Development of an amended friction model
Advanced composite materials are potential candidates for numerous applications due to their remarkable properties such as lightweight and high strength. In particular, carbon fiber-reinforced polymers (CFRPs) are widely used to reduce the weight of structural components in various industries like aerospace and renewable energy. However, CFRPs are generally difficult to cut and machine composites. The presence of fiber fracture, matrix crack and debonding is often an indication of poor machining quality. Besides, machining of CFRPs is characterized by massive tool wear, which makes the process quite costly. These problems are some of the main reasons for the limited application of CFRPs, especially in situations that require high precision and machining quality.
So far, extensive research has been conducted to address the problems above. The available research methods can be classified into three main categories: experimental, analytical and simulations methods. These methods have both advantages and disadvantages. For instance, the experimental approach is more reliable but costly and time-consuming, while the analytical approach is more cost-effective. However, the analytical method is not suitable for a detailed study of the CFRP removal mechanisms.
Interestingly, numerical simulations can investigate the material removal mechanisms from micro-and macroscopic perspectives to overcome the machining difficulties. Unfortunately, most proposed numerical simulation models assume a constant friction coefficient value, which is not always the case in practice. Additionally, the friction model should be nonlinear, as witnessed in the metal machining. Therefore, developing a reliable friction model by accurate calibration of the friction coefficient is highly desirable.
To address the above challenges, Dr. Jie Xu and Professor Yi Ding from Hunan Institute of Engineering, Mr. Chenxi Wang from Xi’an Jiaotong University and Dr. Guiqiang Liang from Tsinghua University developed an amended friction model for simulating the process of unidirectional carbon fiber-reinforced polymer (UD-CFRP) orthogonal cutting. A total of two experiments and five simulations were implemented. The first experiment was friction coefficient calibration to accurately calibrate the friction coefficient for establishing a friction model between the workpiece ad cutting tool during UD-CFRP orthogonal cutting. The authors also conducted an experiment to validate the correctness and accuracy of the amended friction model. The verification experiment comprised an orthogonal cutting assuming a standard cutting force and comparing the real-time chip formation with that recorded by the high-speed camera. The work is currently published in the journal, Composite Structures.
Results demonstrated the nonlinear relationship between the friction coefficient and normal force and the inconsistency of the friction coefficient value in tool-CFRP tangential contact. Consequently, the amended friction model enhanced the numerical model results in terms of chip formation and predicted thrust and cutting forces. For instance, a variation in the friction coefficient from 0.075 to 0.2 and an improvement in the thrust forces by 52% was reported. Furthermore, the authors observed an increase in the normal force with decreased friction force until achieving an optimal value. Thus, a good agreement between the simulation and experimental result was moted. The results also provided detailed information about the two chip formation zones: splash and accumulation zones, characterized by fiber and epoxy resin chips, respectively.
In summary, an amended friction model was successfully developed for numerical simulation of unidirectional CFRP in machining. Base on the results, the amended model significantly improved the performance of the CFRP numerical model by providing ideas for accurate calibration of the friction coefficient value. As such, the study addressed most of the difficulties associated with CFRP machining. For example, the results on chip formation can improve tool design to reduce resin accumulation. In a statement to Advances in Engineering, Professor Yi Ding said the new study will pave the way for the development of more efficient CFRP machining methods based on the tool-chip separation technique.
Xu, J., Deng, Y., Wang, C., & Liang, G. (2021). Numerical model of unidirectional CFRP in machining: Development of an amended friction model. Composite Structures, 256, 113075.