This paper describes research into the development of reliability prediction models for rotor transmission systems in which component failure is caused by underlying aging processes such as fatigue, wear or corrosion. Reliability prediction is based on the stress–strength interference methodology, with stress related to surface damage and strength to the limit of allowable damage. The paper describes how damage accumulation and system failure logic is incorporated within the stress and strength functions. For fatigue‐dominated processes, damage grows with number of cycles in response to applied load and environmental conditions. The concept of ‘operating state’ is used to model statistical damage accumulation. Operating states describe load and lubrication conditions and associated statistical damage accumulation rate parameters. Growth rate variance is related to operating state transitions and can be modelled using stochastic techniques. Fatigue strength is obtained from S–N data. Formulated in this way, reliability can be predicted from design and operational parameters rather than historical failure data. Copyright © 1999 John Wiley & Sons, Ltd.

This paper reports progress towards the development of procedures and techniques for assessing the reliability of components at the design stage. From a fundamental understanding of the degradation and failure processes and their relation to the underlying operational, environmental, materials and design variables, the paper develops procedures to support reliability prediction of mechanical devices using an electromechanical actuator as a case study. The methodology is illustrated by particular reference to the process of sliding wear leading to jamming of the actuator.

Radar methods have been extended to measure the aerial density of small insects. Results obtained during an outbreak of the cereal aphid Metopolophium dirhodum (Walker) in south-eastern England were compared with simultaneous suction trap catches to study the sensitivity of trap effectiveness to windspeed. Two traps were studied: the Rothamsted Insect Survey trap (12-2-m) and a standard aerofoil trap. The Survey trap effectiveness is moderately sensitive to windspeed, decreasing exponentially by a factor of two for each 2-4 m/s (5 knots) of average windspeed. The two trap sensitivities did not differ significantly, but both results are very significantly different (P<0-001) from the published predictions, which were based upon a comparison of catches from suction traps and a combination of a rotary (whirligig) net and a tow net. These differences are discussed. The average catching rate is about 40% of that of an ideal trap. Seven-day catches could vary by a factor of 0-5-2-0 from average due to prolonged periods of extra strong or light winds. Systematic windspeed gradients can corrupt suction trap studies of insect dispersal in relation to vertical density profiles, diurnal flight patterns and geographical distribution. Absolute calibration of the aerofoil trap was achieved by using the remote-sensing IRADIT infra-red system to measure the aerial density of aphid-size insects near to the trap inlet in very light winds; the effectiveness was not statistically different from unity, and the Survey trap is expected to perform similarly. IntroductionThe Rothamsted Insect Survey (12-2-m) suction trap (Taylor & Palmer, 1972) has become a standard tool for monitoring the density of flying insects, particularly aphids. A network of traps, at present at 23 sites, has been managed by the Survey for 15 years in the United Kingdom, and in recent years similar traps have been operated throughout Europe (Taylor et ai, 1981). The Survey trap takes in air from a height of 12-2 m (40 ft) at the rate of approximately 0-8 m 3 /s, through a circular inlet pipe with a diameter of 0-254 m (10 in.) at a speed of about 16 m/s. Trapped insects are removed daily, the aphids identified and weekly bulletins distributed to the agricultural industry giving warnings of impending outbreaks (Woiwod et ai, 1984).The 'efficiency' of suction traps for quantifying the aerial density of passing insects has been assessed by Taylor (1962) by an indirect method. The insect catching rates of a variety of traps were measured relative to that of an aerofoil trap with an inlet diameter of

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A methodology for predicting the reliability of pipes and valves and for assessing the impact of testing and inspection policy on the safe life of a component is described. The method is based on the stress‐strength interference model and enables a combination of physical models and engineering experience to be used to estimate means, variances and associated uncertainties in the life of a component. Particular attention is paid to modelling failures arising from underlying degradation processes. Bayesian routines are used to update the model parameters and to reduce uncertainties using inspection, monitoring or test data. The paper describes the principles of the method together with examples related to subsea gate valves and pipelines.