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Material Characterisation

Structures subjected to blast loads undergo large deformations and tearing in time frames of the order of 10-6 to 10-3s resulting in very high strain rates - of the order of 103 to 106 per second. It is estimated that at these very high strain rates, the temperature of the material rises to around 600°C. As a result of this rapid temperature rise, the material properties change significantly. For example the yield stress of the material could reduce to about 10% of the original tensile test value

One of the most important current objectives of research world-wide in the field of structures subjected to explosive loads is the ability to be able to predict tearing failure of the metal structure. The models available depend upon the understanding of the mechanisms developed in the constitutive equations. These equations require an in-depth understanding of the material properties at high strain rates. It is these material properties that require further research. This is on-going at BISRU and some preliminary work completed at BISRU has provided an insight into these properties. Using a simple temperature dependent material model recent work has resulted in predictions that correlate very well with the experiments.

Regardless of the choice of material model, high quality experimental data is required to determine the values of the material model parameters. Current work at BISRU is focused on material characterisation. This includes high strain rate material testing carried out on split Hopkinson bars, direct impact Hopkinson bars and Taylor test rigs. Furthermore, other studies underway focus on discerning primary damage mechanisms by the micro-structural investigation of failed regions of blast loaded plates.

List of most recent publications

  • CLOETE, TC. AHMED, R, & NURICK, GN. "Peripherally clamped centrally supported blast loaded circular plates: A precision test for code validation". J.Phys. IV France 110 (2003), pp 507-512.
  • OCHOLA, R, MARCUS,K, NURICK, GN. "The impact failure mechanism of glass fibre epoxy using microscopy and finite element analysis." Microscopy Society of Southern Africa - Volume 33 , 2003, p30.
  • NETANGAHENI, PT, MARCUS, K, NURICK, GN. "A microscopic investigation of the failure mechanisms of thermoplastic composites." Microscopy Society of Southern Africa - Volume 33 , 2003, p29.
  • NETANGAHENI, PT, MARCUS, K, NURICK,GN. "An investigation of the failure mechanisms of thermoplastic composites at various rates of strain and temperature." Second International Conference of The African Materials Research Society. Johannesburg, December, 2003, pp 101-102.