Total Equivalent Strain Research Articles

Frictional angular rolling extrusion of interstitial-free steel sheets

Interstitial-free steel sheets were processed using a novel severe plastic deformation technique – frictional angular rolling extrusion (FARE), in order to produce ultrafine grained structures. The deformation was carried out at room temperature and individual sheet specimens were repeatedly processed to various passes. An overall grain size of 200nm was achieved after eight passes (or an equivalent total strain of 5.3). The present paper reports the evolution of microstructures during deformation, which were examined and characterized using electron backscatter imaging and high resolution EBSD in a field emission gun SEM. The mechanisms of grain refinement are discussed.

Study of Microstructure, Mechanical Properties and Wear Rate of High Leaded Tin Bronze after Multidirectional Forging

In this work, the change in microstructure, mechanical properties and wear rate of high leaded tin bronze alloy was studied after multidirectional forging (MDF) process. The total equivalent strain of 0.75 was applied. During MDF process improved ultimate tensile strength, hardness and wear rate along with maintained ductility was reported. The initial average grain size of 120nm was refined to the final average grain size of 37nm. The transmission electron microscope, scanning electron microscope and optical microscope was used for microstructure observation of the sample without MDF, MDF and wear worn surfaces.

Impact simulation of three-dimensional woven kevlar-epoxy composites

The focus of this work is to find the impact loading properties of three types of three-dimensional woven kevlar fabric structures before and after impregnation with epoxy resin. The analysis has been done at different impact times and different magnitude of forces. Total deformation, equivalent strain and equivalent stress created on these fabrics have been noted. First a model of three-dimensional woven fabric composite is generated using SolidWorks 2011. The model is constructed in such a way that it can be readily integrated into commercial finite element programs like ANSYS. Then impact resistance of this model is simulated and studied with impacts at different initial velocities. By incorporating the interface of fabric and matrix, the impact resistance is predicted. The simulated results are validated with experimental data. A compatible resin/matrix system has to be selected along with the fabric in order to develop sufficient resistance to impact. The three-dimensional woven kevlar-epoxy composites prove to be effectively resistant to impact due to interface of fiber and matrix system.

Microstructure evolution during semi continuous equal channel angular extrusion process of interstitial- free steel

In order to produce ultrafine grained structures, interstitial-free steel sheets have been processed using a novel severe plastic deformation technique semi continuous equal channel angular extrusion (SC-ECAE) which is based on equal channel angular extrusion (ECAE) in an incremental way. The deformation was carried out at room temperature and individual specimen was repeatedly processed to various passes. An overall grain size which is 0.55 μm was achieved after 10 passes (or an equivalent total strain of 4.8). The present paper reports the evolution of microstructures during deformation, which were examined and characterized using high resolution EBSD in a field emission gun SEM. The mechanisms of grain refinement are discussed.

Effect of strain and deformation route on grain boundary characteristics and recrystallization behavior of aluminum

The effect of strain and deformation route on the recrystallization behavior of aluminum sheets has been investigated using well lubricated cold rolling and continuous equal channel angular extrusion. Three different deformation routes in plane strain corresponding to (1) simple shear, (2) compression, and (3) the combination of simple shear and compression were performed on 1100 aluminum sheet. Fixed amounts of the equivalent strain of 1.28 and 1.06 were accumulated in each route. In case of the combined deformation route, the ratio of shear strain to the total equivalent strain was varied. The recrystallized grain size was finer if the combined deformation route was employed instead of the monotonic route under the same amount of equivalent strain at either strain level. The density of high angle grain boundaries that act as nucleation sites for recrystallization was higher in materials deformed by the combined route. The orientation imaging micrographs revealed that the change in deformation route is effective for introducing a larger number of new high angle grain boundaries with relatively low misorientation angle.

Experimental and Numerical Investigations of the Plastic Deformation during Multi-Pass Asymmetric and Symmetric Rolling of High-Strength Aluminum Alloys

For understanding the distribution of plastic deformation induced by asymmetric rolling (ASR), multi-pass ASR and symmetric rolling (SR) experiments combined with the finite element simulation were used for high-strength aluminum alloy in the present study. The influence of reduction per-pass on the shear / effective strain distributions were studied via different ASR processes. By measuring the shear angle (θ, the angle between the reference mark before and after rolling) of rolled sheets, redundant shear strain and equivalent strain were calculated. It is shown that with equal total thickness reduction for ASR and SR, ASR can induce much more shear deformation through the thickness. By calculating the evolution of redundant shear strain and total equivalent strain for different ASR routines, it indicates that small pass reduction could be much favorable to the strain accumulation than that of the large pass reduction under a same total reduction in ASR process. Also, the influence of shear stress on the strain distribution and the through-thickness strain distribution were studied and evaluated with FEM analyses.

