Research On Digital Volume Correlation Method For Internal Deformation Field Measurement Of Metal Foam

Metal foam is a new type of structural and functional lightweight material with important application value.On account of the random cellular structure,the deformation of metal foams under different loading conditions is highly non-uniform.The macro-mechanical behavior of the material is thus much more complicated.In this case,accurate measurement of the internal deformation field of metal foams becomes an important foundation for in-depth mechanical research.Digital volume correlation(DVC),a new type of non-contact measurement method that has broad application prospects.With the help of three-dimensional imaging technologies such as CT scanning,DVC method can be used to effectively calculate the internal deformation field of the materials through image registration technique.It shows a high application potential in the research of metal foams.However,despite the good performance of the current DVC method in many test experiments,there are still difficulties when this method is used for deformation measurement of metal foams.The large number of black cell hole regions on the volume image of the metal foams reduce effective image features and may cause large measurement errors.However,there is still a lack of effective verification methods for the DVC measurement results of cellular materials.In addition,metal foam is a typical impact energyabsorbing material,its dynamic mechanical behavior is the focus of research.The current DVC method is generally based on an in-situ scanning system,which has many limitations on the specimen and loading device.DVC method that combined with ex-situ scanning needs urgently to be developed.This paper conducts an in-depth study of the DVC method in view of these several issues.The main research work is as follows:(1)An adaptive image segmentation method suitable for metal foams is proposed to accurately divide the cell wall and cell hole regions on the image.Highly simulated finite element models are constructed with sufficient cell hole number,which helps to increase the credibility of simulation results and lays the foundation for the accurate verification of DVC method.(2)A method that can realize the mutual conversion of volume image and finite element model is first developed.On this basis,a reasonable and reliable method is proposed to verify the DVC results of metal foam deformation field through the finite element simulations.With the help of image-based 3D reconstruction,the accuracy of simulation results is improved.At the same time,the high degree of comparability between the finite element model and the volume image ensures the reliability and accuracy of the DVC result inspection.With the help of this method,the effectiveness of DVC is further analyzed in deformation measurement of metal foams.(3)Aiming at the problem of rigid translation and rotation of the volume image caused by the motion of specimen in the ex-situ scanning experiment,a method that aligns the volume image via rigid block markers is proposed,realizing the compensation and correction of the DVC measurement results.A multiple loading and unloading experiment combined with exsitu CT scanning is carried out to verify the effectiveness of the method.