Abstract:
A device and method for testing a fibre-composite component, which is to be processed by means of bonding, for the presence of at least one substance out of a selection of possible contaminants. A surface heating device for regional heating of a part-zone of the fibre-composite component to be bonded is performed for desorption of contaminants. A sensor array with a plurality of sensors detects contaminants in the gas phase, and a control device ascertains and signals contaminations which are found. An extractor device can be employed to extract machining dust from the fibre-composite component to a desorption device.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
       [0001]    Exemplary embodiments of the present invention relate to a device for testing a fibre-composite component, which is to be processed by means of bonding, for the presence of at least one substance out of a selection of possible contaminants and a method for operation of the device. 
         [0002]    Repairing structural components made from fibre-reinforced plastic (FRP) by gluing joints is problematic because of the possible presence of contaminations in the plastic, which may considerably impair the bond strength of the glued joint. If, in operation, an FRP component is exposed to environmental conditions with liquid or gaseous substances which can diffuse into the plastic, this may massively impair the adhesion point and possibly result in a total failure of the adhesive joint. For this reason the adhesive bonding repair of FRP components was previously prohibited in civil aviation. 
         [0003]    It is possible, by means of sensors such as metal oxide sensors (MOX sensors), non-dispersive infrared sensors (NDIR sensors) and/or humidity sensors to detect or even to measure the contaminants in question. This represents a very considerable expenditure only because each contaminant requires discrete sensors or sensor settings and therefore the examination for the presence of several possible contaminants is very costly both structurally and in terms of process engineering. 
         [0004]    Exemplary embodiments of the present invention are directed to a structurally simple device that can be used in a simple and error-resistant manner by means of which a FRP component can be examined for the presence of a plurality of specific contaminants. 
         [0005]    According to a first aspect of the invention a device for testing a fibre-composite component, which is to be processed by means of bonding, for the presence of at least one substance out of a selection of possible contaminants, wherein in a mobile integral unit this device comprises the following: a surface heating device for regional heating of a part-zone of the fibre-composite component to be bonded for the purpose of desorption of contaminants; a sensor array with a plurality of sensors for detection of all contaminants in the gas phase; a control device for regulating the surface heating device and also for activation and for readout of the sensor array and also for ascertaining and signalling contaminations which are found. 
         [0006]    By the direct heating of a region of the surface to be treated either by means of heat conduction or heat radiation the construction according to the invention enables thermal desorption of contaminants, wherein solid or liquid phases are directly converted into the gas phase. For this purpose it is necessary for the temperature to be monitored during the process of heating of the component, to avoid unacceptably high temperatures that could damage the component. The sensor array has a sufficiently large number of sensors by which all contaminants to be to detected can be detected simultaneously, so that the testing process can be kept brief. If one or more contaminants are ascertained, a corresponding signal is optically and/or acoustically output to the user. A binary testing for the contaminants (present in critical concentration, not present) or a more precise measurement of the detected concentration can be provided, but this increases the required apparatus. An advantage of this is that it is possible to operate without a transport or carrier gas, and so the gas concentration remains undiluted, resulting in an increase in the sensitivity and the sensor speed. Furthermore the walls can be kept easily accessible for collection of the contaminants and thus cleaning and restarting the sensor can be simplified. 
         [0007]    According to an advantageous modification of this embodiment of the invention the surface heating device is constructed as a contact heating device. In this case a heated punch is preferably provided, which is heated internally and has a sufficient thermal mass or thermal capacity, in order to effect the lowest possible temperature fluctuations during the process of heating the structural component. However, this design has the disadvantage that heating or measuring is only possible on accessible and level areas of the FRP structural component. 
         [0008]    A modification provides that the heated punch is disposed centrally and is surrounded by the sensor array, which in turn is surrounded by an outer housing. In this way a very compact design is possible with good detection of the desorbed substances. 
         [0009]    According to an alternative embodiment the device comprises a central heated punch that is surrounded by an annular scattered light chamber with reflecting walls, and also at least one IR light emitter is provided that radiates into the scattered light chamber and several selective photodetectors are disposed in the wall of the scattered light chamber. Both designs can also be combined, that is to say that further MOX sensors can be disposed in the scattered light chamber in addition to the NDIR sensors. 
