JEC COMPOSITES MAGAZINE - Issue #68 Special JEC Asia - October 2011 - 76

bi-angle NCF

Predicting the OHT strength of NCF composites
The progressive damage analysis of open-hole tension (OHT) strength of laminated composite fibre shows significant benefits in using non-traditional bi-angle [0/25] laminates, compared to traditional laminates incorporating 0, ±45, and 90 plies.
Fig. 1: Open-hole tension simulation

MUHAMMAD RIDHA, RESEARCH FELLOW T.E. TAY, PROFESSOR DEPT. OF MECHANICAL ENGINEERING, NATIONAL UNIVERSITY OF SINGAPORE

omposite structures are known to be able to withstand much higher loads than the first ply failure stress. Hence, damage tolerance design and analysis of these structures requires the ability to predict their structural behaviour beyond first ply failure. Recent developments in failure theories and damage mechanics have made it possible to predict the behaviour of structures made of fibrereinforced composite laminates beyond first ply failure. Thus, the structural performance achieved with different laminate designs and ply sequences can be compared and optimized even before the structure is produced. The material property (stiffness) degradation method (MPDM) combined with failure theories is a useful tool to analyse progressive damage in composites. Several new failure theories, such as the MicroMechanics of Failure (MMF) theory developed by Prof. S. K. Ha at the Hanyang University in Korea, can differentiate between matrix- and fibredominated failure modes. Using progressive damage simulations, engineers can now better understand the structural behaviour of fibre-

reinforced composite laminates. The conventional rule of thumb in using a combination of 0, 45 and 90 plies may be replaced by customizing the ply

jec composites magazine / No68 October 2011

angles in order to optimize them for certain loading conditions based on the simulations. A global team of composite researchers and composite manufacturers led by Prof. S. W. Tsai of Stanford University recently proposed fibrereinforced composite laminates made of biangle [0/25] thin NCF pre-plies. These laminates have been shown to have superior strength, manufacturability and toughness. Progressive damage analyses are used to compare the Fig. 2: Stress-strain curves for [12.5/-12.5]s and quasi-isotropic laminates applications of this new

concept. A simple tensile test and a simple open-hole tension case are used to compare their structural performance. Tensile and OHT tests on bi-angle [12.5/-12.5]s and quasiisotropic [0/45/-45/90]s laminates are modelled using Abaqus with an additional user-defined MPDM code. The model was 25.4 mm x 25.4 mm with a 4.24 mm diameter hole in the centre. Test data by Dr. A. T. Nettles from NASA shows that the average strength of an undamaged bi-angle [12.5/-12.5]s laminate is 1,474 MPa (standard deviation of 155 MPa), while the OHT strength is 811 MPa (standard deviation of 31 MPa). The progressive damage data predicts 1,702 MPa and 665 MPa for the undamaged and OHT tests,

JEC COMPOSITES MAGAZINE - Issue #68 Special JEC Asia - October 2011

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #68 Special JEC Asia - October 2011