Relying on the Kyle Measurement and Control M-6000 equipment, we jointly solve the problem of fatigue crack propagation in high-temperature alloys

This article conducts a systematic study on the fatigue crack propagation behavior of GH4169 nickel based high-temperature alloy, a key material for aerospace hot end components, under the coupling effect of high temperature (650 ℃) and overload. The author adopts a single lens 3D digital image correlation system based on double prisms, combined with high-precision electromagnetic measurement and control by KyleDynamic Mechanics TestA new method for synchronously matching images and fatigue loads has been developed, and a hybrid strategy combining incremental polynomial and secant method has been proposed to significantly improve the calculation accuracy of fatigue crack propagation rate. By introducing the new parameter of crack opening ratio, the system analyzed the variation of crack closure effect under different stress ratios (R=0.1 and R=0.5).

The research results indicate that under lower stress ratios (R=0.1), the fatigue crack propagation rate is higher, and the delay effect caused by overload is more significant; The crack closure effect is evident at R=0.1 and almost disappears at R=0.5. In addition, after the application of unimodal overload, the crack closure effect is significantly suppressed in the initial stage, but as the crack passes through the overload induced plastic zone, its effect gradually returns to the pre overload level.

The overall layout of the high-temperature fatigue testing system used in this research institute was demonstrated, with the electromagnetic dynamic mechanical testing system of Kyle Measurement and Control as the core loading equipment, combined with a customized high-temperature furnace and a dual prism single lens 3D digital image acquisition device, to construct a complete high-temperature fatigue testing platform. The system achieved precise synchronization between fatigue loading and full field deformation measurement in a high temperature environment of 650 ℃, providing a reliable experimental basis for studying crack propagation behavior at high temperatures.

The displayed image is of a compact tensile specimen obtained through the BSL 3D DIC system. The surface of the specimen is sprayed with high-temperature resistant matte white paint to form random speckles. This treatment ensures that high-quality DIC analysis data can be obtained while precise load control is performed on the Kyle measurement and control testing machine.

The cyclic load spectra under constant amplitude loading and single peak overload (overload ratio of 1.7) conditions were obtained using the Kael measurement and control system under stress ratios of R=0.1 and R=0.5, respectively. The accuracy and stability of load control provide reliable guarantees for studying the influence of different load histories on crack propagation.

The identification process of crack location was demonstrated by comparing the crack path images of three adjacent measurement cycles under maximum load. The middle image shows the crack morphology of the current cycle, with the top and bottom representing the crack morphology of the front and back cycles respectively. By comparing, the crack can be accurately located, providing a basis for the subsequent arrangement of virtual displacement extensometers.

This study deeply revealed the influence of different stress ratios and single peak overload on the fatigue crack propagation behavior of GH4169 nickel based high-temperature alloy under high temperature conditions of 650 ℃ through the Kyle measurement and control electromagnetic dynamic mechanics test system. The reliability and accuracy of experimental data provide important technical support for understanding the fatigue damage mechanism of nickel based high-temperature alloys under service conditions.