Axial force measuring method utilizing ultrasonic wave

Claim 1

A method of obtaining a measure of an axial force within an article under strain from a variation of natural frequencies of said article, comprising the steps of: applying an ultrasonic wave to said article to generate forced oscillations therein; measuring a first natural frequency of said article when said axial force within said article is substantially zero; measuring a second natural frequency of said article when said article is under strain and said axial force is greater than zero; determining differential (f Epsilon 2-f Epsilon 1) between said first and second natural frequencies; and comparing thus determined differential with calibration data which has been obtained with respect to axial force versus differential to locate the existing axial force; the frequency of said ultrasonic wave being selected to satisfy the equation, (f Epsilon 2-f Epsilon 1)/f Epsilon 1 K(((1- Nu Epsilon 2) square root 1+ Epsilon 1/ (1- Nu Epsilon 1) square root 1+ Epsilon 2 ) -1), where f Epsilon 1 is the first measured natural frequency of said article when the strain thereof is Epsilon 1 ( Epsilon 1 > OR = 0), f Epsilon 2 is the second measured natural frequency of said article when the strain thereof is Epsilon 2 ( Epsilon 2 > 0), K is a constant greater than 3, and Nu is Poisson''s ratio.

Claim 2

A method of obtaining a measure of an axial force within an article under strain from a variation of natural frequencies of said article, comprising the steps of: applying an ultrasonic wave to said article to generate forced oscillations therein; measuring a first natural frequency of said article when said axial force within said article is substantially zero; measuring a second natural frequency of said article when said article is under strain and said axial force is greater than zero; determining differential (f Epsilon 2-f Epsilon 1) between said first and second natural frequencies; and comparing thus determined differential with calibration data which has been obtained with respect to axial force versus differential to locate the existing axial force; the frequency of said ultrasonic wave being selected to satisfy the equation, (f Epsilon 2-f Epsilon 1)/f Epsilon 1 K(((1- Nu Epsilon 2) square root 1+ Epsilon 1/ (1- Nu Epsilon 1) square root 1+ Epsilon 2 ) -1), where f Epsilon 1 is the first measured natural frequency of said article when the strain thereof is Epsilon 1 ( Epsilon 1 > OR = 0), f Epsilon 2 is the second measured natural frequency of said article when the strain thereof is Epsilon 2 ( Epsilon 2 > 0), K is a constant greater than 3, and Nu is Poisson''s ratio.

Claim 3

A method of obtaining a measure of an axial force within an article under strain from a variation of natural frequencies of said article, comprising the steps of: applying an ultrasonic wave to said article to generate forced oscillations therein; measuring a first natural frequency of said article when said axial force within said article is substantially zero; measuring a second natural frequency of said article when said article is under strain and said axial force is greater than zero; determining the ratio of change (f epsilon 2-f epsilon 1/f epsilon 1) between said first and second natural frequencies; and comparing thus determined ratio with calibration data which has been obtained with respect to axial force versus ratio of change; the frequency of said ultrasonic wave being selected to satisfy the equation, (f epsilon 2-f epsilon 1)/f epsilon 1 K(((1- Nu epsilon 2) Square Root 1+ epsilon 1/ (1- Nu epsilon 1) Square Root 1+ epsilon 2)-1) where f epsilon 1 is the first measured natural frequency of said article when the strain thereof is epsilon 1 ( epsilon 1 > or = 0), f epsilon 2 is the second measured natural frequency of said article when the strain thereof is epsilon 2 ( epsilon 2 > 0), K is a constant greater than 3, and Nu is Poisson''s ratio.

Claim 4

A method of obtaining a measure of an axial force within an article under strain from a variation of natural frequencies of said article, comprising the steps of: applying an ultrasonic wave to said article to generate forced oscillations therein; measuring a first natural frequency of said article when said axial force within said article is substantially zero; measuring a second natural frequency of said article when said article is under strain and said axial force is greater than zero; determining the ratio of change (f epsilon 2-f epsilon 1/f epsilon 1) between said first and second natural frequencies; and comparing thus determined ratio with calibration data which has been obtained with respect to axial force versus ratio of change; the frequency of said ultrasonic wave being selected to satisfy the equation, (f epsilon 2-f epsilon 1)/f epsilon 1 K(((1- Nu epsilon 2) Square Root 1+ epsilon 1/ (1- Nu epsilon 1) Square Root 1+ epsilon 2)-1) where f epsilon 1 is the first measured natural frequency of said article when the strain thereof is epsilon 1 ( epsilon 1 > or = 0), f epsilon 2 is the second measured natural frequency of said article when the strain thereof is epsilon 2 ( epsilon 2 > 0), K is a constant greater than 3, and Nu is Poisson''s ratio.