Scratching Forces Research Articles

Surface formation in laser-assisted grinding high-strength alloys

Laser-assisted machining is a promising method to achieve high efficiency and low damage when machining high-strength alloys. To explore the surface formation in laser-assisted grinding high-strength alloys, laser-assisted scratching was performed on a typical high-strength TC17 titanium alloy material using molecular dynamics simulations and experiments at different laser powers. The scratch force, material removal efficiency based on the scratched surface, and subsurface damage were analysed to determine the laser effects. A smaller scratch force can be achieved by laser assistance, and an appropriate laser power can enhance the material removal efficiency. The molecular dynamics simulation results were consistent with those of the experiments, and the subsurface formation process could be characterised by molecular dynamics simulations. In the laser-assisted scratched subsurface, three layers were found to differ from the matrix: amorphous, ultra-refined, and refined layers. The ultra-refined and refined layers were governed by continuous and discontinuous dynamic recrystallisation mechanisms, respectively, accompanied by different features through transmission electron microscopy analysis. These layers were shallower than those in the conventional scratched subsurface because of the annealing effect and smaller scratch force. In particular, annealing plays an important role in the amorphous layer of the machined surface. Laser-assisted belt grinding experiments were conducted for validation. This study provides significant insights into the low surface damage mechanism of high-strength alloys using laser-assisted machining.

Surface and subsurface formation mechanism of SiCp/Al composites under ultrasonic scratching

Rotary ultrasonic machining (RUM) is an effective method of high-quality and high-efficiency machining for advanced composites. However, the machining mechanism and kinematic characteristics of ultrasonic machining of SiC particles-reinforced aluminum matrix (SiC p /Al) composites are yet unclear, limiting the applications of RUM in composites machining. In this study, a rotary ultrasonic vibration-assisted scratch (RUVAS) test was designed for the high-volume fraction of SiC p /Al composites. The kinematic and scratch force model of RUVAS was developed to describe the scratch process of SiC p /Al. Both RUVAS and conventional scratch (CS) tests were performed under various scratch speeds on SiC p /Al. The scratch trajectory was divided into three modes: continuous, semi-continuous, and intermittent. We observed the formation of different surface morphology under different modes. The scratch force difference between RUVAS and CS was insignificant when the scratch speed is high, which indicated that the effect of ultrasonic vibration diminished at a high speed when the ultrasonic frequency was fixed. When assisted by ultrasonic vibration, the scratch morphology of SiC p /Al indicated that the matrix has undergone significant plastic deformation. While the hard SiC particles tended to be ruptured and pressed into the plastic matrix, this mechanism can effectively suppress the initiation and propagation of cracks, which is beneficial to reducing the stress influence zone, healing the surface defects, and improving the surface integrity. The subsurface morphology indicates that the subsurface damage under CS and RUVAS mainly includes particle cracking, matrix tearing, and interface failure. Our experimental result shows that ultrasonic vibration can effectively reduce the subsurface damage of SiC p /Al composites, bringing insight into fundamental mechanisms of ultrasonic machining and providing guidance for the vibration-assisted processing of SiC p /Al composites.

Microstructure and mechanical properties of NiTi nanoporous structures fabricated with dealloying process

Dealloying is an emerging material processing technology to fabricate nanoporous functional surface. Systematic characterization of microstructure and mechanical properties for dealloyed surface is a basis for tailoring dealloying parameters. This paper aims to investigate the effect of dealloying treatment on the evolution of microstructures and mechanical properties of NiTi alloy. Firstly, nanoporous layer is fabricated with electrochemical dealloying method to dissolve nickel element selectively from NiTi alloy. Secondly, the microstructures of dealloyed layer are characterized and analyzed with microscopic test methods. The release characteristics of nickel ions from the sample surface before and after dealloying treatment were evaluated using SBF immersion tests. Thirdly, the mechanical properties of NiTi nanoporous structure are evaluated with nanoindentation and micro scratch tests. The results show that both elastic modulus and nanohardness of the NiTi nanoporous layer are over 80% lower than those of the matrix material. The super-elastic property of NiTi alloy is weakened. Meanwhile, the scratching force at the same scratching depth is reduced by over 30% after dealloying process. Instead of severe plastic deformation, irregular brittle fracture occurs along the scratched groove and it demonstrates the plasticity degradation of dealloyed surface. Finally, the weakening mechanism of nanoporous structures fabricated with dealloying treatment is discussed.

