Destructive testing materials

NDT for and Chcu acterization of Intrinsic Properties of Engineering Importance in Structural Material s, from Proc. of the Interdisciplinary Workshop on Non-destructive Testing-Materials Characterization, sponsored by NSF, Air Force Materials Lab, North American Rockwell Science Center. Report No. AFML-TR-T3-69, Air Force Materials Lab, Air Force Systems Command, Wright-Patterson Air Force Base, Ohio, April 1973. 

USCT in problems of non-destructive testing (NDT) of material defective state ... 

The application of eddy currents in non destructive testing was very developed during the recent years. Adding to the defects characterization, actual studies deal with the metallurgical evaluation of materials. Surface processing allow to increase the material endurance and consequently its life duration. 

Induction laws and experiments show that the impedance of a coil crossed by an AC current put near a conductive piece is modified by the creation of eddy currents. The presence of an anomaly in this material structure modifies the impedance of the generating coil. The impedance variation measure is at the root of non destructive testing by eddy currents. Any variation inside a piece (variation of conductivity or permeability) modifies the intensity and the course of the eddy currents and consequently the coil impedance. 

ASME Section V Non-Destruction Examination American Society for Testing Materials, Part 10,... 

Unless test coupons are produced alongside the lining, the only method of testing the vulcanisation state is with a hand hardness meter. A Shore A or IRHD meter is used for soft rubber linings and a Shore D meter for ebonites. The usual specification is that the hardness has to conform to 5° of the specified hardness. There is no quantitative non-destructive test for the strength of the bond between the lining and the substrate and so such tests are usually carried out in the laboratory on a sample prepared from the materials used. 

Weld strengths are based on destructive testing. 100 + % results indicate that parent material of plastic part g. way while weld remained intact. 

Microindentation hardness normally is measured by static penetration of the specimen with a standard indenter at a known force. After loading with a sharp indenter a residual surface impression is left on the flat test specimen. An adequate measure of the material hardness may be computed by dividing the peak contact load, P, by the projected area of impression1. The hardness, so defined, may be considered as an indicator of the irreversible deformation processes which characterize the material. The strain boundaries for plastic deformation, below the indenter are sensibly dependent, as we shall show below, on microstructural factors (crystal size and perfection, degree of crystallinity, etc). Indentation during a hardness test deforms only a small volumen element of the specimen (V 1011 nm3) (non destructive test). The rest acts as a constraint. Thus the contact stress between the indenter and the specimen is much greater than the compressive yield stress of the specimen (a factor of 3 higher). 

The radiation emitted by radioactive materials is harmful to living matter. Small quantities of radioactive isotopes are used in the process industry for various purposes for example, in level and density-measuring instruments, and for the non-destructive testing of equipment. 

Category 1 the highest class, requires 100 per cent non-destructive testing (NDT) of the welds and allows the use of all materials covered by the standard, with no restriction on the plate thickness. 

Category 2 requires less non-destructive testing but places some limitations on the materials which can be used and the maximum plate thickness. 

Furthermore, a cell header with its 70-100 connections is not easy to replace, and considerable numbers of safety features have to be incorporated into its design. Composite materials do not lend themselves to effective non-destructive testing and a leaking joint may lead to delamination of the chemical-resistant liner from its mechanical support. Since any leaks cannot be detected easily in such circumstances, the entire header must be replaced with a corresponding electrolyser downtime. 

The testing of materials can be based on whether the tested material is chemically changed or is left unchanged. Nondestructive tests are those that result in no chemical change in the material which may include many electrical property determinations, most spectro-analyses, simple phase change tests (Tg and Tm), density, color, and most mechanical property determinations. Destructive tests result in a change in the chemical structure of at least a... 

There is a trend in commercial testing of product quality to introduce non-destructive methods, in other words, tests that leave no defects in the tested materials that would affect their working properties. The use of these methods not only spares products but also permits more frequent testing, and gives better product quality control. This should be considered in the choice of hardness determination method. 

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