High Plastic Deformation Research Articles

Erosion Behavior of AISI 6061-T6

In this work, erosion tests were performed to study the behavior of an aluminium alloy known as AISI 6061-T6 against the impact action of aluminium oxide abrasive particles. This material was selected because of its high ductility and tenacity. An erosion rig based on that in ASTM G76-95 was used to conduct the tests. The alumina particles had a particle size between 300 and 400 μm. Four incident angles, 30&deg, 45&deg, 60&deg and 90&deg were used to conduct the erosion tests. The particle velocity and the abrasive flow rate were 24 ± 2 m/s and 63 ± 0.5 g/min. The room temperature was between 35&degC and 40&degC. Chemical analysis of the material and abrasive particles were obtained using energy dispersive X-ray analysis (EDS). SEM images were employed to identify the wear mechanisms, which were characterized by high plastic deformation. The erosion rates were obtained and the results indicated that the maximum erosion damage was achieved at 30&deg reducing progressively at normal incidence.

Determination of Dynamic Characteristics of Welded Joints Made of Steel S460NL

Examination of the behavior of materials under very high speed plastic deformation are widely used during the designing process of dynamically loaded steel structures. Steel is widely used as a basic material for designing engineering structures. Characteristics of steel obtained under static experiments are different from those obtained during static tests.

The mechanisms of plastic strain accommodation during the high strain rate collapse of corrugated Ni–Al laminate cylinders

The Thick-Walled Cylinder method was used on corrugated Ni–Al reactive laminates to examine how their mesostructures accommodate large strain, high strain rate plastic deformation and to examine the potential for intermetallic reaction initiation due to mechanical stimuli. Three main mesoscale mechanisms of large plastic strain accommodation were observed in addition to the bulk distributed uniform plastic flow: (a) the extrusion of wedge-shaped regions into the interior of the cylinder along planes of easy slip provided by angled layers, (b) the development of trans-layer shear bands in the layers with orientation close to radial and (c) the cooperative buckling of neighbouring layers perpendicular to the radius. These mesoscale mechanisms acted to block the development of periodic patterns of multiple, uniformly distributed, shear bands that have been observed in all previously examined solid homogeneous materials and granular materials. The high-strain plastic flow within the shear bands resulted in the dramatic elongation and fragmentation of Ni and Al layers. The quenched reaction between Al and Ni was observed inside these trans-layer shear bands and in a number of the interfacial extruded wedge-shaped regions. The reaction initiated in these spots did not ignite the bulk of the material, demonstrating that these mesostructured Ni-Al laminates are able to withstand high-strain, high-strain rate deformation without reaction. Numerical simulations of the explosively collapsed samples were performed using the digitized geometry of corrugated laminates and predictions of the final, deformed mesostructures agree with the observed deformation patterns.

Ultrasonic Measurements of Residual Stresses Caused by Severe Thermomechanical Deformation during FSW

In engineering processes, residual stresses can be intense once high plastic deformation and temperature gradient are involved. This is exactly the case for friction stir welding (FSW) in which both rotational and translational movements of the tool induce extreme temperature gradient and plastic deformation. In this research, the extents of longitudinal and transverse residual stresses are measured within the AA7075-T6 plates welded through FSW process using ultrasonic method. According to the obtained results, it can be found that the residual stress is of the tensile type adjacent to the welding line whereas it is of the compressive type far from the welding line. Another observation is that the longitudinal residual stresses are considerably greater than the transverse residual stresses. Furthermore, with the aim of investigating the effects of rotation and traverse velocities of the tool on residual stress, experiments are carried out at three different rotation and traverse velocities. Based on the acquired results, it is observed that upon increasing the rotation and traverse velocities, the longitudinal and transverse residual stresses decrease and increase, respectively.

