Impact Damage Assessment in CFRP laminates using Phased Array Ultrasonics

Ravi, Vadthyavath and Raju, Gangadharan (2019) Impact Damage Assessment in CFRP laminates using Phased Array Ultrasonics. Masters thesis, Indian institute of technology Hyderabad.

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Abstract

Carbon fiber reinforced polymer materials are increasingly used in the aerospace industry for its superior mechanical and lightweight properties. Composite structures have good in-plane stiffness properties, but poor transverse properties, which is a serious concern under impact loading. Nondestructive techniques are used to assess the internal damage introduced in composite structures, and it is quite complicated because of the inherent anisotropy and inhomogeneity of composite materials. In this work, the Phased array ultrasonic technique (PAUT) is used to evaluate the delamination type of damage in composite laminates subjected to impact loading. Initially, the multi-directional carbon fiber reinforced composite laminates with artificial delaminations are fabricated using the hand layup and vacuum bagging technique. Delamination of different sizes are introduced in the thickness direction of the laminate using Teflon inserts. In this work, the PAUT probes of frequency 3.5 MHz (24 elements) and 5 MHz (64 elements) are used to image the delamination in uni-directional, cross-ply and quasi-isotropic laminates of different thicknesses. Also, the conventional immersion ultrasonic inspection is employed to image the artificial delamination in composite laminates to validate the PAUT results. Subsequently, the composite laminates are subjected to impact using a split-Hopkinson bar setup. The impact energy is varied by changing the mass and velocity of the projectile. PAUT is then applied to assess the delamination damage in uni-directional, cross-ply and quasi-isotropic composite laminates. The performance of PAUT in characterizing the barely visible impact damage is studied under different projectile velocities. C-scans and B-scans obtained using PAUT and immersion ultrasonic system are then used to quantify the delamination damage due to impact in composite laminates. This study is useful in investigating the damage tolerant behavior of composite laminates.

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