Search

Data of pollen percaentage (%) and concentration (×103 grains/g) from Lake Shuang

Data of pollen percentage (%) and concentration (×103 grains/g) from Lake Shuang

This paper investigates the effect of depth of cut on chip formation mechanism in machining of CFRP by the orthogonal cutting method. Characteristics of the cutting forces and the specific energy for material’s removal under different depths of cut for different cutting angles are studied. Meanwhile, tool-material interactions are discussed for the effect on the failure mechanism combined with the on-line micro observation of the chipping process. Chip formation is the debonding-bending for 0°, and is the cutting-shearing for 45°. It is the buckling-dominant when the depth of cut is close to the cutting edge radius. Once the depth of cut is much larger than the cutting edge radius, the kinkband-shearing occurs for 90°, and the bending-dominant for 120°. Especially, the effect of the contact between the fiber and the cutting edge is analyzed based on the contact theory. It reveals fibers with strong constraint fracture at local contact area like 45°. However, it becomes a combination of the bending and the local contact due to the large bending deformation with the decrease of the off-axis modulus along the cutting direction like 90°. Furthermore, the bending-dominant chip formation easily results into the severe subsurface damage due to the large bending deformation.

The essence of cutting carbon fibre-reinforced plastic (CFRP) composites is a process of material failure and chip formation. The mechanism of cutting CFRPs can be explained from the perspective of local removal of material on the microscopic level. The morphology of the chips resulting from the cutting process can be determined from the perspective of the overall failure of the material on the macroscopic level. To reveal the mechanism of cutting CFRPs at both levels, a macroscopic model and a microscopic model are established in this study. Orthogonal cutting is applied in both of the models to illuminate the removal process. Combined with experimental observations, the results that obtained from both the macroscopic and microscopic level revealed the different mechanics of cutting CFRPs for different fibre orientations. For example, the forms of fracture that occur at 0° fibre orientation are primary interface cracking and fibre bending; the resulting chips have long shapes.

The cutting edge of the polycrystalline diamond tool easily blunts in high-speed milling of carbon-fiber-reinforced plastic with the tool deterioration. It aggravates the burrs damage due to the change in the tool–material interaction. Therefore, this paper analyzes the tool–material interaction in milling of carbon-fiber-reinforced plastic based on the material-removal mechanism to investigate the tool deterioration mechanism. It reveals that there are two main reasons for the tool deterioration: the extreme crashing and ploughing of the uncut fibers on the tool, and the serious impact of fibers strongly supported on the cutting edge. An indirect measure method is proposed to quantify the tool deterioration including the ploughing-caused wear and impact-caused microchipping. Furthermore, the milling tests are performed to evaluate the tool deterioration under different cutting speeds in the range of 7.33–9.42 m/s. Meanwhile, a modified mathematical model of tool life is proposed based on a strict burr specification in milling of the carbon-fiber-reinforced plastics. Polycrystalline diamond tool has the longest life with the run-in wear and the quasi-steady-state wear for 7.33 m/s cutting speed, and the life rapidly decreases with the increase in the cutting speed in this range. For the cutting speed larger than 8.37 m/s, the wear resistance of polycrystalline diamond tool is very low, because the accelerated state wear occurs instead of the quasi-steady-state wear. Thus, the optimization of the tool geometry and the assisted lubrication should be applied for its improvement.

Carbon fiber-reinforced plastics (CFRPs) have the characteristics of non-homogeneity and anisotropy. Damage occurs frequently in machining of CFRPs, and it can seriously influence the performance of work piece. This study builds a finite element model for machining of CFRPs based on the constitutive relation with damage, the Hashin failure criterion, and the damage evolution. The continuous cutting processes of unidirectional CFRPs with various fiber orientations are simulated. Cutting forces and sub-surface damage are determined from simulations. Furthermore, machining experiments on unidirectional-CFRPs are performed. Cutting processes are monitored, and cutting forces are measured. An artificial neural network (ANN) force model is proposed by using the experimental data, and then simulation results of the cutting forces are validated by these of the ANN model. Cutting force increases when the fiber orientation varies from 0° to 135°. Fiber orientation is the critical factor affecting the cutting force and the sub-surface damage. More sub-surface damage occurs in a fiber orientation range of 90–135°. The primary reasons for the induced sub-surface damage include the damage evolution and the crack propagation of matrix caused by the cutting force. In addition, the effects of cutting parameters and tool geometries on the cutting force and the damage are discussed by simulations. The cutting force thus can be reasonably controlled to reduce the damage.

