Predicting the Delamination Mechanisms of Multidirectional Laminates Using the Energy Release Rate Obtained from AE Monitoring

This study investigates delamination damage mechanisms during the double cantilever beam standard test using the strain energy release rate. The acoustic emission parameter is used to replace the original calculation method of measuring crack length to predict delamination. For this purpose, 24-layer glass/epoxy multidirectional specimens with different layups, and interface orientations of 0°, 30°, 45°, and 60°, were fabricated based on ASTM D5528 (2013). Acoustic emission testing (AE) is used to detect the damage mechanism of composite multidirectional laminates (combined with microscopic real-time observation), and it is verified that the strain energy release rate can be used as a criterion for predicting delamination damage in composite materials. By comparing the AE results with the delamination expansion images observed by microvisualization in real time, it is found that the acoustic emission parameters can predict the damage of laminates earlier. Based on the data inversion of the acoustic emission parameters of the strain energy release rate, it is found that the strain energy release rate of the specimens with different fiber interface orientations is consistent with the original calculated results.

Mechanical model and numerical simulation of composite laminates subjected to low velocity impact

A mechanical model of laminated plates subjected to low velocity impact is proposed in this paper. The model studies the attenuation of impactor velocity affected by air resistance, intra-laminar damage initiation based strain, intra-laminar damage evolution based on damage parameters and delamination damage. Based on this mechanical model and ABAQUS platform, the experiment of Shi is numerically simulated. It is found that the predicted contact force, energy absorption and delamination damage of laminates are in good agreement with the experimental results, indicating that the established mechanical model can be used to predict the mechanical response and damage characteristics of composite laminates subjected to low velocity impact.

Assessment of delamination location in composite laminates based on a chaotic oscillator method

The work aims to study the assessment of delamination location in composite laminates using vibration measurement with a chaotic oscillator method. Delamination is a type of damage that commonly occurs in composite laminates, which can cause a severe degradation of their material properties. The traditional vibration-based methods can encounter difficulties in detecting and locating these delamination-type damages especially when the size of delamination is relatively small and there is a significant level of noise in its vibration measurement. With this particular consideration, a vibration-based method using a non-linear chaotic oscillator was used in this study due to its sensitivity to the change in vibration signal characteristics. A numerical model of composite laminates with delamination damage under harmonic excitation was developed and the vibration signal obtained from composite laminates was processed using the chaotic oscillator method. A feature named Lyapunov Exponent (LE) was used as a delamination damage index to describe the characteristics of the chaotic oscillator for cases with delamination at varying structural locations. The effects of delamination locations on the developed damage index were analyzed in this work. The results showed that there was a strong correlation between the delamination location and the LE feature, even for the case with a relatively high level of measurement noise. The results demonstrated the effectiveness of the method to identify delamination in composite laminates, which has also the potential to be used to detect other types of damages.

MEASUREMENT OF SURFACE QUALITY AND OPTIMIZATION OF CUTTING PARAMETERS IN SLOT MILLING OF GFRP COMPOSITE MATERIALS WITH DIFFERENT FIBER RATIOS PRODUCED BY PULTRUSION METHOD

The final shape of fiber-reinforced polymer (FRP) materials is usually given by machining. However, machining FRP materials is complex and difficult. Appropriate cutting tools and cutting parameters should be determined to overcome these difficulties. In this work, glass fiber-reinforced polymer (GFRP) materials with 60% and 68% fiber ratio, produced by pultrusion method, were machined. End of the milling, surface roughness (Ra), delamination damage factor (Fdd), sound and vibration results were analyzed. Experiments were carried out with Taguchi L[Formula: see text] mixed design and the results were analyzed by Taguchi, ANOVA and Pareto charts. In Taguchi and Pareto analyses, the most effective parameter for surface roughness and delamination damage factor was the feed rate, and the cutting velocity for sound and vibration. Different regression models have been tried. Linear regression was found as most suitable. The significance values of the regression models are 92.04% for surface roughness, 87.12% for delamination damage factor, 98.64% for sound and 73.27% for vibration.

Study on delamination damage evolution of composite L-shaped adhesive joint based on cohesive behavior

The adhesive joint of composite materials is one of the typical structures in aircraft structures, and the delamination damage is one of the most important damage modes in composite adhesive joints. In this paper, static and fatigue tests were carried out on L-shaped adhesive joints to analyze the damage evolution and failure modes of delamination damage under static and fatigue loadings. Based on the cohesive constitutive models, the static and high-cycle fatigue delamination constitutive models were developed. The static and fatigue numerical models of composite L-shaped adhesive joints were established by using finite element software. The stress distribution, deformation modes and delamination propagation laws were systematically studied. The simulation results are in good agreement with the experimental results. The delamination damage initiation, evolution and failure mechanism of L-shaped adhesive joints under static and fatigue loads were revealed by combining the experimental and the numerical results, which will provide theoretical and engineering guidance for strength and fatigue analysis of composite adhesive structures.