Experiment Study On High Temperature Creep And Stress Relaxation Properties Of Polyurethane Foam Material

Polyurethane foam material is a kind of polymer material. Because of excellent mechanical properties, acoustic performance, high specific strength and very low thermal conductivity, it has been widely used, as a new type of structural material and thermal insulation material. Polyurethane foam material failure is mostly caused by the creep and stress relaxation. In this thesis, the mechanical behavior of polyurethane foam material, especially the compression creep and stress relaxation properties were conducted in-depth study through a series of experiments. Then proposed the creep and stress relaxation constitutive model, which helps to predict and evaluate the performance and safety of the structure.(1) We carried out the compression experiment of polyurethane foam material, and established the load-displacement curves of static loading. Then the elastic model and Possion’s ratio of the material were determined according to the curve.(2) In this thesis, we designed and manufactured the room temperature compression creep device of the polyurethane foam material and carried out a 200-hour experiment to study the creep laws according to the experiment data. The results showed that the sample compression creep curves complied with the general nature of the material which consists of two parts, the initial stage and steady stage. Finally we used the theory of viscoelasticity and the concept of creep compliance to find corresponding constitutive model, the results showed that the visco-elastic burgers model can well describe the creep behavior of polyurethane foam material well at room temperature.(3) In this thesis, we designed and manufactured the high temperature compression creep device of the polyurethane foam material and carried out a 60-hour experiment at 50℃-90℃ to study the creep law according to the experiment data. Through in-depth study of the influence of environmental temperature and initial stress on creep behavior of the material, we found that the creep values and steady creep rate of samples are greatly influenced by temperature and stress. Then we proposed the time harding model which comprehensively describes the polyurethane foam material creep behavior under high temperature and different loads.(4) In this thesis, we designed and manufactured the high temperature stress relaxation experiment device of the polyurethane foam material and carried out a 36-hour experiment at 50℃-90℃ to study the stress relaxation law according to the experiment data. Through in-depth study of the influence of environmental temperature and initial strain on stress relaxation behavior of the material, we found that the higher the temperature and initial strain, the stress relaxation behavior of the material is more intense, and the relaxation limit of the material is also affected to some extent. Then the exponential model is proposed to describe the stress relaxation behavior of polyurethane foam material under high temperature environment and different initial strain. In addition, it provides a reference for predicting the relaxation limit of the material at high temperature.