DE102017112804A1 - A control device for controlling a crack propagation test apparatus, a crack propagation test apparatus, and methods for performing crack propagation tests - Google Patents

Abstract

The invention relates to a control device 12 for controlling a crack propagation test device 10 for performing crack propagation tests, comprising a detection and evaluation device 28 for detecting a crack 30, 30a, 30b on a test specimen 16 and for evaluating the crack 30, 30a, 30b, wherein the control device 12 is adapted to control a load application device 14 of the crack propagation test apparatus 10.

Description

The invention relates to a control device for controlling a crack propagation test apparatus for performing crack propagation tests. In addition, the invention relates to a crack propagation test apparatus using such a control device. Furthermore, the invention relates to a method for performing crack propagation tests.

Regulations and standards often require the review of material properties through relevant material testing. For the determination of the material parameters crack propagation tests are often carried out.

From the WO2008 / 148480 A1 and the WO2010 / 043516 A1 Examples of applications for carrying out crack propagation tests on workpiece samples for structural elements of aircraft are known.

Other examples of performing crack propagation tests are in the DE 10 2007 007 901 A1 and the DE 20 2009 013 264 U1 described.

The invention has for its object to automate crack propagation attempts as much as possible and to improve in terms of time and resource savings.

To solve this problem, the invention provides a control apparatus for controlling a crack propagation test apparatus for performing crack propagation test having the features of appended claim 1. A crack propagation test apparatus for automatically performing crack propagation tests using such a control apparatus and a method for performing crack propagation tests are subject matter of the subsidiary claims.

Advantageous embodiments are the subject of the dependent claims.

According to a first aspect, the invention provides a control device for controlling a crack propagation test device for performing crack propagation tests, comprising a detection and evaluation device for detecting a crack on a test specimen and for evaluating the crack, wherein the control device is designed to control a load application device of the crack propagation test device ,

It is preferred that the detection and evaluation device is designed to determine at least one crack parameter from the group of crack length, crack velocity, crack acceleration, crack profile and crack angle.

It is preferred that the control device is designed to influence the load application device due to at least one of the group of cycle number and crack length increasing in the crack propagation test.

It is preferred that the detection and evaluation device has a 2D or 3D imaging detection device and an evaluation device for determining the crack parameters from 2D or 3D data acquired by the detection device.

It is preferred that the detection device is coupled to the evaluation device such that the detection device can be controlled by the evaluation device.

It is preferred that the detection device has at least one detection unit which is selected from the group of camera, CMOS and CCD camera device, X-ray device, infrared device, ultrasound device, eddy current sensor device, potential sensor device.

It is preferred that the detection and evaluation device is designed to distinguish a one-dimensional crack shape from a multi-dimensional crack shape, wherein a multi-dimensional crack shape is characterized by a different crack angle of an angular tolerance.

It is preferred that the control device is designed to end the crack propagation test when the number of cycles has been reached as a successful crack propagation test.

It is preferred that the control device is designed to terminate the crack propagation test when a crack angle deviates from a predetermined angular tolerance as an unsuccessful crack propagation test.

The invention provides, according to a further aspect, a crack propagation test apparatus for automatically performing crack propagation tests, comprising a control device according to one of the preceding embodiments, as well as a load application device, which is designed to load a test specimen with at least one test load, wherein the detection and evaluation device with the Load application device is connected to control the load application to the test specimen in the form of experimental parameters.

It is preferred that the test parameters are selected from the group of test frequency, test load, amplitude, load direction, torsion, thrust, shear, stress ratio, temperature of the test specimen, pressure of the ambient medium, ambient medium temperature, composition of the ambient medium, such as atmosphere composition, Humidity, irradiation, wherein the stress ratio represents a ratio between a first load direction and a second load direction.

• - Aufbringen einer Last auf einen Prüfkörper
• - Erfassen und Auswerten eines Risses
• - Regeln der Lastaufbringung in Abhängigkeit von der Auswertung des Risses.

The invention, in another aspect, provides a method of performing crack propagation tests on a crack propagation test apparatus characterized by the steps of:

• - Applying a load on a specimen
• - Acquisition and evaluation of a crack
• - Rules of load application depending on the evaluation of the crack.

It is preferred that the control of load application include varying test frequency, test load, amplitude, load direction, torsion, thrust, shear, stress ratio, temperature of the test specimen, pressure of the ambient medium, ambient medium temperature, composition of the ambient medium such as, in particular, atmospheric composition, humidity, irradiation and / or stress ratio.

It is preferred that the detection and evaluation of a crack has the determination of at least one crack parameter from the group of crack length, crack velocity, crack acceleration, crack profile and crack angle.

It is preferable that the crack propagation test be completed upon reaching the number of cycles as a successful crack propagation test.

It is preferable that the crack propagation test is terminated when a crack angle deviates from a predetermined angular tolerance as an unsuccessful crack propagation test.

It is preferred that a one-dimensional crack shape is distinguished from a multi-dimensional crack shape by the detection and evaluation device, wherein a multi-dimensional crack shape is characterized by a different crack angle of an angular tolerance.

A particularly preferred embodiment of the invention relates to an automated control of a tensile tester in a crack propagation measurement based on an optically measured crack length.

Particular preference is given to an automated evaluation of the crack progress (length, angle,...) On the basis of imaging instruments.

