Crack depth

Measuring surface crack depth is performed by calibration samples made of the same material like the object being tested. Calibration samples are the plates having narrow grooves like slits of various depth 0.2 mm, 0.5 mm, 1.0 mm, 2.0 mm, 3.0 mm, 4.0 mm, 5.0 mm and made by electric erosion method. The samples have dimensions 50 mm X 150 mm x 6 mm and 25 mmx 150 mm x 6 mm and are made of magnetic... 

Figures Absolute e.m.f. dependence of the probe vs. position for different sub-surface crack depths - theoretical and experimental results...

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

Fig. 7 Error of measuring crack depth in plate by using calibration curve for crack in half space.

The interpretated value of crack depth hi is calculated by means of the algorithm of solving inverse task, the parameters I or T have limit values correspondingly. 

The component of the relative measuring error of crack depth measuring is calculated because real parameter p is replaced by its limit value ... 

The measuring error of crack depth by means of electropotential devices is considered to be approximately 10%[2]. The research work performed gives us an opportunity to maintain it that is practice such a measuring error can be higher in many times et some probably combinations of parameters h, I, T. 

So when measuring cracks depth at the error value of less than 10%, the... 

The algorithm of calculating crack depth is realized in electropotential device Zond IGT-97 for measuring cracks depth. Its structure diagram is shown in Fig. 8 Using quasi-direct current is the device particular feature that made it possible to reduce its dimensions and weight. 

Fig.8 Function diagram of the device ZOND IGT-97 for measuring crack depth.

In order to provide measuring of cracks depth on complicated profile areas there is a special function in the device. The function makes it possible to perform measurements by studying on a samples with defects of the measured depth. 

Appearance of electropotential device Zond IGT - 97 for measuring cracks depth is shown in Fig. 9. 

Cracks depth measurement in the airframe, lending gear, turbine blades etc. 

Cracks depth measurement in billets for determining their use possibility for further machining. 

Cracks depth measurement in pipe - lines, boilers, rotor duct, on turbines blades, in tread rings, welds etc. 

Nominal stress Crack depth Crack growth rate... 

Below about 0.75 T, polymers are brittle (Fig. 23.9). Unless special care is taken to avoid it, a polymer sample has small surface cracks (depth c) left by machining or abrasion, or caused by environmental attack. Then a tensile stress tr will cause brittle failure if... 

Fig. 11. Fracture stress versus crack depth for small flaw fracture tests in IG-11 graphite.

Fig. 14. Mode I stress intensity factor versus crack depth for small flaw fraeture tests on H-451 graphite...

The decrease in with crack depth for fracture of IG-11 graphite presents an interesting dilemma. The utihty of fracture mechanics is that equivalent values of K should represent an equivalent crack tip mechanical state and a singular critical value of K should define the failure criterion. Recall Eq. 2 where K is defined as the first term of the series solution for the crack tip stress field, Oy, normal to the crack plane. It was noted that this solution must be modified at the crack tip and at the far field. The maximum value of a. should be limited to and that the far... 

It is apparent from equation (2.123) that a graph of BD0 against fracture energy Uc (using different crack depths to vary 0) will be a straight line, the slope of which is the material toughness, Gc. 

Example 2.23 A series of Charpy impact tests on uPVC specimens with a range of crack depths gave the following results... 

Figure 4-441. Rate of stress—corrosion crack propagation as a function of crack depth during tensile loading. (From Ref. [183].)...

Turnbull, A. and Newman, R. C., The influence of crack depth on electrochemistry and fatigue crack growth , Proc AIME Conf. on Short Crack Growth, AIME (1986)... 

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