DD221553A1 - TESTING PROCEDURE FOR THE SURFACE TREATMENT OF TRIBOLOGY-BASED MATERIAL SURFACES - Google Patents

Abstract

The invention relates to a test method for the surface fatigue tendency of tribologically stressed material surfaces. The aim is to provide a test method preferably for low-cycle surface fatigue, which makes it possible to specify the surface fatigue tendency of materials for defined load stresses sufficiently precisely with a critical number of oscillatory cycles in order to be able to assess materials significantly more differentiated in their surface fatigue tendency. The essence of the invention is that a Gegenkoerper, consisting of two rigidly attached to a physical pendulum spheres, on a flat base, which forms the Pruefflaeche, by constant pendulum oscillations in an always the same, delimited Pruefbereich at defined load voltages with a continuously Changing ratio between normal and shear stresses produced, the beginning of Oberflaechenermüdung is displayed in the form of cracking by a change in the electrical contact resistance between the base and counter body and the number of oscillations required up to this time as a function of the load as a measure of the surface fatigue tendency of Material is determined.

Description

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embodiment

The invention will be explained below with reference to an embodiment with reference to a drawing. The drawing shows the schematic representation of a device for carrying out the test method. The test procedure compares the surface fatigue tendency of two wear protection layers. A first sample is a base body 3 made of a 210Cr46 steel on which a titanium nitride wear protection layer has been deposited to form a test surface 2. A second sample is a base body 3, which consists of a steel C45, which received a protective layer by gas carbonitriding, which also forms a test surface 2. According to the invention now by means of two, with a physical pendulum rigidly mounted side by side balls, which consist of a low-cyclic load bearing bearing steel and form a counter body 1 and 3 with the base material pairing result, the examination of Oberflächenermüdungsneigung carried out such that the counter body placed on the test surface 2 and loaded with a load m. The pendulum is deflected by an angle φ and vibrated, the amplitude is kept constant by non-contact pulse transmission, thereby always a same, delimited test area of the test area 2 at defined load voltages, that is, with continuously changing ratio between normal and shear stress is checked.

The number of oscillatory games is registered via a conventional counting device. Likewise, an electrical contact resistance between the rolling counter-body 1 and the base body 3 is determined.

The onset of fatigue, that is, the onset of cracking, is indicated by a change in electrical contact resistance. The critical number of scores required until then is registered. From the distance of the fatigue cracks from the zero position of the pendulum that originated on the test surface 2 and can be clearly seen in the microscope, the normal forces F _n and tangential forces F _T acting therefrom and a comparison stress can be calculated via geometric relationships.

By repeating the modified load test m, a dependence of the critical number of cycles on the load is determined, which is the expression of the surface fatigue tendency. For the protective layers to be compared were z. For example, for a comparison stress of 600 MPa for the titanium nitride layer, a critical number of cycles of 8500, while for the protective layer, which was generated by gas carbonitriding, only 1800 cycles were required to the onset of fatigue.

Claims (1)

-1- 258 239 4 Invention claim: Test method for the surface fatigue tendency of tribologically stressed material surfaces using known devices, such. B. a physical pendulum, characterized in that in a tribosystem, consisting of a counter-body (1) consisting of two rigidly mounted with a pendulum balls attached side by side, consisting of low-cyclic stress non-fatiguing material is formed, wherein the counter body (1 ) provided with a defined load (m), set in constant oscillations, a basic body (3) on its test surface (2) in a constant, delimited test area, with a continuously changing relationship between normal and shear stresses low cyclic stressed and during the test the beginning of the surface fatigue, that is, the crack initiation in the test area (2) is indicated by an abruptly changing electrical contact resistance or by means of ultrasound or acoustic emission measurements as a function of a critical number of cycles and load. For this 1 page drawing field of use The invention relates to a test method for the surface fatigue tendency of tribologically stressed material surfaces, preferably for coated or uncoated materials used in the area of low-cycle surface fatigue. Characteristic of the known technical solutions It is known to characterize the surface fatigue tendency of tribologically stressed material surfaces in that the criterion of fatigue is the formation of cracks and pittings. The test is carried out on known chassis dynamometers, e.g. carried out according to SUP 343190, in which the specimens, usually under constant load, so long pressed against each other, until the surface material destruction by cracks and pittings occurs, the number of sustained to fatigue oscillating games (load change) at the respective stress than Measure of fatigue tendency is given. The disadvantage here is that the time of cracking due to a mostly indirect observation of the contact surface is detected incorrectly, which in turn affects the error size when specifying the critical number of cycles game. Another disadvantage is that the test areas constantly change, that is, always other areas of the material surface come into contact with each other. Another disadvantage of the test is that the load stresses acting on the surfaces are indefinable because of the complicated sliding and rolling movements of the test specimens or can only be identified quantitatively with difficulty or not separately. _A Also known are test methods for investigating the frictional fatigue of materials, e.g. the use of a cyclometer. The difference to the o.g. Roller test stands is that a test piece does not roll on the material surface to be tested, but repeatedly slides over them. After certain time intervals, a profile curve is removed from the surface in order to detect the material destruction due to fatigue from the surface profile. The disadvantage is that in this case the time of destruction is detected only inaccurate, constantly changing the test areas, but above all, that the also acting wear mechanisms of abrasion and adhesion are not detected separately. There are also dynamic test methods, z. As for press joints, known in which the Oberflächenermüdungsneigung is tested such that the surfaces in the press-fit surfaces are claimed by low-cycle shear stresses until they move against each other. Even in this test, only a global statement on fatigue is made because the onset of cracking is not detected, but only a final state of fatigue is detected. Object of the invention The invention aims to determine the surface fatigue tendency of tribologically stressed material surfaces, preferably at low cyclic surface fatigue, in such a way that in an always the same demarcated test area at defined load voltages required for surface fatigue, specified critical number of cycles sufficiently and thus materials in their Oberflächenermüdungsneigung quantitative and be judged differentiated. Explanation of the essence of the invention The invention has the object of determining the surface fatigue tendency of tribologically stressed material surfaces, preferably for materials used in the field of low-cycle surface fatigue, in an always identical, demarcated test area, with defined load stresses and a continuously changing ratio between normal and shear stresses in order to determine the influence assessing the load ranges, with the critical number of oscillations required before the crack initiation begins. This object is achieved according to the invention using known devices, such. B. in the form of a physical pendulum, which is placed on a material surface to be tested, with two rigidly attached to a physical pendulum balls attached, which do not tire in the low cycle stress, serve as a fulcrum, achieved in that such a pendulum that with is provided with a defined load, is set in free vibration, whereby a tribosystem is simulated, which corresponds to contact ratios of a ball-level pairing. The examination of the surface fatigue tendency is always carried out in a same, delimited test area at defined load voltages, that is, as a result of an oscillating motion of the ball on the plane, with continuously changing relationship between normal and shear stresses. To detect the onset of cracking, which is considered a hallmark of surface fatigue, electrical contact resistance is constantly registered by the ball / plane contact surface. If first cracks form, this is indicated by a significant change in the resistance. Depending on the load, the number of oscillating cycles required up to this moment is a measure of the surface fatigue tendency of tribologically stressed material surfaces. Furthermore, the Rißbildunasbeainns Anzeiae can also take place by means of ultrasound or Schallemissionsuna.