33 research outputs found
Buckling and free vibration study of variable and constant-stiffness cylindrical shells
No full textThe ability to steer carbon fibre tapes, varying the tow angle, can widen the designs possibilities of cylindrical shells that are one of the main components of aerospace structures. This research presents experimental and numerical investigation of two carbon fibre reinforced plastic cylindrical shells – a cylinder with conventional layup made of unidirectional prepreg and a variable-stiffness cylinder manufactured by applying fibre placement technology. The shells were tested in compression until buckling and later subjected to a vibration analysis. Load-shortening curves and buckling shapes were acquired during the compression tests, while the natural frequencies and the mode shapes were measured during the vibration tests. Both tests provide a useful data set of the mechanical response of the cylinders which can be applied for further validation of models. The acquired experimental results were compared to a simple, approximated numerical model of the variable-stiffness cylinder showing good correlation with the test results.Aerospace Structures & Computational Mechanic
Buckling of 3D-Printed Cylindrical Shells with Corrugated Surface
No full text3D-printing technology opens broad possibilities to manufacture structural shapes which could not be always possible by other methods. In the field of lightweight shells it allows to investigate structures with higher buckling loads than conventional shells. The buckling behavior of 3D-printed shells is studied in this paper where the shape of the cylindrical shells is modified by adding corrugation in the axial or circumferential directions. The shells are characterized by the amplitude of the corrugation and the number of the sinusoidal waves. Their elastic mechanical behavior is analyzed up to the buckling load. The numerical analysis shows that the modified surface can significantly improve the buckling load and reduces the sensitivity towards geometric imperfections. Prototypes of the shells were manufactured and tested to validate the numerical model. Regardless the experimental scatter, the average buckling load of the optimized corrugated shell twice exceeds the buckling load of the reference circular shell. At the same time stiffness and mass of the shell remain the same.Aerospace Structures & Computational Mechanic
Flexural behavior of sandwich panels with cellular wood, plywood stiffener/foam and thermoplastic composite core
No full textA series of experimental tests have been carried out on three types of novel sandwich panels mainly designed for application in lightweight mobile housing. Two types of the panels are manufactured entirely from wood-based materials while the third one presents a combination of plywood for surfaces and corrugated thermoplastic composite as a core part. All sandwich panels are designed to allow rapid one-shot manufacturing. Mechanical performance has been evaluated in four-point bending comparing the data to the reference plywood board. Additionally, finite element simulations were performed to evaluate global behavior, stress distribution and provide the basis for a reliable design tool. Obtained results show sufficient mechanical characteristics suitable for floor and wall units. Compared to a solid plywood board, sandwich alternative can reach up to 42% higher specific stiffness, at the same time maintaining sufficient strength characteristics
Integration and Optimisation of Multifunctionality for Plywood Sandwich Construction
No full textPromocijas darbs ir veltīts multifunkcionālo īpašību (siltuma izolācija, vibrāciju slāpēšana, trieciena izturība) integrēšanai vieglās saplākšņa sendviča-konstrukcijās. Līdzšinējie pētījumi parāda, ka vieglas, liela laiduma pārseguma konstrukcijas ir efektīvākais veids saplākšņa izmantošanai nesošajās konstrukcijās. Tas ļauj taupīt gan materiālus gan arī samazināt konstrukciju pašsvaru. Papildus ir iespēja integrēt citas funkcijas paneļa serdes daļā, ar papildus materiālu vai optimizējot stinguma elementu izvietojumu. Tomēr, lai pilnvērtīgi izmantotu sendvičpaneļu multifunkcionālo īpašību potenciālu nepieciešama droša un pārbaudīta aprēķina metodika. Detalizēts skaitlisko un eksperimentālo pētījumu apkopojums, kā arī aprēķina metodika ir dota izstrādātajā promocijas darbā. Literatūras pārskats 1. Nodaļā apkopo pieejamo svarīgāko informāciju par sendviča paneļiem. Tai skaitā inovatīvos risinājumus tieši saplākšņa sendviča paneļu projektēšanā. Secinot, ka svarīgākā motivācija jaunu risinājumu izstrādē ir primārā nepieciešamība taupīt izejmateriālus, kas nodrošina konstrukcijas vieglumu, kā arī iespēja izmantot koksnes ražošanas atlikumus. Paneļu skaitliskajai modelēšanai nepieciešamās atsevišķu komponenšu mehāniskās un termiskās īpašības tika noteiktas darba ietvaros un apkopotas 2. Nodaļā. Kā izrādās, pastāv būtiska atšķirība starp zāģēta bērza kokmateriāla un viena lobskaidas mehāniskajām īpašībām. 