Investigation of Mechanical Properties, Microstructure and Wear Rate of High Leaded Tin Bronze after Multidirectional Forging

In this work, the change in mechanical properties, microstructure and wear rate of high leaded tin bronze material was studied after multidirectional forging (MDF) process. The total equivalent strain of 0.75 was applied during MDF process result in the improvement of ultimate tensile strength, yield strength, hardness and wear rate along with maintained ductility with the increase in the number of MDF pass. The initial average grain size of 120nm was refined to the final grain size of 37nm. The transmission electron microscope, scanning electron microscope and optical microscope was used for the microstructure study of the undeformed, MDForged and wear worn surfaces.

Evolution of the spread of crystal orientation with plastic deformation in a cold-rolled Cu single crystal

Using scanning electron microscopy, we investigated how the microstructure of a Cu single crystal with a {15 12 9}〈9 10 3〉 orientation evolved from cold rolling. The first 50 % rolling caused its crystal orientation to rotate to {211}〈111〉. Although orientation splitting occurred near the surface of the single crystal, band-like regions with near-{211}〈111〉 orientations were still present after the fourth 50 % rolling. We measured the spread of crystal orientation in the near-{211}〈111〉 regions as a function of the total plastic equivalent strain induced by all rolling steps. When 50 % rolling was performed less than twice, the spread of crystal orientation was proportional to the square root of the plastic equivalent strain. Based on our results, we discussed the relationship between the spread of crystal orientation and the plastic equivalent strain generated by rolling.

Forming limits of Mg alloy ZEK100 sheet in preform annealing process

Preform annealing (PFA) is a new two-stage forming technology with an intermediate annealing step, which extends the formability of light-weight (Al and Mg) alloys that comparable to deep drawing steels. ZEK100 is the only rare-earth containing magnesium sheet alloy that available commercially. The objective of this research is to understand the effect of preform and anneal on the forming limits of ZEK100. Various pre-strain paths and levels were introduced in the preform step followed by an optimum annealing treatment. The total strain-based forming limits of the PFA material are strongly dependent on the pre-strain level and annealing conditions. Based on the strain energy principle, an equivalent strain is employed to evaluate the effects of the pre-strain and anneal on the total limit equivalent strain of the PFA material, which is fitted as a function of the equivalent pre-strain and strain ratio of major strain to minor strain; and there is a critical equivalent pre-strain that leads to the lowest total limit equivalent strain at all strain ratios. Based on this concept, a new forming limit diagram (FLD) is constructed with the equivalent strain and the strain ratio as the horizontal and vertical axes, respectively, to evaluate the formability of Mg sheet in this two-stage forming process with intermediate annealing.

Comparison of microstructures and strengths of an Al–2.5Mg alloy subjected to severe plastic deformation at room and liquid nitrogen temperatures

This work compares microstructural and strength properties of ultra-fine grained Al–2.5Mg alloy produced by multi-axial forging in a channel die at room and liquid nitrogen temperatures. The two ultra-fine grained microstructures after total equivalent strain of 2.3 exhibited similar grain sizes and orientation spread but significantly different respective strengths at room temperature. The difference in the strengths has been attributed to the higher dislocation densities in samples pressed at liquid nitrogen temperature. Dislocation densities were measured on the basis of average misorientations within grains measured using electron-back scattered diffractions.

Finite element analysis of adhesive endo-crowns of molars at different height levels of buccally applied load

This study aimed to evaluate the biomechanical behaviour of adhesive endo-crowns and the influence of their design on the restoration prognosis when four loading positions are applied from the restoration–tooth junction. Two three-dimensional finite element models for the lower first molar were developed: endo-crown as a monobloc and endo-crown of a primary abutment and a full crown. Four crown loading positions were considered: 5, 6, 7 and 8 mm. A force of 1400 N was applied buccally on the middle of the mesiodistal width. No differences were observed for the two endo-crowns concerning restoration displacement and the distribution of equivalent von Mises stress and total equivalent strain. Shifting the position of the applied load to 8 mm resulted in an increase in the displacement from 25 to 42 µm and an increase of equivalent von Mises stress concentration at the tooth. The height of load application on the restoration has a significant role in the prognosis of endo-crowns.

