Nonlocal smeared rotating crack model with transition to scalar damage - RCSDNL

Implementation of nonlocal version of smeared rotating crack model with transition to scalar damage. Improves the classical rotating model (see section 1.5.2) by introducing the transition to scalar damage model in later stages of tension softening. The improved RC-SD (see section 1.5.3) is further extended to a nonlocal formulation, which not only acts as a powerful localization limiter but also alleviates mesh-induced directional bias. A special type of material instability arising due to negative shear stiffness terms in the rotating crack model is resolved by switching to SD mode. A bell shaped nonlocal averaging function is used.

Virgin material is modeled as isotropic linear elastic material (described by Young modulus and Poisson ratio). The onset of cracking begins, when principal stress reaches tensile strength. Further behavior is then determined by exponential softening law.

The transition to scalar damage model takes place, when the softening stress reaches the specified limit or when the loss of material stability due to negative shear stiffness terms that may arise in the standard RCM formulation, which takes place when the ratio of minimal shear coefficient in stiffness to bulk material shear modulus reaches the limit.

Multiple cracks are allowed. The elastic unloading and reloading is assumed. In compression regime, this model correspond to isotropic linear elastic material. The model description and parameters are summarized in Tab. 22.

Table 22: RC-SD-NL model for concrete - summary.

Description	Nonlocal smeared rotating crack model with transition to scalar damage for concrete
Record Format	RCSDNL d(rn) # E(rn) # n(rn) # Ft(rn) # sdtransitioncoeff(rn) # sdtransitioncoeff2(rn) # r(rn) # tAlpha(rn) #
Parameters	- num material model number
	- d material density
	- E Young modulus
	- n Poisson ratio
	- ef deformation corresponding to fully open crack
	- Ft tension strength
	- sdtransitioncoeff determines the transition from RC to SD model. Transition takes place when ratio of current softening stress to tension strength is less than sdtransitioncoeff value
	- sdtransitioncoeff2 determines the transition from RC to SD model. Transition takes place when ratio of current minimal shear stiffness term to virgin shear modulus is less than sdtransitioncoeff2 value
	- r parameter specifying the width of nonlocal averaging zone
	- tAlpha thermal dilatation coefficient
	- regionMap map indicating the regions (currently region is characterized by cross section number) to skip for nonlocal avaraging. The elements and corresponding IP are not taken into account in nonlocal averaging process if corresponding regionMap value is nonzero.
Supported modes	3dMat, PlaneStress, PlaneStrain, 1dMat, 2dPlateLayer, 2dBeamLayer, 3dShellLayer