Contents of Journal of Mechanical Engineering 63, 4 (2012)


                                                                       
NALITOLELA, N. G.: Updating dynamic model parameters from frequency 
response functions by virtual perturbation of system matrices                179

TANCSICS, F., HALBRITTER, E.: Determination of friction coefficient during
upsetting using a kinematically admissible velocity field                    197

ELSHEIKH, M. H., YOUSEF, B. A. A., ALJIBORI, H. S. S., SABRI, M. F. M., 
SHNAWAH, D. A. A.: Effect of cut-out on the buckling behavior of carbon 
fiber/epoxy plate with (0°/90°/0°)s ply orientation                           225

Abstracts

Updating dynamic model parameters from frequency response functions by virtual perturbation of system matrices

N. G. NALITOLELA

Investigation into methods to update dynamic models of structures using measurement data, to obtain credible models that correlate well with measurements, has been an issue of interest to the structural dynamics community since early 1980s. Perturbing a dynamic system, for example by adding masses or stiffness to it and measure a new set of perturbed eigenvalues may increase the measurement database to enable the updating of model parameters from eigenvalues alone. However, major limitations include practicality to perturb a real system physically and an extra effort to solve an eigenvalue problem for each added mass or stiffness. This paper presents an alternative updating method involving virtual perturbation of system matrices and using frequency response functions directly to update the parameters. The proposed updating algorithm involves transforming the frequency domain differential equation of motion of forced vibration of unperturbed system into a free vibration equation of the perturbed system, treating the frequency response functions as eigenvectors. The corresponding frequencies in the frequency response functions then define the natural frequencies and they are compared to those of the analytical model. The updating algorithm is based on eigenvalue sensitivity where the eigenvalues and their eigenvectors are readily available from the frequency response functions. The proposed technique is more effective because it enables large perturbations without physically implementing them on the test structure. Moreover, there is no need to solve an eigenvalue problem for each perturbation.

Determination of friction coefficient during upsetting using a kinematically admissible velocity field

F. TANCSICS, E. HALBRITTER

The first phase of forming in traditional, multi-cavity forging technologies is descaling or pre-forming upsetting between the plain die surfaces. During upsetting there is friction occurring between the contact surfaces of the die to the work-piece, making the work-piece barrel-shaped. In technological designing it is very important to know the friction coefficient and/or the barrelling rate.
In our study, the approximate value of friction coefficient has been innovatively defined based on typical geometrical data of the initial and the barrelling work-piece, and after the friction coefficient has become known, the geometrical model of solid cylindrical bodies expectable after upsetting has been prepared. The constraints of applicability of this method are addressed in a separate section in our study.
This new solution is based on a kinematically admissible velocity field. Our method has been tried and introduced in the Forging Plant of RÁBA Axle Ltd. (Hungary).

Effect of cut-out on the buckling behavior of carbon fiber/epoxy plate with (0°/90°/0°)s ply orientation gears

M. H. ELSHEIKH, B. A. A. YOUSEF, H. S. S. ALJIBORI, M. F. M. SABRI, D. A. A. SHNAWAH

An experimental study of the behavior of woven carbon fiber/epoxy with ply orientation (0°/90°/0°)s composite laminated panels under compression is presented. Compression tests were performed on eighteen fiber-carbon laminated plates with and without different shapes of cut-outs using the compression machine. The maximum load of failure for each of the laminated plates under compression was determined experimentally. A parametric study was performed as well to investigate the effects of varying the centrally located holes and notches cut-out. These results indicate that a cut-out can have a significant effect on buckling, fracture and energy absorption response of a compression-loaded panel. The results indicate that the plates without cut-out exhibit higher fracture load and energy absorption than plates with cut-out. Moreover, cut-out shape optimization was studied.