Failure initiated

Heavy equipment had passed over the site of failure initiation shortly before the rupture was discovered. It is probable that stresses associated with the heavy equipment initiated a fracture in the severely corroded pipe bottom. Once the fracture initiated, it propagated down the length of the line in response to stresses imposed by internal pressure. 

Visually, failure was mostly eohesive within the adhesive (see Figs. 34 and 46). However, there was a small area of apparent interfacial failure ( initiation zone ) located at one end of each substrate. Line scans were eondueted aeross the initiation zone, from the edge of the substrate to the area of cohesive failure within the adhesive. From the line scans, it was apparent that there were patehes of polymer present in the initiation zone, even when failure appeared to be interfaeial (see Fig. 46). SIMS images of the initiation zone were constructed for various mass numbers (see Figs. 47-49). The images showed well-defined cation-rieh... 

The second approach to fracture is different in that it treats the material as a continuum rather than as an assembly of molecules. In this case it is recognised that failure initiates at microscopic defects and the strength predictions are then made on the basis of the stress system and the energy release processes around developing cracks. From the measured strength values it is possible to estimate the size of the inherent flaws which would have caused failure at this stress level. In some cases the flaw size prediction is unrealistically large but in many cases the predicted value agrees well with the size of the defects observed, or suspected to exist in the material. 

The most serious side effects of P-blocker administration early in ACS are hypotension, bradycardia, and heart block. While initial, acute administration of P-blockers is not appropriate for patients who present with decompensated heart failure, initiation of P-blockers maybe attempted before hospital discharge in the majority of patients following treatment of acute heart failure. P-Blockers are continued indefinitely. 

The distribution in network segmental extensibilities controls failure initiation and propagation of the network. The segments with the lowest extensibilities at any given... 

In any structure the entire structure responds to mechanical or thermal loads. It is also necessary to bear in mind that any structure will also experience localized stress concentrations at points of contact or separation in the structure. These points of contact or separation are sites susceptible to damage, cracking or failure initiation. Stress analysis using the finite element method in structures which are bolted, mating surfaces, vessels... 

Wet fluorescent magnetic particle inspection of the remaining journal fillets on this crankshaft revealed the presence of a number of secondary cracks in the same orientation and position as the failure initiation site. A metallographic specimen, including the matching halves of the fracture from the initiation site in the fillet of main journal, was cut, mounted, polished and etched in 2% nital, in preparation for examination with an optical microscope. The polished and etched specimen is shown in Figure 7.44. 

J. E. Marion, A. G. Evans, M. D. Drory, and D. R. Clarke, High Temperature Failure Initiation in Liquid Phase Sintered Materials, Acta Metall., 31, 1445-1457 (1983). 

A flaw may be considered active if its stress concentration factor gives rise to local conditions suitable for craze, shear band, or failure initiation. Similarly the activity of the flaw spectrum may be considered as the collective fraction of all flaws that are active for a given set of conditions. The activity (or active fraction of flaws) depends on the external state of stress or strain and on sample orientation or anisotropy... 

This is obviously an oversimplification of the deformation meehanism, which, as already explained, involves failure initiation and propagation. Nevertheless, this approach facilitates the extraction of useful information from irregular and irrepro-ducible force-displacement curves that would otherwise be viewed as meaningless. 

The failure phenomena of viscoelastic materials consist of two factors. One is the time dependence of the hulk stress-strain relation of the material. For example, higher strain rate increases the stress level of the material and consequently the stress or the strain at break will he different from those of the case of the lower rate. The second factor is the time dependence of the failure mechanism itself, namely, the time dependence of the failure initiation mechanism. 

R. F. Landel (9), and so on during the past twenty years. The subject we have is to connect those phenomenological researches with molecular behavior or with the mechanism of failure initiation inside the materials. The author considers that the technique introduced here will be one of the useful tools for connecting those. 

There are numerous techniques known for adhesion and delamination testing, some of the most common being a tape test, stud-pull test, scratch test, and an indentation test [1]. In the tape test, a tape is pulled off the surface containing a scratch, which provides the failure initiation. In the stud pull test, a stud held with thermosetting epoxy is pulled off the film surface. The indentation test, wherein a ball is pressed into the surface, is used for hard coatings, and the failure pattern indicates acceptable behavior. In the scratch test, where an indenter moves in both vertical (loading) and horizontal (sliding) directions, an acoustic emission sensor allows for detection of the initiation of fiacture, while the scratch pattern indicates the type of failure. 

The influence of unbonded regions at the edges of completed welds on sample failure during overlap-shear testing is illustrated in Fig. 12.47. Failure initiated from unbonded regions located on either side of the spot weld, and as the fracture propagated, the transition from... 

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