Alexei Volkov
In physics, plasticity is a solid material's ability to undergo irreversible deformation in response to applied forces. This is also known as plastic deformation. Concrete is an example of a brittle material, and its plasticity is caused by slip at microcracks. In recent years, research has increased on the nonlinear analysis of reinforced concrete structures, with several mathematical models being created to analyze the behaviour of concrete and its reinforcements.
| Characteristics | Values |
|---|---|
| Definition | Plasticity is the ability of a solid material to undergo permanent deformation, a non-reversible change of shape in response to applied forces. |
| Cause in concrete | Predominantly by slip at microcracks |
| Failure mechanisms | Tensile cracking and compressive crushing of the concrete material |
| Compressive strength | Approximately 20 MPa (2850 lb/in2) for typical construction concrete and 40 MPa (5700 lb/in2) for high-strength concrete |
| Concrete plasticity models | Elasticity, plasticity, continuum damage mechanics, plastic fracturing, endochronic theory, microplane models, phenomenological models, homogenization models, Plastic Damage Model (PDM) |
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What You'll Learn
Plastic deformation
In physics and materials science, plasticity, or plastic deformation, is the ability of a solid material to undergo permanent, non-reversible deformation in response to applied forces. This is observed in most materials, including metals, soils, rocks, concrete, and foams.
In the context of 3D-printed concrete, plastic deformation can occur due to the absence of formwork, resulting in plastic shrinkage and plastic settlement. Plastic shrinkage refers to the shrinkage that occurs during the plastic or fresh stage of concrete, mainly driven by negative capillary pressure caused by water loss. Plastic settlement refers to the vertical deformation caused by gravitational loads during the plastic stage.
The plastic response of reinforced concrete slabs can be analysed through the flow theory of rigid-plastic bodies, considering load-deflection relations and membrane effects at large deflections. This helps understand the behaviour of concrete structures under various loading conditions and contributes to the overall understanding of plastic deformation in concrete.
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Concrete damage plasticity (CDP) model
In physics and materials science, plasticity is the ability of a solid material to undergo irreversible deformation, a permanent and non-reversible change of shape in response to applied forces. In brittle materials such as concrete, this is caused by slip at microcracks.
Concrete is a composite material that displays complex behaviour under various loading conditions due to its heterogeneous nature. Its nonlinear characteristics are due to the presence of cracks, voids, and the interactions between its components. As such, modelling the behaviour of concrete under loading is a significant challenge in structural engineering.
The Concrete Damage Plasticity (CDP) model in Abaqus is a powerful tool for simulating the behaviour of concrete. It combines concepts of plasticity and damage to predict the cracking, softening, and gradual deterioration of concrete under different loading scenarios. This enables engineers to make more accurate predictions about concrete behaviour and achieve optimal designs.
The CDP model captures the anisotropic and quasi-brittle nature of concrete, exhibiting different responses under tensile and compressive stresses. It is derived from the Drucker-Prager model for concrete behaviour, with the main formulation represented by an equation and visualised in 3D. The CDP model has been modified and improved over time, with studies focusing on high-strength concrete under static and dynamic loading conditions. These modifications consider the effect of mesh size and use exponential functions to present tensile damage variables.
The reliability of the CDP model has been tested through numerical simulations and Split-Hopkinson pressure bar (SHPB) tests, showing acceptable agreement with experimental results and high reliability.
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Plasticity in reinforced concrete
In physics and materials science, plasticity is the ability of a solid material to undergo irreversible deformation, a permanent and non-reversible change of shape in response to applied forces. Brittle materials like concrete tend to display plasticity due to slip at microcracks.
Concrete is a widely used construction material, and understanding its plasticity is crucial for structural analysis and design. Reinforced concrete structures are commonly used in construction, combining concrete with steel bars or fibres to enhance its strength and durability.
The book "Plasticity in Reinforced Concrete" by Wai-Fah Chen offers a comprehensive treatment of the mathematical models used in reinforced concrete structural analysis. It covers a range of topics, including stress and strain characteristics of concrete under various load conditions, concrete elasticity, failure criteria, and applications of limit analysis and finite element analysis.
