Characteristics brittle fracture

External mechanical damage, and all dents affecting acetylene girth welds or seam welds that are known to exhibit brittle fracture characteristics, may be repaired with a full encirclement steel sleeve with ends welded to the pipe. 

At the end of the drying process, the clay body attains elastic-brittle fracture characteristics, and has shrunk by about 22vol%. The final dry day body consists of about 70vol% solid day and 30vol% pores. 

The design must take into consideration the minimum operating temperature at which a deflagration may occur. This minimum temperature must be compared with the temperature characteristics of the material of construction of the vessel to ensure that brittle fracture will not result from a deflagration. 

The phenomena of brittle and tough fracture give rise to fairly characteristic stress-strain curves. Brittle fracture in materials leads to the kind of behaviour illustrated in Figure 7.1 fairly uniform extension is observed with increasing stress, there is minimal yield, and then fracture occurs close to the maximum on this graph. 

In this paper the recently developed techniques to characterize the mar resistance of coating systems were presented. The techniques base on methods that create a single scratch onto a surface. Characteristic values like the critical load as a measure for the transition from plastic behaviour to brittle fracture can be determined and used to rank different clearcoat systems and to compare these results with other physical properties. In the field of mar resistance the cross-linking density of the... 

Figures 7.64 and 7.65 provide a view of the fracture surface of a bolt recovered following a fall of ground from a hardrock mine. This is at magnification x 10. A close-up of dimpled areas is presented in Figure 7.66, at a magnification x 1500. The dimples are shallow and inclined characteristic of ductile fracture. No sign of cleavage or quasicleavage, is observed (absence of river pattern that would be associated with brittle fracture). In the upper right part of the photo dimpled areas are masked by oxidation.

When a crack propagates in polystyrene at low crack velocities, the craze ruptures close to its median plane by a mechanism having the approximate characteristics of viscous flow. Each fracture surface is then covered by a thin layer of craze. At higher crack velocities, however, failure occurs along the boundaries between the craze and the adjacent bulk polymer by practically brittle fracture (I). The change in fracture... 

Practical uses of epoxies include load bearing applications such as structural adhesives and composite matrices. In these applications, their most detrimental feature is a characteristic low resistance to brittle fracture. The desire to improve this property has motivated studies on thermoset fracture behavior for the last two decades. Of particular interest is the relationship between the molecular structure and the failure properties of thermosetting epoxies, the subject of this chapter. 

The brittle-ductile transition temperature depends on the characteristics of the sample such as thickness, surface defects, and the presence of flaws or notches. Increasing the thickness of the sample favors brittle fracture a typical example is polycarbonate at room temperature. The presence of surface defects (scratches) or the introduction of flaws and notches in the sample increases Tg. A polymer that displays ductile behavior at a particular temperature can break in the brittle mode if a notch is made in it examples are PVC and nylon. This type of behavior is explained by analyzing the distribution of stresses in the zone of the notch. When a sample is subjected to a uniaxial tension, a complex state of stresses is created at the tip of the notch and the yield stress brittle behavior known as notch brittleness. Brittle behavior is favored by sharp notches and thick samples where plane strain deformation prevails over plane stress deformation. 

Figure 9a shows a typical load-loadline displacement curve of a nylon compact tensiiin specimen. The slight deviation from linear elastic behaviour prior to fracture relates to the presence of a plastic deformation zone confined near the pre-crack tip (Fig. 9b). This stable crack propagation domain is adjoining a wide hackle zone (rapid crack growth domain) characteristic of a brittle fracture.

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