Crack types

This work presents two procedures of quantitative evaluation of the material discontinuities, using the eddy current method. One of the procedures concerns the long surface or subsurface crack-type discontinuities in a flat conductive body. The second procedure allows a quantitative evaluation of short discontinuities, such as voids, inclusions etc. 

No. 2 fuel oil is a petroleum distillate that may be referred to as domestic fuel oil or industrial fuel oil. Domestic fuel oil is usually lighter and straight-run refined it is used primarily for home heating and to produce diesel fuel. Industrial distillate is the cracked type, or a blend of straight-run and cracked. It is used in smelting furnaces, ceramic kilns, and packaged boilers. 

The mechanism postulated by these authors for cracking type reactions, involving carbonium ions held at acid sites on the surfaces, is as follows... 

The four basic carbon black manufacturing processes are either of the partial combustion type (the channel, oil furnace, or gas furnace process) or of the cracking type (the thermal process). 

Description Fresh feedstock and recycle streams are preheated and pyrolized in the presence of dilution steam in highly selective pyro-crack type furnaces (1). Pyrocrack furnaces are optimized with respect to residence time, temperature and pressure profiles for each feedstock, thus achieving the highest olefin yields. Furnace effluent is cooled in transfer line exchangers (TLEs) (2), generating HP steam, and by direct quenching with oil for liquid feedstock processing. 

Fig. 4.4. Crack type classification with a combination of average frequency and RA values.

There are several ways to determine the crack type and orientation of AE sources. One way is to use the polarities of initial P-wave pulses - this is known as the first motion technique. The distribution of the two senses of the wave polarity aroimd the focus is determined by the radiation pattern of the source. Using the distribution of the polarities, it is possible to estimate the orientation of the nodal planes (where no displacement takes place) and thus the mechanism of the source. However, it is important to bear in mind that, due to the symmetry of the radiation pattern, two orthogonal planes can be fitted. These planes are often referred to as the fault plane and the auxiliary plane . 

Manthei [2005] found that the observed AE events were predominantly of tensile type (fracture meehanical Mode I). Most of the events (approximately 90%) showed significant isotropic source components, which is in agreement with the applied deviatoric loading that leads to dilatation. The parameter g and the R values (see Figs. 11.35 and 11.36) tend to values of pure tensile mechanisms (s= 0.37 and K = 67%). He also found, that the tension axes normal to the planes of tensile cracks were predominantly orientated in the radial direction, that is in the direction of the minimum principal stress as expected for this crack type. 

The above experimental observations are reflected in Kendall etal. (1983) who proposed to clearly distinguish the influence of two populations of pores - small gel or colloidal pores entrapped between hydrated particles of about 2 nm in size, and larger crack-type pores of length equal to about 1 mm. The influence of the first population on the concrete strength is proportional to its total volume and is reflected by the law of mixtures or classic Feret s equation where volume of air is taken into account (cf. Section 8.2). 

Rokugo, K., Kanda, T., Yokota, H., Sakata, N. (2007) Outline of JSCE Recommendation for Design and Construction of Multiple Fine Cracking Type Fiber Reinforced Cementitious Composite (HPC), in Int.Workshop HPPRCC 5, RILEM, Proc.53, W. H. Reinhardt and A. E. Naaman eds pp. 203-12. 

Medel (b) For thermal cracking type, the first order reaction kinetics is assumed as a first approximation. The basic equation is... 

The description of the crack types in Section 5.2 has to some extent dealt with this sequence, but it is worthwhile considering the model process... 

Mirazano and Moya have produced more recent equations based on a more fundamental analysis involving the expansion of a spherical cavity modified by the creation of new surface and the shape of the indenter. It is an extension of Chiang s and Hill s analysis in Section 1.4.1.1. As long as c /a is greater than 1.3 these equations can be applied regardless of the crack type ... 

A method independent of crack type is the minimum load-crack nucleation method. To operate this method the minimum load to nucleate cracks, P, has to be determined. By its nature this is a statistical method whereby about 20 indentations are made per load in a range from, say, 0.5 to 50 N. The number of indent corners where cracks appear are counted and expressed as a percentage of indent comers the minimum load for crack nucleation, P, is the load of which 50% of corners project a crack, and then equation (5.60) can be used... 

Change of environment The removal of chlorides, caustic, or other major cracking-type species is an effective solution where possible. However, much less drastic changes are often effective as... 

Stress analysis of failures in the form of cracks due to fatigue of cord-rubber composites was carried out using micromechanical 2D and 3D finite element analysis. The von Mises-Tresca stresses were computed from the results of finite element analysis and compared. Results show that crack type, loading and crack size have a strong effect on the values of the von Mises-Tresca stress. Use of the results of the von Mises-Tresca stress should help in estimating the severity of local failures in cord-rubber composites, it is proposed. 12 refs. 

Furthermore, the three short crack type densities correlate well. Also, the screen display of the simulated specimen surface shows similar patterns of crack spatial distribution (Figs. 23 and 24). 

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