Experimental investigation of bi-modular material coating to enhance damping

Hard coatings can be used to increase damping when applied on the surface of the components of turbomachinery. This can be effective to reduce the resonant vibration level of components working in a high cycle fatigue environment due to the extremely high operational speed. This paper discusses the experimental investigation of a bi-modular material hard coating to enhance damping in structural steel elements. Firstly, a hard coating (Al2O3+MgO) is applied on AISI 304L stainless steel substrate by plasma spraying. After that, a layer of chrome is deposited by chrome plating. Dynamic responses of both coated and uncoated samples are measured. The damping ratio of the test specimen is extracted from the time response by the logarithmic decrement method. Improved damping capacity of the coated steel sample is observed and is mainly attributed to the thin coating of chrome on the steel structure. The natural frequency of coated specimen showed 8 to 10 % improvement, the forced response showed a 30 to 35 % decrement in displacement, the damping ratio showed a 200 % increment, and the time of decaying showed a 20 % decrement. The results of the present study provide new ideas for the development of high-damping structural elements

Buckling prevention in lightweight stiffened structures

The focus of this thesis is to investigate the buckling prevention in lightweight stiffened structures using a finite element model. The emphasis of the investigation presented in this thesis is to find the critical length at which buckling preventers can be attached along the side of a stiffening beam so it can effectively prevent the stiffened structure from buckling. The investigation was conducted using a finite element model of a lightweight structure and the analysis and simulations were carried out using the NX NASTRAN finite element analysis software. The analysis method is based on a general form of argument known as the reductio ad absurdum. During the investigation the critical length Lc was studied as a function of slenderness ratio Sr of a slender beam, where the width t is constant and the height h is variable. The critical length Lc at which the buckling preventer becomes irrelevant was determined for five different slenderness of the beam. The imperial finding is Lc=222,3S_r+981,7 [mm] R^(2 )= 0, 9984 10<S_r<200 ; t=10 ,h=variable where R^(2 ) is the coefficient of determinatio