Some Aspects of Wear and Structural Dynamics

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.