PSI - Issue 13

Markus Könemann et al. / Procedia Structural Integrity 13 (2018) 914–919 Markus Könemann/ Structural Integrity Procedia 00 (2018) 000–000

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1. Introduction Thanks to the further development of modern steels, steel producers are nowadays in a position to offer a large portfolio of possible material property combinations. However, these increased possibilities in the selection of steels are contrasted by older regulations, which hinder the use of these steel concepts with inefficient material parameters (Brinnel, 2017). Another problem is that high-strength steel grades are often produced in thicknesses exceeding 2 mm. For this reason, the possibilities of demonstrating sufficient toughness, for example by Charpy impact tests or more complex fracture mechanic tests, are no longer available. This means that a catastrophic failure of the manufactured components in a brittle fracture cannot be excluded. The only way to qualify components for use is to perform complex and expensive component tests. These circumstances mean that promising material developments cannot be used in industrial applications because on the one hand, values are missing that allow the application of current regulations. On the other hand, there is also a lack of test procedures that can be examined quickly and inexpensively. In order to counter these obstacles, a new method for the impact toughness testing of thin sheets and thin-walled structures has been developed in recent years at the Steel Institute at RWTH Aachen University. The aim of the new process is to maintain the advantages of the Charpy impact test (simple and rapid applicability, reproducibility of the results) and at the same time to qualify it for more relevant stress situations by using damage mechanics methods. The tensile impact test presented in this article can be used to test the impact toughness of sheet metals up to a sheet thickness of 1.5 mm in an impact pendulum similar to the Charpy-V-notch test. The method is based on an already standardized impact test for plastics (DIN 53448), which has been adapted for the examination of steel samples. Furthermore, a sample catalogue was developed which makes it possible to adjust the stress state of the samples in such a way that it corresponds to that of the components to be manufactured. With the new process, it is thus possible to carry out a component-oriented examination of the material properties, which makes it possible to exploit the full performance potential of modern materials in order to contribute to the conservation of resources. 2. Experimental setup The new method for analyzing the toughness properties of thin sheets and thin-walled structures is based on the requirements set out in DIN 53448 for investigating the toughness of plastics. An impact pendulum tester is used to carry out the test, which is equipped with a 50 J impact hammer, Fig. 1.

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Fig 1. (a) Impact pendulum with new hammer for tensile impact test, (b) clamping system with fixed specimen

In contrast to the Charpy impact test the specimen is not bent to fracture, but rather destroyed by tensile stress. The newly designed specimen grips have been designed in such a way that they are able to withstand the high forces that occur with steels. Furthermore, the sample can be tempered in the new test concept, which makes it possible to test the material properties at different temperatures. As in the Charpy impact test, a temperature dependence of