1. Department of Mechanical and Aeronautical Engineering, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa
2. IMT Lille Douai, Univ. Lille, EA 4515-LGCgE Laboratoire de Génie Civil et géoEnvironnement, CERI Matériaux et Procédés, F-59000 Lille, France