Fracture cleavage

A cleavage fracture (microscopically brittle fracture) occurs (almost) without microscopic deformation perpendicular to the largest tensile stress. Bonds between the atoms break. In face-centred cubic metals, the ductility is so large that cleavage fracture can occur in extreme cases only. In body-centred cubic metals, cleavage fracture can occur at low temperature or high strain rates in ceramics, cleavage fracture is the standard case. 

The component or specimen cross section does not fail simultaneously everywhere. Instead, a crack forms locally by bond breaking. On the one hand, this is due to local stress concentrations in the component, which may be caused by the component geometry, its microstructure, or by previous plastic deformations. This is discussed in detail in Lange [90]. On the other 

When grain boundaries are embrittled (for example, by precipitates, see section 6.4.4), cleavage fracture may be intercrystalline. In this case, the grain structure can be clearly seen in a scanning electron microscope picture (see figure 1.10(b)). 

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Cleavage fracture is said to take place when the applied energy is just sufficient to load a few regions of the particle to the point of fracture. Only a few particles result, and their size is comparatively close to that of the original particle. This situation typically arises under conditions of slow compression where fracture immediately relieves the loading on the particle. 

Clear-liquor advance, 5 124 CLEAR process, 23 576 Clear Skies Legislation, 26 45 Cleavage fracture, as failure mechanism, 26 983... 

TRANSITION TEMPERATURE. 1. An arbitrarily defined temperature within die temperature range in which metal fracture characteristics determined usually by notched tests are changing rapidly such as from primarily fibrous (shear) to primarily crystalline (cleavage) fracture. 

Group Species Varieties or Composition Colors Specific Refractive Hardness Cleavage/ fracture... 

Colors Specific gravity Refractive index Hardness Cleavage/fracture... 

Brittle fracture in metals is characterized by a rapid rate of crack propagation, with no gross deformation and very little microdeformation. This is demonstrated by cleavage. Brittle fracture can occur without warning. Cleavage fracture exhibits little or no plastic deformation and occurs along well-defined crystallographic planes. 

Ceramics and the matrix in ceramic composites exhibit cleavage fracture at room temperature as well as at elevated temperatures. This is fortunate since most of the theoretical developments in dynamic fracture are confined to linear elastic fracture mechanics which is then applicable to fracture of the ceramic matrix. However, the additional complexities of crack deflection and fiber-matrix interface cracking, as well as fiber/whisker/particulate pull-outs, are at this time yet to be addressed. 

As a result there is no clear detailed picture of the way in which transfer takes place, although there is a broad understanding of the nature of the process. It is generally accepted that transfer takes place by the movement of crystallites rather than at the molecular level. Where the source of the molybdenum disulphide is a single crystal, a crystallite in transferring to a counterface must be detached from the source crystal. This can take place by cleavage, fracture or shear, or a combination of one or more of these mechanisms. 

Figure 10.9 (a) Cleavage fracture of single crystalline silicon, (b) transgranular fracture of a fine-grained polycrystal-... 

Brittle cleavage fracture is of the most concern in this module. Brittle cleavage fracture occurs in materials with a high strain-hardening rate and relatively low cleavage strength or great sensitivity to multi-axial stress. 

Adsorption-Enhanced Plasticity Models According to fractographic studies the cleavage fracture is not an anatomically brittle process, but occurs by alternate slip at the crack tip in conjunction with the formation of very small voids ahead of the crack. It is also thought that the chemisorption of environmental species facilitates the nucleation of dislocations at the crack tip, promoting the shear process responsible for brittle-like fracture (4). 

The final area of the fracture showed the presence of a shiny granular appearance, indicating a sudden brittle (cleavage) fracture, which was also confirmed by the SEM photographs showing cleavage steps and river pattern. 

Fluang [246] investigated the SCC of AISI 321 stainless steel in acidic chloride solutions by the SSRT technique and fracture mechanics. It was found that the cleavage fracture characterizes the fracture surface. The active dissolution mechanism controls the SCC of AISI 321 stainless steel in acidic chloride solutions and can be inhibited by using KI. The inhibition effect of KI on the SCC is due to inhibition of the anodic reaction of the corrosion process. 

Rossmanith H. P. (1996) George Rankin Irwin the father of fracture mechanics, in Cleavage Fracture The George R. Irwin Symposium, edited by Chan, K. S., Warrendale, PA TMS, pp. 3-38. 

Use of a mechanical X-Y stage, which allows measured movements of the slide in mutually perpendicular directions, enables one to relocate the same particle examined previously, but now in a different RI liquid. Repeated examination with different liquids finally identifies one or more of the refractive indices of the particle. For most minerals, additional optical properties (such as color, pleochroism, twinning, cleavage, fracture, and so on) will be helpful in making the mineral identification. With these data, the tables of optical properties given in many standard optical mineralogy texts may be consulted, especially those in Fleischer, Wilcox, and Matzko (1984) and Winchell and Winchell (1964), who emphasize identification by particle methods instead of thin-section techniques. 

Cleavage, fracture, or parting—how many cleavage directions, intersecting at what angles and parallel to which crystal faces Are microcracks preferentially oriented in the clinker Do they exhibit phase-specific patterns ... 

The proponents of this model reasoned that similar fracture processes occur in liquid-metal embrittlement, hydrogen embrittlement, and S.C.C., with chemisorption facilitating the nucleation of dislocations at the crack tip and promoting the shear processes that result in brittle, cleavage-like fracture. It was found that cleavage fracture occurs by alternate slip at the crack tip and formation of voids ahead of the crack tip [35-37]. 

Cleavage fracture Quasi-static K c, f Jct produced specimen e.g., ASTM E 399, E 1820, E1921, ESIS... 

If a ferritic RPV steel (body-centered-cubic structure) specimen experiences brittle cleavage fracture prior to the full development of a resistance curve, the /-integral value at the onset of fracture, / , is used to calculate an equivalent stress intensity factor, Kj, shown in Table 10.1 and Eq. 10.4. The specimen types used to measure Kj are essentially the same as those shown in Rg. 10.1. The Kj parameter is also used to determine the parameter To, the temperature at which the median fracture toughness (Kq) of a minimum specified number of IT specimens (25.4 mm thick) is 100 MPa Vm. This parameter. To, defines the fracture toughness transition temperature using the Master Curve concept developed by Wallin (1984). The Master Curve concept has been further developed as a consensus test standard in ASTM E 1921 (ASTM, 2013f) and is described in greater detail below. 

The Master Curve methodology uses a mathematical model to describe the probability of cleavage fracture initiation in a material containing a distribution of postulated fracture initiators (flaws). The model includes the temperature dependence of Kj, which was estimated empirically from a data set including various ferritic structural steels. The scatter definition based on the Weibull distribution, the size adjustment and the definition of the temperature dependence are the basic elements of the Master Curve methodology as described in ASTM E 1921. 

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