The objective of this research work is to reproduce in a test specimen, the fatigue failure that occurs in a damaged section of a structure. There is a structural problem, that is, the presence of a fracture at a certain point in the structure of the bus, starting at this point and growing progressively, causing damage. The steps of a methodology were applied to physically reproduce the fatigue failure in a representative specimen of a section of the bus structure, where the failure is located and up to the instrumentation of the testing machine and performance of the fatigue test. Subsequently, the results are analyzed and conclusions are made based on the results obtained in the laboratory test.

This paper presents results of research on the propagation of fatigue cracks in structural steel sheet, subjected to a MIG welding process. The study was conducted on rectangular test pieces with 62.5 x 60 mm and 2 mm thick, MIG welded and non-welded. Samples were tested for fatigue crack propagation at the base material and welded metal. The results show a crack stop in the heat affected zone (HAZ), requiring greater amplitude of the stress intensity factor (KI) so the crack could propagate in a stable manner. Results indicate that the combination of adequate microstructure and residual stress in the HAZ are those factors which can stop the advance of the crack in MIG welded material.

The study of the forces and the pairs of shaking that appear in mechanisms, are of main interest in the study of the dynamics of the internal combustion engines. An internal combustion engine is modeled from a particular arrangement of a set of mechanisms of the connecting-rod-crank type. During the performance of the internal combustion engine, the repetitive movement of the slide or piston induces accelerations and forces that are transmitted and distributed between the connecting rod and the crank or crankshaft. When the crankshaft is subjected to the components of the forces induced by the piston, the shaking torques are generated in turn. The purpose of the analysis of the pairs of shaking is to determine the dynamic values of the counterweights that must be added to each mechanism, with the aim of reducing the set of shaking actions. In the traditional bibliography in which the dynamic equations are presented, the complete analytical developments are not always presented; there are references that present partial results, in this work the algebraic developments are presented that allow to validate the correspondence between the expressions of different bibliographic sources in the teaching of these subjects.

In this work the rigidity of a shaft with diagonal crack in its half part in its elastic range under static conditions simply supported in its ends and with concentrated load to the center is determined. The functional relationship for the variation of the second moment of area of their different cross-sections is deduced. For double numeric integration the slope and the deformation of the shaft is calculated. The frequency in which the cracked system would enter in resonance is calculated. The rigidity of the shaft with crack is smaller that the rigidity of the shaft without crack. Based on the results of the study is concluded that the rigidity of the shaft with crack can be evaluated with the procedure described to determine a range of frequencies in which the system would enter in resonance. Therefore the system would be unstable and detectable.