Verein Deutscher Ingenieure

Development of Fibre-Reinforced Plastics components - Analysis
 N VDI 2014 BLATT 3

Annotation

VDI 2014 Part 3 records the state of the art regarding calculation methods for the development of FRP components. Here the basic principle is that the behaviour of the laminate (Section 5) be traced back to the properties of its individual laminae (Section 4). Designing and dimensioning a laminate includes stacking the laminate in such a way as to enable it to cope with the stresses it encounters (fibre orientations, number of laminae, sequence of laminae); it also includes determining the laminate thickness required, which will be the sum of the thickness of the individual laminae. To a very great extent the guideline is based on approved methods which have already been tried and tested in practice and does not therefore necessarily reflect the very latest research findings. In the case of VDI 2014 Part 3 this affects methods used for strain and stress calculation (Sections 4.1 to Section 4.3, and Section 5.1). In the case of strength calculation (Section 4.5 and Section 5.2) this principle had to be abandoned since the usual procedure could result in seriously incorrect estimates, at least in some branches of industry. Here some new methods have been included which do nevertheless reflect what has been learnt during the course of years of design and development work.

The lamina types introduced in VDI 2014 Part 1 and Part 2 – namely, P-ES, G-ES and W-ES – are retained. However, for reasons associated with the translation of Part 3 into English, the terms UD lamina, WF lamina and M lamina are now used instead. Here, due to the straight, non-crimped unidirectional orientation of its fibres, the UD lamina is of outstanding importance in the design of heavy-duty or highperformance components. For this reason the UD lamina occupies a prominent position in the various analytical methods.

Some uncertainties remain, however, in the theoretical dimensioning of laminates and FRP components – one example of this is fatigue strength (Section 5.4). It is therefore not possible to provide a description here of the correct method, but only of the best method available at the present time.