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**Published:** Jan 1983

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**Source: **STP803V2-EB

A comparison is made between the major proposals recently developed for assessing the stability of a structure which is cracking by ductile mechanisms. These proposals all have in common the concept that stability is ensured if the crack driving force is less than the material's resistance to cracking. They differ, however, in how they define and evaluate the necessary parameters.

The four basic procedures discussed are: 1. Direct graphical comparisons, using the J-integral as a fracture parameter. Different methods of estimating the applied *J* are discussed, together with techniques for comparing the slopes of the applied *J* and the material's resistance curve. 2. An energy-based method which compares the elastic energy release rate and the plastic work dissipation rate during crack extension. 3. Assessment diagram approaches. These include the Central Electricity Generating Board procedure and methods that incorporate strain-hardening effects. 4. Maximum load crack-opening displacement.

The information needed to perform each analysis and its relevance to the practical problem when viewed against the uncertainties inherent in any structural analysis are discussed. Emphasis is given to the treatment of thermal and residual stresses. It is concluded that the confidence obtained in the results varies from procedure to procedure, but this can be greatly enhanced if certain safeguards are applied during the analysis. The safeguards necessary depend upon which approach is adopted.

**Keywords:**

ductile tearing, instability analysis, J-integral, η-factor, crack-opening displacement, crack growth, resistance curve, failure assessment diagram, tearing modulus, strain hardening, stress-intensity factor, plastic collapse load, strip yielding model, J, estimation schemes, design curves, thermal stresses, residual stresses, elasticplastic fracture

**Author Information:**

Chell, GG *Fracture Mechanics Project leader and research officer, General Electricity Research Laboratories, Central Electricity Generating Board, Leatherhead, Surrey*

Milne, I *Fracture Mechanics Project leader and research officer, General Electricity Research Laboratories, Central Electricity Generating Board, Leatherhead, Surrey*

**Committee/Subcommittee:** E08.08

**DOI:** 10.1520/STP36767S