# Strength Calculation and Equal Load-Carrying-Capacity Design of an Undermatched HSLA Lap Joint under Out-of-Plane Bending

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

^{2}), for example. The security of a welding structure requires that the LCC of the joint is equal to that of the base metal; this is a matter that concerns both the material performance and geometrical dimensions. Appropriately increasing the weld size of an undermatched joint can make the LCC of the weld equal to that of the base metal and improve the structural reliability. The shape optimization of the weld toe is imperative to eliminate the stress concentration caused by the increased weld size (weld reinforcement for a butt joint). A Baud streamline [19], a Neuber catenary curve [20], a Schnack transition curve [21], C. Mattheck stretch triangle [22], an elliptic, and a parabola are possible optimal shapes, which can be obtained by grinding [23] or tungsten argon arc welding (TIG) dressing [24,25]. In this way, the failure mode of an undermatched joint turns to ductile fracture, where the joint is no longer the weakness of welded structure; thus, the effectiveness of the base metal HSLA is fully demonstrated.

## 2. Methods

#### 2.1. FE Modeling

#### 2.2. Welding Procedure

#### 2.3. Experimental Testing

## 3. Results and Discussion

#### 3.1. Establishing the Strength Calculation Method of a Lap Joint under Out-of-Plane Bending

#### 3.1.1. The Mechanical Similarity Shown by FE Results

_{y}× 50 mm

^{2}, where L represents the length of the weld, and σ

_{y}represents the yield strength of the filler material), and so were those of situations A0, B, and C0 (Lσ

_{y}× 25 mm

^{2}).

#### 3.1.2. The Strength Calculation Method

#### 3.2. Experimental Results

#### 3.3. Application in the Prediction of Failure and the LCC of a Lap Joint

^{E}of the equalmatched joint and the metallurgical strengthening of the ELCC joint [18].

#### 3.4. Application in the ELCC Design of an Undermatched Lap Joint

^{U}) should be no lower than that of the traditionally designed equalmatched joint (M

^{E}):

^{U}≥ M

^{E}.

^{U}represents the throat depth of the undermatched joint, ${\tau}_{y}^{E}$ represents the shear strength of the equalmatched filler material, a

^{E}represents the throat depth of the equalmatched joint, and $\mu =\frac{{\tau}_{y}^{U}}{{\tau}_{y}^{E}}$ represents the matching ratio.

^{U}is t; therefore, the minimum matching ratio is 0.5 for a single lap joint and 0.6 for a double-welded lap joint.

^{U}= 9.88 mm, and for the convenience of processing and manufacturing, 10 mm was adopted. The average F of an ELCC joint was 96.90% of an equalmatched joint, even if a

^{E}has been enlarged. The similarities between an ELCC joint and an equal-matched joint in LCC (F) illustrate that the ELCC design method proposed here is reasonable and feasible.

## 4. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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Materials | C | Si | Mn | Cr | Mo | Ni | Tensile Strength σ_{u} (MPa) | Yield Strength σ_{y} (MPa) | Elongation Rate A (%) |
---|---|---|---|---|---|---|---|---|---|

HQ785 | 0.10 | 0.20 | 1.41 | 0.56 | 0.33 | - | 840 | 790 | 18 |

ER110S-G | 0.09 | 0.55 | 1.68 | - | 0.43 | 1.02 | 835 | 760 | 20 |

ER70S-6 | 0.10 | 0.90 | 1.65 | - | - | - | 560 | 405 | 32 |

Joint Type | Welding Process | Current Type/Polarity | Welding Current (A) | Arc Voltage (V) | Welding Speed (mm/s) | Shielding Gas/Flow Rate (L/min) | Preheating Temperature (°C) |
---|---|---|---|---|---|---|---|

Equalmatched | MAG | DC/− | 270 | 30 | 5.5 | CO_{2}/5 Ar/18 | 80 ± 5 |

Undermatched | MIG | DC/− | 200 | 19 | 2 | Ar/13 | - |

Sample Type | Base Metal | Equalmatched Joint | ELCC Joint | ||||||
---|---|---|---|---|---|---|---|---|---|

Sample No. | 1 | 2 | 3 | 1 | 2 | 3 | 1 | 2 | 3 |

F (kN) | 23.38 | 23.22 | 23.29 | 45.02 | 44.88 | 44.77 | 44.96 | 44.06 | 41.48 |

Average of F (kN) | 23.30 | 44.89 | 43.50 | ||||||

Bending Angle (°) | 125 | 121 | 108 |

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**MDPI and ACS Style**

Guo, J.; Dong, Z.; Fang, H.; Wang, J.
Strength Calculation and Equal Load-Carrying-Capacity Design of an Undermatched HSLA Lap Joint under Out-of-Plane Bending. *Metals* **2021**, *11*, 161.
https://doi.org/10.3390/met11010161

**AMA Style**

Guo J, Dong Z, Fang H, Wang J.
Strength Calculation and Equal Load-Carrying-Capacity Design of an Undermatched HSLA Lap Joint under Out-of-Plane Bending. *Metals*. 2021; 11(1):161.
https://doi.org/10.3390/met11010161

**Chicago/Turabian Style**

Guo, Junli, Zhibo Dong, Hongyuan Fang, and Jiajie Wang.
2021. "Strength Calculation and Equal Load-Carrying-Capacity Design of an Undermatched HSLA Lap Joint under Out-of-Plane Bending" *Metals* 11, no. 1: 161.
https://doi.org/10.3390/met11010161