Gerald Ernst

In this paper, a novel orthotropic layer based failure criterion for modelling progressive failure of non-crimp fabrics is presented. The strength parameters and stiffnesses needed for this failure criterion are obtained from virtual material tests. Therefore, a finite element multiscale algorithm is used to model the effect of lower scale inhomoge...

In this article, a constitutive formulation of a transversely-isotropic material and failure model for fiber-reinforced polymers is presented comprising pre-failure material nonlinearities, a novel invariant based quadratic failure criterion (IQC) as well as post failure material softening. The failure surface of the IQ criterion is assumed to take...

The experimental determination of stiffness and strength of textile composites is expensive and time-consuming. Experimental tests are only capable of delivering properties of a whole textile layer, because a decomposition is not possible. However, a textile layer, consisting of several fiber directions, has the drawback that it is likely to exhibi...

For the strength analysis of unidirectional laminae an unit cell approach is illustrated. The unit cell is modeled with an approximate voxel mesh instead of a conventional mesh. Strengths are determined with continuum damage mechanics. A fracture energy formulation is applied to alleviate mesh dependency in the softening behavior. For direct loads...

For the prediction of composite strengths with representative volume elements (RVE) a thorough understanding of the ongoing failure mechanisms is needed. This again is influenced by the manufacturing process. Therefore, a brief overview on fabrication, material characteristics and failure mechanisms for Prepreg and textile composites is given in th...

Industrialised infusion processes enable a cost-effective possibility to produce textile composite structures compared to pre-impregnated composite systems (Prepregs). Particularly with regards to high performance structures one has to be familiar with the material behaviour and the failure characteristic to apply fibre reinforced composites profit...

Kraftfelder sind eine bewährte Methode für die Berechnung atomarer Strukturen wie Kohlenstoffnanoröhren. Die Bedeutung des Auftretens von Defekten für die mechanischen Eigenschaften der Kohlenstoffnanoröhren kann mit einem auf Kraftfeldern basierenden finiten Element nachgewiesen werden. Bei einer Belastung der Kohlenstoffnanoröhren kommt es in Abh...

Inelastisches Materialverhalten ist die Folge einer st?ndigen Umordnung von chemischen und physikalischen Bindungen. Am Beispiel eines f?r Elastomerwerkstoffe entwickelten mikromechanischen Ersatzmodells wird gezeigt, dass sich auf Grundlage der rein elastischen Potentialfunktionen des Kraftfeldansatzes, also ohne Verwendung von D?mpfer- oder Reibe...

The molecular structure of a material determines its mechanical, thermal and chemical properties. Thus, to better understand characteristic mechanical properties like damping behavior or softening, in principle, one just has to model the interactions of a sufficiently large number of atoms. Various force field approaches have been proposed for that...

Like any other geometric structure or building, carbon nanotubes may break down due to either material failure or structural failure. In this paper, it is shown that the failure mechanism-of carbon nanotubes not only depends on the type and direction of loading but also on the location and number of defects. For the finite element simulations we us...

Kraftfeldansätze für die Berechnung atomarer Strukturen können in die Finite Elemente Methode eingebettet werden. Standard-Elemente sind jedoch nicht in der Lage, die Atomphysik adäquat wiederzugeben. Anhand von Berechnungen von Kohlenstoffnanoröhren wird gezeigt, dass ein neues 4-Knoten-Element geeignet ist, atomare Strukturen zuverlässig zu berec...

Zur Berechnung von Nanostrukturen wie z.B. Kohlenstoff-Nanoröhren stehen eine Reihe von Kraftfeld-Ansätzen (force fields) zur Verfügung, die sich aus molekulardynamischen Untersuchungen bzw. quantenmechanischen “ab initio” Berechnungen herleiten lassen. Sie liefern die potentielle Energie einer Struktur in Abhängigkeit von der Art und Anzahl der ch...

The complex three-dimensional structure of textile composites makes the experimental determination of the material parameters very difficult. Not only the number of constants increases, but especially through-thickness parameters are hardly quantifiable. Therefore an information-passing multiscale approach for computation of textile composites is p...

Textile composites describe a broad range of polymer composite materials with textile reinforcements, from woven and non-crimp commodity fabrics to three dimensional textiles. In a general manner textile composites are based on textile preforms manufactured by some textile processing technique and on some resin infiltration and consolidation techni...