Deformation Of Metallic Materials Research Articles

Mechanical analysis of ultrasonic welding considering knurl pattern of sonotrode tip

Abstract Ultrasonic welding is attracting increasing attention in dissimilar material joining. The knurl pattern of sonotrode tip strongly affects the contact status and friction coefficient at the sonotrode/workpiece interface and thus plays a significant role on joint formation. Finite element models, with/without consideration of geometrical feature of sonotrode tip, were constructed to reveal the role of sonotrode geometry during ultrasonic welding process of copper to aluminum. The coupled thermal–mechanical fields and high-strain-rate deformation of metallic materials were incorporated in the models. The simulated results showed that the serrated knurl pattern of sonotrode tip greatly influenced the in-process variables (including stress, strain and displacement) at the contact surfaces of specimens. The localized concentration of plastic strain caused by the specific design of serrated tip knurl pattern, turned out to be the major cause for joint formation. Based on the evolution of average state variables in the bond area, ultrasonic welding process could be divided into three periods. Specimen deformation and material flow mainly occurred in the initial period of welding process. The simulated results were further verified by comparing specimen deformation and temperature evolution with experimental results.

Surface State Control by Ultrasonic Plastic Deformation at the Final Machining Stage

Basic results of research into the process of the surface geometry formation during ultrasonic plastic deformation of metallic materials are presented. The results of mathematical modeling of the microgeometry and surface undulation formation in the machining of materials of different hardness are also presented. Experimental validation of the adequacy of the proposed models is provided.

Mathematical modeling of the plastic deformation of a material with an FCC matrix and strengthening particles with L12 superstructure

A mathematical model of the plastic deformation of metallic materials containing a strengthening phase with L12-type ordering that exhibits both coherent and incoherent coupling with a matrix in various ratios is used to study the effect the scale characteristics of the strengthening phase has on the features of deformation strengthening at different temperatures and strain rates.

Contour-parallel tool path generation for three-axis mesh surface machining based on one-step inverse forming

Recently, mesh surfaces have become the focus of considerable interest due to its simplicity for data exchange and geometric computation. However, for mesh surface machining, there are few tool path planning strategies but iso-planar method. In this article, a contour-parallel tool path method is presented for machining complicated mesh surfaces with holes or islands by introducing a so-called one-step inverse approach based on physical plastic deformation of metal materials. By rapidly simulating for the inverse forming process of sheet metal of auto-body panels, the machined surfaces are flattened into its initial flat blank on which the cutter contact points are calculated by iteratively offsetting the inner and outer contours of the blank. Then, using the mapping from the machined surfaces to the blank as a guide, the planar offset curves without self-intersection are inversely mapped onto the original mesh surfaces, forming the final contour-parallel tool paths. Benefiting the flattening method based on one-step inverse approach, the task of generating tool paths is reduced from a physical surface to a plane so that geometric computation of tool path generation is greatly simplified, especially for self-intersection elimination in offset curves. Moreover, a new data structure of offset curve is also introduced, which is used to effectively compute the self-intersections. The proposed method has been tested on several sample surfaces, and the experimental results show that the proposed method can deal with complicated mesh surfaces with holes or islands and is also more efficient compared with the traditional methods.

Constitutive Modeling of Mechanical Behavior of Metallic Materials with Nanocrystalline Surface Layer

A constitutive model, adopting the modified Khan, Huang and Liang (KHL) viscoplastic model to describe plastic deformation of metallic materials with different grain sizes in the range of nanometers to micrometers at different strain rates, was presented to simulate the mechanical behavior of iron sample with nanocrystalline surface layer. Stress-strain curve and yield stress of the iron sample were calculated by means of this model. Influence of grain size distribution in the cross section was also investigated. The simulation results indicate that the yield stress can be increased after the formation of the nanocrystalline surface layer. And an increment of the fraction of the nanocrystalline layer can improve the yield stress further.

Plastic deformation nonuniformity and localization during metal forming

The nonuniformity of deformation of metallic materials during metal forming, the causes of its appearance, its mechanisms, the effect of the deformation nonuniformity on the limiting strain of a billet, the loss of stability and its causes during plastic deformation are discussed. Experimental results are given for the loss of stability during longitudinal flat rolling. These results are important for understanding metal flowing under various loading conditions.

Nanodipoles of partial disclinations as carriers of non-crystallographic shear and crystal-lattice reorientation in nanocrystalline nickel and vanadium

Using electron microscopy, an investigation is performed of microstructure features of re-orientation microbands formed in nickel and V–4Ti–4Cr alloys under severe plastic deformation in the Bridgman anvils. It is shown that their formation could be described within the framework of a quasi-elastic mechanism of motion of partial-disclination dipoles, which is controlled by the flows of non-equilibrium point defects in the fields of local gradients of normal stress-tensor components. Operation of this mechanism offers an additional advantage of nanostructuring the defect substructure during plastic deformation of metallic materials, followed by formation of the structure states wherein the nanocrystallites measure a few nanometers.

