Single Scratch Research Articles

Evaluation of Hardness and Elastic Modulus of Polymer Materials Through Micro-Scratch Method: An Empirical Study

ABSTRACT A number of researchers have focused on scratch methodologies to examine the surface properties of materials. Scratch testing is primarily employed to examine tribological behavior and coating failure. This study attempts to determine the hardness (H) and elastic modulus (E) of polymeric materials via the scratch method. The research performed a progressive loading scratch test on Poly-(ether-ether ketone) (PEEK), Poly(methyl methacrylate) (PMMA), Poly-tetra-fluoro-ethylene (PTFE), polyvinyl chloride (PVC), and High-density polyethylene (HDPE). The least-squares curve fitting model was used to develop two models for assessing the H and E of materials based on indentation and scratch parameters. The H is determined by tangential force, scratch width, residual depth, and E calculated from the recovered depth and additional scratch parameters. Validation of both models indicates a maximum error of around 5%, indicating that the recently established models align well with experimental data. This study presents two robust models for assessing material surface attributes derived from a single scratch test with additional parameters.

Retention and interfacial failure mechanism of single diamond grains in resin-bonded grinding tools

Abrasive grains and the associated bonding agent are the two significant components in the manufacturing of fixed abrasive machining tools. The material properties and interfacial bonding behavior between the grains and the bonding matrix determine machining performance. In precision machining processes with diamond abrasives, the primary failure modes of fixed abrasive tools are grain dislodgement and premature loss, leading to abrupt change in machining load and ultimately causing inaccurate and inefficient machining performance. This study develops a comprehensive model for understanding abrasive grain retention and interfacial failure mechanisms in resin-bonded diamond tools. Finite element analysis of a single diamond grain embedded in a resin matrix was conducted to examine the influence of the grain shape, protruding height, and orientation angle on critical interfacial failure force. A series of single diamond scratching experiments validated the model, revealing that the maximum retention force reached 43.56 N for grains with a 0.9 mm protruding height and a 60° orientation angle. The results also show that, within a specific grain size range, grain shape—quantified by the sphere deviation coefficient proposed in this paper, has the greatest impact on retention and failure behavior. Protruding height plays a secondary role, while the contribution of orientation angle is minimal. These findings provide valuable insights for the design, manufacture, and optimization of precision abrasive machining tools, particularly for applications requiring high precision and reliability.

Debonding Fiber Damage Mechanism Modeling for Machining Damage Inhibition During Rotary Ultrasonic Face Grinding SiO2f/SiO2

Abstract The debonding fiber defects on the grinding surface of SiO2f/SiO2 ceramic matrix composites deteriorate the service performance of related components. The low-damage process window is the key information to suppress machining damage by controlling grinding parameters. A mechanism model for debonding fiber damage on SiO2f/SiO2 surface was first proposed in this paper by the large deformation analysis for SiO2 fibers during rotary ultrasonic face grinding (RUFG). The established mechanism model built a bridge between grinding parameters and damage inhibition by integrating the ultrasonic stress effect, grinding force calculation, and critical fracture curvature cutting-off criterion of SiO2 fibers. The modeling mechanism for fiber deformation and fracture in grinding was validated by in situ observation of single abrasive grit scratching experiments. Besides, the low debonding damage process window predicted by the model was verified by experimental results and could be adopted to suppress the debonding fiber damage in grinding. The affected mechanism of fiber orientation, ultrasonic amplitude, and fiber-matrix interface strength on the low debonding damage process window was analyzed based on the theoretical and experimental results. The damage inhibition effect of the RUFG process was limited by the low fiber-matrix interface strength and axial cutter-relieving movement component. The ultrasonic-assisted vibration exerted its auxiliary effects through the ultrasonic stress effect and force reduction effect. The prerequisite for exerting the damage inhibition effect of RUFG was that the fiber-matrix interface strength was sufficient to resist the negative influence of the ultrasonic stress effect.