In order to know about the real-time operating condition and the remaining life of the wind turbine bearings in time, a method of life prediction was proposed based on Wiener process. Firstly, the relationship model of bearing temperature parameters and speed parameters of wind turbine was established by using multiple linear regression; Secondly, the established relationship model was been used to build the real-time monitoring and performance degradation model of the wind generator bearings; Thirdly, Linear Wiener process and nonlinear Wiener process were respectively used to establish the remaining life prediction model of wind turbine bearing; Finally, the feasibility and effectiveness of the method in practical application were verified by analyzing the temperature data of a wind turbine’s gearbox.

Inward-bonded Patch technology is a common method for repairing defects and damage of (Fiber Reinforce Plastics) FRP parts. In the project, there is an urgent need for an in-situ machining machine with a concave step structure in the method. Such thin-walled, weakly rigid parts are easily deformed under pressure. Therefore, the machine beam is lightly designed to reduce the influence of compression deformation on the machining quality. In this paper, the annular (basalt fiber polymer composite) BFPC beam of a certain type of in-situ machining machine prototype is taken as the research object. Firstly, based on the analysis of the prototype working conditions, the comprehensive performance index of the beam is clarified. Using the topology optimization technology, the beam topology of the optimal topology is obtained. Finally, the establishment is established. The multi-objective optimization function with regular structural parameters as variables and minimum beam quality and deformation as the target has obtained the optimal topology and optimal performance of the beam structure.

Carbon Fiber Reinforced Plastics (CFRP) are widely used in the aerospace application. However, the machining induced sub-surface damage is critical to them. Because it would significantly reduce the reliability and the service life of the components. Particularly when the cutting angle is obtuse. The main purpose of this paper is to research the effect of the cutting parameters on the sub-surface damage in machining of CFRPs with obtuse cutting angle. And the numerical simulation is an effective method to study and observe the sub-surface damage under different cutting parameters. Despite some researches have been carried out on the effects of the cutting parameters on sub-surface damage through two-dimensional cutting models of CFRPs. The out-of-plane force also has influences on the change of the depth of the subsurface damage. And the generated cutting forces are unequal under different cutting widths during the cutting of the CFRPs. Therefore, the effects of the cutting width on the sub-surface damage still need to be studied. In this paper, a three-dimensional numerical model for the orthogonal cutting of CFRPs was developed based on the AbaqusTM. And the stress-strain relationship in the out-of-plane direction when machining CFRPs was considered in this model. Particularly, the mode I fracture in the transverse direction of the CFRPs was indicated by the damage factor of the tensile failure in the transverse direction to describe the sub-surface damage. The 135o cutting of the CFRPs under different cutting widths were simulated by this model, and the change of the depth of the sub-surface damage were analyzed. In addition, the simulation results were validated by experiments. The model provides an effective method for the prediction of the sub-surface damage, which is helpful for the optimization of the design of the tool.

The present paper studies the material removal mechanism of machining carbon fiber reinforced polymer (CFRP) by a micro-mechanical model, and proposes prediction models of cutting forces from the microscale to the macroscale. At the microscale, the micro-mechanical model for cutting a fiber in orthogonal cutting CFRP is established via the elastic foundation beam theory with explicit description of the carbon fiber and the matrix. The deflection and failure of the fiber constrained by the surrounding composite are analyzed under the cutting effects by the tool edge. In addition, the fiber failure under the pressing of the flank face is analyzed based on the undulating fiber theory. Analytical expressions are established at the microscale for evaluating the force for cutting a single fiber and the compression force for a single fiber from the flank face. At the macroscale, the chip length is determined by analyzing the characteristics of the cutting force signals of orthogonal cutting experiments. The characteristic chip length is used for establishing the trans-scale prediction model of cutting forces from the microscale to the macroscale. The total cutting and thrust forces at the macroscale during the formation of a chip are predicted based on the micro-mechanical results and the characteristic chip length, which agree well with the experimental results for orthogonal cutting of CFRP. Furthermore, the fiber failure modes and the debonding between the fiber and the matrix under different supporting conditions are discussed by the micro-mechanical model, by which subsurface damages are recognized.