C-C composite is a kind of typical difficult-to-machine materials due to its high hardness, high strength, and obvious anisotropy features. But, water-based or oil-based coolant cannot be used during its machining process. As a result, the machining defects, including burrs, orifice ripping, and interlayer delamination, are always unavoidable. In this article, taking the liquid nitrogen as coolant, C-C composite cryogenic drilling is researched experimentally. Taking the way of LN2 external spray cooling, a series of cryogenic drilling experiments were designed. Comparing with dry drilling, the thrust force was reduced, the machining defects were significantly inhibited, and a better roundness of holes was achieved in cryogenic drilling. It indicates that cryogenic condition has a positive effect on improving the C-C composite drilling quality.
To characterize the residual stress distribution is very crucial for workpiece fatigue lifetime and structural integrity assessment. An energy-based residual stress field reconstruction approach using limited measurements is proposed. Firstly, the Ferguson spline interpolation technique is employed as the stress interpolation base of the 2-order stress tensor. Then, an initial stress field can be reconstructed using the overall boundary conditions by minimizing strain energy. Further, the stress distribution is modified according to strain compatibility equation. At last, a typical stress unit from the artificial stress field constructed by FEM, was picked up as an input set to verify the validation of the developed model and algorithm numerically. It was demonstrated that the energy-based scheme was efficient and reliable to reconstruct the residual stress field from limited measurements.
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