In the following some advantages of preferred embodiments of the invention will be explained in more detail.

The crack propagation test can be carried out fully automatically. The crack length is determined according to preferred embodiments of the invention directly, preferably in real time.

In preferred embodiments of the invention, adjustment of the parameters (e.g., amplitude) may be based on the detected crack length or crack angle, respectively. As a result, it is possible to control the crack propagation speed and the crack angle (crack progression). Also, the experimental parameters such as crack speed and / or crack acceleration can be controlled.

In preferred embodiments of the invention, the deviation (or angle) of the crack progression can be detected accurately and the experiment can be stopped early if necessary. This significantly reduces the overall test time.

Earlier considerations for the partial automation of crack propagation tests include, for example, a measurement of the potential, a crack-measuring foil or the so-called compliance method. These methods will be described below.

In the potential measuring method, current is passed through the test piece. As the crack progresses, the detected voltage drop increases. Only the voltage drop is measured perpendicular to the direction of force. A formula can be used to determine the crack length by means of the voltage drop. There are different methods such as e.g. DC potential method (standard ASTM E647) or the AC potential method.

In the crack-measuring film method, a conductive film is applied to the test piece. The voltage drop across the film is measured, which increases as the crack progresses. As with the potential measuring method, only the voltage drop is measured perpendicular to the direction of the force. A formula can be used to determine the crack length. Non-conductive materials can also be tested with the Crack Measurement Film Method.

In the compliance method, the crack length is determined by the stiffness drop due to the crack. In the area of the defined by a notch crack opening of the specimen is a Crack opening displacement sensor (COD pickup, Crack Opening Displacement). A formula is used to determine the crack length, whereby the formula to be used for this purpose takes into account only the crack propagation perpendicular to the direction of the force.

In preferred embodiments of the invention, because of the preferred imaging, e.g. optical, evaluation no restrictions on the material to be tested, even materials that are not suitable for conducting electricity, can be tested.

Due to the preferred imaging, e.g. optical evaluation, you need no additional measuring aids, such. Crack measuring films, apply to the workpiece. Crack propagation in different directions can be measured.

Preferably, the crack length is determined directly. In this case, deviations of the crack propagation, and also deviations from the perpendicular to the direction of loading, can preferably also be detected.

It is recognized that from a certain deviation to the vertical of the loading device, the experiment is considered invalid. In particularly preferred embodiments of the invention, such a deviation can be detected in the shortest possible time during the experiment, while in earlier crack propagation attempts only after the end of the experiment (eg after 100,000 cycles) or by a permanent visual observation of the sample during the experiment by test personnel possible was. Due to a complete detection of the crack propagation, it is now also possible to regulate the amplitude.

In preferred embodiments of the invention, it is also possible to respond automatically, even automatically, to an angular deviation of the crack, in order to obtain e.g. to abort the attempt automatically if the required tolerances are exceeded.

In particularly preferred embodiments, a measurement or determination of multidimensional cracks, in particular 2D cracks or - with corresponding detection methods such. material penetrating radiation (e.g., X-ray) - also allows measurement of 3D cracks.

Particularly preferred are now a control of the measurement and not only a control of the measurement possible.

In previous crack propagation test methods, both an evaluation and a control of a servohydraulic testing machine are carried out manually. The test piece is subjected to a crack propagation test e.g. clamped in a tensile testing machine and claimed with a defined amplitude and frequency. After a certain number of cycles (for example, 1,000 cycles), the experiment is paused for a short time to take a picture of the test piece with the crack. The evaluation of the crack profiles as well as the control of the testing machine during the crack propagation test are carried out manually by the laboratory personnel. For this purpose, the images taken at different cycle numbers are loaded into an image processing program and the crack length is measured manually.

In preferred embodiments of the invention, it is now possible to continuously track the crack. An interruption of the experiment, as it has been done for the generation of a photo of the crack propagation test so far, can be avoided. Particularly preferably, the crack parameters such as the crack length are used for the control of the testing machine (for example servohydraulic testing machine, in particular tensile testing machine) as well as the regulation of the further course of the crack. This is preferably done when the crack propagates too fast during the crack propagation test with predetermined experimental parameters. In this case, in the embodiments according to the invention, the ongoing crack propagation test no longer needs to be interrupted and no new test with adapted test parameters needs to be started, instead a control can take place so that a defined maximum value of the crack propagation speed is not exceeded.

Now, the crack length can be directly changed, e.g. determine parameters that exist on the basis of images; This is possible, for example, with an imaging method. Not only is the crack propagation perpendicular to the load direction taken into account, but also deviations, such as a different crack angle, can be detected by an angular tolerance (for example greater than 10 degrees).

The crack propagation test is temperature dependent. For this reason, the threshold value used in currently used methods is quite complex. In preferred embodiments of the invention, the threshold value can be determined automatically. The following method is to be understood as an example.

For example, in the crack propagation test, the load is gradually reduced. A cyclic load is applied until the crack has grown, for example, by 0.1 mm. Subsequently, the cyclic load is reduced to, for example, 80%. The cycles are run with this load until again a crack of, for example, 0.1 mm is formed. Subsequently, the cyclic load is again reduced to, for example, 80%. This is done until no further crack growth occurs after, for example, 1,000,000 cycles. The threshold value thus denotes the cyclic load at which no crack propagation takes place. The threshold value determination can now be automated with embodiments of the invention.

