Fatigue failures of motor crankshafts operating in thermoelectric power plants have recently been reported. Stress fields provided by finite element calculations at critical points of a crankshaft that failed in service are used to test the structural integrity of the component. Taking into account the fact that the stresses acting at a given point are most likely out of phase, multiaxial fatigue criteria based on the von Mises stress are considered to be most suitable for predicting the fatigue behavior of the crankshaft. Using the von Mises stress, it was also possible to apply octahedral shear stress-based criteria and the results obtained have indicated that the crankshaft made of DIN 34CrNiMo6 steel should not suffer fatigue failure under the action of the stress fields in question. However, such failures have been occurring and this apparent discrepancy is presented and briefly discussed in the present study.

This study aimed to evaluate the variation of the mechanical properties of a polyester matrix composite reinforced by sponge gourd fibers as a function of immersion time in water. The characterization of the composite was performed using bending mechanical test and a sonic test. The Young's modulus and the sound propagation characteristics of the composite were evaluated as a function of immersion time. The water diffusion coefficient was also determined. The results indicate that the percentage of water absorbed increases rapidly, but stabilizes at around 2 weeks after the start of the absorption process. The variation of elastic modulus and damping factor showed a direct correlation with water content in the composite, and both properties remained constant when the absorbed water content stabilized. These results were interpreted as an indication that the composites suffered only physical aging due to water absorption, at the immersion times used in this work. The mechanical properties evaluated by the bending test decreased after absorption of water, but the obtained variations were small. The results obtained indicate that the absorbed water acts as a plasticizer in this composite, but does not cause chemical aging.