Long crack .

Selected sensor systems are moved over long cracks of different widths. The output signals are pre-calculated by using eq.(6). Measured and pre-calculated data are compared in 4.2.3.. 

This work presents the theoretieal results and their experimental verifications concerning two possible methods for predicting the material discontinuities shape and severity. The methods are developed for the case of the eddy current transducer with orthogonal coils, for two situations for long crack-tjfpe discontinuities, a metod based on the geometrical diffraction has been used, while in the ease of short discontinuities the holographic method is prefered. 

Fig. 4 Calibration characteristics of electropotential transformer in case of distance between current electrodes (R. ) varying for long cracks.

Fig. 6 Error of measuring limit length crack depth by using calibration curve for infinitely long crack.

Example 2.19 During tensile tests on 4 mm thick acrylic sheets of the type shown in Fig. 2.63(a), the force-displacement characteristics shown in Fig. 2.64(a) were recorded when the crack lengths were as indicated. If the sheet containing a 12 mm long crack fractured at a force of 330 N, determine the fracture toughness of the acrylic and calculate the applied force necessary to O acture the sheets containing the other crack sizes. 

Figure 19.24 Cross section of a long crack in the wall of a mold containing a metastable liquid. The crack extends normal to the page.

Almost every discussion on the hazards of plant modifications uses this accident as an example of the need to control plant modifications. The authors, almost without fail, center their attention on the 20-inch (500 mm) diameter piping that was improperly installed to bypass the No. 5 Reactor which had developed a 6-ft.-long crack. But the reason for the crack is usually just briefly mentioned. 

In summary, short cracks form epsilon CTPZ development, whereas long cracks usually lack the required shear components to generate the shear-band pair, niis creates the anomalous short crack behavior. When epsilon CTPZs form, the shear bands stabilize the crack, thus allowing the DCG process to continue to much higher apparent AK, values, further differentiating from the non-epsilon CTPZ DCG crack growth behavior. 

Fig. 40. Experimental data for cracks growing from notches in a 1026 steel, compared with the predictions of a simple short-crack model (solid line) and a long-crack model (broken line) [76]. Reproduced with permission.

Symptoms In the dead of winter, a combination of heat and cold can cause sunken areas or long cracks to form in the bark of woody plants. Damage is most common on the southwest side of a trunk. The last light of day warms the bark, then the bark rapidly cools as the sun drops below the horizon. For symptoms on fruit, see Frost Damage on the opposite page. 

Two types of specimens are typically used, smooth crack-free specimens or specimens containing long cracks, i.e., cracks of dimensions that are large with respect to the structural features of the material. 

For the specimens with long cracks, the situation is not unlike that dealt with in the previous section, except that instead of measuring v versus K, the crack growth rate per cycle dc/dN is measured as a function of AiTj, defined as... 

Figure 12.12 Cyclic fatigue long-crack propagation data for several ceramics compared to those for some typical metals.TZPs are tetragonal zirconia polycrystals (see Chap. 11).

Typical long-crack data for a number of ceramics are shown in Fig. 12.12, where the og dc/dN) versus log AA i curves are linear and very steep, implying high values of q. These studies also indicate that under cyclic loading, the thresholds for crack growth can be as low as 50 percent of the fracture toughness measured under monotonically increasing loads. 

The actual situation is more complicated, however, because the results shown in Fig. 12.12 are only applicable to long cracks. Short cracks have been shown to behave quite differently from long ones furthermore, the very high values of q imply that marginal differences in either the assumed initial crack size or component in-service stresses can lead to significant variations in projected lifetimes (see Prob. 12.13). 

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