Trwałość obliczeniowa a trwałość rzeczywista struktury statku powietrznego.

Proces oceny trwałości struktury płatowca trwa w czasie życia statku powietrznego. Trwałości rzeczywistej dokładnie nie sposób przewidzieć gdyż jest ona zmienna w zależności od warunków eksploatacji, wiedzy i umiejętności zarówno pilotów, jak i obsługi naziemnej, nierzadko również zdarzeń losowych. Na etapie konstruowania wyznacza się trwałość w oparciu o widmo obciążeń charakterystyczne dla przodków. Ze względu na trwałość planuje się remonty. Wiąże się to z pojęciem resursu. Istnieje potrzeba doskonalenia metod realistycznej oceny stanu technicznego SP, badania poziomu niezawodności z akceptowalnym społecznie poziomem bezpieczeństwa SP i śledzenia trwałości on-line.

---

The process of durability estimation of an aircraft structure lasts during the aircraft service life. There is no way for the durability to be exactly expected, because the one depends on maintenance and operation conditions, konowledge and ability of both the pilots and ground service staff members. One can observe also, sometimes, important influence of casual events. When designing the aircraft, the fatigue life of aircraft structure can be preliminary defined basing on load spectrum known from the aircraft being in service just now or from the not far past. The making use of structure durability is scheduled taking into account the programme of its repairs. This is connected with hard-time maintenance concept. There is need to improve the methods for realistic assessment of aircraft structure technical state to investigate the reliability level of flight safety, acceptable from the public point of view and to follow the on-line durability, as well. The efficient methods for the durability determination should include such the circumstances like the time data setting, trends of changes in the determined number of the flights executed by the same pilot as well as within the determined periods of calender time, for instance the one year periods ect. Important for the aircraft structure durability are, particularly, the elements, exchange of which is really not possible or of too high costs. The fatigue phenomena, corrosion, tribological effects, delamination of composit structure etc. are of significant influence on aircraft structure durability, therefore the durability is to be seen as very difficult to be measured and is considered as different for each one aircraft. In order to receive the accurate results of calculations, some investigations on the aircraft's population or on separate aircraft are necessary to be conducted. Especially useful are the ones based on NDT determining the location, size and structure of damages. The investigation of aircraft's population are to be executed with the use of statistical methods. Aircraft are the technical objects, which can be modelled as a dynamic system of continuous energy transmission within the man-technical object-environment system. This leads to the need of functional-energetic optimization of aircraft structure elements on all stages of its service life. Such the optimization requires some opinion procedures for exploitation durability to be determined. The most general cases of structural elements loading are the random external aircraft loads. As the result of such the loads some fatigue processes can be induced and propagated. Important degradation process of airframe is the result of fatigue damage, therefore the assessment of fatigue life is related to the airframe elements. The efficiency of criterion correction when selecting the methods and systems of operational potential to be assessed in order to evaluate the level of airframe durability requires the safety and reliability problems to be investigated as well as the economical problems to be analysed. Therefore the strong demand exists on new, more effecttive methods for airframe durability assessment. There is economically motivated need for airframe operational potential using, which has been create during the design working out stage. The airframe designer defines the level of operational potential basing on the calculated fatigue life of the model as close as possible to the real structure, taking into acount the modern methods of evaluation, computer aided techniques, published experimental tests results and standarts, as well. The level depends, of course, on calculation methods and techniques used in computational work under the aircraft structure as well as on the experimental test results confirmation. The argued tests results on the aircraft structure durability are basically carried out on some selected parts or elements of the structure named Significant Structure Items (SSI). The tests are carried out with the use of accelerated tests system. The possibility for approach to the crack propagation to be observed is very important property of the airframe when assessing the diagnostic susceptibility resulting from the conceptual decision performed by designer.