TECHNICAL CONDITION EVALUATION OF CONSTRUCTION MATERIALS OF A TURBO-REFRIGERATION UNIT PARTS OF AN AIRCRAFT AIR CONDITIONING SYSTEM BY CHANGING THE LEVEL OF RESIDUAL STRESSES
One of the frequent causes of aviation incidents and accidents is the failure of technical equipment and the destruction of aircraft (AC) constructions resulting from unacceptable deformations and structural destruction of the parts operating under high mechanical loads. Operation of parts, assemblies and units of aeronautical equipment in the most typical cases does not allow their plastic strain. Thus, in accordance with the airworthiness standards, aeronautical equipment should not be used under the conditions leading to the occurrence of dangerous permanent yielding and fatigue damage to the material in its structures. The probability of these negative factors is determined by the stress condition of the aircraft structural component material during operation. An important factor that determines the stress condition as well as the technical condition of an object of technology is residual stresses, most often available in the material of the part. In particular, the summation of the residual stresses with the stresses of the operating load can lead to the exceedance of the critical values stress condition indicators, for example, the fatigue margin or the yield point of the material. In view of this, the development of new technologies that will provide information on the actual technical condition of the structure of each aircraft during its operation considering residual stresses is a critical task. The article describes a possible approach to evaluating and predicting the technical condition of the structural materials of assemblies and units operating under cyclic loading based on determining the change of residual stresses level on the surface of the parts during their operation. As a method for determining residual stresses, the X-ray diffractometric method was chosen, as it is characterized by high accuracy and reliability of the results obtained. The developed approach was tested on the components of the aircraft air conditioning system (turbo-refrigeration unit). The results of evaluating the technical condition of the parts conform to the facts of their operational damage. In these circumstances, although the proposed approach cannot currently be used directly on board an aircraft for continuous monitoring of the technical condition of aircraft structural materials, however, its development seems to the authors to be promising for these purposes.