Study On Mechanical Properties Of Narrow Gap Reinforced Bars Connected By CO₂ Gas Shielded Welding

From the reinforced concrete structure since its inception, there has been a series of steel connection technology: lashing connection, mechanical connection and welding. In the steel construction technology, welding and efficient connections construction steel butt welding methods commonly used are: flash butt welding, pressure welding, lap welding, narrow gap arc welding. CO₂ gas shielded welding have been applied to steel narrow gap welding in Japan and other developed countries, and it played a good effect in engineering applications, but there is no research and application on this technology in China.In this paper, theoretical analysis, based on use of CO₂ gas to protect the mechanical properties of steel welded joints carried out a large number of experimental research and numerical simulation method of the joint force analysis of the characteristics of the aim for this joint on a wide range of applications in engineering and promotion and lay a solid theoretical foundation and experimental basis for study of the paper mainly include the following aspects:(1) CO₂ gas shielded arc welding steel welding and mechanical behavior of the theory are summarized and analyzed. this paper derived CO₂ gas shielded welding process parameters on the basis of the basic welding theory and narrow gap CO₂ gas shielded welding test. Through the wire and the base materials for welding consumables match the theoretical guidance for matching experiment to find suitable wire for welding steel bars of China CO₂ gas shielded welding, and obtain mechanical indicators for different grades of steel welding wire range. Summary of basic mechanical properties of reinforced joint principles, including: stretching, bending, impact, fatigue properties and fracture mechanics mechanism.(2) Experimental study of reinforced through the use of CO₂ gas shielded welding connections stretching, bending and impact to study the basic mechanical properties. Static load of reinforced welded joint tensile test tensile properties of joints, welding defects in the absence of circumstances, with good matching can be achieved and other joints and even super strong connections with low yield strength steel welded joints in favor. Connector has good bending performance, good plasticity. High-impact toughness of weld joints match is not less than the base metal, heat affected zone toughness is much smaller than the base material is a joint in the heat-affected zone fracture important reasons.(3) Through the experimental study of high stress and repeated tension and compression fittings, large deformation of repeated tension and compression and fatigue testing. Measured by high stress and tension and compression joints hysteresis curve, verify joints under dynamic load capacity of plastic deformation. Joint fatigue performance validation tests meets regulatory requirements, while the fatigue strength increasement of HRB400 and HRB335 steel reinforced joints is less than strength increasement of joints base metal. Macro metallographic and hardness test results show that: weld hardness is higher than the weld heat affected zone hardness, both higher than the steel hardness; fusion line hardness is slightly lower than that on both sides, near the weld fusion line hardness tended to increase over-heated areas, which a hard brittle characteristics of the region result in decreased mechanical properties of joints.(4) The joint force characteristics by finite element numerical simulation results show that: joint finite element simulation results coincide with the corresponding test analysis, the joint welding residual stress and deformation of small and not solder joint due to defects in breach. Pores and cracks of reinforced joint defects caused by defects in the regional stress concentration, the formation of cracks under load and thus embryo nuclear expansion crack initiation until breakage.