Tool wear condition monitoring is an important component of mechanical processing automation, and accurately identifying the wear status of tools can improve processing quality and production efficiency. This paper studied a new deep learning model, to identify the wear status of tools. The force signal was transformed into a two-dimensional image using continuous wavelet transform (CWT), short-time Fourier transform (STFT), and Gramian angular summation field (GASF) methods. The generated images were then fed into the proposed convolutional neural network (CNN) model for further analysis. The calculation results show that the accuracy of tool wear state recognition proposed in this paper was above 90%, which was higher than the accuracy of AlexNet, ResNet, and other models. The accuracy of the images generated using the CWT method and identified with the CNN model was the highest, which is attributed to the fact that the CWT method can extract local features of an image and is less affected by noise. Comparing the precision and recall values of the model, it was verified that the image obtained by the CWT method had the highest accuracy in identifying tool wear state. These results demonstrate the potential advantages of using a force signal transformed into a two-dimensional image for tool wear state recognition and of applying CNN models in this area. They also indicate the wide application prospects of this method in industrial production.

The initial reaction mechanism of energetic materials under impact loading and the role of crystal properties in impact initiation and sensitivity are still unclear. In this paper, we report reactive molecular dynamics simulations of shock initiation of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) crystals containing a cube void. Shock-induced void collapse, hot spots formation and growth, as well as spalling are revealed to be dependent on the shock velocity. The void collapse times are 1.5 and 0.7 ps, for the shock velocity of 2 and 4 km·s^–1, respectively. Results indicate that the initial hot spot formation consists of two steps: one is the temperature rise caused by local plastic deformation and the other is the temperature increase resulting from the collision of upstream and downstream particles during the void collapse. Whether hot spots will continue to grow or quench depends on sensitive balance between energy release caused by local physical and chemical reactions and various heat dissipation mechanisms. In our simulations, hot spot would grow for U_p = 4 km·s^–1; hot spot is weak to some extent for U_p = 2 km·s^–1. The tensile wave reflected by the shock wave after reaching the free surface causes the spalling, which depends on the initial shock velocity. Typical spalling occurs for the shock velocity 2 km·s^–1, while the tensile wave induces the microsplit region in RDX crystals in the case of U_p = 4 km·s^–1. Chemical reactions are studied for Rankine–Hugoniot shock pressures P_s = 14.4, 57.8 GPa. For the weak shock, there is almost no decomposition reaction of the RDX molecules near the spalling region. On the contrary, there are large number of small molecule products, such as H₂O, CO₂, NO₂, and so forth, around the microsplit regions for the strong shock. The ruptures of N–NO₂ bond are the main initial reaction mechanisms for the shocked RDX crystal and are not affected by shock strength, while the microsplit slows down the decomposition rate of RDX. The work in this paper can shed light on a thorough understanding of thermal ignition, hot spot growth, and other physical and chemical phenomena of energetic materials containing voids under impact loading.

Wire Arc Additive Manufacturing (WAAM) for the fabrication of lightweight Al alloy represents a burgeoning area of research. Despite this, the presence of porosity defects, coarse surface grain sizes, and the clustering of precipitated phases in WAAM-produced Al alloy samples have been identified as detrimental to their mechanical properties, rendering them inadequate for contemporary service requirements. In this investigation, an innovative approach termed Ultrasonic-Rotating Extrusion-Wire Arc Additive Manufacturing (U-RE-WAAM) was proposed, which integrates the synergistic effects of ultrasonic and mechanical force fields into the WAAM process. Comparative analysis were conducted on defects, microstructure and mechanical properties between WAAM and U-RE-WAAM samples to investigate the impact of U-RE-WAAM on aluminum alloy samples. The results show that the mechanical force field causes a large amount of plastic deformation, which refines the grain size and restructures the precipitation phase from clustered aggregates to a fine dispersion. Furthermore, the U-RE-WAAM process achieves a reduction in porosity and an enhancement in grain size and precipitated phase distribution by the coupling of mechanical force field and ultrasonic energy field. Consequently, the mechanical properties of U-RE-WAAM samples are markedly superior, with a 32.8% increase in hardness and significant improvements in yield strength 81%, ultimate tensile strength 41%, and elongation 38.9%.

The initial response process of PETN containing nanoscale spherical cavities under impact loading was investigated using the ReaxFF-lg force field combined with the molecular dynamic method. The impact-induced void collapse process, hot spot formation and growth, and chemical reaction processes were determined. The hot spot formation goes through four stages: (1) overall temperature rise due to initial impact compression; (2) temperature rise on the upper surface of the void caused by local plastic deformation; (3) rapid temperature rise caused by molecules entering the interior of the void colliding with the downstream surface of the void; and (4) thermal diffusion between the hot spot and the surrounding region, resulting in a decrease in the temperature of the center of the hot spot and a slow increase in the temperature of the neighboring region. With weak impact, the void shape remains basically symmetric during the void collapse, and the void collapse is mainly caused by local plastic deformation. A strong impact will lead to a more intense material focusing. The void collapse caused by strong impact has a greater effect on the heating of the surrounding material, and the secondary compression formed by the collision between particles makes the hot spot area expand and the central region of the hot spot evolve into an approximate triangular cone. NO₂ is produced in large quantities as the initial product during the void collapse to form the hot spot, indicating that the void activates the chemical reactivity of the PETN crystal.

The initial response of PETN under the coupling of preheating, impact and defects was simulated by Multiscale Shock Technique (MSST) method and molecular dynamics. The temperature change of PETN during impact compression can be divided into three stages: (1) the elastoplastic change of the system caused by initial compression; (2) part of PETN decomposes and releases energy to raise temperature; (3) a secondary chemical reaction occurs, resulting in rapid temperature rise. Under the given conditions, a higher initial preheating temperature will lead to faster decomposition of PETN; The existence of defects will accelerate the decomposition of PETN molecules; Coupling the highest preheating temperature with defects will lead to the fastest decomposition of PETN molecules, while in the defect-free PETN system with a preheating temperature of 300 K, the decomposition of PETN molecules is the slowest. For the case of U_s = 8 km·s⁻¹, the effect of defects on the initial PETN reaction is greater than the initial preheating temperature; When the impact velocity is greater than 9 km·s⁻¹, the impact velocity is an important factor affecting the decomposition of PETN molecules. For U_s = 10 km·s⁻¹, NO₂ is the main initial product in the defective PETN crystal, while in the perfect PETN crystal, it is the combination of NO₂ and HONO. The chemical reaction kinetics analysis shows that the preheating temperature and defects will accelerate the decomposition of PETN. The higher the preheating temperature, the faster the decomposition of PETN. For the case of U_s = 7 km·s⁻¹, 8 km·s⁻¹ and 9 km·s⁻¹, the existence of defects will increase the decomposition rate by more than 50% regardless of the initial preheating temperature. In the case of Us = 10 km·s⁻¹, the improvement of decomposition rate by defects is not as significant as the initial preheating temperature.