High-speed deformation of metallic materials using channel angular pressing for producing an ultrafine-grained structure

The possibility of producing an ultrafine-grained structure of metals and alloys by dynamic channel angular pressing is discussed using titanium, copper, and aluminum-based alloys as an example. It is established that even one-pass deformation allows one to produce a submicrocrystalline structure with a grain size of 30–350 nm and to enhance the strength properties at a high retained plasticity.

Scaling of structural parameters and mechanical properties of metals and alloys

The paper gives the statistical distribution curves, which are normalized to the most probable value, for parameters of the relaxational structure formed during or after deformation of metallic materials as well as for mechanical properties of some heat-resistant steels. It is shown that, in all studied cases, the dependences can be represented by one and the same statistical distribution curve, which is justified theoretically. The obtained results give grounds to speak about the scaling of relaxational parameters of strain-induced structures, which define the mechanical properties of materials in a wide temperature interval.

Studying elastic deformation behaviour of cast irons by acoustic emission

The deformation of metallic materials includes both an elastic and a plastic deformation. In the case of cast irons, the elastic region becomes less pronounced as the graphite changes from spheroidal to flake shaped, as observed in nodular and grey cast iron, respectively. The present study aims to correlate the shape of the graphite phase with the deformation behaviour, where the plastic deformation and other strain accommodating events are quantified by measurements of the acoustic emission events occurring in the interior of the material at loading. It also aims to explain how the appearance of cast iron stress–strain curves depends on the graphite morphology where, for instance, spheroidal graphite cast irons exhibit a seemingly linear elastic behaviour in contrast to flake graphite cast irons. The present study includes a series of pearlitic cast iron material grades with differences in nodularity and carbon equivalent, respectively. It is shown that as the roundness of the graphite phase increases, the ability to absorb energy increases. The measured acoustic emission indicates that plastic deformation occurs in the seemingly linear elastic region regardless of the cast iron grade, i.e. no cast iron grade exhibits perfect linear elasticity. The plastic deformation rate in the elastic region increases as the roundness of the graphite decreases and as the carbon equivalent increases. It is shown that the plastic deformation governs the resulting modulus of elasticity in all kind of cast irons, i.e. the modulus of elasticity decreases as the yielding of the material increases. The present study improves the understanding of the deformation behaviour in the elastic region of different cast irons. The survey shows that acoustic emission testing is a useful method when studying the deformation behaviour of cast irons.

Numerical Simulation and Experimental Evidence for Surface Modification by High Current Pulsed Electron Beam

The simulation of the temperature reveals an ultra high heating/cooling rates in the order of 108~109 K/s and melted layer thickness micrometers in depth. A temperature-induced dynamic thermal stress fields can then generate three principal stress, the quasi-static stress, the thermoelastic stress, and the shock stress, the latter two being stress waves. The thermoelastic stress wave has small amplitudes less than 0.1 MPa. The shock stress wave however is a typical nonlinear wave, several hundreds of MPa in amplitude, much stronger than the thermoelastic stress wave, and has a strong impact on materials structure and properties far beyond the heat-affected zone. The maximum compressive quasi-static stress in the surface layer in aluminum reaches several hundreds of MPa, which easily induces surface deformation in metallic materials.

301 超微細粒金属材料の超塑性変形(関東支部 茨城講演会)

301 超微細粒金属材料の超塑性変形(関東支部 茨城講演会)

Characteristics of the Deformed and Recrystallised Grains Obtained after Hot Plane Strain Compression of a Model Fe-30wt%Ni Alloy

The development of physically-based models of microstructural evolution during hot deformation of metallic materials requires knowledge of the grain/subgrain structure and crystallographic texture characteristics over a range of processing conditions. A Fe-30wt%Ni based alloy, retaining a stable austenitic structure at room temperature, was used for modelling the development of austenite microstructure during hot deformation of conventional carbon-manganese steels. A series of plane strain compression tests was carried out at a temperature of 950 °C and strain rates of 10 s-1 and 0.1 s-1 to several strain levels. Evolution of the grain/subgrain structure and crystallographic texture was characterised in detail using quantitative light microscopy and highresolution electron backscatter diffraction. Crystallographic texture characteristics were determined separately for the observed deformed and recrystallised grains. The subgrain geometry and dimensions together with the misorientation vectors across sub-boundaries were quantified in detail across large sample areas and the orientation dependence of these characteristics was determined. Formation mechanisms of the recrystallised grains were established in relation to the deformation microstructure.

