Influence of Predetermined Surface Defect to the Bendability of Ultra-High-Strength Steel

2012 ◽  
Vol 504-506 ◽  
pp. 901-906 ◽  
Author(s):  
Antti Määttä ◽  
Antti Järvenpää ◽  
Matias Jaskari ◽  
Kari Mäntyjärvi ◽  
Jussi A. Karjalainen
Keyword(s):  
Surface Defects ◽  
High Strength Steels ◽  
Steel Structures ◽  
High Strength ◽  
Crack Size ◽  
Critical Crack ◽  
Bending Radius ◽  
Ultra High Strength Steels ◽  
Materials Used ◽  
Critical Crack Size

The use of ultra-high-strength steels (UHS) has become more and more popular within last decade. Higher strength levels provide lighter and more robust steel structures, but UHS-steels are also more sensitive to surface defects (e.g. scratches). Practically this means that the critical crack size decreases when the strength increases. The aim of the study was to study if the formula of critical crack size is valid on forming processes of UHS-steels. Surface cracks with different depths were created by scratching the surface of the sheet by machining center. Effect of the scratch depth was determined by bending the specimens to 90 degrees. Bents were then visually compared and classified by the minimum achieved bending radius. Test materials used were direct quenched (DQ) bainitic-martensitic UHS steels (YS/TS 960/1000 and 1100/1250). Results from the bending tests were compared to the calculated values given by the formula of critical crack size.

Incremental Bending of Ultra-High-Strength Steels

2011 ◽  
Vol 473 ◽  
pp. 53-60 ◽  
Author(s):  
Antti Määttä ◽  
Kari Mäntyjärvi ◽  
Jussi A. Karjalainen
Keyword(s):  
Automotive Industry ◽  
Rolling Direction ◽  
High Strength Steels ◽  
High Strength ◽  
Roll Forming ◽  
Complex Phase ◽  
Bending Angle ◽  
Bending Radius ◽  
Ultra High Strength Steels ◽  
Traditional Manner

Utilisation of ultra-high-strength steels (UHS) has increased, particularly in the automotive industry. By using these materials vehicle structures can be lightened. However, one of the problems of UHS is weak formability. Materials fracture easily with small bending radii and the minimum bending radii are rather large. In this study, the tested materials were complex phase (CP) bainitic-martensitic UHS steels (YS/TS 960/1000 and 1100/1250). The steels were incrementally bent with a press brake in the rolling direction and perpendicular to it, and the final bending angle was 90 degrees. The incremental bending angles were 150°, 130°, 110° and 90°. The punch was unloaded after every incremental bending step. The test materials were bent with different bending radii. The aim was to find the minimum bending radius which produces an acceptable bend. Every incremental bend was compared with a bending performed in the traditional manner. The aim of this study was to examine how well the results of incremental bending compare to roll forming. In addition, clarification studies of when the bend started to fracture were made. It is well known that steels are more efficiently bent by roll forming compared with traditional bending. The results presented in this study demonstrate that incremental bending does not produce better results than traditional bending. Nevertheless, it has been shown that the examined steels can be bent incrementally against manufacturer’s recommendations.

scholarly journals Overview on the digitized production of welded steel structures

2022 ◽  
Author(s):  
Tuomas Skriko ◽  
Antti Ahola ◽  
Timo Björk
Keyword(s):  
High Strength Steels ◽  
Steel Structures ◽  
High Strength ◽  
Production Quality ◽  
Robotic Welding ◽  
Human Errors ◽  
Welded Steel ◽  
Short Run ◽  
Ultra High Strength Steels ◽  
Cost Efficient

Abstract This paper presents a concept and practical topics involved in digitized production. The term “production” denotes the design, fabrication, and service life of a product, which in this case elaborates on welded steel structures. This includes the required information for guiding all the process stages of the chosen material back to its re-melting, following the material flow in a fully digitized form. This concept enables an increase in production quality at a higher level while minimizing the risk of human errors. Automation of the short-run production of steel structures for demanding applications is also a key goal, together with securing a cost-efficient process. Typically, such structures are fabricated from high- or ultra-high-strength steels. Though challenging, reaching these aims seems to be realistic by applying advanced fatigue design methods, using high-quality robotic welding and receiving information about the real loading of the structure.

scholarly journals Strain distribution during air bending of ultra-high strength steels

2021 ◽  
Author(s):  
Aki-Petteri Pokka ◽  
Anna-Maija Arola ◽  
Antti Kaijalainen ◽  
Vili Kesti ◽  
Jari Larkiola
Keyword(s):  
Surface Defects ◽  
Numerical Models ◽  
Measurement Data ◽  
High Strength Steels ◽  
High Strength ◽  
Image Correlation ◽  
Bending Tests ◽  
Air Bending ◽  
Bending Process ◽  
Ultra High Strength Steels

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.

