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Title: Improving Fatigue Performance of AHSS Welds

Abstract

Reported herein is technical progress on a U.S. Department of Energy CRADA project with industry cost-share aimed at developing the technical basis and demonstrate the viability of innovative in-situ weld residual stresses mitigation technology that can substantially improve the weld fatigue performance and durability of auto-body structures. The developed technology would be costeffective and practical in high-volume vehicle production environment. Enhancing weld fatigue performance would address a critical technology gap that impedes the widespread use of advanced high-strength steels (AHSS) and other lightweight materials for auto body structure light-weighting. This means that the automotive industry can take full advantage of the AHSS in strength, durability and crashworthiness without the concern of the relatively weak weld fatigue performance. The project comprises both technological innovations in weld residual stress mitigation and due-diligence residual stress measurement and fatigue performance evaluation. Two approaches were investigated. The first one was the use of low temperature phase transformation (LTPT) weld filler wire, and the second focused on novel thermo-mechanical stress management technique. Both technical approaches have resulted in considerable improvement in fatigue lives of welded joints made of high-strength steels. Synchrotron diffraction measurement confirmed the reduction of high tensile weld residual stresses by the two weldmore » residual stress mitigation techniques.« less

Authors:
 [1];  [1];  [1];  [1];  [2];  [2];  [2];  [3];  [3];  [3]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. ArcelorMittal USA, Harriman, TN (United States)
  3. Colorado School of Mines, Golden, CO (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). High Flux Isotope Reactor (HFIR)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1209200
Report Number(s):
ORNL/TM-2014/680
VT0505000; CEVT230
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English

Citation Formats

Feng, Zhili, Yu, Xinghua, Erdman, III, Donald L., Wang, Yanli, Kelly, Steve, Hou, Wenkao, Yan, Benda, Wang, Zhifeng, Yu, Zhenzhen, and Liu, Stephen. Improving Fatigue Performance of AHSS Welds. United States: N. p., 2015. Web. doi:10.2172/1209200.
Feng, Zhili, Yu, Xinghua, Erdman, III, Donald L., Wang, Yanli, Kelly, Steve, Hou, Wenkao, Yan, Benda, Wang, Zhifeng, Yu, Zhenzhen, & Liu, Stephen. Improving Fatigue Performance of AHSS Welds. United States. doi:10.2172/1209200.
Feng, Zhili, Yu, Xinghua, Erdman, III, Donald L., Wang, Yanli, Kelly, Steve, Hou, Wenkao, Yan, Benda, Wang, Zhifeng, Yu, Zhenzhen, and Liu, Stephen. Sun . "Improving Fatigue Performance of AHSS Welds". United States. doi:10.2172/1209200. https://www.osti.gov/servlets/purl/1209200.
@article{osti_1209200,
title = {Improving Fatigue Performance of AHSS Welds},
author = {Feng, Zhili and Yu, Xinghua and Erdman, III, Donald L. and Wang, Yanli and Kelly, Steve and Hou, Wenkao and Yan, Benda and Wang, Zhifeng and Yu, Zhenzhen and Liu, Stephen},
abstractNote = {Reported herein is technical progress on a U.S. Department of Energy CRADA project with industry cost-share aimed at developing the technical basis and demonstrate the viability of innovative in-situ weld residual stresses mitigation technology that can substantially improve the weld fatigue performance and durability of auto-body structures. The developed technology would be costeffective and practical in high-volume vehicle production environment. Enhancing weld fatigue performance would address a critical technology gap that impedes the widespread use of advanced high-strength steels (AHSS) and other lightweight materials for auto body structure light-weighting. This means that the automotive industry can take full advantage of the AHSS in strength, durability and crashworthiness without the concern of the relatively weak weld fatigue performance. The project comprises both technological innovations in weld residual stress mitigation and due-diligence residual stress measurement and fatigue performance evaluation. Two approaches were investigated. The first one was the use of low temperature phase transformation (LTPT) weld filler wire, and the second focused on novel thermo-mechanical stress management technique. Both technical approaches have resulted in considerable improvement in fatigue lives of welded joints made of high-strength steels. Synchrotron diffraction measurement confirmed the reduction of high tensile weld residual stresses by the two weld residual stress mitigation techniques.},
doi = {10.2172/1209200},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Mar 01 00:00:00 EST 2015},
month = {Sun Mar 01 00:00:00 EST 2015}
}

