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:

$$t_n = \left (\frac{\pi}{2} + \arctan (s_m \bar\delta)\right) \frac{k_t}... ...eft (\frac{\pi}{2} - \arctan (s_m \bar\delta)\right) \frac{k_n}{\pi} \bar\delta$$ (223)

$$s_m = \mathit{smoothMag}$$ (224)

$$\delta_0 = \mathit{transitionOpening}$$ (225)

$$\bar\delta = \delta_n + \delta_0$$ (226)

$$k_t = k_n \cdot \mathit{stiffCoeffKn}$$ (227)

where smoothMag controlls smoothing magnitude. Tangential stiffness for normal direction is found by differentiating Eq. (223)

$$k_{nn} = \left (\frac{\pi}{2} + \arctan (s_m \bar\delta)\right) \frac{k_t}{\pi} + \left (\frac{\pi}{2} - \arctan (s_m \bar\delta)\right) \frac{k_n}{\pi} +$$ (228)

$$+ \frac{s_m \cdot k_t \bar\delta}{\pi(s_m^2\bar\delta^2+1)} - \frac{s_m \cdot k_n \bar\delta}{\pi(s_m^2\bar\delta^2+1)}$$ (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