WO2006116782A1

WO2006116782A1 - Method for carrying out fatigue tests on a sample body and test device

Info

Publication number: WO2006116782A1
Application number: PCT/AT2006/000173
Authority: WO
Inventors: Johann Kollegger; Bernd KÖBERL; Herbert Pardatscher; Markus Vill
Original assignee: Technische Universität Wien
Priority date: 2005-05-02
Filing date: 2006-04-27
Publication date: 2006-11-09
Also published as: AT501168B1; EP1877749A1; AT501168A4

Abstract

The invention relates to a method for carrying out fatigue tests on a test body (7) which, in order to increase the frequency of testing, in particular with high loading of the test body is characterised in that the test body (7) is subjected to a static load by a system comprising a spring resistance and is additionally subjected to an oscillating load by means of an oscillation generator (9) with generation of a closed force path in the system for static loading.

Description

Method for carrying out fatigue tests on a test specimen and test device

The invention relates to a method for carrying out fatigue experiments on a test specimen and a device for carrying out the method.

In the construction industry and in mechanical engineering, many constructions experience damage to the material structure as a result of recurring loading, even if this is far below the static strength of the material. If the stress is sufficiently frequent, the progressive damage can lead to fatigue failure of the material.

Structures whose fatigue behavior is to be taken into account in dimensioning are either dimensioned according to standards or sufficient resistance to fatigue failure by means of fatigue tests can be demonstrated.

Fatigue tests are used, for example, for assessing the fatigue behavior of angled cables and cable-stayed anchors for cable-stayed or cable-stayed bridges, as well as for coupling tensioning cables in prestressed reinforced concrete structures.

Investigations on the fatigue behavior of anchorages on stay cables are usually carried out for 2 million load changes. The upper loads, which correspond to 45% of the nominal tensile strength of parallel stranded cables, and the acceptance criteria are based on the relevant standards, e.g. the PTI Recommendations for stay cable design, testing and installation. The vibration ranges with which the tests are carried out depend on the maximum vibration widths that can occur in the structure. The relationship between the vibration widths in the test and in the structure is determined for the individual structure and is not normatively regulated.

The fatigue behavior is influenced by the following factors:

- Training or casting of the rope head

- corrosion

- Local friction

- Training of saddles

- deflections within the anchorages The fatigue tests for diagonal cables are normally carried out with axial load. The angle changes at the anchoring points, which result from deflections of the deck slab, were simulated in tests accordingly. Guidelines also show the possibility of twisting the rope anchorage during the test by a defined angle.

Fatigue tests on small components (Prüfkraflt up to 2500 kN) can be performed with servo-hydraulic testers or Hydropxύsanlagen with high frequencies (20 to 100 Hertz). For large components, such as Slanted cable anchors, which require a basic force of approx. 2500 kN, reduce the test frequency of servo-hydraulic test systems to approx. 1 hertz. Hydropulse systems are only offered by test equipment manufacturers in the force range up to a maximum of 2500 kN. At present, there are three large plants in Europe where fatigue tests are carried out for large components, e.g. Slanted cable, can be performed.

In the test apparatus of the Technical University of Munich, three static cylinders are used to apply the basic force and three cylinders to apply the dynamic load. The swinging load is generated by the extension and retraction of the three cylinders for dynamic loading. With this device test frequencies on the order of 1 hertz are achieved. An attempt for 2 million load changes therefore takes about 23 days. The retraction and extension of the cylinder is accomplished via servo-hydraulic control valves and requires a high energy input, mainly for cooling the hydraulic oil.

A second test facility is located at the Eidgenossen Materialprüfanstalt in Dübendorf, Switzerland. The basic force is applied with hydraulic presses. The oscillating load is applied by the servo-hydraulically controlled extension and retraction of hydraulic presses. The achievable test frequency is therefore in the order of 1 Hertz. There are the same disadvantages as stated above.

The third test device is located at the Laboratoire central de ponts et chaussees, France. The basic force is applied to the test specimen (length approx. 5.20 m) by means of three hydraulic presses and to a temporary cable (length 13.80 m). The swinging load is generated by small dynamic presses. As a result, slightly higher test frequencies than at the test facility of the Technical University of Munich and the EMPA are possible. The invention has for its object to provide a method and a test device that allow fatigue experiments with much higher frequencies and with a lower energy input than in the known designs.

This object is procedurally achieved in that the specimen is exposed in a spring stiffness system having a static stress and is additionally exposed by means of a vibration exciter vibrational stress, wherein in the system for the static stress, a closed power flow is generated.

