Damage growth and failure detection in hybrid fiber composites using experimental in-situ optical strain measurements and smoothing element analysis:
TL;DR: In this paper, the failure initiation and development in hybrid fiber laminates was successfully monitored and determined, and a novel damage monitoring approach was proposed, which is used to detect failure initiation.
Abstract: In previous study the failure initiation and development in hybrid fiber laminates was successfully monitored and determined. In current investigation a novel damage monitoring approach is proposed...
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TL;DR: In this paper , the development of the Gauss curvature across the CFRP is computed from DIC displacement data, and a sudden onset of curvature in the vicinity of the bolts is observed as a precursor to bearing failure.
4 citations
TL;DR: In this article , the first investigation of the inverse finite element method (iFEM) coupled with the genetic algorithm (GA) to optimize sensor placement models of plate/shell structures for their real-time and full-field deformation reconstruction is reported.
Abstract: This paper reports the first investigation of the inverse finite element method (iFEM) coupled with the genetic algorithm (GA) to optimize sensor placement models of plate/shell structures for their real-time and full-field deformation reconstruction. The primary goal was to reduce the number of sensors in the iFEM models while maintaining the high accuracy of the displacement results. Here, GA was combined with the four-node quadrilateral inverse-shell elements (iQS4) as the genes inherited through generations to define the optimum positions of a specified number of sensors. Initially, displacement monitoring of various plates with different boundary conditions under concentrated and distributed static/dynamic loads was conducted to investigate the performance of the coupled iFEM-GA method. One of these case studies was repeated for different initial populations and densities of sensors to evaluate their influence on the accuracy of the results. The results of the iFEM-GA algorithm indicate that an adequate number of individuals is essential to be assigned as the initial population during the optimization process to ensure diversity for the reproduction of the optimized sensor placement models and prevent the local optimum. In addition, practical optimization constraints were applied for each plate case study to demonstrate the realistic applicability of the implemented method by placing the available sensors at feasible sites. The iFEM-GA method’s capability in structural dynamics was also investigated by shape sensing the plate subjected to different dynamic loadings. Furthermore, a clamped stiffened plate and a curved shell were also considered to assess the applicability of the proposed method for the shape sensing of complex structures. Remarkably, the outcomes of the iFEM-GA approach with the reduced number of sensors agreed well with those of the full-sensor counterpart for all of the plate/shell case studies. Hence, this study reveals the superior performance of the iFEM-GA method as a viable sensor placement strategy for the accurate shape sensing of engineering structures with only a few sensors.
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TL;DR: In this paper, the observation of photosensitivity in Ge-doped core optical fibers is reported. The photosensitivity is manifested by light-induced refractive index changes in the core of the waveguide.
Abstract: The observation of photosensitivity in Ge‐doped core optical fibers is reported. The photosensitivity is manifested by light‐induced refractive‐index changes in the core of the waveguide. Narrowband reflectors in a guide structure have been fabricated using this photosensitivity and the resulting DFB reflectors employed as laser mirrors in a cw gas laser in the visible.
2,294 citations
"Damage growth and failure detection..." refers methods in this paper
...Another method for strain measurements in fiber reinforced laminates is usage of embedded Fiber Bragg gratings (FBG) sensors (Hill et al., 1978) inside the laminates....
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TL;DR: In this paper, a review aims to explain basic mechanisms of these hybrid effects and describes the state-of-the-art models to predict them, and an overview of the tensile, flexural, impact and fatigue properties of hybrid composites is presented to aid in optimal design of hybrid composite materials.
Abstract: Fibre-reinforced composites are rapidly gaining market share in structural applications, but further growth is limited by their lack of toughness. Fibre hybridisation is a promising strategy to toughen composite materials. By combining two or more fibre types, these hybrid composites offer a better balance in mechanical properties than non-hybrid composites. Predicting their mechanical properties is challenging due to the synergistic effects between both fibres. This review aims to explain basic mechanisms of these hybrid effects and describes the state-of-the-art models to predict them. An overview of the tensile, flexural, impact and fatigue properties of hybrid composites is presented to aid in optimal design of hybrid composites. Finally, some current trends in fibre hybridisation, such as pseudo-ductility, are described.
598 citations
"Damage growth and failure detection..." refers background in this paper
...Since carbon plies of the hybrid laminate possess higher elastic modulus as compared to their glass counter parts, major stress is carried by them and they transfer the load to glass plies after failure either through pseudo-ductility or catastrophic interlaminar delamination (Swolfs et al., 2014)....
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...(Swolfs et al., 2014, 2016)....
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TL;DR: In this paper, a displacement methodology for Mindlin elements, recently employed in the development of an efficient, four-node quadrilateral (MIN4), is the basis for a three-node, explicitly integrated triangular element (MIN3).
263 citations
"Damage growth and failure detection..." refers background in this paper
...…ði ¼ 1; 2; 3; j ¼ 2; 3; 1; k ¼ 3; 1; 2Þ (4b) and the area of the triangular element calculated as: S ¼ 1 2 ða3b2 a2b3Þ (4c) On the other hand, the C1-continuous anisoparametric shape functions namely f1i and f2i, are originally obtained for triangular element, MIN3 (Tessler and Hughes, 1985)....
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TL;DR: In this paper, the post-fabrication FBG spectra were studied to examine the influence of manufacturing variables (such as composite stacking sequence and resin flow during processing) on the final profile of the spectrum and the functionality of the sensor.
232 citations
TL;DR: In this article, two-dimensional and three-dimensional (3D) Digital Image Correlation (DIC) techniques were employed to obtain full-field surface strain measurements in carbon-fibre/epoxy M21/T700 composite plates with different stacking sequences in the presence of an open circular hole.
Abstract: High performance composite materials, such as Carbon–Fibre Reinforced Plastic (CFRP) composites, are being increasingly used in aerospace industry, such as fuselage primary structures in Boeing 787 or Airbus 350, where high strength and stiffness are required at minimum weight [1] . The design of composite structures frequently includes discontinuities such as cut-outs for access and fastener holes for joining and they become critical regions under thermo-mechanical loading. Understanding of notched specimen behaviour is necessary for the design of complex structures where parts are mostly connected with bolts and rivets [2] . The effect of these discontinuities on the behaviour of composite materials is an important topic because it causes a relatively large reduction in strength compared to the unnotched laminate [3] . In the first part of the current work, the assessment of the damage process taking place in notched (open-hole) specimens under uniaxial tensile loading was studied. Two-dimensional (2D) and three-dimensional (3D) Digital Image Correlation (DIC) techniques were employed to obtain full-field surface strain measurements in carbon–fibre/epoxy M21/T700 composite plates with different stacking sequences in the presence of an open circular hole. Penetrant enhanced X-ray radiographs were taken to identify damage location and extent after loading around the hole. DIC strain fields were compared to numerical predictions. In the second part of the study, DIC techniques were used to characterise damage and performance of adhesively bonded patch repairs in composite panels under tensile loading. This part of work relates to strength/stiffness restoration of damaged composite aircraft that becomes more important as composites are used more extensively in the construction of modern jet airliners. In the current work, external bonded patches have been studied. Adhesively bonded repairs are the most common type of repair carried out with composite materials [1] , [4] . The behaviour of bonded patches under loading was monitored using DIC full-field strain measurements. Location and extent of damage identified by X-ray radiography correlates well with DIC strain results giving confidence to the technique for structural health monitoring of bonded patches.
174 citations
"Damage growth and failure detection..." refers methods in this paper
...DIC technique is favored as compared to other methods since it provides measurements with least sensitivity to vibration and optics anomalies (Caminero et al., 2013)....
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