Deformation and damage evolution of a full-scale adhesive joint between a steel bracket and a sandwich panel for naval application (original) (raw)
Related papers
Damage assessment and monitoring of composite ship joints
Composite Structures, 2005
This paper describes the research activities associated with the damage assessment of maritime structures, conducted within the Cooperative Research Centre for Advanced Composite Structures, which aims to develop the capability to predict the criticality of typical damage in a ship joint and to develop and test techniques for its structural health monitoring (SHM). The research is focused on modelling and testing of a typical monolithic glass fibre reinforced polymer composite T-joint, which is subjected to disbonds at various interfaces. Methods for determining critical disbond sizes and two semi empirical methods have been evaluated. Embedded optical fibre Bragg grating sensors have been assessed for SHM. Issues have been addresses, involving embedding optical fibres into the joint interface and a technique has been developed for successful embedding and positioning of sensors. The performance of embedded Bragg grating sensors in such joints has been shown to be satisfactory and the effects of artificially induced disbonds on the strain distribution have been determined via finite element modelling and have been experimentally verified. The use of the random decrement signature of the structural response to turbulence has been assessed for SHM. Models and experiments involving typical joints with artificially induced disbonds have indicated that this technique could be successfully used to detect and characterise damage.
Determination of the strain distribution in adhesive joints using Fiber Bragg Grating (FBG)
Journal of Adhesion Science and Technology, 2012
This work focuses on the development and testing of a technique used to measure strain levels inside an adhesive joint. As more industries adopt high performance structural adhesives, the need for structural monitoring and quality control of adhesive joints rises. The method presented in this work, based on optic fibers, is proposed as a possible mean for real-time health monitoring of adhesive connections. In the first part of this work a procedure for embedding optical fibers etched with Bragg sensors is explained. Instrumented, single lap joints were manufactured and subjected to tensile test. The results were compared with finite element models to ensure the accuracy and provide a better understanding of the measurement process. Lastly, improvements to the procedure were suggested.
Experimental analyses of metal-composite bonded joints: damage identification
Applied Adhesion Science, 2014
The advent of composite co-cured and co-bonded integrated construction in aircraft structures has lead to the replacement of fastened joints with bonded joints between the skins and the stiffeners. Skin-stiffener debondings could occur due to impact or other operational reasons and it is usually internal failure. Damage identification of bonded components, which are often vital elements in many structures, is crucial for the prevention of failure of the entire structure. Thus, different researchers have investigated vibration-based methods as an alternative technique to be used in the structural health monitoring (SHM) systems. Hence, this work consists of investigating experimentally through the vibration-based method, the dynamic behavior changes in a bonded metal-composite structure by using piezoelectric transducer and accelerometers in order to monitory the damage. The damage is an artificial debonding in the joint, which was simulated by inserting Teflon™ tapes within the joint. In-situ inspection as ensured by accelerometer and piezoelectric transducers (PZT) bonded to the structure. Indeed, with a simple comparison of the frequency response functions is difficult to conclude if there is damage in the structure, unless a large damage is presented. However, by using damage metrics, it is possible to identify the damage with more accuracy. Thus, the experimental results obtained by the accelerometers were compared to the data provided by the smart composite sensors (PZT). Finally, it was discussed the advantages and limitations of the experimental analyses and the identification technique proposal.
Tensile fracture characterization of adhesive joints by standard and optical techniques
Engineering Fracture Mechanics, 2015
The use of adhesive joints has increased in recent decades due to its competitive features compared with traditional methods. This work aims to estimate the tensile critical strain energy release rate (G IC ) of adhesive joints by the Double-Cantilever Beam (DCB) test. The J-integral is used since it enables obtaining the tensile Cohesive Zone Model (CZM) law. An optical measuring method was developed for assessing the crack tip opening (d n ) and adherends rotation (h o ). The proposed CZM laws were best approximated by a triangular shape for the brittle adhesive and a trapezoidal shape for the two ductile adhesives.
The Journal of Adhesion, 2017
Failure behaviour of two types of adhesively bonded joints (composite-to-metal, metal-to-metal) has been studied under failure modes (Mode I: double cantilever beam (DCB) and Mode II: three-point end notch flexures (3-ENF)) using acoustic emission (AE) technique. The bonded specimens were prepared using two types of adhesive bond materials with three variations of adhesive bond quality. The effect of the presence of interfacial defects along the interface on the residual strength of the joint has also been studied. It was possible using the maximum AE amplitude method to select the AE events of mechanical significance. However, it proved difficult to propose a definitive AE trait for the mechanical phenomena occurring within specific AE event signals, for all adhesive types, bond qualities, and substrate configurations; therefore, all specimen combinations. There was a notable shift in spectral energy proportion as the AE source of mechanical significance varied along the specimen length for specimen combinations. However, it was difficult to confirm this distinctive trait for all specimen combinations due to difficulty in confirming the location and exact mechanical source. The proposed measurement technique can be useful to assess the overall structural health of a bonded system and may allow identification of defects.