Preferably, the spring stiffness of the oscillating mass system is adjusted to obtain the first natural frequency that constitutes the test frequency, either adjusting the spring stiffness and / or increasing or decreasing the vibrating masses, and performing the fatigue test at that first natural frequency.

According to the invention, at high base loads - such as e.g. over 2500 IcN - to test high frequencies compared to the prior art; Preferably, a test frequency of the fatigue test is set between 5 and 100 Hz, in particular between 25 and 50 Hz.

A preferred variant is characterized in that the test specimen is fastened in a test rig having a high rigidity, the force flow being closed via the test frame, the test specimen and via a resilient connection.

Here, the rigidity of the test frame is expedient at least 5 times, preferably at least 10 times, higher than the rigidity of the test specimen.

Preferably, the vibrations are caused mechanically or electromechanically.

A suitable variant is characterized in that the vibration is damped.

In this case, a dynamic enlargement factor, which increases the force generated by the vibration generator, is advantageously set via an attenuator provided in the force flow. A test device for carrying out the method according to the invention is characterized by the combination of the following features: a test frame with at least one support for coupling a

Test specimen with at least one of its end regions, - a loading device for applying a Grandkraft on the

Test specimen, one acting between the specimen and the test frame

Spring device, and a mechanically couplable with the test specimen vibration exciter.

Suitably, the spring device is mechanically coupled on the one hand via the loading device with the test frame and on the other hand with the test specimen, wherein the vibration exciter is preferably provided at the coupling point between the spring means and the test specimen.

According to a preferred variant of the vibration generator is designed as a mechanical vibration exciter and provided on a arranged between the spring means and the test body holding means, such as a housing, wherein preferably on the holding means balancing masses are attached

A further advantageous embodiment is characterized in that the vibration exciter is designed as an electromechanical vibration exciter and on the one hand to the test frame immobile and on the other hand coupled via a mechanical coupling with the test specimen and the spring means at the coupling point of the spring means with the test specimen

In a horizontal arrangement of the test apparatus, the vibration exciter is suitably guided in the direction of vibration by means of a guide device, preferably formed by a suspension device or a linear guide, such as a slide bearing.

To test a Umlenksattels for a diagonal cable tester is characterized in that the test piece is coupled with one end portion on the test frame and the other end via the loading device to the test frame, and that the vibration generator is coupled via the spring means to the test frame and on the Test body acts between its end regions, wherein the vibration exciter is preferably designed as a mechanical vibration exciter. A test device for bending fatigue tests is characterized in that the test body is coupled with its end portions with the test frame and claimed between its end via at least one spring means which is attached on the one hand to the test frame and on the other hand via the loading device with the test body, subjected to bending is, where appropriate, the vibration exciter is coupled to the test specimen optionally with the interposition of balancing weights

For the spring device offer both tension members and pressure members.

The invention is explained in more detail below with reference to the illustrated in FIGS. 1 to 13 different embodiments.

It shows:

Fig. 1 a fiction, contemporary test apparatus for fatigue experiments in a standing arrangement for testing an anchorage of an inclined cable (The vibration stress is applied by means of a mechanical unbalance exciter).

Fig. 2 is a section along the line II-II of Fig. 1st

Fig. 3 shows a second embodiment of the test device in a vertical arrangement for testing a tendon coupling (The vibration stress is applied with two electromechanical vibration exciters).

4 shows a section along the line IV-IV of FIG. 3 and FIG. 5.

5 shows a section along the line V-V of FIG. 3 and FIG. 4.

6 shows a plan view of a third embodiment of the test device in a horizontal arrangement for testing a tendon coupling (the vibration stress is applied by means of a mechanical unbalance exciter.) The structure for receiving the unbalance exciter, the additional masses and the two anchors is suspended upwards with steel cables.

7 is a section along the line VII-VII of FIG. 6th

8 shows the layout of a fourth embodiment of the test apparatus in a horizontal arrangement for testing an anchoring cable (The vibration stress is applied by means of a mechanical unbalance exciter.) The steel structure for receiving the unbalance exciter, the additional masses and the two anchors is mounted on a plain bearing).

9 is a section along the line IX-IX of FIG. 8th 10 shows a fifth embodiment of the test device for testing a saddle of a

Angled cable (A saddle is used to deflect an inclined cable in the pylon of a

Cable-stayed bridge).

