DE19703484A1 - Method of non-destructive testing of materials and composites for internal defects using thermography - Google Patents

Abstract

the method involves generating a forced heat flow through the region (2) under investigation. The flow is disturbed by any internal defects, which affects the surface temp. distribution, whose local and time variations are detected using a temp. measurement device (3) and evaluated for fault detection. The forced heat flow is generated by heaters which heat the surfaces of the test object (5) in the vicinity of the region under investigation. Alternatively, internal heat sources (6) are used to set up a temp. gradient in the region being investigated using a defined heating programme.

Description

The aim of the method is to demonstrate internal defects ( 1 ) in materials and material composites, in particular in plastic constructions and connections, without destruction over a large wall thickness and depth range, e.g. B. pores, foreign matter inclusions, cracks, insufficient material binding and other defects.

The application is particularly useful for plastics and composite materials made of plastic classic non-destructive testing methods such as radiographic testing and Ultrasonic testing problematic.

Due to the small density differences between the radiographic tests Material and inner defects a little contrast.

The error pattern is also often due to the complicated geometry of the test item Part overlaid.

The radiographic test requires radiation protection measures so that during the test Disruptions to the normal workflow arise.

In the ultrasonic test, the test is due to the strong sound attenuation and also difficult due to influences of the workpiece geometry.

In addition, the method of ultrasound testing is only limited as an imaging Procedures can be used, which limits the clarity of the test results.

The thermographic examination method described below is an alternative applicable. So far, thermographic methods have been successful in detection near-surface error applied.

The new process is capable of using a special heat and application high-resolution temperature measuring devices to prove deeper internal faults. The Testing does not hinder the workflow in the test environment. As a result of the test this creates an error pattern linked to the component geometry. Influences of component geometry can be eliminated.

To detect internal faults, a heat flow is forcibly generated in the area ( 2 ) to be examined. This is disturbed at the imperfections of the material or the material connection and causes a distortion of the surface temperature field compared to the error-free state.

The surface temperature field is made visible by a temperature measuring device ( 3 ). The resolution of this temperature measuring device ( 3 ) must be sufficiently fine over a wide temperature range. This requirement is met, for example, by existing industrial infrared thermography cameras.

To generate the heat flow through the area to be examined ( 2 ), temperature control units ( 4 ) are applied to the surfaces of the test object ( 5 ) in the vicinity of this area ( 2 ). The temperature control units ( 4 ) work in such a way that some act as heating elements, the others as cooling elements. The surface temperatures are regulated by means of the temperature control units ( 4 ) according to a predetermined heat program, so that a certain heat flow through the area ( 2 ) to be examined results. The surface of the area to be examined ( 2 ) is left to its own devices. The analysis of the local and temporal surface temperature distribution on this free surface is used for error detection.

The following heating programs are used:

• 1. All temperature control units ( 4 ) regulate the surface temperature over time. After a certain time, which is determined, among other things, by the temperature conductivity of the material to be examined and the heat transfer from the temperature control device ( 4 ) to the material, the surface temperature distribution approaches a steady state. By extending the holding time, smaller and deeper internal defects ( 1 ) can be detected. In addition to the local distribution of the surface temperature, the local distribution of the temperature setting time can also be used for error detection.
• 2. The temperature control units ( 4 ) work in such a way that the surface temperatures change temporally and in particular periodically in their area. The switching period or rate of change varies depending on the material thickness and the thermal conductivity of the material to be examined. In addition to recording the local surface temperature distribution, the local distribution of the phase of the periodically changing temperature or the rate of change in temperature is also used for error detection.
• 3. The temperature control devices ( 4 ) work so that the surface temperature in the contact area is briefly increased or decreased. The temporal and local course of the temperature on the surface of the area to be examined is also used for error detection.

A further possibility for generating a forced heat flow through the material area ( 2 ) to be examined is the use of an internal heat source ( 6 ), for example in the form of heating elements present in the material composite, conductive layers, HF radiation-absorbing layers or when heating or cooling media. The heat programs mentioned above can also be implemented here.

