Method for non-destructive determination of fatigue limits and fracture toughness in components of various shapes

• US 5,767,415 A
• Filed: 06/25/1996
• Issued: 06/16/1998
• Est. Priority Date: 06/25/1996
• Status: Expired due to Fees

• Current Assignee: Vladimir Azbel
• Original Assignee: Vladimir Azbel
• Inventors: Azbel, Vladimir
• Primary Examiner(s): Dombroske, George M.
• Assistant Examiner(s): Noori, Max H.
• Application Number:
  US08/670,388
• Time in Patent Office: 721 Days
• Field of Search: 73/760, 73/805, 73/806, 73/808, 73/814, 73/794, 73/795, 73/847
• US Class Current: 73/847
• CPC Class Codes: G01N 2203/0067 Fracture or rupture
• CPC Class Codes: G01N 2203/0222 Temperature
• CPC Class Codes: G01N 2203/0688 Time or frequency
• CPC Class Codes: G01N 3/32 by applying repeated or pulsating forces

Abstract

A method for non-destructive determination of a fatigue limit for a component includes two sub-methods which may be performed separately, or in any order. A direct-deformation sub-method includes measuring micro-plastic deformation corresponding to each of a plurality of different known values of stress applied to the component, and identifying a critical value of stress corresponding to a change in the relationship between stress and micro-plastic deformation. An internal-friction damping method includes initiating torsional oscillations in the component, measuring an initial angular amplitude of oscillation, A₀, and a final angular amplitude of oscillation, A_n at the end of the number, n, of oscillations. This process is repeated a number of times and, for each pair of measurements, a corresponding measure of damping is calculated. A critical value of initial angular amplitude corresponding to a change in the relationship between amplitude and damping is then calculated. All testing is preferably performed torsionally, thereby making the method applicable to a wide range of real components of different shapes. Applied stresses are limited to below the yield point of the materials tested and do not affect the properties of the material.

Claims

1. A non-destructive method of determining a flexural fatigue limit for a component, the method comprising the steps of:

(a) measuring a micro-plastic deformation corresponding to each of a plurality of different known values of torsional stress applied to the component;

(b) identifying a critical value of stress corresponding to a change in the relationship between stress and micro-plastic deformation; and

(c) multiplying said critical value of stress by a torsional-to-flexural conversion coefficient.

2. A method as in claim 1, further comprising the steps of:

(a) initiating torsional oscillations in the component;

(b) measuring an initial angular amplitude of oscillation, A₀ ;

(c) counting a number, n, of oscillations after measurement of said initial angular amplitude;

(d) measuring a final angular amplitude of oscillation, A_n at the end of said number, n, of oscillations;

(e) repeating at least steps (c) and (d) a plurality of times for different initial angular amplitudes to obtain a plurality of pairs of measurements A₀, A_n ;

(f) for each of said pairs of measurements, calculating a measure of damping corresponding to said initial angular amplitude; and

(g) identifying a critical value of initial angular amplitude corresponding to a change in the relationship between amplitude and damping.

11. A method as in claim 1, further comprising a step of applying to the component an environmental condition likely to affect the fatigue limit during said step of measuring.

12. A method as in claim 11, wherein said environmental condition includes exposure to an elevated temperature.

3. A non-destructive method of determining a fatigue limit for a component, the method comprising the steps of:

(a) initiating torsional oscillations in the component;

(b) measuring an initial angular amplitude of oscillation, A₀ ;

(c) counting a number, n, of oscillations after measurement of said initial angular amplitude;

(d) measuring a final angular amplitude of oscillation, A_n at the end of said number, n, of oscillations;

(e) repeating at least steps (c) and (d) a plurality of times for different initial angular amplitudes to obtain a plurality of pairs of measurements A₀, A_n ;

(f) for each of said pairs of measurements, calculating a measure of damping corresponding to said initial angular amplitude; and

(g) identifying a critical value of initial angular amplitude corresponding to a change in the relationship between amplitude and damping.

4. A method as in claim 3, wherein said oscillations are at a frequency of between about 1 and 100 Hz.

5. A method as in claim 3, wherein the fatigue limit of interest is the flexural fatigue limit, the method further comprising a step of multiplying said critical value of stress by a torsional-to-flexural conversion coefficient.

6. A method as in claim 3, further comprising a step of applying to the component an environmental condition likely to affect the fatigue limit during making of said measurements.

7. A method as in claim 6, wherein said environmental condition includes exposure to an elevated temperature.

8. A method as in claim 3, further comprising the steps of:

(a) measuring a micro-plastic deformation corresponding to each of a plurality of different known values of stress applied to the component; and

(b) identifying a critical value of stress corresponding to a change in the relationship between stress and micro-plastic deformation.

9. A non-destructive method of deriving information relating to fracture toughness for a component, the method comprising the steps of:

(a) initiating torsional oscillations in the component;

(b) measuring an initial angular amplitude of oscillation, A₀ ;

(c) counting a number, n, of oscillations after measurement of said initial angular amplitude;

(d) measuring a final angular amplitude of oscillation, A_n at the end of said number, n, of oscillations;

(e) repeating at least steps (c) and (d) a plurality of times for different initial angular amplitudes to obtain a plurality of pairs of measurements A₀, A_n ;

(f) for each of said pairs of measurements, calculating a measure of damping corresponding to said initial angular amplitude; and

(g) calculating at least one rate of change in the relationship between amplitude and damping.

10. A method as in claim 9, further comprising a step of identifying first and second critical points corresponding to changes in the relationship between amplitude and damping, and wherein one of said rates of change is calculated from measurements falling between said first and second critical points.