The analysis of instability and strain concentration during superplastic deformation

Chung, Li Chuan; Cheng, Jung-Ho

doi:10.1016/s0921-5093(00)01983-3

Cited by 9 publications

(13 citation statements)

References 16 publications

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“…C cr is not a material constant, since it depends on the constitutive equation and using a double power law equation, for example, makes it depend also on strain-rate. However, the C cr value determined here using the Dunne et al equation set is similar in value to that of [3] at 900 o C. 3. Fig 3 shows that both void growth models give predictions consistent with the failure of the 5×10 -3 s -1 case and the successful forming of the 1×10 -3 s -1 case.…”

Section: Resultssupporting

confidence: 61%

“…The value arrived at for C cr for Ti-6Al-4V was 2.939 at 900 o C, using constitutive equation with constants corresponding (presumably) to the target (optimum) strain rate for the forming process, although this information was not provided. The FLF approach has been implemented here in a CREEP user subroutine in ABAQUS, following [3]. …”

Section: Failure Modelsmentioning

confidence: 99%

“…it was shown that the deformation SPF deformation has been presented by Chung and Cheng[3], based on an instability criterion developed by Ding et al[4]. Ding et al considered a thin superplastic sheet under biaxial stretching and, using a procedure analogous to that of Marciniak and Kuczynski[5], analysed the conditions under which a local neck, assumed to form perpendicular to the major principal stress, σ 1 , becomes unstable.…”

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confidence: 99%

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A comparison of failure prediction methods for superplastic deformation

2008

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Section: Resultssupporting

confidence: 61%

Section: Failure Modelsmentioning

confidence: 99%

mentioning

confidence: 99%

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A comparison of failure prediction methods for superplastic deformation

2008

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“…The first one consists of the use of Hart's stability criterion, which defines the stability of deformation as function of a strain hardening coefficient and the strain rate sensitivity [57,58]. Chung and Cheng [61,62] expanded this approach by developing a flow localisation factor to propose a fracture criterion which could be used for the design of optimal superplastic forming cycles. The second approach involves the use of classical forming limit diagrams (FLDs).…”

Section: Superplastic Formingmentioning

confidence: 99%

Superplasticity in Ti–6Al–4V: Characterisation, modelling and applications

2015

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The processing regime relevant to superplasticity in the Ti-6Al-4V alloy is identified. The effect is found to be potent in the range 850-900°C at strain rates between 0.001/s and 0.0001/s. Within this regime, mechanical behaviour is characterised by steady-state grain size and negligible cavity formation; electron backscatter diffraction studies confirm a random texture, leaving grain-boundary sliding as the overarching deformation mechanism. Outside of the superplastic regime, grain size refinement involving recrystallisation and the formation of voids and cavities cause macroscopic softening; low ductility results. Stress hardening is correlated to grain growth and accumulation of dislocations. The findings are used to construct a processing map, on which the dominant deformation mechanisms are identified. Physically-based constitutive equations are presented which are faithful to the observed deformation mechanisms. Internal state variables are used to represent the evolution of grain size, dislocation density and void fraction. Material constants are determined using genetic-algorithm optimisation techniques. Finally, the deformation behaviour of this material in an industrially relevant problem is simulated: the inflation of diffusion-bonded material for the manufacture of hollow, lightweight structures.

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“…Several investigators used this expression to predict thinning and rupture without success. Since the parts formed using SPF have complex geometries, where analytical expressions for the forming pressure are not available, the attention of researchers was shifted towards finite element (FE) analysis to generate forming pressure profiles (Ref [6][7][8][9][10][11][12]. The FE simulation of superplastic forming is a complex problem which involves highly non-linear aspects such as large deformation, history-dependent material behavior, and long forming durations.…”

Section: Introductionmentioning

confidence: 99%

The Effects of Stress State and Cavitation on Deformation Stability During Superplastic Forming

Nazzal

Khraisheh

2007

J. of Materi Eng and Perform

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The current available models describing superplastic deformation do not account for a number of important characteristics, leading to the current limited predictive capabilities of deformation and failure. In this work, the effects of cavitation and stress state on deformation stability during superplastic forming are investigated using Finite Element simulations. The simulations are performed using constant strain rate forming and using a proposed optimization approach based on a multiscale failure criterion that accounts for stress state, geometrical necking, and microstructural evolution including grain growth and cavitation. The simulations are conducted for the superplastic copper-based alloy Coronze-638 and the superplastic aluminum alloy Al-5083 which are known to develop significant cavitation during deformation. The results clearly show the importance of accounting for microstructural evolution during superplastic forming, especially when the state of stress is biaxial. Furthermore, the results highlight the effectiveness of the proposed optimization technique in reducing the forming time and maintaining the integrity of the formed parts.

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The analysis of instability and strain concentration during superplastic deformation

Cited by 9 publications

References 16 publications

A comparison of failure prediction methods for superplastic deformation

A comparison of failure prediction methods for superplastic deformation

Superplasticity in Ti–6Al–4V: Characterisation, modelling and applications

The Effects of Stress State and Cavitation on Deformation Stability During Superplastic Forming

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