Preferred embodiments of the invention can react to an angular deviation of the crack, so that, for example, the crack propagation test can be aborted automatically if the required tolerances are exceeded. Furthermore, 2D crack shapes can be measured or determined.

In particular, by preferred embodiments of the invention, an adaptation of the test parameters on the basis of the detected crack propagation speed or the crack angle. As a result, it is possible to control the crack propagation speed and the crack length, crack speed, crack acceleration, crack angle and crack course.

Crack progress tests could be carried out so far controlled, but not regulated. The control device according to the invention is designed to regulate a load application device of the crack propagation test device. Thus, a crack propagation test can be carried out fully automatically. The crack parameters such as crack length, crack speed, crack acceleration, crack angle and crack profile are preferably determined directly (in real time) with the detection and evaluation device and not calculated by means of formulas via the change in the crack opening of the test specimen.

By means of embodiments of the invention, adaptation of experimental parameters (eg test frequency, test load, amplitude, load direction, torsion, thrust, shear, stress ratio, temperature of the test specimen, pressure of the ambient medium, temperature of the ambient medium, state of aggregation, nature and composition of the ambient medium, atmospheric composition, humidity , Irradiation and stress ratio) on the basis of a detected crack parameter (for example, crack length and crack angle). As a result, it is possible to control the crack propagation speed and the crack angle, the crack acceleration and the course of the crack.

In the crack propagation tests, for example according to standard ASTM E647, only certain crack deviations perpendicular to the load direction are allowed. In embodiments of the invention, the angular deviation of the crack can be detected accurately and the crack propagation test can be stopped early if necessary. This can significantly reduce the overall test time.

In embodiments of the invention, the determination of the fracture toughness threshold value and thus the crack propagation tests can be automated. This significantly reduces the overall test time and saves resources.

• 1 eine Prinzipskizze einer Ausführungsform einer Rissfortschrittsversuchsvorrichtung zum Durchführen von Rissfortschrittsversuchen;
• 2 eine Prinzipskizze eines Prüfkörpers mit Aufbringung einer Last in einer ersten Lastrichtung;
• 3 eine Prinzipskizze eines Prüfkörpers mit Aufbringung einer Last in einer zweiten Lastrichtung;
• 4 die Vorderseite eines eingespannten Prüfkörpers vor dem Test;
• 5 die Rückseite eines eingespannten Prüfkörpers vor dem Test;
• 6 die Vorderseite eines eingespannten Prüfkörpers nach 478 Zyklen;
• 7 die Rückseite eines eingespannten Prüfkörpers nach 478 Zyklen;
• 8 die Vorderseite eines eingespannten Prüfkörpers nach 2557 Zyklen;
• 9 die Rückseite eines eingespannten Prüfkörpers nach 2557 Zyklen;
• 10 die Vorderseite eines eingespannten Prüfkörpers nach 3577 Zyklen;
• 11 die Rückseite eines eingespannten Prüfkörpers nach 3577 Zyklen;
• 12 die Vorderseite eines eingespannten Prüfkörpers nach 4539 Zyklen;
• 13 die Rückseite eines eingespannten Prüfkörpers nach 4539 Zyklen;
• 14 die Vorderseite eines eingespannten Prüfkörpers nach 5229 Zyklen;
• 15 die Rückseite eines eingespannten Prüfkörpers nach 5229 Zyklen;
• 16 die Vorderseite eines eingespannten Prüfkörpers nach 5573 Zyklen;
• 17 die Rückseite eines eingespannten Prüfkörpers nach 5573 Zyklen;
• 18 die Vorderseite eines eingespannten Prüfkörpers nach 5790 Zyklen;
• 19 die Rückseite eines eingespannten Prüfkörpers nach 5790 Zyklen;
• 20 einen eingespannten Prüfkörper nach 0 Zyklen;
• 21 einen eingespannten Prüfkörper nach 878.881 Zyklen;
• 22 einen eingespannten Prüfkörper nach 1.386.898 Zyklen;
• 23 einen eingespannten Prüfkörper nach 1.503.210 Zyklen;
• 24 einen eingespannten Prüfkörper nach 1.677.083 Zyklen;
• 25 einen eingespannten Prüfkörper nach 0 Zyklen;
• 26 einen eingespannten Prüfkörper, wobei der Rissverlauf nach 878.881 Zyklen von der senkrechten der Belastungsrichtung abweicht;
• 27 einen eingespannten Prüfkörper, wobei der Rissverlauf durch eine automatisierte Anpassung von relevanten Parametern anhand der optischen Risserfassung in einen definierten Verlauf gebracht wird;
• 28 eine Prinzipskizze eines Prüfkörpers mit zwei unterschiedlichen Rissverläufen und verschiedenen Rissparametern;
• 29 eine Prinzipskizze einer weiteren Ausführungsform einer Rissfortschrittsversuchsvorrichtung zum Durchführen von Rissfortschrittsversuchen mit unterschiedlichen Lastaufbringungen;
• 30 eine Prinzipskizze einer weiteren Ausführungsform einer Rissfortschrittsversuchsvorrichtung mit weiteren Einrichtungen.

