Experimental Study On Mechanical Properties Of Reinforcement At Cryogenic Temperatures

This dissertation is the sub-project of the Natural Science Foundation project‘Material Properties of Reinforced Concrete at Cryogenic Temperature’. In this paper,mechanic properties of reinforcement at cryogenic temperatures were experimentallyresearched.The experiments shall be conducted at cryogenic temperatures. According to thisrequirement, the specimens were cooled down by liquid nitrogen and tested on theelectronic universal experimental machine which was equipped by self-designcryogenic environment box and tensile thread fixture. Relevant researches are asfollows:1. Considering the practical situation of the Material Testing Laboratory ofTianjin University, cryogenic environment box and tensile thread fixture weredesigned autonomously, after investigating the colling equipments and thermalinsulating equipments in China and abroad.2. HRB335, HRB400and cryogenic reinforcements were chosen in thisexperiment and were classified into three groups, A group, B group, and C group.Each group were respectively tested at seven temperatures,20℃,-40℃,-80℃,-100℃,-120℃,-140℃and-165℃. There were63specimens in total, divided into21groups and3specimens in each group.The following are the conclusions obtained from this research:1. As the temperature decreases, the yield strength fyand tensile strength fuof thereinforcement improve to different extent.2. With the decreasing temperature, the reinforcement shows reducing plasticity,because of the minishing elongation after fracture δ and contraction of area ψ.3. The fact that the elastic modulus Esfluctuates around a certain value indicateslittle relevance to the changing temperature.4. The shape of the stress-strain curve changes little at different temperatures.5. The cooling environment leads to the improving brittleness, reflected in thedropping ultimate strain.6. The reinforcement tends to generate brittle fracture instead of ductile fracturewith the dropping temperature.