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Experimental investigation and modelling of hot forming B₄C/AA6061 low volume fraction reinforcement composites

Zheng K., Lin J., Wu G., Hall R. W., Dean T. A.

Journal of Theoretical and Applied Mechanics

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2018

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Vol. 56 nr 2

457--469

EN

This paper presents an experimental investigation of the hot deformation behaviour of 15% B₄C particle reinforced AA6061 matrix composites and the establishment of a novel corresponding unified and physically-based visco-plastic material model. The feasibility of hot forming of a metal matrix composite (MMC) with a low volume fraction reinforcement has been assessed by performing hot compression tests at different temperatures and strain rates. Examination of the obtained stress-strain relationships revealed the correlation between temperature and strain hardening extent. Forming at elevated temperatures enables obvious strain rate hardening and reasonably high ductility of the MMC. The developed unified material model includes evolution of dislocations resulting from plastic deformation, recovery and punching effect due to differential thermal expansion between matrix and reinforcement particles during non-steady state heating and plastic straining. Good agreement has been obtained between experimental and computed results. The proposed material model contributes greatly to a more thorough understanding of flow stress behaviour and microstructural evolution during the hot forming of MMCs.

2

On micro-damage in hot metal working. P. 2 Constitutive modelling

Lin J., Foster A. D., Liu Y., Farrugia D. C., Dean T. A.

Engineering Transactions

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2007

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Vol. 55, iss. 1

43-60

EN

Damage constitutive equations are formulated to model the evolution of grain boundary and plasticity-induced damage for free-cutting steels under hot forming conditions. During high temperature, high strain rate deformation, material degradation has characteristics of both creep damage at grain boundaries, and ductile damage surrounding hard inclusions. This has been experimentally observed and is reported in the companion paper. This paper describes the development of unified viscoplastic-damage constitutive equations, in which the nucleation and growth of both damage types are considered independently. The effects of deformation rate, temperature, and material microstructure on damage evolution are modelled. The proposed damage evolution equations are combined with a viscoplastic constitutive equation set, enabling the evolution of dislocation hardening, recovery, recrystallisation, grain size, and damage to be modelled. This set of unified, mechanism-based, viscoplastic damage constitutive equations is determined from experimental data of a freemachining steel for the temperature range 1173- 1373 K. The fitted model is then used to predict damage and failure features of the same material tested using a set of interrupted constant strain rate tests. Close agreement between the predicted and experimental results is obtained for all the cases studied.

3

On micro-damage in hot metal working. Part 1: Experimental investigation

Liu Y., Foster A. D., Lin J., Farrugia D. C. J., Dean T. A.

Engineering Transactions

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2006

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Vol. 54, iss. 4

271-287

EN

An experimental programme was defined and performed to investigate the characteristics of micro-damage for a plain CMn and a free machining steel under hot forming conditions. To investigate damage locations - at grain boundaries and around second phase inclusions - a series of constant strain rate tests were carried out on the free machining steel, which contained manganese sulphide inclusions. Specimens from both materials were strained to failure under tension using a Gleeble material simulator at a constant temperature of 1273 K, with strain rates = 0.01-10 s-1. The damage characteristics of the two different steel microstructures was analysed through microstructural examinations of the tested specimens. Particular attention is focussed on damage locations and features. To investigate the recovery of materials between the intervals of hot deformation, a series of two-step tensile tests were carried out at 1273 K and 10 s-1. The two-step specimens were initially deformed to a strain varying from 0.3-0.7, held for varying recovery periods of 0.3-10 s, then stretched to failure. Flow stress features and strains to failure during the second stage of deformation were analysed with respect to different recovery periods and strain levels at the first stage of deformation. The damage features discovered from the experimentation and microstructural examination provide theoretical evidence to form unified viscoplastic damage constitutive equations for hot forming of free machining steels, which are described in the companion paper.