Fig. 1 1 is a section along the line XI-XI in Fig. 10. Fig. 12 shows a sixth embodiment of the test apparatus for testing a beam

Reinforced concrete (The basic force is with four hydraulic presses on the four

Federeinrichtungen and the test body applied). 13 is a section along the line XIII-XIII in Fig. 12th

A test frame 1, formed by two vertically directed longitudinal columns 2, which are connected to a main frame with transverse heads 3, 4 above and below, is mounted on a foundation block 5. Between the upper and lower crosshead 3, 4, a test arrangement 6 is provided centrally and parallel to the longitudinal columns 2, formed by a test piece 7 fixed to the lower crosshead 4, a holding device 8 coupled to the test piece 7 for a vibration exciter 9 and one with the holding device 8 coupled spring device 10, designed as a pull rope. The upper end of the traction cable 10 is coupled to the upper crosshead 3 via a hydraulic cylinder 11, such as a hydraulic press. Between the crosshead 3 and the hydraulic cylinder 11, a damping element 22 is provided.

On the holding device 8, which is formed as the vibration exciter 9 receiving housing, additional masses 12 for adjusting the first natural frequency - which forms the test frequency - are mounted.

The vibration exciter 9 is a mechanical unbalance exciter, as it e.g. from "Building Dynamics Practical" by Rainer Flesch, Bauverlag GmbH, Wiesbaden and Berlin, is known, trained.

In the test piece 7 is a piece of a cable, which is provided at its ends with anchors 13, which are also or actually subjected to the test.

The rigidity of the test frame 1 is at least 5, preferably 10 times greater than that of the test arrangement 6. The test frame 1 forms with the test assembly 6, ie the test body 7, the vibration exciter 9 with the holding device 8 and acting as a spring device traction cable 10, a system , which has a certain spring stiffness, wherein the power flow is closed in the system. The dynamic system is in the resonance state (ie in the first natural frequency) during the experiment. This first natural frequency or the natural angular frequency depends essentially on the stiffness of the spring device 10, the test body 7, the holding device 8 and the test frame 1 and on the mass density of the system. The first natural frequency of the system can be adjusted over the length and thickness of the traction cable 10 and the mass of the vibrator 9 and the additional masses 12 at the coupling point between the test piece 7 and 10 traction cable. Thus, it is possible to vary the test frequency between 5 and 100 Hertz by the correct choice of additional masses 12 and the tensile rigidity of the tension cable 10.

The excitation force of the mechanical unbalance exciter depends on the rotating masses and the set speed. This excitation force is multiplied by the resonant dynamic magnification factor (e.g., 50% attenuation equal to 1%).

The main advantages of this test device are the very high test speed and the low energy consumption during the tests compared to conventional systems. The energy costs for the operation and possible cooling of the vibrator 9 amount to only a fraction of the cost of operating and cooling a hydraulic unit. The duration of the test is reduced for 2 million load changes at a frequency of 40 hertz to 13.9 hours compared to 23 days at a frequency of 1 hertz.

According to the embodiment shown in FIGS. 3, 4 and 5, a vibration exciter 9 operating on an electromechanical basis is provided, which is supported on the foundation block 5 for the test frame 1 and coupled via a cross member 14 to the traction cable 10 and the test body 7. The test specimen is formed by two tendon pieces, which are connected to a coupling 15.

Vibration exciters 9 on mechanical (counter-rotating masses) and electromechanical basis are available in the desired test range of 5 to 100 hertz and for the required forces on the market.

The arrangement of the test device can be both upright and lying and depends on the circumstances of the test hall. In a horizontal arrangement of the vibration exciter 9 must be stored accordingly, so that movement in Longitudinal direction of the test piece 7 is given. This can be realized by a corresponding rolling or sliding bearing, as shown in FIGS. 8 and 9, or a suspension 17 according to FIGS. 6 and 7.

10 and 11 show a test device for testing a saddle 18 for a cable 19. The vibration generator 9 is attached to the saddle 18 and the spring device 10 - also a pull rope 10 - is in the direction of vibration, starting from the coupling with the saddle 18 to the test frame 1 directed and coupled with this also. The tensile force is applied here with a hydraulic press 11 on the both sides with the test frame 1 coupled cable 19.

FIGS. 12 and 13 illustrate a test frame 1 for carrying out a fatigue test on a load-bearing beam 20, such as a reinforced concrete beam. The force causing the bending is applied by hydraulic presses 11 ₃ which are mounted transversely to the carrier 20 cross members 21, applied, between the hydraulic presses and the test frame 1 spring elements 10, for example, tie rods, are provided, over which the power flow is closed.

Between the carrier 20 and the test frame 1, a damping element 22 is provided in the direction of action of the vibration generated by a mechanical vibration generator 9. Additional masses 12 are provided here between the vibration exciter 9 and the carrier 20.

