|"Reinforced Elastomers: Fracture Mechanics, Statistical Physics and Numerical Simulations"|
September 8th - 10th, 2008 in Dresden
We thank the "Deutsche Forschungsgemeinschaft" (German Research Foundation, DFG) and the EUROMECH Society for financial and organisational support.
Both natural and synthetic elastomers are widely used in various fields such as automotive industry, medical applications and household products among others. In the industrial context, elastomers are generally reinforced with particle such as carbon black and silica. Thus, the unique properties of elastomeric parts (tires, tubes, dampers, gloves, seals, …) depend on the intrinsic properties of the rubber matrix but also on the characteristics of the reinforcing additives. Furthermore, rubber material are subjected to different loadings from which material failure can result. This failure is caused by initiation and propagation of cracks that often result in catastrophic events involving loss of life and capital, e.g. when a tire bursts or a rubber O-ring seal fails.
Physical understanding of rubber reinforcement and modelling of their mechanical response is still a challenge in fundamental research. Particularly, the improvement of design tools for rubber parts (finite element software) necessitates new investigations focused on the influence of reinforcement particles on the properties of these materials.
Moreover, the characterisation of fracture mechanical and durability features are of significant importance for the reliability and the quality of products and, therefore, are a key aspect of investigation and a central design aspect.
The goal of the Euromech Colloquium 502 was to focus on recent advances in understanding of physical, mechanical and durability properties of reinforced elastomers as well as in simulating related problems. Both, theoretical and experimental approaches were presented allowing an exchange of ideas.
There were altogether 74 participants from 14 countries, among them young scientists, researchers from rubber industry and reputable scientists such as Prof. A. G. Thomas from the Queen Mary University of London, one of the pioneers of the fracture mechanics of rubber compounds, see also the list of participants.
Reoccurring issues addressed in the 29 presentations and discussed were:
- Rubber Reinforcement
Although there are huge conceptual differences, both microscopic and macroscopic, finite element based approaches come to the conclusion that the mechanical behaviour of reinforced elastomers can only be understood by means of hydrodynamic reinforcement, i.e. the strain amplification due to the presence of hard filler, and the interaction of different filler particles.
- Interfaces and interphases
The interaction between the polymer and filler particles is relevant for the mechanical behaviour of composite materials. However, its incorporation in FE-based approaches, e.g. in form of cohesive elements for delamination problems or as graduation of interface stiffness, is mainly done in a phenomenological manner. Experimental investigations, such as NMR, neutrons scattering and mechanical measurements, give more detailed insights into the coupling between polymer and filler that can lead to more physically based descriptions.
- Fracture and fatigue behaviour
Experimental characterisation of fracture initiation and crack growth behaviour in elastomeric compounds under quasi-static, impact, sinusoidal and pulsating loading is important for the correct material selection in practical applications. Different concepts such as J-integral, essential work of fracture and tearing energy are used for characterisation. From the theoretical point of view, approaches based on Eshelbian mechanics are used for characterisation of fracture and as fatigue predictors. Furthermore, the presented phase field approach of fracture has been proven to be a promising approach in order to describe the interaction between macroscopic fields in the vicinity of the crack tip and the microscopic fracture process whose influence on the crack path is not negligible.
- Deformation and crack growth mechanisms
The elucidation of deformation and crack growth processes is essential for the understanding how structural modifications of the material influence the mechanical behaviour. Online-measurements of the strain field and the structure characterisation using scattering techniques as well as the in-situ observation of fracture processes and cavity formation and the post-mortem analysis of fracture surfaces give further insight into the proceeding mechanisms.
- Molecular dynamics of stretched polymer chains
When pre-cracked rubber samples are loaded then the polymeric chains in the vicinity of the crack tip are strongly stretched. Theoretical studies of the mechanical relaxation properties of strongly stretched chains with analytical and numerical methods and its implications for chain rupture lead to a detailed understanding of the fracture process in elastomeric materials.
- Constitutive models and finite element analysis
The design of rubber components is often accompanied by appropriate finite element calculations. The development of material models is therefore an important task. The modelling of filler-induced softening, viscoelastic and viscoplastic finite strain behaviour as well as the modelling of an inherent anisotropy were presented and can be used for large scale calculation of structural components.
In spite of the progresses in research of the behaviour of elastomeric materials, many aspects revealed in experimental and theoretical investigations are not fully understood. Hence, the colloquium offered a platform for communication and the discussion of new trends and approaches.
Download of the picture gallary of the colloquium as zip file.
Deutsches Institut für
für Polymerforschung Mainz
Institut für allgemeinen Maschinenbau
Institut für Statik und
Dynamik der Tragwerke