Embodiments of the invention are explained below with reference to the accompanying drawings. It shows:

• 1 a schematic diagram of an embodiment of a crack propagation test apparatus for performing crack propagation tests;
• 2 a schematic diagram of a specimen with application of a load in a first load direction;
• 3 a schematic diagram of a specimen with application of a load in a second load direction;
• 4 the front of a clamped specimen before the test;
• 5 the back of a clamped specimen before the test;
• 6 the front of a clamped specimen after 478 cycles;
• 7 the back of a clamped specimen after 478 cycles;
• 8th the front of a clamped specimen after 2557 cycles;
• 9 the back of a clamped specimen after 2557 cycles;
• 10 the front of a clamped specimen after 3577 cycles;
• 11 the back of a clamped specimen after 3577 cycles;
• twelve the front of a clamped specimen after 4539 cycles;
• 13 the back of a clamped specimen after 4539 cycles;
• 14 the front of a clamped specimen after 5229 cycles;
• 15 the back of a clamped specimen after 5229 cycles;
• 16 the front of a clamped specimen after 5573 cycles;
• 17 the back of a clamped specimen after 5573 cycles;
• 18 the front of a clamped specimen after 5790 cycles;
• 19 the back of a clamped specimen after 5790 cycles;
• 20 a clamped specimen after 0 cycles;
• 21 a clamped specimen after 878,881 cycles;
• 22 a clamped specimen after 1,386,898 cycles;
• 23 a clamped specimen after 1,503,210 cycles;
• 24 a clamped specimen after 1,677,083 cycles;
• 25 a clamped specimen after 0 cycles;
• 26 a clamped test specimen, wherein the crack pattern deviates after 878,881 cycles from the vertical of the loading direction;
• 27 a clamped test specimen, wherein the crack profile is brought into a defined course by an automated adaptation of relevant parameters on the basis of the optical crack detection;
• 28 a schematic diagram of a test specimen with two different cracks and different crack parameters;
• 29 a schematic diagram of another embodiment of a crack propagation test apparatus for performing crack propagation tests with different load applications;
• 30 a schematic diagram of another embodiment of a crack propagation test device with other facilities.

In the 1 . 29 and 30 are embodiments of a crack propagation test apparatus 10 shown. The crack propagation test device 10 has a control device twelve and a load application device 14 on.

The load application device 14 is designed to be a test specimen 16 to apply at least one test load. For example, the load application device 14 a tensile testing machine 18 on that a first clamping mechanism 20 for clamping the test specimen 16 and a second clamping mechanism 22 for clamping the test specimen 16 having. The clamping mechanisms 20 . 22 have for example by means of screws fixable jaws and are in the 4 to 25 together with the clamped test specimen 16 presented in different examples for the implementation of crack propagation tests.

In particular, the load application device 14 a servohydraulic testing machine 24 on. The testing machine 24 can as tensile testing machine 18 a tensile load on the specimen 16 in a first load direction 26 exercise, like this in 2 which schematically illustrates a first mode for crack propagation tests. Next, the testing machine 24 in a preferred embodiment, which is also closer in 29 is indicated, a shear load on the specimen 16 in a second load direction 27 exercise, like this in 3 is shown. 3 shows an example of a second mode for crack propagation tests.

Also conceivable are other one- or multi-dimensional load types such as pressure, tension, torsion or thrust.

The testing machine can be designed, for example, as a resonance testing machine, testing machine with electrical actuators, piezomaschine, or as a testing machine with electrical, servohydraulic or pneumatic actuators.

The control device twelve serves to control the crack propagation test device 10 , In particular, the control device twelve adapted to the load application device 14 to regulate. For this purpose, the control device twelve a detection and evaluation device 28 on that for detecting a crack 30 and to evaluate the crack 30 is trained. Next is the control device twelve with the load application device 14 connected to the load application device 14 depending on the evaluation of the crack 30 to regulate.

The detection and evaluation device 28 has a detection device 32 on, which is designed for the imaging of the crack. For example, the detection device 32 as a registration unit 34 a camera 36 , a CMOS camera device, a CCD camera device, an X-ray device or an infrared device, by means of which 2D data or 3D data of the crack 30 let record.

The detection and evaluation device 28 also has an evaluation device 38 on that with the detection device 32 is connected to receive the 2D data or 3D data, and which is designed to determine at least one crack parameter, such as in particular crack length, crack speed, crack acceleration, crack profile and / or crack angle. The evaluation device 28 is especially implemented in software and uses known in principle Image data processing methods, such as edge detection mechanisms, for detecting the crack parameters.

The control device twelve has control routines by means of which the load application device 14 is controlled by the detected crack parameters. This will be explained in more detail below by means of different examples of crack propagation tests.

The test piece 16 For example, is form-fitting with the clamping mechanisms 20 . 22 with actuators of the load application device 14 connected. The actuators, which may be embodied, for example, as hydraulic servo cylinders or motor-driven spindle drives, are designed to apply a load to the test body.

In a standard experiment, such as in 2 is displayed (eg according to ASTEM E647), a load is only in one load direction (eg first load direction 26 ) applied. The load is applied with an amplitude or a test load and a test frequency, wherein the control device twelve is designed to control these experimental parameters. In a standard test only certain cracks are perpendicular to the load direction (first load direction 26 ) allowed. The detection and evaluation device 28 is designed to accurately detect the deviation or the crack angle. If tolerance values are exceeded, the control device stops twelve if necessary, try early. This significantly reduces the overall test time.

