Appraising the suitability of a hybrid piston for internal combustion engines and its fatigue characteristics

Abstract

Automotive engine pistons are not normally expected to be made of plastics or even composites, but before now the latter have been applied to an Over Head Cam follower of an automotive engine. As such this research work sought to demonstrate that the composite Carbon fibre Phenolic composite of the grade used is suitable enough to be employed in a hybrid piston. This work covered three broad areas; Constitutive modelling, Optimization and Fatigue. Numerical/simulation and empirical methods were employed to accomplish the tasks involved. The design of the piston was presented and this design took into account the fact that a composite was involved. A contact analysis was carried out to analyse the stresses arising from the interference of the composite piston skirt and the aluminium cap just in case interference fit is adopted as the method of assembly. Empirical analyses of tubular carbon fibre composite samples as well as carbon fibre Phenolic composite prepregs were carried out to determine the tensile, compressive and flexural capabilities of the materials as the case may be. Young’s and Shear modulus values as well Poisson’s ratio values were deduced leading to the establishment of the constitutive model of the composite’s lamina and consequently that of the laminate for the various samples that were deemed suitable based on the nature of their testing and preparation as well as a piston cap model. With the constitutive models worked out and the piston cap model developed, fatigue analysis of the structure and piston cap followed, and in other to get the best out of the structures or materials and the piston cap optimization followed after which yet more fatigue analysis was done for the optimization outcomes. To a great extent one of the Elastic Modulus values obtained empirically can be said to be sufficiently reliable as its empirical test was simulated numerically and it turned out satisfactory; the maximum stress value from the test was 158.5 MPa while that of the simulation was 158.267 MPa. All the results were almost the same apart from the strain values that were significantly divergent. The adopted Elastic Modulus value of 61049.6757 MPa stemmed from this empirical and numerical analyses and since these two differed only in the strain values and agreed in pretty much in all other the parameters it can be said that this adopted Elastic Modulus value was indeed sufficiently reliable. It also implies that the outcomes of all the other numerical analyses that were carried out with it can be trusted. In the Results and Discussion chapter numerical Crack Propagation was discussed for various crack lengths of a finite element model.