Existence Of Friction Forces Research Articles

A general formulation for the contact between superellipsoid surfaces and nodal points

The superellipsoids, part of the family of superquadratics, have geometric and mathematical properties that not only make them suitable for the representation of solids, ranging from spheres to relatively thin sheets, but also allow describing a very broad number of complex geometries. Their mathematical description favors a very efficient numerical treatment, in particular when used in the context of contact mechanics. Here, the contact between superellipsoids and nodal meshes, such as those used in finite elements, is analyzed. Based on the analytical properties of the implicit form of the superellipsoid equations, defined in a local coordinate frame, all the quantities necessary to handle a contact problem are derived. Recognizing that one of the most expensive tasks in contact mechanics is the contact detection, a three-stage contact search strategy is envisaged and implemented. Only in the close proximity between a node and the superellipsoid is a detailed contact search performed. In case of contact, the contact forces and their application points are evaluated using a continuous contact force model based on a penalty formulation. The existence of friction forces is considered. The methods developed and implemented for the contact between superellipsoids and nodal meshes are demonstrated and discussed with two contact scenarios comprising the impact of a superellipsoid on a hanging ‘towel’, and the contact of several superellipsoids with a flexible elastic platform.

Numerical Fracture Analysis of Compact Tension Shear (CTS) Specimens with Tortuous Crack Fronts

The aim of the contribution is to assess the influence of the microstructure of materials on the effective values of stress intensity factors. In this paper some results of 3D-finite element analyses of a CTS-specimen with a tortuous crack are presented. The specimen is subject to an in-plane shear remote loading (mode II) and tortuous crack flanks simulate rough cracks in polycrystalline materials. Finite element calculation by using the commercially available FE-code ANSYS has been carried out to determine stress/strain distribution in the vicinity of crack front and the local values of stress intensity factors are evaluated along the crack front. The existence of friction forces generated by sliding of crack wake asperities is included into calculations. Respective effective values are determined in dependence of the roughness of crack flanks. Results achieved allows to characterize the influence of microstructure to crack growth.

Discussions on Fracture Factors of Brittle Materials under the Shear-Compression Condition

Based on fundamental ideas in tribology and basic concept of stress state in solid mechanics, the existence of frictional force on shear plane is discussed under uniaxial compression of brittle materials. On account of macroscopic fracture forms and mesoscopic fracture mechanisms, the key factors influencing shear fracture angle are analyzed. The results show that, when brittle materials are compressed and shear fracture occurs, shear fracture surface at the crack initiation point is consistent with the maximum shear stress. But the reason of shear fracture angle examined in experiment greater than 45º lies in that, the existence of frictional force between endface of specimen and pressure head of testing machine, and additional tensile stress produced in the materials when harder crystalline grain wedge in softer medium have changed original uniaxial compression stress state and the direction of maximum shear stress on next fracture path.