Method for assessing the damage to a paint-covered composite material, measuring two separate criteria on the spectrogram

Abstract

A method for assessing damage to a composite material covered with a polyurethane-type paint is provided. Two separate criteria are measured on a spectrogram obtained by infrared spectrometry, thereby characterizing thermal ageing of the paint, each separate criteria being a measurement on a curve of a spectrum of the spectrogram of a height of a particular peak, thereby giving two independent assessments of the thermal ageing. Then, the two separate criteria are combined together in order to obtain a result of a level of the damage.

Claims

1. A method for assessing damage to a composite material covered with a polyurethane-type paint comprising: bringing an apparatus into contact with the composite material, measuring two separate criteria on a same spectrogram obtained by infrared spectrometry, thereby characterizing thermal ageing of the paint, each separate criteria comprising a measurement on a curve of a spectrum of the same spectrogram of a height of a particular peak, thereby giving two independent assessments of the thermal ageing and combining the two separate criteria to obtain a result of a level of the damage to the composite material without destruction of the composite material.

2. The assessment method according to claim 1, wherein in order to obtain a first criterion of the two separate criteria, the height of the particular peak is measured relative to a base line passing through a first two immediately adjacent troughs on each side of the peak.

3. The assessment method according to claim 1, wherein in order to obtain a second criterion of the two separate criteria, the height of the particular peak is measured relative to a base line passing through a first two significant troughs on each side of the peak.

4. The assessment method according to claim 1, wherein the two separate criteria are disposed along two axes of a graph in order to determine a level of thermal degradation of the composite material.

5. The method according to claim 1, wherein a wave number of the particular peak is about 1300/cm.

6. The method according to claim 5, wherein a wave number of the particular peak is between 1288 and 1314/cm.

7. The assessment method according to claim 5, wherein in order to obtain a first criterion of the two separate criteria, the height of the particular peak is measured relative to a base line passing through a first two immediately adjacent troughs on each side of the peak, and in order to obtain the first criterion, a first trough of one of the adjacent troughs between 1322 and 1374/cm is considered, and a second trough of the adjacent troughs between 1236 and 1247/cm is considered, the value 1247/cm being retained if the second trough is not pronounced on the curve.

8. The assessment method according to claim 5, wherein in order to obtain a first criterion of the two separate criteria, the height of the particular peak is measured relative to a base line passing through a first two immediately adjacent troughs on each side of the peak, and in a case where the particular peak is no longer observable, a largest height between the base line and the curve is measured between 1288 and 1314/cm, in order to obtain the first criterion that is negative.

9. The assessment method according to claim 5, wherein in order to obtain a second criterion of the two separate criteria, the height of the particular peak is measured relative to a base line passing through a first two significant troughs on each side of the peak, and in order to obtain the second criterion, a first significant trough between 1951 and 2051/cm and a second significant trough between 901 and 1102/cm are considered.

10. The assessment method according to claim 9, wherein in a case where the particular peak is no longer observable, then a height between the base line and the curve at a 1288/cm value is measured, in order to obtain the second criterion.

Description

DRAWINGS

(1) In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

(2) FIG. 1 is an infrared spectrogram obtained for the analysis of a composite material with a method according to the present disclosure;

(3) FIG. 2 is a detail view of this spectrogram showing the measurement of a first criterion of this method, for a highly visible particular peak;

(4) FIGS. 3 and 4 present a method for measuring the first criterion for a dimly visible particular peak;

(5) FIGS. 5 and 6 present a method for measuring the first criterion for a non visible particular peak;

(6) FIG. 7 presents the value of the first criterion as a function of the exposure time of the material and the reached temperature;

(7) FIG. 8 presents a method for measuring the second criterion;

(8) FIG. 9 is a graph presenting the principle of thermal exposure variation as a function of the two criteria; and

(9) FIG. 10 is the same graph showing, for identical thermal exposures, measurements for paints including different conditions of implementation.

(10) The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

(11) The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

(12) FIGS. 1 and 8 present, as a function of the wave number per centimeter N/cm, the curve obtained for a spectrometry on a panel made of composite materials and covered with a primary 5014-type polyurethane paint. The measurement is performed for a wave number comprised between 4000 and 650/cm.

(13) It is possible in particular to perform this analysis on parts made of carbon fiber and bismaleimide-type resin (“BMI”), covered with the primary polyurethane.

(14) The obtained spectrum is characteristic of a primary polyurethane paint with this reference, it evolves as a function of temperature exposure, comprising the temperature level and the exposure time.

(15) The spectrometry is carried out with a portable apparatus brought into contact with the part, according to the diffuse reflection technique, adapted to the surface condition of the composite material panel. The surface condition of the part is prepared beforehand through a cleaning with a solvent, in order to eliminate pollution that might disturb the measurements and modify the spectrogram.

(16) From this spectrogram, two different criteria C1 and C2 are identified on the curve in order to characterize the thermal ageing.

(17) The use of two criteria allows obtaining, via a comparison of these criteria, an assessment of the thermal ageing which is independent from the parameters of implementation of the polyurethane paint and from the measurement conditions, thereby making the measurement reliable. It will be noted that the use of one single criterion does not allow any comparison, we remain dependent on the parameters of implementation and on the measurement conditions, which does not give a reliable result.