The control device should regulate based on certain variables increasing in the course of the test (for example number of cycles, crack length) and adapt the test parameters according to a previously defined specification. Here, for example, the test frequency, test load, torsion, thrust, shear, temperature of the test specimen, pressure of the ambient medium, temperature of the ambient medium, atmospheric composition, humidity, irradiation and the voltage ratio are to be regulated.

In a particularly preferred embodiment, the evaluation and detection device is capable of detecting the number of cycles. For this purpose, for example, an interface (not shown) is provided for obtaining data on the applied test frequency and a counter for obtaining the number of cycles from the test frequency (for example by means of time recording or simply by counting the cycles). The detected number of cycles can be provided in addition to or as an alternative to the crack parameters as a variable, on the basis of which the control of the test parameters takes place.

Furthermore, a particularly preferred embodiment of the crack propagation test device 10 capable of performing a mixed-mode experiment. In this case, the test specimen in a first mode, the in 2 is indicated, in a first load direction 26 and in a second mode, in 3 is indicated, in a second load direction 27 be charged. The mixed-mode experiment can be carried out fully automatically. The mixed-mode experiment is a crack propagation experiment with different Mode I ( 2 ) to Mode II ( 3 ) Ratios. Under Mode I here is the tensile load and Mode II is understood here as the thrust load.

In the various crack propagation tests, adaptation of the experimental parameters (such as, in particular, amplitude, load or test frequency) may be performed, for example. on the basis of the detected crack length, crack propagation speed, crack acceleration, the crack angle (crack profile) and / or the number of cycles. This will be clarified below by means of several examples.

In 1 and 29 are examples of possible control circuits 40 shown. As test specimen 16 is for example a crack progression test 42 provided, which is formed from a material or material structure to be checked and a notch 44 at which there is a crack 30 training, which must be evaluated accordingly. The crack advance test 42 is in the tensile testing machine 18 clamped and is with the detection device 32 detected. The detection device 32 is for example as an optical measuring system 46 educated. Instead of the optical measuring system 46 Of course, other measuring equipment such as X-ray equipment (eg a CNC X-ray inspection system, as it is available from Fill Gesellschaft mbH, Austria) can be used.

The detection device 32 provides via a first signal connection 48 (wired or wireless) the collected data to the evaluation 38 , which is designed for example as a device for data processing and is adapted to determine from these data via known methods for image recognition, the crack length, the crack speed and / or the crack angle. Next is the evaluation 38 capable of detecting 32 , in particular with regard to data rate or the like to control.

The evaluation device 38 is via a second signal connection 50 with the tensile testing machine 18 connected to at least one of the experimental parameters such as in particular test load, amplitude, frequency or load direction to control depending on at least one of the detected crack parameters (possibly also depending on the number of cycles). The second signal connection 50 can also for Transmission of data on the number of cycles from the tensile testing machine 18 be used to the evaluation.

While 1 as an example of the load application device 14 a tensile testing machine 18 shows is in 27 eg a servohydraulic testing machine 24 shown with due to a plurality of differently oriented actuators 52 Loads in different load directions 26 . 27 on the test specimen 16 let raise.

The detection device 34 has the at least one detection unit 36 which is preferably based on imaging methods. This is especially the optical measuring system 46 used, for example, a camera 36 , a CMOS and / or CCD camera device. In other embodiments not shown here, the detection unit is an X-ray device, an infrared device or an ultrasound device. Likewise, an eddy current sensor device and potential sensor device are possible embodiments of the detection unit.

Further measuring systems are, for example, infrared camera, ultrasound, eddy current method, potential probe + optics.

The measurement with an X-ray device would be a three-dimensional image of the crack 30 deliver. However, a two-dimensional mapping is derivable here. An advantage of the X-ray device is that the crack course in the material can be observed. The same can be done with an ultrasonic detection device.

The detection device 32 is with the evaluation device 38 for example via a signal connection 48 coupled. Preferably, it is further provided that the detection device 32 through the evaluation device 38 is controllable. Thus, for example, reaction parameters with respect to data recording such as images per second can be automatically adjusted.

The evaluation device 38 For example, it may be implemented as an integrated circuit of a data processing system that is designed to be part of the detection unit 34 evaluate received data and continue to process accordingly. Depending on the evaluation result, the evaluation device is available 38 a signal which, via the second signal connection 50 to a drive control of the load application device 14 is transmitted. The drive control can subsequently control the actuators 28 to the of the evaluation 38 adjust reported receivables, such as reducing the test load.

2 and 3 show an example of the test specimen 16 , The material of the test specimen 16 may be, for example, a metallic or a non-metallic material such as plastic or rubber. The test piece 16 has a notch 44 on. For holding the test specimen 16 through the clamping mechanisms 20 . 22 are provided attachment areas, such as holes 54 through which fastening means of the clamping mechanisms 20 . 22 can intervene. In the so-called case "Mode I", which in 2 is shown, the load according to the indicated arrows, which is the first load direction 26 represent, applied accordingly.

In 3 is appropriate 2 the case "Mode II" shown, in which the load in the second load direction 27 is applied.

