Determination the residual stresses in the surface layer of gas turbine engine parts by small hole drilling

Abstract

A methodology for measuring residual stresses based on drilling small diameter holes with subsequent fixation of deformation using a strain gauge as applied to thin-walled complex parts of gas turbine engines has been presented. It is known that the bulk of the details of small-sized short-life aircraft engines are thin-walled and have a complex profile and a variable cross-section in the direction of the main axes of symmetry. At the same time, the geometrical features of the parts and the specifics of the technology of their manufacture can lead to the formation of uneven high residual stresses on the surface and depth. Stresses with technological and structural stress concentrators can lead to premature occurrence and propagation of fatigue cracks at relatively low cyclic voltages. The measurement of residual stresses by hole drilling has great potential for modern aircraft mechanical engineering of gas turbine engines. Measurement of residual stresses and their depth distribution on thin-walled folding-profile surfaces of titanium alloy parts hardened by steel balls in an ultrasonic field was performed. It was used tensometric method of measuring deformation after drilling holes. The method of measuring residual stresses is based on measuring strain by a strain gauge outlet during step-by-step drilling of a hole. It was shown that the method of drilling small holes has several advantages over the method of layer-by-layer removal of thin layers of metal, which is widely used in the aviation industry. It was also established that the accuracy of determining the magnitude of stresses is significantly affected by the following factors: the accuracy of the positioning of the drill relative to the plane of the part being studied, its temperature, the actual drilling depth at each step, the dwell time at each depth, the frequency and time of interrogation of the sensors, calibration of the tensor sockets and strain gauge, etc. The proposed method for measuring residual stresses makes it possible to take into account their nature and shape of distribution, as well as to evaluate their value on folding thin-walled aerodynamic surfaces of parts made of titanium alloy after ultrasonic hardening or diamond smoothing.

Keywords

• residual stresses
• surface layer
• component
• gas turbine engine
• deformation
• hole
• depth
• hardening
• strain gauge.