Correlation of Tensile Test Parameters and Bendability of High-Strength Steels

2013 ◽  
Vol 554-557 ◽  
pp. 12-20
Author(s):  
Janne Lämsä ◽  
Anu Väisänen ◽  
Jouko Heikkala ◽  
Antti Järvenpää
Keyword(s):  
Tensile Test ◽  
High Strength Steels ◽  
High Strength ◽  
Test Results ◽  
Bending Properties ◽  
Testing Method ◽  
Test Parameters ◽  
Tension Properties ◽  
Bending Radius ◽  
Materials Used

The aim of the study was to investigate correlation between bendability and tensile properties of high-strength steels. Strength and elongation in tensile test have traditionally been basic values in evaluating bending properties. Advanced high-strength (AHS) steels often have tendency for strain localization, causing risk of fractures and impairing the shape of the bend. Practice has shown that tensile test results, indicating bendability well, are not sufficiently accurate when using AHS steels. Since tensile test is a fast, simple and cheap testing method, it would be beneficial to rework it to suit better for predicting of bendability. In this study, the usability of tensile test results to predict failures in bending AHS steels has been investigated. The most common failures and failure mechanisms in bending are also presented. Test materials used were 6 mm thick AHS wear-resistant, protection and structural steels with good and poor bending properties. Minimum bending radii were determined and then compared with ten-sile test results to estimate the correlation. Conventional tensile test results, fracture surfaces and necking through width and thickness were analyzed. Correlation coefficient for measured tension properties and minimum bending radius was calculated. Results showed that in tensile test, have the best correlation with minimum bending radius with necking through the thickness and actual strain in necking area.

High Strain Rate Fracture Properties of High Strength Steels and Their Application

2011 ◽  
Author(s):  
Alan M. Clayton ◽  
John Dabinett
Keyword(s):  
Strain Rate ◽  
High Strain ◽  
Cast Steel ◽  
High Strength Steels ◽  
High Strength ◽  
Crack Size ◽  
Strength Properties ◽  
Strain Rates ◽  
Critical Crack ◽  
Welded Steel

The evaluation of fracture of ferritic steels using the methods in ASME Code Case 2564 for impulsively loaded vessels requires the static reference temperature T0 and the upper shelf toughness, and these are used together with the Master Curve to define the transition temperature curve. The effect of high rates of strain on the ductile-brittle transition is determined in the code case using a correlation due to Wallin. Two steels used for impulsively loaded vessels, welded steel similar to HY80 plate and a cast steel similar to HY100 have been evaluated to obtain their static fracture and strength properties. Additional instrumented pre-cracked Charpy testing using a draft ISO standard has determined the shift in T0 with high strain rates and the results have been compared to the Wallin correlation. The strain rate correlation is used to evaluate the fracture response of vessels made of these steels when subjected to internal blast. By using the instantaneous strain rates of the vessel wall vibration considerable gains in critical crack size can be obtained compared to using the highest rate throughout the whole of the transient.

Texture analysis and joint performance of laser-welded similar and dissimilar dual-phase and complex-phase ultra-high-strength steels

2021 ◽  
Vol 174 ◽  
pp. 111035
Author(s):  
Ajit Kumar Pramanick ◽  
Hrishikesh Das ◽  
Ji-Woo Lee ◽  
Yeyoung Jung ◽  
Hoon-Hwe Cho ◽  
...  
Keyword(s):  
Texture Analysis ◽  
High Strength Steels ◽  
High Strength ◽  
Dual Phase ◽  
Complex Phase ◽  
Joint Performance ◽  
Ultra High Strength Steels

Favourable Steel Structures using High Strength Steels

ce/papers ◽  
2021 ◽  
Vol 4 (2-4) ◽  
pp. 1530-1536
Author(s):  
Fengyan Gong ◽  
André Dürr ◽  
Jochen Bartenbach
Keyword(s):  
High Strength Steels ◽  
Steel Structures ◽  
High Strength

Effect of Rotational Stiffness Evolution at Crack Part on Critical Crack Size in SFR

2012 ◽  
Author(s):  
Takashi Wakai ◽  
Hideo Machida ◽  
Shinji Yoshida
Keyword(s):  
Evaluation Method ◽  
Large Diameter ◽  
Crack Size ◽  
Evolution Model ◽  
Piping System ◽  
Rotational Stiffness ◽  
Critical Crack ◽  
Rotational Spring Model ◽  
Size Evaluation ◽  
Critical Crack Size

This paper describes the efficiency of the deployment of rotational stiffness evolution model in the critical crack size evaluation for Leak Before Break (LBB) assessment of Sodium cooled Fast Reactor (SFR) pipes. The authors have developed a critical crack size evaluation method for the thin-walled large diameter pipe made of modified 9Cr-1Mo steel. In this method, since the SFR pipe is mainly subjected to displacement controlled load caused by thermal expansion, the stress at the crack part is estimated taking stiffness evolution due to crack into account. The stiffness evolution is evaluated by using the rotational spring model. In this study, critical crack sizes for several pipes having some elbows were evaluated and discuss about the effect of the deployment of the stiffness evolution model at the crack part on critical crack size. If there were few elbows in pipe, thermal stress at the crack part was remarkably reduced by considering the stiffness evolution. In contrast, in the case where the compliance of the piping system was small, the critical crack size could be estimated under displacement controlled condition. As a result, the critical crack size increases by employing the model and LBB range may be expected to be enlarged.

Sign in / Sign up

Export Citation Format

Share Document