The Study of CFRP Variable Feed Drilling Method Based on Sinusoidal Curve

In order to reduce the delamination damage of carbon fiber reinforced polymer (CFRP) drilling and improve the drilling quality. A variable feed drilling method based on sinusoidal curve was proposed, that is, when the drill at a distance of 1mm from the hole exit, the feed rate of the drill would be reduced according to the rule of sinusoidal curve. The method is compared with the traditional feed drilling by experiment, and the influence of the variable feed drilling on thrust force, delamination factor, surface quality, surface roughness of hole wall and exit hole wall morphology are analyzed. The results show that compared with constant-feed drilling, the variable-feed drilling based on sinusoidal curve reduces the thrust force near the hole exit, and greatly improves the delamination factor, surface quality and hole wall morphology at the exit. But the influence on the hole wall roughness is not particularly obvious.

Stability Evaluation Method of Hole Wall for Bored Pile under Blasting Impact

Blasting impact load may be encountered during the construction of some pile foundation projects. Due to the effect of blasting impact, hole collapse can easily occur in the hole-forming stage of pile foundation construction. In order to prevent hole collapse, it is very necessary to evaluate the stability of a pile hole wall before pile foundation construction. The calculation of hole collapse can usually be attributed to an axisymmetric circular hole stress concentration problem. However, the existing collapse failure theory of pile hole hardly considers the effect of blasting impact load. In view of this, this paper proposes the stability evaluation method of a pile hole wall under blasting impact. Compared with the existing collapse failure theory, the proposed method fully considers the effect of blasting impact stress. Using Mohr–Coulomb strength theory and symmetry analysis, the strength condition of collapse failure is established in this work for accurate evaluation of the stability of a hole wall. The proposed stability evaluation method is demonstrated by a pile foundation construction project of a bridge. Moreover, a shaking table test on the pile hole model was performed to verify the proposed method by experimental data. The results indicate the effectiveness and usability of the proposed method. The proposed method provides a feasible way for the stability analysis of a pile hole wall under blasting impact.

Research on Fiber Bragg Grating Sensor Group for Three Dimensional In-situ Stress Measurement

The observation and estimation of deep crustal stress state is a key and difficult problem in in-situ stress measurement. The borehole wall strain gauge based on the overcoring stress relieving method is one of the main methods of in-situ stress measurement. In this paper, a strain sensing array based on FBG is designed by using the main structure of the classical hollow inclusion cell, and its layout scheme on the hollow inclusion is studied. According to the layout scheme, the in-situ stress inversion algorithm of hole-wall strain to stress is deduced; then, the triaxial loading and unloading experiment platform is built, and the calibration experiment of FBG strain sensor is designed; Finally, Abaqus finite element software is used to simulate the in-situ stress measurement process of the overcoring stress relieving. The FBG strain values of each measurement direction before and after the overcoring process are extracted, and the stress inversion equation is used to carry out the stress inversion. Through the comparison of the inversion results, it is proved that the FBG strain sensor group is feasible and reliable. The quasi-distributed FBG sensor module designed in this paper can invert the three-dimensional in-situ stress by measuring the hole-wall strain, which lays a theoretical and experimental foundation for the development and application of FBG hole wall strain gauge. It fairly makes up for the deficiency of the existing hole-wall strain gauge based on resistance strain gauge, provides direct and accurate observation way for hole wall strain measurement, and has important practical value for the development of in-situ stress measurement technology.

Research on Rapid Evaluation of Rock Mass Quality Based on Ultrasonic Borehole Imaging Technology and Fractal Method

The distribution of discontinuities in the deep stratigraphic rock mass is random and irregular, and the spatial distribution has statistical self-similarity, which can be analyzed by fractal theory. The borehole wall image obtained based on the ultrasonic borehole imaging technology can clearly reflect the rich structural surface information such as the inclination, density, and crack width of the structural surface in the rock mass. Due to its inherent fractal characteristics, the fractal box dimension of the hole wall image can be used to describe the complexity of the structural surface. In the study, the fractal box dimension of the hole wall image and the RQD value of the rock mass are compared, and it is found that there is a linear correlation between the two. Therefore, the rock quality can be evaluated according to the fractal box dimension value of the hole wall image. Finally, a rapid quantitative evaluation method for rock mass quality classification is established based on ultrasonic borehole imaging technology and fractal method.

Study on Interference Connection Based on Shape Recovery of NiTiNb Shape Memory Alloy

Interference connection is an effective method for improving the fatigue life of bolt connections. In this paper, a new method of interference connection was designed based on the shape memory effect of shape memory alloy. Using the method of numerical simulation, a finite element model was established to analyze the stress–strain rule of the bolt and the hole wall under different interference fit sizes. The results show that the stress concentration is formed at the orifice of the connecting plate. When the interference fit size is less than 1%, the connection hole has elastic deformation. When the interference fit size is 1.5%, the hole wall has plastic deformation. When the interference fit size is 2.5%, the maximum stress on the connecting plate is close to the tensile limit of the material. If the interference fit size continues to increase, the strength of the connection structure will be damaged. The connection experiments with different interference fit size were designed, and the interference force was calculated by the pull-out force. The experimental results were compared with the numerical simulation results. The change trend of the interference force with the interference fit size is consistent, which verifies the rationality of the finite element simulation.

Improved Hole Wall Roughness and Corrosion Resistance of U-Shaped Hole Prepared by Casting

The corrosion resistance of the cooling water channel in the water-cooled mold has an important impact on the application of the mold. In this paper, the influence of experimental temperature on roughness and corrosion resistance of U-shaped cooling channels prepared by casting is analyzed in detail. The results show that the experimental temperature increased from 998K to 1048K, the hole wall roughness of the U-shaped hole decreased from 83.264 to 76.287. However, the hole wall roughness increased with a further increase in temperature. Because the low experimental temperature will promote the formation of micro bulges and river ripples on the hole wall. However, with the temperature gradually increased, it will promote the aluminum matrix to react with the carbon fiber, which will increase the roughness. The corrosion performance analysis results show that a reasonable experimental temperature is beneficial to reduce the roughness of the hole wall and improve the corrosion resistance of the cooling channel. When the roughness is large, the ravines on the rough surface are easy to be the starting point of corrosion. At the same time, it is easy to cause the aggregation of Si elements to the hole wall at high experimental temperature, which will also cause corrosion. As a result, reasonable experimental temperature plays an important role in improving the corrosion resistance of the U-shaped cooling channel.