Fatigue Performance of High- and Low-Strength Repaired Welded Steel Joints

Large portions of infrastructure buildings, for example highway- and railway bridges, are steel constructions and reach the end of their service life, as a reason of an increase of traffic volume. As lifetime extension of a commonly used weld detail (transverse stiffener) of these structures, a validated approach for the weld repair was proposed in this study. For this, welded joints made of S355J2+N and S960QL steels were subjected to cyclic loading until a pre-determined crack depth was reached. The cracks were detected by non-destructive testing methods and repaired by removal of the material around the crack and re-welding with the gas metal arc welding (GMAW). Then, the specimens were subjected to cyclic loading again. The hardness, the weld geometry, and the residual stress state was investigated for both the original- and the repaired conditions. It was determined that nearly all repaired specimens reached at least the fatigue life of the original specimen

Fatigue Performance of High- and Low-Strength Repaired Welded Steel Joints

Large portions of infrastructure buildings, for example highway- and railway bridges, are steel constructions and reach the end of their service life, as a reason of an increase of traffic volume. As lifetime extension of a commonly used weld detail (transverse stiffener) of these structures, a validated approach for the weld repair was proposed in this study. For this, welded joints made of S355J2+N and S960QL steels were subjected to cyclic loading until a pre-determined crack depth was reached. The cracks were detected by non-destructive testing methods and repaired by removal of the material around the crack and re-welding with the gas metal arc welding (GMAW). Then, the specimens were subjected to cyclic loading again. The hardness, the weld geometry, and the residual stress state was investigated for both the original- and the repaired conditions. It was determined that nearly all repaired specimens reached at least the fatigue life of the original specimen

Influence of Internal Imperfections on the Fatigue Resistance of Cast Steel - Testing Methodology

Tensile fatigue specimen of G20Mn5 and G22NiMoCr5-6 were tested to quantify the influence of internal defects on the fatigue resistance of cast steel components. Defects with varying sizes, geometric shapes and distribution were enforced by influencing the solidification and recorded by computer tomography (CT). Besides the characteristics of the detected cavities, the surrounding fungoid microstructure is classified and evaluated. Later the specimens were tested under cyclic tension and S/N-curves are derived. These data form the basis for extensive numerical simulations of the damage process and the crack growth of every individual specimen. Both processes are affected by the local multiaxial stress states and have their origin in the inside of the specimen. For validation, knowledge of the crack initiation time and propagation properties are essential. Therefore, all specimens respectively the properties of the internal defects are monitored during testing with three different state-of-the-art non-destructive testing (NDT) methods. Background and application of these NDT techniques are described within this paper. Finally, fracture surface analyses show different failure modes and provide further information for model validation

Anwendungspotential von Laserstrahl- und Laserhybridschweißnähten für Stumpfstoßverbindungen ultrahochfester Feinkornbaustähle

Im Kranbau und verwandten Industriebereichen werden hoch-, höchst- und ultrahochfeste Feinkornbaustähle eingesetzt und in Konstruktionsdetails als Blechbauteile häufig durch manuelles oder teilautomatisiertes MAG-Schweißen gefügt. Die Festigkeit der Schweißverbindung erreicht dabei nicht die Grundwerkstofffestigkeit von ultrahochfesten Feinkornbaustählen (Streckgrenzen e 1100 MPa), da ein niederfester Schweißzusatz (sog. undermatching) eingesetzt werden muss. Des Weiteren wirken sich insbesondere die schweißprozessbedingt entstehenden metallurgischen sowie geometrischen Kerben negativ auf die Schwingfestigkeit aus. Deshalb werden gegenwärtig in höchstbeanspruchten Bereichen, wie beispielsweise in zugbeanspruchten Zonen eines Teleskopauslegers, konstruktiv aus Sicherheits- und Festigkeitsgründen keine Schweißnähte platziert. Mit Hilfe der hier untersuchten Laserschweißprozesse, d. h. Laserhybrid- und Laserstrahlschweißen, ist die Möglichkeit gegeben, die Festigkeit solcher Schweißverbindungen reproduzierbar zu steigern. Dies wird an stumpfgestoßenen Blechen aus S1100QL und S1300QL mit einer Dicke von 8 mm ohne und mit Blechdickensprung auf 6 mm Blechdicke überprüft. In Verfahrensprüfungen zeigen sich als Vorzüge u. a. ein geringer Schweißverzug, insbesondere für das Laserstrahlschweißen, eine geometrisch optimierte Nahtausprägung und eine geringere Anzahl von Unregelmäßigkeiten, wenn eine dem Prozess entsprechende Nahtvorbereitung erfolgt. Das Festigkeitspotential dieser Verbindungen wird sowohl unter statischer Beanspruchung als auch anhand erster Schwingfestigkeitsergebnisse gezeigt. Diese erstrecken sich entsprechend der Beanspruchungssituation im Kranbau bis in den Kurzzeitfestigkeitsbereich