Papers by Keyword: Edge Cracks

Abstract: Aiming at the problem that temperature filed changes can lead to edge cracks emerge to Al-Si alloy 4004 in the process of hot rolling, in this paper, finite element model of temperature field variations in the process of rolling have been established by the method of finite element numerical simulation. The relationship between temperature field variations and edge crack defects has been analyzed. The results show that temperature field of rolled piece is gradient variations, low in the center and high in the edge, metal accumulation in the edge, leading to stress concentration and forming cracks source, resulting in edge cracks arising in edge of roller piece. Finally, the reliability and accuracy of the numerical simulation method have been verified by hot-rolled tests and tensile tests. All the studies provide ideas for theoretical analysis of temperature variation during hot rolling and have important significance on improve the quality of products.

Abstract: This paper presents the effect of eccentric cracks on the behavior of stress intensity factors (SIF) of single edge crack in bi-material plates. According to literature, it is found that most of the research conducted previously more on central single edge crack and it is well understood. However, not many research conducted on the eccentric stress intensity factor of single edge crack in bi-material plates. In order to evaluate the SIFs of eccentric edge cracks, ANSYS finite element software is used to model plain strain single edge crack in a plate subjected mode I loadings. The present SIFs are then validated with the existing central crack and it is well agreed to each others. According to the present results, it is found that mode I SIFs decreased insignificantly and mode II SIFs decreased asymptotically when the crack situated away from the central line. As expected all types of SIFs increased when crack length is increased.

Abstract: Magnesium alloys show low deformability at low temperature because of hcp structure and inactiveness of basal slip. Manufacturing of thin sheet is difficult in industries. Some approaches, such as small-draft multi-pass rolling, intermediate annealing, isothermal rolling and high-speed rolling were proposed to overcome the deformability. However, small edge cracks are still formed on the sheet. In this study, rolling speed of 1000m/min was employed to warm-roll AZ31B magnesium alloy in a single pass at different temperatures. The edge cracks formed after the rolling were classified into three main groups: minor, regular and zigzag edge cracks. ‘Crack contact length’ are introduced to explain the morphology of edge cracks. The results show that the critical reduction for crack initiation depends on the pre-heating temperature. The spacing between edge cracks increases linearly with the crack contact length regardless of roll diameter, speed and reduction. It is suggested that this approach is useful to understand the formation mechanism of edge cracks and to evaluate the rollability of magnesium alloys.

Abstract: In this study, interacting crack growth in an infinite plate is analyzed with new, fast and accurate Boundary Cracklet Method (BCM) developed by Phoenix and Yavuz. An interior crack is under consideration to watch its propagation because of cyclic loading which is very common for aerospace, naval and civil engineering structures. BCM is very useful to determine the overall stress field as well as stress intensity factors for crack tips and singular wedges at crack kinks. BCM uses integral equations expressed in terms of unknown edge dislocation distributions along crack lines. These distributions derive from an accurate representation of the crack opening displacements using power series basis terms obtained through wedge eigenvalue analysis, which leads to both polynomial and non-polynomial power series. The process is to choose terms of the series and their exponents such that the tractions on the crack faces are virtually zero compared to the far field loading. Applying the method leads to a set of linear algebraic equations to solve for the unknown weighting coefficients for the power series basis terms to make no use of numerical integrations unlike in other methods. Thats why, solution takes just a few seconds on a PC. A simple crack growth emanating from a triangular hole in an infinite plate is analyzed. The fatigue crack growth is assumed to follow Paris-Erdogan Law. The results are compared to those of other numerical methods. A parametric study is performed via graphs and tables to demonstrate the ability of BCM in analysis of fatigue crack growth.

Abstract: The unique imaging and microanalytical capability of the electron-probe microanalyser (EPMA) has been exploited in conjunction with light microscopy for exploring the genesis of some defects, which are detrimental to steel product quality. Investigations of surface and internal defects have revealed that defects in the finished steel product are often inherited at upstream stages and accentuated in the later stages of steel processing. While the occurrence of surface defects such as “slivers” in hot-rolled sheets and “linear cracks” in hot-rolled rounds has been largely attributed to subsurface non-metallic inclusions and slag/casting powder entrapment, microprobe analysis of internal defects such as “centre-line cracking” of thick plates have revealed the deleterious role of C and Mn macrosegration inherited during the continuous casting of steel slabs. The paper elucidates some of these findings, as unravelled by both qualitative and quantitative microprobe analysis.