Among the different classes of materials, i.e. metals, concrete, wood, polymers etc., few materials face the same world-wide increase in demand and use as polymers do. There are two main reasons for the current growth:
- Production of artificial polymers (in contrast to rubber and other natural polymers) has been possible for some decades only, and it takes time for a rather new class of material to be accepted as an alternative to the materials traditionally used. Now, it is time for polymers to challenge the existing design solutions.
- Polymers have attractive properties: cheap, easy to form, low density, large ductility etc.
Polymers are promising for use in several applications, and of particular interest for the CRI programme, such materials may have excellent energy absorption characteristics. The experience in using polymers in impact protection systems, however, is limited, and there are several challenges which call for research. One of the most obvious is the lack of robust material models in commercial finite element codes, which are essential tools in today’s engineering design. Material models for polymers should be capable to handle large temperature and strain-rate effects, deformation-induced anisotropy, viscosity, and other features commonly observed for polymers.
Modelling of polymer behaviour at impact situations is a rather new activity at SIMLab. Therefore, the first year of the CRI project was used to establish an in-house state-of-the-art competence where we as far as possible utilized our prior knowledge in behaviour of metallic materials. The research projects within the Polymer programme in 2007, see below, reflected this starting position.
The main strategy for the polymer research at SIMLab is similar as for our activities within constitutive modelling of metals during the last 15 years. Material tests in our laboratory provide insight in which observed phenomena the model should be able to represent. This is most likely to be an iterative process where the model is gradually improved. In addition to material tests, required for calibration of the coefficients involved in a model, well-defined experimental component tests will serve as bench-mark cases for numerical validation of the model.