Abstract: This paper summarizes the work conducted to assess the root cause of the failure of a medium commercial vehicle leaf spring failed in service. Macro- and micro-fractographic analyses by scanning electron microscope as well as material verification tests were conducted in order to understand the failure mechanisms and root cause of the failure. Findings from the fractographic analyses indicated that failure mechanism is fatigue. Crack initiation was identified to have occurred from a point on the top surface near to the front face and to the left side. Two other crack initiation points were also observed, however, these cracks did not propagate. The propagation mode of the fatigue crack revealed that the cyclic loads resulting in crack initiation and propagation were unidirectional bending. Fractographic analyses have also showed that the root cause of the fatigue crack initiation and propagation was loading the part above design stress. Material properties of the part were also verified by chemical composition analysis, microstructural analysis by optical microscopy and hardness tests.
Abstract: The incidence of mechanical fracture of an
automobile piston rings prompted development of fracture analysis
method on this case. The three rings (two compression rings and one
oil ring) were smashed into several parts during the power-test (after
manufacturing the engine) causing piston and liner to be damaged.
The radial and oblique cracking happened on the failed piston rings.
The aim of the fracture mechanics simulations presented in this paper
was the calculation of particular effective fracture mechanics
parameters, such as J-integrals and stress intensity factors. Crack
propagation angles were calculated as well. Two-dimensional
fracture analysis of the first compression ring has been developed in
this paper using ABAQUS CAE6.5-1 software. Moreover, SEM
fractography was developed on fracture surfaces and is discussed in
this paper. Results of numerical calculations constitute the basis for
further research on real object.