Cohesive interface material - cohInt

A simple interface material with generally different stiffness in compression, tension and shear. It is intended for simulating a contact with low stiffness in tension and high in compression. The parameter transitionOpening specifies initial gap embedded in an element which causes transition from tension to compression. For example, transitionOpening=0.01 m means that there exists the embedded gap which needs displacement jump 0.01 m to close. Traction-separation law for normal direction takes the following form:
$\displaystyle t_n$ $\displaystyle =$ $\displaystyle \left (\frac{\pi}{2} + \arctan (s_m \bar\delta)\right) \frac{k_t}...
...eft (\frac{\pi}{2} - \arctan (s_m \bar\delta)\right) \frac{k_n}{\pi} \bar\delta$ (223)
$\displaystyle s_m$ $\displaystyle =$ $\displaystyle \mathit{smoothMag}$ (224)
$\displaystyle \delta_0$ $\displaystyle =$ $\displaystyle \mathit{transitionOpening}$ (225)
$\displaystyle \bar\delta$ $\displaystyle =$ $\displaystyle \delta_n + \delta_0$ (226)
$\displaystyle k_t$ $\displaystyle =$ $\displaystyle k_n \cdot \mathit{stiffCoeffKn}$ (227)

where smoothMag controlls smoothing magnitude. Tangential stiffness for normal direction is found by differentiating Eq. (223)
$\displaystyle k_{nn}$ $\displaystyle =$ $\displaystyle \left (\frac{\pi}{2} + \arctan (s_m \bar\delta)\right) \frac{k_t}{\pi} + \left (\frac{\pi}{2} - \arctan (s_m \bar\delta)\right) \frac{k_n}{\pi} +$ (228)
  $\displaystyle +$ $\displaystyle \frac{s_m \cdot k_t \bar\delta}{\pi(s_m^2\bar\delta^2+1)} - \frac{s_m \cdot k_n \bar\delta}{\pi(s_m^2\bar\delta^2+1)}$ (229)

Shear stiffness remains constant during all possible loadins and there is no influence of normal direction.


Table 48: Cohesive interface material - summary.
Description Cohesive interface material
Record Format cohInt (in) # kn(rn) # ks(rn) # [ stiffCoeffKn(rn) #] [ smoothMag(rn) #] [ transitionOpening(rn) #]
Parameters - material number
  - kn (penalty) stiffness in compression
  - ks stiffness in shear
  - stiffCoeffKn ratio (tensile stiffness / compression stiffness)
  - smoothMag smoothing parameter for transition between tensile/compressive behavior
  - transitionOpening embedded gap in the element
Supported modes _1dInterface,_2dInterface,_3dInterface


Borek Patzak
2019-03-19