Stress evaluation method and apparatus therefor

• US 6,240,784 B1
• Filed: 09/17/1996
• Issued: 06/05/2001
• Est. Priority Date: 09/28/1993
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Naito, Shinji, Sasaki, Tsukasa, Takahashi, Fuminobu, Kamimoto, Shuuji, Musha, Yosinori, Koike, Masahiro, Inoue, Hideki
• Primary Examiner(s): MCCALL, ERIC SCOTT
• Application Number:
  US08/715,221
• Time in Patent Office: 1,722 Days
• Field of Search: 735/97, 737/94, 737/61, 737/86, 737/88
• US Class Current: 73/597
• CPC Class Codes: G01N 2291/0258 Structural degradation, e.g. fatigue of composites, ageing of oils
• CPC Class Codes: G01N 2291/0421 Longitudinal waves
• CPC Class Codes: G01N 2291/0422 Shear waves, transverse waves, horizontally polarised waves
• CPC Class Codes: G01N 2291/2675 Seam, butt welding
• CPC Class Codes: G01N 29/07 by measuring propagation velocity or propagation time of acoustic waves
• CPC Class Codes: G01N 29/30 Arrangements for calibrating or comparing, e.g. with standard objects

Abstract

A stress evaluation method for evaluating stress acting on a test piece includes the steps of transmitting acoustic waves including a surface wave, a longitudinal wave, and a shear wave through the test piece; receiving the acoustic waves after they have propagated through the test piece; obtaining acoustic velocities of the surface wave at a non-loaded portion and a loaded portion of the test piece based on the received acoustic waves; evaluating a stress in a surface layer of the test piece based on a difference between the surface wave acoustic velocities at the non-loaded portion and the loaded portion and a predetermined relationship between surface wave acoustic velocities and stresses; obtaining an acoustic velocity of the longitudinal wave at the non-loaded portion based on the received acoustic waves; calculating an acoustic velocity of the shear wave at the loaded portion based on the received acoustic waves and the longitudinal wave acoustic velocity at the non-loaded portion; evaluating an internal average stress in the test piece based on the shear wave acoustic velocity at the loaded portion; evaluating an internal stress distribution in the test piece by correcting a hypothetical internal stress distribution in the test piece based on the stress in the surface layer and the internal average stress; and conducting a diagnosis of the test piece based on the internal stress distribution.

Claims

1. A stress evaluation method for evaluating stress acting on a test piece to be tested from changes in an acoustic velocity of an acoustic wave which propagates through said test piece, wherein the stress evaluation method comprises the steps of:

changing a propagational direction of a surface wave which propagates in a surface layer of said test piece both at a non-loaded portion and a loaded portion of the test piece;

measuring an acoustic velocity of said surface wave; and

evaluating stress at the loaded portion of said test piece based on a difference in acoustic velocities of said surface wave between the non-loaded portion and the loaded portion of said test piece.

2. A diagnosis method for diagnosing a test piece to be tested comprising the steps of:

evaluating stress in the test piece by means of the stress evaluation method according to claim 1 to obtain an evaluated stress value; and

comparing the evaluated stress value with a predetermined allowable stress value.

3. A diagnosis method for diagnosing a test piece to be tested according to claim 2, further comprising the steps of:

repeating the step of evaluating stress in the test piece if the evaluated stress value is smaller than the predetermined allowable stress value; and

identifying a mode of material degradation in the test piece based on time variations of said evaluated stress value.

4. A welding procedure management method comprising the steps of:

evaluating residual stress in a test piece which has been subjected to a first welding and heat treatment by the stress evaluation method according to claim 1 to obtain an evaluated residual stress value; and

applying a second welding and heat treatment process to the test piece if said evaluated residual stress value is greater than a predetermined allowable residual stress value.

5. The welding procedure management method according to claim 4, wherein conditions of the second welding and heat treatment process are the same as conditions of the first welding and heat treatment process.

6. The welding procedure management method according to claim 5, further comprising the steps of:

reevaluating a residual stress in the test piece which has been subjected to the second welding and heat treatment process by repeating the step of evaluating residual stress in the test piece to obtain a reevaluated residual stress value;

applying to the test piece a third welding and heat treatment process having conditions which are different from the conditions of the first and second welding and heat treatment processes if said reevaluated residual stress is greater than said predetermined allowable residual stress value; and

repeating the step of evaluating residual stress in the test piece.

7. The welding procedure management method according to claim 4, wherein conditions of the second welding and heat treatment process are different from conditions of said first welding and heat treatment process.

9. The stress evaluation method according to claim 1, wherein the stress evaluated at the loaded portion of the test piece is a surface stress in the surface layer of the test piece at the loaded portion of the test piece.

8. A stress evaluation apparatus having

acoustic wave propagation means for propagating an acoustic wave through a test piece to be inspected,

receiver means for receiving an acoustic wave which has propagated through said test piece, and

means for evaluating stress in said test piece in response to an acoustic wave received at said receiver means and based on a change in an acoustic velocity of said acoustic wave propagating through said test piece,

wherein the stress evaluation apparatus comprises:

acoustic wave propagation direction varying means for variably changing a propagational direction of a surface wave propagating through a surface layer of said test piece under inspection both at a non-loaded portion and a loaded portion of said test piece;

acoustic velocity measuring means for measuring an acoustic velocity of said surface wave; and

stress evaluation means for evaluating stress at said loaded portion of said test piece based on a difference in acoustic velocity of said surface wave both at said non-loaded portion and said loaded portion of said test piece.

10. The stress evaluation apparatus according to claim 8, wherein the stress evaluated at the loaded portion of the test piece is a surface stress in the surface layer of the test piece at the loaded portion of the test piece.