Wear mechanisms description in nanoscale by SEM/TEM of multilayer Zr/ZrN coatings in dependence on phases ratio.

As a result of loading with an external force during the wear process, coating deforms uniformly. After a certain limit load is exceeded, coating deformation is localised through the formation of the so-called shear bands. It has been showed experimentally the process of shear bands formation. The microstructural characterisation before and after the mechanical tests was performed using scanning and transmission electron microscopy (SEM and TEM) on cross-sections of the samples. The analysis indicated that in the case of multilayer coatings where the ratio of the metallic to the ceramic phase is 1:1, the shear bands are formed at an angle of 45°. With a greater proportion of the ceramic phase to metallic (ratio 1:2), the shear band changed the shear angle from ∼45° to ∼90°. Mechanical in situ tests were carried out in the chambers of SEM and TEM. The scratch tests in the SEM were done with the simultaneous observation of the phenomena occurring on the surface of the tested materials showed that at a scratch force of 0.04 N, the additional outer a-C:H layer was damaged, which was shown in the form of a fault in the force-displacement diagram, and in the form of splits visible in the SEM image. However, the application of this additional layer had a positive effect on the wear mechanism of the entire coating structure. The test also indicated that in the case of coatings with phases ratio 1:2 and 1:4 (metallic to ceramic), the characteristics of the brittle material were demonstrated, unlike the coating with a 1:1 phase ratio, where plastic properties predominated. However, for the 1:2 phase ratio coating, the chip was more ductile than for the chip formed when testing a 1:4 phase ratio coating. For in situ mechanical testing in the TEM, a straining holder was used. The test showed that the shear band angle for a 1:1 ratio coating has changed from 45° to 90° due to the different direction of force interaction.

Experimental study on the removal behavior of SiCf/SiC by traditional and ultrasonic vibration assist scratching with single grain diamond

Due to their excellent mechanical properties at elevated temperatures, Ceramic Matrix Composites (CMCs) are increasingly used in the manufacture of critical components for industries such as aerospace, nuclear and automotive. However, its high hardness, brittleness, anisotropy, and non-homogeneity lead to severe tool wear and uneven cutting process during material removal machining, making it difficult to control the surface quality. To gain an in-depth understanding of the material removal mechanism of CMCs for grinding processing, variable depth-of-cut scratch tests along different scratch directions under conventional and ultrasonic assist conditions were conducted. The results showed that ultrasonic assist scratch (UAS) caused more severe groove exit damage when scratching along the longitudinal direction of the fibers. The high-frequency hammering effect of ultrasonic vibration reduced the bending fracture of the fibers and increased the material removal when scratching along the transverse direction of the fibers, and reduced the area of groove edge chipping. In terms of scratching force, the scratching force along the longitudinal direction of the fibers is less than that along the transverse direction. In addition, ultrasonic vibration makes the material change from the original brittle fracture removal caused by extrusion, shear, and tension to the brittle fracture crack intersection removal prompted by hammering-scratching action, reducing the scratching force.

