Effects Of Hardness,Temperature,and Strain Rate On Static And Dynamic Mechanical Properties Of Polyurethane Elastomers

Polyurethane elastomers have received a lot of attention due to their excellent shock absorption and energy absorption properties.Polyurethane elastomers have high application value and development prospects as part of protective structures for shock resistance,shock absorption and cushioning tasks.In this paper,three hard polyurethane elastomers are prepared using castor oil and MDI 8617 as raw materials.The effects of hardness,temperature,and strain rate on the static and dynamic mechanical properties of polyurethane elastomers have been investigated.The main points are as follows:Quasistatic compression and hysteresis tests were performed on polyurethane elastomers with three hardness levels at normal and cryogenic temperatures.It has been shown that the stress level of polyurethane elastomers under quasi-static loading increases with increasing hardness and strain rate and decreasing temperature.In the quasi-static compression test at room temperature,the elastic modulus is strongly affected by the hardness,and at low temperatures,by the temperature.The energy absorption properties of polyurethane elastomers are enhanced with decreasing temperature and increasing hardness.Dynamical compression tests of polyurethane elastomers with three hardness levels at low and normal temperatures were performed with Hopkinson bar.It has been shown that the stress peaks of polyurethane elastomers increase with increasing hardness and strain rate and with decreasing temperature,which weakens the effect of initial hardness on the mechanical properties of polyurethane elastomers.At room temperature,the higher the hardness of the sample,the more pronounced the strain rate effect.At low temperatures,decreasing the temperature has a stabilizing effect on the increase of the stress peak and elastic modulus,while increasing the hardness has a temperature dependence.Different hyperelastic constitutive models were used to fit the test results,and it was shown that the third-order polynomial constitutive model gave the best fit.The viscoelastic part of the ZWT constitutive model is combined with the third-order polynomial constitutive model to form the viscous-hyperelastic constitutive model as a constitutive model for polyurethane elastomer.The fit of the viscous-hyperelastic constitutive equation to the static and dynamic test results is evaluated and the parameters of the constitutive equation for the fitted curves for different loading conditions are obtained for further investigation.It is found that the variational law of the constitutive parameter of the hyperelasticity with increasing strain rate is similar to that of the exponential function.This point of view is verified by fitting the two with exponential functions.At the same strain rate,the constitutive parameter changes exponentially with increasing temperature.The stress-strain curve of polyurethane elastomer was predicted by using Python neural network.The test results were divided into training set and test set.Using the training set data to train the neural network,the trained neural network can accurately predict the data in the training set,and the accuracy is better than the fitting of the constitutive equation.The prediction results of the test set data show that the neural network has a good prediction effect on the stress-strain curve at normal temperature,and a good prediction effect on the elastic stage and plastic stage of the curve at low temperature.