Ring-Stiffness Evaluation and Optimization of Structured-Wall Polyethylene Pipes

The main objective of the current study is the development of a fast and accurate numerical simulation of the standardized ring flexibility test according to the standard BS EN 1446: 1996 [1]. This standard specifies a method to measure the flexibility of a thermoplastic pipe with a circular cross section. With this simulation the pipe's performance can be improved by optimization of its cross section. A requirement for accurate simulations is reliable material properties. Thus extensive material tests are conducted in order to quantify the dependency of the elastic modulus upon temperature and strain rate. Another pre-requisite for an accurate finite element (FE) simulation is precise geometry data capturing the cross-section of the structured wall as manufactured. Therefore, samples are cut of real profiles and their cross sections are scanned. The scanning process returns files of discrete data points, distributed over the entire cross section. These points have to be processed prior to the creation of the FE model. Programs have been developed to automatically carry out that task, as well as the generation of the FE models. Various FE models are developed within the work, which provide different degrees of accuracy and efficiency. That is to say different element types and boundary conditions are investigated to provide a suitable combination for any specific requirement. Finally an optimization procedure is presented that only consists of open-source or user-developed programs. It is capable of size and shape optimization. An application to a specific pipe is compared to the results of the in-built optimization tool in Altair Optistruct.