Digital image correlation and optical strain measuring in bendability assessment of ultra-high strength structural steels

Arola, Anna-Maija; Kaijalainen, Antti; Kesti, Vili; Pokka, Aki-Petteri; Larkiola, Jari

doi:10.1016/j.promfg.2019.02.154

Cited by 10 publications

(4 citation statements)

References 6 publications

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“…DIC is an advanced digitalized method to measure displacements and strain quantities over a material tested, by tracking a unique distribution of pixel intensities of a grey scale image called a pattern or template [11]. The cameras detect the measuring surface by identifying a black dot pattern painted on white background.…”

Section: Test Set-up and Measurement Systemmentioning

confidence: 99%

Testing of a Novel Induction Heat Treated Steel Brace with Enhanced Buckling Behaviour

Jamshiyas,

Skalomenos

2023

ce papers

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Steel braces are widely used to stabilize steel structures forming horizontal or vertical truss structures; however, their relatively poor buckling behaviour is often lead to overdesigned structures. Induction Heat (IH) treatment technology is a novel contactless material transformation process to effectively strengthen local areas of steel sections. Utilizing IH to increase the strength of the middle length of steel brace sections, buckling behaviour can be improved. The present study experimentally investigates the compression behaviour of the novel braces fabricated by IH‐treated circular hollow steel sections. A Digital Image Correlation (DIC) system is used to measure the experimental deformation quantities, such as axial displacements, out‐of‐plane deformations, and strain distributions along the brace length. Four specimens were tested with two set of different slenderness ratios (λ). Each set includes one conventional steel brace (CSB) and one IH‐treated steel brace (IHSB) with a stronger section at its mid‐length. The specimens were subjected to a monotonic displacement‐controlled loading history until reaching an axial compressive strain of 2.5%. It was found that buckling load can increase up to 20% in IHSBs. IH treatment was also beneficial in improving the post‐buckling behaviour of the brace. The compression strength was found to be more than double in IHSBs than in CSBs at a ductility level of 5 (ductility is defined as the ratio of the target axial displacement to the yielding axial displacement). Moreover, out‐of‐plane displacements were reduced by 28% for the IHSBs at an axial strain of 1% showing a more evenly distribution of strain demands along the brace length.

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Section: Test Set-up and Measurement Systemmentioning

confidence: 99%

Testing of a Novel Induction Heat Treated Steel Brace with Enhanced Buckling Behaviour

Jamshiyas,

Skalomenos

2023

ce papers

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“…Likewise, the differences in the extent of multi-breakage and the bend shapes are studied, and these observations are correlated with the findings from the bending force and strain measurements and tensile tests. Bending tests with DIC strain measuring have been previously done by many authors [6,[20][21][22][23][24][25], some of which have also measured the strain evolution during bending [20,23,24].…”

Section: Pourboghrat and Stelsonmentioning

confidence: 99%

Strain distribution during air bending of ultra-high strength steels

Pokka¹,

Arola²,

Kaijalainen³

et al. 2021

Esaform 2021

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Air bending is a widely used method for forming ultra-high strength steels (UHSS). However, the limited formability of UHSS poses some challenges for the bending process in the form of strain localisation, surface defects, punch detachment (multi-breakage) and pseudo-polygonal “nut-like” shape of the bend. In this study, the bendability of three UHSS grades (700, 900 and 1100 MPa) is investigated with 3-point bending tests, utilising Digital Image Correlation (DIC) for measuring the strain distributions on the outer curvature. The differences in the extent of multi-breakage and the bend shapes are also studied, and these observations are correlated with the findings from the bending force and strain measurements. The differences between the investigated UHSS grades are significant. The 900 MPa grade produces more localised strain distributions and pronounced multi-breakage compared to the other grades, along with a more polygonal “nut-like” geometry. The reasons and effects of the multi-breakage phenomenon, as well as the causes for the observed differences in the behaviour of the materials are discussed in this paper. The presented results and the measurement data provide more information about the behaviour of the investigated materials in bending, and can be used for improving bending simulation, numerical models, and workshop instructions.

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“…However, research on the root of the phenomenon, i.e., the causes and effects of the strain distribution development in air bending, has been relatively scarce. Strain distributions in air bending have been studied by several authors [1,[9][10][11][12][13][14], but not for a large selection of materials and punch radii, that would allow thorough analysis of the effects of certain tool parameters and material properties. Research in this area is therefore necessary.…”

Section: Introductionmentioning

confidence: 99%

Total strain on the outer surface of steel sheets in air bending

Pokka

2023

Materials Research Proceedings

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Abstract. Air bending is a commonly used method for sheet-metal forming. However, several challenges exist around the bending behavior of materials with poor global formability, that are difficult to study using conventional bending test methods, and thus may not be fully understood. In this study, nine thermomechanically rolled steel grades with various strengths and ductility properties are bent using three different punch radii. The strain distributions on the outer surface are measured using Digital Image Correlation (DIC). The relationships between the strain distribution, peak strain, and total strain (area under the strain distribution curve) are determined. The total strain is observed to be independent from the peak strain and the shape of the strain distribution. The total strain is found to depend on the bend angle and sheet thickness. An analytical formula for approximating the total strain is derived. Potential for further approximations of the total strain, strain distribution and bend shape are discussed.

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Digital image correlation and optical strain measuring in bendability assessment of ultra-high strength structural steels

Cited by 10 publications

References 6 publications

Testing of a Novel Induction Heat Treated Steel Brace with Enhanced Buckling Behaviour

Testing of a Novel Induction Heat Treated Steel Brace with Enhanced Buckling Behaviour

Strain distribution during air bending of ultra-high strength steels

Total strain on the outer surface of steel sheets in air bending

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