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The present review gives a brief summary of the work performed in the Netherlands in the field of aeronautical fatigue, during the period from March 1993 until March 1995. The contributions come from three different sources, namely: The National Aerospace Laboratory (NLR) • The Department of Aerospace Engineering, Delft University of Technology (DUT) Fokker Aircraft B.V. The names of the principal investigators and their affiliation are presented between brackets at the end of each topic title

A brief review is given of work performed in the Netherlands in the field of aeronautical fatigue. Where possible, applicable references have been presented.

The paper starts with a general discussion on various aspects of life re-assessment. Specific attention is paid to the possibility of re-assesgrnent by means of comparative fatigue tests on specimens. As an illustration of this method, the paper gives a description of the life-re-assessment procedures applied by the Royal Netherlands Airforce for their NF 5A/B aircraft. Paper presented at the Xth ICAF-Symposium, 16-18 May 1979, Brussels, Belgium.

Due to the development of servo hydraulic fatigue testing machines, fatigue tests under realistic loading conditions have become possible. In these tests, standardized load sequences can be applied. The paper describes the main properties of such sequences, including TWIST and FALSTAFF. Various examples of application of these sequences are presented. The paper ends with a discussion on the future development of stemdard sequences. Paper presented at the 2nd AIFA (Italian Association on Aeronautical Fatiguw) Meeting, Naples, 26-28 February 1980.

Many military aircraft are used more severely and over a longer periodthan originally intended. Consequently, a careful life management, including service load monitoring has become indispensable. This paper describes the development of a simple method to quantify the severity in terms of "potential crack growth" of recorded load spectra. This Crack Severity Index accounts for load interaction effects under spectrum loading. Crack growth tests under a variety of different load spectra have proved the validity of the CSI-concept. It is shown that the CSI-concept can also be used as a tool in studies to influence fatigue life consumption by operational measures.

In dit rapport, dat een vervolg is op het NLL rapport TM S.548, wordt de numerieke oplossing van warmtegeleidingsvraagstukken met behulp van differentiemethoden nader bestudeerd. Twee differentiemethoden worden aan de hand van een eenvoudig rekenvoorbeeld vergeleken. Als voorbeeld voor de berekening van temperatutirsverdelingen in aërodynamisch verhitte vliegtuigconstructies wordt een numerieke oplossing gevonden voor de in rapport S.548 op analytische wijze bestudeerde huidplaat-lijfplaatcombinatie. Ten slotte wordt aandacht besteed aan het probleem der thermische weerstand van verbindingen in vliegtuigconstructies.

In this Report the analysis of the response of the "Fokker Bond Tester" on single lap joints, given in NLR Report M.2080, is extended to the case of douhle lap joints. Theoretical results are compared with measurements, indicating a good agreement "between theory and experiment.

The paper starts with a review of the various types of loading acting on the aircraft structure and our ability to accurately predict their magnitude and frequency of occurrence for a given aircraft usage. Next, attention is paid to the variation in load experience and its causes, with specific reference to the variation in aircraft usage. For transport type aircraft these variations are largely defined by the variation in flight length and payload. For combat type aircraft, on the other hand, the variability is considerably larger and consequently the prediction of load spectra considerably more difficult. For the assessment of actual service load spectra, operational flight load measurements and/or service usage monitoring are required. The rapid development of electronics during the last decades has opened the possibility for advanced processor based service fatigue load monitoring systems at relatively low price. However, it will be argued that specifically for transport aircraft simple usage monitoring may already provide highly relevant information. For combat type aircraft, the determination of average "mission type" spectra from in flight multiparameter recordings, in combination with mission usage monitoring for individual airplane tracking appears to be an adequate solution.

A statistical analysis was made of flight load data pertaining to about 10000 RNLAF F-104G operational flights. The distributions of load experience per flight could be fairly well approximated by Weibull-distribution functions. Specific attention is paid to the differences in load experience per aircraft. The paper concludes with a discussion on basic aspects of Fatigue Load Monitoring.

Paper presented at the 17th ICAS Congress, Stockholm, September 1990. The actual service load experience of aircraft may differ appreciably from design assumptions. The necessity to monitor service loads is generally recognized now for military aircraft. This paper starts with a general review of the overall life management procedure commonly used today. Specific elements in this procedure are discussed in some detail. Specific attention is paid to the amount of scatter in severity between different flights and the required sample sizes of flight load measurements for obtaining reliable average load spectrum data. Possible causes for variation in load experience between different aircraft flying the same duty are analysed. It is concluded that Individual Aircraft Tracking (lAT), if necessary at all, can usually be adequately accomplished by administrative means, indicated as Usage Monitoring.

