Prediction of ductile fracture initiation for powder metallurgical aluminum-copper preforms using FEM

Proceedings of the Institution of Mechanical Engineers, Part C:

Richard³

2021

In the present work, localised heating has been adopted at the damage site of the cold upset materials and the role of this mechanism on the workability has been analysed. Cylindrical specimens containing 96% aluminium and 4% titanium were prepared through powder metallurgy technique with an aspect ratio (height to diameter) of 1 by suitable pressures. A series of cold upsetting test was conducted and the material properties for various preforms initial relative densities (80%, 85% and 90%) were determined under the stable strain rate. The flow of metals was analysed using a finite element tool and it was observed that the metal flow starts from near the centre zone to the equatorial zone and the damage happens in the outer position because of more amount of accumulated stresses and the pores. These stresses and pores decrease the workability of the final component. Hence, the present research is intended to reduce the stresses and minimize the pores by applying a localized heating (100 °C–250 °C) at the equatorial sites of the components and thereby increasing the workability of the material. Also, heating selectively at the equatorial site of the workpiece improves the workability due to change in grain size and it was noticed that the grain size of the developed porous preforms was high for the higher heating conditions due to the growth of the grains. Therefore, the localized heating adopted in this work is a superior method to enhance the workability of the powder samples and this novel technique could be useful in improving the workability of the structural components that have extensive applications in the automobile and aerospace industries.

Section: Theoretical Calculationsmentioning

confidence: 97%

Section: Role Of Local Heating On Stress and Strain Ratio Parameter C...mentioning

confidence: 99%

Role of localized heating on the workability of powder metallurgical Al–4% Ti components in cold compression

Tharmaraj

Proceedings of the Institution of Mechanical Engineers, Part C:

Richard³

2021

“…Narayanasamy et al 35 proposed the formability strain parameter which is given by where e m and e eff are the mean and effective strain, respectively, calculated using equations (5) and (6). The pore closure rate index (P) is a function of formability strain index (b), relative density (R), strain hardening index (n) and strain rate sensitivity (m).…”

Section: Theoretical Calculationsmentioning

confidence: 99%

“…5 The occurrence of fracture is a major limitation to govern the forming limits of the components during the deformation process. 6,7 Gouveia et al 8 investigated the ductile fracture of lead alloy using various fracture criteria by conducting experimental work and compared the results with the finite element method during the metalworking process. In a metalworking process, formability can be achieved without the occurrence of a defect.…”

Section: Introductionmentioning

confidence: 99%

Influence of selective heating on strain-based formability and pore closure rate of sintered powder metallurgy preforms during upsetting

Tharmaraj

Proceedings of the Institution of Mechanical Engineers, Part B:

2019

An investigation on strain-based formability and pore closure rate of selectively heated sintered powder metallurgical aluminum–titanium composites has been carried out to evaluate the role of heating on the curing of stresses accumulated during mechanical working. Samples with an initial relative density of 90% and an aspect ratio of 1 were prepared through the powder metallurgy technique by applying suitable powder compaction pressures with different titanium contents such as 2%, 4% and 6%. A series of upsetting tests have been carried out on the prepared porous specimens using a 0.5 MN capacity hydraulic press and the failure zone was identified through the experimental work. It was found that failure occurs in the equatorial region of the workpiece due to the accumulation of stresses and the presence of higher amounts of pores. The magnitude of these accumulated stresses and the level of pores affect the formability of the components during cold upsetting. Therefore, there is a need to relieve the accumulated stresses and reduce the pores at the failure zone of the metals. Hence, this work is aimed at relieving the accumulated stresses, reducing the porosity amounts by adopting a novel mechanism of heating in the equatorial region of the samples for various temperatures such as 100 °C, 140 °C, 195 °C, 220 °C and 250 °C. As a result, the forming limit and pore closing rate were found to improve by selectively heating the specimens at locations where stresses have accumulated. Selectively heating this location relieves the accumulated stresses and decreases the number of pores present in the preforms, thereby enabling the metal to reach still higher strain levels before the onset of failure.

“…Wolla et al. 2 performed upsetting tests on Al%Cu preforms and estimated the fracture locus under different friction conditions. The experimental results confirmed the improved fracture limits with an increase in the relative density and size of the cylinder followed by decrease in the friction.…”

Section: Introductionmentioning

confidence: 99%

Analysis of anisotropy in the upsetting process of AA2014 cast alloy embedded with fly ash

Krishna¹,

Dumpala

Proceedings of the Institution of Mechanical Engineers, Part C:

et al. 2020

Developing new metal matrix composites for a wide variety of applications and analyzing the formability aspects are challenging in the area of manufacturing. In the current study, solid cylindrical samples with AA2014 as matrix material and fly ash as reinforcement were used for the investigation. AA2014 was heated to a pouring temperature of 750 ℃ and the preheated fly ash was added to the molten AA2014 in different compositions. The whole mixture was stirred to prepare composite rods of AA2014, AA2014 + 3% fly ash and AA2014 + 6% fly ash. Each set of cylindrical samples were compressed between a set of dies till fracture by employing grease, white grease and no lubrication conditions. The varying friction conditions and composition influence the anisotropy of the billets at fracture. Empirical equations were modeled to investigate the effect of anisotropy on the stress trixiality and fracture strain at the onset of fracture. The developed equation is useful in estimating critical damage constants for any material and for any lubrication condition. A correlation between damage anisotropy factor, damage constant and fracture strain was established to understand the formability limits for different anisotropy coefficients.