Matteo Dotta

Dynamic Behaviour of Reinforcing Steel Bars in Tension

In this paper the preliminary results of the tensile behavior of reinforced steel in a large range of strain rates are presented. Tensile testing at several strain rates, using different experimental set-ups, was carried out. For the quasi-static tests a universal electromechanical testing machine with the maximum load-bearing capacity of 50 kN was used, while for the intermediate and high-strain rate regimes a hydro-pneumatic apparatus and a JRC-Split Hopkinson Tensile Bar respectively were used. The target strain rates were set at the following five levels: 10-3, 30, 250, 500, and 1000 1/s. The specimens used in this research were round samples having 3mm in diameter and 5mm of gauge length obtained from reinforcing bars. Finally, the material parameters for Cowper-Symonds and Johnson-Cook models were determined.

Strain-Rate Effect on the Tensile Behaviour of High Strength Alloys

In this paper the first results of the mechanical characterization in tension of two high strength alloys in a wide range of strain rates are presented. Different experimental techniques were used for different strain rates: a universal machine, a Hydro-Pneumatic Machine and a JRC-Split Hopkinson Tensile Bar. The experimental research was developed in the DynaMat laboratory of the University of Applied Sciences of Southern Switzerland. An increase of the stress at a given strain increasing the strain-rate from 10-3 to 103 s-1, a moderate strain-rate sensitivity of the uniform and fracture strain, a poor reduction of the cross-sectional area at fracture with increasing the strain-rate were shown. Based on these experimental results the parameters required by the Johnson-Cook constitutive law were determined.

Tensile behaviour of reinforcing steels at high strain rate and high temperature

The performance of reinforced concrete structures under combined effects of blast and fire is growing in interest of the research and engineering communities specially after the recent terrorist attacks as well as severe accidents (i.e. Gotthard tunnel, etc.). The mechanical behaviour of concrete and reinforcing steel when are subjected to extreme temperatures, impacts or blast has still many aspects open to investigation. In this paper the behaviour of AISI304, B500B and B500A reinforcing steel at high strain rate (500 s-1) and at three levels of temperature (200, 400 and 600°C) is presented. The results were obtained by using a Split Hopkinson Tensile Bar (SHTB) equipped with a heating system.