology

Abstract Various mechanisms of solid–solid and solid–liquid friction are studied in this review, and their relation to the surface roughness hierarchy is discussed. For ideal solid bodies with conservative forces acting between them, there would be no friction. Different deviations from the ideal state, such as the surface roughness, contamination and chemical heterogeneity, bulk material deformation and non-conservative adhesive bonds, lead to energy dissipation. Most heterogeneities involved into various dry friction mechanisms are associated with small ratios of magnitudes and of characteristic lengths of the forces at the interface and in the bulk. This small ratio leads to an almost linear dependence of the friction force upon load (the Coulomb law). However, the heterogeneities lead also to non-linear and multiscale effects. Mapping of dry friction mechanisms is proposed based upon the characteristic length parameters. It is discussed also how hierarchical friction mechanisms lead to biological hierarchical surfaces with reduced or increased adhesion and friction. Current advances in nano- and bio-tribology reveal a growing number of hierarchical (multiscale) surfaces. From the lotus leaf and gecko foot to self-affine and textured engineering surfaces, the hierarchy plays a fundamental role in frictional energy dissipation.

Modeling of hydrogen-assisted ductile crack propagation in metals and alloys

This paper presents a finite element study of the hydrogen effect on ductile crack propagation in metals and alloys by linking effects at the microstructural level (i.e., void growth and coalescence) to effects at the macro-level (i.e., bulk material deformation around a macroscopic crack). The purpose is to devise a mechanics methodology to simulate the conditions under which hydrogen enhanced plasticity induces fracture that macroscopically appears to be brittle. The hydrogen effect on enhanced dislocation mobility is described by a phenomenological constitutive relation in which the local flow stress is taken as a decreasing function of the hydrogen concentration which is determined in equilibrium with local stress and plastic strain. Crack propagation is modeled by cohesive elements whose traction separation law is determined through void cell calculations that address the hydrogen effect on void growth and coalescence. Numerical results for the A533B pressure vessel steel indicate that hydrogen, by accelerating void growth and coalescence, promotes crack propagation by linking simultaneously a finite number of voids with the crack tip. This “multiple-void” fracture mechanism knocks down the initiation fracture toughness of the material and diminishes the tearing resistance to crack propagation.

МЕХАНИКА ИЗМЕЛЬЧЕНИЯ ПРОКАТЫВАЕМЫХ В ТОЛСТОМ СЛОЕ МАТЕРИАЛОВ

Powder rolling conditions are systematized with the purpose of their compacting and milling. The generalized condition of solid and free-flowing bulk material deformation is proposed in the paper. The analytical solution of a stressed state of powder being shaped mechanically that ensures milling of its particles has been obtained.

Study on ring compression test using physical modelling and FE simulation

This paper presents a study of the ring compression test using physical modelling experiments and finite element (FE) simulation. Using commercially available modelling clay, material stress–strain relationships were obtained from compression tests of solid cylindrical specimens. A series of ring compression tests were carried out to obtain friction coefficients for a number of lubricants including vaseline, zinc stearate and talcum powder. FE simulations were used to derive the friction calibration curves and to evaluate material deformation, geometric changes and load–displacement results. Friction coefficient values of the tested lubricants are in agreement with the results obtained by other researchers. Further investigation is necessary to determine the effects of material properties, test conditions and use of calibration curves on the ring compression test. It is suggested that the combined use of physical modelling experiment and FE simulation provides a simple and effective means in the study of frictional mechanisms for bulk material deformation.

Cyclic deformation of polycrystalline Cu films

Fatigue impairs the reliability of macroscopic metallic components utilized in a variety of technological applications. However, the fatigue behaviour of thin metal films and small-scale components used in microelectronics and mechanical microdevices has yet to be explored in detail. The fatigue behaviour in submicrometre thin films is likely to differ from that in bulk material, since the volume necessary for the formation of dislocation structures typical of cyclic deformation in bulk material is larger than that available in thin films. The thin-film dimensions and microstructure, therefore, affect the microscopic processes responsible for fatigue. The fatigue behaviour of Cu films 0.4, 0.8 and 3.0 µm thick on polyimide substrates was investigated. The specimens were fatigued at a total strain amplitude of 0.5% using an electromechanical tensile-testing machine. This work focuses on the characterization of fatigue mechanisms and the resulting fatigue damage of thin Cu films. Extrusions similar to those observed in bulk material were found at the film surfaces after cyclic loading. Voids observed beneath the extrusions, close to the film-substrate interface, contributed significantly to thin-film failure. Thinner films were more fatigue resistant and contained fewer and smaller extrusions than thicker films did. A small thickness appears to inhibit void nucleation. This observation is explained in terms of vacancy diffusion and annihilation at free surfaces or grain boundaries. Transmission electron microscopy investigations confirmed that no long-range dislocation structures have developed during fatigue loading of the films investigated.

