I. INTRODUCTION

II. DAMAGE DETECTION METHODOLOGY

III. DISPERSION CURVES

IV. FE SIMULATION MODEL

V. DAMAGE DETECTION STRATEGY

VI. DAMAGE LOCATION ESTIMATION

VII. DAMAGE SIZE ESTIMATION

VIII. INFLUENCE OF NOISE ON DAMAGE ESTIMATION

IX. DISCUSSION OF RESULTS

X. CONCLUSION

REFERENCES

The damage detection method for composite laminates introduced in this research uses piezoelectric (lead zirconate titanate, PZT) transducers to excite/sense the Lamb wave signals. The complicated wave signals scattered by damage are accurately processed using a continuous wavelet transformation (CWT) based on the Gabor wavelet. The transducers are arranged on a composite laminate in the form of a network of square detection cells and triangular subcells. The damage location is estimated using the concept of centroid in two-stage detection method. The first stage detection is carried out by exciting a transducer at the center of each detection cell to locate the damaged cell and subcell. The damage localization is improved by exciting an additional transducer at the corner of the damaged subcell during the second stage detection. The damage size is then quantitatively estimated using cubic spline curve (CSC) and elliptical parametric (EP) methods based on the damage edge points. The damage location is estimated in two detection stages for high-accuracy because the damage edge points are calculated with reference to the estimated location of the damage. The arrangement of transducers and signal processing technique remain the same at all the stages of damage detection. Results from previous detection stages contribute to the improvement of damage detection in the subsequent stages. The size of detection cell plays a crucial role in designing the detection stages, and the proposed method can accurately quantify both location and size of the damage in composite laminate.

INTRODUCTION

The properties of composite materials can be tailored to exhibit superior properties such as high strength to weight ratio, high modulus and high resistance to aggressive environmental conditions. Composite materials are increasingly employed to achieve the desired performance in wide range of applications from various industries like aerospace, automotive, naval and wind turbine etc. However, the mechanical properties and structural integrity of composite structures can be compromised by various types of fabrication and in-service defects. A small damage in composite structure can grow and lead to the catastrophic failure of the entire structure. Therefore, a continuous monitoring of the structural components, for damage detection at an early stage, is required for efficient repair and maintenance. Researchers have developed many computational and intelligent techniques for structural health monitoring (SHM) of composites [1]. The SHM techniques based on Lamb waves are commonly used for damage detection in composite laminates. The Lamb waves are highly sensitive to small imperfections, and have the ability to propagate relatively a long distance with low attenuation. The change in the Lamb wave propagation due to forward and backward scattering from damage can be analyzed to evaluate the damage. The PZT (lead zirconate titanate) transducers are frequently used to excite and sense the Lamb wave signals because they are small, lightweight, consume low power, and produce a frequency response in wide region [2].