This paper deals with numerical methods, developed to analyze plane stationary cracks in piezoelectric structures under dynamic electromechanical loading conditions. In the first part an explicit finite element scheme is presented, which has been developed to solve the transient coupled electromechanical boundary value problem. A special technique is implemented in the algorithm, accounting for the limited electrical permeability of the crack. In contrast to well known algorithms for static calculations it does not require any iteration. In order to calculate dynamic stress and electric displacement intensity factors for arbitrary crack configurations, the interaction integral is generalized for electromechanical problems. The efficient applicability and the high accuracy of the implementations are demonstrated by numerical examples, giving insight into several effects occuring with dynamically loaded cracks in piezoelectrics.

This paper deals with the calculation of the J-integral for electrically limited permeable cracks in piezoelectrics. The electromechanical J-integral is extended to account for electrical crack surface charge densities representing electric fields inside the crack. To avoid the costly implementation of the line integral along the crack faces, an alternative is proposed replacing the line integral by a simple jump term across the crack faces. Previous work by other authors related to the same subject is critically illuminated. The derivation was inspired by the Dugdale-Barenblatt cohesive zone model and yields an expression containing solely the local jump of displacements and electric potentials across the crack faces. This approach is shown to be exact for the Griffith crack. Numerical examples give evidence that the simplified approach works well for arbitrary crack configurations too.

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In order to assess the safety against fracture of nuclear shipping casks, drop tests are simulated using the finite element method. The simulations are based on a global model without defects. From the results positions are derived at which a crack initiation from a defect would be most likely. At each of these positions a submodel with a crack is inserted. The insertion of the crack changes the stiffness and therefore the stress of this region. Depending on the submodel size the calculated fracture mechanics parameters deviate from the reference value found without using the submodel technique. The objective is to determine this deviation only from one submodel. A practicable method for the determination of the required submodel size is developed calculating the difference of the traction vector between the submodel with opened and with closed crack. Its scalar product with the weight function results in the contribution of the submodel boundary to the deviation. Integrated over the boundary it yields the deviation of the submodel. The shape of the submodel can be optimized by expanding sections of the submodel boundary with a high contribution.

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Maintenance work and extension of gas pipelines have to be done mostly with the pipeline being in operation to ensure continuous network coverage. Therefore, in-service welding operations are inevitable for both situations. The present paper focuses on a circumferential fillet weld connecting a high-pressure gas pipeline with a T-fitting, which is suitable for stoppling and the construction of connection branches. Against the background of safety assessment and process optimization the welding procedure is investigated by means of experiment and simulation. The simulation is based on the finite element method and predicts the temperature field as well as the evolution of the microstructure and the residual stresses during welding and cooling. The heat input during welding is modeled using the double ellipsoid heat source by Goldak, which is adapted to multi-pass welding and implemented in the commercial software ABAQUS. The microstructure evolution is analyzed by a phase transformation model based on the Avrami equation. A subsequent stress analysis provides results regarding the residual stresses. The simulation is validated by welding experiments dealing with a three-pass fillet weld. The experimental and numerical results are presented and compared by means of macrosections and thermocouple measurements.