For the spheroidal graphite cast iron materials, also known as ductile cast iron (DCI), EN-GJS-400-18-LT and EN-GJS-450-18, different welding procedures were examined for potential repair welding. A repair weld was performed on thick cast iron plates using the optimum procedure in each case. The weld was evaluated for all areas of the welded joint (weld metal, fusion line/heat-affected zone and base metal). In addition to the metallographic microstructural analysis, the characterization of the repair weld was carried out by means of hardness distribution measurements, static tensile testing and notched bar impact testing as well as fracture mechanics investigations under static and under cyclic loading in a wide load ratio range. On this basis, a generalized description of cyclic crack growth could be made according to the NASGRO® MODEL. NASGRO® is a fracture mechanics and fatigue crack growth software. In accordance with the possible operating conditions of repair-welded, thick-walled components, the static and impact tests were performed in the temperature range down to $$-$$ - 40 $${}^{\circ }\text {C}$$ ∘ C .

Kurzfassung Der vorliegende Beitrag gibt einen Überblick zu den bruchmechanischen Prüfmethoden bei statischer, dynamischer und zyklischer Beanspruchung. Die prinzipielle Vorgehensweise bei der experimentellen Ermittlung der entsprechenden bruchmechanischen Kennwerte wird erläutert. Auf die zurzeit aktuellen Prüfstandards wird aufmerksam gemacht. Die Kennwertermittlung wird am Beispiel spezieller Werkstoffe demonstriert. Auf bestehende Korrelationen zwischen den bruchmechanischen und den konventionellen mechanischen Kennwerten wird hingewiesen. Die Auswertung des Schrifttums erfolgt unter Hinweis auf spezielle, außerhalb der Prüfstandards zum Einsatz kommende Prüfmethoden und auf Beispiele für die geforderte und erfolgreich praktizierte bruchmechanische Bauteilbewertung.

Fracture mechanics test methods for determination of material parameters under static, cyclic and dynamic loading. The present paper gives a review about the fracture mechanic test methods for static, dynamic and cyclic loading. The principle procedure for the experimental determination of the corresponding fracture mechanic parameters will be commented. The current standards will be pointed out. The determination of the characteristic values will be demonstrated by means of specific materials. Correlations between fracture mechanically and conventionally parameters will be shown. The score of the literature was carried out in direction to specific testing methods outside of the testing standards and also in direction to examples of required and successful realised fracture mechanical validation of components.

The determination of dynamic crack resistance curves from single specimen fracture tests requires information about the crack advance during the experiment. Here, attention is focused on crack resistance curves for nodular cast iron based on experimental data from instrumented Charpy tests. In order to estimate the actual crack length a key curve method (KCM) is employed. On the other hand, the Charpy impact tests were realized numerically using finite element calculations in conjunction with a continuum damage model (CDM) to simulate ductile crack growth. The parameters of the CDM model were determined from the experimental data of single specimen fracture tests. Equivalence between the experimental and the numerical realization of a fracture test was ensured by validating the predictions of the numerical simulations by means of low blow fracture tests. Comparison between the crack advance predicted by the numerical simulations and the results obtained using the proposed KCM shows a sufficiently well agreement with the actual crack length. Furthermore, crack resistance curves obtained from single specimen tests using either standard estimation schemes in conjunction with the KCM or numerical simulations are compared with the predictions based on low blow fracture tests.

The evaluation of fracture mechanics properties at intermediate strain rates can be carried out on the basis of different standards. The starting point of the lecture is a comparative evaluation of the relevant standards and test procedures [1, 2, 3, 4]. The aim of the fracture mechanics test at intermediate strain rates are not only generally materials characterizations but often the portability of the determined parameters on bigger sizes in case of evaluation of real components. In this situation the definition of component transferable material parameters is an important problem. In this context the crack initiation point gets an all-dominant importance [5, 6]. In case of multiple specimens testing typically the definition of the crack initiation point based on the results of stretch-zone measurements.

Für die konstruktive Auslegung stationär zyklisch beanspruchter Maschinenteile werden heute im allgemeinen die aus einachsigen Wöhlerversuchsreihen ermittelten zyklischen Werkstoffkennwerte verwandt. Bei der bedeutendsten Werkstoffgruppe, den Stählen, werden der Beanspruchungsgeometrie (Zug-Druck, Biegung, Torsion) zugeordnete Kennwerte ermittelt, die "dauerfest", d.h. > 2*106…107 Lastzyklen, ertragen werden. Hinsichtlich des Einflusses einer in gleicher Richtung wirkenden statischen Beanspruchung auf die zyklischen Festigkeitswerte existiert ebenfalls eine umfangreiche Datenbasis. Zur Veranschaulichung der Wirkung von einachsigen gleichgerichteten statischen Beanspruchungen auf die zyklischen Festigkeitswerte hat sich die Darstellung in den Diagrammen nach Smith oder Haigh bewährt. Abbildung 1 zeigt das Haigh-Diagramm für Grauguß mit Lamellengraphit GG-22 (nach [1]).

For a new generation of thermomechanically rolled high-strength structural steel grades of qualities S355ML to S460ML, with a plate thickness up to 120 mm, an excellent toughness behavior based on very fine and highly homogeneous grain is proven by metallographic and conventional as well as fracture mechanical valuation. For high plate thickness and other factors promoting brittle fracture such as low use temperature and impact loads, this results in a strong argument for using such high-toughness steel grades.