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Ultrasonic fatigue testing machines working at approximately 20 kHz allow extending the number of testing cycles to the 108-1010 range, which would be prohibitive using conventional servo-hydraulic machines (up to 100 Hz). One of the questions that arise, however, is if the results from these very high frequency tests are comparable to the ones obtained from conventional tests performed at lower frequencies. This paper compares the high cycle fatigue (HCF) behavior of four cast aluminum alloys under two test frequencies (75 Hz and 20 kHz). It is shown that the S-N curve for some alloys is very sensitive to the testing frequency.

The effect of temperature and preload on the bolt load retention (BLR) behavior of AZ91D and AE42 magnesium die castings was investigated. The results were compared to those of 380 aluminum die castings. Test temperatures from 125 to 175°C and preloads from 7 to 28 kN were investigated. The loss of preload for AZ91D was more sensitive to temperature than that observed for AE42, especially at low preloads. In general, retained bolt-load was lowest in AZ91D. All test assemblies were preloaded at room temperature and load levels increased when the assemblies reached test temperature. The load-increase was dependent on the preload level, test temperature, alloy, and results from thermal expansion mismatch between the steel bolt and the magnesium alloy components, mitigated by the onset of primary creep. Thermal exposure (aging) of AZ91D at 150°C improved BLR behavior.

Recently, there has been increased interest in titanium alloys for advanced automotive engine components to satisfy current demands for increased fuel economy. Titanium alloys offer a unique combination of high strength-to-weight ratio, good corrosion resistance and favorable high temperature mechanical properties. While widespread acceptance has been limited by production cost relative to other competing common materials, new technology improvements will enhance utilization of these alloys by decreasing material processing costs and increasing productivity. For the applications to automotive engine components, high temperature near-α type titanium alloys, mainly, were considered and Mechanical properties were charcterized at room temperature and elevated temperatures. Especially, for these applications, there is a need to understand creep behavior as a function of microstructure at 650°C and 760°C where creep will be one of the important limiting factors in service life time.