         [0010]    According to another modification the surface heating device is constructed as a heat radiating device. It is particularly preferable to use a halogen lamp, which can be used with lenses and mirrors for targeted irradiation of surface regions of almost any shape. In this case the temperature of the irradiated surface is measured directly, preferably by means of a radiation thermometer, wherein the radiant heat generation can be adjustable by suitable control devices as a function of the recorded temperature. 
         [0011]    In a preferred modification of the invention the heat radiating device is disposed centrally and the sensor array is disposed around the radiation range, and an optical thermometer coupled to a control device is provided for measuring the temperature of the irradiated part-region. This structurally compact arrangement ensures that the desorbed substances remain in the detection region and can be reliably detected. 
         [0012]    In a preferred modification of the invention the surface heating device and the sensor array can be disposed on different sides of the fibre-composite component. This embodiment has the advantage that contaminants are “pushed out” by the heat, i.e. diffuse in the matrix in a substantial part against the temperature gradients. 
         [0013]    According to a second aspect of the invention a device for testing a fibre-composite component, which is to be processed by means of bonding, for the presence of at least one substance out of a selection of possible contaminants, includes an extractor device for extraction of machining dust from the fibre-composite component; a filter device for collecting the machining dust particles a desorption device for thermal desorption of contaminants out of the dust particles; a sensor array with a plurality of sensors for detection of all contaminants in the gas phase; a control device for regulating the desorption device, activation and for readout of the sensor array, and ascertaining and signalling of contaminations that are found. 
         [0014]    In this embodiment there is no heating of the structural component itself, so that a thermal damage thereto can be ruled out. Instead, the milling or grinding process which is necessary before an adhesive joint is utilised in order to analyse the removed material. This construction has the advantage that a substantially larger quantity of contaminants can be desorbed by the massively enlarged surface, so that a substantially more precise detection of the contaminants is possible. Also there is no need to adhere to thermal limiting values of the structural component, it is only necessary to ensure that no thermal decomposition processes of the plastic occur that can falsify the measurement results. A disadvantage of this construction is the substantial cost of apparatus, because the machining dust must be extracted, collected and then delivered to a desorption device. 
         [0015]    According to an advantageous modification of both aspects of the invention the sensor array comprises a number of metal oxide gas detectors (MOX), which are each sensitive for individual contaminants. These sensors are structurally simple and can be adapted to different substances to be detected. 
         [0016]    According to an advantageous modification of both aspects of the invention the sensor array comprises at least one humidity sensor. Since the moisture content of a FRP component influences the adhesion of a bond, a high moisture content is just as harmful as contamination by special substances. 
         [0017]    According to an advantageous modification of both aspects of the invention the sensor array comprises at least one non-dispersive infrared sensor (NDIR). A plurality of infrared sensors are preferably provided which are selective for specific frequency ranges, and of which the selectivities are adapted to the substances to be detected. 
         [0018]    According to an advantageous modification the individual sensors of the sensor array are selective for one or more of the following contaminants (usual English names or trade names used in the aviation industry in brackets): 
         [0019]    surfactants (aircraft surface cleaner) 
         [0020]    synthetic esters (jet oil 2) 
         [0021]    alcohols, glycols and mixtures thereof (runway deicer) 
         [0022]    alcohols (developer U89) 
         [0023]    petrol, kerosene 
         [0024]    butyl phosphates, phenyl phosphates, phosphate esters (hydraulic fluids, z.B. Skydrol) 
         [0025]    mineral oils (turbine oil 500) 
         [0026]    potassium acetates, sodium formiates (Clariant safeway) 
         [0027]    phosphates, silicates (wet cleaner Surtec 121) 
         [0028]    water, moisture 
         [0029]    butanones, methyl ethyl ketone (MEK solvent) 
         [0030]    hydrocarbons, silicones, fluorocarbons (release agent) 
         [0031]    synthetic oils and lubricants. 
         [0032]    According to an advantageous modification of the invention the composite component is an aircraft component. Thus, by the use of the device according to the invention, composite components in aircraft can be tested for the presence of contaminants and can optionally be repaired by bonding, which hitherto has not been allowable. 
