Showing papers in "Strength, fracture and complexity in 2014"
TL;DR: In this paper, an algorithm of multi-scale hy-brid mechanics from the nano-scale to the macro-scales is described to solve the problem of structural safety under time-dependent fracture conditions.
Abstract: To solve the problem of structural safety under time-dependent fracture conditions, an algorithm of multi-scale hy- brid mechanics from the nano-scale to the macro-scales is described. The paper presents an algorithm that links the physics of materials with life prediction determined by creep crack growth and addresses practical application which enables "predic- tion of fracture" to be developed from "the science of clarification of fracture mechanism" on the basis of the algorithm. In particular, in order to predict the fracture life of real components, the importance of the link between void mechanics caused by vacancy diffusion (micro mechanical factor), the stress tri-axiality, TF (a structural mechanical factor), and the material structure (a meso-mechanical factor) is shown in the proposed formulation for the activation energy of the thermally activated process of creep crack growth. A detailed discussion on these issues as well as on the algorithm relevant to the establishment of the law of creep crack growth life based on the multi-scale analysis is included ranging from the scale of micro damage to structural brittleness.
10 citations
7 citations
TL;DR: In this article, the authors investigated the reasons and mechanisms of wear of the hinge-lever tilting mechanism bearings of the continuous billet casting machine mold operating in the rolling motion mode.
Abstract: The results are considered of the investigations into the reasons and mechanisms of wear of the hinge-lever tilting mechanism bearings of the continuous billet casting machine mold operating in the rolling motion mode. The types of defects of the outer and inner rings of the bearing are determined, as well as their shape and relative position. The optical and electron- microscopic analysis of the surface of the defect is performed. It is established that the static and dynamic loading parameters have a significant effect on the mechanisms of friction and wear, as well as on the formation of dents in the bearing races. The results obtained allow assessing the reasons for wear of the hinge-lever tilting mechanism bearings, and laying the ground for the development of the technique for their elimination or minimization.
7 citations
TL;DR: In this article, the tensile strength of arc stud welded joints with weld reinforcement and without weld reinforcement, and the friction-welded stud joints without burrs were 233, 231 and 180 MPa, respectively, and all joints fractured near the weld zone at a bending angle of approximately 20°.
Abstract: Stud joints of 5083 aluminum alloy were welded by arc stud welding and friction welding, and their joint strengths were examined. In the weld zone of the arc stud welded joint, no change occurred in the hardness distribution. In contrast, the weld zone of the friction-welded stud joint softened slightly on the plate side and hardened on the bar side. The tensile strengths of the arc stud welded joints with weld reinforcement and without weld reinforcement, and the friction-welded stud joints without burrs were 233, 231 and 180 MPa, respectively, and all joints fractured at the weld zone. In the bending test, all joints fractured near the weld zone at a bending angle of approximately 20°. In the fatigue test, the fatigue strengths of the arc stud welded joints were higher than those of the friction-welded stud joints, and the fatigue limits of the arc stud welded joints with weld reinforcement and without weld reinforcement, and the friction-welded stud joints without burrs were 43, 40 and 13 MPa, respectively.
6 citations
TL;DR: In this article, the mixed-mode I/II/III crack loading conditions can be generated by loading the MMF sandwich beam by an inclined force, at the force inclination varying from 0 to 90 degrees.
Abstract: Static fracture in foam core composite sandwich beams under mixed-mode I/II/III crack loading conditions is studied theoretically by the Mixed Mode Flexure (MMF) beam configuration The basic idea of this paper is that mixed-mode I/II/III crack loading conditions can be generated by loading the MMF sandwich beam by an inclined force (usually, the MMF beam, loaded by a vertical force, is used for investigating mixed-mode I/II fracture in continuously fiber reinforced polymer com- posites) Three-dimensional finite element simulations of the MMF sandwich beam are performed using the ANSYS program system The methods of linear-elastic fracture mechanics are applied The fracture behavior is studied in terms of the strain energy release rate The virtual crack closure technique is applied to analyze the strain energy release rate mode components distribution along the crack front in the MMF beam at the force inclination varying from 0 ◦ (force parallel to the crack front) to 90 ◦ (vertical force) The analysis revealed that the MMF beam loaded by an inclined force can be used to study the mixed-mode
5 citations
TL;DR: In this paper, Cottrell's leading researches on one of several materials-based topics that he led: the dislocation mechanics of fracturing are discussed. And 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 Cottree: The physically-weaker mortals are supported With stronger materials, needfully, more so every day.
Abstract: 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.
4 citations
3 citations
TL;DR: The ICF-WASI metamorphosis into the World Academy of Structural Integrity was discussed at the ICF13 Cottrell Symposium in Beijing, China.
Abstract: 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.
2 citations
2 citations
TL;DR: Hirsch as mentioned in this paper highlighted some of the contributions that Cottrell made to Fracture and to Structural Integrity, and recalled some personal memories. But he did not mention the importance of the Copley Medal of the Royal Society.
