# Numerical and Experimental Analysis of Material Removal and Surface Defect Mechanism in Scratch Tests of High Volume Fraction SiCp/Al Composites

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

_{2}O

_{3}p/Al with reinforcement-matrix cohesive behaviors to conduct a series of studies, including tool-workpiece interactions and the effect of cutting speed on such interactions; in their models, the position and shape of reinforcements were regular.

## 2. Materials and Methods

#### 2.1. Specimen

#### 2.2. Finite Element Modelling

#### 2.2.1. Microscopic Structural Modeling and Mesh of SiCp/Al Composites

^{3}) for the first two sub-processes is shown in Figure 3, and the size of the SiCp/Al composite for the third sub-process is 200 × 200 × 200 μm

^{3}.

#### 2.2.2. Material Properties of Al Matrix, SiC Particle and Diamond Intender

#### 2.2.3. Particle-Matrix Interfacial Modeling

^{12}MPa⋅mm

^{−1}.

^{2}. Obviously, the two above conclusions are very close; therefore, the cohesive interfacial strength is set as ${t}^{\mathbf{0}}={t}_{n}^{0}={t}_{s}^{0}={t}_{t}^{0}=133\mathrm{MPa}$, and $\Gamma =0.0919$ mJ/mm

^{2}in the work.

#### 2.2.4. Particle-Particle, Indenter-Particle and Indenter-Matrix Contact Modeling

#### 2.2.5. Loads and Boundary Conditions

#### 2.3. Single-Grit Scratch Experiments

## 3. Results and Discussion

#### 3.1. Material Removal Process

#### 3.1.1. The Initial Scratch Process

#### 3.1.2. The Middle Scratch Process

#### 3.1.3. The Final Scratch Process

#### 3.2. The Scratched Groove Topography

#### 3.3. Experimental Verification

## 4. Conclusions

- (1)
- The scratch depth plays a crucial role in the material removal process. SiC particles are primarily removed in ductile mode under a small scratch depth ranging from 0 to 0.011 mm, and then brittle fracturing of SiC particles becomes more evident with an increase of the scratch depth. It is eventually exhibited as the primary removal model under a large scratch depth ranging from 0.0385 to 0.0764 μm. The above phenomenon is attributed to transport of SiC particles within the Al matrix. Small-scale transport of SiC particles induced by a small scratch depth barely results in particle-particle collision; in this case, SiC particles are mainly sustained by the Al matrix which provides a flexible support that is beneficial to ductile removal of SiC particles. The increase of SiC particle transport with scratch depth raises the occurrence of particle-particle collision, which provides a hard support and shock for the scratched particles; therefore, brittle fracturing gradually becomes the major removal mode of SiC particles as the scratch depth increases. The Al matrix is removed in ductile mode during the whole scratch process.
- (2)
- The removal model of SiC particles plays a significant role in the deformation of the scratched surface. If ductile removal of SiC particles is predominant, the scratched surface is considerably smooth and exhibits very few defects, whereas if brittle fracturing of SiC particles occurs more prevalently, the deteriorative and coarse surface becomes more significant, on which various surface defects are observed; i.e., particle-matrix interfacial debonding, lateral cracks, small SiC fragments pushed ahead and then pressed into the matrix, cavies filled with residually broken particles and fragmented particles remaining in the matrix.
- (3)
- Numerical and experimental analyses both reveal that lateral cracks are one of primary surface defects, which were barely referred in previous simulation literature. The formation mechanism of the lateral cracks is as follows: the lateral cracks initiate at several particle-matrix interfacial debonding sites (micro-cracks), and then grow through the matrix as the indenter advances; these interfacial micro-cracks ultimately link together to evolve into large-scale lateral cracks. The formation process simulation of lateral cracks was performed successfully in the study.
- (4)
- A defect, cavities without any residual SiC fragments due to complete pushing out of a SiC particle, barely occurs on the single-grit scratched surface, while that is one of major defects on turning and milling SiCp/Al surface [9,12], which is attributed to the difference between the grit with a negative rake and turning (milling) tool with a positive rake. This indicates that grinding is more beneficial to improving the processed surface quality of PRMMCs than turning and milling.
- (5)
- The von Mises stress distribution shows that SiC particles bear the vast majority of load; thus, they present greater stress than the surrounding Al matrix. Namely, they impede stress diffusion within the Al matrix.
- (6)
- The SEM images of the scratched surface obtained from the single-grit scratch experiments verify the numerical analysis. Due to the importance of scratch depth for SiC particles removal and surface quality, it can be suggested that a relatively small scratch depth be applied to improve surface quality.