Influence of composition, grain size, and oxide particles on the strength of consolidated ball-milled iron

In this paper iron powders with two oxygen content (0.2 and 0.6% wt.) have been mechanically milled and consolidated by hot static pressing at different temperatures to obtain different grain sizes. At lower temperatures the grain size was in the nanostructured and ultrafine range and with increasing temperature abnormal grain growth was observed for both compositions. This led to the development of bimodal grain size distributions. In the samples with lower oxygen content the grain size and the percentage of coarse grain areas were larger than in the case of high oxygen content.The strength and ductility have been determined by tensile tests. For low oxygen content, the presence of large coarse grains allowed plastic strain in some cases, and for the samples consolidated at higher temperatures, yield strength of 865 MPa with a 8% total strain were obtained. For the samples with high oxygen content plastic deformation was no possible in any case.The observed stress for both compositions was analysed by two approaches, one based exclusively in grain boundary strengthening and the other one based in two effects acting at the same time: grain boundary and particle strengthening. Whereas grain boundary strengthening seems to fit with the strength of the samples in the nanostructured range, when coarse ferrite grains appear the addition of particle strengthening help to get better results. This indicates that the presence of oxides dissolved inside the large grains reinforce the structure of ball-milled iron.

Analysis of internal crack healing mechanism under rolling deformation.

A new experimental method, called the ‘hole filling method’, is proposed to simulate the healing of internal cracks in rolled workpieces. Based on the experimental results, the evolution in the microstructure, in terms of diffusion, nucleation and recrystallisation were used to analyze the crack healing mechanism. We also validated the phenomenon of segmented healing. Internal crack healing involves plastic deformation, heat transfer and an increase in the free energy introduced by the cracks. It is proposed that internal cracks heal better under high plastic deformation followed by slow cooling after rolling. Crack healing is controlled by diffusion of atoms from the matrix to the crack surface, and also by the nucleation and growth of ferrite grain on the crack surface. The diffusion mechanism is used to explain the source of material needed for crack healing. The recrystallisation mechanism is used to explain grain nucleation and growth, accompanied by atomic migration to the crack surface.

Effect of surface parameters on finite element method based deterministic Gaussian rough surface contact model

Three-dimensional rough surface contact models enrich the understanding of the influence of surface texture in rough surface contacts. Most of the existing contact models did not consider the effect of elasto-plastic deformation and neighboring asperity interactions for the rough surface contact analysis, or only to a limited extent. In the present work, three-dimensional contact analyses of Gaussian rough surfaces are carried out using finite element method. By fast Fourier transform approach, Gaussian rough surfaces having auto-correlation lengths of 0.5, 2.0, 5.0, and 10 µm and surface roughness of 0.001, 0.01, and 0.1 µm are generated. The generated rough surfaces are transferred to finite element method based ANSYS package for micro-contact analysis. The continuity of elastic, elasto-plastic, and plastic deformations of near realistic feature-based asperities and effects of asperity interactions are inherently included in the present analysis. Each rough surface contact analysis is carried out in such a manner to cover the entire asperity distribution with incremental displacements. The contact load, real area of contact, and contact pressure are extracted from each analysis. The results showed that the surface having low surface roughness, the asperities deform mostly elastically whereas in medium and high surface roughness surfaces, the elasto-plastic and plastic deformation of asperities are significant and also in low auto-correlation length surface, the intensification of sub surface stresses cause the mean contact pressure ratio to reach peak value whereas in high auto correlation length surface, the larger size of asperities and the neighboring asperity interaction keep the mean contact pressure ratio at low level.

Controlling the length scale and distribution of the ductile phase in metallic glass composites through friction stir processing

We demonstrate the refinement and uniform distribution of the crystalline dendritic phase by friction stir processing (FSP) of titanium based in situ ductile-phase reinforced metallic glass composite. The average size of the dendrites was reduced by almost a factor of five (from 24 μm to 5 μm) for the highest tool rotational speed of 900 rpm. The large inter-connected dendrites become more fragmented with increased circularity after processing. The changes in thermal characteristics were measured by differential scanning calorimetry. The reduction in crystallization enthalpy after processing suggests partial devitrification due to the high strain plastic deformation. FSP resulted in increased hardness and modulus for both the amorphous matrix and the crystalline phase. This is explained by interaction of shear bands in amorphous matrix with the strain-hardened dendritic phase. Our approach offers a new strategy for microstructural design in metallic glass composites.

