Showing papers by "Michael R Wisnom published in 2011"

Full-Field Strain Measurement and Identification of Composites Moduli at High Strain Rate with the Virtual Fields Method

Abstract: The present paper deals with full-field strain measurement on glass/epoxy composite tensile specimens submitted to high strain rate loading through a split Hopkinson pressure bar (SHPB) device and with the identification of their mechanical properties. First, the adopted methodology is presented: the device, including an Ultra-High Speed camera, and the experimental procedure to obtain relevant displacement maps are described. The different full-field results including displacement, strain and acceleration maps for two mechanical tests are then addressed. The last part of the paper deals with an original procedure to identify stiffnesses on this dynamic case only using the actual strain and acceleration maps (without the applied force) by using the Virtual Fields Method. The results provide very promising values of Young’s modulus and Poisson’s ratio on a quasi-isotropic glass-epoxy laminate. The load reconstructed from the moduli and strains compares favourably with that from the readings.

A new semi-empirical model for stress ratio effect on mode II fatigue delamination growth

Abstract: A new semi-empirical law for mode II delamination growth in moderately tough fibre reinforced epoxies at various stress ratios is introduced and validated. The new semi-empirical law is valid for positive stress ratios. The quality of the data fit obtained using the new semi-empirical equation is comparable to that achieved using alternative models from the literature, but the model presented here requires only two material parameters to represent the fatigue behaviour for the whole positive stress ratio range. The first validation data set comprises tension–tension fatigue tests performed by the authors on IM7/8552 using central cut ply specimens. Further validation cases have been considered from the literature; these include end-notch flexure fatigue tests on T800H/#3631 and E-glass/913 central cut ply samples tested in alternate tension.

High fidelity modelling of tapered laminates with internal ply terminations

Abstract: This paper describes the development and validation of finite element modelling tools for the analysis of delamination in tapered laminated composites under quasi-static and fatigue loading. Novel meshing tools are used to generate high-fidelity ply-level models with custom cohesive elements between every ply.