Triaxial Stress State Condition Research Articles

Influence of microstructural refinement on cold deformation behavior of nanocrystalline Al–Zn–Mg alloy processed by solid-state mechanical milling and hot pressing

This research work was aimed at studying the workability behavior of Al–Zn–Mg alloys during a cold upsetting process. Nanocrystalline Al 7017 alloys were synthesized by mechanical milling (MM) at different milling times and consolidated by hot-pressing. The nanocrystalline Al 7017 alloy samples were incrementally deformed with a load step of 0.5 ton in a universal testing machine. Artificial image capturing and comparison techniques were introduced in this study and deformed images were captured using a high-resolution camera. For each incremental load (without removing the sample from the platens), different parameters such as the height of the deformed samples, and the corresponding contact diameters (top and bottom) were measured and analyzed using Matlab software (image processing). Cold upsetting was performed until the first crack formed. The influence of milling time on cold workability and strain hardening behavior was investigated under triaxial stress state conditions. The results revealed that the Al 7017-10 h nanocrystallite alloy exhibited improved deformation properties in terms of various tri-axial stress, strain hardening, formability stress index, and stress ratio parameters owing to the fine grain size, lower amount of dislocation pile-up, and fewer migrated atoms near the grain boundaries compared to other samples (after10 h). The microstructure and phase evolution were studied using an X-ray diffractometer and various electron microscopes. Several strengthening mechanisms are also discussed among which the dislocation strengthening mechanism plays a major role in the deformation behavior. Finite element analysis (FEA) was performed to examine the equivalent stress distribution during cold-upset forging.

Influence of intermediate principal stress ratio on strength and deformation characteristics of frozen sandy soil under different moisture contents

Frozen ground often contain non-uniform moisture content and are under true triaxial stress state and their practical engineering application are still explored. The present study is carried out to investigate the strength and deformation characteristics of frozen soil with different moisture contents under true triaxial stress state conditions. A series of true triaxial tests were conducted on frozen soil specimens having constant minimum principal stress (σ3) and constant intermediate principal stress ratio (b). The experimental test results showed that the stress-strain curves represent the strain-hardening characteristics under different test conditions. The intermediate principal stress ratio (b) has a dual effect of strengthening and weakening on the strength of frozen sandy soil. When 0 ≤ b ≤ 0.5, the strengthening effect was found to be dominant in the frozen soil specimen, whereas, the weakening effect was dominant when 0.5 < b ≤ 1. The strength of frozen soil under true triaxial stress state is 8.18% to 36.33% higher under different water content conditions, compared to that under generalized triaxial compression stress state. The difference in deformation between the direction of the intermediate principal stress and the minimum principal stress increased with the increment in the intermediate principal stress ratio value. The volumetric strain in the soil sample initially exhibited the characteristics of shear contraction and then shear dilation.

Experimental Investigations of Al-Cr3C2 Composite Preform Densification and Deformation

This investigation on strain hardening, densification and workability of the Sintered aluminium- Chromium Carbide composition of (Al-Cr3C2 of 2, 4 and 6%) preforms subjected to upsetting were investigated in this research. Industrial practitioners needed the workability data and densification mechanisms to plan and envisage the failure strains. In the current study, under triaxial stress state conditions Al-Cr3C2 preform with primary preform densities and various aspect ratios were compressed. Strain hardening, densification behaviors of aluminium- Chromium Carbide be investigated by gradually increasing the load till the fracture occurs. The outcome of adding Cr3C2 to Al and the impact of aspect ratio on formability was also extensively investigated. We looked at the parameters of stress ratio, instant varying strain rate, work hardening exponent, instantaneous density coefficient and densification attained.

