# Characteristics of GMAW Narrow Gap Welding on the Armor Steel of Combat Vehicles

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Experimental Procedures and Results

#### 2.1. Welding Joint Design

#### 2.2. Comparision of Mechanical Properties

#### 2.2.1. Tensile Test

#### 2.2.2. Low-Temperature Impact Test

#### 2.3. Hardness Distribution

## 3. Measurement and Prediction of Residual Stress Distribution

#### 3.1. Measuring Residual Stress Using XRD

#### 3.2. FEM Prediction of Welding Process

#### Thermal Analysis

_{L}, and the solidus temperature, T

_{S}, are assumed to be 1500 °C and 1450 °C, respectively. The liquidus temperature and solidus temperatures were typed into the solidus and liquidus temperature module of MSC Marc software.

_{c}is the heat transfer coefficient, T

_{S}is the surface temperature of the workpieces, and T

_{0}is the ambient temperature. For a surface element of a solid body contacted by flowing gas or liquid, the heat flow density q

_{r}is, according to Newton’s law, proportional to the difference between surface temperature, T

_{S}, and gas or liquid temperature, T

_{0}, through the coefficient of convective heat transfer h

_{c}.

_{S}) in relatively extensive surroundings (body temperature, T

_{0}) occurs by means of radiation in accordance with Equation (3). Thermal conductivity and specific heat are used as the temperature-dependent thermal properties as shown in Figure 7. The element activation and deactivation methods are used to model the deposition of weld metal during multi-pass welding. The elements of the weld deposition are activated and then heated to model the moving heat source.

#### 3.3. Mechanical Analysis

^{e}, ε

^{p}, and ε

^{th}are the elastic, plastic, and thermal strains, respectively. The elastic strain is modeled using Hooke’s law with a temperature-dependent elastic modulus. The Von Mises yield surface and temperature-dependent material properties are employed to model the plastic strain. Figure 8 shows the temperature-dependent properties [14]. The effect of work hardening is not considered in this study.

#### 3.4. Heat Input Model

_{f}and f

_{r}are parameters that give the fractions of heat deposited in the front and rear parts, respectively [16]. The temperature gradients in the front and rear are expressed by Equation (7):

_{f}+ f

_{r}= 2.0. This is done because the temperature gradient in the front leading part is steeper than that in the trailing edge. Therefore, two ellipsoidal sources are combined: one for the front half and the other for the rear half.

_{1}, and c

_{2}are related to the characteristics of the welding heat source [16,17]. The values of these parameters used in the present study are summarized in Table 6.

_{w}is the power of the welding heat source, which can be calculated according to the welding current, the arc voltage, and the arc efficiency (8). The arc efficiency, η, is assumed to be 0.7. The heat input energy of each weld pass is determined using the following equation:

#### 3.5. Measurement and Prediction of Residual Stress

## 4. Ballistic Test

## 5. Discussions

## 6. Conclusions

- When applying NGW, the tensile strength, and low-temperature impact characteristics of the welding part improved compared with those of the existing X-groove method.
- When applying NGW, the tensile residual stress of the welding part decreased compared with that of the existing X-groove welding part, as confirmed by testing and FEM.
- When applying NGW to the MIL-STD-12560 grade armor steel, its protection performance, as required by the standards, is ensured.

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**Figure 5.**(

**a**) Measuring position of the hardness distribution and residual stress of NGW. (

**b**) Measuring position of the hardness distribution and residual stress of X-groove.

**Figure 9.**(

**a**) Heat distribution (temperature) of the FEM analysis results of NGW. (

**b**) Heat distribution (temperature) of the FEM analysis results of X-groove.

C | Si | Mn | Ni | Cr | Mo | P | S |
---|---|---|---|---|---|---|---|

0.16 | 0.24 | 0.22 | 2.94 | 1.46 | 0.37 | 0.006 | 0.003 |

0.06 | 0.33 | 1.35 | 1.75 | 0.10 | 0.34 | 0.004 | 0.008 |

Yield Strength | Tensile Strength | Elongation |
---|---|---|

970 | 1040 | 14 |

Identification | Current (A) | Voltage (V) | Welding Speed (cm/min) | Heat Input (kJ/mm) | Remarks |
---|---|---|---|---|---|

NGW | 280 | 28.5 | 25.0 | 1.9 | 8 layers |

X-groove | 280 | 28.5 | 10.0 | 4.8 | 8 layers |

Identification | Tension Stress (MPa) | Yield Stress (MPa) | Elongation (%) |
---|---|---|---|

X-groove | 675.5 | 753.0 | 19.6 |

NGW | 688.3 | 805.9 | 22.4 |

Identification | Fusion Line | Fusion Line + 1 mm |
---|---|---|

X-groove | 124.4 | 132.0 |

NGW | 134.6 | 153.2 |

Parameter | Value (mm) | |
---|---|---|

NGW | X-groove | |

A | 5.5 | 6.5 |

B | 5.0 | 6.0 |

c1 | 2.5 | 3.0 |

c2 | 10.0 | 12.0 |

Thickness of Plate (mm) | Projectile | Striking Velocity (km/h) | Maximum Allowable Cracking (mm) |
---|---|---|---|

32 mm | 75 mm PP M1002 | 320 | 380 |

Thickness of Plate (mm) | Striking Velocity (km/h) | Results (Crack Length) |
---|---|---|

32mm | 387 | Acceptable |

380 | Acceptable |

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**MDPI and ACS Style**

Kim, J.-S.; Yi, H.-J.
Characteristics of GMAW Narrow Gap Welding on the Armor Steel of Combat Vehicles. *Appl. Sci.* **2017**, *7*, 658.
https://doi.org/10.3390/app7070658

**AMA Style**

Kim J-S, Yi H-J.
Characteristics of GMAW Narrow Gap Welding on the Armor Steel of Combat Vehicles. *Applied Sciences*. 2017; 7(7):658.
https://doi.org/10.3390/app7070658

**Chicago/Turabian Style**

Kim, Jae-Seong, and Hui-Jun Yi.
2017. "Characteristics of GMAW Narrow Gap Welding on the Armor Steel of Combat Vehicles" *Applied Sciences* 7, no. 7: 658.
https://doi.org/10.3390/app7070658