Abstract

Abstract

Complex composite structures have unexpected mechanical behaviour, specially under high dynamic loads or in bucking conditions. The complexity and the number of sensors of these types of structural testing require non-standard instrumentation in order to detect local phenomena before critical failure appears. The main problem introduced by accelerometers or strain sensors is the cabling, due to the weight and complexity introduced. Digital Image Correlation (DIC) is a strain and deformation measurement technique well know and extendedly applied in composite structural testing. In this paper it is proposed a new DIC methodology based on project the aleatory patter over the structure instead of paint it. Furthermore, an UAV wing full made of composite will be tested at high frequency and vibrations modes will be observed with a stroboscope and, simultaneously, the aleatory patter will be projected in order to measure the shape of the vibration mode applying the DIC technique. Additionally, strain and shape sensing at high frequencies will be validated with Distributed Fiber Optic at high frequency rates. In this paper, the different technologies will be tested and compared in order to validate their capabilities and limitations.

Abstract

Abstract

A procedure for measuring simultaneously the coefficients of thermal expansion (CET) in the in-plane and the thickness directions in L-shaped composite laminated samples is presented. Measurements are carried out using digital image correlation, from which the displacements in one of the faces of the samples are measured when de sample undergoes a temperature increment inside an oven.

From the in-plane displacement measurements, the in-plane strain tensor components and the corresponding CTE are determined. Results show that the presented technique is capable of determining these CTE with high accuracy.

Displacement measurements in the direction normal to the face, enables determining the rotation of the face and consequently the difference between the CTE in the thickness direction and the CTE in the in-plane direction affected by the curvature.

Results obtained for the CTE in the thickness direction show, first, values significantly higher than the CTE of the material in the in-plane direction normal to the fibres and, second, a high dispersion from one stacking sequence to another. These discrepancies were expected and are caused by the misalignment of the fibres in the corner zone of the samples.