Method for evaluating measured values for identifying a material fatigue

• US 20090306909A1
• Filed: 04/19/2006
• Published: 12/10/2009
• Est. Priority Date: 04/20/2005
• Status: Active Grant

• Current Assignee: Hottinger Bruel & Kjaer GmbH
• Original Assignee: Hottinger Baldwin Messtechnik GmbH (Spectris PLC)
• Inventors: Mattes, Johannes
• Granted Patent: US 7,930,112 B2
• Time in Patent Office: Days
• US Class Current: 702/36
• CPC Class Codes: G01M 5/0016 of aircraft wings or blades
• CPC Class Codes: G01M 5/0033 by determining damage, crack or wear
• CPC Class Codes: G01M 5/0075 by means of external apparatus, e.g. test benches or portable test systems G01M5/005 takes precedence
• CPC Class Codes: G01N 2203/0005 Repeated or cyclic
• CPC Class Codes: G01N 2203/0016 Tensile or compressive
• CPC Class Codes: G01N 2203/0017 Tensile
• CPC Class Codes: G01N 2203/0048 Hydraulic means
• CPC Class Codes: G01N 3/36 generated by pneumatic or hydraulic means

Abstract

The invention relates to a method for the evaluation of measured values for the recognition of defect conditions due to material fatigue on aircraft parts, in which strain sensors (6) are applied on the critical locations of an aircraft (1) or the parts thereof, wherein the measured values of the strain sensors at different loading conditions are detected, amplified and stored through several measuring circuits and from which an evaluating apparatus (9) derives, signals or indicates a material fatigue by comparison of current measured values with previous measured values. In that regard, the evaluating method is characterized in that the critical aircraft parts (1) are impinged on with a plurality of prescribed loading conditions by a plurality of loading elements (3), and in that the strain effect caused thereby is detected by a plurality of measuring circuits, and the evaluating apparatus (9) forms, for at least each loading condition and each measuring circuit, an allocated reference value and a permissible limit value range, which is subsequently coupled with the current measured values in such a manner so that the exceeding of the limit value range represents a material fatigue manifestation.

Claims

1. Method for the evaluation of measured values for the recognition of defect conditions due to material fatigue on aircraft parts, in which strain sensors (6) are applied on the critical locations of an aircraft (1) or its parts, whereby the measured values of the strain sensors are detected at different loading conditions through several measuring circuits, are amplified, and are stored, and from which an evaluating apparatus (9) derives a material fatigue through comparison of current measured values with previous measured values and signals or indicates the material fatigue, characterized in that the critical aircraft parts (1) are impinged on with a plurality of prescribed loading conditions by a plurality of loading elements (3), and in that the strain effect caused thereby is detected through a plurality of measuring circuits, and the evaluating apparatus (9) for at least each load condition and each measuring circuit forms an allocated reference value and a permissible limit value range, which is subsequently coupled with the current measured values so that the exceeding of the limit value range represents a material fatigue manifestation.

2. Method for the evaluation of measured values according to claim 1, characterized in that, for the force introduction in the carrying out of the different loading conditions, at least 10 loading elements (3) are provided on the aircraft parts to be tested, and in that for the detection of the caused strain effect on the critical aircraft parts at least 100 strain sensors (6) are applied and are connected with at least 100 measuring circuits, whereby the loading elements (3) are actuated by a control system (4), and the measured values are cyclically detected by a data acquisition apparatus (5), amplified and digitized and are evaluated by a connected evaluating apparatus (9) for the recognition of material fatigue manifestations already during carrying out the testing process.

16. Method for the evaluation of measured values according to claim 1, characterized in that the detected strain measured values from the strain sensors (6) and the detected load measured values from the loading elements (3) are intermediately stored in a database (8) and are read out for the evaluation by the evaluating apparatus (9) and are coupled with one another in a program-controlled manner.

17. Method for the evaluation of measured values according to claim 1, characterized in that, according to the detected strain measured values X_M for each loading condition, from the first existing current measured values for each measuring circuit these are evaluated as reference measured values (X_R) and therefrom an absolute limit value range is calculated for each reference value (X_R) through prescription of a permissible deviation (n_GW%).

18. Method for the evaluation of measured values according to claim 17, characterized in that, from the current strain measured values (X_M) after each repetition of a certain loading condition these are compared with the associated reference measured values (X_R) and upon exceeding the respective limit value range determined therefor this is evaluated as material fatigue manifestation for the applicable measuring circuit.

19. Method for the evaluation of measured values according to claim 1, characterized in that, for the repetition of certain loading conditions, the associated strain measured values (X_M) are summed-up during a prescribed repetition number N and therefrom an average value ( X) is formed, which represents an average reference baseline value X_R for further current strain measured values (X_M) and therefrom an absolute limit value range is calculated through prescription of a permissible deviation (n_GW%) for each reference base value (X_R).

