Application prospects of deep in-situ condition-preserved coring and testing systems

Obtaining samples of deep in-situ conditions is first step to explore the mysteries of the earth requires. In view of the current problems of insufficient pressure maintaining capacity of the existing equipment, we independently developed the in-situ fidelity coring system and designed the osmotic pressure controller based on the geometry of square cover. The finite element method is used to analyze the pressure maintaining capacity of the pressure controller. It is found that it would produce large deformation and stress concentration when the pressure was applied on, resulting in low pressure maintaining capacity. Then the structural optimization schemes of conical sealing contact surfaces with 25?, 35?, 40?, and 45? apex angles and spherical sealing contact surface are proposed, and the spherical contact surface structure is found to be optimal. Finally, the material is optimized, and a higher strength material such as 45CrNiMoVA alloy is used. Based on the pressure controller with spherical contact surface, the pressure maintaining capacity increased to nearly 70 MPa. The research results obtained in this paper provide the basis for the development of the coring system, the deep exploration of the earth and the establishment of rock mechanics theory.

Inconel 718 alloy is widely used in aero-engines and high-temperature environments. However, residual stress caused by processing and molding leads to an uneven distribution of internal pressure, which reduces the reliability of service process. Therefore, numerical simulation of the nanoindentation process was applied to evaluate the effect of residual stress on the machined subsurface of Inconel 718. A gradient material model of Inconel 718 was established in ABAQUS finite element software. Mechanical properties based on nanoindentation testing showed an influence of residual stress in combination with indenter geometry. The orthogonal experimental results show that under diverse residual stress states, the indenter’s geometry can affect the pile-up of the material surface after nanoindentation and significantly influence the test results. With increases in piling-up, the error caused by residual stress on the characterization of the mechanical properties of the hardened layer increases. Through the establishment of a numerical model, the influence of residual stress can be predicted within nanoindentation depths of 300 nm.