Finite element based vibration fatigue analysis for a new free piston engine component

Abstract EN

Structures and mechanical components are frequently subjected to the oscillating loads which are random in nature.

Random vibration theory has been introduced for more then three decades to deal with all kinds of random vibration behaviour.

Since fatigue is one of the primary causes of component failure, fatigue life prediction has become a most important issue in almost any random vibration problem [1–4].

Nearly all structures or components have been designed using the time based structural and fatigue analysis methods.

However, by developing a frequency based fatigue analysis approach, the accurate composition of the random stress or strain responses can be retained within a greatly optimized fatigue design process.

Fatigue analysis is generally thought of as a time domain approach, that is, all of the operations are based on time descriptions of the load function.

This paper demonstrates that an alternative frequency domain [4,8,9] fatigue approach can be more appropriate.

A vibration analysis is generally carried out to ensure that structural natural frequencies or resonant modes are not excited by the frequencies present in the applied load.

Sometimes this is not possible and designers then have to estimate the maximum response at the resonance caused by the loading.

These are the best performed in the frequency domain using the power spectral density functions of input loading and stress response.

It is often easier to obtain a PSD of stress rather than a time history [10, 11].

The dynamic analysis of complicated finite element models is considered in this study.

It is valuable to carry out the frequency response analysis instead of a computationally intensive transient dynamic analysis in the time domain.

A finite element analysis based on the frequency domain can simplify the problem.

The designer can perform the frequency response analysis on the finite element model (FEM) to determine the transfer function between the load and stress in the structure.

This approach requires that the PSD of load is multiplied by the transfer function to obtaining the PSD of stress.

The main purpose of this paper is to predict fatigue life when the component is subjected to statistically-defined random stresses.