Temperature–stress fields and related phenomena induced by a high current pulsed electron beam

Physical models and numerical simulations are applied to describe the thermal–dynamical processes of the high current pulsed electron beam (HCPEB) treatment. The simulation of the temperature distributions reveals an ultrahigh heating/cooling rate in the order of 10 8–10 9 K/s, as well as rapid melting and re-solidification within microseconds in time and micrometers in depth. It is also pointed out that the melting starts at a sublayer about 1–2 μm in depth, which constitutes the crater formation mechanism. A temperature-induced dynamic thermal stress fields can then generate three principal stress, the quasi-static stress, the thermoelastic stress and the shock stress, the latter two being stress waves. The thermoelastic stress wave has small amplitudes less than 0.1 MPa. The shock stress wave however is a typical nonlinear wave, several hundreds of MPa in amplitudes, much stronger than the thermoelastic stress wave, and has a strong impact on materials structure and properties far beyond the heat-affected zone. The maximum compressive quasi-static stress in the surface layer reaches several hundreds of MPa, which easily induces surface deformation in metallic materials.

Deformación a velocidad variable de hierro ARMCO

The hot deformation of metallic materials is the overall balance between two antagonistic mechanisms. On one hand the material undergoes work hardening, and on the other hand, due to the thermal activation, it undergoes softening by dynamic recovery and recrystallization. Both phenomena are usually studied by mechanical tests carried out at constant true strain rate. However, most of the real processes are carried out under variable strain rate or interrupted deformation. The present work is focused on introducing a descriptive model of the hot working behaviour of an ARMCO iron under variable strain rates conditions. The model is based on a theory where the strain rate is constant.

Highly Efficient and Energy-Saving Production Technology of Wires of Different Profiles

A significant increase of the knowledge of the phenomena occurring during deformation of metallic materials made it possible to control their structure through externally induced changes in the deformation path. Such a procedure guarantees both the limitation of the role of the fine, multi-system slip strengthening the material, and the strong domination of the energy-saving mechanism of localized plastic flow in shear bands. This is manifested, in industrial scale, by the possibility of increasing the total strain of the deformed material and decreasing the temperature of the process (economical and ecological advantages), while retaining the desired structure and the functional properties of the products. The new, presently implemented production technology (KOBO-type Forming) of the aluminum wires of different profiles, is directly based on the knowledge of the evolution of sub/structure in the course of the changing of the loading scheme (deformation path), and it consists in the realization of two operation in one pass at ambient temperature, i.e. rolling (cross section reduction ≃ 10%) and extrusion (extrusion ratio λ ≃ 13) with simultaneous reversible torsion.

種々の階層における塑性理論の発展 ５． 相変態による金属材料の変形現象

種々の階層における塑性理論の発展 ５． 相変態による金属材料の変形現象

Modeling the plastic deformation of metallic materials with allowance for the evolution of dislocation substructures

A model is presented to describe the mechanical behavior of metal-based materials. Experimentally established laws governing the evolution of the microstructure are used to construct the model. Also, a method is proposed for using experimental data on the evolution of defect substructures to construct models that describe the behavior of metallic materials beyond the elastic range.

The structure based design of metal forming operations

The work summarizes the recent experimental studies and theoretical considerations on the nature of plastic deformation in metallic materials. Specifically, it concentrates upon the rules which the heterogeneous deformation obeys and which differ radically from those of the homogeneous deformation. Formulation of such rules is based upon the experiments which provide the very fundamental information about the criterion of slip in crystalline materials, choice and sequence of operation of slip systems and conditions under which “crystallographically determined” slip may be replaced by transgranular shear. The correlation of this form of slip with metal structure and global mechanical properties is given. The results of the studies allow to predict the onset of heterogeneous mode of deformation and what is even more important, they show the means due to which the mode of deformation may have taken under control. The very practical aspect of the work consists itself in the concept “of the structure based design” of metal forming operation. It is shown, that the scheme and sequence of straining in a particular forming operation appears extremely important from the point of view of the energy consumption of the process and the final structure of the metal. The examples of “energy saving” metal forming operations, designed according to the concept, are presented.

Relaxation processes in metals at high strain rates

Mathematical modeling is used for experiments involving the loading of plates by plane shock waves to study the relaxation of shear stresses during the high-rate deformation of metallic materials. It is established that the characteristic relaxation times vary broadly — from fractions of a nanosecond to several microseconds. Such variation is indicative of a change in the mechanism responsible for relaxation. As a result, there is a difference between the quasi-equilibrium shear stresses in the elastic precursor and the same stresses behind the shock front. Metallic materials remain capable of resisting plastic deformation behind the front. Structural irregularities created by high-rate deformation result in localization of plastic flow at the microscopic level, which in turn causes the parameters of the stress-strain state at this level to differ from the corresponding parameters on the macroscopic scale.