Nano-Structuring of 316L Type Steel by Severe Plastic Deformation Processing Using Two-Dimensional Linear Plane Strain Machining

Using a novel plastic deformation technique, termed linear plane-strain machining, large shear strains up to ~2.3 have been imparted to 316L stainless steel at rates of up to 1700/s. Combinations of hardness and magnetic measurements, X-ray diffraction (XRD) and transmission electron microscopy (TEM) experiments were used to monitor the microstructural and mechanical property changes for the room temperature plastic deformation processing. Grain refinements to the ultra-fine grained and even the nanocrystalline size regime have been achieved without formation of significant volume fractions of strain-induced martensite. The mechanical strength enhancements in the linear plane-strain machined 316L have been attributed to grain refinement and stored strain. The suppression of martensite formation has been correlated to significant adiabatic heating of the 316L during high strain rate plastic deformation processing.

High-strength ultrafine grain Mg–7.4%Al alloy synthesized by consolidation of mechanically alloyed powders

Highly-dense ultrafine grain Mg–7.4%Al bulk samples with grain size of about 300nm have been produced by powder metallurgy through hot consolidation of mechanically alloyed powders. Room temperature compression tests of the consolidated bulk material reveal remarkable mechanical properties: high compressive strength of about 690MPa combined with a plastic strain exceeding 9%. The high strength of the alloy can be attributed to the combination of three different strengthening mechanisms: grain size refinement, dispersion strengthening and solid solution strengthening. The fracture surface shows trans-granular quasi-cleavage fracture in nature. The MgO rich regions often acted as the microcrack initiation source and thereby stop the main crack. Uniformly distributed intermetallic (γ-Al12Mg17) particles in the matrix deflected main crack and resulted a tortuous crack path. These results demonstrate that powder metallurgy, mechanical alloying combined with hot consolidation is a suitable method for the production of nanostructured Mg-based materials characterized by high strength and considerable plastic deformation.

Seismic demand on steel reinforcing bars in reinforced concrete frame structures

Modern design standards for reinforced concrete (r.c.) buildings allow the achievement of ductile structures, able to globally dissipate seismic energy through the development of plastic deformations located in the dissipative regions (i.e. plastic hinges). The hysteretic capacity of r.c. structures is related to the ability of reinforcing steel bars to sustain many cycles of high plastic deformations without the exhibition significant decrease of strength and stiffness; this condition, typically due to cyclic/seismic action, shall be widely investigated in order to obtain a full and detailed knowledge of the structural behaviour of modern r.c. buildings. In the present paper, elaborated inside the European research project “Rusteel”, the evaluation of the seismic ductile demand on steel reinforcing bars due to real earthquake events was carried out. Representative r.c. case study buildings were designed following the actual European and Italian prescriptions and analyzed using the Incremental Dynamic Analysis technique for the assessment of the behaviour under real seismic events. The elaboration of a simplified mechanical model for the steel reinforcing bars, calibrated on the basis of experimental monotonic and cyclic tests, allowed the evaluation of the effective level of deformation and energy dissipation required by earthquakes and the assessment of the ability of the actual European production to satisfy the effective seismic ductile requirements.

The Effect of Repeated Impingement on UHMWPE Material in Artificial Hip Joint during Salat Activities

In Indonesia, a country with largest Muslim population in the world, the necessity to study the artificial hip joint which allows Muslim patients with total hip replacement to have normal Salat becomes important issues. This paper discusses the effect of impingement which occurs during one of the Salat movements. i.e. last tashahhud sitting motion. An artificial hip joint model, proposed by previous researcher from developed country, is simulated using finite element analysis to perform last tashahhud sitting motion. The result shows that impingement occurs and causes the plastic deformations and plastic strains in the acetabular liner component which is manufactured from UHMWPE material. The repetition of Salat movement induces repeated impingements and higher plastic deformation. It experiences dimensional change in the liner lip and has a potency to cause clinical failure of total hip replacement. A new design of the artificial hip joint is required to be proposed to avoid the repeated impingement and deformations.