Acoustic emission applied to mode I fatigue damage monitoring of adhesively bonded joints
e-Journal of Nondestructive Testing, 2023
The use of adhesively bonded joints has increased considerably due to their lightweight, relevant strength-weight ratio and possibility to join multi-materials. Nevertheless, there are still some challenges in the application of this kind of joints in primary structures, such as guaranteeing their reliability during the components' useful life. Structural health monitoring methods are suggested to ensure in-service safety and reliability of adhesive joints. The acoustic emission appears promising because it can detect the elastic waves produced within the material when it is under damage or straining. This research focuses on mode I fatigue damage monitoring metallic double cantilever beam adhesively bonded joints using the acoustic emission method. Digital image correlation and visual evaluation were applied during fatigue interruptions to track the crack-tip position within the adhesive and correlate them with the acoustic emission outcomes. The acoustic emission method is susceptible and different kinds of waves (background, friction and damage) can be easily assessed during the tests, producing an immense amount of data. So, unsupervised artificial neural networks for patterning recognition were proposed. Self-organising maps and k-means algorithms were used for data clustering and then classified regarding their sources. Finally, the acoustic emission results, digital image correlation and visual evaluations were compared.
Health monitoring of marine composite structural joints using fibre optic sensors
Composite Structures, 2006
This paper describes a methodology for the health monitoring of composite marine joint structures based on strain measurements under operational loading using embedded fibre Bragg grating sensors. Finite element modelling indicated that the presence of a disbond significantly altered the bond-line longitudinal strain distribution. This was verified qualitatively through an experimental test program. The experimental results are examined in relation to the FE predictions and the implications for a practical strain-based SHM system are discussed. A technique is developed, based on novel signal processing and statistical outlier detection. This enables the sensor measurements to be used for damage detection without reference to a high-fidelity numerical model of the structure which is often difficult and resource-intensive to generate. The technique is shown to provide successful damage diagnoses with an acceptable level of accuracy. Further improvement in diagnostic accuracy may be achieved by increasing the sensor density.
Detection of failures of adhesively bonded joints using the acoustic emission method
Holzforschung, 2000
Wooden glued constructions require touch-free monitoring of destructive processes, especially in adhesive bonds that are most exposed to failure. The objective of the investigations was to describe failure processes in the adhesive bond of wood joints, in particular to determine their initiation, propagation, and destruction. The acoustic emission (AE) method was employed as the carrier of information about changes occurring in glued joints, whereas the numerical method was applied to determine values of distribution of tangential stresses generated in adhesive bonds. The acoustic phenomena examined were described using the AE cumulative counts. The authors analysed acoustic signals generated in loaded wooden and plastic overlap samples glued together using polyethyl methacrylate glue as well as in solid samples. On the basis of the acoustic emissions obtained, it was possible to establish characteristic places and stages of escalating structural defects generated from bonds of adhe...
Through-thickness strain field measurement in a composite/aluminium adhesive joint
Composites Part A: Applied Science and Manufacturing, 2009
This paper presents an experimental procedure, which enables us to assess the shear strain field in an adhesive joint between composite and aluminium. In practice, this strain field is representative of the progressive stress transfer between a loaded structure and a composite patch used for reinforcement purposes. Digital image correlation (DIC) is used to measure the displacement field through the thickness of a patched specimen subjected to a tensile test. The shear strain field derives from the measured displacement field. The shear strain clearly decreases when the distance from the free edge of the adhesive increases, as predicted by numerical and analytical models of the joint. These measurements are used to estimate the in situ shear modulus of the adhesive. It is observed that the shear modulus decreases when the shear stress increases, thereby illustrating the non-linear response of the adhesive.
Composite Structures, 2015
This work addresses the experimental identification of mode I cohesive law of wood bonded joints. The approach combines the double cantilever beam (DCB) test with both digital image correlation (DIC) and embedded fibre Bragg grating (FBG) sensors. The spectrum geometric mean of the FBG reflected spectral response was determined, and the wavelength evolution was used to define the fracture process zone (FPZ) development phase. This evaluation allowed a consistent selection of experimental range of over which the identification procedure of mode I cohesive law is build up. Mode I crack length, Resistancecurve and cohesive law parameters are characterised and discussed. The strain energy release rate (G I) is determined from the P-d curve by the compliance-based beam method (CBBM). The crack tip opening displacement (w I) is determined by post-processing displacements measured by DIC. The cohesive law in mode I (r I-w I) is then obtained by numerical differentiation of the G I-w I relationship.