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The recently increased interest in very high cycle fatigue properties of materials has led to extended use and further development of the ultrasonic fatigue testing technique. Specimens are stimulated to resonance vibrations at ultrasonic frequency, where the high frequency allows collecting lifetime data of up to 1010 cycles and measuring crack propagation rates down to 10−12 m per cycle within reasonable testing times. New capabilities and methods of ultrasonic testing and outstanding results obtained since the year 1999 are reviewed. Ultrasonic tests at load ratios other than R = −1, variable amplitude tests, cyclic torsion tests and methods for in situ observation of fatigue damage are described. Advances in testing at very high temperatures or in corrosive environments and experiments with other than bulk metallic materials are summarized. Fundamental studies with copper and duplex steel became possible and allowed new insights into the process of very high cycle fatigue damage. Higher cyclic strength of mild steels measured at ultrasonic frequency because of plastic strain rate effects are described. High‐strength steels and high‐alloy steels are less prone to frequency influences. Environmental effects that can lead to prolonged lifetimes in some aluminium alloys and possible frequency effects in titanium and nickel and their alloys are reviewed.

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We examined the natural variation of nitrification potentials (NPs) of surface sediments and macrofaunal tubes and burrow walls in relation to sediment NH,' level, season, and macrofaunal species. NP (the ability of a unit of sediment to oxidize NH,' when NH,+ and O2 are not limting) is an index of the abundance and activity of nitrifying bacteria which we measured in slurries with the chlorate block technique (nmol NO2--N produced g-' dry weight sediment h -' ) . The NP of the tubes of the polychaete Loimia medusa was positively related to sediment NI I<+ (KC]-extractable) concentration at 3 sites where tubes were collected in June 1990 (Spearman rank correlation coefficient rs 0.90. p = 0.03), as was the NP of surface (0 to 1 cm) sediment (r2 = 0.92, p = 0.002). The degree to which tube NP exceeded the NP of surface sediment was, however, negatively associated with sediment NH4+ (rS = -0.84, p = 0.05). Tube NP of L. medusa did not vary significantly with date (February, April, and June 1990). Tubes or burrow walls of Macoma balthjca (bivalve), Leptocheirusplumulosus (amphipod), and the polychaetes Macroclymene zonalis, Pectinaria gouldll, L. medusa, and Diopatra cuprea had NPs significantly greater (2 to 20 times) than that of adjacent sediment from the same depth interval, indicating that these species stimulated nitrification. Except for burrows of M. balthjca, the NPs of these structures were significantly (p 2 0.05) greater (1.5 to 61 times) than that of surface sediment. The duration of macrofaunal irrigation activity, but not irrigation rate, was positively associated (rS = 0.72, p = 0.01) with the enhancement of NP in tubes and burrow walls relative to surface sediment. These findings indicate that macrofaunal tubes and burrows tend to be sites of enhanced NP and that this enhancement varies among species due to variations in irrigation behavior. The NP of macrofaunal structures also varies among sites in relation to sediment NH,' concentrations.

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