The temperature distributions, phase distributions, distributions of the setting times or temperature change speeds are stored digitally and made visible as an image. The error representations are contrasted on a computer ( 7 ) by means of image processing methods adapted to the test problem.

The test method described can be used, inter alia, for the non-destructive testing of butt weld connections on plastic parts, in particular for testing butt weld connections on plastic pipes ( FIG. 1). For this purpose, heating-cooling sleeves ( 8 ) are attached to both sides of the pipe weld seam, which enable the heating programs described above to be implemented. The temperature distribution image in the weld area or derived forms of representation are generated by an infrared thermography camera and transferred to a computer for processing. Furthermore, the method for testing heating coil socket weldings on plastic parts, in particular plastic pipes, can be used ( FIG. 2). The heating coil can be used here as a heat source.

Reference list

1

Inner error

2nd

Area to be examined

3rd

Temperature measuring device

4th

Temperature control elements

5

Test item

6

Internal heat source

7

computer

8th

Heating-cooling sleeves.

Fig. 1 schematic diagram of the method for the non-destructive testing of butt butt welded joints on molded parts made of plastic.

Fig. 2 schematic diagram of the method for the non-destructive testing of heating coil socket welded connections.

Claims (9)

1. A method for the non-destructive testing of materials and material composites for deeper internal defects ( 1 ), characterized in that a heat flow is forcibly generated by the area to be examined ( 2 ), which is disturbed by internal defects of the area to be examined ( 2 ) and there are repercussions on the surface temperature distribution, which is recorded by means of a temperature measuring device ( 3 ) in its local and temporal course and evaluated for error detection. 2. The method according to claim 1, characterized in that the forced generation of a heat flow through temperature control devices ( 4 ), which temper the surfaces of the test object ( 5 ) in the vicinity of the area to be examined ( 2 ), or using internal heat sources ( 6 ) , a temperature gradient being set in the area ( 2 ) to be examined according to a specific heat program. 3. The method according to claim 1 and 2, characterized in that of the temperature control devices ( 4 ) or of internal heat sources ( 6 ) at their contact surfaces constant in time (a), time-varying (b), in particular periodically changing (c) or briefly increased or decreased (d) surface temperatures. 4. The method according to claim 1 to 3, characterized in that the temperature control devices ( 4 ) at their contact surfaces to the test object ( 5 ) set a constant temperature and maintain this at least until a maximum error contrast is reached. 5. The method according to claim 1, characterized in that the temperature measuring device ( 3 ) provides images of the surface temperature distribution in the area to be examined and this in digital form for storage and further processing a computer ( 7 ). 6. The method according to claim 1, characterized in that an infrared thermography camera is used as the temperature measuring device ( 3 ), which has a temperature resolution <0.1 K over a temperature range of -20 ° C to 250 ° C. 7. The method according to claim 1, characterized in that the measured value analysis means special image processing algorithms that take place in addition to the local temperature distribution from image sequences also local distributions of temperature setting times, Velocity of temperature change and phase position with periodic heat application calculate and work out error contrasts, reducing the noise component and contrasts that arise from the component geometry are eliminated. 8. The method according to claim 1 to 6 for the non-destructive testing of butt butt weld connections on plastic components, in particular on pipes made of plastic, characterized in that the forced generation of the heat flow through the pipe weld seam by means of two heating-cooling sleeves ( 8 ) as temperature control devices ( 4 ) , which are arranged on both sides of the weld and a heating program according to claim 3 (ad) is selected. 9. The method according to claim 1 for non-destructive testing of heating coil sleeves welded joints, characterized in that the heating coil of the welding sleeve is used as the internal heat source ( 6 ) and a heating program according to claim 3 (ad), in particular the pulsed heating (d) by means of a brief current flow the heating coil is selected.