Guided waves have been extensively explored in the field of Structural Health Monitoring (SHM) and Non-Destructive Testing (NDT) over many years. Guided waves are usually excited and registered by using an array of piezoelectric transducers attached to the surface of the inspected structure. However, in some cases, piezoelectric transducers cannot be used directly on the structure and noncontact wave excitation methods are preferable. This paper is a continuation of authors’ previous research on complete non-contact NDT methods in which low-cost resonant-based ultrasonic transmitters together with scanning laser Doppler vibrometer are used. The aim of the paper is the comparison of guided wave actuation ability in a composite plate by using the single ultrasonic transmitter, flat ultrasonic transmitter array and spherical ultrasonic transmitter array. Full wavefield of propagating guided waves was registered on a fine grid of points by using laser vibrometer and processed by using the wavenumber filtering method. Finally, the accuracy of delamination localization and size was estimated for each actuation setup.
Sandwich-structured composites consisted of two outer skins and a lightweight internal core. Due to structural and geometrical properties, these composites are light, have a relatively high flexural strength and could have high thermal insulating characteristics. Therefore, such materials are widely used in many industrial applications (e.g. aeronautics, civil engineering, road vehicles, and ships) especially where high strength to weight ratio is required. In such applications, it is often important to control the loads and operation conditions e.g. temperature. Apart from strength requirements, due to the safety issues, there is a big need for equipping structures in structural health monitoring (SHM) systems. One of the promising monitoring methods base on Fiber Bragg Grating (FBG) sensors. It is due to the advantages of FBG sensors such as small size and weight, high corrosion resistance. The paper presents an application of FBG sensors for assessment of load and temperature influences on a composite sample. For this purpose glass fiber - foam sandwich-structured composite sample with embedded FBG sensors was handmade. A relationship between temperature and strain as well as a relationship between static point load and strain determined from FBG sensors measurements were analyzed. Structural responses for static point load applied in selected locations on the sample surface were studied.
Advanced composite materials have gained popularity in high-performance structural designs applications that require light weight components with superior mechanical properties in order to perform in demanding service conditions as well as provide energy efficiency and safety to mankind and nature. Damage can appear by external impacts or internal failures. The structural damage can occur due to many factors which are difficult to predict in advance, e.g.: sudden impact loads. An external impact can cause an internal damage with no visible marks on the external surfaces of the element. The possible hidden damage can be the source of a further mechanical deterioration of the composite structural element. Recently one of the promising monitoring method is based on Fiber Bragg Grating (FBG) sensors. It is due to the advantages of FBG sensors such as small size and weight, high corrosion resistance or no calibration requirements. Also it is very easy to multiplex FBG sensors and make rosettes arrays that can be implemented on/ into structures. The goal of the research is to analyse impact detection capability of different FBG strain rosettes types. Additionally the sensitivity and area of working of an individual rosette will be considered. The experiment will be carried out on a sandwich plate with the use of impact hammer. The proposed impact detection method by a rosette network can be applied on structures like plane wings, turbine blades or ship masts. The locations of detected impacts can be further analysed by more sophisticated method (terahertz spectroscopy or infrared thermography).