Creep Damage Mechanics and Micromechanisms

Ashby, Michael F.; Dyson, B. F.

doi:10.1016/b978-1-4832-8440-8.50017-x

Cited by 153 publications

(79 citation statements)

References 38 publications

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“…20 In the present case of TSP in coarse-grained Ti-6Al-4V, almost no cavitation damage was detected (Fig. 3), and all of the specimens were pulled to failure at a fine point.…”

Section: Tensile Creep and Tsp Fracturementioning

confidence: 90%

Tensile fracture during transformation superplasticity of Ti–6Al–4V

Schuh¹,

Dunand

2001

J. Mater. Res.

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During thermal cycling through the ␣-␤ phase transformation under the action of a small external biasing stress, Ti alloys exhibit an average deformation stress exponent of unity and achieve superplastic strains. We report tensile experiments on Ti-6Al-4V with an applied stress of 4.5 MPa, aimed at understanding the failure processes during transformation superplasticity. The development of cavities was assessed as a function of superplastic elongation, and macroscopic neck formation was quantified at several levels of elongation by digital imaging techniques. The effects of thermal inhomogeneity on neck initiation and propagation were also elucidated experimentally. Tensile ductility during transformation superplasticity is compared with that during isothermal creep at the average, effective cycling temperature, and a numerical model is used to show the effect of thermal gradients in limiting superplastic elongation.

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“…20 In the present case of TSP in coarse-grained Ti-6Al-4V, almost no cavitation damage was detected (Fig. 3), and all of the specimens were pulled to failure at a fine point.…”

Section: Tensile Creep and Tsp Fracturementioning

confidence: 90%

Tensile fracture during transformation superplasticity of Ti–6Al–4V

Schuh¹,

Dunand

2001

J. Mater. Res.

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“…It has been termed mobile dislocation strainsoftening (Othman et al, 1993) and is shown schematically in Figure 1(a). Creep in these materials is therefore not controlled by dislocation recovery but is best thought of in terms of the kinetics of dislocation multiplication and subsequent motion (Ashby and Dyson, 1984a). By treating the velocity of dislocation around 0 particles as one of diffusive drift-whose spacing is very much less than that of the dislocations, secondary and tertiary creep in superalloys under various loading conditions can be modeled by the introduction of mobile dislocation damage.…”

Section: Damage Due To Multiplication Of Mobile Dislocationsmentioning

confidence: 99%

A Review on Damage Mechanisms, Models and Calibration Methods under Various Deformation Conditions

Lin

Liu

Dean

2005

International Journal of Damage Mechanics

143

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The development of microdamage under the deformation conditions of high temperature creep, cold metal forming, superplastic forming, and hot metal forming has been reviewed and discussed, and typical constitutive equations developed to model the individual damage mechanisms are summarized. Based on the microstructural analysis of the key damage features for metallic materials under a wide range of deformation conditions, a set of schematic diagrams is designed to illustrate the major types of damage mechanisms. This helps researchers and engineers to understand the major cause of failure of materials under different deformation conditions and to select simple and appropriate mechanism-based damage equations to predict the damage evolution. Further discussions are carried out on the dominant damage mechanisms in hot metal forming conditions and it is concluded that the dominant damage mechanism can be 'grain boundary (creeptype) damage' or 'plasticity-induced (ductile) damage' depending on the material microstructure and deformation rate. In the case of grain boundary damage in hot forming, the shape of microdefects is different from those in high temperature creep and superplastic forming although all of those result in intergranular failure of materials. Furthermore, damage calibration techniques for different conditions of plastic deformation are summarized and discussed.KEY WORDS: damage mechanisms, damage calibrations, creep and viscoplasticity, cold and hot metal forming.

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“…[20] Theoretical calculation has predicted that when λ ranges from about 1-2.5, grain-boundary cavities and cracks attribute significantly to tertiary creep and final rupture. [55] In the present study, the λ values ranged between 1.4 and 2.5, which implies that grain boundary cavities and cracks may play an important role in the creep rupture. The in-situ observations confirmed that grain boundary cavities were present in the tertiary creep stage.…”

Section: Creep Rupture Mechanismsmentioning

confidence: 93%

Creep and Fracture Behavior of Peak-Aged Mg-11Y-5Gd-2Zn-0.5Zr (wt pct)

Yin

Wang

Boehlert

et al. 2012

Metall Mater Trans A

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The tensile-creep and creep-rupture behavior of heat-resistant peak-aged Mg-11Y-5Gd-2Zn-0.5Zr (wt.%) (WGZ1152) was investigated at T=523-598K (0.58-0.66T m ) and stresses between 30MPa to 140MPa. The minimum creep rate of the alloy was almost two orders of magnitude lower than that for WE54-T6, and was comparable to that for HZ32-T5. The creep behavior exhibited an extended tertiary creep stage, which was believed to be associated with precipitate coarsening. The creep stress exponent value was 4.5, suggesting that dislocation creep was the rate-controlling mechanism. The activation energy for creep (221±20kJ/mol) was higher than that for self-diffusion in magnesium, and was believed to be associated with the activation of non-basal slip and cross slip. This was consistent with the surface deformation observations, which revealed a transition from basal slip to non-basal slip and cross slip with increasing temperature. The minimum creep rate and rupture time followed the original and modified Monkman-Grant relationships. The microcracks and cavities preferentially nucleated at grain boundaries and at the interface between Mg matrix and the second phase. In-situ creep experiments highlighted the intergranular cracking evolution.

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Creep Damage Mechanics and Micromechanisms

Cited by 153 publications

References 38 publications

Tensile fracture during transformation superplasticity of Ti–6Al–4V

Tensile fracture during transformation superplasticity of Ti–6Al–4V

A Review on Damage Mechanisms, Models and Calibration Methods under Various Deformation Conditions

Creep and Fracture Behavior of Peak-Aged Mg-11Y-5Gd-2Zn-0.5Zr (wt pct)

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