Experimental investigation on microstructures and mechanical properties of PG4 flash-butt rail welds

Yong Pang; Nicolò Grilli; Hang Su; Wencheng Liu; Jun Ma; Siu Fung Yu

doi:10.1016/j.engfailanal.2022.106650

Experimental investigation on microstructures and mechanical properties of PG4 flash-butt rail welds

Yong Pang, Nicolò Grilli, Hang Su, Wencheng Liu^*, Jun Ma, Siu Fung Yu

^*Corresponding author for this work

Department of Mechanical Engineering

Research output: Contribution to journal › Article (Academic Journal) › peer-review

12 Citations (Scopus)

Abstract

Flash-butt welding (FBW) has recently been employed to construct continuously welded rails. However, the failure mechanisms of FBW joints remain unclear. In this study, the weldability of mobile flash-butt welded joints was investigated in terms of microstructures, mechanical properties, and residual stresses. The microhardness test results indicated that the heat-affected zone (HAZ) of the PG4 welds showed significant reductions in hardness of up to 140 HV, whereas the digital image correlation (DIC) measurements showed high heterogeneous strains of up to 4%. Crystallographic analysis indicated that the grains in the HAZ underwent plastic strain with a lattice reorientation of approximately 80% and 55% in the face- and body-centred cubic phase, respectively. The uniaxial tensile tests established the phenomenological relationship between the bond strength and HAZ width: specifically, the bond strength was relatively high at the foot and head of the rail, progressively decreased at the web, and was inversely correlated with the HAZ width. A fractographic analysis confirmed that the shrinkage cracks, inclusions, and flat spots in the rail web were the main cause of early failure in uniaxial tensile tests. Residual stress measurements also showed that FBW can introduce high residual stresses in the rail web of up to 436.76 ± 18.10 MPa and 225.80 ± 12.94 MPa in the vertical and longitudinal directions, respectively. The results of this study reveal that the bond strength of mobile FBW can be assessed based on their HAZ width and provide reliable guidelines for improving the safety and stability of railway systems.

Original language	English
Article number	106650
Journal	Engineering Failure Analysis
Volume	141
DOIs	https://doi.org/10.1016/j.engfailanal.2022.106650
Publication status	Published - Nov 2022

Bibliographical note

Funding Information:
The authors also acknowledge use of facilities within the Monash Centre for Electron Microscopy and Institute of Railway Technology, Monash University. The authors would like to acknowledge the financial support from the Rail Manufacturing Cooperative Research Centre (funded jointly by participating rail organisations and the Australian Federal Government's Business Cooperative Research Centres Program) for Project R3.7.7: system for real-time monitoring and sensing railway conditions by laser light. This work is sponsored by the National Nature Science Foundation of China [Grant Number: 12002211].

Funding Information:
The authors would like to acknowledge the financial support from the Rail Manufacturing Cooperative Research Centre (funded jointly by participating rail organisations and the Australian Federal Government’s Business Cooperative Research Centres Program) for Project R3.7.7: system for real-time monitoring and sensing railway conditions by laser light.

Funding Information:
This work is sponsored by the National Nature Science Foundation of China [Grant Number: 12002211 ].

Publisher Copyright:
© 2022 Elsevier Ltd

Keywords

Digital image correlation
Flash-butt welding
Residual stresses
Weldability

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@article{5730e85f02c14bc7a92ccdf069a482aa,

title = "Experimental investigation on microstructures and mechanical properties of PG4 flash-butt rail welds",

abstract = "Flash-butt welding (FBW) has recently been employed to construct continuously welded rails. However, the failure mechanisms of FBW joints remain unclear. In this study, the weldability of mobile flash-butt welded joints was investigated in terms of microstructures, mechanical properties, and residual stresses. The microhardness test results indicated that the heat-affected zone (HAZ) of the PG4 welds showed significant reductions in hardness of up to 140 HV, whereas the digital image correlation (DIC) measurements showed high heterogeneous strains of up to 4%. Crystallographic analysis indicated that the grains in the HAZ underwent plastic strain with a lattice reorientation of approximately 80% and 55% in the face- and body-centred cubic phase, respectively. The uniaxial tensile tests established the phenomenological relationship between the bond strength and HAZ width: specifically, the bond strength was relatively high at the foot and head of the rail, progressively decreased at the web, and was inversely correlated with the HAZ width. A fractographic analysis confirmed that the shrinkage cracks, inclusions, and flat spots in the rail web were the main cause of early failure in uniaxial tensile tests. Residual stress measurements also showed that FBW can introduce high residual stresses in the rail web of up to 436.76 ± 18.10 MPa and 225.80 ± 12.94 MPa in the vertical and longitudinal directions, respectively. The results of this study reveal that the bond strength of mobile FBW can be assessed based on their HAZ width and provide reliable guidelines for improving the safety and stability of railway systems.",

keywords = "Digital image correlation, Flash-butt welding, Residual stresses, Weldability",

author = "Yong Pang and Nicol{\`o} Grilli and Hang Su and Wencheng Liu and Jun Ma and Yu, {Siu Fung}",