Effect of anisotropy on 4H-SiC cracking behavior during diamond wire sawing

Cracking behavior caused by the anisotropy of single-crystal silicon carbide (SiC) brings challenges to the quality of the diamond wire sawing and grinding process. In this study, the effects of SiC anisotropy on machanical properties is analyzed based on Griffith’s theory. The results indicate that the fracture toughness and the fracture strength exhibit anisotropy. At the same time, an analytical model for the initiation and deflection of the surface radial crack is proposed based on the scratching stress field. On the basis of these results, the anisotropic machanism of the surface radial crack initiation, deflection, the surface radial crack initiation (SRCI) depth, and the residual scratching depth are investigated in combination with the single abrasive scratching experiment. The shear stress and the maximum principal stress are the primary driving forces for the initiation and deflection of surface radial crack, respectively. The direction of the minimum shear strength and the fracture strength determines the anisotropy of cracking behavior. Meanwhile, the anisotropy of the SRCI depth and the residual scratching depth is caused by the fracture strength anisotropy. This research offers fundamental insights into the anisotropic cracking behavior of SiC, thereby contributing to the precise control of crack damage and improve the quality of the SiC diamond wire sawing and the as-cut wafers grinding process.

Friction-induced temperature rise at energetic β-HMX crystal interfaces: Part I. Role of contact pressure and speed under dry sliding friction

In this study, the friction behavior and surface temperature of beta-phase octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (β-HMX), a widely used energetic crystal in modern weapon industry, is systematically investigated by varying the contact pressure and sliding speed as well as sliding cycles. Experimental results reveals that the maximum temperature rise on β-HMX surface can be well-correlated with the frictional power density involving the friction coefficient and contact pressure and sliding speed. The frictional work-heat conversion rate of β-HMX surface decreases with the frictional power density and then stabilized at ∼43.7 % upon single scratch and it decreases with sliding cycles upon reciprocating scratch. These findings can provide deep insights into the frictional safety of energetic materials.

Fracture mechanism of ultrasound-assisted scratching 2D-SiCf/SiC composite fibers with different fiber orientations

The aim of this paper is to investigate the grinding characteristics and mechanism of 2D- SiC/SiC composites with 0°/90° orthogonal anisotropic structured surfaces under different scratching fiber angles (angle between scratch direction and fiber orientation, SFA). A series of surface single abrasive scratching tests were conducted. The effects of the scratch fiber angle on the grinding force, surface morphology and roughness were investigated. The results show that the scratch force and surface roughness at different scratch fiber angles are in the order of 0° > 30°> 45°; SFA also has an important effect on the surface microstructure. The grinding mechanism of 2D-SiCf/SiC composites was analyzed by single-particle scratching test. The results of the scratch force and surface morphology provide strong evidence of the differences produced during the grinding process. The advantages of ultrasonic vibration over conventional machining were further identified by comparing specific scratch energies. This study elucidates the damage behavior of 2D-Sicf/sic composites in correlation with the influence of angle, and these results provide a new guideline for ultrasonic vibratory grinding of woven fiber-reinforced ceramic matrix composites for machining quality.

Forest hardening and Hirth lock during grinding of copper evidenced by MD simulations

Through the use of molecular dynamics (MD) simulation, grinding process of a single crystal copper with two scratch configurations (i) near spacing (NS) between adjacent scratches, and (ii) far spacing (FS) between adjacent scratches were simulated and compared to the control samplei.e.,a single scratch (SS). FS configuration revealed the highest material removal, whereas NS configuration showed that the material removal is affected by various types of defects in the sub-surface which include FCC intrinsic stacking fault, a coherent twin boundary next to an intrinsic stacking fault and two adjacent intrinsic stacking faults. The formation of a Stair-rod 1/6 〈110〉 due to the reaction between two Shockley partial dislocations 1/6 〈112〉 was seen as a distinct feature of the NS configuration which forms the onset of hardening.