Establishment of scratching force model for micro-removal of SiCp/Al composites by ultrasonic vibration

In the process of micro-removal machining SiCp/Al, the real-time prediction of cutting force is of great significance to ensure the surface quality of the workpiece and safe production. Based on the two major sources of cutting forces: the elastic-plastic deformation resistance of the machined material and the friction between the tool and the material, this paper established an ultrasonic vibration-assisted scratching force model by considering four aspects: chip formation force, SiC particle breaking force, tool and Al matrix friction force and rolling friction force. The model was experimentally validated by a self-built ultrasonic scratching device, and the effects of scratching speed, SiC particle volume fraction, and ultrasonic amplitude on the scratching force were investigated. The results showed that the scratching force is minimum when the scratching speed is 400 mm/min for both ordinary scratching (OS) and ultrasonic vibration-assisted scratching (UVAS). As the volume fraction of SiC particles increases, the scratching force gradually increases. Under the same experimental conditions, the force of UVAS is much smaller than OS. The maximum error between the experimental value and the predicted value of the model is 33% and gradually decreases with the increase of scratching speed and SiC volume fraction. The overall trend of the two is consistent, which proves the feasibility of the scratching force model. This study can provide some theoretical guidance for the force control when machining SiCp/Al. The ultrasonic vibration-assisted scratching force model was established by considering the chip formation force, SiC particle breaking force, tool matrix friction force, rolling friction force and ultrasonic vibration applied. And the model was verified by experiments. • A new machining process of ultrasonic vibration-assisted scratching was proposed. • An ultrasonic vibration-assisted scratching force model was established. • The experimental values were in good agreement with the model predicted value, which verified the feasibility of the established model.

Effect of grinding damage on cutting force and ductile machining during single grain scratching of monocrystalline silicon

Understanding the initiating and suppression mechanisms of existing defects are the key to optimizing the ultra-precision grinding process of hard and brittle materials. This paper discusses the effects of grinding damage on material removal mechanism from the perspectives of residual scratch depth, scratch morphology and normal scratching force, through conducting the contrast variable-depth nano-scratch experiment on polished and ground monocrystalline silicon and establishing the single grain scratching Smoothed Particle Hydrodynamics (SPH) model. The experimental and simulation results show that radial crack on ground silicon surface is almost invisible due to the existence of grinding marks, which indicates that it is difficult to judge the ductile brittle transition (DBT) point by the traditional method of observing cracks. With the increase of penetration depth, pop-in will occur in the residual scratch depth of polished and ground silicon, indicating that the material removal mode has transformed, which provides an important basis for judging the DBT point. The DBT critical normal scratching force (38.93 mN) and residual scratch depth (−0.14 μm) of ground silicon are much higher than those of polished silicon, implying ground silicon is easier to achieve ductile processing. Meanwhile, when the penetration depth is the same, compared to polished silicon, the normal scratching force of ground silicon is generally larger. Finally, a single grain scratching SPH model of pre-stressed silicon is established. And the simulated phenomenon and conclusions are consistent with the experiment, which proves that the surface compressive stress is an important factor that causes the removal characteristics of ground silicon to be different from polished silicon. This study provides a theoretical basis for understanding the ultra-precision grinding removal mechanism of hard and brittle materials.

Scratch and multi-pass scratch behavior of poly (methyl methacrylate) (PMMA)

Polymer materials with high specific strength properties are widely used in engineering applications. Poly (methyl methacrylate) (PMMA) is a rigid and brittle thermoplastic with a high glass transition temperature. It is used in many engineering applications due to its low density, lightweight, high transparency, chemical resistance, and high toughness properties. Intense research efforts have been carried out in recent years regarding the scratching behavior of polymers. The scratch test is performed by moving a hard abrasive indenter across the surface of relatively soft material and is used to determine the mechanical resistance of the surfaces of materials. Scratches on the surfaces of amorphous polymeric materials such as PMMA cause optical and mechanical performance loss. For this reason, it is important to determine the scratching behavior of materials under different operating conditions. Within the scope of the study, the scratching behavior and multi-pass scratch behavior of PMMA were investigated. Experimental studies were carried out with Rockwell and Vickers abrasive indenters at different scratch force and velocity values. Scratch and wear marks were examined by means of an optical microscope, optical profilometer and Scanning Electron Microscope (SEM), and scratch hardness, volumes removed, surface topographies and surface morphologies are presented. It has been observed that these results vary remarkably depending on the type of abrasive indenter, scratch force and velocity.

