Comparison of the Mechanical Properties of A588 Weathering Steel and Titanium Alloys Under Fatigue Loading and Elevated

Weathering steel A588 is commonly utilized as a construction material due to its high durability and resistance to corrosion. On the other hand, titanium alloys are extensively used in many industries due to their high strength-to-weight ratios, excellent fatigue properties, and outstanding biocompatibility. This study aims to compare the mechanical properties of A588 weathering steel and titanium alloys under fatigue loading, elevated temperatures, and strain rates.

Materials and Methods:

The test specimens were machined from either A588 weathering steel or titanium alloys (Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo). The specimens were subjected to fatigue loading at various strain amplitudes ranging from 0.1% to 0.5% and frequencies ranging from 10 Hz to 100 Hz using a servo-hydraulic fatigue testing machine. The elevated temperature tests were conducted at temperatures ranging from 20°C to 600°C using a high-temperature furnace. The strain rate tests were performed at different strain rates ranging from 10^-4/s to 10/s using a high-rate compression testing machine.

Results:

Under low strain amplitudes (less than 0.2%), the fatigue strength of A588 weathering steel was higher than that of titanium alloys. However, at higher strain amplitudes, the fatigue strength of titanium alloys was superior to that of A588 weathering steel. Furthermore, the fatigue limit of titanium alloys was higher than that of A588 weathering steel at all frequencies tested, particularly at 100 Hz. At high temperatures, both A588 weathering steel and titanium alloys experienced a decrease in their mechanical properties. Nonetheless, the decrease in the fatigue strength of A588 weathering steel was much more significant than that of titanium alloys. The strain rate sensitivity of A588 weathering steel was higher than that of titanium alloys.

Discussion:

The results of this study suggest that A588 weathering steel is more suitable for applications that require low strain amplitudes and low frequencies. On the other hand, titanium alloys are more applicable for high strain amplitude and high-frequency applications due to their higher fatigue limits. The superior fatigue strength of titanium alloys may be due to their high strength-to-weight ratios and excellent fatigue properties. Furthermore, the reduced fatigue strength of A588 weathering steel at high temperatures may be attributed to the oxidation of the steel's surface, which can lead to the formation of microcracks and ultimately lower fatigue strength. Conversely, titanium alloys have excellent oxidation resistance, and their fatigue strength is not significantly impacted by high temperatures. Finally, the higher strain rate sensitivity of A588 weathering steel may be due to the Bauschinger effect, where the direction of deformation changes under compressive loading conditions, leading to increased yield stress and ultimate tensile stress.

Conclusion:

In conclusion, this study illustrated that A588 weathering steel and titanium alloys offer different mechanical properties under different conditions. A588 weathering steel is more suitable for low strain amplitude and low-frequency applications, while titanium alloys are more applicable for high strain amplitude and high-frequency applications. Furthermore, titanium alloys have excellent oxidation resistance and are less sensitive to strain rates than A588 weathering steel. These findings may aid in the selection of optimal materials for various applications based on their expected loading and environmental conditions.