A brief review is given of work performed in the Netherlands in the field of aeronautical fatigue. Where possible, applicable references have been presented. This review will be presented at the 25th ICAF Conference, Edinburgh, United Kingdom, 16-17 June 1997.

A brief review is given of work performed in the Netherlands in the field of aeronautical fatigue. Where possible, applicable references have been presented.

Modern aircraft structures have a finite fatigue life. During the design an estimation of the aircraft usage and the associated load experience will be made. Safe service lives and inspection schedules are determined by analysis and tests on the basis of this design load spectrum. However, the actual service usage can deviate appreciably from design assumptions. In that case a re-assessment of lives and inspection schedules will be necessary. This paper gives a brief review of methods for monitoring fatigue loads in service.

The contents of this report will become part of an AGARDograph with the title: "Helicopter Fatigue Design Guide". After a general definition of counting principles, a detailed description of the so called Range Pair- Range or Rainflow Counting Method is presented. Flow diagrams are included. The method is illustrated by means of a worked-out example.

Modern aircraft structures are designed to be damage tolerant and to have an adequate durability. The Damage Tolerance provides structural safety in case of inadvertent cracking, the Durability determines the time that the structure can be kept in service in an economically acceptable way. Many aircraft are planned today to be kept in service considerably longer than the original design life, and knowledge of the actual durability of the aircraft becomes important. Unfortunately, only a lower limit of that durability, determined in a full scale durability test is-known, however. The present report investigates how estimates of the actual durability can be made on the basis of the absence of cracks at a certain lifetime. "Durability" is loosely defined: In the present study, two Durability Criteria are investigated. In the one, it is assumed that the Durability Life ends when a specific number of cracks has occurred. The other criterion assumes that Durability life ends when a certain crack rate, that is the number of new cracks developing per flight hour, is reached. Using a simple statistical model, the concept is quantified and the influence of the various parameters involved is investigated. Some examples quantify the predictions that can be made and indicate that the methodology defined can be applied in practical cases.

The present course book has been prepared as lecture notes for a summer course given at the Technical University of Bandung (ITB) in the summer of 1984. This course took place within the framework of the TTA-79 Technical Assistance Project as agreed between the Governments of Indonesia and the Netherlands. The subjects of the course are listed in the contents. In general, the set-up of the course has been to give the student an overview of the types of loading and an insight into,the physical aspects of aircraft loads rather than to provide a full mathematical treatment. Only the chapters dealing with the dynamic response of aircraft and the description of continuous atmospheric turbulence require more than average mathematical training for understanding.

Using a relatively simple model, calculations are made of the effect of various load spectrum variations on fatigue damage accumulation for fighter aircraft, with specific reference to RNLAF F-16 A/B aircraft. As the larger part of the total damage is due to manoeuvres with peak value between An = 3.5 and An = 6, reduction of manoeuvring in this range is most effective in reducing fatigue damage. Truncation of the load spectrum, by restricting the maximum load factor, has an unfavourable effect on fatigue damage.

Standard methods for the calculation of Design Continuous Gust Loads cannot be applied in the case of aircraft with nonlinear response characteristics. In such cases, Design Loads can be calculated using stochastic simulation techniques. These techniques, however, require a very large computational effort. Hence, alternative methods, indicated as "Deterministic Spectral Gust Methods" have been developed. This report gives a brief review and comparison of three of these methods. A proposal is formulated for a Cooperative Working Activity, to evaluate and validate these methods as an "acceptable means" for the Definition of Design Continuous Gust Loads for nonlinear aircraft.

The present paper gives a brief review of current and planned research at NLR related to the problems associated with Ageing Aircraft. This research is primarily directed towards the prevention of Ageing Aircraft problems in future aircraft and is concentrated on two areas: - prevention of MSD in lap joints; - improved knowledge on operational load experience. The major part of this research is carried out in some form of international cooperation. The Memorandum of Cooperation between FAA and the Netherlands Civil Aviation Department in the area of aviation safety provides an effective framework for the coordination of research efforts related to ageing aircraft problems. NLR experiences this cooperation with and support from FAA are very stimulating,