COMSOL 6.4 - Concrete Damage–Plasticity Material Tests

Concrete Damage–Plasticity Material Tests

This example shows the behavior of the coupled damage–plasticity model for concrete when subjected to different loading conditions. Several material tests that are commonly used to characterize concrete are set up for this purpose

For details on the coupled damage–plasticity material model, see the section Coupled Damage–Plasticity in the Structural Mechanics Module User’s Guide, and Ref. 1 and Ref. 2.

Model Definition

The feature is used to test the material model when subjected to different loading conditions. Hence no specific geometry is required for the base component of the model. Concrete is, however, a so-called quasibrittle material which means that its response is size dependent, especially in tension. The size of the test specimen used by is therefore important for the tests to give representative results. Here a characteristic size of 0.1 m is used.

In total six different tests are set up:

Uniaxial compression

Uniaxial tension

Biaxial compression, with a biaxiality ratio of 0.5

Isotropic (triaxial) compression

Uniaxial cyclic loading (tension to compression to tension)

Uniaxial cyclic loading (compression to tension)

A generic set of material proprieties are used for the concrete, (see Table 1), but the model can be used to verify the model response for other properties as well. Note that these material properties are sufficient to define the model parameters of the coupled damage–plasticity model, but there are many more parameters available to modify the response of the material model that are here kept equal to their default value.

Table 1: Material properties of the concrete.
Material property	Symbol	Value
Young’s modulus	E	25 GPa
Poisson’s ratio	ν	0.2
Compressive strength	σuc	20 MPa
Tensile strength	σut	2 MPa
Fracture energy	Gft	100 J/m2

Results and Discussion

Figure 1 shows the results of the first two tests. The characteristic anisotropy of concrete in compression versus tension is clearly observable.

Figure 1: Stress versus strain for concrete subjected to monotonic uniaxial loading.

Results from the biaxial compression test are shown in Figure 2, which shows the stress in the main loading direction versus all three normal components of the strain tensor.

Figure 2: Stress versus strain for concrete subjected to monotonic biaxial compression.

Results from the isotropic compression test are shown in Figure 3, where it is clearly visible that the model response is ductile. The transition from a quasibrittle to a ductile response as the stress state goes toward isotropic compression is an important characteristic of concrete subjected to severe loading.

Figure 3: Stress versus strain for concrete subjected to monotonic isotropic compression.

Figure 4 and Figure 5 show results from the two cyclic tests. It is clearly visible how the response during cyclic loading deviates from the monotonic stress versus strain curve since there is irreversible deformation. In Figure 4 one can also note that all available plastic deformation occurs when the specimen is loaded in tension and starts to crack. Hence, there is no plastic hardening when the stress is reversed to compression; instead the response is “elastic” until softening starts.

Figure 4: Stress versus strain for concrete subjected to cyclic uniaxial loading going tension to compression and back to tension. The dotted black curve shows the stress versus strain for monotonic loading.

Figure 5: Stress versus strain for concrete subjected to cyclic uniaxial loading going from compression to tension. The dotted black curve shows the stress versus strain for monotonic loading.

References

1. P. Grassl and M. Jirásek, “Damage-plastic model for concrete failure,” Int. J. Solids Struct., vol. 43, pp. 7166–7196, 2006.

2. P. Grassl, D. Xenos, U. Nyström, R. Rempling, and K. Gylltoft, “CDPM2: A damage-plasticity approach to modelling the failure of concrete,” Int. J. Solids Struct., vol. 50, pp. 3805–3816, 2013.

Geomechanics_Module/Verification_Examples/concrete_damage_plasticity

Modeling Instructions

From the menu, choose .

New

In the window, click

Model Wizard

In the window, click

In the tree, select > .

In the toolbar, click

Solid Mechanics (solid)

Linear Elastic Material 1

In the window, under > click .

Concrete 1

In the toolbar, click

and choose .

In the window for , locate the section.

From the list, choose .

Add Material

In the toolbar, click

to open the window.

Go to the window.

In the tree, select > .

Click the button in the window toolbar.

In the toolbar, click

to close the window.

Materials

Concrete (mat1)

In the window for , locate the section.

In the table, enter the following settings:


Property	Variable	Value	Unit	Property group
Tensile strength	sigmaut	2[MPa]	Pa	Yield stress parameters
Compressive strength	sigmauc	20[MPa]	Pa	Yield stress parameters
Tensile fracture energy	Gft	100[J/m^2]	J/m²	Fracture parameters