Formability and densification behavior of two-layered structure powder metallurgical hot-pressed Al-Cu/Al composites during hot-upsetting

An experimental investigation has been performed on the hot formability and densification characteristics of Al-Cu/Al two-layered structure composites. The two-layered composites having different Cu compositions in the Al-Cu layer such as (Cu: 5wt. %, 10wt. %, and 15wt. %) were prepared using the powder metallurgy (P/M) route. The composites were hot-pressed as layer by layer in a steel cylindrical die at 550°C temperature with 0.9 initial relative density (IRD) and 0.1 s−1strain rate. The preforms were hot deformed between two flat dies with a capacity of 50-ton hydraulic press machine at a temperature range of 150°C – 450°C under triaxial stress state condition. The hot-upsetting behaviour of preforms was analyzed until the cracks begin on the cylindrical preform at the outer surface. The effect of different Cu composition and various deformation temperatures on two-layered preforms were discussed. Results revealed that the (10wt. %Cu) preform achieved good cooperative deformation behaviour between Al-Cu and Al layers at the interface region. The relationship between the process parameters was discussed such as the effect of axial stress ([Formula: see text]), relative density ( R) on axial strain ([Formula: see text]) and formability stress index ( β), different stress ratio parameters ([Formula: see text], [Formula: see text]) on relative density ( R).

Workability, Densification and Failure Characteristics of Selective Heated Sintered Powder Metallurgy Preforms during Upsetting

A study on workability, densification and failure characteristics of porous aluminum–titanium components has been performed by adopting a selective heating method under triaxial stress state condition. The required specimens were made using the powder metallurgy method with 90% of initial relative density and an aspect ratio of 1 through the appropriate compaction pressures. A sequence of upsetting has been executed on the powder metallurgical compacts using a hydraulic press for different titanium compositions (2-6%). In the upsetting process, the damage of the specimens mainly relies on the accumulation of stresses at the damage site. Hence, the damage site of the compacts was identified for various specimens using finite element simulation software. Once the damage position was identified, the compacts were heated at the damage sites (selective heating) for different temperatures, namely 100, 140, 195, 220 and 250 °C using a portable gas cartridge. As a result, the failure initiation is arrested thereby increasing the workability and densification. Selectively heating the damage zone of the components has relieved the accumulated stresses and has reduced the porosity (from 11.385 to 6.702% for Al-2%Ti, from 12.797 to 7.920% for Al-4%Ti and from 13.215 to 8.611% for Al-6%Ti) of the preforms. Thus, the damage limit of the components can be increased during upsetting by the selective heating process.

Study on formability and strain hardening index: influence of particle size of boron carbide (B4C) in magnesium matrix composites fabricated by powder metallurgy technique

In the present investigation, Magnesium composites have been fabricated with boron carbide (B4C) as reinforcement by powder metallurgicaltechnique. Two different particle sizes—micro and nano B4C particles with weight percentage of 0%, 5% and 10% has been studied. The green compacts were prepared by cold pressing and then sintering the specimens before being subjected to cold upsetting under triaxial stress state condition in order to study the phenomenon of workability and instantaneous strain hardening index. Powder characterizations are discussed using x-ray Diffraction peaks, Scanning Electron Microscope images and Energy Dispersive Spectrum analysis. Cold upsetting has been preferred to investigate the performance of the composites. The values of formability stress index factor (βσ), various stress ratio (σθ/σeff, σm/σeffandσz/σm) parameters and instantaneous strain hardening index (ni) are observed for increase in % of B4C particles and its sizes. The experimental results were analyzed pertaining to relative density. The results reveal that Mg-10% nano B4C composite has higher relative density, formability stress index factor and hence high workability than the other composites. The addition of B4C particles as reinforcement affects the strain hardening index due to geometric and work hardening of the composites.

