Noritoshi Nakagawa

Transfer characteristics in the collision of two elastic bars. Consideration from time domain and frequency domain.

This paper clarifies the mechanism of the impact phenomena of elastic bars by both wave propagation theory and the concept of mechanical impedance in the frequency domain, and investigates the optimum combination of elastic bars to obtain the maximum restitution. The method of the Laplace transformation is used for these analyses. The relation between the contact time of the col llsion and the mechanical impedance is clarified to obtain the maximum restitution coefficient.

Modified theory of Bayesian estimation method to parameter identification of structures.

In the Bayesian parameter estimation method, the uncertainties of both experimental responses and theoretical model parameters are taken account of to identify the finite element model from experimental modal test results such as the natural frequencies and mode shapes of a structure. This paper presents a modified theory of the Bayesian parameter estimation method. In this theory, the Bayesian parameter estimation method is extended by normalizing the error function, and a constant that weights the parameter valuesto the test data can be reasonably determined; that is, a parameter identification that weights the experiment, or that weights the theory can be carried out quantitatively and easily. And constants that denote the various uncertainties of each parameter and response reflect the identified values. The effects of relative parameter and measurement uncertaities on the identified values are illustrated by two five-degrees-of-freedom models.

Wave propagation in a conical bar subjected to impulsive loadings and impact fracture.

The study of wave propagation in the machine-structures with varying cross-sectional parts has become very important from the view point of the impact strength of structures.In the present paper, first, the stress wave propagation and the impact fracture of a conical bar were treated experimentally. The changes of the crack location and the number of fracture points were investigated at several different impact velocities. Next the wave propagation in a conical bar was calculated by the finite element method, and its change with time was considered in detail. Furthermore the estimation of a crack location was tried.The results obtianed are as follows:(1) The wave speed, obtained from the experiment of the wave propagation in the conical bar, agreed with that of the one-dimensional theory.(2) When the impact velocity increased, the number of fracture points increased and the crack location approached to the top end of the conical bar.(3) The wave front of compressive strain was reflected at the top end as the tensile strain. These reflected tensile waves were superposed to the following tensile wave, and high tensile stress appeared often as observed in the experiment.(4) The crack location simulated in a conical bar of gypsum agreed fairly well with the experimental result.