By changing the load application in a first load direction 26 and the load application in a second load direction 27 a voltage ratio can be generated, wherein the first load direction 26 from the second load direction 27 differs by a certain angle. This is used in the so-called mixed-mode experiment. This is also fully automated feasible. The mixed-mode trial is a crack progression trial with various Mode II to Mode I ratios. Mode I is the load application to the test specimen in the first load direction, analogously to this, in the case of mode II, the load introduction is understood in a second load direction.

With the Mode I test, the test piece is subjected to tension, the Mode II test to shear, and a Mode III test to shear.

The 4-19 are photographs of a first example of a crack course during a crack propagation test. In this example, the crack course is perpendicular to the load direction (ie, the load direction). This type of crack propagation could, in principle, be calculated using known methods mentioned at the outset. With the control device present here, however, no such indirect determination by calculation, but a detection in real time, so that a control of the crack propagation test is possible. For example, the amplitude and frequency of the load application can be regulated according to the crack length or according to the crack speed.

In 4 the front of a clamped specimen is shown before the test. In 5 the back of a clamped specimen is shown before the test. 6 shows the front and 7 the back after 478 cycles. 8th shows the front and 9 the back after 2557 cycles. 10 shows the front and 11 the back after 3577 cycles. twelve shows the front and 13 the back after 4539 cycles. 14 shows the front and 15 the back after 5229 cycles. 16 shows the front and 17 the back after 5573 cycles. 18 shows the front and 19 the back after 5790 cycles. A comparison of the photographs shows here a well measurable rectilinear course of the crack 30 , It is not necessary to cancel because of deviation of the crack.

20-24 show an example of a crack propagation test in which the crack 30 from the perpendicular to the load direction 26 differs. It is the development of a 2D crack depending on the number of cycles represented by photographs. The deviating from the perpendicular to the loading direction crack propagation can with the detection and evaluation 28 be determined. When carrying out a standard test, the test can be prematurely terminated if it deviates from the specified tolerance. The experiment then shows an inadmissible crack propagation in the examined sample. The 20 to 24 show the backs of the specimen at 0 cycles, after 87,881 cycles, after 138,668 cycles, after 150,332 cycles, and after 16,77083 cycles. Reflection in the specimen is the objective of the optical measuring system 46 to recognize. Thus, the crack profile can be detected and determined and also used to control the crack propagation test.

19 shows therefore a one-dimensional crack 30a and 24 shows a two-dimensional crack 30b , Both types of crack are through the detection and evaluation 28 detectable in terms of their different parameters.

25 and 26 show an example of a possible control task. In 25 is a test piece 16 at the beginning (after 0 cycles) of a crack propagation test. In the course of the crack propagation test, the course of the crack deviates from the vertical of the loading direction. 26 shows a different crack pattern after 878881 cycles. The deviating crack profile is determined by the control device 10 on the basis of the detection device 32 recorded images detected. The test parameters relevant for the test (for example test frequency, test load, torsion, thrust, shear, temperature of the test specimen, pressure of the ambient medium, temperature of the ambient medium, atmospheric composition, humidity, irradiation and the stress ratio) are adapted and / or regulated accordingly.

27 shows another example of a possible control task. The crack progression is controlled by automated adaptation of the relevant test parameters (eg test frequency, test load, torsion, thrust, shear, temperature of the test specimen, pressure of the ambient medium, ambient medium temperature, atmospheric composition, humidity, irradiation and stress ratio) based on optical crack detection brought (see black line).

In 28 is a schematic diagram of a specimen 16 shown with a 1D and a 2D crack 30a, 30b. The test piece 16 has a notch in the left area 44 on that through a certain crack opening 62 which is specified by two directional baselines 64 be limited. Furthermore, the specimen 16 above and below the notch holes 54 on.

The score 44 has a notch tip in the right area 66 on, being in the area of the notch tip 66 a starting point 68 located. Starting from this starting point, a crack 30 proceed as a function of the test parameters in the test specimen.

After the notch there are two borderlines 70 leading to the directional baselines 64 the score 44 represent parallel lines and a tolerance range 72 to mark.

For a detection of the crack 30 it makes sense that the the detection and evaluation unit 28 a measuring base 78 (Starting point of the measurement for the length) and a direction base (comparison direction for the crack course) is given. With the aid of a directional base, the angle and / or the direction can be determined from a recorded image. The crack 30 is subsequently compared with this direction. The directional base may be, for example, the directional baseline 64 be shown.

From a starting point 68 can the crack length 74 and the crack angle 76 from a captured image. The starting point 68 can also only after a certain crack length 74 kick off.

Starting from the starting point 68 out are two cracks 30 shown schematically. A crack 30 each has the crack parameters crack length 74 , Crack course 60 as well as crack angle 76 on.

The crack length 74 is the distance traveled from the starting point 68 from measured over the course of the crack to its end in the test specimen 16 ,

The crack angle 76 indicates the angle under which a crack 30 from the directional baseline angled runs.

The crack course 60 indicates which shape the crack has assumed. Crack speed indicates the speed in path per unit time within which a crack propagates into the specimen.

The crack acceleration indicates the value with which the propagation velocity increases per unit time.

On the specimen 16 are two different cracks 30 shown, with crack 30a represents a 1D crack (solid line, crack profile A) and 30b represents a 2D crack (dash-dot line, crack profile B). Both cracks 30a . 30b can with the detection and evaluation 28 recorded and evaluated. Hereinafter, 1D and 2D crack 30a, 30b will be explained in more detail.