20. Method for the evaluation of measured values according to claim 19, characterized in that the current strain measured value (X_M) is detected after the repetition of N loading conditions that are provided for the formation of the average reference base value X_R and is compared with the average reference base value X_R by the evaluating apparatus (9), and upon exceeding the determined limit value range this is evaluated as material fatigue manifestation for the applicable measuring circuit.

21. Method for the evaluation of measured values according to claim 1, characterized in that the evaluating apparatus (9), after the detection of at least two different load values (y_i) of a certain loading element (3) and the allocated strain measured values (X_i) caused thereby, forms therefrom linearity coefficients (K_L) and upon a deviation that exceeds a prescribed limit range evaluates this as material fatigue manifestation.

22. Method for the evaluation of measured values according to claim 1, characterized in that from the strain measured values (X_i) of a prescribed number N of repetition measured values of a certain loading condition, in the evaluating apparatus (9), a reference standard deviation (σ

_R) is calculated therefrom, and an allocated limit value range is calculated therefrom through prescription of a permissible deviation (n_GW%) for each reference standard deviation (σ

_R).

23. Method for the evaluation of measured values according to claim 22, characterized in that in the evaluating apparatus (9), after repetition of a certain loading condition, which follows at least after the number N of for the formation of the reference standard deviation, with the aid of the current strain measured value (X_i) calculates a current standard deviation (σ

), which is compared with the reference standard deviation (σ

_R) and is evaluated as material fatigue manifestation upon exceeding of the associated limit value range.

24. Method for the evaluation of measured values according to claim 1, characterized in that from the strain measured values (X_i) of a prescribed number N of repetition measured values of a certain loading condition, in the evaluating apparatus (9), the reference standard deviation (σ

_R) is calculated therefrom and forms a limit value range for the standard deviation with the aid of a prescribed multiple n of the reference standard deviation (σ

_R).

25. Method for the evaluation of measured values according to claim 24, characterized in that thereafter from the N previous repetition measured values (X_i), continuously a sliding average value X and therefrom a current standard deviation (σ

) is calculated, which in the following represents a trend, which is evaluated as material fatigue manifestation upon exceeding of the limit value range.

26. Method for the evaluation of measured values according to claim 1, characterized in that for each detected measured value (X_i) an absolute measuring inaccuracy deviation is calculated and this is compared with the respective absolute limit value range, whereby the detected measured value (X_i) is only taken into consideration for the evaluation when the limit value range is larger than the measuring inaccuracy deviation.

27. Method for the evaluation of measured values according to claim 1, characterized in that:

immediately after the start of the testing method;

at first an evaluation according to an individual measured value comparison takes place characterized in that, according to the detected strain measured values X_M for each loading condition, from the first existing current measured values for each measuring circuit these are evaluated as reference measured values (X_R) and therefrom an absolute limit value range is calculated for each reference value (X_R) through prescription of a permissible deviation (n_GW%);

and for corresponding number N of repetition measurements of certain loading conditions;

a baseline comparison takes place, characterized in that, for the repetition of certain loading conditions, the associated strain measured values (X_M) are summed-up during a prescribed repetition number N and therefrom an average value ( X) is formed, which represents an average reference baseline value X_R for further current strain measured values (X_M) and therefrom an absolute limit value range is calculated through prescription of a permissible deviation (n_GW%) for each reference base value (X_R),

a linearity evaluation takes place, characterized in that the evaluating apparatus (9), after the detection of at least two different load values (y_i) of a certain loading element (3) and the allocated strain measured values (X_i) caused thereby, forms therefrom linearity coefficients (K_L) and upon a deviation that exceeds a prescribed limit range evaluates this as material fatigue manifestation,

a formation of the reference values according to the standard deviation (σ

) takes place, characterized in that from the strain measured values (X_i) of a prescribed number N of repetition measured values of a certain loading condition, in the evaluating apparatus (9), a reference standard deviation (σ

_R) is calculated therefrom, and an allocated limit value range is calculated therefrom through prescription of a permissible deviation (n_GW%) for each reference standard deviation (σ

_R), and

a trend evaluation takes place, characterized in that from the strain measured values (X_i) of a prescribed number N of repetition measured values of a certain loading condition, in the evaluating apparatus (9), the reference standard deviation (σ

_R) is calculated therefrom and forms a limit value range for the standard deviation with the aid of a prescribed multiple n of the reference standard deviation (σ

_R), and thereafter from the N previous repetition measured values (X_i), continuously a sliding average value X and therefrom a current standard deviation (σ

) is calculated, which in the following represents a trend, which is evaluated as material fatigue manifestation upon exceeding of the limit value range.

28. Method for the evaluation of measured values according to claim 1, characterized in that corresponding to certain definitions of objects, at least two different evaluation methods are combined with one another by the evaluating apparatus (9) in such a manner so that the evaluation takes place as simultaneously as possible with the current measured value detection, the evaluation is sufficiently accurate and fulfills the necessary safety requirements in the air travel.

3-15. -15. (canceled)