Plastic Deformation of Metal Thin Films without Involving Dislocations and Anomalous Production of Point Defects

Evidence for plastic deformation of crystalline metal thin films without involving dislocations is presented. Direct observation of the films during deformation under an electron microscope confirmed the absence of dislocations even for heavy deformation. In fcc metals, including aluminum, deformation leads to the formation of an anomalously high density of vacancy clusters, in the form of stacking fault tetrahedra. These vacancy clusters distribute uniformly when deformation is completed rapidly, but they disappear upon additional deformation, leading to nonuniform distribution of vacancy clusters. Vacancy cluster formation is suppressed when deformation speed is below a certain limit, and this is explained by the escape of deformation-induced vacancies during deformation. Some clusters are formed directly by deformation, and they grow by absorbing deformation-induced vacancies. A new atomistic model for plastic deformation of crystalline metals without involving dislocations is proposed, in which 'glide elements' execute deformation and their reaction produces point defects. Conditions required for operation of the new deformation mechanism is sought in the increase of internal stress under conditions where dislocations tend not to be generated. The possibility of high-speed deformation of bulk materials by this new mechanism is suggested.

An upper-bound analysis of friction in metal forming

In the analysis of metal forming processes, a knowledge of friction is important, especially when the microstructure evolution and criteria for limiting phenomena are predicted by numerical simulation. The friction wave model has been studied by several researchers. Their analyses are mainly based on the assumption that there is no plastic deformation of the bulk material. However, it is necessary to clarify the influence of bulk material deformation on the surface asperity deformation. This paper deals with the development of a friction wave model by considering the influence of bulk material on the surface asperity deformation. The situation of rough tool—smooth workpiece (RT—SW) contact during forming process has been investigated. Based on this condition, an admissible velocity field is constructed for the upper bound analysis. The relationship between the normal pressure and the sliding resistance is established over a large range of pressure. The role of surface roughness, bulk displacement and bulk strain on metal forming friction is analysed.

Microplasticity at room temperature of single-crystal titanium carbide with different stoichiometry

Single crystals of titanium carbide with a C-to-Ti range of 0.64 to 0.99 were plastically deformed at room temperature with a hardness indenter and a drill. The operating slip systems were determined by hardness anisotropy and transmission electron microscopy. The results were characteristic for bulk material deformation of TiC, below, as well as above, the brittle-to-ductile transition temperature. A typical low temperature behaviour is the formation of cracks and dislocation motion along the slip systems {1 1 0} 〈1 1 0〉 and {1 0 0} 〈1 1 0〉, which are both common in the rock-salt structure. The high temperature deformation is characterized by the slip system {1 1 1} 〈1 1 0〉. The degree of plastic deformation and the importance of the slip system {1 1 1} 〈1 1 0〉 increases as the C-to-Ti ratio decreases from 0.99 to 0.64.

はめあいに及ぼす形状誤差の影響(第1報)

Contact pressure and displacements in a shaft and ring as a pair on interference fit having cylindricity error of axially symmetrical profiles are analyzed by means of finite element method (FEM) with some assumptions: the deformation of bulk material is elastic, roughness of fitting surface is negligible, and the frictional condition on the contact surface obeys Coulomb's law. The analytical results are as follows: (1) Mean contact pressure is almost constant when mean interference is equal and the profile errors are small comparing with it, although displacements and local contact pressure vary according to the change of profile errors. (2) When the contact between shaft and ring comes to break locally as the profile errors increase mean contact pressure can not be estimated by mean interference any more. It is necessary to modify the mean interference by the way of cutting the interference off where the shaft and ring separate. (3) There is no remarkable change of contact pressure and displacements by the change of the coefficient of friction, however there is a little change of them at the ends of fitting surface.

あらさを有する平面と球の接触に関する研究(第2報)

The deformations of a sphere and a rough plane in contact with a normal load are numerically analyzed with some assumptions: the rough plane has nondirectional asperities whose distribution is Gaussian, the deformations of asperities are full plastic, and the deformation of bulk material is elastic. The analytic results are as follows: 1) The elastic deformation of the bulk material can be expressed by a quadratic equation with sufficient accuracy. 2) As the surface roughness increases, the elastic deformation of the bulk material decreases. But, the total indentation increases because of the asperities deformation. 3) As the surface roughness increases, or the flow pressure of the material decreases, the maximum shear stress in the bulk material decreases. Experimental results of the penetrating tests are shown to verify the validity of the analysis.

Dynamic deformation of compressible bulk materials

1. Deformation of bulk materials with a granular or porous structure under dynamic loads depends on the loading rate in the pressure impulse. This dependence is characterized by exponential damping as the loading rate increases. 2. For any material, there is a limiting loading rate, beyond which its effect on the deformation process is negligible. 3. The loading rate exerts a considerable effect on the deformation in the range of loads not exceeding the pressure corresponding to complete closure of free pores. Beyond this pressure, the σ=σ(e) diagram is virtually independent of the time factors. 4. The yield point (ultimate strength) of bulk materials with weak skeleton bonds under dynamic loads is almost twice as large as the static value of σs. 5. The second viscosity determines to a considerable extent the dynamic characteristics of the investigated disperse materials at a certain stress level (up to total closure of pores).