Study On Acoustic Emission Identification And Localization Method For Plain Weave Composite Laminate Damages

Composite material is extensively used in engineering structures due to its high intensity and light quality.Early damage detection for composite material will aid in preventing failure of the structure and reducing the cost on maintenance of replacement and ensuring the structure operates safely and efficiently during its whole intended life.Acoustic emission(AE)technique can be applied to discriminate various damage modes occurring in the composite material under external loading.The objective of this work is to identify,locate and assess the damage in plain weave composite material by conducting theory analysis,finite element(FE)analysis and experiment analysis combinely.(1)FE analysis for plain weave composite laminateThe three dimensional finite element models for plain weave carbon fiber reinforced and glass fiber reinforced composite laminates were developed.The progressive failure analysis under three point bending test was conducted according to the continuous damage mechanic(CDM)theory.The stress distribution with time in different fiber directions was obtained to determine failure behaviors in different layers.The failure processes of failure modes including matrix crack,fiber breakage and delamination were characterized by Tsai-Wu criterion.The performance of composite laminates gained from FE analysis provided the basis for the further experimental study.(2)The propagation rule of AE signal in composite materialDuring propagation,AE signal attenuated seriously and propagated without direction,which increase the difficulties in damage detection using AE technique.It is of great important to understand the propagation rule in composite material.The AE signal propagation experiments were conducted by considering the dimension and the fiber of propagation medium,prapagation direction and distance.Results showed that the attenuation and propagation velocity of AE signal were affected by the fiber direction and material of propagation medium.(3)The identification of damage characteristics in plain weave composite laminatesThe three point bending tests were conducted in both plain weave carbon fiber reinforced and glass fiber reinforced composite laminates along with AE monitoring.Each failure process was divided into three stages based on energy count analysis and four failure modes were recogonized through crack types obtained from association diagram of AE parameters.Cross correlation was performed to exclude unrelated AE parameters and the dimension was further reduced by principal component analysis(PCA)or laplacian eigenmap(LE)method.Based on the AE signal which has low correlation and dimensionality,the four failure modes presented by the four failure modes were classified by K means and the relationship between the failure modes and AE parameters was built.(4)The localization of damage in plain weave composite laminatesA localization algorithm was established to locate the damage in plain weave composite laminate.The set of the possible AE source points was first determined according to the dispersion characteristics of plate wave and the delta-T location method.Then the line position for the AE source was calculated by the mathematical algorithm based on the three formed sensors.According to the distance between the line and the points,the AE source is searched by a best match point algorithm.This method does not require the knowledge of the sensor location or wave speed.The experiment results from both plain weave carbon fiber reinforced and glass fiber reinforced composite laminates were under an acceptable location error.It showed that the location algorithm is approachable.(5)The evaluation of damage in plain weave composite laminatesAn assessment matrix was established to predict and evaluate the damage condition in plain weave composite laminate.The assessment matrix which consisted of severity degree of the damage indexed by the failure modes and the probability of occurrence of the damage quantified by the b value divided the failure into four levels.The assessment matrix explained the damage condition appropriately.