Abstract: A Finite Element (FE) based scheme is presented
for quantifying guided wave interaction with Localised Nonlinear
Structural Damage (LNSD) within structures of arbitrary layering
and geometric complexity. The through-thickness mode-shape of the
structure is obtained through a wave and finite element method. This
is applied in a time domain FE simulation in order to generate
time harmonic excitation for a specific wave mode. Interaction of
the wave with LNSD within the system is computed through an
element activation and deactivation iteration. The scheme is validated
against experimental measurements and a WFE-FE methodology for
calculating wave interaction with damage. Case studies for guided
wave interaction with crack and delamination are presented to verify
the robustness of the proposed method in classifying and identifying
damage.
Abstract: Composite materials are one answer to the growing demand for materials with better parameters of construction and exploitation. Composite materials also permit conscious shaping of desirable properties to increase the extent of reach in the case of metals, ceramics or polymers. In recent years, composite materials have been used widely in aerospace, energy, transportation, medicine, etc. Fiber-reinforced composites including carbon fiber, glass fiber and aramid fiber have become a major structural material. The typical defect during manufacture and operation is delamination damage of layered composites. When delamination damage of the composites spreads, it may lead to a composite fracture. One of the many methods used in non-destructive testing of composites is active infrared thermography. In active thermography, it is necessary to deliver energy to the examined sample in order to obtain significant temperature differences indicating the presence of subsurface anomalies. To detect possible defects in composite materials, different methods of thermal stimulation can be applied to the tested material, these include heating lamps, lasers, eddy currents, microwaves or ultrasounds. The use of a suitable source of thermal stimulation on the test material can have a decisive influence on the detection or failure to detect defects. Samples of multilayer structure carbon composites were prepared with deliberately introduced defects for comparative purposes. Very thin defects of different sizes and shapes made of Teflon or copper having a thickness of 0.1 mm were screened. Non-destructive testing was carried out using the following sources of thermal stimulation, heating lamp, flash lamp, ultrasound and eddy currents. The results are reported in the paper.
Abstract: Structural relaxation processes in optical coatings represent a fundamental limit to the sensitivity of gravitational waves detectors, MEMS, optical metrology and entangled state experiments. To face this problem, many research lines are now active, in particular the characterization of new materials and novel solutions to be employed as coatings in future gravitational wave detectors. Nano-layered coating deposition is among the most promising techniques. We report on the measurement of acoustic loss of nm-layered composites (Ti2O/SiO2), performed with the GeNS nodal suspension, compared with sputtered λ/4 thin films nowadays employed.
Abstract: A novel method is presented for obtaining the stress
field induced by an edge dislocation in a multilayered composite. To
demonstrate the applications of the obtained solution, we consider the
problem of an interfacial crack in a periodically layered bimaterial
medium. The crack is modelled as a continuous distribution of edge
dislocations and the Distributed Dislocation Technique (DDT) is
utilized to obtain numerical results for the energy release rate (ERR).
The numerical implementation of the dislocation solution in
MATLAB is also provided.
Abstract: Vibrations of circular cylindrical shells made of
layered composite materials are considered. The shells are weakened
by circumferential cracks. The influence of circumferential cracks
with constant depth on the vibration of the shell is prescribed with the
aid of a matrix of local flexibility coupled with the coefficient of the
stress intensity known in the linear elastic fracture mechanics.
Numerical results are presented for the case of the shell with one
circular crack.
Abstract: In this study, the contact problem of a layered composite which consists of two materials with different elastic constants and heights resting on two rigid flat supports with sharp edges is considered. The effect of gravity is neglected. While friction between the layers is taken into account, it is assumed that there is no friction between the supports and the layered composite so that only compressive tractions can be transmitted across the interface. The layered composite is subjected to a uniform clamping pressure over a finite portion of its top surface. The problem is reduced to a singular integral equation in which the contact pressure is the unknown function. The singular integral equation is evaluated numerically and the results for various dimensionless quantities are presented in graphical forms.