A Novel Continuum Damage Constitutive Model for Predicting the Formability of AA7075 Alloy at Elevated Temperatures

Creep properties both in hot hydrogen and in air of a vanadium-modified CrMo steel 2.25Cr1Mo0.25V, widely used in hydroprocessing reactors in petrochemical industry, were investigated to determine the effect of hydrogen on high-temperature creep behavior of the low-alloy ferritic steel. The minimum creep strain rate in hydrogen is higher than that in air, whereas the creep strain at failure in hydrogen is relatively smaller. Many tiny spherical cavities are dispersively distributed in the ruptured specimen under hydrogen, which has relatively higher Vickers hardness. Based on the thermodynamics theory, the pressure of methane generated by the so-called “methane reaction” in the vanadium-modified CrMo steel can be calculated by using corresponding thermodynamic data, assuming that methane can reach its equilibrium state during cavitation. Meanwhile, a creep constitutive model based on continuum damage mechanics (CDM) was proposed, taking methane pressure into consideration. The results show that methane pressure increases nonlinearly with increase of hydrogen pressure while it decreases gradually with increase of temperature. The constitutive model considering the damage induced by methane pressure can be used to predict the effect of hydrogen pressure and temperature on creep life, indicating that the influence of hydrogen at elevated temperatures becomes smaller when increasing temperature or decreasing hydrogen pressure.

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Behavior of Chinese Dahurian Larch Wood after High-Temperature Exposure: Degradation of Mechanical Properties and Damage Constitutive Model

Advances in Materials Science and Engineering ◽

10.1155/2018/8614740 ◽

2018 ◽

Vol 2018 ◽

pp. 1-10

Author(s):

Qifang Xie ◽

Lipeng Zhang ◽

Zhenglei Yang ◽

Long Wang ◽

Yaopeng Wu

Keyword(s):

Mechanical Properties ◽

Tensile Strength ◽

Compressive Strength ◽

Shear Strength ◽

Constitutive Model ◽

Elevated Temperatures ◽

Dahurian Larch ◽

Water Cooling ◽

Residual Compressive Strength ◽

Damage Constitutive Model

Wood has been extensively used in Chinese ancient buildings, and it is important to clearly understand the mechanical properties of wood after exposure to elevated temperatures. In this paper, three kinds of tests with 102 clear wood specimens fabricated with Chinese Dahurian larch for each kind of test were conducted. The residual compressive strength, tensile strength, and shear strength parallel to grain of specimens after exposure to different temperatures (100°C, 150°C, 200°C, and 250°C) with various exposure times (15 min, 30 min, and 45 min) and different cooling methods (natural cooling and water cooling) were obtained. Results indicate that exposure to elevated temperatures causes great degradation of compressive strength, tensile strength, and shear strength parallel to grain. When the exposure temperatures exceed 200°C, the relative compressive strength, tensile strength, and shear strength parallel to grain decrease greatly with the increase of exposure time. The residual compressive strength, tensile strength, and shear strength of specimens after water cooling are lower than that after natural cooling. Exposure temperatures also have a great impact on the weight loss and color change of wood. Based on the test data, degradation models for the residual compressive strength, tensile strength, and shear strength of wood were developed. Furthermore, the damage constitutive model of compressive (CDMC) and tensile (CDMT) parallel to grain was established and validated reasonably by tests.

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On the Kachanov-Rabotnov continuum damage model

Rakenteiden Mekaniikka ◽

10.23998/rm.82528 ◽

2020 ◽

Vol 53 (2) ◽

pp. 125-144

Author(s):

Harm Askes ◽

Juha Hartikainen ◽

Kari Kolari ◽

Reijo Kouhia ◽

Timo Saksala ◽

...

Keyword(s):

Free Energy ◽

Constitutive Model ◽

Tensile Test ◽

Helmholtz Free Energy ◽

Damage Model ◽

Continuum Damage ◽

Dissipation Potential ◽

Continuum Damage Model ◽

Damage Constitutive Model ◽

Basic Features

In this paper two partially complementary formulations of the simple phenomenological Kachanov-Rabotnov continuum damage constitutive model are presented. The models are based on a consistent thermodynamic formulation using proper expressions for the Helmholtz free energy or its complementary form of the dissipation potential. Basic features of the models are discussed and the behaviour in tensile test and creep problems is demonstrated.

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Constitutive Description for Drawing Limit of Magnesium Alloy Tube Based on Continuum Damage Mechanics

Materials Science Forum ◽

10.4028/www.scientific.net/msf.610-613.951 ◽

2009 ◽

Vol 610-613 ◽

pp. 951-954 ◽

Cited By ~ 4

Author(s):

Ying Tong ◽

Guo Zheng Quan ◽

Bin Chen

Keyword(s):

Magnesium Alloy ◽

Constitutive Model ◽

Damage Mechanics ◽

Continuum Damage Mechanics ◽

Plastic Behavior ◽

Continuum Damage ◽

Rigid Plastic ◽

Alloy Tube ◽

Limit Graph ◽

Damage Constitutive Model

The elasto-plastic behavior and the drawing limit of a kind of magnesium alloy tube were investigated based on the foundational theories of the larger deformation of material and continuum damage constitutive model. The corresponding finite element numerical algorithm was developed based on the constitutive model. The non-mandrel drawing limit graph according to the diameter at different tube thickness of an AZ31B tube with diameter 10mm at 250°C and drawing velocity 100mm/s was achieved, and safe & unsafe area got partitioned. The maximum damage value was evaluated to be 0.324 according to height reduction ratio limit and rigid-plastic FE analysis.

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An Improved Continuum Damage Constitutive Model for Creep Deformation of Cast 20Cr32Ni1Nb Steel

Volume 5: High-Pressure Technology; ASME Nondestructive Evaluation, Diagnosis and Prognosis Division (NDPD); SPC Track for Senate ◽

10.1115/pvp2017-65583 ◽

2017 ◽

Author(s):

Xiaofeng Guo ◽

Jianming Gong ◽

Luyang Geng

Keyword(s):

Constitutive Model ◽

Creep Damage ◽

Aging Treatment ◽

Continuum Damage ◽

Variable Theory ◽

Centrifugally Cast ◽

Proposed Model ◽

Damage Constitutive Model ◽

Life Predictions

An improved continuum damage constitutive model is presented to describe the creep behavior of centrifugally cast 20Cr32Ni1Nb stainless steel. In order to determine the internal softening mechanisms of the steel, microstructural observations of damage in 20Cr32Ni1Nb steel are made using the long-term iso-thermal aging treatment. Based on the physics of microstructural processes, a two state variable theory which represents two damage mechanisms related to particle coarsening and microcrack is employed to account for tertiary creep. The kinetic equation which describes the coarsening of the precipitates with time is coupled with Liu-Murakami creep damage constitutive model. Good agreement between predicted and experimental data proves the validity of the proposed model. Compared with the failure times predicted by power law based models, such as Kachanov-Robotnov and Liu-Murakami model, life predictions based on the proposed model are found to be more reasonable over a wide stress range. Additionally, the proposed model is also applied to analyze the accumulation and development of damage in 20Cr32Ni1Nb manifold components.

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