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

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**Figure 6.**Experimental method: (

**a**) MFT-4000 Scratch Tester for Material Surface Properties; (

**b**) schematic diagram of scratch with a linearly increasing down force.

**Figure 7.**Simulated initial scratch process at a depth of 0 to 0.011 mm: (

**a**) scratch depth h = 0, (

**b**) h = 1.01 × 10

^{−5}mm, (

**c**) h = 3.96 × 10

^{−3}mm, (

**d**) h = 5.77 × 10

^{−3}mm, (

**e**) h = 8.43 × 10

^{−3}mm, (

**f**) h = 0.011 mm.

**Figure 8.**Von Mises stress distribution of the initial scratch model sectioned along the scratch direction: (

**a**) scratch depth h = 0, (

**b**) h = 1.01 × 10

^{−5}mm, (

**c**) h = 3.96 × 10

^{−3}mm, (

**d**) h = 5.77 × 10

^{−3}mm, (

**e**) h = 8.43 × 10

^{−3}mm, (

**f**) h = 0.011 mm.

**Figure 9.**Von Mises stress distribution on the initial scratch model sectioned perpendicularly to the scratch direction: (

**a**) Sectioning scheme, (

**b**) t = 0.294 s, (

**c**) t = 0.315 s, (

**d**) t = 0.336 s, (

**e**) t = 0.356 s, (

**f**) t = 0.419 s.

**Figure 11.**Simulated middle scratch process at a depth of 0.011 to 0.0385 mm: (

**a**) h = 0.011 mm, (

**b**) h = 0.0122 mm, (

**c**) h = 0.0162 mm, (

**d**) h = 0.0212 mm, (

**e**) h = 0.0290 mm, (

**f**) h = 0.0385 mm.

**Figure 12.**Von Mises stress distribution on the middle scratching model sectioned along the scratching direction: (

**a**) h = 0.011 mm, (

**b**) h = 0.0122 mm, (

**c**) h = 0.0162 mm, (

**d**) h = 0.0212 mm, (

**e**) h = 0.0290 mm, (

**f**) h = 0.0385 mm.

**Figure 13.**Von Mises stress distribution on the middle scratching model sectioned perpendicularly to the scratching direction: (

**a**) sectioning scheme, (

**b**) t = 0.157 s, (

**c**) t = 0.209 s, (

**d**) t = 0.235 s, (

**e**) t = 0.261 s, (

**f**) t = 0.365 s.

**Figure 15.**Simulated final scratching process at a depth of 0.0385 to 0.0764 mm: (

**a**) h = 0.0385 mm, (

**b**) h = 0.0442 mm, (

**c**) h = 0.0476 mm, (

**d**) h = 0.0571 mm, (

**e**) h = 0.0654 mm, (

**f**) h = 0.0764 mm.

**Figure 16.**Von Mises stress distribution on the middle scratching model sectioned along the scratching direction: (

**a**) scratching depth h = 0.0385 mm, (

**b**) h = 0.0442 mm, (

**c**) h = 0.0476 mm, (

**d**) h = 0.0571 mm, (

**e**) h = 0.0654 mm, (

**f**) h = 0.0764 mm.

**Figure 17.**Von Mises stress distribution on the final scratching model sectioned perpendicularly to the scratching direction: (

**a**) sectioning scheme, (

**b**) t = 0.445 s, (

**c**) t = 0.594 s, (

**d**) t = 0.693 s, (

**e**) t = 0.842 s, (

**f**) t = 0.941 s.

**Figure 19.**Forming process of the scratched groove topography during the initial scratching stage at a depth of 0 to 0.011 mm: (

**a**) scratching depth h = 1 × 10

^{−5}mm, (

**b**) h = 3.843 × 10

^{−5}mm, (

**c**) h = 0.00246 mm, (

**d**) h = 0.00486 mm, (

**e**) h = 0.00702 mm, (

**f**) h = 0.011 mm.

**Figure 20.**Forming process of the scratched grooves topography during the middle scratching stage at a depth of 0.011 to 0.0385 mm: (

