| Contact: | M.Sc. Michael Niebler |
Contact mechanics
Fundamentals:
Imply disontinuity into FE; asymmetric system of equation
Contact constraints cannot be considered by ordinary boundary conditions
Possible states of the contact:
• Frictionless contact: (= normal contact)
- Contact only sustains normal stress N (a)
- Any stretching/tension leads to the vanishing of the contact interaction (b)
• Frictional contact (only if the contact is closed (F>0)) -> additionally
• Stick -> no relative displacement and infinite shear stress T (c)
• Slip -> relative displacement and transmission of shear stress T (d)
• poor sliding -> Frictionless and no transmission of shear stress T
Possible modelling approaches for the shear component
Modelling through Interface-/Continuums Elements (small-sliding)
Surface-Contact:
• Neglicting contact interaction
- Rough (infinite stiff)
- Frictionless (smooth)
• Coulomb friction law
• Specially developed contact models (interaction between T and N)
• Application of existing material models:
- Representation of the shear zone:
• Transfer of entire shear stresses between soil and structure
• Thickness ds = 5 - 10 x d50
• Dependence on state variables analogous to adjacent soil
- Applied assumptions:
• tan g = u / ds
• Stress state of shear zone analogous to adjacent soil
(Staubach et al. (2022))
• Behaviour tangential direction independent of normal direction
• No consideration of jamming (increase of stress) and unjamming (relaxation)
Capabilities of objective numerical observation of shear zone development
Regulatory methods:
• Non-local theory
• Polar (Cosserat) theory
• Gradient theory
• Discrete Element Method (DEM)