ENIDH - EMM - Artigo Científico
Permanent URI for this collection
Browse
Browsing ENIDH - EMM - Artigo Científico by Author "Afonso Fonte, M."
Now showing 1 - 2 of 2
Results Per Page
Sort Options
- Failure analysis of a crankshaft of a helicopter enginePublication . Afonso Fonte, M.; Freitas, M.; Infante, V.A detailed analysis of a crankshaft failure belonging to a helicopter engine is presented. The main objective of this work was to analyze the characteristics of the failure and determine the root cause of the failure of the crankshaft. In order to determine the causes of the crankshaft failure, a material analysis was performed, followed by a detailed observation of the failure mechanisms through macroscopic, microscopic and microstructural examinations of the fracture surface. A preliminary observation of the fractured crankshaft indicates that this failure occurred by a fatigue process where the fracture surface shows obvious signs of cyclic propagation mechanisms. The existence of a large number of beachmarks indicates significant crack growth characterized by the effect of successive starts and stops of the engine by the operating conditions. These beachmarks cover about two-thirds of the total area of the fracture surface and the uniform geometric pattern of the crack front, along the entire propagation zone, allows to conclude that the fatigue process occurred from a loading state consisting essentially of cyclic bending stresses between the crankweb and the main journal of the crankshaft. No original defect was observed either on the surface or inside the material that could be the source of the crack initiation and growth and subsequent final fracture of the component. The analysis of the shell bearings applied to the main journal revealed a significant damage, with fractured location lugs, that are believed to be at the origin of the crack initiation of the crankshaft.
- Failure mode analysis of a damaged diesel motor crankshaftPublication . Afonso Fonte, M.; Reis, L.; Freitas, M.A case study of a catastrophic failure of a diesel motor crankshaft is presented. The aim of this failure analysis is to investigate the root cause of this important mechanical component. This crankshaft belonged to a particular vehicle (140 cv, at 4000 rpm, 1968 cm3 displacement) that fractured after 180,000 km and 8 years in service. The motor was disassembled, and the crankpin No. 3 and the main bearing cap No. 4 were broken. Defects of material and machining defects were not found at the crack initiation sites by optical and SEM microscope. Results shown that the crankpin and the main bearing cap clearly failed by fatigue, and the root cause seems to be related with deficient tightening of the main bearing cap No. 4, which fractured due to a crack developed on the its outer side. The main journal No. 4 did run out of support, and the crankthrow No. 3 increased the alternating stress amplitude, whereby an inevitable catastrophic crankshaft failure happened.