**a**) scratching depth h = 0.0139 mm, (

**b**) h = 0.0177 mm, (

**c**) h = 0.0194 mm, (

**d**) h = 0.0254 mm, (

**e**) h = 0.03 mm, (

**f**) h = 0.0385 mm.

**Figure 21.**Forming process of the scratched grooves topography during the final scratching stage at a depth of 0.0385 to 0.0764 mm: (

**a**) scratch depth h = 0.0427 mm, (

**b**) h = 0.0476 mm, (

**c**) h = 0.0571 mm, (

**d**) h = 0.0629 mm, (

**e**) h = 0.0764 mm.

**Figure 22.**SEM images of the single single-grit scratched groove: (

**a**) the overall surface topography, (

**b**) the magnified view of the identified area on the initial scratching surface, (

**c**) the magnified view of the identified area on the final scratching surface, (

**d**) the magnified view of lateral cracks in (

**c**) and (

**e**) the magnified view of other defects in (

**c**). I—the SiC particle which is marked with a red dot; II—small SiC fragments pushed ahead and pressed into the matrix; III—a cavity filled with residual particles; IV—fragmented particles remaining in the matrix.

**Table 1.**Recently simulation studies of Particle reinforced metal matrix composite (PRMMC) machining.

Study | Machining Mode Type | Modeling of Reinforced Particles | Particle-Matrix Interfacial Modeling | Partilce-Particle Contact |
---|---|---|---|---|

Zhu [6] | 2D micro-orthogonal cutting | Geometric model: polygon, random size and position Material model: - Volume fraction: low | Perfectly bonded with tied node, no interfacial debonding | No |

Pramanik [7] | 2D micro-orthogonal cutting | Geometric model: circle, constant size and regular position Material model: perfectly elastic material without fracture Volume fraction: 20% | Perfectly bonded with tied node, debonding by Al matrix element failure | No |

Wang [8] | 2D micro-orthogonal cutting | Geometric model: circle/polygon, random size and position Material model: perfectly elastic material with normal stress fracture criterion Volume fraction: 65% | Perfectly bonded with tied node, debonding by Al matrix element failure | No |

Zhou [9] | 2D micro-orthogonal cutting | Geometric model: polygon, random size and position Material model: perfectly elastic material with brittle cracking model Volume fraction: 55% | Perfectly bonded with tied node, no interfacial debonding | No |

Teng [10] | 2D micro-orthogonal cutting | Geometric model: circle, constant size and regular position Material model: perfectly elastic material with brittle cracking model Volume fraction: 10% | Perfectly bonded with tied node, no interfacial debonding | No |

Wang [11] | 3D micro-orthogonal cutting | Geometric model: sphere, constant size and regular position Material model: perfectly elastic material with brittle cracking model Volume fraction: 20% | Perfectly bonded with tied node, debonding by Al matrix element failure | No |

Umer [12] | 2D micro-orthogonal cutting | Geometric model: circle, constant size and regular position Material model: linear elastic without considering fracture Volume fraction: 20% | Cohesive zone elements, debonding by cohesive zone elements failure | No |

Ghandehariun [13,14,15] | 2D micro-orthogonal cutting | Geometric model: circle, constant size and regular position Material model: perfectly elastic material with brittle cracking model Volume fraction: 10%/20% | Perfectly bonded with tied node, debonding by Al matrix element failure | No |

Scratch length | 5 mm |

Scratch velocity | 10 mm/min |

Loading rate | 40 N/min |

maximum load | 20 N |

SiC [20] | 5083Al [21] | Diamond [22] | |
---|---|---|---|

Young’s modulus (MPa) | 420,000 | 70,000 | 650,000 |

Poisson’s ratio | 0.14 | 0.3 | 0.25 |

Density (tonne/mm^{3}) | 3.13 × 10^{−9} | 2.71 × 10^{−9} | 1.19 × 10^{−8} |

Thermal conductivity (mJ/s/mm/K) | 81 | 173 | 35 |

Thermal expansion (K−1) | 4.90 × 10^{−6} | 2.36 × 10^{−5} | 4.00 × 10^{−6} |

Thermal specific heat (Mj/T/K) | 4.27 × 10^{8} | 9.1 × 10^{8} | 15 × 10^{8} |

Inelastic heat fraction | 0.9 | 0.9 | 0.9 |

**Table 4.**Johnson Cook constitutive model parameters for 5083Al [23].

A (MPa) | B (MPa) | n | m | ${\mathit{T}}_{\mathbf{melt}}\left(\mathit{K}\right)$ | ${\mathit{T}}_{\mathbf{room}}\left(\mathit{K}\right)$ | C | ${\dot{\mathit{\epsilon}}}_{0}$ |
---|---|---|---|---|---|---|---|