Stress-induced phase transformation characteristics and its effect on the enhanced ductility in continuous columnar-grained polycrystalline Cu–12 wt % Al alloy

The microstructure evolution and stress-induced phase transformation (SIPT) characteristics of continuous columnar-grained (CCG) polycrystalline Cu–12wt%Al alloy during the tensile deformation process were investigated to understand the ductility enhancement mechanism, which shows a tensile elongation of 28%, nine times as high as that of the conventional as-cast polycrystalline counterpart. The results show that the CCG alloy has highly-oriented 〈001〉β texture and straight low-energy grain boundaries (GBs) along solidification direction, which significantly promote grains compatibility during plastic deformation. Additionally, besides β1'→α1' transformation, β1'→γ1'→α1' SIPT was also observed simultaneously in the CCG polycrystalline Cu–12wt%Al alloy, which is different from single crystalline and conventional polycrystalline counterparts. As a consequence of the special phase transformations, high phase transformation plasticity (15–20%) and prominent subsequent plastic deformation (8–13%) of the phase transformation product α1' martensite can be obtained.

Facile mechanical alloying of titanium sponge

The mechanical alloying of titanium with 3wt% chromium was performed starting directly from Hunter or Kroll titanium sponge. A small quantity of calcium was added as a process control agent (PCA) to obtain a high process yield, uniform microstructure and homogeneous chemical composition.The milled powder was then sintered using spark plasma sintering (SPS) at low temperature to achieve the best mechanical properties and a high-quality microstructure. Samples were also heat treated at high temperature to understand the behavior of the chlorine content of the titanium sponge.The mechanical properties were tested by three-point bending. Depending on the kind of starting titanium sponge, high transverse rupture strength (TRS) and high plastic deformation were obtained for all of the alloys in both the as-sintered and heat-treated condition: the high TRS was correlated to the total interstitial elements content.Tensile tests on samples obtained from Hunter titanium sponge yielded results comparable with those of wrought Ti6Al4V, and after high-temperature heat treatment, the samples obtained from the mechanical alloyed powders showed much better properties due to their much smaller grain size compared with that of Ti6Al4V.

Hollow cone high-pressure torsion: Microstructure and tensile strength by unique severe plastic deformation

Hollow cone high-pressure torsion (HC-HPT) is proposed as a new severe plastic deformation to produce ultrafine-grained (UFG)/nanocrystalline microstructure materials. UFG Cu with an average grain size of 550 nm and well-developed high-angle grain boundary after HC-HPT of only 1 turn of torsion exhibited a high tensile strength of 414 MPa and a fracture elongation of 25%. A higher plastic deformation in the inner region, the unique deformation mode of HC-HPT, was analyzed using the finite element method.

Morphology and Mechanical Properties of HDPE/Bio-Polymer as Compounding Materials

The effect of bio-polymer as compounding material in mechanical properties of HDPE is described in this study. 10% of bio-polymer was added to the HDPE and then mixed by using Brabender Plastograph machine using mixer and roller screw and then test specimens were prepared by injection moulding. The origin bio-polymer (VOP), HDPE and the compounding bio-polymer/ HDPE (CDM) were compared by using tensile test and the microstructure was investigated through scanning electron microscopy (SEM) for the fractured surface of the samples. The tensile strength of CDM was found to increase that is 17.47 MPa compared to pure VOP that only 5.69 MPa while pure HDPE has the highest tensile strength that is 20.98 MPa. By adding 10% bio-polymer to the HDPE was increased up the strength at about 207.16% while pure HDPE produced 268.91% increment with VOP as the precursor. SEM of the VOP produced brittle fracture surface while CDM have brittle and ductile surface and HDPE has totally ductile surface with highest plastic deformation properties of all.

