In Chapter B.7 the influence of ageing to the critical energy release rate is described which was investigated experimentally for seven modifications of basic and technical epoxy and polyurethane adhesives. It is discussed that the main contribution to the critical energy release rate is provided by rate dependent deformation mechanisms altered by the (mainly reversible) influence of water. The local dissipative deformation shields the crack tip from the applied load. The amount of shielding and the measured critical energy release rate depend on the volume of the deformation zone. The deformation zone size is determined by the competition between the loading rate, the deformation rate of the adhesive, the crack propagation rate, and the thickness of the adhesive layer. Each modification of adhesive which was investigated shows its characteristic behaviour. A quantitative understanding on the basis of generic mathematical fracture mechanical models is hindered by the violation of the assumption of homogeneity and isotropy since the dissipative mechanisms probably are activated in the entire region between the adherends in the direction of thickness.

The Tapered Double Cantilever Beam (TDCB) test is an established method to determine the critical strain energy release rate of adhesives in mode I. Provided that the adherends stay elastic, that the adhesive layer is not too flexible and that inertia effects can be neglected, the experiment allows to identify the work required by the adhesive layer per area of crack growth. The evaluation according to the standard does not permit to distinguish between different sources of dissipation in the adhesive layer or at the adhesive-adherend interfaces, though. This paper proposes two approaches to gain a more detailed understanding of the dissipation in mode I crack growth of adhesive layers.The first investigation method uses detailed finite element simulations of the TDCB test based on an elastic-plastic adhesive material model derived from tests on bulk specimens. The simulation is used to distinguish between the work required for the plastic deformation of the entire adhesive layer and the work consumed by the crack and the adhesive in its vicinity. The dependence of this distribution of work on the adhesive layer thickness is studied. The second approach adds a temperature measurement by an infrared camera to the TDCB test. This measurement allows observation of the thermo-elastic effect in the adhesive layer and of the heat generation at the crack. Finally, the results of the two approaches are employed to estimate the energy balance in the TDCB test. The application to a ductile epoxy adhesive shows the feasibility of the proposed methods. (C) 2016 Elsevier Ltd. All rights reserved.

The mechanical properties of crash-optimized adhesive BETAMATE 1496V are characterized over a wide range of strain rates. The information gathered from the mechanical tests are used for developing a fully rate-dependent constitutive law for cohesive interface elements considering both, the strain rate dependency of the initiation stress and the strain rate dependency of the fracture toughness. The model is calibrated and verified against experimental data for tapered double cantilever beam (TDCB) and tapered end notched flexure (TENF) tests. Finally, the model is validated against quasi-static and dynamic experimental results on an adhesively bonded T-joint. The numerical predictions show good correlation with the experimental results. (C) 2014 Elsevier Ltd. All rights reserved.

Presently, there are various cohesive zone models implemented in LS-DYNA. The simplest one consists of a bi-linear traction separation-law in both modes I and II. Further models allow more complicated shapes of the traction-separation law, such as the material model of Tvergaard and Hutchinson or the General Cohesive Zone Model. However, none of these implemented models consider rate-dependency or effects of plasticity.

Für den Offshore-Windenergieanlagenbau sind aufgrund der zunehmenden Leistung einerseits gröβere und schlankere Rotorblattstrukturen erforderlich, andererseits ist der Einfluss besonderer Umgebungs- bedingungen zu berücksichtigen. In diesem Kontext interessieren die Ermittlung von Wöhlerlinien für neue am Markt verfügbare Faserverbundmaterialien, die Temperatur- und Feuchtigkeitseinflüsse auf die Schwingfestigkeit sowie die Weiterentwicklung und Validierung von Konzepten zur Bauteilberechnung.

Der verschärfte Wettbewerb zwingt zu immer kürzeren Produktentwicklungszyklen. Vorversuche und Bauteilerprobung sind aus Zeit- und Kostengründen auf das unbedingt erforderliche Mindestmaß zu begrenzen. Nach dem Vorbild des rechnergestützten Designprozesses bei der Produktentwicklung besteht deshalb die Forderung, eine weitgehend rechnergestützte Dimensionierung von Bauteilen und -gruppen zu realisieren. An zwei ausgewählten Beispielen aus dem Schiffbau werden im Folgenden die Möglichkeiten numerischer FE-Analysen bei der Auslegung von Klebverbindungen vorgestellt und diskutiert.

Effects of the bond line thickness on the fracture mechanical behaviour of structural adhesive joints