Thermal measuring and testing – Temperature measurement – Combined with diverse art device
Patent
1996-06-03
1998-06-02
Gutierrez, Diego F. F.
Thermal measuring and testing
Temperature measurement
Combined with diverse art device
374180, 73799, 324718, 324715, G01K 708, G01N 2720
Patent
active
057589704
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device and to a method for the simultaneous measurement of the extent and the temperature of an open crack at the surface of an electrically conductive solid body. It applies especially to the determination of the influence of the temperature conditions on crack propagation, for example when studying the characteristics of the crack resistance of new construction materials for components and assemblies of critical importance in mechanical constructions, as well as components and structures themselves, such as aircraft cell structures or aircraft engine components.
2. Discussion of the Background
Studying the progress of cracks under varied stress conditions, such as temperature variations during mechanical cycling, is a very important problem as it makes it possible to design optimum constructions which ensure a predetermined damage tolerance and a predetermined safety factor.
Various procedures and devices exist for determining the crack parameters in constructions and test specimens. In particular, it is known, from French Patent Application published under No. 2,400,706, to determine the extent of an open crack at the surface of a solid body consisting of an electrically conductive material by studying its electrical resistance; this study is carried out by applying, to this body, an electric current of constant strength in a direction which is preferably as close as possible to the perpendicular to the crack and by measuring the potential difference between two measurement points located on either side of the open crack. In the vicinity of the crack, the current lines are deflected and go around the crack, the increase in path length of these current lines being a function of the extent (depth and/or length) of the crack. The potential difference measured between the two measurement points is therefore representative of the electrical resistance of the body between the two measurement points. The potential difference may be measured by means of two electrical wires placed at two measurement points and connected to a measurement apparatus such as, for example, a crack follower.
In the case of studying crack propagation in an environment subjected to temperature variations, it is also necessary to be able to determine the temperature of the test piece at the crack tip accurately. Temperature measurements may be carried out conventionally by means of a thermocouple pressed against the surface of the test piece. However, this arrangement of the thermocouple does not enable the temperature to be measured at the very place of the crack and does not enable sufficient measurement reproducibility and reliability to be achieved.
SUMMARY OF THE INVENTION
The object of the invention is to solve this problem and to produce a method and a device for the simultaneous measurement of the extent and the temperature of an open crack at the surface of an electrically conductive solid body at the very place of this crack and without using an external thermocouple. To do this, the invention consists in connecting, at two measurement points located on either side of the crack, two electrical wires forming a thermoelectric couple, in periodically applying a DC electric current of constant strength in the body in a direction preferably perpendicular to the crack, in measuring the potential difference between these two measurement points respectively during two successive phases of application and of interruption of the electric current, in processing the potential difference values measured in order simultaneously to deduce therefrom the extent of the crack and the temperature at the crack tip.
According to the invention, the device for the simultaneous measurement of the extent and the temperature of a crack at the surface of an electrically conductive solid body, a DC electric current of constant strength passing periodically through this body in a direction which is as close as possible to the perpendicular to the crack, is characterized in
REFERENCES:
patent: 2612779 (1952-10-01), Mulford
patent: 3258957 (1966-07-01), Smart
patent: 3756067 (1973-09-01), Cushman
patent: 4677855 (1987-07-01), Coffin, Jr. et al.
patent: 4924708 (1990-05-01), Solomon et al.
patent: 5574376 (1996-11-01), Topp et al.
Patent Abstracts of Japan, vol. 17, No. 553 (P-1625) 5 Oct. 1993 (JP. 5-157721, 25 Jun. 1993) (only abstract considered).
Patent Abstracts of Japan, vol. 18, No. 78 (P-1689) 8 Feb. 1994 (JP 5-288706, 2 Nov. 1993) (only abstract considered).
Gutierrez Diego F. F.
Societe Nationale d'Etude et de Construction de Moteurs d'Aviati
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