Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1996-09-17
2001-06-05
McCall, Eric S. (Department: 2855)
Measuring and testing
Vibration
By mechanical waves
C073S794000
Reexamination Certificate
active
06240784
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a stress evaluation method using acoustic waves and an apparatus therefor which is capable of evaluating stress acting on a test piece under inspection.
It is well known to use acoustic waves to obtain a magnitude of stress acting on the test piece on the basis of changes in acoustic velocity.
Namely, according to a prior art method which uses a relationship obtained in advance between a ratio of changes in acoustic velocity and stress values, a magnitude of stress acting on a particular point can be obtained from the acoustic velocity measured at that point.
The stress evaluation method using a surface wave for evaluating stress present in the surface layer of the test piece has been disclosed, for example, in JP-A-61-254849.
Further, there is a method to obtain a measure of internal stress in the test piece as an average value from a difference in acoustic velocities between a shear wave which oscillates in the parallel direction relative to the stress and a shear wave which oscillates in the orthogonal direction relative to the stress, as disclosed in JP-A-56-90228.
SUMMARY OF THE INVENTION
In the prior art methods described above, however, no particular attention has been paid to the fact that an acoustic velocity will change depending on the texture orientation of the test piece.
Further, in the case where the thickness of the test piece is unknown, it is necessary to obtain acoustic velocities of two kinds of shear waves by changing their oscillating directions relative to each other, and, consequently, to obtain stress from a slight difference between these two acoustic velocities. Therefore, it has been difficult to improve the precision of detection, and in addition, the stress value thus obtained merely indicates an average stress in the thickness direction, without regard to the stress distribution.
A main object of the invention is to improve the precision of stress evaluation of a test piece on the basis of changes in acoustic velocity.
Another object of the invention is to facilitate usage of a stress evaluation method having an improved precision.
A first aspect for accomplishing the main object of the invention provides for a method for implementing evaluation of the stress acting on a test piece on the basis of changes in acoustic velocity of a sound which propagates through the test piece, the method comprising the steps of modifying the propagational direction of a surface wave propagating through the surface layer of the test piece between a non-loaded portion and a loaded portion therein, measuring the acoustic velocity of said surface wave, and evaluating a surface stress in the loaded portion of the test piece from a difference in the acoustic velocities of the surface wave between the non-loaded and loaded portions of the test piece. A second aspect of the invention likewise provides a stress evaluation method comprising the steps of causing a longitudinal wave and a shear wave to be propagated in the loaded portion in the thickness direction thereof, obtaining respective propagation times for the longitudinal wave and the shear wave in the test piece upon reception of reflected waves from the bottom surface of the test piece in the thickness direction, calculating the thickness at the loaded portion from the longitudinal wave acoustic velocity at the non-loaded portion, which has been obtained according to a ratio between the calculated thickness and the propagation time, evaluating the shear wave acoustic velocity from the calculated thickness and the propagation time of the shear wave at the loaded portion, and evaluating the magnitude of the internal average stress exerted in the thickness direction inside the loaded portion. A third aspect of the invention likewise provides a stress evaluation method comprising the steps of correcting a hypothetical stress distribution in the thickness direction in the test piece such that, in the hypothetical stress distribution in the thickness direction of the test piece which was predetermined, the surface stress in the test piece is corrected by a surface stress value which has been evaluated according to the first aspect described above, and the average stress of the stress distribution in the thickness direction likewise is corrected by an internal average stress value which has been evaluated by the second aspect described above, so as to establish a correct internal stress distribution in the thickness direction of the test piece. A fourth aspect for accomplishing still another object of the invention provides for a plant diagnosis method comprising the steps of evaluating the stress in a test piece through the stress evaluation method according to the first aspect or the third aspect of the invention, and interrupting the operation of equipment including the above test piece or the plant if a value of the stress which has been evaluated becomes greater than an allowable stress value which has been predetermined. Likewise, a fifth aspect of the invention provides for a plant diagnosis method comprising the steps of repeating a stress evaluation if the stress value evaluated according to the fourth aspect described above is smaller than the predetermined allowable stress value, and classifying modes of material degradation in the test piece based on time variations of the evaluated stress values. Likewise, a sixth aspect of the invention provides for a welding procedure management method comprising the steps of evaluating a residual stress in a test piece subjected to an initial welding and heat treatment by means of the stress evaluation method of the first aspect or the third aspect of the invention, and applying a subsequent welding and heat treatment to the test piece in the case when the residual stress evaluated above is greater than a predetermined allowable stress value. Likewise, a seventh aspect of the invention provides for a welding procedure management method comprising the step of providing the same conditions as the initial welding and heat treatment conditions for a subsequent rewelding and heat treatment carried out after employing the sixth aspect of the invention. Likewise, an eighth aspect of the invention provides for a welding procedure management method comprising the steps of reevaluating a residual stress in the test piece subjected to rewelding and heat treatment in accordance with the seventh aspect by means of a stress evaluation method according to the first aspect or the third aspect, applying another welding and heat treatment to the test piece after the reevaluation by modifying the welding and heat treatment conditions to be different from the initial conditions, if the residual stress reevaluated above is greater than the foregoing predetermined allowable value, and executing still another reevaluation thereof. Likewise, a ninth aspect of the invention provides for still another welding procedure management method according to the sixth aspect further comprising the step of modifying the welding and heat treatment conditions to be different from the initial welding and heat treatment conditions. A tenth aspect for accomplishing the main object of the invention provides for stress evaluation equipment which is provided with means for propagating an acoustic wave through a test piece, means for receiving the acoustic wave propagated through the test piece, and means for evaluating stress in the test piece on the basis of a signal received by the receiving means and from a variation of the acoustic velocity of the acoustic wave which has propagated through the test piece, wherein the stress evaluation equipment comprises acoustic wave propagational direction varying means for varying at a non-loaded portion and a loaded portion of the test piece the propagational direction of a surface wave which propagates through the surface layer of the test piece, measuring means for measuring the acoustic velocity of each surface wave described above, and evaluation means for evaluating stress at the loaded portion of the test
Inoue Hideki
Kamimoto Shuuji
Koike Masahiro
Musha Yosinori
Naito Shinji
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
McCall Eric S.
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