M.S.U. Chowdhury

On the probability of failure by yielding of hull girder midship section

Abstract Based on the first order second moment principles (FOSM) a detailed methodology has been developed to predict the failure probability of an idealized hull-girder mid-ship section by yielding. The probability is related to the age of the ships when corrosion causes wear of the structural components. Three different corrosion models have been discussed. A numerical example is presented with full details.

The changes in mean and variance of midship section properties due to uniform corrosion wear

Abstract A typical midship section is represented by a deck, inner bottom, outer bottom, side shells and round bilge corners. As an example, angle bar stiffeners were used throughout and symmetric I-beams are placed as girders. Accurate expressions were developed for the section properties of both stiffeners and then the midship section. The properties considered include cross-sectional area, moment of inertias and section modulus. The first order second moment (FOSM) approximation was used to derive the mean and standard deviation of the midship section properties. The changes in section properties due to uniform corrosion wear are considered. The main focus of this article is to derive accurate empirical relationships for the mean and standard deviation of any given midship section as simple functions of corrosion loss. It has been observed that all geometric properties are linear functions of total corrosion loss, and there is a single constant relevant to the section which specifies the property completely. This constant is termed as the configuration constant. However, the standard deviation is better approximated by a fourth order polynomial in total corrosion loss and hence requires four configuration constants.

Finite element analysis of notched bars subjected to elastic-plastic deformation

For many years engineers and scientists have speculated about the relationship between the load carrying capacity of notched bars and their stress concentration factors. However, past attempts to quantify this relationship have failed and the problem remains largely unresolved. This study strongly supports the view that this relationship exists, and that there are correlations between load carrying capacity and stress concentration for notched bars subjected to tension. The study was done with the use of computer aided technology and finite element analysis, which allowed for more rigorous testing procedures when compared with conventional tensile testing methods. Two studies were conducted: firstly, an analysis which assumed perfectly elastic conditions, and secondly, an analysis which assumed realistic elastic-plastic conditions. Variables of interest included maximum strain energy density, plastic collapse load, elastic stress concentration factor, elastic-plastic stress concentration factor, root radius and the distance between the notch surface to the maximum load. It was found that these variables correlate to one another and that most of them are dependent on material properties. Both linear and non-linear relationships were found. Linear relationships were quantifiable and were represented by equations. Equations for most of the non-linear relationships could not be substantiated, as there were not enough data points present.

An investigation of structural composite laminates

The following presentation is divided into two parts, A and B. The ultimate objective of this investigation is to compute the ‘extreme’ loading conditions that will cause failure of one or more of the constituent laminas in a laminate. The failure criterion used here is that of the maximum stress. The ‘extreme’ loading condition is computed by the application of conventional Linear Programming (LP) techniques. This aspect is discussed in Part B. However, in order to form the LP problem it was felt necessary to develop a suitable method of analysis of the laminate under most general loading conditions. Part A gives the aspects of this stand-alone version of a laminate analysis method using matrix notations. The analysis is based on simple Classical Laminate Theory (CLT). The outcomes of this part are the so-called stress and strain coefficient matrices.

Optimisation procedure for X-80 steel blast tolerant transverse bulkheads

An optimisation procedure to be used to develop optimised X-80 steel blast tolerant transverse bulkheads is described. Three different structural arrangements have been investigated and optimised. This work has been stimulated by the increased interest in naval platform survivability over the past decade and the development of X-80 steel.