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SIMPLIFICATIONS FOR CONSERVATIVE STRUCTURAL INTEGRITY

ASSESSMENT

Petar Agatonović

D-85244 Röhrmoos, Deutschland

1. INTRODUCTION

Stress analysis is very important topic for design and fracture mechanics. From the

beginning of the so-called industry revolution, the concern against structure integrity has

lead to its great progress. From Hook (1578) up today the stress analysis has developed to

include theories of material strength and elasticity, visco-elasticity and plasticity. Rapid

increase of computer capacity brought to the further large progress in using numerical

methods for the calculation and analysis of stresses with finite elements. At the same time

the knowledge concerning material behaviour brought to the new constitutive theories as

dislocation theory, theory of plasticity and failure mechanisms. This demanded the

development of new disciplines, like fracture mechanics, fatigue of materials, corrosion

theory and non-destructive examination methods. Simultaneously with this, new and

stronger materials were developed and their resistance to fracture have been improved by

alloys design, production processes and heat treatment.

All these advancements will remain inconceivable without simplifications of the

corresponding problems to find out practical solutions. In accordance to the definition,

under the notion of the simplification one understands the reduction of given conditions

with the aim to get of some acceptable approximate solution of the problem. Even though

the consequence of the simplifications is the getting away from the reality, they help by

arriving to the solution, to better understand the corresponding relationships and correct

assess the importance and ways of acting of different parameters. Under this condition,

the simplifications are necessary and desirable.

Although the area of fracture analysis looks as the new research discipline, people

were confronted for ages with this problem. However, the processes met in solid body

fracture are so complicated and diverse that one can’t expect that the corresponding

phenomena will be described by simple formulas and criteria. Because of this, the

development of fracture mechanics was falling back in some way behind other

disciplines. But, today very abundant information concerning different fracture aspects

exists, obtained through broad theoretical and experimental researches. This knowledge

allows designer to deal with the problem of the structures safe against fracture in a more

rational ways than it was possible in the past. Especially in the last 15 years extensive

progress has been reached in the development and application of the fracture mechanics

in design with light and high strength materials. At the same time, broad experiences

show that the treatment of such structures without fracture mechanics is insufficient and

can lead to the unexpected failure due to neglecting of unavoidable defects.

Accordingly, for the purposes of the safety of the metal structures, it is necessary to

accept that as the result of production cycles in structural components crack-like defects

always exist, at least at the size not detectable by non-destructive-inspection (NDI)

methods applied, due to limited sensitivity of these methods. These cracks can lead to the