Some Aspects of Wear and Structural Dynamics

Detta är en avhandling från Division of Solid Mechanics Lund University, Box 118, SE-221 00 Lund, Sweden

Sammanfattning: The topic of this thesis is dynamics and wear of structures. In the six appended papers different aspects of wear and dynamics of a model system are studied. The considered system consists of a long slender rod with unilateral supports, subject to harmonic and stochastic excitation. The rod is held at one end with stiff springs preventing translation and rotation and constrained by loose supports near the other. In the first two papers the vibration and impact dynamics of the model system subject to periodic and stochastic forcing are analysed. The wear work rates at impact points are evaluated with or without friction. Model computations are compared with measurements of contact forces and displacements made on a loosely supported rod with nuclear fuel dimensions. The comparison validates the modeling. The first two papers also contain global bifurcation analysis of idealized versions of the model system for both harmonic and stochastic loading. Regions of periodic and stochastic response are identified for the case of periodic forcing. The regions of stable periodic response are subjected to stability and bifurcation analyses in the third paper. The fourth paper focuses on the transition from stable periodic to chaotic response and the existence of stable multi periodic solutions within the chaotic regime. The third paper also contains an evaluation of the wear work rate along the identified stable paths of period one solutions. In the fourth paper a wear law is introduced which enables life time predictions of such stable solutions. The basin of attraction for a stable solution is also discussed. The sliding amplitude is usually in the fretting range for impacting systems such as the model considered in this thesis. The fifth paper deals with fretting wear maps to differentiate different regimes of fretting contact. A systematic method to compare fretting wear data from different sources with different contact geometries is developed. The method is applied to experimental data and new maps are presented in the form of dimensionless variables. The last paper deals directly with breakdown of materials due to wear induced loads. An idealized spring model is used to show that breakdown of disordered media due to applied shear forces behaves like a first order phase transition in condensed matter systems. Finally, the burst size distribution during rupture is evaluated and it is shown that the system behaves like the fiber bundle model with global load sharing.