{"title":"Automated Method for Pre-Straining of Steels for Bake Hardenability Testing","authors":"A. Agha","doi":"10.1007/s40799-024-00735-8","DOIUrl":null,"url":null,"abstract":"<div><p>The bake hardening effect in steel, characterized by a boost in yield strength resulting from initial deformation and subsequent heat treatment, holds significant promise for the automotive sector. Bake hardening is characterized by the Bake Hardening Index (BHI), as outlined in the test standards EN 10325:2006 and JIS G 3135:2018. The suggested test procedure involves pre-straining the dogbone samples and subjecting them to thermal cycling. However, the current standards lack specificity regarding the pre-straining procedure and the estimation of elastic recovery in metals, leading to inconsistencies in results across different materials and laboratories. This study addresses this gap by proposing a standardized and fully automated method utilizing in-situ strain measurements to precisely pre-strain uniaxial tension samples to any desired level of plastic strain. This method offers precise control over strains and accurate estimation of strain overcompensation, which accounts for elastic recovery during unloading. In this paper, the proposed method is validated using optical strains using digital image correlation, however the proposed method is independent of the choice of strain measurement method and works with clip-on extensometers, optical extensometers and even the crosshead transducers in the load frame. The foundation and effectiveness of the proposed method are demonstrated through statistical data obtained from testing 11 different steel grades, including bake hardenable steels and Advanced High Strength Steels commonly used in the automotive industry. The proposed method is independent of the choice of steel grade and consistently delivers satisfactory results for all tested steel grades, producing test samples with plastic strains that adhere to the specifications of the testing standards.</p></div>","PeriodicalId":553,"journal":{"name":"Experimental Techniques","volume":"49 1","pages":"181 - 186"},"PeriodicalIF":1.9000,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Experimental Techniques","FirstCategoryId":"5","ListUrlMain":"https://link.springer.com/article/10.1007/s40799-024-00735-8","RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"ENGINEERING, MECHANICAL","Score":null,"Total":0}
引用次数: 0
Abstract
The bake hardening effect in steel, characterized by a boost in yield strength resulting from initial deformation and subsequent heat treatment, holds significant promise for the automotive sector. Bake hardening is characterized by the Bake Hardening Index (BHI), as outlined in the test standards EN 10325:2006 and JIS G 3135:2018. The suggested test procedure involves pre-straining the dogbone samples and subjecting them to thermal cycling. However, the current standards lack specificity regarding the pre-straining procedure and the estimation of elastic recovery in metals, leading to inconsistencies in results across different materials and laboratories. This study addresses this gap by proposing a standardized and fully automated method utilizing in-situ strain measurements to precisely pre-strain uniaxial tension samples to any desired level of plastic strain. This method offers precise control over strains and accurate estimation of strain overcompensation, which accounts for elastic recovery during unloading. In this paper, the proposed method is validated using optical strains using digital image correlation, however the proposed method is independent of the choice of strain measurement method and works with clip-on extensometers, optical extensometers and even the crosshead transducers in the load frame. The foundation and effectiveness of the proposed method are demonstrated through statistical data obtained from testing 11 different steel grades, including bake hardenable steels and Advanced High Strength Steels commonly used in the automotive industry. The proposed method is independent of the choice of steel grade and consistently delivers satisfactory results for all tested steel grades, producing test samples with plastic strains that adhere to the specifications of the testing standards.
钢的烘烤硬化效应,其特点是由于初始变形和随后的热处理而导致屈服强度的提高,在汽车行业具有重要的前景。烘烤硬化的特征是烘烤硬化指数(BHI),如测试标准EN 10325:2006和JIS G 3135:2018所述。建议的测试程序包括预先拉伸狗骨样品并使其进行热循环。然而,目前的标准缺乏关于预应变程序和金属弹性恢复估计的特异性,导致不同材料和实验室的结果不一致。本研究通过提出一种标准化和全自动的方法来解决这一差距,该方法利用原位应变测量来精确地预应变单轴拉伸样品到任何所需的塑性应变水平。该方法可以精确地控制应变,准确地估计应变过补偿,从而解释卸载过程中的弹性恢复。本文利用数字图像相关技术对光学应变进行了验证,但该方法与应变测量方法的选择无关,可以与夹紧式延伸计、光学延伸计甚至负载框架中的十字头传感器一起工作。通过对11种不同钢种(包括汽车工业常用的可烘烤硬化钢和高级高强度钢)的测试统计数据,验证了该方法的基础和有效性。所提出的方法独立于钢材等级的选择,并始终为所有测试钢材等级提供满意的结果,生产具有符合测试标准规格的塑性应变的测试样品。
期刊介绍:
Experimental Techniques is a bimonthly interdisciplinary publication of the Society for Experimental Mechanics focusing on the development, application and tutorial of experimental mechanics techniques.
The purpose for Experimental Techniques is to promote pedagogical, technical and practical advancements in experimental mechanics while supporting the Society''s mission and commitment to interdisciplinary application, research and development, education, and active promotion of experimental methods to:
- Increase the knowledge of physical phenomena
- Further the understanding of the behavior of materials, structures, and systems
- Provide the necessary physical observations necessary to improve and assess new analytical and computational approaches.