Surface Instability Of Rubber Material Under Compressive Stress

Rubber has various excellent properties and is a widely used polymer material.However,due to the superelastic properties of rubber materials,large deformations easily occur under pressure.Especially when subjected to in-plane compressive loads parallel to the free surface,when the compressive strain is less than the critical value,the smooth free surface can still maintain continuity.Once the compressive strain exceeds its critical strain,various free surfaces will appear.The surface of the sample is destabilized and forms wrinkles or creases on the surface.The appearance of surface instability shows that on the one hand,the structure reduces the original performance and even fails.On the other hand,the mechanical properties of the structure can be measured by the surface destabilization topography and the morphology can be controlled.Therefore,it is necessary to have a surface on the surface.Instability studies.In this paper,considering the surface destabilization of rubber materials,considering the incompressible characteristics of rubber hyperelastic materials and the large deformation and nonlinear characteristics of the surface instability,the surface of the rubber was studied by combining the theory of continuum mechanics and incremental deformation.Stability critical conditions and evolutionary laws of instability morphology.Firstly,the constitutive model of rubber hyperelastic material was analyzed.Based on the continuum mechanics and incremental deformation theory,the critical strip of rubber material was deduced theoretically.As an example,a critical condition analysis of the surface instability was performed on a hyperelastic material characterized by a Neo-Hookean constitutive model.The theoretical results show that the critical compressive strain at which the surface instability occurs is approximately 0.456,which is related to the relevant literature reports.The results are consistent,which proves the correctness of the theoretical derivation in this paper.Secondly,the uniaxial plane strain compression experiments were performed on the experimental specimens.By compressing the displacement of the experimental specimen parallel to the free surface,it is observed in the experiment that with the constant increase of the compressive load,the smooth free surface first produces uniform and continuous deformation.In the process of deformation,the free surface always remains flat.As the amount of compression continues to increase,when the compressive strain reaches around 0.35,a creased and destabilized appearance suddenly forms on the otherwise smooth free surface,and as the strain increases,the crease slowly penetrates the surface.The area of selfcontact continues to increase,and its depth gradually deepens.Finally,a finite element analysis model for surface creases and fold instability was established.The crease-instability of the rubber material under large deformation and the evolution of the post-deformation morphology were simulated by introducing a crease defect with no initial stress on the free surface.The simulation results showed that creases began to appear around 0.348 strain,and The experimentally observed results are consistent.Through the buckling analysis,the critical condition and the post-buckling morphology evolution of the surface wrinkle instability of the rubber material were analyzed.The influence of different aspect ratios on the critical strain was investigated during the analysis.The results showed that the aspect ratio was critical to the fold instability.Strain has little effect,but it has an important influence on stress distribution and instability mode.The theory,experiment and simulation analysis of this paper will help to further study the phenomenon of surface instability of rubber materials under the coupling of multiple fields.