As spring elements 10 can - as described - traction cables or tension rods (made of steel or plastic, optionally fiber-reinforced) but also pressure rods are used.

Claims

claims:

1. A method for performing fatigue tests on a test specimen (7, 15, 18, 19, 20), characterized in that the test body (7, 15, 18, 19, 20) is exposed in a spring stiffness system having a static stress and additionally subjected to oscillatory stress by means of a vibrator (9), wherein in the system for static stress a closed flux of force is generated.

2. The method according to claim 1, characterized in that the spring stiffness of the system with oscillating masses (12) is adjusted to obtain a first Bigenfrequenz, which forms the test frequency, either the spring stiffness is adjusted and / or the oscillating masses (12). be increased or decreased, and that the fatigue test is performed with this first natural frequency.

3. The method according to claim 1 or 2, characterized in that a test frequency of the fatigue test between 5 and 100 Hz, preferably between 25 and 50 Hz, is set.

4. The method according to any one of claims 1 to 3, characterized in that the test body (7, 15, 18, 19, 20) is mounted in a high stiffness test frame (1), wherein the flow of force on the test frame (1) , the test body (7, 15, 18, 19, 20) and via a resilient connection (10) is closed.

5. The method according to any one of claims 1 to 4, characterized in that the rigidity of the test frame (1) at least 5 times, preferably at least 10 times, is higher than the rigidity of the test body (7, 15, 18, 19, 20).

6. The method according to any one of claims 1 to 5, characterized in that the vibrations are caused mechanically or electromechanically.

7. The method according to any one of claims 1 to 6, characterized in that the vibration is damped.

8. The method according to any one of claims 1 to 7, characterized in that a dynamic magnification factor, which increases the force generated by the vibration generator (9), is set via an attenuator provided in the force flow (22).

9. test device for on a test specimen (7, 15, 18, 19, 20) to be performed fatigue tests according to one of claims 1 to 8, characterized by the combination of the following features: a test frame (1) with at least one support for coupling a test body (7 , 15, 18, 19 ₃ 20) with at least one of its end regions, a loading device (1 1) for applying a basic force to the test body (7, 15, 18, 19, 20), one between the test body (7, 15, 18 , 19, 20) and the test frame (1) acting spring means (10), and

- One with the test body (7, 15, 18, 19, 20) mechanically coupled vibration exciter (9).

10. Device according to spoke 9, characterized in that the spring device (10) on the one hand via the loading device (11) with the test frame (1) and on the other hand mechanically coupled to the test body (7), wherein the vibration exciter (9) preferably at the Coupling point between the spring means (10) and the test body (7) is provided (Fig. 1).

11. The device according to claim 10, characterized in that the vibration generator (9) is designed as a mechanical vibration exciter and at one between the spring means (10) and the test body (7) arranged holding means (8), such as a housing, is provided preferably on the holding device (8) balancing weights (12) are attachable (Fig. 1).

12. The device according to spoke 9, characterized in that the vibration exciter is designed as an electromechanical vibration exciter and on the one hand to the test frame (1) immovable and on the other hand via a mechanical coupling with the test body (7) and the spring means (10) at the coupling point of the spring means (10) is coupled to the test body (7) (FIG. 4).

13. Device according to one of claims 9 to 12, characterized in that the vibration exciter (9) is guided in the direction of vibration by means of a guide device, preferably formed by a suspension device (17) or a linear guide (16), such as a sliding bearing (Fig , 9).

14. The device according to claim 9, characterized in that the test body (18, 19) with an end portion on the test frame (1) and with the other end portion via the loading device (11) is coupled to the test frame (1), and that the vibration exciter (9) is coupled via the spring device (10) to the test frame (1) and acts on the test body (18, 19) between its end regions, wherein the vibration exciter (9) is preferably designed as a mechanical vibration exciter (FIG. 10).

15. The device according to claim 9, characterized in that the test body (20) is coupled with its end portions with the test frame (1) and between its end regions via at least one spring device (10), on the one hand on the test frame (1) is fixed and on the other is coupled via the loading device (11) with the test body (20), is subjected to bending (Fig. 12).

16. The apparatus according to claim 15, characterized in that the vibration exciter (9) with the test body (20) optionally with the interposition of balancing masses (12) is coupled (Fig. 12).

17. Device according to one of claims 9 to 16, characterized in that the spring device (10) is formed by at least one tension member or pressure member.

18. Device according to one of claims 9 to 17, characterized in that between the test frame (1) and the vibration exciter (9), a damping device (22) is provided.