Surface crack testing

This paper compares experimental data for aluminium and steel specimens with two methods of solving the forward problem in the thin-skin regime. The first approach is a 3D Finite Element / Boundary Integral Element method (TRIFOU) developed by EDF/RD Division (France). The second approach is specialised for the treatment of surface cracks in the thin-skin regime developed by the University of Surrey (England). In the thin-skin regime, the electromagnetic skin-depth is small compared with the depth of the crack. Such conditions are common in tests on steels and sometimes on aluminium. 

A method has been worked out for eddy current testing of surfaces and surface cracks or corrosion under dielectric or non-magnetic metal layer of up to 10 mm. The method is based on excitation of eddy currents by a coil with U - type core and information reading by a sensitive gradientometric element located on a axis of symmetry of the core (fig. 1). 

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... 

Depending on the requirements, C-scan or a cascading display are used. These types of display facilitate tests for internal damage below the surface with low-frequency eddy currents in addition to high-frequency tests for surface cracks. 

The properties of a single crystal creeping wave probe The a single crystal creeping wave probe is suitable for testing various artificial defects such as surface cracks, FBH, columned hole and SDH etc. and its distance amplitude cruve is shown in Fig.6... 

J. C. Newman, Jr. A Review and Assessment of the Stress Intensity Factors for Surface Cracks," Part-Through Crack Fatigue Life Prediction, ASTM STP 687, J.B. Chang, Ed, American Society for Testing and Materials, 1979, pp. 16 42. 

This transitory behavior was observed to arise from all the weathering agents considered in this study except ozone. Instead, test coupons exposed to ozone exhibited an initial decline in the crosslink density of the silicone with the formation of surface cracks, which were difficult to distinguish with the naked eye. With continued exposure to ozone, however, the material would begin to crosslink. We proposed that ozone s greatest affinity... 

Let us now examine the antioxidant test results for the various phenols alkylated by a-olefins. They have been evaluated in several tests, but data are presented in Table III for only four different test procedures, chosen to illustrate the effect of increasing severity of test conditions. The least severe of these is the 140°C. stress-crack life test using a 65-mil thick molded bar. The 160 °C. oven-life test using the same molded bar is somewhat more severe. Increasing severity is shown by the 140°C. oven-life test and the 160°C. oven-life test using 5-mil film test pieces. The relatively thick bars used in the first two tests provide a reservoir of antioxidant to replace that lost from the surface. These tests probably measure the inherent effectiveness of the antioxidant. In the tests using... 

The method requires the use of a reference standard sample in order to set the sensitivity level before an unknown sample is tested for discontinuities. The type of reference discontinuities used in a particular application has been specified by the American Society for Testing Materials and the American Petroleum Institute. Some reference standards are depicted in Figure 2.10. Some of the discontinuities detected are seams, laps, cracks, slivers, scabs, pits, slugs, open welds, miswelds, improperly or misaligned welds, black or gray oxide weld penetrators, pinholes, hook cracks and surface cracks. 

Experimental 1x6 inch test specimens of the unprotected and protected vulcanizates were elongated 20% and ozonized for 15 minutes at room temperature, using a stream of ozonized oxygen flowing at 0.10 cubic meter per hour and furnishing approximately 1 X 10 mole of ozone per hour. The test strips were examined visually during ozonization to determine the time required to obtain initial surface cracking. 

Figure 6-1. Penetrant testing is used primarily to detect surface cracks and porosity.

The samples are placed in an upright position in a tray which is immersed into hot water for a given time, then transferred to a cold water bath. Temperatures of both baths are closely controlled. Samples are examined before and after the tests for outside surface cracks or breakage. The amount of thermal shock a bottle will withstand depends on its size, design and glass distribution. Small bottles will probably withstand a temperature differential of 60-80°C, and 1 pint bottles 30-40°C. A typical test uses a 45°C temperature difference, hot to cold. 

As it was mentioned above, GeoDeck boards of the first level, made at the end of 2002 and tested by an independent testing company in February 2003, were described in their ICC-ES report as "There was no marked evidence of surface cracking, blistering, flaking, color change, or any other deleterious effects observed of the test specimens f... 

A number of physical tests have been proposed for the estimation of catalytic activity, but except for purposes of control in catalyst manufacture none of these is an acceptable substitute for direct cracking tests. In general, such tests as the measurement of the selective adsorption of an aromatic hydrocarbon from a standard binary mixture of aromatic and paraffinic components (Scheumann and Rescorla, 19), or the measurement of the heat of wetting with methanol (Mills, 20) merely reflect the extent of available surface. With a given catalyst composition, these methods may have some utility in following the decline of activity due to the effects of temperature or steam (but not of sulfur) or as a rapid and approximate control method in the manufacture of a catalyst. 

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