| As a common polymer,plexiglass has become one of the most widely used engineering plastics in the fields of engineering construction,aerospace and national defense due to its good transparency,stable dimensional properties,excellent mechanical properties,light weight and easy processing and forming.However,its environment during service is relatively complex.In order to make full use of its mechanical properties during service,it is necessary to more comprehensively understand the mechanical response of plexiglass under different stress states.Therefore,this paper studies from the following three aspects through the method of combining theory and experiment:（1）Uniaxial tensile and uniaxial compression tests at four temperatures（T=20℃,40℃,60℃and 80℃）and three strain rates(（?）=0.0001s-1,（?）=0.001s-1和（?）=0.01s-1)were carried out on the plexiglass samples,and the test results were analyzed.The results show that the temperature and strain rate have a great influence on the initial yield strength and hardening law of the plexiglass material.The lower the temperature is,the higher the strain rate is,the greater the initial yield strength of tensile and compressive materials is.In the studied range,the tensile fracture is brittle and the compressive failure is ductile;Compared with the change of strain rate,the change of temperature has a greater influence on the tensile yield strength.The higher the temperature is and the faster the strain rate is,the more obvious the softening of the material is after the initial yield strength of the compression.（2）According to initial yield locus of plexiglass obtained from experiments,finding the applicable constitutive model.A new constitutive equation can be obtained by introducing temperature term and rate-dependent term based on the above constitutive model,which is used to describe the effects of different temperatures and strain rates on the initial yield strength of the plexiglass under tensile and compression conditions and compared with the experimental data,it shows good descriptive ability;Based on the initial yield function of plexiglass,Johnson-Cook hardening model was introduced to describe the influence of different temperature and strain rate on the compressive hardening behavior of materials.It was found that the hardening phenomenon was more obvious with the increase of strain rate,while the hardening rate was slower with the increase of temperature.A new constitutive equation was constructed by combining the initial yield function with Johnson-Cook hardening rule to describe the effect of temperature and strain rate on the subsequent yield stress of materials.The reliability of the new constitutive equation was verified by combining experiment with theory.（3）During the loading process of the sample,the cross-sectional area of the cross-section is not constant,but decreases（stretching）or increases（compressing）with the loading.For insight into the temperature and strain rate effects on plexiglass true strain,in this paper,the DIC（Digital Image Correlation）test technology is used to study the change of the true strain of the material at different temperatures and different strain rates.The test data is analyzed and it is found that there is no strain concentration phenomenon during the tensile loading process.The higher the temperature is,the larger the strain is,and the larger the strain rate is,the smaller the strain is.In the compression process,there is strain concentration and the intermediate strain is the largest.The strain change rate increases with the increase of temperature and strain rate.These experiments and analysis of the results can provide some data and theoretical reference for the engineering research and application of plexiglass and polymer. |
