Micromechanism of Cleavage Fracture of Metals
Micromechanism of Cleavage Fracture of Metals

Author: Jianhong Chen

Publisher: Butterworth-Heinemann

Published: 2014-09-15

Total Pages: 488

ISBN-13: 0128010517

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In this book the authors focus on the description of the physical nature of cleavage fracture to offer scientists, engineers and students a comprehensive physical model which vividly describes the cleavage microcracking processes operating on the local (microscopic) scale ahead of a defect. The descriptions of the critical event and the criteria for cleavage fracture will instruct readers in how to control the cleavage processes and optimize microstructure to improve fracture toughness of metallic materials. - Physical (mechanical) processes of cleavage fracture operating on the local (microscopic) scale, with the focus on the crack nucleation and crack propagation across the particle/grain and grain/grain boundaries - Critical event, i.e., the stage of greatest difficulty in forming the microcrack, which controls the cleavage fracture - Criteria triggering the cleavage microcracking with incorporation of the actions of macroscopic loading environment into the physical model - Effects of microstructure on the cleavage fracture, including the effects of grain size, second phase particles and boundary - Comprehensive description of the brittle fracture emerging in TiAl alloys and TiNi memory alloys

The Effect of Microstructure on the Fracture Toughness of Low-alloy Steels
The Effect of Microstructure on the Fracture Toughness of Low-alloy Steels

Author: Syavash Ensha

Publisher:

Published: 1974

Total Pages: 198

ISBN-13:

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A theoretical model has been used to relate the cleavage fracture toughness of the low-alloy steels to their microstructure. The cleavage fracture toughness of low-alloy steels depends upon three metallurgical parameters: the microscopic cleavage strength, the yield strength, and the effective root radius. Variations in fracture toughness with microstructure can be explained through the effect of the microstructure on these parameters. The major objective of this investigation has been the study of the effect of microstructural variables on these parameters, and hence the effect of microstructure on fracture toughness. The theoretical model for the cleavage fracture toughness of the low-alloy steels can be successfully applied provided the assumptions are not strongly violated. This requires low microscopic cleavage strength/yield strength ratio values and low work-hardening rates. Lower temperatures and higher strain rates both favor these conditions. (Modified author abstract).

Analysis of Fracture Toughness Mechanism in Ultra-fine-grained Steels
Analysis of Fracture Toughness Mechanism in Ultra-fine-grained Steels

Author: Toshihiro Hanamura

Publisher: Springer

Published: 2014-09-04

Total Pages: 71

ISBN-13: 4431544992

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In this book, advanced steel technologies mainly developed at the National Institute for Materials Science (NIMS), Japan, for structure control, mechanical properties, and the related mechanisms are introduced and discussed. NIMS has long worked on developing advanced steel techniques, namely, producing advanced steels by using only simple alloying elements such as carbon, manganese, and silicon, and also by utilizing steel scrap. The hope is that this approach will lead to a technology of a so-called steel-to-steel recycling process, with the ultimate goal of a recycling process such as an automotive-steel-to-automotive-steel recycling process to take the place of the current cascade-type recycling system. The main idea is to utilize ultra-grain refining structures and hetero structures as well as martensite structures. In particular, the focus of this book is on tensile strength and toughness of advanced steels from both the fundamental and engineering points of view. Fundamentally, a unique approach to analysis is taken, based on fracture surface energy as effective grain size is employed to better understand the mechanism of property improvement. From the engineering point of view, in fracture toughness such factors as crack tip opening displacement (CTOD) of advanced steels are evaluated in comparison with those of conventional steels.

Micromechanisms and Toughness for Cleavage Fracture of Steel
Micromechanisms and Toughness for Cleavage Fracture of Steel

Author: A. R. Rosenfield

Publisher:

Published: 1986

Total Pages: 14

ISBN-13:

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A complete understanding of the fracture mechanisms of steel in the ductile/brittle transition region requires analysis not only of crack initiation, but also of crack propagation. This paper reviews micrographic and fractographic experiments that give insight into both phenomena, and suggests a frame-work through which both may be related. Unstable cleavage crack initiation can occur after some blunting of the original fatigue precrack or after some stable crack growth. In either event, instability appears to be triggered by the fracture of a brittle micro-constituent ahead of the precrack. The large scatter in reported KIc values within the transition region reflects the size distribution and relative scarcity of these trigger particles. While a large number of models have attempted to correlate toughness in the ductile/brittle transition regime to events occurring ahead of the crack tip, surprisingly little attention has been paid to events occurring behind the crack front. Fractographic evidence as well as metallographic sectioning of arrested cracks show that the mechanism of rapid crack propagation by cleavage is affected strongly by partial crack-plane deflection which leaves unbroken ligaments in its wake. The tearing of these ligaments by dimple-rupture is the dominant energy-absorbing mechanism. Etch-pit experiments using an Fe-Si alloy show that the crack-tip stress intensity based on plastic zone size is extremely low. Keywords: HSLA(High Strength Low Alloy), Ductile fracture, Shear fracture, Fracture toughness.

Fracture Behavior of Ultra-Low-Carbon Steel Plate and Heat-Affected-Zone
Fracture Behavior of Ultra-Low-Carbon Steel Plate and Heat-Affected-Zone

Author:

Publisher:

Published: 1990

Total Pages: 96

ISBN-13:

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This report describes research carried out to investigate the fracture of ultra-low-carbon bainitic steels. Eight materials have been evaluated using notched-bar bend tests, tensile strength tests and Charpy V- notch impact tests, which were performed over a range of temperatures from -1965 C to +1005 C. These tests measured the cleavage fracture strength and the ductility to brittleness transition temperature under impact loading. The materials evaluated had carbon levels of less than 0.03%, manganese level from 1% to 2%, and microalloys additions of niobium, titanium and boron. Some low alloy steels contained molybdenum and nickel. Some of the materials were subjected to simulated heat-affected-zone (HAZ) thermal cycle and other thermal- mechanical treatments. The fracture surfaces of the specimens were examined using the scanning electron microscope and energy dispersive x-ray analysis. The results of the fracture tests and analyses indicate that the cleavage fracture strength of these materials can vary from 1650 to 2300 MPa. High cleavage fracture strength may be achieved with either a polygonal ferrite or an acicular/bainitic structure, but the high cleavage fracture strength of the polygonal ferrite structure material was reduced of a simulated thermal HAZ cycle.