Computational aspects of steel fracturing pertinent to naval requirements

Abstract

Modern high strength and ductile steels are a key element of US Navy ship structural technology. The development of these alloys spurred the development of modern structural integrity analysis methods over the past 70 years. Strength and ductility provided the designers and builders of navy surface ships and submarines with the opportunity to reduce ship structural weight, increase hull stiffness, increase damage resistance, improve construction practices and reduce maintenance costs. This paper reviews how analytical and computational tools, driving simulation methods and experimental techniques, were developed to provide ongoing insights into the material, damage and fracture characteristics of these alloys. The need to understand alloy fracture mechanics provided unique motivations to measure and model performance from structural to microstructural scales. This was done while accounting for the highly nonlinear behaviours of both materials and underlying fracture processes. Theoretical methods, data acquisition strategies, computational simulation and scientific imaging were applied to increasingly smaller scales and complex materials phenomena under deformation. Knowledge gained about fracture resistance was used to meet minimum fracture initiation, crack growth and crack arrest characteristics as part of overall structural integrity considerations.

Report of Committee III.2: Fatigue and fracture

“…The complexity increases when a change in stress distribution during crack growth is to be accounted for. With the aid of advanced computation techniques, the application of crack growth approaches in the ship and offshore structures have become more common in recent years (Yeter et al, 2014a, b, Matic et al, 2015, Yeter et al, 2015b, a, e).…”

“…Numerical simulations With the aid of high-performance computers, the numerical simulation is an alternative way for extensive parametric studies, replacing a large amount of costs on the experimental set up to conduct fatigue crack experimental tests. Progress in the computational modelling of fracture and fatigue with the advent of cohesive zone theory and more recently with the extended finiteelement techniques will improve the basic understanding of fracture processes (Matic et al, 2015). The progress of computation techniques such as finite method and meshless methods makes the calculation of stress intensity factors (SIF) and crack shape development easier for ship details and offshore structures.…”

“…One of the main influencing factors on the fatigue performance of materials is the initial crack size, and there have been a large number of research efforts devoted to investigating the impact (Matic et al, 2015, Reddy et al, 2016. Although there is a need for a unified definition of the fatigue crack initiation and propagation, there is no agreement in which the phases of the fatigue crack growth could be divided with an exact definition: microscopic, small and macroscopic.…”

Fracturing across the multi-scales of diverse materials

“…Related theoretical analyses in the former case are in [63,64] and, for glass material, to essentially static hardness testing by Rouxel [55] and applied to hierarchical structural aspects of tooth enamel by Yilmaz et al [65]. Other benefits of structural considerations dealing with experimental fractographic analyses, building onto Hull's attribution to Hooke [3], are provided in [66,67], relating also to an exposition of ductile versus brittle fracturing considerations in the articles by Tekoglu et al [68], Armstrong [48], Knott [69] and Matic et al [70].…”

“…Quite a few years earlier, Orowan [29] had remarked in pioneering work that fracturing is a mechanismsensitive process, hence such added descriptions as 'fatigue fracturing', 'creep fracturing', etc. Such consideration applies to any number of different type observations made in the already referenced articles [42,49,50,53,59] and relates to other variable stress aspects of controlled fracture testing as exemplified in the articles by Atkinson et al [74], Matic et al [70] and Mughrabi [75].…”