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A computer-based technique was used to produce fatigue life predictions for a variety of steels using service histories recorded from several automotive components. The materials considered, both hot and cold-rolled sheets, ranged in yield strength from 200 MPa (30 ksi) to 580 MPa (84 ksi) and included most of the steels currently under consideration for material substitution to achieve vehicle weight reduction. The results of these computations were used to produce estimates of the weight savings potential, in fatigue limited designs, of the substitution of higher strength materials for conventional hot or cold-rolled low carbon steel; the indicated weight savings were from 16 to 50% depending on the nature of the loading of the component. This wide variation in savings is an indication of the importance of design in the engineering for minimum weight. Differences in the fatigue notch sensitivities of the materials were found to be an important factor in the predicted fatigue lives.

Titanium alloys offer a unique combination of high strength-to-weight ratio, good corrosion resistance and favorable high temperature mechanical properties. While the high cost of titanium has severely restrained consideration of titanium usage in mass produced automobiles, there are certain components for which titanium alloys are particularly well suited from a design viewpoint. The most promising of these applications include suspension springs and engine components such as valves, valve springs and valve retainers. The technical advantages offered by the use of titanium alloys in these applications include reductions in vehicle weight and improvements in performance, fuel economy and packaging efficiency. This paper reviews characteristics of the several types of titanium alloys.

The recent development of TiAl-based alloys by the aerospace community has provided an excellent material alternative for hot components in automotive engines. The low density combined with an elevated temperature strength similar to that of Ni-base superalloys make TiAl-based alloys very attractive for exhaust valve applications. Lighter weight valvetrain components improve performance and permit the use of lower valve spring loads which reduce noise and friction and enhance fuel economy. However, difficult fabricability and a perception that TiAl alloys are high cost, low volume aerospace materials must be overcome in order to permit consideration for use in high-volume automotive applications. This paper provides a comparison of properties for several exhaust valve alternative materials. The density of TiAl alloys is lower than Ti alloys with creep and fatigue properties equivalent to IN-751, a current high performance exhaust valve material.

Titanium is a strong, lightweight metal which is used extensively in aerospace applications. By virtue of these properties plus low elastic moduli it is particularly suitable as a spring material. Compared to steel springs of equivalent performance, titanium springs weigh less than half as much and can be designed to be more compact. The current need to reduce vehicle weight to improve fuel economy has led to a prototype development program to assess the weight saving potential of suspension springs. Front suspension springs made of β-titanium alloy were designed, fabricated and tested. The results indicate that such springs could serve as direct replacements for steel springs with a weight saving of 53%, while satisfying fatigue life, spring rate and design load requirements. Suggestions for improvements in the processing of the spring wire and fabrication have been identified which could result in even greater weight saving and lower cost.