Papers by Keyword: Edge Crack

Abstract: Edge cracking is an essential local formability phenomenon encountered in specific forming operations, such as stretch flanging, which is broadly employed in the automotive industry. However, the prediction of the edge cracks is challenging, and the hole expansion test is widely carried out to detect the edge cracking performance. This research analyzed quenched and partitioned steel (QP), one of the third-generation advanced high-strength steels widely adopted in the automotive industry to replace conventional high-strength steels due to its superior global formability features. However, its local formability has been a bottleneck due to its microstructure nature and shows strong anisotropy dependency. Therefore, a modeling framework is needed that consistently incorporates anisotropy in both plasticity and fracture. In this study, the hole expansion performance of QP1000 steel was evaluated through a fully anisotropic fracture model based on the Yld2004-18p anisotropic yield criterion and the DF2016 ductile fracture model. To this end, the standard uniaxial tensile tests in seven material orientations, the bulge test, and the tensile tests of different fracture samples were conducted. These samples were picked out to characterize the broad spectrum of loading conditions and cut in rolling, diagonal, and transverse directions to establish the fully anisotropic fracture model. It was seen that the edge cracking metrics, which are the hole expansion ratio and the fracture initiation zone, were accurately captured by the developed model.

Abstract: Attention to the fatigue cracks in steel structures and bridges has been paid for long time. In spite to efforts to eliminate the creation and propagation of fatigue cracks throughout the designed service life, cracks are still revealed during inspections. Note, that depending on location of initial crack, the crack may propagate from the edge or from the surface. The theoretical model of fatigue crack progression is based on linear fracture mechanics. Steel specimens are subjected to various load (tension, three-and four-point bending, pure bending etc.). The calibration functions for short edge cracks are compared for various load and the discrepancies are discussed.

Abstract: During the forming of high-strength steels, edge cracks occur unexpectedly on sheared edges e.g. during collar forming. A non-contact measurement method based on the well-known tensile test was developed. It allows the investigation of the formation of edge cracks under tensile loads and determining general criteria to predict the formation of edge cracks during a specific forming process. The criteria are validated experimentally by means of the collar-forming test. In conjunction with the proposed line-fit-method these criteria can be implemented easily in FEM software in the near future for the prediction of edge cracks.

Abstract: Edge cracking is a commonly observed phenomenon in cold rolling process, but researchers appear to be far from fully understanding its failure mechanism due to the complex stress conditions of steel strip under the rolling condition. In this research, the shear modified GTN damage model coupled with Nahshon-Hutchinson shear damage mechanism was applied to investigate the damage and fracture behavior of steel strip in cold rolling. The results show that the shear modified GTN damage model is competent to predict the damage and fracture behavior of steel strip in cold rolling. By comparison to the cold rolling experiment, it presents that the prediction of edge crack occurrence of the shear modified GTN damage model is more accurate than that of the original GTN damage model.

Abstract: In this paper the characterization of the edge crack in the strip steel are studied by using numerical simulation method. The developments of the stress and strain near the crack tip are obtained and the value of the J-integral of edge crack under the rolling process is then examined. FE simulation result shows that the J-integral is not always path independent in the whole rolling process. When the crack is far away from the roller, the J-integral is path independent. When the crack enters the cold rolling region, the unload phenomena will occur near the crack tip which cause the incremental theory of plasticity failed and the conservation of the J-integral is not valid any more. The J-integral failure region is then determined by a series of FE simulations.

Abstract: To characterize the degradation of material at low triaxiality, the shear modified GTN damage model proposed by Nahshon and Hutchinson (2008) was introduced in this study. The details of the numericalimplementation and validation of the model was conducted. And the shear modified parameter was determined by the comparisons of experimental and simulation results of the shear test. Then, the damage model was employed to simulate the cold rolling process, and the results showed that the shear modified GTN model can reveal the damage behavior and predict edge crackingof ductile materials in cold rolling.

Abstract: Aim for calculating stress intensity factor (short for SIF) of different width plates with edge crack, and the change tendency between different widths and SIF, the crack model is built by finite element software, and the SIF change tendency line with different width plates is got. It is seen from the von Mises stress cloud chart of ANSYS that the deformation of plate is effected by crack; as the decreasing of width, SIF is increasing. When the width of plate is down to 3/8, SIF is increasing fiercely, that means, the plate at this time has already reached the edge of fracture. If continue loading the stretch, the crack will be apparent on the plate. And the curvature equation is got by index decay adapting.

Abstract: To introduce feature and microstructure of edge crack of rolled coil, character and distribution of transverse corner crack of continuous cast slab (hereafter referred to as transverse corner crack), trace out rolling process of defective continuous cast slab, transverse corner crack of slab causes edge crack of rolled coil, the corner inclusions of slab and rolling process are also significant factors. To give some suggestions to resolve two dimensional heat transfer and high cooling intensity about control of transverse corner cracks. Inclusions cause stress concentration to lead to edge cracks of coils. Edge cracks of coils are related to transverse corner cracks of slabs, but not an exact one-for-one relation. Tiny transverse corner cracks may be removed by scarfing or furnace. Uneven or low temperature of the edge of rolled piece cause uneven extension of edge metal to form “fold”, namely “edge filament”. By research and practice, the quality of slab has been substantially improved in Shougang Qiangang.

Abstract: This paper presents a theoretical investigation of free vibration analysis of a functionally graded beam (FGM) under the bending-torsion loading using a classical elasticity theory. The FG beam is assumed to have an open edge crack. It is assumed that the material properties of the simply-supported cracked beam, vary along the beam thickness following a polynomial distribution in the thickness direction. This analysis is based on the linear fracture mechanics. First of all, governing equations and boundary conditions of the FG beam are derived using Hamilton's principle. The governing equations are solved using generalized differential quadrature (GDQ) method. By applying GDQ method, the governing differential equations convert to a linear system of algebraic equations. Then solving the eigenvalue problem, natural frequencies of the FG beam can be found. The results indicate that natural frequencies in the presence of a crack are affected by the crack ratio and location.

Abstract: Bi-material has been widely used in engineering. Due to the edge singularity, failure usually occurs from interface edge. For the evaluation of such failures, fracture mechanics approach is considered useful to avoid the edge singularity, by introducing an edge crack with various directions. However, this evaluation method is inconvenient for engineering application due to its complicity. In this paper, based on a huge amount of numerical analysis, an empirical formula of stress intensity factors (SIFs) for cracks initiated from the interface edge with various directions and crack length has been proposed. Since the cracks initiated from the interface edge is induced and dominated by the edge singular stress field, which can be characterized by the singular order and the corresponding stress intensity coefficient (SIC), this empirical formula relates their SIFs with the SIC and singular order of the edge singular stress field. With this empirical formula, it is possible to evaluate the fracture occurring from the interface edge by fracture mechanics approach, only with the numerical analysis of non-cracked bonded dissimilar materials.