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Adhesively bonded interfaces of glass fiber– reinforced plastics (GFRP) composite to rubber and rubber to propellant were investigated for planar interfacial defects with a spatial resolution of 100 μm. Single-sided low-field nuclear magnetic resonance (NMR) with a magnetic field strength of 0.3 T (12.88 MHz proton frequency) has been used for noninvasive inspection of planar defects in GFRP-based multilayered composite structures. Further, in this paper, the application of low-field NMR for adhesive liner thickness measurement is also demonstrated. The investigation revealed applicability of single-sided low-field NMR for onsite field applications. Results were compared with other nondestructive evaluation (NDE) techniques: acousto-ultrasonic and radiographic testing (RT). It is observed that single-sided low-field NMR is an excellent NDE tool to study adhesive bonds and defects such as debonding, variations in thickness to accuracies ranging from 50 to 200 μm, and degradation. In comparison with the acousto-ultrasonic technique and RT, single-sided low-field NMR is observed to be more sensitive.

Polymer-based Glass composite cylindrical structures consisting of multi-layered configuration for special applications were tested with low magnetic field nuclear magnetic resonance (NMR) techniqu...

Aerospace structural components are made by adhesively bonded layers of different materials for achieving specific properties for industrial applications. One such advanced structural material is made of glass fibre reinforced plastic (GFRP) composite. This is a layered engineered material with composite adhesively bonded to rubber to one of the surfaces. Such engineered materials can withstand structural, thermal and corrosive environments. GFRP composite have to be bonded with rubber using rubber solution or other adhesive to keep them structurally bonded. Any separation of these two layers will make the engineered structure redundant. In this paper, we report application of various NDE methods for evaluating bonded interfaces of engineered structural composite materials. Conventional methods such as X-ray radiography and ultrasonic (acousto-ultrasonic) methods were experimentally verified for identifying defects at the adhesively bonded interfaces. Disadvantages of these conventional methods were overcome by using advanced single sided nuclear magnetic resonance (NMR) technique. The use of low frequency single sided portable NMR for characterising defects at the adhesively bonded interfaces is discussed. In addition to the defect detection, application of NMR for measuring thickness of adhesive layers coated over rubber is also presented. Advantages of using NMR technique over other conventional methods is discussed.

In the present work, the flexural strength of delaminated composite plate has been analysed numerically and compared with experimental results. For the numerical investigation, a general mathematical model of the laminated composite plate with and without delamination has been developed using two higher-order kinematic models. The desired governing equation is obtained using variational approach and discretised with the help of the isoparametric finite element steps. The flexural responses of the delaminated structure computed numerically through a generic in-house computer code developed in MATLAB environment. The consistency of the developed numerical models is checked and validated by comparing the bending responses with the available published results. Now, the experimental bending responses of both intact and delaminated composites are evaluated using three-point bend test and compared with numerical responses of the presently developed higher-order models. Finally, the effect of different materials and geometrical parameters including the size, location and position of the delamination on the bending behaviour of the laminated composite plate have been analysed numerically and discussed in detail.

In this article, the effect of delamination on the free vibration behaviour of the laminated composite curved panels of different geometries (cylindrical, spherical, elliptical, hyperboloid and flat) is investigated. The laminated structure with seeded delamination is modelled mathematically using two different higher-order shear deformable kinematic models. The desired governing equation is obtained using classical Hamilton's principle and discretised with the help of finite element steps. The frequency responses are computed numerically through an in-house computer code developed in MATLAB environment. The convergence behaviour of the present numerical models have been checked and validated by comparing the frequency responses with those of the available published results. Further, the responses are also computed experimentally using CDAQ-9178 (National Instruments) in conjunction with LABVIEW software for the laminated plate with different delamination (size, location and position) and compared with present numerical results. In addition, the frequencies are also computed for the laminated structure with and without delamination using commercial finite element package ANSYS APDL. Finally, the effect of different materials and geometrical parameters including the size, location and position of the delamination on the free vibration behaviour of laminated composite shell panel has been analysed numerically and discussed in detail.

This paper is concerned with the development of model for the finite element analysis of the conical space adapter which is subjected to axial compression. It also provides the information about the parameters required for generating the input for modelling the structure. Analysis is performed using Ansys, i.e. software for finite element analysis. The results of analysis include the behaviour of the adapter under axial compression, e.g. stresses in the helical and circumferential ribs, displacement of the space adapter, critical buckling load and global buckling. Modal analysis has been carried out to study the modes of vibrations and obtain the frequency of vibration of the structure.