One of the key challenges in reinforced concrete is managing cracking and crushing problems. Different techniques are employed to address fracture issues, ensuring the structural integrity and longevity of reinforced concrete structures.
Additionally, the plasticity of reinforced concrete is influenced by factors such as deformation speed and prior deformation. The rate of deformation is typically proportional to the applied stress, and materials deformed by prior processes, such as cold forming, may require higher stresses for further deformation.
Overall, the plasticity of reinforced concrete is a complex topic that involves the interplay of various factors. It is a critical aspect of structural engineering, and ongoing research and mathematical modelling aim to enhance our understanding and optimise the use of reinforced concrete in construction.
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Plastic deformation in crystalline materials
Plasticity, or plastic deformation, is the ability of a solid material to undergo irreversible deformation in response to applied forces. This is a common phenomenon observed in most materials, including metals, soils, rocks, concrete, and foams.
In crystalline materials, plastic deformation occurs due to the movement of dislocations within the crystal lattice. Dislocations are defects in the lattice structure that allow atoms to slide past each other more easily than in a perfect crystal. When external stress is applied, these dislocations move through the lattice, facilitating plastic deformation. The presence of dislocations also increases the likelihood of planes slipping past each other, resulting in a permanent change of shape within the crystal.
There are two primary modes of deformation in a crystal lattice: slip and twinning. Slip is a shear deformation where atoms move through multiple interatomic distances relative to their initial positions. It is the most common mode of plastic deformation, with dislocations moving along specific planes and directions known as slip planes and slip directions. The choice of slip system is influenced by the crystal structure; for example, Face-Centered Cubic (FCC) crystals have multiple slip systems, making them highly ductile.
Twinning, on the other hand, is a plastic deformation that occurs along two planes due to a set of forces applied to a given metal piece. It is less common than slip but can be significant in certain materials. Twinning involves a portion of the crystal lattice shifting to create a mirrored region of the crystal structure.
The plastic deformation of crystalline materials is influenced by various factors such as temperature, strain rate, material composition, and microstructure. Elevated temperatures generally increase the mobility of dislocations, making the material more ductile and easier to deform plastically. The presence of alloying elements and impurities can also impact plastic deformation by hindering dislocation movement or providing additional slip systems. The size, shape, and distribution of grains and phases within the material's microstructure can further influence its plastic behaviour.
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Plastic behaviour in soils
In physics and materials science, plasticity is the ability of a solid material to undergo permanent deformation—a non-reversible change of shape in response to applied forces. Plastic deformation is observed in most materials, including soils.
Inelastic deformations of rocks and concrete are primarily caused by the formation of microcracks and sliding motions relative to these cracks. This is also true for other brittle materials such as bone. In contrast, plasticity in ductile metals is caused by tensile loading, which causes elastic behaviour until a threshold—the yield strength—is exceeded, resulting in permanent deformation.
Soils, like other materials, can exhibit perfect plasticity, undergoing irreversible deformation without any increase in stresses or loads. Materials that have been hardened by prior deformation, such as cold forming, may require higher stresses to deform further. The plasticity of a material is directly proportional to its ductility and malleability.
Plastic contamination in agricultural soils has become a global issue, with plastic particles ending up in the soil through various human activities. These plastic particles can break down into microplastics and nanoparticles, which can have toxic effects on organisms and disrupt the soil ecosystem. They can also act as vectors for diseases in the environment and enter the food chain, potentially affecting both human and animal health.
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Frequently asked questions
Plasticity is the ability of a solid material to undergo permanent deformation, a non-reversible change of shape in response to applied forces.
In brittle materials such as concrete, plasticity is caused predominantly by slip at microcracks. Inelastic deformations of concrete are primarily caused by the formation of microcracks and sliding motions relative to these cracks.
Perfect plasticity is a property of materials to undergo irreversible deformation without any increase in stresses or loads.
A concrete damage plasticity (CDP) model is used to replicate the plastic behaviour of concrete elements. It is used to analyse the behaviour of unconfined concrete.
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