Figure 10 compares the equivalent von Mises stress amplitudes (i。e。 Sf from equation 2) for the different locations identified in Fig。 6 obtained from static as well as quasi-dynamic analyses。 As can be seen from this figure, the stress amplitude based on the static analysis is higher at all locations。 The differ- ence is about a factor of two at some locations, including typical failure locations at 3 and 4。 Such a difference in stress amplitude results in orders of magnitude difference in fatigue lives。 Therefore, static analysis of a connecting rod can yield unrealis- tic stresses, whereas quasi-dynamic analysis pro- vides more accurate results better suited for fatigue design and/or optimization of this high volume pro- duction component。

6CONCLUSIONS

The following conclusions can be drawn from this study。

1。Static analysis of a connecting rod that is typically performed can yield unrealistic stresses, whereas quasi-dynamic analysis provides more accurate results better suited for fatigue design and optim- ization analysis of this high volume production component。

2。Using the overall operating load range of the con- necting rod which comprises the maximum static tensile and compressive loads, rather than the load range at the maximum power output, can

Fig。 10 Comparison of equivalent von Mises stress amplitudes under static and quasi-dynamic loading conditions

lead to an overly conservative design of the component。

3。Maximum and mean stresses increase with increas- ing engine speed because of the increase in the iner- tia load。 The stress range (or amplitude), however, is independent of the engine speed。

4。The load ratio or the mean load varies over the length of the connecting rod。 The  stress ratio and therefore mean stress, also varies with location in the connecting rod, as well as with engine speed at a location。

5。The bending stress produced as a result of dynamic loading is significant and bending stiff- ness in the shank should be considered as an important design factor。

6。In spite of the fact that typical testing and analysis of connecting rod is conducted under uniaxial stress state, the state of stress is multiaxial at criti- cal locations and mainly results from stress con- centrations。   The   use   of   an    equivalent stress approach is necessary to account for the stress multiaxiality。

ACKNOWLEDGEMENTS

The American Iron and Steel Institute (AISI) is acknowledged for providing financial  support  for this study。 Dr M。 Pourazady of the University of Toledo helped with the quasi-dynamic FEA in this work and his help is   appreciated。

REFERENCES

1 Balasubramaniam, B。, Svoboda, M。, and Bauer, W。 Structural optimization of I。C。 engines subjected to mechanical and thermal loads。 Comput。 Meth。 Appl。 Mech。 Engrg, 1991, 89, 337 – 360。

624 P S Shenoy and A  Fatemi

2Webster, W。D。, Coffell, R。, and Alfaro, D。 A three dimensional finite element analysis of a high  speed diesel engine connecting rod。 SAE Technical Paper 831322, 1983。

3Ishida, S。, Hori, Y。, Kinoshita, T。, and Iwamoto, T。 Development of technique to measure stress on connect- ing rod during firing operation。 SAE Technical Paper 951797, 1995, pp。 1851 – 1856。

4Rice, R。 C。  (Ed。)  SAE   Fatigue   design   handbook, 3rd edition, 1997 (Society of Automotive Engineers, Warrendale, PA)。

5Athavale, S。 and Sajanpawar, P。 R。 Studies on some modelling aspects in the finite element  analysis  of small gasoline engine components。 Proceedings of the small engine technology conference, Society of Automo- tive Engineers of Japan, Tokyo, 1991, pp。 379 – 389。论文网