Deformation and failure behaviour of open cell Al foams under quasistatic and impact loading

Metal foams show efficient and almost isotropic energy absorption during compression making them interesting materials for the design and development of impact resistant components. The (mechanical) properties of metal foams are determined (i) by the properties of the alloy they are made of and (ii) by their complex meso- and microstructures. While the dynamic mechanical properties of Al foams have been investigated by several groups, the deformation mechanisms at higher strain rates has been considered to a much lesser extent.To gain a deeper understanding of the relationship between the specific properties of the hierarchical structural elements (e.g. cell, strut, microstructure of the struts) and the macroscopic properties we combine mechanical testing with different imaging methods. Compression tests on open cell Al (A356) foams, which have been produced by investment casting and which have very low relative densities (1.7–2.2%), were performed under quasistatic (dε/dt=5×10−4s−1) and dynamic (10s−1) loading conditions. Video recordings allow us to evaluate the failure mechanisms in the foams on a macroscopic scale, while in-situ testing in the µCT or SEM provides important information on the deformation behaviour as well as the crack formation and development on the microscale. Metallographic sections of specimens deformed to defined strain values are furthermore investigated to gain insight into the role of microstructural features with higher resolution.The deformation behaviour and the mechanical properties of the quasistatically and the dynamically tested specimens are very similar. Higher strain rates result in a more homogeneously distributed deformation, however with a negligible influence on the plateau stress, densification strain and energy absorption characteristics. The highly efficient energy absorption during the plateau phase is due to microstructural mechanisms such as plastic bending of struts (mostly C- and S-curved) and different types of crack formation and growth in the struts. Local differences of the strut microstructure cause locally different mechanical behaviour of struts: while high plastic deformation leads to a more homogeneous macroscopic deformation, we assume brittle fracture of single struts promotes the formation of deformation bands.

Influence of Machined Workpiece Surface Integrity on Fatigue Performance

The effect of machined workpiece surface topography and surface integrity were studied. Modifications of surface layers after mechanical surface treatments were also reviewed. Conflict ideas exist in publications about which parameters can better define fatigue endurance. The traditional one was Arithmetic Average Roughness, although deepest surface feature and the square root of the defect area were proposed. The combinations of these factors including high temperature, metallurgical alternations and plastic deformations, rather than the residual stress alone affect surface topography and surface integrity. They should be examined carefully in order to gain a better understanding of fatigue.

Formation of long-period stacking ordered phase only within grains in Mg–Gd–Y–Zn–Zr casting by friction stir processing

Friction stir processing (FSP) was applied to Mg–Gd–Y–Zn–Zr casting, resulting in significant dissolution of large grain boundary eutectic β-Mg3RE and long-period stacking ordered (LPSO) phases. A fine-grained structure with a grain size of ∼2.4μm was developed in the FSP sample. Besides, fine LPSO lamellae with a width of ∼5 to ∼200nm were distributed only within the grains in the FSP sample, which is different from that observed in both solution-treated and other plastically deformed counterparts. Formation of such special structure is attributed to the high temperature severe plastic deformation generated by FSP. The FSP Mg–Gd–Y–Zn–Zr exhibited high mechanical properties with a yield strength of ∼345MPa and an elongation of ∼21.5%. This study provides an effective way for mechanical property optimization in LPSO-contained magnesium alloys.

The mechanism of instability and localized reaction in the explosively driven collapse of thick walled Ni-Al laminate cylinders

Thick-walled cylinders constructed from alternating concentric layers of Ni and Al foils were explosively collapsed. The prevalent mode of the high strain, high strain rate plastic deformation was the cooperative buckling of the foils originating in the interior layers. This phenomenon was reproduced in numerical simulations. Its mechanism is qualitatively different than that of shear localization seen in all previously investigated homogeneous solid and granular materials and from the independent buckling of single thin-walled cylinders. Localized chemical reactions were observed in the apex areas of the Ni foils, consistent with the localization of temperature due to high strain plastic deformation.