         [0033]    A method for testing a fibre-composite component, which is to be processed by means of bonding, for the presence of at least one substance out of a selection of possible contaminants provides for the use of the device described herein for performing an analysis of the machining dust. Thus in the grinding process for preparation of the adhesive surface the machining dust can preferably be collected and then analysed. If no contaminants are revealed, a subsequent surface analysis can either be omitted completely or can be carried out in simplified form. On the other hand, if contaminants are ascertained, a precise analysis of the substances is carried out by means of the device described herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0034]    The invention is explained further below on the basis of preferred embodiments with reference to the appended drawings. In the drawings: 
           [0035]      FIG. 1  shows a diagram with a principal component analysis relating to three contaminants; 
           [0036]      FIG. 2  shows a first preferred embodiment of an examination device; 
           [0037]      FIG. 3  shows a second preferred embodiment of an examination device; 
           [0038]      FIG. 4  shows a third preferred embodiment of an examination device; 
           [0039]      FIG. 5  shows a detection device for a fourth preferred embodiment of the invention; and 
           [0040]      FIG. 6  shows a desorption device for a fourth preferred embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0041]      FIG. 1  shows a diagram of a principal component analysis (PCA) for three contaminants frequently occurring in composite components in the aviation industry, namely kerosene, Skydrol and water, using the device proposed according to the invention. The three substances could be reliably distinguished by the use of two principal components. Kerosene can be distinguished from Skydrol and water by using principal component  1  (X axis) and Skydrol can be distinguished from water by principal component  2  (Y axis). 
         [0042]      FIG. 2  shows a first preferred embodiment of a testing device  10   a  in a schematic cross-section, which device consists substantially of a thermally insulating outer housing  12  in which a preferably metallic heated punch  14  is disposed centrally, wherein the punch has a heating surface  15  and can be heated internally via a heating element  16 . The heating surface  15  is formed so that it can rest suitably on a composite component to be tested. In  FIG. 2  the heating surface  15  has convex shape, but also a planar surface or in an individual case also a concave shape is conceivable. It is also possible to provide the heating surface  15  with a heat conductive resilient coating, in order to ensure optimal heat transfer into the interior of the composite component. 
         [0043]    Furthermore, a thermometer  18  is disposed in the interior of the heated punch  14  and is connected together with the heating element  16  to a thermostat  20 . The heated punch  14  is surrounded by an annular sensor array  22  which is coupled to a control device  24 . The thermostat  20  is likewise by the control device  24  coupled. 
         [0044]    The sensor array  22  comprises a number of MOX and/or NDIR sensors (not shown in greater detail) and preferably also a humidity sensor. The individual sensors of the sensor array  22  are configured so that they are capable of detecting a predetermined selection of contaminants. 
         [0045]    In operation, the testing device  10   a  is placed onto the surface of a composite component  26  be tested so that the heating surface  15  rests on the site to be tested. By means of the heating element  16  controlled by way of the thermostat  20 , the heating surface  15  and thus also the region of the composite component  26  also in contact therewith is heated to a temperature of approximately 160-220° C. (the precise temperature depends upon the material of the composite component  26  and is selected so that the material is not damaged but the most comprehensive possible diffusion and thus better detection of possible contaminants is achieved). Any contaminants present come out of the composite component  26  heated via the heating surface  15  and collect in the collecting chamber  28  on both sides of the contact surface the heating surface  15 . The sensor array  22  is disposed precisely above this annular collecting chamber  28  and thus is able to detect these contaminants. For this purpose the sensor array  22  also set back somewhat relative to the heating surface  15  in order to enable the construction of the collecting chamber  28  for collecting the substances coming out of the composite material. The signals from the sensor array  22  are delivered to the control device  24 , in which in particular by means of a principal component analysis (see  FIG. 1 ) the presence or in a more complex embodiment also the concentration of contaminants is determined and corresponding optical and/or acoustic signals are output to the user. 
         [0046]      FIG. 3  shows a second preferred embodiment of a testing device  10   b  in a schematic cross-section. In this case the same components as in  FIG. 1  are provided with the same reference signs. This testing device  10   b  uses a halogen lamp  30  to generate heat in order to heat up the composite component  26 . In this embodiment the thermometer  18  is a radiation thermometer that can directly measure the temperature of the heated surface so that a more precise temperature monitoring and thus a higher temperature is possible, which increases the quantity of outcoming substances and thus enables a lower detection threshold. 