Coupling of double grains enforces the grinding process in vibration-assisted scratch: Insights from molecular dynamics

Coupling of multiple abrasive grains is crucial for the efficiency in the grinding process and grinder design. Here the coupling effect in a double-grain model in vibration-assisted scratch of single-crystal silicon carbide (SiC) have been investigated using the molecular dynamics simulations for both simultaneous and sequential scratch processes. The coupling between the double abrasive grains affect the scratch force, stress, amorphous layer and surface morphology. The reduction ratios of tangential and normal force and the influenced material volume show that the critical distance for the inhibition of the coupling of vibration-assisted scratch is significantly greater than that in conventional scratch. The change of overlap ratio can reflect the change trend of the scratch force reduction ratio. In the vibration-assisted grinding, the increase of overlap ratio also intensifies the coupling of the abrasive grains, resulting in faster material removal, smaller scratch force and better surface finish. Insights obtained through the molecular dynamics analysis in this work into the coupling effects of abrasive grains in the vibration-assisted grinding process is believed to be beneficial in the development of grinding wheels and the optimization of machining processes.

Comparison of Vibration-Assisted Scratch Characteristics of SiC Polytypes (3C-, 4H- and 6H-SiC).

Single-crystal silicon carbide (SiC) is widely used because of its excellent properties. However, SiC is a typical hard and brittle material, and there are many challenges in realizing its high efficiency and high-precision machining. Grinding is the main method used to achieve the high-efficiency processing of SiC, but the contradiction between processing quality and processing efficiency is prominent. Vibration-assisted grinding is an effective method to realize high-efficiency and precision machining of SiC. To reveal the vibration-assisted grinding mechanism of SiC, the vibration-assisted nano-scratch process is studied using the molecular dynamics method, and the material removal process and damage formation mechanism in the vibration-assisted scratch are analyzed. Aiming at the three main structural crystal types, 3C-, 4H- and 6H-SiC, scratch simulations were carried out. The vibration-assisted scratch characteristics of SiC polytypes were evaluated from the perspectives of scratch force and the amorphous layer. It was found that the effects of vibration-assisted scratch on different crystal structures of SiC differ, and 3C-SiC is quite different from 4H- and 6H-SiC. Through vibration-assisted scratch simulations under different scratch conditions and vibration characteristics, the influence laws for machining parameters and vibration characteristic parameters were explored. It was found that increasing the frequency and amplitude was beneficial for improving the machining effect. This provides a basis for vibration-assisted grinding technology to be used in the high-efficiency precision machining of SiC.

Comparison of Masonry Homogenization Methods – Macromodelling and Micromodeling of Walls Behaviour Made of Autoclaved Aerated Concrete Masonry Units

The adopted method of empirical homogenization strictly determines the degree of faithful reproduction of the masonry structure's work in terms of the analysis of cracking forces, destructive forces, and the mechanism of structure destruction. The high level of detail of the numerical model may make it impossible to perform calculations and predict internal forces for larger structures or entire buildings. The study aims to compare two different masonry homogenization techniques and determine the advantages and disadvantages of the adopted methods. The concept of a micromodel, in which the contact of two materials - a masonry unit and a mortar, was simulated using contact elements in the interface planes and a macromodel in which the wall was modelled as a homogeneous, isotropic material, omitting contact surfaces. The analysis subjects were standard wall models made of autoclaved aerated concrete (AAC) masonry units in axial and diagonal compression tests. In the numerical calculations, the elasto-plastic model with degradation implemented. The Menetrey William boundary surface describes the compression phase, and the Rankine criterion determines the tensile phase. In the axially compressed walls, the relations of forces and vertical and horizontal deformations compared, and in the shear walls, the forces and values of strain angles analyzed. In both models, the mechanisms of wall destruction and scratching were considered. The initial parameters of the elasto-plastic model derived from the results of wall tests using various model validation techniques. The calibration coefficient was used in the micromodel, determined as the quotient of the wall's compressive strength and masonry unit's compressive strength. The fracture energy value was also corrected. In the macromodel, the masonry's modulus of elasticity and the tensile strength value calibrated. Calculations based on the micromodel were consistent with the test results at the relative error level of 2%. The observed damage and scratches to the walls after the tests were consistent with the numerical projection. The macromodel calculations showed the convergence of the results in scratch morphology, scratching and destructive forces. The most significant differences occurred in shear deformations. The macromodelling approach allowed for capturing the wall's global tendency to deteriorate without opening the contact surfaces locally (cohesive cracks), as is the case during the tests.