Thus draws a crack 30 Due to the fact that with its full crack length is within the tolerance range, so the crack 30 from the evaluation device 38 classified as 1D crack 30a and the crack propagation test is valid. Thus, under a 1D crack 30a, a crack becomes almost perpendicular to the first load direction 26 Understood.

A 2D crack, on the other hand, can be caused by a crack 60 which is almost perpendicular to the first load direction 26 runs, deviate. Due to material-specific properties such as material defects, it may be that a crack course 60 during a crack propagation test and a certain crack angle 76 strikes. Is the crack 30 with the total crack length 74 within the tolerance range 72 , then the classification of the crack takes place 30 to a 1D crack 30a. Leaves the crack 30 during the crack propagation test the tolerance range 72 Thus, the crack is classified as a 2D crack 30b. Can not correct the crack history 60 take place by a control, the crack propagation test by the control device twelve being stopped.

While previously only a controlled measurement was possible, which is a measurement in which the experiment is stopped manually after a certain crack length and / or crack deviation, a controlled measurement is now possible in which reacts to the respective crack length and / or crack deviation, for example, that the amplitude is changed.

The tolerance for a deviation is, for example, in the evaluation device 38 can be stored or set by self-learning systems directly from a computer.

29 shows another embodiment of the crack propagation test apparatus 10 , In contrast to the embodiment, which in 1 is described, the load application device 14 multidimensional actuators 52 formed, different loads (for example, the same or different sizes, directions and / or combinations thereof) in the form of train, pressure, torsion and thrust on the specimen 16 applied. Exemplary act in the in 29 illustrated embodiment loads in the form of torsion 80 and traction 82 on the test specimen 16 one. The actors 52 are each via a first and a second clamping mechanism 20 . 22 with the test piece 16 connected.

Furthermore, in this embodiment, the evaluation and detection unit 28 be integrated in a common housing.

30 shows another embodiment of the crack propagation test apparatus 10 , In this embodiment, the test specimen 16 in a test chamber 84 be arranged, the test chamber 84 a medium 86 having. The medium 86 For example, it may be a fluid, such as a gas, gas mixtures, a liquid and / or liquid mixtures.

To the test chamber 84 is a pressure-influencing device 100 connected, by means of which the pressure within the test chamber 84 can be set. The pressure-influencing device 100 can a pump 102 , a control valve 104 , a pressure reservoir 106 , such as compressed gas cylinder, etc. have. The pressure-influencing device 100 is to the control device twelve connected so that the pressure within the test chamber 84 by means of the control device twelve controlled and also depending on crack parameters and in particular also dependent on experimental parameters, such as time, number of cycles, frequency, can be controlled.

Next is the test chamber 84 an ambient medium influencing device 108 connected to influence the nature, composition and / or state of the ambient medium. For example, the pressure influencing device 100 Part of the ambient medium influencing device 108 be. For example, different medium reservoirs, in particular the compressed gas cylinders, and a selector valve 110 provided by means of different media compositions within the test chamber 84 let generate. Further, as an example, a fluid reservoir 112 represented by means of one or more liquid media, for example via a valve 113 in the Test chamber can be initiated. Also, a drain valve for draining media (not shown) may be provided.

Also the ambient medium influencing device 108 is to the control device twelve connected and controllable by these and also dependent on other parameters.

The test chamber 84 is designed to genierieren in interaction of various environmental parameters such as pressure of the medium, temperature of the medium and humidity desired environments during the test, the corrosion behavior of the test specimen 16 to investigate. In the test chamber 84 can the specimen 16 a radiation, for example, exposed to UV radiation, wherein the Prüfköper 16 for this purpose, with a UV light source (not shown) is irradiated.

The test chamber 84 is further adapted to the medium 86 and / or the test specimen 16 to cool and / or to heat. This makes it possible to regulate temperature dependent test parameters. This is in 30 indicated by a tempering device 114. Also the tempering device 114 is through the control device twelve controllable and also adjustable depending on different parameters.

The test chamber 84 can also be a sensor unit 90 have, wherein the sensor unit 90 For example, has a temperature sensor and / or humidity sensor.

During a crack propagation test, test curves or load profiles are automatically driven. Test curves or load profiles have, for example, the control of the pressure of the medium, the temperature of the medium and / or the test specimen 16 and the test frequency, for example, to simulate a complete flight in a crack propagation test.

A regulation can be carried out, for example, as follows: By changing test parameters (for example, reducing the test load, changing the stress ratio, and the like), it is automatically investigated at which parameter values no crack propagation occurs. This parameter value can be a value for the material resistance and the strength of the test specimen 16 be.

For example, by controlling with the control device twelve automatically, the load application device 14 driven at an increased number of cycles with less and less load until crack propagation no longer occurs, if the predetermined number of cycles, which may be reached maximum, has not already been exceeded. The crack is detected depending on the number of cycles and the corresponding force.

In other experiments, crack propagation may be investigated depending on frequency or on correlative environmental conditions. In order to study samples for aircraft materials, it is also possible to simulate the stresses which will be exerted on the aircraft material during a flight and to automatically examine and evaluate the crack propagation. If the crack deviates from its predefined direction or if cracking speed or crack acceleration are outside desired values, the test can be terminated and displayed in such a way that the material of the test specimen did not withstand this crack propagation test.