Abstract: Sir Peter Hirsch’s tribute to Sir Alan’s many achievements in Academic circles and National “Corridors of Power” appeared in the FESI Bulletin 6(1) (2012). Chief Scientific Advisor to the Government; Master of Jesus College; Vice-Chancellor of Cambridge University; Writer of seminal Monographs; an inspiration to hundreds, if not thousands, of Metallurgists, Materials Scientists and Materials Engineers the World over, Peter regards him as the most outstanding and influential Physical Metallurgist of the 20th Century: the only one to be awarded the Copley Medal of the Royal Society. In my Materials Science and Technology editorial of July 2009, written to celebrate Sir Alan’s 90th birthday, I was moved to write “If anyone can be said to ‘bestride the World like a Colossus’ it is Sir Alan”. In this piece, I hope to highlight some of the contributions that he made to Fracture and to Structural Integrity, and to recall some personal memories. I first became aware of Professor Cottrell, as the author of Theoretical Structural Metallurgy (1948) and of Dislocations and Plastic Flow in Crystals (1953), when I was an undergraduate at Sheffield: probably in my second year, 1957/1958. In the summer of 1958, I had a vacation job at the Royal Aircraft Establishment, Farnborough and, perhaps strangely, in the light of all the interest in fatigue following
2 citations
TL;DR: In this article, the tensile behaviour of alloy D9 after ageing at 823-1123 K for 10-10,000 h has been studied using acoustic emission (AE), where tensile tests along with AE monitoring were conducted at room temperature at nominal strain rate of 1.33 × 10 −3 s −1.
Abstract: BACKGROUND: Hexagonal wrapper tubes in fast breeder reactor (FBR) contain smaller circular tubes called fuel pins made of austenitic 15Cr–15Ni–Ti modified stainless steel (alloy D9). This is used in 20% cold worked condition. At maximum service temperature of fuel clad (around 973 K), prolonged exposure to high temperature could remove the effect of cold work. Thermal ageing of cold worked alloy D9 at 823–1123 K results in carbide precipitation which affect the subsequent deformation behaviour. OBJECTIVE: The tensile behaviour of alloy D9 after ageing at 823–1123 K for 10–10,000 h has been studied using acoustic emission (AE). METHODS: Tensile tests along with AE monitoring were conducted at room temperature at nominal strain rate of 1.33 × 10 −3 s −1 . RESULTS: Strength decreased and elongation increased with ageing temperature. Till 1000 h ageing time, AE parameters (up to yield) decreased with ageing temperature. But for 5000 and 10,000 h, they increased first and then decreased with a peak at around 973 K. This coincides with a trough in elongation at around 973 K. CONCLUSIONS: The trough in elongation has been attributed to increasing difficulty of plastic deformation by pinning of dislocations. A correlation exists among tensile, Larson–Miller (LMP) parameter and AE parameters.
TL;DR: In this paper, the disturbed region of atom arrangements around a crack tip were clarified under the local stress field by crack and dislocation, which is in good agreement with the scale obtained from experimental consideration by R. Ritchie.
Abstract: Brittle fracture at a crack tip is considered to be caused within a specified local region, that is, process region. However, the determination of this scale has not yet been theoretically clarified. The difficulty of this determination will be due to the wide range scale analysis from the range of nano scale (atomic scale) to macro scale (crack size scale). In this paper, on the basis of the atomic mechanics using super atom and hybrid method of the fractal concept which concerns self-similarity with the proposed analysis of scale projection from macro to nano scales, the disturbed region of atom arrangements around a crack tip were clarified under the local stress field by crack and dislocation. This disturbed region was related to fracture dominating region (process region) which is in good agreement with the scale obtained from experimental consideration by R. Ritchie.
TL;DR: A critical survey has been made of tensile, fracture, shear banding and fatigue measurements and interpretations reported for different types of materials and test conditions as mentioned in this paper, showing that the mechanical properties of the materials are largely determined by microscopic plastic strain concentrations which depend on the inhomogeneity of the material microstructure.
Abstract: A critical survey has been made of tensile, fracture, shear banding and fatigue measurements and 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.
TL;DR: In this paper, 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 cracks growth rate and creep crack initiation life were summarized in terms of Q ∗ parameter, which has been proposed as fracture mechanics parameter to describe the growth rate.
Abstract: 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.
TL;DR: In this paper, the effects of crack relative depth, aspect ratio and heat transfer coefficient on the stress intensity factor along the crack front are studied, and the results show that the small inner surface crack due to thermo-mechanical loading sometimes is more critical than that for the deeper one.
Abstract: METHODS: In this paper, based on the three-dimensional finite element method, the local thermal stress intensity factor is computed using ANSYS software. The weight function method is also used to determine closed-form stress intensity factors at the deepest point of the crack. The effects of crack relative depth, aspect ratio and heat transfer coefficient on the stress intensity factor along the crack front are studied. The results show to be in accordance with those cited in the literature in the special case of loading. CONCLUSIONS: The obtained results show that the small inner surface crack in a cylinder due to thermo-mechanical loading sometimes is more critical than that for the deeper one. It is also shown that the maximum of thermal stress intensity factors are always in the case of conductive heat transfer instead of the convective one.
TL;DR: In this article, the authors established the trailer/semi-trailer integral axle mechanical model and analyzed the force conditions under the vertical load (impact dynamic load) and the tangential load (braking torque) of the axle from theoretic.
Abstract: Through establishing the trailer/semi-trailer integral axle mechanical model, analyzing the force conditions under the vertical load (impact dynamic load) and the tangential load (braking torque) of the axle from theoretic. Aid the ADAMS conduct the force simulation analysis for the 11 tons trailer/semi-trailer's integral axle. Furthermore, analyze the fracture mechanism of XCQ16 seamless sample through the tensile and impact fracture specimens by SEM scanning.