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One notch specimens (dt.: Einlochproben) Show image information

One notch specimens (dt.: Einlochproben)

Fatigue Life Manipulation

Technical components are subjected to various stresses during operation. They are responsible for the limited service life of the components. Fatigue cracks are often observed far below strength limitations. The life time in components under fatigue loading is divided into crack initiation and fatigue crack propagation. Using crack growth retardation methods, substantially higher fatigue life can be achieved. Figure 1 shows the effect of notches on the life time during crack growth period. The reason for the difference in life time can be found in the crack growth behavior during initiation. The holes positioned in the crack path lead to a new crack initiation at each notch. The significantly higher number of load cycles within the crack initiation period (compared to the number of cycles during crack propagation) will be used to manipulate the total life time.

Figure 1: Schematic illustration of life time manipulation caused by notches

The main goal of this project is to extend the total life time of components. Using intrinsic advantages of additive manufacturing processes, notched parts will be produced in order to manipulate the fatigue life, Figure 2. It is expected that due to changes in stress distribution caused by the notch the crack growth behavior will be influenced. By variations of the various notch forms, notch sizes and notch orientations basic knowledge about crack behavior in SLM processed components will be obtained.

Figure 2: Schematic illustrations of notch form, notch position and notch orientation for life time manipulation

At the beginning, preliminary studies regarding the simulation of unnotched and notched structures considering the period of crack initiation and fatigue crack propagation were performed. The effect of heat treatment on lifetime was studied by simulations of crack growth in solid components. In this case, the software tool NASGRO was used for lifetime calculations. The results of the components’ lifetime simulations show the absolute necessity of heat treatment. Depending on the maximum value of cyclic loading, the residual lifetime can be increased by the factor 34 and 17 respectively. In order to perform the simulation of notched parts including crack initiation and fatigue crack propagation, -the software tool Franc/FAM was employed.

In the first step of experimental research, preliminary tests on modified CT-specimens containing one hole will be performed, Figure 2. In this step, different parameter like hole size or hole position will be examined. Furthermore, the number of holes will be elevated to a row of holes, positioned inside the specimen. In the next step, samples with different notch positions will be produced in order to investigate life time manipulation due to crack deflection. After that, elongated holes with different orientations will be tested in order to investigate life time manipulation due to different crack deflection situations. In the last step, the number of rows will be heightened to an array of holes. The findings of this test series will be used to describe the crack growth performance in high-grade notched structures.

Further project information
Project statusIn progress
Project duration24 month

50 % Land of North Rhine-Westphalia
50 % DMRC industry partner

Project managerProf. Dr.-Ing. Hans Albert Richard
Project coordinator

Dr. Dieter Schwarze (SLM Solutions GmbH)
Dr. Danzig (EOS GmbH)
Peter Keller (EOS GmbH)
Sylvia Monsheimer (Evonik Industries AG)
Martin Schäfer (Siemens AG)


Scientific staff

M. Sc. Wadim Reschetnik

Involved chairsInstitute of Applied Mechanics (FAM)
+49 5251 60-5324
+49 5251 60-5322
IW 1.875

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