# Mechanical Property Test of Grass Carp Skin Material Based on the Digital Image Correlation Method

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Measurement Principle of the Binocular Stereo DIC System

#### 2.1. Principle of DIC

_{ZNCC}) is selected as follows:

#### 2.2. Binocular Imaging

_{w}(X

_{w}

_{,}Y

_{w}

_{,}Z

_{w}) on the object surface in 3D space was transformed into a point P

_{c}(X

_{c}

_{,}Y

_{c}

_{,}Z

_{c}) in the camera coordinates by rigid body. The process only involved the proportional conversion between 3D coordinates, and no change of form was required to obtain the external parameters of the cameras. After perspective projection, the camera coordinates were projected as a point P(X

_{,}Y

_{,}Z) in the image coordinate system. The projection process involved only the internal parameters of the camera. In general, the internal parameters of the camera were a constant value, which could be found once.

**R**

_{i}and

**T**

_{i}are the rotation matrix and translation vector of the two cameras with respect to the world coordinate system on the calibration plate, respectively. The 2D coordinates could be converted between different units, and the imaging plane coordinates were converted to the form expressed in pixels by the internal parameters of the camera. Therefore, the perspective projection can be written as

_{w}. Using the coordinates of camera 1 as the reference coordinates of the binocular system, the relationship between the two cameras is

**A**

_{i},

**R**

_{i}and

**T**

_{i}of the two cameras were found by calibration; then, the correspondence between the two binoculars was established.

_{1}, k

_{2}, and k

_{3}are the radial distortion coefficients; p

_{1}and p

_{2}are the tangential distortion coefficients; and ${r}^{2}={x}^{2}+{y}^{2}$.

#### 2.3. Speckle Pattern Evaluation Method

## 3. Experiments

#### 3.1. Binocular Stereo DIC Experimental Setup

^{−1}. The clamping head of the tension machine is shown in Figure 3a. The tension machine provided a stable output of uniaxial stretching power during the stretching process.

#### 3.2. Accuracy Calibration of Tensile Machine

#### 3.3. Sample Preparation

^{2}. The laboratory temperature was kept constant at about 23 °C, and GFSA was divided into two states of hydrophilic and dry for multiple experiments to find its mechanical properties. The skin extraction process did not destroy its surface structure to ensure the integrity of the fish skin. Fresh fish skins were kept in physiological saline for a short period of time without chemical reagents for treatment, and the experiments were completed within 3 days. Meanwhile, the dry state of GFSA was naturally dried at room temperature, and the specimens were covered with a thin plate for pressing to prevent the curling of fish skin during the drying process. The reason is that this condition affects the measurement effect.

#### 3.4. Speckle Evaluation

## 4. Results

## 5. Discussion

#### 5.1. Verification of Displacement Accuracy

#### 5.2. Verification of Strain Accuracy

_{i}is the change in volume.

## 6. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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**Figure 4.**Displacement calibration: (

**a**) displacement calibration curve of tensile machine; (

**b**) displacement calibration error.

**Figure 6.**Grayscale images of GFSA: (

**a**,

**b**) are the effects of the epidermis without artificial speckle and sprayed with artificial speckle, respectively; (

**c**,

**d**) are the effects of the dermis without artificial speckle and sprayed with artificial speckle, respectively.

**Figure 7.**Grayscale histogram of GFSA. (

**a**) epidermis without artificial speckle; (

**b**) epidermis with artificial speckle; (

**c**)dermis without artificial speckle; (

**d**)dermis with artificial speckle.

**Figure 9.**Cloud map of displacement and strain measured by DIC: (

**a**) axial displacement; (

**b**) axial strain.

Sequence | Size/Pixel | Duty Cycle | Average Grayscale Gradient |
---|---|---|---|

a | 18.78 | 65.95% | 3.87 |

b | 13.12 | 37.19% | 6.05 |

c | 25.08 | 54.87% | 2.80 |

d | 4.91 | 55.64% | 9.08 |

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## Share and Cite

**MDPI and ACS Style**

Zhang, M.; Ge, P.; Fu, Z.; Dan, X.; Li, G.
Mechanical Property Test of Grass Carp Skin Material Based on the Digital Image Correlation Method. *Sensors* **2022**, *22*, 8364.
https://doi.org/10.3390/s22218364

**AMA Style**

Zhang M, Ge P, Fu Z, Dan X, Li G.
Mechanical Property Test of Grass Carp Skin Material Based on the Digital Image Correlation Method. *Sensors*. 2022; 22(21):8364.
https://doi.org/10.3390/s22218364

**Chicago/Turabian Style**

Zhang, Mei, Pengxiang Ge, Zhongnan Fu, Xizuo Dan, and Guihua Li.
2022. "Mechanical Property Test of Grass Carp Skin Material Based on the Digital Image Correlation Method" *Sensors* 22, no. 21: 8364.
https://doi.org/10.3390/s22218364