Characterization, formability, various stresses and failure analysis on workability of sintered Mg-5%B4C composite under triaxial stress state condition

The present study focuses on hardness and workability behavior of Magnesium (Mg) and Mg-5%B4C composites using online Acoustic Emission (AE). The Mg preform and Mg-5%B4C sintered samples are prepared by using Powder Metallurgy (P/M) route with the support of die-punch setup and Universal Testing Machine (UTM) having a maximum capacity of 1MN with an aspect ratio of one. The characterization of powders and composites are discussed using Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) and Energy Dispersive Spectrum (EDS) analysis. Electron Back Scattered Diagram (EBSD) for grain size is carried out for the Mg and Mg-5% B4C composite. The Cold upsetting process under triaxial stress state condition is preferred for the workability study. AE tests are conducted simultaneously to detect the crack initiation in the preform. The AE test result displays that Mg-5%B4C composite has excellent AE waveform distribution owing to the presence of B4C in the matrix. The effect of formability stress index factor (βσ) and various stress ratio parameters (σθ/σeffand σm/σeff) are established. The result exhibits that Mg-5%B4C composite has greater hardness, higher workability parameter, triaxial stresses and initial relative density than the pure Mg preform due to the addition of the B4C.

Hot workability and densification behavior of sintered powder metallurgy Al-B4C preforms during upsetting

The workability and the densification behavior of a porous Al–B4C preforms have been carried out in the present investigation. Hot upsetting tests have been carried out on Al–B4C powder metallurgy (P/M) preforms having an initial preform density of 0.9 and having different B4C compositions of 2%, 4% and 6%. The samples were compressed between two flat dies in a hydraulic press of 50 ton capacity under varying deformation temperatures such as 200°C, 300°C, 400°C and 500°C under the tri–axial stress state condition. The workability and densification behavior of Al–B4C preforms were analyzed till the initiation of cracks on the outer surface of the preform. The experimental results were analyzed for the various deformation parameters such as axial strain, relative density, formability stress index and different stress ratio parameter under the tri–axial stress state condition. The formability and densification behavior were discussed with the axial strain (εz) during the hot upsetting process. The relationships between the various stress ratio parameters (σq/σeff, σm/σeff) and formability stress index (βσ) as a function of the relative density under the tri–axial stress state condition were established.

Preoblikovalnost Cu-TiB2 predoblik izdelanih z metalurgijo prahov med hladnim kovalnim preizkusom

An investigation was carried out to find the workability behaviour of a Cu-TiB2 composite under triaxial stress-state conditions. Initially, the TiB2 powder was prepared by using a self-propagating high-temperature synthesis (SHS) technique and the same was added to a Cu matrix in order to make Cu-TiB2 composites. Cylindrical preforms with three different TiB2 weight percentages (2 %, 4 % and 6 %) with aspect ratios of 0.50, 0.75 and 1 were prepared using a uniaxial load. Then the preforms were pressureless sintered in a tubular furnace with a continuous flow of pure argon gas at 950 °C for a period of 1 h. The cold upsetting test was carried out on the sintered specimens. The relationships between the various stresses, strains and the relative density were determined. The results for the various stress-ratio parameters, namely ( / eff) and ( m/ eff), the formability stress index ( ) under triaxial stress-state conditions were systematically analysed. The formability stress index was found to increase with the increase in preform fractional density and it decreased with the aspect ratios. This was because the preform contains more pores and the porous bed height is high. A statistical fitting method was performed on the curve drawn between the axial strain and the stress-formability index. The compacts with a higher value of the aspect ratio and the initial preform density showed a very high fracture strain.

Experimental Investigations on the Densification and Deformation Behaviour of Al-TiB2 Composite Preforms

The present investigation dealt with the study on the workability, densification and strain hardening behaviour of sintered aluminium-titanium diboride composite (Al-5%TiB2, Al-10%TiB2) preforms subjected to upsetting process. The workability data and densification mechanisms were essential for the industrial practitioners to design the process and to predict the failure strains. In the present study, Al-TiB2 composite preforms with different aspect ratios and initial preform densities were compressed under triaxial stress state condition. The densification and strain hardening behaviour were analyzed by incrementally loading them till the onset of failure. The effect of the addition of TiB2 content to aluminium and the effect of aspect ratio on formability were discussed in detail. The work hardening exponent, stress ratio parameters, the instantaneous density coefficient, instantaneous strain rate sensitivity and densification attained were studied.

