Imaging of sub-surface defect in CFRP laminate using A0-mode Lamb wave: Analytical, numerical and experimental studies.

Lamb wave propagation in the anisotropic material is characterized by the prominent directivity of wave energy transfer governed by the fiber direction. Due to this anisotropic behavior, it is difficult to define the location of defects by using the arriving time of reflected signals. In this article, A0-mode Lamb wave-based damage detection technique has been illustrated which can detect the overlapping region of incident and scattered wave in the vicinity of the finite defect region in CFRP composite plate-like structure. A 5-cycle Hanning windowed tone burst of 30 kHz has been allowed to propagate through a 2 mm thickness [0/90]4S CFRP plate with subsurface cylindrical defect. In the near field region of the defect, the incoming and reflected wave overlaps and the dynamic shear strains of the out-of-plane displacement evaluated consequently. A covariance matrix is developed consisting of the shear strains. The proposed technique can detect the overlapping regions by measuring the determinant of covariance matrix, thus the image of the defect can be reconstructed. In this article, the analytical model of the proposed wavelet-based technique for the subsurface cylindrical defect is discussed and their physical meanings are investigated through numerical and experimental studies in a cross-ply laminate.

Effect of chemical treatments on properties of injection molded Nypa fruticans fiber reinforced polypropylene composite.

The rise in environmental awareness prompted consideration of environment friendly materials. Natural fiber, on the contrary, has a structure that allows it to absorb moisture attributable to its hydrophilicity, which hinders its wide application and leads to poor interfacial bonding with the polymer matrix. Therefore, fiber surface modification is inevitable, which is usually based on using the functional group of some chemicals to replace the hydrophilic hydroxyl group to make it more moisture resistant and ameliorate the boding between fiber and polymer matrix. In this study, injection molded nypa fiber reinforced polypropylene composites were fabricated. Three different chemical modification i.e., mercerization, H2O2 treatment, maleic anhydride polypropylene (MAPP) compatibilizer, were employed. Other parameters on which the properties of the composite depend, i.e., fiber volume (30%), manufacturing process, etc. were kept the same. Field emission scanning electron microscopic (FE-SEM) images were also investigated to verify the result of experiments. Moisture resistance of the composite was also evaluated. The tensile and flexural properties of treated composite were significantly enhanced than the untreated one. The maximum strength was obtained for MAPP treated composite. The chemical treatment has a less impact on the impact strength of the composite. Better moisture resistance was observed for treated fiber composites. This study provides the insight of using chemical treatment for better adhesion between the fiber and the polymer.