Jiangsu University of Technology

Abstract. To address the issue of exit delamination and burr defects during the drilling of carbon-fiber-reinforced plastics (CFRPs), this study employs rotary ultrasonic-assisted drilling (RUD) technology. A three-factor, three-level drilling experiment was designed using the Box–Behnken method to analyze the morphology of drilling-induced defects. Based on response surface methodology (RSM), the influence of process parameters on exit defects was quantitatively evaluated, the interactions among process parameters were investigated, and the RUD parameters were optimized. The results indicate that delamination damage and burr defects are prone to occur at the drill exit. Increasing the spindle speed (7000 r min−1) effectively suppresses delamination, while reducing the feed rate (30 mm min−1) and using a coarse-grit tool (60 grits) significantly minimize fiber tearing and burr formation. The optimal parameter combination (7000 r min−1, 30 mm min−1, 60-grit tool), obtained through multi-objective optimization, was experimentally validated. The delamination factor and burr height coefficient were reduced to 1.047 and 0.016, respectively, consistent with the model predictions. This study provides a process strategy for high-precision drilling of CFRP that enables synergistic control of multiple defects.

Multi-group linear models with measurement errors are frequently employed in situations where covariates cannot be precisely measured, thereby compromising the validity of between-group comparisons. However, the study of experimental design theory for these models is currently at an underdeveloped stage. This paper is concerned with the problem of constructing locally c-, DA- and D-optimal designs of multi-group linear models with measurement errors for estimating parameters or contrasts in the model parameters. Equivalence theorems are established to confirm the optimality of the designs for such models under each criterion, and the generalization of Elfving’s theorem is proved to describe the geometrical characterization of locally c-optimal designs for such models. Furthermore, the locally D-optimal designs for a class of multi-group linear models with measurement errors can be explicitly determined. It is shown that the locally D-optimal design for such models is given by the product of the locally D-optimal designs for linear measurement error models corresponding to those groups. To illustrate these concepts, several examples are provided.

Collision and wear are common phenomena in revolute clearance joints, caused by the positional deviation between the journal and bearing centers. The freedom of motion and contact–impact characteristics are reflected in the mechanism’s movement. The penetration behavior of the clearance joint is described using modified elastic contact model combined with Coulomb’s friction. In addition, the dynamic model of a high-precision mechanism with a clearance joint is established using Largrange’s equation. A dynamic performance experiment is also conducted. The results prove the validity of the proposed method. The kinematic accuracy of this mechanism is then used to evaluate the stability and motion error in a case study. Furthermore, the influence of the clearance joint on the dynamic behavior of the high-precision mechanism is thoroughly analyzed. The results show that the fluctuation range of the slider’s dynamic repeated precision for slider is only 0.022 mm under high-speed conditions, meeting the design requirement.