Failure Assessment of Shell-like Structures

mike2.jpgLie Zhang has recently passed his PhD viva at Wessex Institute of Technology with a thesis entitled "Failure Assessment of Shell-like Structures". His work was conducted within the industrial research division at Wessex Institute of Technology. His research was financially supported by European Union's NATURALHY project.  His external examiner was Prof Vitor Leitao from IST-URL, Portugal and the internal was Dr Andrés Peratta.

Lie Zhang received his first degree in mechanical engineering from East China University of Science and Technology. Afterwards he moved to Imperial College London, where he obtained a master's degree in advanced mechanical engineering. In 2005 he came to WIT and started his PhD programme under the supervision of Dr Robert Adey and Dr Sharon Mellings.

During the course of Lie's research, he proposed a criterion called "strain energy difference" for coupling a BE submodel and an FE global model for solving crack growth problems in 2D and 3D shell structures. This approach showed some advantages over traditional automatic growth methods such as the Dual Boundary Element Method and the Finite Element Method with local remeshing technique. It was found that there is no need to construct a ring of rosette like elements around the crack tip when the submodel is remeshed.  The boundary conditions for the submodel are updated only when the strain energy difference between two consecutive crack propagation increments is above the prescribed threshold value. The results obtained from this method were compared with the literature and it was observed that the proposed method was more efficient than the traditional methods.

The other part of his research focused on the probabilistic of failure evaluation for shell-like structures containing crack-like defects. The improved Stratified Monte-Carlo method was proposed by Lie in order to solve a complex problem involving a large number of non-normally distributed variables. For this method, only important parameters were stratified whereby the overall efficiency of the sampling scheme was improved. A software tool based on the proposed approach was developed for the NATURALHY project which was dedicated to transporting natural gas-hydrogen mixtures using existing natural gas pipelines. The prediction of the POF of a pipeline after replacing the natural gas with hydrogen was a matter of much importance as it can provide essential information on the safety, management and economics of the pipeline. A complete procedure based on BS7910 failure assessment diagram (FAD) for computing POF was also proposed. This procedure not only considered the failure assessment of the pipeline but also the inspection and repair procedure as well, whereby an optimal maintenance scheme was found.

Both examiners congratulated Lie on the work presented and recommended that he be awarded the degree of Doctor of Philosophy.