Research on the Wear of Groove Structured Grinding Wheel Based on the Simulation and Experiment of Single Abrasive Particle Scratching

Research on the Wear of Groove Structured Grinding Wheel Based on the Simulation and Experiment of Single Abrasive Particle Scratching

Characterization, quantitative evaluation, and formation mechanism of surface damage in ultrasonic vibration assisted scratching of Cf/SiC composites

Carbon fiber reinforced silicon carbide ceramic matrix composites (Cf/SiC composites) have a wide range of applications in aerospace, nuclear energy, braking systems owing to its excellent mechanical performance. Nevertheless, the hardness, brittleness, heterogeneity, and anisotropy of Cf/SiC composites give rise to difficulties in machining them. In addition, the characterization and formation mechanism of surface damage in the grinding of Cf/SiC composites have not been fully elucidated. The purpose of this paper is to provide a characterization method for surface damage of Cf/SiC composites and an evaluation index for surface edge chipping damage (SECD) through conventional scratching (CS) / ultrasonic vibration assisted scratching (UVAS) tests with single abrasive. Towards revealing the surface damage behavior of Cf/SiC composites during scratching, as well as the impact of fiber orientation on surface damage. The findings indicate that main forms of surface damage of Cf/SiC composites in single abrasive scratching are fiber breakage, fiber fracture-shedding, fiber fracture, fiber-matrix interface debonding, interface fragmentation, matrix cracking, and matrix microcracks. Further, ultrasonic vibration could help to suppress the SECD, and the SECD factor was smallest when scratching along the perpendicular fiber. Furthermore, the fiber orientation can significantly affect the scratching force and cross-sectional area of scratches on Cf/SiC composites via single abrasive scratching. The tangential scratching force was usually smaller as compared to the normal scratching force, and the cross-sectional area of scratches in UVAS is smaller than that in CS. Based on the above findings, this study elucidates the formation and evolution of surface damage after scratching under different fiber orientations, filling the research gap in surface damage under ultrasonic assisted machining of Cf/SiC composites and providing technical guidance for the machining.

Atomic understanding of the evolutionary mechanism of fused glass densification generation during single particle scratching

The densification of fused glass during processing has a significant impact on the performance and application of fused glass components. However, the precise atomic mechanisms underlying densification remain elusive. In this study, we explore the atomic mechanisms responsible for densification in fused glass during single particle scratching, with a focus on the scratching depths and environmental humidity. We employ reactive force field molecular dynamics (ReaxFF MD) simulations for our investigation. We subjected models to scratching under various humidity conditions using a spherical virtual indenter with a 20 Å radius. The scratching depths were set at 10 Å and 15 Å, respectively, with a constant scraping speed of 40 m/s. Our findings indicate that water molecules impede lateral atom movement on the fused glass surface while enhancing vertical flow. Furthermore, water molecules facilitate the volume recovery of fused glass following scratching. The transfer of hydrogen (H) atoms within the fused glass, facilitated by Si–O–H⋯O–Si structures, plays a crucial role in promoting volume recovery. The ultimate density distribution of fused glass results from a combination of atomic displacement during scratching and subsequent volume recovery. This study enhances our atomic-level understanding of densification generation in fused glass.

Insight into crack propagation induced by fiber orientations during single grain scratching of SiCf/SiC composites using FEM

Due to the multiphase structure and anisotropy of ceramic matrix composites (CMCs), crack propagation is extremely complex during grinding. However, there is no full comprehension of the crack propagation law of CMCs in varying fiber directions, which limits high-quality CMCs machining. Based on experimental and numerical results, the effect of fiber directions on crack propagation of SiCf/SiC composites was analyzed. Results demonstrate that the change in crack propagation path is the primary reason why the removal behavior of CMCs is different from traditional ceramics. For CMCs, the interface is the priority path of crack propagation no matter along any fiber direction. Besides, the fiber orientation determines the propagation paths of radial and subsurface cracks, which affects material removal behavior. Comparing the scratched groove, the groove edge damage is the most severe when scratching along the fiber transverse direction, whereas the scratched groove surface quality is best in the perpendicular direction.

Effect of optical fiber end face scratches on laser-induced damage threshold.