Investigation of material removal mechanisms and ductile-brittle transition zone of zirconia ceramics sintered at various temperatures

Sintering is a comprehensive process that involves the complex evolution of material microstructures and properties, being recognized as a critical factor to improve the machinability of ceramics. The present work aims to address the evolution of the material removal mechanisms of the 3mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) during the sintering process based on the micro scratching tests. The impacts of sintering temperatures on the material removal behaviors, including scratching forces, scratch morphologies, specific scratching energies, and critical transition depths, were rigorously studied. The acquired results indicate that the intergranular bonding strength is a critical factor that determinines the material removal mechanisms of 3Y-TZP, and 1100°C signifies the transition threshold for the material removal mode. After 1100°C, the material removal mechanism has gradually converted into the typical ductile-brittle removal regime. Moreover, the critical depth in ductile regime at 1200°C is about 1.89 times that at 1500°C, and the critical depth of ductile-brittle transition at 1200°C is approximately 2.08 times that at 1500°C.

Wear evolution of microstructured diamond grains in WC/Co cemented carbide single grain scratching

In this study, the wear evolution and wear mechanism of microstructured diamond abrasive grains in scratching WC/Co were investigated. Surface microstructures with 0° groove arrays, 45° groove arrays, square arrays, rhombus arrays, and wave groove arrays were initially fabricated using a nanosecond pulsed laser without obvious surface damage. The grain wear evolution process, characteristics of the scratching surface, and impact on the specific scratching force were then analysed. The results show that surface microstructuring affects the life extension of the diamond grains, the effectiveness of which can be sorted in the following descending order: square arrays, rhombus arrays, 45° groove arrays, 0° groove arrays, no microstructure, and wave groove arrays. Finally, the wear evolution process of the microstructured diamond grains was identified, which mainly covers adhesion→cracking→micro-fracture of the unit-abrasives→macro-fracture of the unit-abrasives→macro-fracture of the grain→pull-out, and the wear mechanism of the diamond grains was also explored.

Mechanical response of ZrxCu100-x layer on Cu(001) substrate using molecular dynamics

The molecular dynamics simulations method is applied to survey the deposition and annealing processes of ZrxCu100-x film on a Cu(001) surface. The influences of ZrxCu100-x compositions and depths on the force, deformation behavior, pile-up, and hardness are investigated using nano scratching and nanoindentation processes. We find out that the structure of ZrxCu100-x alloy has stability increases when decreasing the Zr content. The surface roughness of Zr-Cu film increases when improving the Zr content. After annealing, the morphology surface of the Zr-Cu amorphous alloy becomes smoother. The scratching forces and average friction coefficient of the Zr20Cu80 film surge as the scratching depth rises. While the pile-up height, normal force, and friction force decrease as increasing the Zr ratio. Under the plastic and elastic deformations, shear transformation zones are formed in the Zr-Cu amorphous film. While in the nanoindentation process, the hardness of ZrxCu100-x film amorphous film tends to decrease when increasing the Zr content.

