Adiabatic Shearing Phenomenon in High-Speed Cutting
In the field of precision manufacturing, high-speed cutting technology is highly regarded for its efficiency and precision. However, behind this technology lies a complex physical process known as the "adiabatic shearing phenomenon." So, what is the adiabatic shearing phenomenon in high-speed cutting? Today, let's unveil the mystery behind this technology.
Adiabatic Shearing Band (ASB) is a localized plastic deformation phenomenon that occurs in materials under high strain rates. This phenomenon is usually accompanied by the formation of adiabatic shear bands, which are local high-temperature regions caused by the inability of heat to dissipate from within the material, leading to more intense plastic deformation. Adiabatic shear bands typically exhibit distinct "white bright band" characteristics and may be accompanied by micro-cracks and micro-voids.
The adiabatic shearing phenomenon is prevalent in the dynamic deformation processes of materials such as metals, metallic glasses, and engineering plastics, including penetration, explosive fragmentation, high-speed stamping and forming, and cutting. "Adiabatic" refers to the phenomenon where, during high-speed deformation, the deformation time is extremely short (on the order of microseconds), causing most of the plastic work to convert to heat that cannot dissipate to the surroundings in time. An adiabatic shear band is a narrow region of highly localized shear deformation, typically 10-100 μm in width, where shear strains of 10-100, strain rates of 10^5-10^7 s^-1, and temperature rises of 100-1000 K can occur. The formation of adiabatic shear bands is closely related to the dynamic fracture of materials, indicating a decline or loss of load-bearing capacity within the material or component. Thus, the study of adiabatic shear deformation holds significant theoretical value and engineering application potential. For example, adiabatic shear is one of the primary failure mechanisms in armor materials; materials used to manufacture kinetic energy penetrators require strong adiabatic shear sensitivity; the failure mode of thin shells under explosive loading is mainly adiabatic shear failure, with characteristic parameters such as fracture time and fragment size distribution closely related to adiabatic shear.
High-speed cutting is an advanced manufacturing technology that can remove a large amount of material in a short time while maintaining high machining precision and surface quality. During high-speed cutting, adiabatic shearing is a critical phenomenon involving the simultaneous action of cutting forces and cutting heat, along with intense friction between the tool and the workpiece material. Adiabatic shearing causes severe plastic deformation on a microscopic scale, affecting cutting performance and forces.
The theory of adiabatic shearing is a core aspect of high-speed cutting research. It focuses on the series of physical and chemical changes triggered by the rapid cutting speed, which prevents the material from dissipating heat promptly, leading to local high temperatures. Researchers aim to establish models that can accurately describe and predict adiabatic shearing behavior through experiments and theoretical analysis.
In experimental research, various techniques such as optical microscopy, microhardness testing, X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are used to observe and study the formation of adiabatic shear bands and white layers in different materials. For instance, researchers at Dalian University of Technology have studied the mechanisms of adiabatic shear band and white layer formation in serrated chips of 30CrNi3MoV high-strength steel through high-speed cutting experiments.
In theoretical research, multiple models have been constructed to describe the formation and evolution of adiabatic shear bands. For example, a propagation model of thermoplastic shear waves and a shear band width model based on this model have been proposed and experimentally validated. Additionally, other studies have used linear perturbation analysis to predict adiabatic shearing behavior in high-speed cutting and explored the impact of various factors on adiabatic shearing.
The impact of adiabatic shearing on high-speed cutting is significant. It can cause fluctuations in cutting force and cutting temperature, accelerate tool wear, and affect the quality of the machined surface. Additionally, adiabatic shearing can lead to changes in chip morphology, such as the formation of serrated chips. Therefore, understanding and predicting the behavior of adiabatic shearing is crucial for optimizing the high-speed cutting process.