Workability studies on Al+2.5%TiO2+Gr powder metallurgy composites during cold upsetting

Al+2.5%TiO2+Gr composites were synthesized through powder metallurgy technique and their workability behavior has been studied under tri-axial stress state condition. The powders were compacted using suitable punch and die in 400 kN hydraulic press and sintered at a temperature of about 590 ºC for a period of 3 hours in an electric muffle furnace. The sintered preforms were characterized by XRD and SEM analysis. Then the preforms were subjected to incremental compressive loading of 10 kN until the cracks found at the free surface. The true axial stress (σz), true hoop stress (σ}), true hydrostatic stress (σσm) true effective stress (σeff), formability stress index (β) and stress ratio parameters [(σz/σeff), (σm/σeff), (σ}/σeff)] were calculated for all the preforms and these are correlated with the true axial strain (e z). It is inferred that, the addition of TiO2 and Gr to the Al matrix material increases the stress ratio parameters and formability stress index (β). A hardness test was also conducted for sintered and cold forged preforms and results are reported.

Densification Behavior in Forming of Stir Casted Aluminium Boron Carbide Composite Perform during Cold Upsetting

The forming behavior of AA6061 boron carbide composites produced by stir casting process was investigated with the cold upsetting test. The composites containing 0%, 5%, 10% and 15% of B4Cp reinforcements were investigated with the cold upsetting test in Universal Testing Machine under tri-axial stress state condition. SEM images were taken to identify the presence of B4Cp particle in aluminium matrix. From the analysis, it was found that the hardness of composite was increased due to increasing amount of boron carbide particle in the composite and the density was decreased due to the lower value of density of boron carbide. The maximum true axial stress, true hoop stress and hydrostatic stress were gradually increased in the event of increasing order of B4Cp in the composites. Finally, it was found that in the stress – strain curve, the boron carbide was the main factor in improving the compressive strength of composites because of its high hardness.

Effect of TiO2 in aluminum matrix on workability behavior of powder metallurgy composites during cold upsetting

Abstract Aluminum-based metal matrix composites with various weight percentages (0, 2.5, 5, 7.5, and 10) of TiO2 reinforcement were synthesized by means of powder metallurgy and their workability behavior under triaxial stress-state conditions was completely studied during cold upsetting. Green cylindrical compacts were made using a 400 kN hydraulic press with suitable punch and die, sintered at (590 ± 10) °C for a period of 3 h, furnace cooled and machined to obtain samples with 0.5 aspect ratio. The cold upset tests were carried out in steps of 10 kN and the results were studied for the workability behavior of the composites. The formability stress index (β) and stress ratio parameters (σz/σeff), (σm/σeff), and (σθ/σeff) were calculated for all composites and correlated with true axial strain (∊ z ). It was observed that the addition of TiO2 to the Al matrix material increases the stress ratio parameters and formability stress index (β).

Study of Pore Closure Mechanism of Aluminium Composite Processed through Powder Metallurgy Route

Hot swaging experiments were carried out on as-sintered Al composite preforms in order to evaluate its pore closure characteristics. The effect of tungsten carbide and iron carbide in plain aluminium has been investigated under triaxial stress state condition. Cylindrical preforms with 0.5 aspect ratio and 88% fractional theoretical density have been produced for pure Al, Al-2WC and Al-2WC-4Fe3C through classical powder metallurgy route. Then, the as-sintered preforms are hot swaged to various height strains to further enclose the residual porosities; thereby to enhance density and mechanical properties. It is observed that induced strain substantially helped to close the porosities; however this largely depends on the reinforcing carbide particles in the Al-matrix.

Simulation studies on the densification behaviour of sintered aluminium preforms

The densification behavior of sintered aluminium has been investigated by performing simulation studies using DEFORM 2D software. The results have been compared with the experimental values. The deformation characteristics of the sintered preforms have been studied and the relationship between the various stresses such as true stress, true strain, hoop stress, hoop strain, hydrostatic stress, hydrostatic strain, effective stress, effective strain and relative density in both the experimental and simulations has been discussed for uniaxial, plane stress and triaxial stress state conditions. A good agreement is found between the experimental and simulation results.

