Fracture Analysis of Welded Steel Connections in Pre-Crack Condition

Extended finite element method (XFEM) can effectively describe the phenomenon of steel node cracks growth and extension. In this paper, extended finite element method is used for the beam weld node end under the concentrated load to analyze node fracture under no initial crack and pre-crack condition. The result shows that: under the no initial crack condition, crack appears near the weld root, where the bottom and upper of the weld is easy to crack than the middle,because of the necking phenomenon,which means that both end stress is higher than the middle. Crack firstly appears in the weld bottom, extending from the bottom to up. The crack tip makes stress concentration, which accelerates the crack extension. The location of the pre-crack has the influence on the node fracture, which means that the farther the position from the weld root is, the harder it is to crack and grow. Pre-crack position coincides with no initial crack extension path, promoting crack growth and extension.

Comparison of Vibration Signal Analysis Methods for Effective Gear Fault Detection

Reduction unit for high-speed train is an important component. However if faults of reduction unit occurred, the damages such as material and human damage have been caused. To prevent the damage, it is necessary to study reduction unit monitoring for high-speed train. We conducted spur gear specimen test which was crack, breakage and pitting tests and analyzed FFT, Sideband energy ratio (SER), RMS, crest factor, and kurtosis. There was not distinct difference between no-fault and pitting condition at RMS, crest factor and kurtosis. But SER increased depending on crack condition. In breakage test, all parameters had difference between no-fault and breakage condition.

Measurement and Evaluation of Ferrite Surface Crack

An acquisition of ferrite surface images has been taken with a LY-WN-YH Hyper-depth measurement system, from which the crack condition was analyzed with MATLAB. Based on the contradistinction between experimental data from ferrite work pieces of different quality, a preliminary conclusion has been drawn that the surface quality of ferrite materials has a direct link to the quantity and length of the crack on them. By measuring the quantity and length of the crack, an initial criterion was obtained for judging the surface quality of ferrite.

Experimental Study of Dynamic Test Characteristics on Nanjiang Road Bridge

Dynamic test has been carried out to completed road bridge of Nanjiang Port inTianjin. When cars were passing through the bridge, the dynamic deflections, the maximum amplitudes, the relation between amplitude and velocity, the Natural frequency and the damping ratio were gained. Dynamic modulus, vibration characteristics and crack condition of the bridge were determined so as to ascertain the reliability of the bridge.

Vibration Based Sun Gear Damage Detection

Seeded fault experiments were conducted on the planetary stage of an OH-58C helicopter transmission. Two vibration based methods are discussed that isolate the dynamics of the sun gear from that of the planet gears, bearings, input spiral bevel stage, and other components in and around the gearbox. Three damaged sun gears: two spalled and one cracked, serve as the focus of this current work. A non-sequential vibration separation algorithm was developed and the resulting signals analyzed. The second method uses only the time synchronously averaged data but takes advantage of the signal/source mapping required for vibration separation. Both algorithms were successful in identifying the spall damage. Sun gear damage was confirmed by the presence of sun mesh groups. The sun tooth crack condition was inconclusive.

Damage Condition Assessment of Expressway Asphalt Pavement Based on RBF Neural Network

In order to make the performance evaluation of highway asphalt pavement more scientific and reasonable, carrying out pavement maintenance management is more necessary. Taking advantage of excellent adaptability of neural network technology to deal with nonlinear mapping problem, a breakage condition evaluation model based on radial basis function (RBF) neural network is presented. This model considers four main affecting factors including pavement rut condition, crack condition, pit slot condition and repair condition. Certain number of sample data is chosen to train and simulate the RBF neural network model. The tests results, accordant with expectation, indicate that the model is qualified for practical engineering applications.