Strength,Fracture and Complexity

This paper is designed to address aspects of the immense contribution and enduring legacy of Sir Alan Cottrell FRS FREng FICF (1919–2012) – especially in the context of the creation and development of ICF – at the “ICF13 Memorial International Cottrell Symposium”. One theme of this paper builds on the ICF0 paper of Cottrell in 1959, Cottrell's Opening Address at ICF2 in 1969 and Cottrell's ICF4 contribution “Fracture and Society” in 1977. A second theme of this paper is the BCS model of fracture and other models of fracture devised by Cottrell in the context of Cottrell's seminal 20th century contributions to the very creation of our disciplines of Structural Integrity and Materials Science: including archival research on the early work of Cottrell 1939–1941 on welding and cracking of low alloy steels at Birmingham. In particular, with the analytical BCS Model, Cottrell anticipated the numerical Cohesive Zone Models by at least two decades. This paper also addresses possible ways forward in this challenging 21st century for ICF-WASI following ICF13 in Beijing guided by the legacy of Cottrell's and Yokobori's ideas, inspiration and principles in establishing ICF during 1959–1969. At ICF13 the formal launch is arranged for the metamorphosis of ICF into “The World Academy of Structural Integrity”. This is an ICF brand-development project explored at Sendai with Yokobori in 2010 and then initiated in 2011 at an ICF Interquadrennial Conference with ASTM in Anaheim, USA. This is much more than simply a name change but a comprehensive evolution in substance which like the original ten year creation process of ICF 1959–1969 is designed as a ten-year process 2011–2021. During the ICF13 Cottrell Forum in Beijing (as at the Sendai Interquadrennial in 2010) we seek full debate on the optimum ways forward for this metamorphosis.

A critical survey has been made of tensile, fracture, shear banding and fatigue measurements and their interpretations reported for different types of materials and test conditions. The mechanical properties of the materials are shown to be largely determined by microscopic plastic strain concentrations which depend on the inhomogeneity of the material microstructure, especially including importantly inhomogeneity of the dislocation substructure. Understanding this inhomogeneity is shown to provide a number of connections between seemingly disparate phenomena. The evolution of the dislocation substructure and its relationship to crystallography and various levels of microstructure are critically important. Professor Cottrell made seminal contributions to understanding the fundamental mechanisms involved in determining such strain concentrations. His work continues to provide clarity and guidance to current research accomplishments.

On the basis of the analytical method using the concepts of super atoms, super dislocation and self similarity, the atomic distribution from super atoms to those with small scale was found to show the self similarity and the possibility of analyzing the behaviors of actual atoms using projection method was validated and the following results were obtained. The direct method and Verlet method were found to give the same results on the atomic distribution, however calculating time is different. Using our proposed method, the dominating regions of fracture were shown to be derived and they were in good agreement with those obtained experimentally by Ritchie et al. These analyses were found to predict quantitative values of process region or end region proposed by Kanninen and Broberg.

Sir Alan Cottrell led the transformation of metallurgy from an observational science to analytical description. The following ditty, written for an analysis of the influence of polycrystal grain size on mechanical strength properties, could very well have been inspired by subliminal guidance from Cottrell:

The physically-weaker mortals are supported

With stronger materials, needfully, more so every day.

How so, you say – by brain power exhorted

To restrict the role that cracks and dislocations play!

The following account is an honoring contribution in recognition of the great man's leading researches on one of several materials-based topics that he led: the dislocation mechanics of fracturing.

The validity of constitutive equation and numerical method of potential induced particle diffusion were discussed. In the analysis of potential induced particle diffusion by finite difference method (FDM), α multiplication method which multiplies potential induced terms was found to be valid to realize correct particle diffusion behaviors driven by the potential gradient term. In this paper, the significance of the concept of α multiplication method for the numerical analysis on the potential induced particle diffusion problem were discussed and its validity was proved.

W added high Cr ferritic heat-resistant steels have been developed as a boiler material. Most of boiler component structures are mainly fabricated by welding which are likely to the regions of crack initiation and propagation. However, the method of predicting the life of creep crack initiation and growth have not been clearly established for weldments of high Cr ferritic heat resistant material due to many factors such as the variation in micro-structures and the residual stress caused by welding and thermal cycles. In the present study, the experiments of creep crack growth using a circular notched round bar specimen with variation of notch location in HAZ were conducted and the characteristics of creep crack growth rate and creep crack initiation life were summarized in terms of Q* parameter, which has been proposed as fracture mechanics parameter to describe creep crack growth rate.