FATIGUE ASSESSMENT OF CORRODED DECK LONGITUDINALS OF TANKERS

Fatigue life of deck longitudinals of oil tankers is analysed based on linear elastic fracture mechanics. A parametric formulation for the estimation of stress intensity factors and the Paris-Erdogan law are applied. Long-term effects of corrosion are modelled based on regression equations fitted to thickness measurements made during inspections of two tankers. Parametric studies are performed in order to investigate the importance of the governing parameters of crack propagation. A comparison of the fatigue analyses performed by linear fracture mechanics and S-N approaches is presented.

Crack behaviour at the interface of a surface layer applied on a steel substrate by laser cladding

An influence of the bi-material interface between a steel substrate and a thin protective layer applied through laser cladding was investigated. A range of elastic properties and thicknesses of the layer were considered to cover the behaviour of a short crack in the selected materials such as bronze, nickel or cobalt alloys. The special case of the crack terminating directly at the interface was investigated, which is connected to the necessity of application of generalized approaches of linear elastic fracture mechanics. The results contribute to better understanding of fracture response of selected materials and to a more reliable decision on choosing a proper material of the protective layer.

Effects of mechanical and electronic properties for B2 FeAl modified by several kinds of point defects: First-principles study

Elastic, fracture and deformation behavior of B2 FeAl intermetallics modified by ternary additions as well as Al/Fe vacancy defects and anti-sites have been investigated based on density functional theory (DFT). Formation enthalpy indicates that ternary additions Sc, Y, Mo and W have a preference for Al site. While Fe site is more easily replaced by ternary Cu and Zn. Moreover, vacancy and antisite defects can be stable in FeAl. Pugh criteria ([Formula: see text] ratio), Poisson’s ratio [Formula: see text] and Cauchy pressure show that Sc, Y, Mo, W and Al vacancy (Al anti-site by Fe atom) can effectively improve the ductility of FeAl. Dislocation emission and micro-cracks propagation show that the improved ductility is due to the promoted dislocation emission but suppressed micro-cracks propagation. Bonding analyses reveal that the improved ductility is mainly own to the weakened the covalent interactions and strengthened the metallic interactions.

Theoretical limits in detachment strength for axisymmetric bi-material adhesives

Reversible dry adhesives rely on short-ranged intermolecular bonds, hence requiring a low elastic modulus to conform to the surface roughness of the adhered material. Under external loads, however, soft adhesives accumulate strain energy, which release drives the propagation of interfacial flaws prompting detachment. The tradeoff between the required compliance, for surface conformity, and the desire for a reduced energy release rate, for better strength, can be achieved with a bi-material adhesive having a soft tip and a rigid backing. This design strategy is widely observed in nature across multiple species. However, the detachment mechanisms of these adhesives are not completely understood and quantitative analysis of their adhesive strength is still missing. Based on linear elastic fracture mechanics, we analyze the strength of axisymmetric bi-material adhesives. We observed two main detachment mechanisms, namely (i) center crack propagation and (ii) edge crack propagation. If the soft tip is sufficiently thin, mechanism (i) dominates and provides stable crack propagation, thereby toughening the interface. We ultimately provide the maximum theoretical strength of these adhesives obtaining closed form estimation for an incompressible tip. In some cases, the maximum adhesive strength is independent of the crack size, rendering the interface flaw tolerant. We finally compare our prediction with experiments in the literature and observe good agreement.