         [0047]      FIG. 4  shows a third preferred embodiment of a testing device  10   c  in a schematic horizontal section. This is similar to  FIG. 2  and likewise comprises a heated punch  14  that is heated internally by means of a heating element  16  and of which the temperature is regulated by means of the thermometer  18  and the thermostat  20 . An annular scattered light chamber  28  is provided radially outside the heated punch  14  and the inner and outer walls of the chamber are designed to be reflecting. At least one IR radiation emitter  34  and a number of photodetectors  36  (for reasons of clarity only two are shown) are disposed in the outer wall  32  of the scattered light chamber  28 . 
         [0048]    In operation the heated punch  14 —analogous to the construction according to FIG.  2 —heats the composite component (not shown in  FIG. 4 ) so that any contaminants present in the collecting chamber  28  escape. The scattered light chamber  28  is traversed by IR radiation  38  emitted by the IR radiation emitter  34  and reaches the photodetectors  36 , being reflected several times due to the reflectivity of the inner and outer wall  32  (and the reflectivity of the upper wall which is not shown). If contaminating substances (and also other substances) are present in the scattered light chamber  28 , certain spectra of the radiation are absorbed, which is ascertained by the photodetectors  36  selected by means of filters at specific frequencies or frequency bands. In practice, instead of the two shown a plurality (in particular 6 to 20) of detectors  36  will be provided, so that the individual substances can be not only detected but also selected relative to one another, as shown in  FIG. 1 . An unfiltered reference detector is preferably provided. 
         [0049]      FIGS. 5 and 6  show a third preferred embodiment of a testing device  10   d  that differs from the previous designs in that the collection of the contaminated particles and the desorption of the contaminants are separate from one another. In  FIG. 5  a composite component  26  is shown that is machined by means of an abrasive tool  40  (for example a grinding or milling device). In this case machining dust  42  is generated and is drawn off by means of an extractor device  44 . A two-part filter housing  46  with an easily removable filter membrane  48 , on which the machining dust particles  42  are collected, can be disposed in the extractor device. A suction pump (not shown) is located behind the filter housing  46 . 
         [0050]      FIG. 6  shows as part of the testing device  10   d  a desorption and detection unit  50 , which comprises an analysis chamber  51  defined by a two-part housing  52  in which a dust-laden filter membrane  48  can be placed. The detection unit  50  also includes a movable heated punch  54  which with a heating element  56  and a thermometer  58  is connected for the purpose of temperature control to a thermostat  60  in order to ensure a constant temperature of the heated punch  54 . The detection unit  50  comprises sensor array  62  with several gas detectors which are preferably constructed as MOX and/or NDIR sensors and/or humidity sensors. 
         [0051]    In operation of the testing device  10   d  during the process of machining of the composite component  26  the machining dust is drawn off and concentrated on the filter membrane  48  ( FIG. 5 ). Then the filter housing  46  is opened and the filter membrane  48  is removed and placed in the desorption and detection unit  50  ( FIG. 6  left). Then the heated punch  54  is moved against the filter membrane  48  ( FIG. 6  right), so that the contaminants present in the machining dust particles  42  can be desorbed at the elevated temperature and can be detected by means of the gas detectors  62 . 
         [0052]    The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof 
       LIST OF REFERENCE SIGNS 
       [0053]      10   a - d  testing device 
         [0054]      12  outer housing 
         [0055]      14  heated punch 
         [0056]      15  heating surface 
         [0057]      16  heating element 
         [0058]      18  thermometer 
         [0059]      20  thermostat 
         [0060]      22  sensor array 
         [0061]      24  control device 
         [0062]      26  composite component 
         [0063]      28  scattered light chamber 
         [0064]      30  halogen lamp 
         [0065]      32  outer wall 
         [0066]      34  radiation emitter 
         [0067]      36  photodetectors 
         [0068]      38  IR radiation 
         [0069]      40  tool 
         [0070]      42  machining dust 
         [0071]      44  extractor device 
         [0072]      46  filter housing 
         [0073]      48  filter membrane 
         [0074]      50  detection unit 
         [0075]      51  analysis chamber 
         [0076]      52  housing 
         [0077]      54  heated punch 
         [0078]      56  heating element 
         [0079]      58  thermometer 
         [0080]      60  thermostat 
         [0081]      62  sensor array