Investigation of nanoscratch anisotropy of C-plane sapphire wafer using friction force microscope

In this study, nanoscratch experiments using side-forward multiple scans by friction force microscope with triangular pyramidal monocrystalline diamond tip were conducted on a (0001) plane sapphire wafer substrate to clarify the ductile-regime machining mechanism including its anisotropy. Various characteristics, such as scratch force, depth and specific energy for each scratch direction on C-plane of sapphire, were manifested by a friction force microscope, and the specific scratch energy showed a trend of three-fold symmetry. Subsequently, cutting chips which adhere to the diamond tip exhibited plastic deformations features were testified by a scanning election microscope. Based on slip/twinning systems of sapphire, Schmid factor was calculated for each scratch direction using the resultant force, and the calculated Schmid factors on the rhombohedral planes became the highest. Following the results, the resolved shear stresses along the twinning directions on the rhombohedral planes were calculated using a simple chip formation model, and they were several times larger than the critical resolved shear stress for rhombohedral twinning. As a result, it was found that when the scratch direction is set so that one of the three faces of the diamond tip is close to parallel to one of the rhombohedral planes, the rhombohedral plane acts as the chip shear plane and the specific scratch/cutting energy can be minimized. The cross-sectional transmission electron microscope images of scratched sub-surface also distinctly displayed the existence of subsurface damages consisting of twins and stacking faults relating rhombohedral planes.

Atomic-Scale Friction Studies on Single-Crystal Gallium Arsenide Using Atomic Force Microscope and Molecular Dynamics Simulation

This paper provides a fresh perspective and new insights into nanoscale friction by investigating it through molecular dynamics (MD) simulation and atomic force microscope (AFM) nanoscratch experiments. This work considered gallium arsenide, an important III–V direct bandgap semiconductor material residing in the zincblende structure, as a reference sample material due to its growing usage in 5G communication devices. In the simulations, the scratch depth was tested as a variable in the fine range of 0.5–3 nm to understand the behavior of material removal and to gain insights into the nanoscale friction. Scratch force, normal force, and average cutting forces were extracted from the simulation to obtain two scalar quantities, namely, the scratch cutting energy (defined as the work performed to remove a unit volume of material) and the kinetic coefficient of friction (defined as the force ratio). A strong size effect was observed for scratch depths below 2 nm from the MD simulations and about 15 nm from the AFM experiments. A strong quantitative corroboration was obtained between the specific scratch energy determined by the MD simulations and the AFM experiments, and more qualitative corroboration was derived for the pile-up and the kinetic coefficient of friction. This conclusion suggests that the specific scratch energy is insensitive to the tool geometry and the scratch speed used in this investigation. However, the pile-up and kinetic coefficient of friction are dependent on the geometry of the tool tip.

Analysis of Nanoscratch Mechanism of C-Plane Sapphire with the Aid of Molecular Dynamics Simulation of Hcp Crystal.

In this study, single groove nanoscratch experiments using a friction force microscope (FFM) with a monocrystalline diamond tip were conducted on a c-plane sapphire wafer to analyze the ductile-regime removal and deformation mechanism including the anisotropy. Various characteristics, such as scratch force, depth, and specific energy for each representative scratch direction on the c-plane of sapphire, were manifested by the FFM, and the results of the specific scratch energy showed a trend of six-fold symmetry on taking lower values than those of the other scratch directions when the scratch directions correspond to the basal slip directions as . Since this can be due to the effect of most probably basal slip or less probably basal twinning on the c-plane, a molecular dynamics (MD) simulation of zinc, which is one of the hexagonal close-packed (hcp) crystals with similar slip/twining systems, was attempted to clarify the phenomena. The comparison results between the nanoscratch experiment and the MD simulation revealed that both the specific scratch energy and the burr height were minimized when scratched in the direction of the basal slip. Therefore, it was found that both the machining efficiency and the accuracy could be improved by scratching in the direction of the basal slip in the single groove nanoscratch of c-plane sapphire.

