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Potentials of in situ monitoring of aluminum alloy forging by acoustic emission

Behrens B. A., Bouguecha A., Buse C., Wolki K., Santangelo A.

Archives of Civil and Mechanical Engineering

2016

Vol. 16, no. 4

724--733

Deviations during forging processes lead to workpiece failure when the forming limits of the material are exceeded. In production processes an early detection of manufacturing faults is preferred. The acoustic emission (AE) technique is examined with respect to its ability to detect deviations in lubrication conditions and in the structural integrity of different aluminum part geometries and alloys during forming. In a first step, an upsetting of varying specimen shapes was performed in order to study correlations of occurring defects as well as changing friction conditions with acoustic emission response. Afterwards, a cross joint was forged and AE was analyzed. The results suggest that crack detection during forging is feasible but limited by material ductility. In addition, it is shown that the characteristics of the acoustic emission during forming strongly depend on the respective alloy. With respect to faultless warm forging it is found that different stages are reflected in the AE signal, facilitating the detection of process deviations.

On nonuniform asymptotic stability of impulsive differential equations

Buse C.

Demonstratio Mathematica

1998

Vol. 31, nr 3

485-497

Necessary and sufficient conditions for the nonuniform exponential stability of Impulse Differential Systems are given. Well known results of R. Datko in [Da], are extended for nonuniform exponential stability. Obtained results also contain, as particular cases, the results of M. Reghis in [Re2] and the author in [B].