note = "Funding Information: The authors also acknowledge use of facilities within the Monash Centre for Electron Microscopy and Institute of Railway Technology, Monash University. The authors would like to acknowledge the financial support from the Rail Manufacturing Cooperative Research Centre (funded jointly by participating rail organisations and the Australian Federal Government's Business Cooperative Research Centres Program) for Project R3.7.7: system for real-time monitoring and sensing railway conditions by laser light. This work is sponsored by the National Nature Science Foundation of China [Grant Number: 12002211]. Funding Information: The authors would like to acknowledge the financial support from the Rail Manufacturing Cooperative Research Centre (funded jointly by participating rail organisations and the Australian Federal Government{\textquoteright}s Business Cooperative Research Centres Program) for Project R3.7.7: system for real-time monitoring and sensing railway conditions by laser light. Funding Information: This work is sponsored by the National Nature Science Foundation of China [Grant Number: 12002211 ]. Publisher Copyright: {\textcopyright} 2022 Elsevier Ltd",

year = "2022",

month = nov,

doi = "10.1016/j.engfailanal.2022.106650",

language = "English",

volume = "141",

journal = "Engineering Failure Analysis",

issn = "1350-6307",

publisher = "Elsevier",

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T1 - Experimental investigation on microstructures and mechanical properties of PG4 flash-butt rail welds

AU - Pang, Yong

AU - Grilli, Nicolò

AU - Su, Hang

AU - Liu, Wencheng

AU - Ma, Jun

AU - Yu, Siu Fung

N1 - Funding Information: The authors also acknowledge use of facilities within the Monash Centre for Electron Microscopy and Institute of Railway Technology, Monash University. The authors would like to acknowledge the financial support from the Rail Manufacturing Cooperative Research Centre (funded jointly by participating rail organisations and the Australian Federal Government's Business Cooperative Research Centres Program) for Project R3.7.7: system for real-time monitoring and sensing railway conditions by laser light. This work is sponsored by the National Nature Science Foundation of China [Grant Number: 12002211]. Funding Information: The authors would like to acknowledge the financial support from the Rail Manufacturing Cooperative Research Centre (funded jointly by participating rail organisations and the Australian Federal Government’s Business Cooperative Research Centres Program) for Project R3.7.7: system for real-time monitoring and sensing railway conditions by laser light. Funding Information: This work is sponsored by the National Nature Science Foundation of China [Grant Number: 12002211 ]. Publisher Copyright: © 2022 Elsevier Ltd

PY - 2022/11

Y1 - 2022/11

N2 - Flash-butt welding (FBW) has recently been employed to construct continuously welded rails. However, the failure mechanisms of FBW joints remain unclear. In this study, the weldability of mobile flash-butt welded joints was investigated in terms of microstructures, mechanical properties, and residual stresses. The microhardness test results indicated that the heat-affected zone (HAZ) of the PG4 welds showed significant reductions in hardness of up to 140 HV, whereas the digital image correlation (DIC) measurements showed high heterogeneous strains of up to 4%. Crystallographic analysis indicated that the grains in the HAZ underwent plastic strain with a lattice reorientation of approximately 80% and 55% in the face- and body-centred cubic phase, respectively. The uniaxial tensile tests established the phenomenological relationship between the bond strength and HAZ width: specifically, the bond strength was relatively high at the foot and head of the rail, progressively decreased at the web, and was inversely correlated with the HAZ width. A fractographic analysis confirmed that the shrinkage cracks, inclusions, and flat spots in the rail web were the main cause of early failure in uniaxial tensile tests. Residual stress measurements also showed that FBW can introduce high residual stresses in the rail web of up to 436.76 ± 18.10 MPa and 225.80 ± 12.94 MPa in the vertical and longitudinal directions, respectively. The results of this study reveal that the bond strength of mobile FBW can be assessed based on their HAZ width and provide reliable guidelines for improving the safety and stability of railway systems.

AB - Flash-butt welding (FBW) has recently been employed to construct continuously welded rails. However, the failure mechanisms of FBW joints remain unclear. In this study, the weldability of mobile flash-butt welded joints was investigated in terms of microstructures, mechanical properties, and residual stresses. The microhardness test results indicated that the heat-affected zone (HAZ) of the PG4 welds showed significant reductions in hardness of up to 140 HV, whereas the digital image correlation (DIC) measurements showed high heterogeneous strains of up to 4%. Crystallographic analysis indicated that the grains in the HAZ underwent plastic strain with a lattice reorientation of approximately 80% and 55% in the face- and body-centred cubic phase, respectively. The uniaxial tensile tests established the phenomenological relationship between the bond strength and HAZ width: specifically, the bond strength was relatively high at the foot and head of the rail, progressively decreased at the web, and was inversely correlated with the HAZ width. A fractographic analysis confirmed that the shrinkage cracks, inclusions, and flat spots in the rail web were the main cause of early failure in uniaxial tensile tests. Residual stress measurements also showed that FBW can introduce high residual stresses in the rail web of up to 436.76 ± 18.10 MPa and 225.80 ± 12.94 MPa in the vertical and longitudinal directions, respectively. The results of this study reveal that the bond strength of mobile FBW can be assessed based on their HAZ width and provide reliable guidelines for improving the safety and stability of railway systems.

KW - Digital image correlation

KW - Flash-butt welding

KW - Residual stresses

KW - Weldability

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DO - 10.1016/j.engfailanal.2022.106650

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SN - 1350-6307

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JO - Engineering Failure Analysis

JF - Engineering Failure Analysis

M1 - 106650

ER -

Experimental investigation on microstructures and mechanical properties of PG4 flash-butt rail welds

Abstract

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Keywords

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