The scratches on the fiber end face can enhance the local electrical field, which lowers the damage threshold. The damage mechanism of a high-energy laser is investigated. The effect of scratches on the electric field is simulated by the finite difference time domain (FDTD) solution. The results show that the depth of the scratch has a greater ability to influence the electric field than the width, and multiple scratches have a stronger modulation than a single scratch. In calculation, the damage threshold of the scratch-free end face is 0.456J/c m 2 when the incident light electric field intensity is 50M V/c m, compared to 0.345J/c m 2 in the presence of the scratch on the end face.

Grinding surface roughness prediction for silicon nitride ceramics: A dynamic grinding force and frequency domain approach

The existing surface roughness theoretical predictive models exhibit high parameter sensitivity and complexity, resulting in low reliability. Moreover, machine learning-based predictive models are constrained by the training parameter range, limiting their precision and generalization. In response to these limitations and from the frequency domain perspective, this paper proposes an innovative surface roughness (Ra) predictive model for silicon nitride ceramics grinding based on the dynamic grinding force model. First, a dynamic grinding force model was established using single grain scratch test results from both ductile and brittle removal stages, with model parameter estimation assisted by Genetic Algorithm. The results demonstrated a Mean Relative Error (MRE) of 19.51% between experimental and theoretical dynamic grinding force values, and a Relative Error (RE) of 9.37% for average grinding force. Subsequently, the frequency domain characteristics of both experimental grinding force signals and surface topography texture curves were extracted, which exhibited a significant correlation based on cosine similarity and Kendall's tau. Finally, leveraging the frequency domain characteristics of grinding force, the surface roughness predictive model was developed through the Convolutional Neural Network. The predictive model achieved an MRE of 12.79%, with random grinding experiments further confirming the model's accuracy with an MRE of 13.65%. These findings indicate that the proposed surface roughness predictive model offers high generalization capability and accurate prediction across a broader parameter range.

The effects of scratching speed in ultrasonic vibration-assisted single diamond scratching process

Ultrasonic vibration-assisted machining has been widely used in manufacturing hard and brittle materials. Previous studies have shown that the vertical ultrasonic vibration in ultrasound-assisted single diamond scratching can affect the scratching forces, surface quality, and material removal mechanism by two mechanisms: changing the contact mode between the single diamond and the workpiece and increasing the speed of the single diamond relative to the workpiece. However, some studies point out that increasing the speed has little effect on the scratching force and material removal mechanism. Therefore, it is necessary to conduct an investigation that takes into account the effects of both scratching velocity and ultrasonic vibration on scratching force, surface quality, and material removal mechanisms. In this study, the single diamond conventional scratching (CS) and ultrasonic vibration-assisted scratching (UAS) experiments have been conducted at different scratching speeds to investigate the material removal mechanism of ultrasonic vibration-assisted machining. The effects of increasing the scratching speed on cutting forces, material removal mechanism, and machined surface quality are investigated. The results show that in both CS and UAS processes with low to medium scratching speeds (less than1000 mm/s), increasing the scratching speed leads to more brittle material removal and lower surface quality. At the same time, the scratching speed has almost no effect on the scratching speed force.

A Tiny Accelerator for Mixed-Bit Sparse CNN Based on Efficient Fetch Method of SIMO SPad

Convolution neural networks (CNNs) have been implemented with custom hardware on edge devices since its algorithms were successful in many artificial intelligence applications. Although lots of unstructured pruning and mix-bit quantization algorithms have been proposed to successfully compress CNNs, there are few hardware accelerators which can support both sparse and mix-bit CNNs. Besides, sparse matrix computation consumes lots of hardware resources such as registers or BRAM to fetch the needed input activations into processing element (PE). This paper presents a tiny accelerator for mixed-bit sparse CNNs featuring a novel scheme of single vector-based compressed sparse filter (CSF) method and single input multiple output scratch pad (SIMO SPad) to effectively compress weight and fetch the needed input activation. SIMO SPad is shared by multiple PEs, which saves 13.34% CLB LUTs, 46.24% CLB Registers. Furthermore, the accelerator supports mixed-bit sparse computation to obtain better accuracy and performance. When tested on VGG16, compared with 8-bit non-sparsity baselines, the performance of mixed-bit sparsity on Cifar10 and ImageNet improved by 4.85× and 3.33×, respectively, with small accuracy decrease degradation. Compared to state-of-the-art accelerators, the accelerator achieves 1.40× to 2.98× greater DSP efficiency, and offers 1.91× greater energy efficiency.

