Page 334 - Biaxial Multiaxial Fatigue and Fracture

318 l?.l LINO ET AL.

CONCLUSIONS
Fatigue life of aluminium pressure diecastings is influenced by the size and amount of defects
(essentially pores). The mean level of pores detected in the aluminium brake pedals, considered
acceptable and unacceptable, was 1.9% and 2.9%, respectively. The comparison of acceptable
and unacceptable lots of parts, have shown similar fatigue limits (91 and 87 MPa), however
with a slightly larger standard deviation for the unacceptable samples. The amount of pores in
the fracture surface, 2.2% for acceptable samples and 2.7% for unacceptable ones, was very
similar to the one obtained in the cross section of the brake pedals, 1.9% for acceptable and
2.9% for unacceptable ones.
The Woehler curves obtained have shown that for high alternating stresses, defects size have
a significant effect on fatigue life reduction. Combining the results obtained with the image
analysis and the fatigue tests it was possible to develop an equation that relates simultaneously
the stress amplitude applied to an aluminium component and the maximum defect size detected
in the non-destructive control. The equation developed in this study represent one first rough
tool for fatigue life prediction of pressure diecastings. It is expected that more fatigue tests, to
be performed soon in real components, will improve the reliability of the model presented here.

Fig. 21. Aluminium rocking arm.

REFERENCES

1. Spada, A. T. (1999). Aluminium Casters Discuss Porosity, h-Jt Quality, Mo~,rn Casting.
5th International AFS Conference on Molten Aluminium Processing, 58-60.
2. Nguyen, T., and Carrig J. (1986). Water Analogue Studies of Gravity Tilt Casting Copper
Alloy Components, AFS Transactions 94, MEM 92,519-528.
3. Nyamekye, K., An, Y. K., Bain, R., Cunningham, M., Askeland, D., Ramsay, C. (1994).
Expert System for Designing Gating System for Permanent Mould Tilt-Pour Casting
Process. AFS Transactions 150. 127-131.