167 | 596 | 0.551 | 0.859 | 893 | 293 | 0.001 | 1 |

**Table 5.**Johnson Cook damage law parameters for 5083Al [23].

${\mathit{D}}_{1}$ | ${\mathit{D}}_{2}$ | ${\mathit{D}}_{3}$ | ${\mathit{D}}_{4}$ | ${\mathit{D}}_{5}$ | ${\overline{\mathit{u}}}_{\mathit{f}}^{\mathit{p}\mathit{l}}$ |
---|---|---|---|---|---|

0.0261 | 0.263 | −0.349 | 0.147 | 16.8 | 2.1×10^{−5} |

**Table 6.**JHB model material parameters used for SiC [20].

Line 1 | ${\mathit{\rho}}_{\mathbf{0}}$(tonne/mm^{3}) | $\mathit{G}$(MPa) | ${\mathbf{\sigma}}_{\mathit{i}}$(MPa) | ${\mathit{P}}_{\mathit{i}}$(MPa) | ${\mathbf{\sigma}}_{\mathit{f}}$(MPa) | ${\mathit{P}}_{\mathit{f}}$(MPa) | $\mathit{C}$ | ${\dot{\mathbf{\epsilon}}}_{\mathbf{0}}$ |

3.13 × 10^{−9} | 1.93 × 10^{5} | 4.92 × 10^{3} | 1.5 × 10^{3} | 1 × 10^{2} | 2.5 × 10^{2} | 0.009 | 1.0 | |

Line 2 | $\mathit{T}$(MPa) | ${\mathbf{\sigma}}_{\mathit{i}}^{\mathbf{max}}$(MPa) | ${\mathbf{\sigma}}_{\mathit{f}}^{\mathbf{max}}$(MPa) | $\mathbf{\beta}$ | ${\mathit{D}}_{\mathbf{1}}$ | ${\mathit{D}}_{\mathbf{2}}$ | ${\overline{\mathbf{\epsilon}}}_{\mathit{f},\mathbf{min}}^{\mathit{p}\mathit{l}}$ | FS |

7.5 × 10^{2} | 1.22 × 10^{2} | 2 × 10^{2} | 1.0 | 0.16 | 1.0 | 999 | 0.2 | |

Line 3 | ${\mathit{K}}_{\mathbf{1}}$(MPa) | ${\mathit{K}}_{\mathbf{2}}$(MPa) | ${\mathit{K}}_{\mathbf{3}}$(MPa) | - | - | - | - | - |

2.2 × 10^{5} | 3.61 × 10^{5} | 0 | - | - | - | - | - |

Loading Mode | Automatically Load |
---|---|

Loading range | 0.25 N~200 N automatic loading continuously, the precision is 0.25 N |

Scratch length | 2 mm~40 mm |

Scratch velocity | 10 mm/min |

Loading rate | 1 N/min~100 N/min |

Measuring range | 0.5 μm~30 μm |

Friction measuring range | 10 N~100 N, precision is 0.25 N |

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**MDPI and ACS Style**

Zhao, X.; Gong, Y.; Cai, M.; Han, B.
Numerical and Experimental Analysis of Material Removal and Surface Defect Mechanism in Scratch Tests of High Volume Fraction SiCp/Al Composites. *Materials* **2020**, *13*, 796.
https://doi.org/10.3390/ma13030796

**AMA Style**

Zhao X, Gong Y, Cai M, Han B.
Numerical and Experimental Analysis of Material Removal and Surface Defect Mechanism in Scratch Tests of High Volume Fraction SiCp/Al Composites. *Materials*. 2020; 13(3):796.
https://doi.org/10.3390/ma13030796

**Chicago/Turabian Style**

Zhao, Xu, Yadong Gong, Ming Cai, and Bing Han.
2020. "Numerical and Experimental Analysis of Material Removal and Surface Defect Mechanism in Scratch Tests of High Volume Fraction SiCp/Al Composites" *Materials* 13, no. 3: 796.
https://doi.org/10.3390/ma13030796