Processing strategy of SiCf/SiC composites during single grain scratching under minimum quantity lubrication

Processing strategy of SiCf/SiC composites during single grain scratching under minimum quantity lubrication

Study on the transformation and control mechanism of amorphous damage during the grinding process of monocrystalline silicon considering grain shapes by MD method

To address the debate surrounding the stress criterion for a-Si transformation during the scratching process caused by the particular grain, atomic-scale single grain scratching MD models for monocrystalline silicon considering grain shapes are developed. The simulation results show that the critical octahedral shear stress (10.5 GPa) for a-Si transformation remains stable across different grains, while the critical hydrostatic pressure (−5.5 ∼ −7.5 GPa) fluctuates greatly. Furthermore, the a-Si transformation is mainly due to the extrusion effect, supplemented by the shear effect of grain. Finally, conical grains are not recommended due to the larger SSD depth compared to spherical and truncated octahedral grains. This study offers a theoretical basis for reducing amorphous damage during the ultra-precision grinding processing of monocrystalline silicon.

Single diamond grit scratching of unidirectional Cf/SiC composite: Mechanical responses and fracture mechanism

Cf/SiC composite is a typical heterogeneous brittle composite material, its precision machining has always been affected by the complicated removal mechanism. This paper conducted a single diamond grit scratching experiment on the unidirectional Cf/SiC composite to investigate the material’s mechanical response under different loads and scratching depths. The scratching force and acoustic emission signals were measured to reveal the removal characteristics. The scratching removal behavior of SiC matrix and carbon fibers in the two-phase component of unidirectional Cf/SiC composites was analyzed based on the fracture size and fiber fracture morphology. The results show that the parallel scratching process could produce a better strength resistance with mild rupture features of fiber extrusion fracture and shear removal. While the perpendicular scratching process is generally resulting in crack propagation along the fiber direction with interface failure and bending fracture failure along the moving direction.

Engineering dislocation‐rich plastic zones in ceramics via room‐temperature scratching

AbstractIn this communication, we demonstrate a simple but powerful method to engineer dislocations into large plastic zones in various single‐crystal ceramic materials via room‐temperature scratching. By using a Brinell indenter with a diameter of 2.5 mm, we successfully produced plastic zones with a width and depth of ∼150 µm in a single scratch track, while the length of the scratch track can be arbitrarily long depending on the sample size. Increasing the number of repetitive scratching cycles increases the dislocation density up to ∼1013 m−2 without visible crack formation. The outlined experimental procedure is showcased on single‐crystal SrTiO3, MgO, ZnS, and CaF2 to demonstrate the general applicability of this technique. In light of the increasing research interest in dislocation‐tuned functional and mechanical properties in ceramics, our method will serve as a simple, fast, and robust technique to pave the road for scaling up the required large plastic zones for dislocation engineering in ceramics.

Multiple Scratching: An Atomistic Study

Using molecular dynamics simulation, we investigate multiple scratching processes in which a tip moves through a groove that has already been formed during a previous scratch. We use a conical indenter such that the friction coefficient is independent of the scratch depth. First, a single scratch to a depth of 4 nm is compared with a 2-cycle scratch in which a scratch at depth 2 nm is followed by a second scratch to the full depth of 4 nm. We observe that the second cycle shows a smaller friction coefficient as long as the tip moves through the pre-formed groove without touching the front end. In addition, we studied 5 cycles of scratching, in which the scratch depth was increased by 2 nm in each cycle. These results confirm and generalize the findings for the 2-cycle scratch. A constant-load 2-cycle scratch simulation emphasizes that the reduction in transverse load—and, consequently, in the friction coefficient—is caused by the fact that, despite a large normal area supporting the normal load, only a thin area is available to resist the transverse movement of the scratch tip. The work done during scratching is in good approximation proportional to the scratch volume showing that the transverse hardness is approximately constant in all scratch processes investigated here.