Wavelet analysis for gear crack identification

There are many typical damages and faults that can cause problems in relation to gear unit operation, a crack in the tooth root being probably the least desirable among them. It often results in failure of gear unit operation. Fault analyses presented in this article are based on gear units with real damages or faults, produced on the basis of real operating conditions. A test plant has been used. A possible damage can be identified by monitoring vibrations. The influences of a crack in a single-stage gear unit on produced vibrations are presented. A fatigue crack in the tooth root causes significant changes in tooth stiffness, whereas, in relation to other faults, changes of other dynamic parameters are more expressed. Different methods are used to analyse signals acquired by experiments. Signal analysis has been carried out in relation to a non-stationary signal, using the family of Time Frequency Analysis tools, such as Wavelets Analyses. Typical spectrogram and scalogram patterns resulting from reactions to faults or damages indicate the presence of damages in a very reliable way.     

Detecting cracks in the tooth root of gears

A crack in the tooth root is the least desirable damage caused to gear units and often leads to failure of gear unit operation. A possible damage in gear units can be identified by monitoring vibrations. In relation to that, different methods of time signals analysis are presented. Signals have been obtained by experiments. Significant changes in tooth stiffness are the result of a fatigue crack in a tooth root. As a consequence, dynamic response differs from the one in concern to an undamaged tooth. Amplitudes of time signal are, by frequency analysis, presented as a function of frequencies in spectrum with time frequency analysis.     

Raman microprobe analysis of elastic strain and fracture in electrophoretically deposited CdSe nanocrystal films

The mechanical stability of nanocrystal films is critical for applications, yet largely unexplored. Raman microprobe analysis used here to probe the nanocrystal cores of thick, fractured electrophoretically deposited films of 3.2 nm diameter CdSe nanocrystals measures approximately 2.5% in-plane tensile strain in cores of unfractured films. The crack dimensions determine the overall in-plane film strain, approximately 11.7%, and the film biaxial modulus, approximately 13.8 GPa, from which the biaxial modulus of the trioctylphosphine oxide ligand matrix is inferred, approximately 5.1 GPa.     

Modeling and Design of Experiments of Laser Cladding Process by Genetic Programming and Nondominated Sorting

Laser deposition of materials represents a modern additive technology that has a number of advantages over remaining technologies for depositing metallic materials. Besides a low-energy input, a quality bond, and minimal heat-affected zone, this technology is also characterized by the good mechanical properties of the deposited material that is a result of rapid cooling. Despite the prospects, this technology is still at the developing phase. New materials and techniques for determining optimal process parameters are being introduced. In this article, we developed a system for modeling (predicting) the properties of the deposited material and used design of experiments (DOE) for the laser cladding process parameter selection. Based on the experimental data obtained during cladding process, models were made for predicting the volume and roughness of the deposited material. Genetic programming was used for modeling the process. Then, a set of several thousand possible combinations (settings) of the machine parameters was produced on the basis of the obtained model. The most appropriate machine (process) parameters were selected in terms of deposition speed, powder efficiency, and surface roughness. These parameters were determined by nondominated sorting. The results offer the operator of the machine a set of appropriate process parameters that enable the production of high-quality products.