Stretchability of Prior Cold Worked AISI Type 304 Stainless Steel Sheet

The article presents the results of an investigation of the effect of prior cold work on the stretchability of type 304 stainless steel sheet. The forming limit diagrams show decreased levels with increasing prior work. However, when the limits are plotted as total equivalent strain as a function of strain ratio, the ductility increases with prior cold work. Also, for a substantial range of strain ratios from plane strain towards equibiaxial, sheets with lower levels of prior cold work show sharply increasing ductility. The first observation is explained in terms of the adiabatic temperature rise and the temperature sensitivity of the strain-induced transformation (that occurs in type 304 stainless steel), which influences the strain hardening in the material. The second observation is understood in terms of the kinetics of the transformation, which depends on the state of stress. Finite element simulations using a model taking into account the strain-induced transformation also reveal many of the trends observed in the experiments.

Analysis of Multiple Open Hot Die Forging for a General Cylinder Based on Numerical Simulation

Numerical simulation of the die for cylinder upsetting is done by Marc AutoForge software on base of elastic-plastic theoretical mechanical model to analyze transient temperature field, equivalent total strain field and thermal strain field. Then qualitative and quantitative relationship is found between these Factors and die-damage. A new method-Heat Exchange Balance Method is put forward to solve the cooling problems of hot -forging die by combinating with production practice , research practice and using basic theory of finite element and thermal.

An Investigation of the Dynamic Recrystallisation Behaviour of Magnesium AZ31 Alloy at 450°C Using Plane Strain Compression Testing as a Tool

The dynamic recrystallisation (DRX) behaviour of magnesium AZ31 is investigated using a plane strain compression (PSC) testing machine at 450°C. The variables included strain rate, double hit including intermittent anneal and double hits with different strain rate at each hit. The alloy shows higher peak stress and strain with increasing strain rates. Predominant basal texture with different intensities are observed at different strain rates. The annealing treatment between double tests leads to strong basal texture. Reversal of strain rate during double hit results in similar flow curves. This shows that in AZ31 alloy, DRX mechanism is independent of the initial microstructure and only depends on the test condition viz. temperature, strain rate and total equivalent strain.

Comparative Analysis of Plastic Flow and Grain Refinement in Pure Aluminium Subjected to Simple Shear-Based Severe Plastic Deformation Processing

In the present work, effects of loading scheme and strain reversal on structure and hardness evolution have been studied by using high pressure torsion (HPT) and twist extrusion (TE) techniques. High purity aluminium (99.99%) was processed at room temperature up to a maximum total equivalent strain of εmax ≈ 8 by TE, and HPT in monotonic and reversal deformation modes with strain increment Δεmax = 1. Minimum subgrain sizes reached in this study were 1.6 µm for TE and 1.1 µm for HPT. It was revealed that microstructural change with straining was a common consequence of severe plastic deformation (SPD) processing and was not affected significantly by the loading scheme. Among the SPD methods used in this study, HPT in monotonic regime produced the smallest grain size, while the most homogeneous microstructure was obtained by TE due to specific vortex-like flow field imposed by the tool geometry.

Load path sensitivity and fatigue life estimation of 30CrNiMo8HH

A set of strain-controlled biaxial proportional and non-proportional tests were conducted on solid and tubular specimens of 30CrNiMo8HH steel. The effect of the phase angle on fatigue life was studied. This effect becomes noticeable when applying a 90° out-of-phase loading, reducing the fatigue life by a factor up to 5. It has been shown that the material has no additional hardening due to out-of-phase loading. To account for this severe path dependency, a material dependent non-proportionality modification factor is proposed. This path dependent sensitivity factor is applied to six different fatigue parameters including maximum equivalent total strain, maximum equivalent stress, Smith–Watson–Topper, Fatemi–Socie, plastic strain energy density and total strain energy density to correlate the fatigue results. The predicted fatigue lives are compared with the experiments. The cyclic plasticity models of Mroz and Chaboche were successfully employed to model the cyclic behavior of 30CrNiMo8HH steel. It has been shown that estimations based on the proposed non-proportionality modification factor agree well with the experimental results.