Achieving a desirable combination of strength and workability in Al/SiC composites by AHP selection method

Aiming the selection of an Al/SiC composite with best combination of strength and workability, the analytical hierarchy process (AHP) method was applied. Several composites produced for a certain purpose, through powder metallurgy routes having different manufacturing parameters such as size and fraction of reinforcement, milling time and relative density were ranked by AHP method. The instantaneous density coefficient (Ai), instantaneous strain-hardening exponent (ni) and formability stress index (β) were measured under triaxial stress state conditions. AHP results revealed that Al/10wt.%SiC (16μm) with relative density of 95% and milled for 12h, was the preferred composite material. It was also concluded that the relative density of the composite was the most significant property which may affect the mechanical properties of the material.

Synthesis and Forming Behavior of&lt;i&gt; In Situ&lt;/i&gt; AA 7075 - TiC Composites

The forming behavior of a particulate reinforced AA 7075-TiC composite produced by in-situ stir casting process was investigated with cold upsetting test using graphite as lubricant. The prepared composites containing 0%, 4% and 8% of TiC reinforcement was completely investigated under tri-axial stress state condition. The various stress parameters were evaluated for all the above said composites and its variation with respect to axial strain was plotted, studied and discussed. Microstructural characterization of the composites was also done to study the distribution of the reinforcement in the metal matrix composite.

Effects of thickness and texture on mechanical properties anisotropy of commercially pure titanium thin sheets

Simultaneous effects of thickness and texture on the anisotropy of mechanical properties and fracture behaviors of commercially pure titanium thin sheets were studied. The activation of different deformation systems, due to the split distribution of basal texture, led to mechanical properties anisotropy. The crack initiation and propagation energies, when the loading direction was parallel to the initial rolling direction, decreased with increasing thickness ranges from 0.25 to 1mm. The changes of size, shape and distribution of dimples with increasing thickness confirmed the restriction of deformation systems and the development of triaxial stress state and plane-strain condition at the notch tip. However, in transverse-directed specimens, the energy release rate increased with increasing specimen thickness up to 0.75mm and then decreased. The fractography of these specimens explained the simultaneous effects of thickness and texture on structural stability and high accommodated plastic deformation at the notch tip.

Influence of carbon content on workability behavior in the formation of sintered plain carbon steel preforms

Complete experimental investigation on the workability behavior of sintered plain carbon steel cylindrical preforms with carbon contents of 0%, 0.35%, 0.75%, and 1.1%, under cold upsetting, has been studied in order to understand the influence of carbon content on the workability process. The abovementioned powder metallurgy sintered preforms with constant initial theoretical density of 84% and aspect ratio of 0.4 were prepared using a suitable die set assembly on a 1 MN capacity hydraulic press and sintered for 90 min at 1,200°C. Each sintered preform was cold upset under nil/no frictional constraint. Under triaxial stress state condition, densification, axial stress, hoop stress, hydrostatic stress, effective stress, and formability stress index against axial strain relationship were established and presented in this work. Further, attained density is considered to establish formability stress index and various stress ratio parameters’ behavior.

Workability studies on sintered Cu–10SiC preforms during cold axial upsetting

An investigation has been carried out for the determination of the workability behavior of Cu–10SiC composite under triaxial stress state condition. Cylindrical preforms with three different initial preform densities (namely 85%, 90% and 95% of the theoretical density), possessing aspect ratios of 0.60, 0.50 and 0.40 were prepared using a die and punch assembly with a 1.0MN capacity Universal Testing Machine (UTM). Then the preforms were sintered in a muffle furnace at a temperature of 850±10°C for a period of 1h. Based on the experimental results the phenomena like axial strain (εz), various stress ratio parameters, namely (σθ/σeff) and (σm/σeff), the formability stress index (βσ) under triaxial stress state conditions were systematically analysed. It was found that lower initial aspect ratio with higher initial relative density preforms exhibited enhanced formability stress index compared to higher aspect ratio with lower initial relative density preforms.