Research On The Power Design Of Slow Strain Rate Tensile Test Machine For The Metallic Materials

The mechanical devices such as aerocraft,space shuttle are usually acted upon by a certain tensile stress during normal operation.After a period of time,the cases being elongated and thin often occurs to them.Especially for metallic materials in a corrosive environment,the combined action of stress and corrosion will result in stress corrosion cracking of materials different from traditional form of brittle fracture.To select metallic materials safely and reliably,it is necessary to measure the stress corrosion cracking susceptibility of materials under the condition of slow strain rate tests method.Therefore,mechanical properties of material under the effect of slow strain rate tensile test have a great influence on reliability and operational life of the design of mechanical equipment such as space shuttle and petroleum refinery process units.And the machine is needed to finish tensile test at the slow strain rate.However,the existing machine has many problems,including unclear design of motor power,instability running at constant rate,single control mode and low degree of automation and intelligence,which have a serious effect on the accuracy of the mechanical properties of material at slow strain rate.In order to solve unclear design of motor power for the machine,the paper firstly used molecular dynamics method to simulate slow tensile deformation process of aluminum.This method aims at exploring the deformation mechanism of aluminum under the effect of slow strain rate from a microcosmic view.Moreover,experimental platform at slow tensile rate was self-designed by basic principle that PLC can send out pulses to control servo motor.It aims at achieving slow tensile test at required rate.Finally,method of data fitting is used to fit and analyze the data obtained from simulation of molecular dynamics and experiment.And it can help to explore possible relations between sectional dimension and power consumption.The main conclusions of this paper are as follows:(1)The essence of plastic deformation for aluminum in the process of slow tensile is the result that aluminum atoms gradually happen to slip.This process is accompanied by the energy consumption and release.(2)While self-designed experimental platform uses PLC to send pulses to servo motor,the motor also outputs pulses for driver by connecting line of encoder.This method can construct a closed-loop system to accurately control servo motor.Finally,after PLC is set to send out 10000 pulses per second,it can be proved that the platform is able to work successfully at 6.94×10-4s-1 rate.(3)The mechanical properties of metallic aluminum obtained at slow strain rate are quite different from those obtained at normal rate.When the tensile rate is reduced from 6.7 ×10-3s-1 to 6.94×10-4s-1,yield strength and tensile strength don’t change significantly because of being less sensitive to the change of strain rate for aluminum.And the strain increased from 0.227 to 0.281 with the increment of 23.97%.In terms of the effect of power consumption caused by sectional dimension,it was found that tensile rate and sectional dimension have little influence on starting power of test machine.Besides,it is necessary for the overall power design of the test platform to not only take into account power loss required for the deformation of the tensile specimen,but also consider power loss caused by resistance of intermediate transmission link from motor to clamping chuck.During the entire process of slow tensile deformation,the changes between sectional dimension and power demand obtained from experiments have a good correlation with the results of simulation of molecular dynamics.That is,power consumption increased progressively as increasing the sectional dimension of specimens.The relationship between the maximum demand power and the sectional size is P0.5=-3.052 + 6.072d.However,it is unable to get specific analytic form about sectional dimension and total demand power from experiments because of the influence of intermediate resistance,so other methods should be used to further confirm and analyze the result.