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• Omega is observed as a more descriptive parameter to the steady-state fracture propagation. • The current analytical model explains and highlights the influence of the testing geometrical set-up on CTOA in relation to the Fracture Propagation. • Omega is observed to be independent of the Fracture Speed within the investigation range. Dynamic ductile fracture in pressure vessels is an increasingly important topic. Recent catastrophic pressurised pipeline failures highlighted the critical needs of reliable pipeline infrastructures. The ability for line pipe steels to resist fracture is a critical design factor for governing the severity level of fracture failures given that it determines if fracture propagates for several kilometres or is arrested quickly. Developing a reliable fracture toughness test to systematically evaluate new steel products' quality is therefore important. In the current work, a novel small-scale fracture toughness parameter Omega was implemented and compared to the well-established parameter CTOA, with respect to their performance of characterizing steady-state fracture propagation and their dependencies to Fracture Speed. The current experimental data were collected from a 3-point bend dynamic Drop Weight Tear Test (DWTT) for 9 line pipe steels with different thicknesses and impact conditions. It was found that the Omega gives significantly better description for steady-state fracture propagation; and it is found to be independent of the Fracture Speed. The current study confirmed that in DWTT, CTOA values decrease with increasing Fracture Speed. Finally, a simple analytical model is proposed to describe this dependency (CTOA-Fracture Speed) from a geometrical standpoint. [ABSTRACT FROM AUTHOR]

The development of ultra/advanced high strength steels (U/AHSS) has challenged traditional forming methods due to their higher strength and reduced formability. An alternative method is flexible roll forming, which allows the manufacture of sheet metal of high strength and limited ductility into complex and weight-optimized components. However, one major problem in flexible roll forming is the web-warping defect, which is the deviation in height of the web over the length of the profile. The authors' previous work developed an analytical model to predict the magnitude of web-warping. That model was purely geometric and neglected the effect of material properties. This work develops an analytical solution for the prediction of web-warping that considers both geometric and material parameters. The model results were validated by comparison with numerical and experimental results. The impact of this new model will be the ability to provide a rapid initial design assessment before an intensive numerical analysis of flexible roll forming is conducted. [ABSTRACT FROM AUTHOR]

The resistance to ductile fracture propagation remains a weak point in gas transmission pipelines' safety since the emerging of this risk more than half a century ago. Full-scale burst tests of pressurized gas pipeline sections are performed to verify the ability of pipeline steel to arrest the crack propagation. However, motivated by the commitment to specific predictive models, the main outcome from full-scale burst tests (FSBT) has been in form of a binary "propagation/arrest" metric corresponding to each pipe in the test section. In the absence of a reliable laboratory-scale test demonstrating correlation with the full-scale resistance to ductile fracture propagation, such approach does not appear reasonable since it leaves line pipe manufacturers with very little clue regarding the preferential metallurgical designs. This work aims to better quantify the crack propagation resistance in FSBT providing metallurgists with a target property and facilitating the development of a new laboratory-scale mechanical test that shows reasonable correlation with FSBT. In order to improve FSBT testing methodologies, the pipe wall strain related to the crack propagation should be assessed along the entire test line. This can be implemented by means of modern 3D-measurement technologies that can digitize very large objects with high accuracy at a reasonably low cost. The method is demonstrated in the current work using the results of a recent FSBT carried out on X80 grade pipes. The results indicated that the plastic strain zone in FSBT can spread from the fracture surface over distances equivalent to tens of pipe wall thicknesses, while in the widely adopted drop weight tear test (DWTT) this spread hardly reaches one specimen thickness. Single-edge notched tensile (SENT) configuration provides much larger extent of the plastic zone into the specimen gauge when compared to DWTT whose major deformation mode is bending. Furthermore, the correlations between the strain parameters in different tests are discussed, and conclusions are drawn to promote a new laboratory test method for ductile fracture propagation resistance assessment in high strength steel pipe. • The commitment to predictive models based on impact-bending tests has led to dead end. • Full-scale burst test results can be better assessed by means of 3D-measurements. • Full-scale crack propagation is associated with extremely large zone of plastic strain. • In the impact-bending tests the plastic zone spread is constrained. • A new dynamic single-edge notched tensile test based on drop-weight principle has been proposed. [ABSTRACT FROM AUTHOR]