Technical Report:

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  • Weld fatigue performance is a critical aspect for application of advanced high-strength steels (AHSS) in automotive body structures. A comparative study has been conducted to evaluate the fatigue life of AHSS welds. The material studied included seven AHSS of various strength levels - DP 600, DP 780, DP 980, M130, M220, solution annealed boron and fully hardened boron steels. Two conventional steels, HSLA 590 and DR 210, were also included for baseline comparison. Lap fillet welds were made on 2-mm nominal thick sheets by the gas metal arc welding process (GMAW). Fatigue test was conducted under a number of stressmore » levels to obtain the S/N curves of the weld joints. It was found that, unlike in the static and impact loading conditions, the fatigue performance of AHSS is not influenced by the HAZ softening in AHSS. There are appreciable differences in the fatigue lives among different AHSS. Changes in weld parameters can influence the fatigue life of the weld joints, particularly of these of higher strength AHSS. A model is developed to predict the fatigue performance of AHSS welds. The validity of the model is benchmarked with the experimental results. This model is capable to capture the effects of weld geometry and weld microstructure and strength on the fatigue performance experimentally observed. The theoretical basis and application of the newly developed fatigue modeling methodology will be discussed.« less
  • The fatigue performance of gas metal arc welding (GMAW) joints of advanced high strength steels (AHSS) are compared and analyzed. The steel studied included a number of different grades of AHSS and baseline mild steels: DP600, DP780, DP980, M130, M220, solution annealed boron steel, fully hardened boron steels, HSLA690 and DR210 (a mild steel). Fatigue testing was conducted under a number of nominal stress ranges to obtain the S/N curves of the weld joints. A two-phase analytical model is developed to predict the fatigue performance of AHSS welds. It was found that there are appreciable differences in the fatigue S/Nmore » curves among different AHSS joints made using the same welding practices, suggesting that the local microstructure in the weld toe and root region plays non-negligible role in the fatigue performance of AHSS welds. Changes in weld parameters can influence the joint characteristics which in turn influence fatigue life of the weld joints, particularly of those of higher strength AHSS. The analytical model is capable of reasonably predicting the fatigue performance of welds made with various steel grades in this study.« less
  • This report provides updated calculated LOCE lifetimes of welds in designated LOFT Class 1 piping systems. For each weld, lifetime is defined as the greatest number of cycles of the governing transient such that cumulative usage factor does not exceed 1.0. Results are presented in tabular form. For parts of the pressurizer relief system, the number of relief cycles rather than LOCE cycles govern and are so shown.
  • The work described in this report was aimed at determining the effect of root imperfections allowed by API 1104 on the fatigue properties of girth welds, and to recommend a S-N curve appropriate for girth welds in pipelines. To accomplish this objective, S-N curves were developed for single-sided girth welds without a backing strip using pipe strip specimens containing the various sizes of incomplete root penetration and lack-of-root sidewall fusion; these imperfections are currently allowed by API 1104. The different root imperfection sizes investigated in this project were 1/16- x 0.5-in. (1.6 x 12.7 mm), 1/16- x 1.0-in. (1.6 xmore » 25.4 mm), and 1/8- x 1.0-in. (3.2 x 25.4 mm). Baseline fatigue data for nominally sound weld joints were also developed. The results from the baseline weld pipe strip specimens were compared to the full pipe section results available from the literature. It was concluded that the results from the baseline pipe strip specimens adequately represent the fatigue performance of full pipe sections loaded axially or in bending. Therefore, a baseline weld design curve was developed using both pipe strip specimens and full pipe section data. All test results for axial or bending loads lie above the proposed fatigue design curve. The lack of definitive data on pipes subjected to fluctuating internal pressure confounds attempts to extend the applicability of the proposed fatigue design curve to this important loading condition. The influence of root imperfection size on the fatigue performance was also assessed. Again, the lack of definitive data for full pipe sections confounds attempts to extend the applicability of the proposed fatigue curves to this loading condition. In summary, S-N design curves are proposed for nominally sound girth welds and for girth welds containing various sizes of root imperfections that are loaded axially or in bending. 18 refs., 31 figs., 16 tabs.« less