Method for measuring stress on steel by determining the reverse magnetic permeability under a magnetic bias field

• US 5,010,299 A
• Filed: 03/09/1990
• Issued: 04/23/1991
• Est. Priority Date: 03/17/1989
• Status: Expired due to Fees

• Current Assignee: Nikkoshi Co., Ltd.
• Original Assignee: Nikkoshi Co., Ltd.
• Inventors: Utsunomiya, Tomoaki, Nishizawa, Hidekazu
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US07/491,423
• Time in Patent Office: 410 Days
• Field of Search: 324/209
• US Class Current: 324/209
• CPC Class Codes: G01L 1/125 by using magnetostrictive means magnetostrictive sensors H10N35/101
• CPC Class Codes: G01L 1/127 by using inductive means G01L1/122, G01L1/125 take precedence
• CPC Class Codes: G01N 27/72 by investigating magnetic variables

Abstract

A rapid and reliable non-destructive method is proposed for the determination of stress in a steel material by determining the reversible magnetic permeability μ under a magnetic bias field H₀ in the range of approach to the saturation magnetization, calculating the factor M in the equation μ=1+M/H₀³ by using the value of μ, and calculating σ₁, σ₂ and θ by solving the equation ##EQU1## in which σ₁ is a principal stress, σ₂ is the principal stress perpendicular to σ₁, θ is the angle between σ₁ and the direction of measurement of μ, a is the value of √M in a stress-free state and b is the stress sensitivity, a and b being determined separately.

Claims

1. A method for the determination of a stress in a steel material which comprises the steps of:

(a) determining the reversible magnetic permeability μ

by using a stress detector of steel materials utilizing the phenomenon of magnetostriction under a magnetic bias field H₀ within the range of approach to the saturation magnetization;

(b) calculating the value of M, which is the first-order factor on 1/H₀³ for the reversible magnetic permeability μ

of the steel material in the equation μ

=1+M/H₀³, utilizing the values of μ

; and

(c) calculating the values of a principal stress σ

₁ in the steel material, the other principal stress σ

₂ in the steel material which is in the direction perpendicular to the direction of σ

₁ and the angle θ

between the direction of σ

₁ and the direction at which the reversible magnetic permeability μ

is determined, from the equation ##EQU5## in which a is the value of the square root of M in a stress-free state and b is the stress sensitivity.

2. A method for the determination of a stress in a steel material which comprises the steps of:

(a) determining the reversible magnetic permeability μ

by using a stress detector of steel materials utilizing the phenomenon of magnetostriction under a magnetic bias field H₀ within the range of approach to the saturation magnetization in at least three directions not parallel to each other;

(b) calculating the values of M, which is the first-order factor on 1/H₀³ for the reversible magnetic permeability μ

of the steel material in the equation μ

=1+M/H₀³, utilizing the three values of μ

obtained in step (a); and

(c) calculating the values of a principal stress σ

₁ in the steel material, the other principal stress σ

₂ in the steel material which is in the direction perpendicular to the direction of σ

₁ and the angle θ

between the direction of σ

₁ and the direction at which the reversible magnetic permeability μ

is determined, by solving a set of at least three simultaneous equations obtained by substituting the three values of M obtained in step (b) in the equation ##EQU6## in which a is the value of the square root of M in a stress-free state and b is the stress sensitivity.