Search Results

The performance of a large diesel engine piston has been investigated to determine a mechanism for the failures encountered during engine research testing. During engine testing, it was found that the pistons were failing to retain the ring groove insert and fracture of the top land above the insert was observed. The finite element analysis was performed on the piston to ascertain the combined thermal and mechanical stresses on the piston and its ring groove insert. Finite element models were employed to study the effects of a crack growing in the Alfin bond between the ring groove insert and the aluminum alloy of the piston. The data showed that as a crack in the bond between the ring groove insert and the aluminum alloy of the piston grows, the stresses in the bond area drastically increase.

The mechanical properties of an aluminum silicon alloy reinforced with ceramic fibers has been investigated as part of a much larger program to develop metal matrix composite Pistons for diesel engine applications. Tensile and fatigue tests were carried out over a range of temperatures typical of those experienced during engine operation. The influence on the properties of non-fibrous extrinsic particles, which originate from the fiber manufacturing process, are considered in detail. These data show that the tensile and fatigue characteristics are much improved over those of unreinforced materials at temperatures in the range of the maximum engine operating temperature. The presence of extrinsic defects has little effect on the tensile properties but causes a reduction in the fatigue life, which may be greater than one order of magnitude at a given load.

The effect of time dependent damage on elevated temperature fatigue performance has been investigated for a squeeze formed aluminum-silicon piston alloy. From the results of elevated temperature fatigue, creep and dwell tests carried out, it has been shown that creep damage has little effect at short lives but at longer lives leads to a reduction in fatigue life. It is perceived that although this damage does not directly cause the initiation of a fatigue crack, the overall resistance of the material to damage is reduced. The observed micromechanisms are related to those observed in engine tested components and the use of damage mechanisms to predict lifetimes explored. It has been shown that linear damage accumulation based on creep and fatigue mechanisms may be used to produce a first estimate of life in the materials tests.