Cracks of fractal geometry with unilateral contact and friction interface conditions

1993 ◽  
Vol 60 (4) ◽  
pp. 293-310
Author(s):  
P. S. Theocaris ◽  
P. D. Panagiotopoulos
Keyword(s):  
Fractal Geometry ◽  
Unilateral Contact ◽  
Interface Conditions ◽  
Unilateral Contact And Friction

scholarly journals Study of the Residual Strength of an RC Shear Wall with Fractal Crack Taking into Account Interlocking Interface Phenomena

2013 ◽  
Vol 2013 ◽  
pp. 1-14
Author(s):  
O. Panagouli ◽  
K. Iordanidou
Keyword(s):  
Residual Strength ◽  
Fractal Geometry ◽  
Complex Geometry ◽  
Shear Wall ◽  
Unilateral Contact ◽  
Interface Phenomena ◽  
Wall Element ◽  
Rc Shear Wall ◽  
Unilateral Contact And Friction ◽  
Fractal Crack

In the present paper, the postcracking strength of an RC shear wall element which follows the construction practices applied in Greece during the 70s is examined by taking into account the complex geometry of the crack of the wall and the mixed friction-plastification mechanisms that develop in the vicinity of the crack. Due to the significance of the crack geometry, a multiresolution analysis based on fractal geometry is performed, taking into account the size of the aggregates of concrete. The materials (steel and concrete) are assumed to have elastic-plastic behaviour. For concrete, both cracking and crushing are taken into account in an accurate manner. On the interfaces of the crack, unilateral contact and friction conditions are assumed to hold. For every structure corresponding to each resolution of the interface, a classical Euclidean problem is solved. The obtained results lead to interesting conclusions concerning the influence of the simulation of the geometry of the fractal crack on the mechanical interlock between the two faces of the crack, a factor which seems to be very important to the postcracking strength of the lightly reinforced shear wall studied here.

scholarly journals Thermomechanical Component Mode Synthesis for Blade Casing Interaction Prediction

2017 ◽  
Author(s):  
Nicolas Guerin ◽  
Fabrice Thouverez ◽  
Claude Gibert ◽  
Mathias Legrand ◽  
Patricio Almeida
Keyword(s):  
Thermal Stresses ◽  
Unilateral Contact ◽  
Synthesis Technique ◽  
Multiphysics Simulations ◽  
Modal Synthesis ◽  
Thermomechanical Behaviour ◽  
Mode Method ◽  
Blade Tip ◽  
Thermal Dilatation ◽  
Unilateral Contact And Friction

Increasing the efficiency of turbomachines is a major concern as it directly translates into lower environmental impact and improved operational costs. One solution is to reduce the blade-casing operating clearance in order to mitigate aerodynamic losses at the unavoidable cost of increased structural unilateral contact and friction occurrences. In centrifugal compressors, the dynamic behaviour of the structures interacting through unilateral contact and friction is not yet fully understood. In fact, the heat generated during such events may affect the dynamics through thermal stresses. This paper presents a complete thermomechanical modelling strategy of impeller rotor and casing, and of blade-tip/casing contact events. A fully coupled thermomechanical modal synthesis technique is introduced and applied to turbomachinery-related models. The blisk is reduced via a hybrid modal synthesis technique combining the Craig-Bampton method and the characteristic constraint mode method. The casing model is reduced using an axisymmetric harmonic modal synthesis. Both strategies involve thermomechanical modes embedding thermal dilatation effects. The contact modelling algorithm is then introduced. It handles unilateral contact and friction occurrences together with heating effects. This algorithm uses the above mentioned reduced-order models as input data to avoid CPU-intensive simulations. The results show that the thermomechanical behaviour of the structures is well preserved by the reduction strategy proposed. Contact simulations on simple cases show qualitative results in accordance with expectations. Further work is needed in order to validate the strategy based on experimental results. However, this methodology opens the way to extended multiphysics simulations of contact events in turbomachinery.

Fractal interfaces with unilateral contact and friction conditions

1992 ◽  
Vol 99 (2-3) ◽  
pp. 395-412 ◽  
Author(s):  
P.D. Panagiotopoulos ◽  
E.S. Mistakidis ◽  
O.K. Panagouli
Keyword(s):  
Unilateral Contact ◽  
Unilateral Contact And Friction

scholarly journals Nonsmooth Modal Analysis: Investigation of a 2-DOF Spring-Mass System Subject to an Elastic Impact Law

2015 ◽  
Author(s):  
Anders Thorin ◽  
Mathias Legrand ◽  
Stéphane Junca
Keyword(s):  
Modal Analysis ◽  
Autonomous System ◽  
Unilateral Contact ◽  
Unilateral Constraints ◽  
Mass System ◽  
Elastic Impact ◽  
Nonsmooth Systems ◽  
Community Of Researchers ◽  
Unilateral Contact And Friction ◽  
Nonlinear Smooth

The well-known concept of normal mode for linear systems has been extended to the framework of nonlinear dynamics over the course of the 20th century, initially by Lyapunov, and later by Rosenberg and a growing community of researchers in modal and vibration analysis. This effort has mainly targeted nonlinear smooth systems — the velocity is continuous and differentiable in time — even though systems presenting nonsmooth occurrences have been increasingly studied in the last decades to face the growing industrial need of unilateral contact and friction simulations. Yet, these systems have nearly never been explored from the standpoint of modal analysis. This contribution addresses the notion of modal analysis of nonsmooth systems. Developments are illustrated on a seemingly simple 2-dof autonomous system, subject to unilateral constraints reflected by a perfectly elastic impact law. Even though friction is ignored, its dynamics appears to be extremely rich. Periodic solutions are sought for given numbers of impacts per period and nonsmooth modes are illustrated for one and two impacts per period in the form of two-dimensional manifolds in the phase space. Also, an unexpected bridge between these modes in the frequency-energy plots is observed.

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