Impact Damage Detection And Mechanical Properties Evaluation Of Composite Materials Based On Infrared Thermography

Carbon fiber reinforced polymer(CFRP)composite materials are susceptible to low-velocity impact in service,resulting in matrix cracking,fiber breakage and delamination.These damages can cause significant strength and stiffness reduction,leading to lower loading capacity and shorter service life of the CFRP structures.Therefore,it is very important to detect the impact damage and evaluate the mechanical properties of CFRP composites.Infrared thermography has the advantages of non-contact,convenience and full field scanning,so it is very suitable for low-velocity impact damage.However,the traditional thermal signal reconstruction method cannot only effectively eliminate the system noise and the non-uniform background caused by uneven heating,but also it is unable to identify the details of different damage effectively.In this paper,the traditional principal component method was improved based on the pulse thermal imaging technology,and it was applied to low-velocity impact damage detection and fatigue damage monitoring of CFRP composite laminates to achieve nondestructive evaluation and quantitative identification of impact damage.The main contents and conclusions of the paper are as follows:(1)By using Gaussian filter pretreatment,standardization of thermal data and combination of different principal components,the traditional principal component thermal signal reconstruction method was effectively improved to obtain more accurate defect or damage information of spatial and temporal changes.By this method the signal-to-noise ratio of infrared thermography detection was improved.(2)The low-velocity impact test of T300/#2510 composite laminates with different ply parameters was carried out.By using infrared thermography to evaluate and quantify the impact damage,it was found that the impact damage is proportional to the impact energy.With the increase of the impact energy,the damage propagates faster along the X direction than Y direction.The parameters of the adjacent ply have significant effect on the impact resistance of the laminates.Under the same impact energy,the laminates which have more layers with same laying angle have the larger the impact damage area.(3)Static compression tests of the laminates with low-velocity impact damage were carried out.The results showed that the low-velocity impact damage has a great effect on the compressive strength of the composite.When the impact energy penetrates through the laminates,the residual strength of the laminates is only about 40 of that of the lossless laminates,and under the same impact energy the residual strength of the laminates which have more layers with same laying angle is more lower.(4)The compress-compress fatigue test of the laminates with low-velocity impact damage were carried out,and by using Pulse infrared thermography and DIC(Digital Image correlation)to monitor the damage evolution online.It was found that the damage extension can be divided into three stages under fatigue load,and the fatigue life of laminates is seriously reduced by low-velocity impact damage.Compared with the impact energy and fatigue stress level,the effect of laying sequence on fatigue life is relatively small.