(18) For the calculation of the first criterion C1 presented in FIG. 1, the height of a particular peak 6 is measured on the spectrogram relative to a base line 8 passing through the first two immediately adjacent troughs 2, 4 on each side of this peak. For the calculation of the second criterion C2 presented in FIG. 8, the height of the particular peak 6 is measured relative to a base line 8 passing through the first two significant troughs 40, 42 on each side of this peak.

(19) It will be noted that the troughs on the curve representing low-emission points which vary slightly during thermal ageing, constitute references allowing to measure the evolution of the height of the peak 6.

(20) In this example with a 5014-type polyurethane primary paint, the particular peak 6 is chosen close to the 1300/cm wave number, being between 1288 and 1314/cm.

(21) FIGS. 1 and 2 present the case of a spectrogram having the particular peak 6 easily observable thanks to a first point 2 corresponding to the trough located just to the left, and to a second point 4 corresponding to the trough located just to the right. Then, the height of this peak 6 is measured relative to the base line 8 connecting the two points 2, 4, in order to obtain the first criterion C1.

(22) FIGS. 3 and 4 present the case of a spectrogram having a particular peak 6 which is reduced through the presence of a second peak 10 located to the right, at about 1200/cm, without the second trough between the particular peak 6 and this second peak 10.

(23) In this case, there is arranged a base line 8 which passes through the first point 2 corresponding to the left trough 2, and through a second point of the curve 12 considered at the value 1247/cm. The height of the particular peak 6 is measured, in the same manner, relative to this base line 8, in order to obtain the second criterion C2.

(24) FIGS. 5 and 6 present the case of a spectrogram having a particular peak 6 which is not observable because of the presence of the second peak 10 located to the right, at about 1200/cm, which is very developed. Then, there is a total absence of troughs at 1250/cm.

(25) In this case, there is also arranged a base line 8 which passes through the first point 2 corresponding to the left trough, and through the second point of the curve 12 considered at the value 1247/cm. Afterwards, the largest height between this base line 8 and the curve, comprised between 1288 and 1314/cm, is measured in order to obtain the first criterion C1. In this example, the height is negative, this first criterion C1 is then negative.

(26) In a general manner for the calculations of the first criterion C1, the base line 8 passes through a first point corresponding to the left trough 2 comprised between 1322 and 1374/cm, and through a second point 4 corresponding to the right trough comprised between 1236 and 1247/cm, or without right troughs through a second point 12 at the value 1247/cm.

(27) FIG. 7 presents, as a function of the exposure time indicated on a logarithmic scale, the value of the first criterion C1 presented on referenced curves 20, 22, 24, 26, 28, 30, respectively corresponding to the temperatures of 100, 150, 170, 200, 250 and 300° C.

(28) It is observed that this first criterion C1 is actually characteristic of thermal ageing, with a variation depending both on the temperature level and on the exposure time.

(29) FIG. 8 presents the calculation of the second criterion C2, which measures the height of the particular peak 6 relative to a base line 8 connecting the first significant trough 40 located to the left at 2000/cm, comprised between 1951 and 2051/cm, to the second significant trough 42 located to the right at 1000/cm, comprised between 901 and 1102/cm.

(30) In the case where the particular peak 6 is no longer observable through the presence of a second peak located to the right at about 1200/cm which is very developed, as presented in FIGS. 5 and 6, then the height between the base line 8 and the curve at the value 1288/cm is measured, in order to obtain the measurement of the second criterion C2.

(31) FIG. 9 presents a graph comprising the first criterion C1 on a horizontal axis and the second criterion C2 on a vertical axis, on which the measured criteria of the material to be analyzed are disposed.

(32) Through their path, the main arrows 50 then 52 present a modification of the two criteria C1, C2 giving a more and more significant thermal exposure, whether by the higher temperature level that has been reached or by the longer exposure time, which will give a more and more significant degradation of the material.

(33) In contrast, along their directions, the transverse arrows 54 present a modification of the two criteria C1, C2 corresponding to a variation of the parameters of implementation of the polyurethane paint or of the surface conditions, which do not displace the points along the direction of the main arrows 50, 52, which gives a similar thermal degradation of the material.

(34) FIG. 10 presents, on the same graph, different measurements which confirm the principle presented above. Each set of measurements groups, substantially around an axis with a constant slope, aligned along the directions of the transverse arrows 54, a set of points corresponding to the same thermal ageing, on a polyurethane paint implemented under different conditions.

(35) In particular, there is a first axis 60 corresponding to an temperature exposure of 150° C. for five months, a second axis 62 corresponding to 200° C. for eight days, a third axis 64 corresponding to 300° C. for one hour, a fourth axis 66 corresponding to 170° C. for five months, a fifth axis 68 corresponding to 250° C. for twenty-four hours, and a sixth axis 70 corresponding to 200° C. for five months. There is also a group of points 72 corresponding to 200° C. for one month, which is located proximate to the first criterion C1 equal to zero.

(36) Thus, is obtained in a simple and rapid manner, without destruction of the material, an accurate assessment of the thermal engagement level of the materials which is independent from the parameters of implementation of the primary paint, and from the measurement conditions.