Formation of nanoparticles from ultrafast laser condensates of metal targets

Optimised ultrafast laser ablation can result in almost complete ionisation of the target material and the formation of a high velocity plasma jet. Collisions with the ambient gas behind the shock front cools the material resulting in the formation of mainly spherical, single crystal nanoscale particles in the condensate. This work characterises the nanoscale structures produced by the ultrafast laser interactions in He atmospheres at STP with Ni and Al. High resolution transmission electron microscopy was employed to study the microstructure of the condensates and to classify the production of particles forms as a function of the illumination conditions.

Analysis of CFRP strap-strengthened reinforced concrete beams using the modified compression field theory (MCFT)

External, prestressed carbon fiber reinforced polymer (CFRP) straps can be used to enhance the shear strength of existing reinforced concrete beams. In order to effectively design a strengthening system, a rational predictive theory is required. The current work investigates the ability of the modified compression field theory (MCFT) to predict the behavior of rectangular strap strengthened beams where the discrete CFRP strap forces are approximated as a uniform vertical stress. An unstrengthened control beam and two strengthened beams were tested to verify the predictions. The experimental results suggest that the MCFT could predict the general response of a strengthened beam with a uniform strap spacing < 0.9d. However, whereas the strengthened beams failed in shear, the MCFT predicted flexural failures. It is proposed that a different compression softening model or the inclusion of a crack width limit is required to reflect the onset of shear failures in the strengthened beams.