This opens up a variety of new possibilities for crack testing.

LIST OF REFERENCE NUMBERS

10

Crack propagation test machine

12

control device

14

Loading device

16

specimen

18

tensile testing machine

20

first clamping mechanism

22

second clamping mechanism

24

Servohydraulic testing machine

26

first load direction

27

second load direction

28

Detection and evaluation device

30

Crack

30a 1

D plan

30b

2D plan

32

detector

34

acquisition unit

36

camera

38

evaluation

40

loop

42

Crack propagation test

44

score

46

optical measuring system

48

first signal connection

50

second signal connection

52

actuator

54

hole

60

crack path

62

crack opening

64

Towards baseline

66

notch tip

68

starting point

70

boundary line

72

tolerance

74

crack length

76

crack angle

78

measuring base

80

torsion

82

traction

84

test chamber

86

medium

90

sensor unit

100

Pressure influencing device

102

pump

104

Control valve

106

pressure reservoir

108

Ambient medium influencing device

110

selector valve

112

fluid reservoir

113

Valve

114

tempering

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2008/148480 A1 [0003]
• WO 2010/043516 A1 [0003]
• DE 102007007901 A1 [0004]
• DE 202009013264 U1 [0004]

Claims (15)

A control device (12) for controlling a crack propagation test device (10) for performing crack propagation tests, comprising detection and evaluation device (28) for detecting a crack (30, 30a, 30b) on a test specimen (16) and for evaluating the crack (30, 30). 30a, 30b), wherein the control device (12) is adapted to control a load application device (14) of the crack propagation test device (10). Control device (12) after Claim 1 , characterized in that the detection and evaluation device (28) is adapted to determine at least one crack parameter from the group of crack length (74), crack speed, crack acceleration, crack profile (60) and crack angle (76). Control device (12) after Claim 1 or 2 , characterized in that the control device (12) is adapted to influence the load application device (14) due to at least one of the group of cycle number and crack length (74) increasing in the crack propagation test. Control device (12) according to one of the preceding claims, characterized in that the detection and evaluation device (28) comprises a 2D or 3D imaging detection device (32) and an evaluation device (38) for determining the crack parameters by the detection device (32). recorded 2D or 3D data. Control device (12) according to one of the preceding claims, characterized in that the detection device (32) with the evaluation device (38) is coupled such that the detection device (32) by the evaluation device (38) is controllable. Control device (12) according to one of the preceding claims, characterized in that the detection device (32) has at least one detection unit (34) which is selected from the group of camera (36), CMOS and CCD camera device, X-ray device, infrared device, Ultrasonic device, eddy current sensor device, potential sensor device. Control device (12) according to one of the preceding claims, characterized in that the detection and evaluation device (28) is adapted to distinguish a one-dimensional crack shape from a multi-dimensional crack shape, wherein a multi-dimensional crack shape by a different crack angle (76) of a Angular tolerance distinguishes. Control device (12) according to one of the preceding claims, characterized in that the control device (12) is adapted to the crack propagation test a) upon reaching the number of cycles as a successful crack propagation test and b) if a crack angle (76) of a predetermined angle tolerance deviation finish successful crack advance attempt. A crack propagation test apparatus (10) for automated crack propagation testing, comprising a control device (12) according to any one of the preceding claims, and load applying means (14) adapted to apply a test load (16) to at least one test load; and evaluation device (28) is connected to the load application device (14) in order to regulate the load application to the test body (16) in the form of test parameters. Crack propagation test device (10) after Claim 9 , characterized in that the test parameters are selected from the group of test frequency, test load, amplitude, load direction, torsion, shear, shear, temperature of the specimen, pressure of the ambient medium, ambient medium temperature, atmospheric composition, humidity, irradiation and stress ratio, the Stress ratio represents a ratio between a first load direction (26) and a second load direction (22). A method for performing crack propagation tests on a crack propagation test apparatus (10), characterized by the steps of: - applying a load to a test piece (16) - detecting and evaluating a crack (30, 30a, 30b) - controlling the load application as a function of the evaluation of the Crack (30, 30a, 30b). Method for performing crack propagation tests Claim 11 Characterized in that the rules of the load application having varying test frequency, test load, amplitude, load direction, torsion, shear, shear, tension, temperature of the specimen, pressure of the surrounding medium, temperature of the surrounding medium, atmospheric composition, humidity, radiation, and / or voltage ratio , Method for performing crack propagation tests Claim 11 or twelve , characterized in that the detection and evaluation of a crack, the determination of at least one crack parameter from the group of Crack length (74), crack velocity, crack acceleration, crack history (60) and crack angle (76). Method for carrying out crack propagation tests according to one of the preceding claims, characterized in that the crack propagation test a) is terminated upon reaching the number of cycles as a successful crack propagation test and b) if a crack angle deviates from a predetermined angular tolerance as an unsuccessful crack propagation test. Method for carrying out crack propagation tests according to one of the preceding claims, characterized in that a one-dimensional crack shape of a multi-dimensional crack shape of the detection and evaluation device (28) is distinguished, wherein a multi-dimensional crack shape is characterized by a different crack angle (76) from an angular tolerance ,

Images