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Item type:Publication, Access status: with files , Investigation of constraint effect on fatigue crack growth rate measurements(2018); For the purpose of reliable life prediction the fatigue crack growth behaviour of a material has to be well-known. Therefore standardized fatigue crack growth tests are made with test specimens of the material. The obtained fatigue crack growth data is taken as material specific data and is given without any information of the test conditions and used specimen geometry. However, in several studies a geometry dependency of the test specimen on the fatigue crack growth data is found. Hence in this investigation experiments on fatigue crack growth behaviour are made with two different specimen geometries, the middle tension specimen M(T) and the compact (tension) specimen C(T). The direct current potential drop (DCPD) method is used to determine the crack lengths which is calibrated with the aid of beach marks and crack detection gauges. Two different configurations of the DCPD method are implemented to gain acceptable results. With the obtained data fatigue crack growth curves are established which are analysed regarding the geometry influence of the used test specimens. Discrepancies in the fatigue crack growth curves between the tested specimens are found. With these findings an approach is tested to create a material curve which is independent of the specimen geometry. However, this approach is not leading to satisfactory results. The implementation of the DCPD method in its main configuration on the used experimental setup proves to be applicable for fatigue crack growth tests on different geometries and will be used in further studies at low temperatures.Publicationtype: Master Thesis332 1320 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Fatigue crack growth rate measurements in GL D36 grade welded structural steel(2018); In this master thesis, the differences in the crack growth behavior of welded and base material is investigated. The direct current potential drop method is used to document the crack propagation. The material are tested using middle tension samples. The test is carried out with cyclic loading, a force ratio of 0.1 and a frequenze of approximately 33 Hz. Based on the test result a calibration curve is created using the Johnson formular. With the help of crack and strain gauges the calibriation curve is validated. It is shown that the Johnson formular generates an accurated description of the crack propagation. The calibration curve gives an electric current independent comparision of crack propagation and voltage drop. The conducted work in this thesis has shown that the welded material has a higher crack resistance, then the base material. The difference is especially apparent for low stress intensity factor. The findings in this thesis can be used to investigated welded and base material at low temperatures.Publicationtype: Master Thesis685 885