Development of Elastoplastic-Damage Model of AlFeSi Phase for Aluminum Alloy 6061

Material properties affect the surface finishing in ultra-precision diamond cutting (UPDC), especially for aluminum alloy 6061 (Al6061) in which the cutting-induced temperature rise generates different types of precipitates on the machined surface. The precipitates generation not only changes the material properties but also induces imperfections on the generated surface, therefore increasing surface roughness for Al6061 in UPDC. To investigate precipitate effect so as to make a more precise control for the surface quality of the diamond turned Al6061, it is necessary to confirm the compositions and material properties of the precipitates. Previous studies have indicated that the major precipitate that induces scratch marks on the diamond turned Al6061 is an AlFeSi phase with the composition of Al86.1Fe8.3Si5.6. Therefore, in this paper, to study the material properties of the AlFeSi phase and its influences on ultra-precision machining of Al6061, an elastoplastic-damage model is proposed to build an elastoplastic constitutive model and a damage failure constitutive model of Al86.1Fe8.3Si5.6. By integrating finite element (FE) simulation and JMatPro, an efficient method is proposed to confirm the physical and thermophysical properties, temperature-phase transition characteristics, as well as the stress–strain curves of Al86.1Fe8.3Si5.6. Based on the developed elastoplastic-damage parameters of Al86.1Fe8.3Si5.6, FE simulations of the scratch test for Al86.1Fe8.3Si5.6 are conducted to verify the developed elastoplastic-damage model. Al86.1Fe8.3Si5.6 is prepared and scratch test experiments are carried out to compare with the simulation results, which indicated that, the simulation results agree well with those from scratch tests and the deviation of the scratch force in X-axis direction is less than 6.5%.

Experiment and Smooth Particle Hydrodynamics Simulation for the Wear Characteristics of Single Diamond Grit Scratching on Sapphire

Abrasive single crystal diamond (SCD) grit is widely used in the machining process of sapphire. The wear of SCD grit has a significant influence on the surface quality of sapphire. In this paper, smooth particle hydrodynamics (SPH) method is employed to reveal the wear mechanism of SCD grit with Steinberg constitutive equation and Grüneisen state equation. The wear morphology, wear volume and scratching forces are measured and analyzed by combination of SPH simulations and experiments. The results show that the scratching forces fluctuate in a certain range and decrease with the increasing of workpiece material removal volume. Different degrees of cleavage and fracture appear in the front and rear of SCD grit. The shear stress and extrusion stress are the main stresses of SCD grit during the scratching process. The wear progress and wear form are mainly determined by the stress state. Different stress state leads to different wear progress of the SCD grit. The SPH method is able to reflect and illustrate the wear characteristics of SCD grit scratching on sapphire.

Research on the plastic flow characteristics of metal material in mechanical scratching

The plastic flow characteristics of the metal material in mechanical scratching is determined on the important parameters of the negative rake angle, the material deformation amount, the scratching force, the groove quality, and the tool wear. However, the chip flow angle and the plastic flow direction of the metal material in the cutting or mechanical scratching are often derived from the approximate solution according to the metal cutting theory and assumptions. Meanwhile, there is no theoretical model of the plastic flow characteristics suitable for the mechanical scratching the metal material with diamond wedge scratching tool (irregular triangular pyramid tool). Therefore, the unit plastic flow vector (PFV), the working negative rake angle, and the chip flow angle (CFA) theoretical model are established in this paper. And the evolution law of plastic flow angle of the unit PFV and CFA under the influence of the multi-scratching factors was also studied. It can be known that the PFA is related to the elevation angle of the scratching tool, but independent on the speed and material, while the CFA is related to the above multi-scratching factors. Meanwhile, the evolution law of theoretical PFA is consistent with the experimental value, and the maximum deviation is 6.687°, which verifies the theoretical model. In addition, compared with the CFA, the PFV can directly reflect the material plastic flow direction on the contact surface.