Showing papers by "Michael May published in 2013"

Investigation of Static and Dynamic Failure Behaviour of Composite T-Joints

Abstract: An experimental and numerical study of the failure behaviour of composite T-joints under quasistatic and high-rate dynamic loads is presented, including the investigation of different joint designs to increase damage tolerance and failure resistance. Three different T-joint designs using the same carbon fibre composite base material were used in this study. Two pure composite solutions and a hybrid design with arrow head-shaped metallic reinforcement pins in the through-thickness direction are presented. Specimen manufacturing and testing is described in detail. The test campaigns covering 0° T-pull and 30° T-bending tests were conducted under quasi-static and high-rate dynamic conditions in order to assess potential strain rate effects. The hybrid solution with the pin-reinforcement showed significantly increased post-damage load levels and energy absorption with the pins being pulled out of the laminate under large global deformations. The utilisation of a modern toughened epoxy resin in comparison to a conventional untoughened resin also showed significant improvements. In addition to the experimental test campaign, numerical simulations with the explicit Finite Element code LS-DYNA were conducted on micro, meso and macro level. The models were validated against the test results and applied to a ballistic impact simulation of a composite fuel tank structure under hydrodynamic ram loading.

Improvements to the Prototype Micro-Brittle Linear Elasticity Model of Peridynamics

Abstract: This paper assesses the accuracy and convergence of the linear-elastic, bond-based Peridynamic model with brittle failure, known as the prototype micro-brittle (PMB) model. We investigate the discrete equations of this model, suitable for numerical implementation. It is shown that the widely used discretization approach incurs rather large errors. Motivated by this observation, a correction is proposed, which significantly increases the accuracy by cancelling errors associated with the discretization. As an additional result, we derive equations to treat the interactions between differently sized particles, i.e., a non-homogeneous discretization spacing. This presents an important step forward for the applicability of the PMB model to complex geometries, where it is desired to model interesting parts with a fine resolution (small particle spacings) and other parts with a coarse resolution in order to gain numerical efficiency. Validation of the corrected Peridynamic model is performed by comparing longitudinal sound wave propagation velocities with exact theoretical results. We find that the corrected approach correctly reproduces the sound wave velocity, while the original approach severely overestimates this quantity. Additionally, we present simulations for a crack growth problem which can be analytically solved within the framework of Linear Elastic Fracture Mechanics Theory. We find that the corrected Peridynamics model is capable of quantitatively reproducing crack initiation and propagation.

Berechnung nach dem Kohäsivzonenmodell (Teil 1)

Abstract: Im Laufe der vergangenen Jahre wurden diverse Modelle zur Beschreibung von geklebten Verbindungen entwickelt [1, 2]. Ein interessanter, numerisch effizienter Ansatz zur Beschreibung klebtechnischen Versagens ist die Verwendung sogenannter Kohäsivzonenmodelle. Da allerdings bisher eine mögliche Verzerrungsratenabhängigkeit der Schädigungsinitiierungsspannung und Bruchenergie keine Berücksichtigung fand, wurde dies jetzt gründlicher untersucht.

Berechnung nach dem Kohäsivzonenmodell (Teil 2)

Abstract: Ein numerisch effizienter Ansatz zur Beschreibung klebtechnischen Versagens ist die Verwendung sogenannter Kohäsivzonenmodelle. Im Rahmen eines Forschungsprojektes wurde eine mögliche Verzerrungsratenabhängigkeit der Schädigungsinitiierungsspannung und Bruchenergie untersucht. Nach Beschreibung der Modellansätze und nötigen Experimente in der Ausgabe 7-8, S. 32, geht es im Folgenden um die Parameteridentifikation und Validierung.