Development of a novel severe plastic deformation method for tubular materials: Tube Channel Pressing (TCP)

A new severe plastic deformation (SPD) method entitled Tube Channel Pressing (TCP) is proposed. In this study, the ability of TCP on strength improvement and grain refinement is assessed. This method is based on pressing a tube through a tubular channel die with a neck zone. Utilization of a mandrel fitted inside the tube prevents the crumpling of tube and preserves its initial dimension. Due to the symmetric design, after one pass, the die is rotated upside down and the second pass is applied by pressing the tube in inverse direction. Ultimate strength of a commercial purity aluminum tube after 5 successful passes is improved to 2 times of the initial strength. Analytical calculations and simulation of this process accompanied by commercial finite element code ABAQUS/Explicit demonstrate that the total average equivalent strain of 1.2 is imposed in each pass. Furthermore, hardness distribution through tube thickness is assessed. Then, ability of TCP in grain refinement of tubular samples after each pass is determined.

Microstructure and texture of copper/niobium composites processed by ECAE

The structure refinement is a challenge for conductors used for the winding of resistive coils producing non-destructive pulsed magnetic fields over 80T. These nanocomposite conductors composed of a conducting multiscale Cu matrix embedding Nb reinforcing nanofilaments are usually manufactured by using a Severe Plastic Deformation (SPD) process based on hot extrusion, accumulative cold drawing and bundling (ADB) steps [Thilly et al. Philos Mag A 82:925, 2002]. Equal-channel angular extrusion (ECAE) is investigated here as an alternative route since it may provide faster refinement to obtain the ultrafine structure needed for optimized electrical and mechanical properties of the conductors. Therefore, copper-niobium specimens obtained by hot extrusion were processed by ECAE at room temperature. The specific die of the ECAE tool used here is constituted by a round channel with three angles corresponding to a total equivalent strain of about 2.5. Deformed samples were examined by optical microscopy and characterized by hardness profiles and x-ray diffraction (texture pole figures). After one ECAE-pass, the shape of the samples is modified but no trace of damage appeared at the Cu-Nb interfaces. An increase of the hardness values localized in the copper matrix is revealed whereas the hardness of the niobium remains unchanged. Prior to ECAE, the hot extrusion process induced a fibre texture for both copper and niobium. Two fibre texture components were observed for copper: and . A single fibre texture component is evidenced for the niobium. After ECAE a significant variation of the texture is observed in relation with the strong shear induced by this process.

Creep analysis of a thin tube and continuum damage mechanics application

In this paper, the behavior of a thin walled tube, which is widely used in many industries, under a constant internal pressure and a cyclic temperature gradient across its wall thickness was studied. In order to study the stress–strain variation across the thin walled tube during the cyclic loading, a coupled elastoplastic and creep continuum damage law was used and the necessary stress–strain relations were developed. The creep strain rate was obtained for different combinations of constant mechanical and cyclic thermal loadings by using an incremental numerical procedure. The results were shown in the Bree's diagram. Four different regions were obtained on the Bree's diagram for different normalized total equivalent strain rate order which varied from less than 0.001 to more than 0.1.

Ultra Grain Refinement in a Plain Carbon Steel by Means of Warm Torsion Testing

Ultra grain refinement of a plain carbon SAE-AISI 1010 steel has been obtained by means of warm torsion testing. Tests were conducted at 500°C, constant strain rate of 0.1 s -1 and total equivalent strain of 0.8, 1.6, 4.0 and 5.6. The average ferritic grain size obtained was smaller than 0.5μm. The steel microstructure consisted of elongated ferrite grains and fragmented and spheroidized cementite particles, similar to the microstructures found in carbon steel severely plastic deformed, like in the ARB and ECAP processes. The average ferritic grain size is reasonably predicted by the Hall--Petch equation. The mechanisms by which ultra grain refinement has been achieved here has been attributed to dynamic recovery and continuous dynamic recrystallization of the ferrite during warm plastic deformation. Warm torsion testing proved to be a suitable tool to study grain refining mechanism through severe plastic deformation.