Research On Response Characteristics Of Defects In Fiber Reinforced Composite Plates And Its Application In Optics-mechanics Detection

Fiber-reinforced resin matrix composites have been widely used in aerospace,rail transportation,energy and other fields.In the process of manufacturing and service,due to the change of environmental temperature and humidity,fiber prestressing,curing temperature and so on,various randomly distributed defects in composites are generated,such as fibre wrinkling,weak bonding interface,delamination and so on.These randomly distributed defects will reduce the strength and bearing capacity of composite structures.Thus,it is of great importance to carry out defect detection and evaluation during the manufacturing and service of composites.The material science,mechanics and optics that optical non-contact measurement technology involves are closely coupled together,which makes it a multi-field and multidisciplinary technology.At present,when applying the non-contact measurement technology,there are still some problems such as lack of theoretical guidance,over-reliance on experience,and difficulty in explaining special testing results.How to design an effective detection scheme to detect different defects by appropriate optical measurements,the prediction of mechanical behaviors for structures with defects is important to realize the optics-mechanics detection of composite structures.The research on response characteristics of wrinkle and weak bonding in fiber reinforced composite plates and its application in optics-mechanics detection were studied.The main content and conclusions are presented as follows:(1)The micromechanical models of fiber wrinkles and weak bonding defects were established based on the two-step homogenization technique and asymptotic homogenization method,respectively.The algorithm implantation of mechanical models of two types of defects was realized by finite element procedure.Results showed that wrinkles can decrease the equivalent elastic modulus in fiber direction and increase in ply thickness direction.Weak bonding will weaken the stiffness coefficients in all directions,and with the decrease of interfacial bonding strength,the reduction of E_x is limited,while E_z will reduce to 0.(2)A testing method considering the physical heterogeneity model of defects and its spatial random distribution model was established,and the mechanical behavior of fiber reinforced composite laminates with random defects was predicted.The characteristic responses under various loading modes can provide theoretical guidance for the optics-mechanics detection of composite defects,including loading mode,load size,measurement mode and estimation of measured value.Further,the random distribution of heterogeneity defects is considered,the quantitative relationship between the defect parameters and the mechanical responses of components can be established by multiple calculations.The method can aid to design compoite structures where random defects cannot be ignored.(3)The optics-mechanics detection scheme for composite wrinkle and weak bonding defects was established based on the characteristic response.A new reconstruction algorithm to obtain the out-of-plane displacement based on the digital grating projection measurement technology was proposed.Results showed that under micro tensile loads,the digital grating projection measurement technology can well capture the increased displacements caused by wrinkles or debonding,and judge the inhomogeneous distribution and severity of defects according to displacement fields.Because the reconstruction algorithm is proposed to deal with point cloud data,the measured deviation caused by the surface quality and rigid displacement can be eliminated.This method has the advantages of full-field measurement,measuring information rich and high measurement precision.