To reduce weight and improve passenger safety there is an increased need in the automotive industry to use Ultra High Strength Steel (UHSS) for structural and crash components. However, the application of UHSS is restricted by their limited formability and the difficulty of forming them in conventional stamping. An alternative method of manufacturing structural auto body parts from UHSS is the flexible roll forming process, which allows the manufacture of metal sheet with high strength and limited ductility into complex and weight-optimized components. One major problem in the flexible roll forming of UHSS is the web-warping defect, which is the deviation in height of the web area over the length of the profile. It has been shown that web-warping is strongly dependant to the permanent longitudinal strain formed in the flange of the part. Flexible roll forming is a continuous process with many roll stands, which makes numerical analysis extremely time intensive and computationally expensive. An analytical model of web-warping is therefore critical to improve design efficiency during the early process design stage before FEA is applied. This paper establishes for the first time an analytical model for the prediction of web-warping for the flexible roll forming of a section with variable width. The model is based on evaluating longitudinal edge strain in the flange of the part. This information is then used in combination with a simple geometrical model to investigate the relationship between web-warping and longitudinal strain with respect to process parameters. [ABSTRACT FROM AUTHOR]

• A novel Ω [mm−1 concept was proposed shear-dominated fracture initiation and propagation. • The Ω concept possesses important characteristics that were found in the well-established CTOA/D approach; • A dimensionless quantity – Normalised Omega Ω ¯ was proposed that is independent to both in and out-plane specimen configurations. Our engineered metallic materials are being designed to be more and more ductile with an increase in strength. Consequently, the failure mode has changed – from brittle to ductile fracture, which leads to a limited applicability of the previously used parameters that quantify the material resistance developed for brittle fracture. This is owing to that a considerable amount of plastic strain is introduced to the fracture process. Shear-dominated ductile fracture failure is commonly observed in many of the structural metals. In the current work, a novel measure Omega Ω is proposed, which fundamentally describes the material's ability to motivate relative mass motion in response to Mode Ι shear-dominated fracture propagation. The effects of specimen geometry, fracture tip constraint and deformation modes on Ω were discussed and analysed, which inspired the ideas of normalisation approaches that lead to the development of a dimensionless parameter Normalised Omega Ω ¯. Accompanying with this concept, our systematically conducted experimental results (DWTT and SENT) indicated, that Ω ¯ is independent to both in-plane and out-plane (specimen thickness) specimen configurations. So that it possesses the characteristic of being an intrinsic material constant for ductile fracture under shear mode. [ABSTRACT FROM AUTHOR]

The classical theory of folded developables suggests that curved crease folding can be applied to sheet metal of high strength to manufacture parts with complex geometries. However, its application has been limited to sheet metals with low strength and requires grooving or perforation of the material at the fold lines. Applying the geometrical concept otherwise remains unexplored despite its potential in sheet metal-intensive industries like automotive, transportation, and construction. The current study introduces a novel sheet metal forming technique called developable forming. The theory of folded developables is applied to design a die tool for flange drawing a developable-shaped steel sheet. A developable connection is produced from high-strength material without resorting to thickness accommodation techniques. Experimental findings establish that the novel process does not follow the premises of the theory of folded developables. New shape effects are observed and the terms curving and coning are introduced to describe these. Additionally, significant redundant strains are identified in the flange, highlighting the different deformation modes in the developable forming process. A higher formability is achieved for a material with limited uniaxial elongation highlighting the need for further investigation on the mechanisms involved in the novel process. [ABSTRACT FROM AUTHOR]