| Steel structures are widely used in various buildings due to their high strength,plasticity and toughness.However,steel structures often take some time to be repaired after being damaged by seismic loads,and strain aging effects occur during this period of time.The strain aging effect changes the mechanical properties of the steel:the strength and hardness increase,while the plasticity and toughness decrease significantly,and the change of mechanical properties will affect the continued serviceability of the steel structure.Therefore,it is necessary to study the effect of strain aging on the basic mechanical properties of the steel.To provide a basis for studying the influence of strain aging on the mechanical behavior of the overall structure.Strain aging is a special problem commonly encountered in the process of forming,manufacturing and using steel pipes for oil,gas and other conveying pipelines,especially the damage caused by strain aging embrittlement,which increases the possibility of brittle failure of pipelines.In the past few years,it has received much attention in the field of pipelines.Most of the researches on the aging of domestic scholars are to calculate the strain aging sensitivity coefficient of steel by measuring the impact absorption energy of steel before and after strain aging,and the research on the influence of variable aging on the mechanical properties of steel is not deep enough.Therefore,this paper In-depth study on the effect of strain aging on the mechanical properties of Q345 steel was carried out.In this paper,the strain aging test and theoretical analysis of Q345 steel were carried out to study the mechanical properties of Q345 steel after different pre-strain and aging.Three different test pieces were designed for the test,which were standard monotonic tensile test pieces,standard tensile and compression test pieces and butt weld test pieces.Among them,the standard monotonic tensile test piece and the standard tension-pressure cyclic test piece are based on the strain aging effect test of Q345 steel itself,the purpose is to study the mechanical properties of Q345 steel under different loading modes after strain aging.Considering the existence of welds in the actual steel structure,this paper also carried out the strain aging test on the test piece with butt weld,and studied the change of the mechanical properties of the butt weld test piece before and after the strain aging,making up for the steel itself.Research on strain aging,and lack of research on strain aging of butt weld specimens.Based on the strain aging test of Q345 steel and its butt weld specimens,the influence of strain aging on the basic mechanical properties of Q345 steel and its butt welds is analyzed.Based on the test results,the Ramberg-Osgood model is used to correspond to Q345 after aging effects.The steel stress-strain curve was fitted and analyzed,and the constitutive relationship model of Q345 steel after different strain aging factors was established.The research results are as follows:(1)After the strain aging treatment,the yield strength and tensile strength of the standard monotonic tensile test specimens increase,the yield ratio increases and finally stabilizes at about 0.9,the ultimate strain and strain at break decrease,and the structure is brittle.The possibility of bad is improved.The standard monotonic tensile specimen has a pre-strain of 12.5%,and the specimen with a aging period of 14 days has a 10%increase in tensile strength,a 46% reduction in ultimate strain,and a 33% reduction in fracture strain.(2)After the strain-aging treatment of the standard tension-pressure cyclic test piece,the hysteresis curve is from the full shape of the unstrained aging to the long and short hysteresis curve after the strain aging treatment,and the pre-strain and aging are larger,and the hysteresis is The more severe the curve pinch,the significantly lower the energy consumption and the poorer seismic performance.(3)The mechanical properties of the butt weld test specimens are similar to those of the standard monotonic tensile test specimens.The yield strength and tensile strength are improved,and the ultimate strain and strain at break are reduced.The butt weld can reflect the change of mechanical properties of the real steel structure after being damaged in actual engineering.Although its yield strength and tensile strength are significantly improved,the ultimate strain and strain at break are significant,especially the pre-strain is 20 At %,the strain at break decreases by nearly 50%,indicating that the strain aging effect significantly increases the possibility of brittle failure of the structure.(4)Increasing the pre-strain and aging can affect the mechanical properties of Q345 steel to a certain extent,and the change of mechanical properties of Q345 steel caused by pre-strain is greater than the change of mechanical properties of Q345 steel caused by increasing aging.The improvement of the pre-strain on the mechanical properties of Q345 steel is more significant.(5)Based on the stress-strain relationship curve of Q345 steel after strain aging effect,the characteristics of the yielding platform are not obvious.The Ramberg-Osgood model suitable for materials without obvious yield point is used to fit the test data to establish the influence of strain aging.Q345 steel constitutive relationship model.The results show that the stress-strain curve obtained by the constitutive model is consistent with the experimental curve.The constitutive model can better describe the stress-strain relationship of Q345 steel affected by strain aging.The research results can provide a basis for the finite element analysis of the influence of strain aging on the overall mechanical properties of steel structures and the design of steel structures considering the effects of strain aging. |