3. Nodaļā tiek demonstrēts, ka izmantojot detalizētu skaitliskā aprēķina modeli, kas validēts ar eksperimentāliem rezultātiem, ir iespējams precīzi prognozēt sendvičpaneļa deformācijas. Balstoties uz validētu aprēķina modeli un optimizāciju, ir izstrādāta metodoloģija pilnajam saplāksnim līdzvērtīgas veiktspējas sendvičpaneļu atrašanai. Lai vēl vairāk palielinātu klāja nestspēju tiek piedāvāts izmantot viļņotu termoplastiska kompozīta serdi. Viena piegājiena izgatavošanas metode šāda veida paneļiem ir izstrādāta un detalizēti aprakstīta 4. Nodaļā. Bezkontakta mērīšanas sistēmas priekšrocības apkopotas 5. Nodaļā, izmantojot sendvičpaneļus ar šūnveida koksnes serdi. 6. Nodaļā ir analizēts mehāniskās darbības un siltumizolācijas optimizācijas piemērs sendvičpaneļiem ar dabīgās izcelsmes PU serdi. Balstoties uz Pareto optimuma fronti ir iespējams izvēlēties labākos sendvičpaneļa risinājumus starp trīs atbildes reakcijām. Izvērtējot vibrāciju slāpēšanas rezultātus 8. Nodaļā var teikt, ka sendvičpaneļiem ir priekšrocība pār parasta saplākšņa plātnēm, galvenokārt zemāka stinguma dēļ. Trieciena testu apskats 9. Nodaļā parāda, ka plānas, elastīgas vidus kārtas ievietošana saplāksnī būtiski palielina tā trieciena penetrācijas enerģiju. Liela biezuma paneļos trieciena izturība galvenokārt atkarīga no virsmām
Numerical modelling and optimization of all-plywood sandwich panels with rib-stiffened cores
No full textThe current paper deals with numerical modelling of all plywood sandwich panels
with rib-stiffened core. Commercially available finite elements code ANSYS has been
implemented to simulate mechanical behaviour of sandwich panels in bending, according to the
EN 789 standard. It has been confirmed that in order to simulate plywood a multilayered panel
model with shell type elements could adequately represent the mechanical behaviour of such a
structure sufficiently well. Developed parametrical model has been initially validated with
experimental results showing less than 10 % scatter among finite element model and physical
model. Following this a validated numerical model has been implemented for structural
parameter optimization resulting in significant improvement of initial panel design
Non-Contact Measuring System ARAMIS for Sandwich Panels Research
No full textOptical measuring systems based on digital image correlation method (DIC) becoming increasingly popular over last few years by substituting the conventional data acquisition systems implemented during the physical tests of different materials and structures. In current research the gom/ARAMIS 3D strain measuring system has been utilised to acquire full strain and displacements map over the specimen surface for small scale sandwich specimens with DendroLight® core. A 4-point bending setup has been used to demonstrate that ARAMIS could deliver much more detailed in-plane and out-of-plane strain data compared to conventional strain-gauges. Developed strain patterns on the specimen surfaces acquired with DIC have been compared with finite element model by ANSYS computer code with shell type finite elements. A general good agreement has between achieved among numerical and experimental results in small deflection region - below 1/250 of span length
Simulation of Mechanical Behavior of Sandwich Panels with Dendrolight Cellular Wood Material Core
No full textIn order to introduce a new type of sandwich panels with DendroLight® core a special attention must be paid for development of design practice capable in detailed representation of mechanical behaviour for cellular wood structure. A validation between detailed cellular core finite element analysis and experimental tests in bending and compression should lead to evaluation of design procedure for engineering design praxis [1]. Moreover computational time consumption makes it impractical to rely on the FE analysis exclusively, thus requiring a simple however reliable design tools and guidelines. The aim of this research is to create finite element model of sandwich panel with DendroLight® core, to match the mechanical behaviour of experimental bending and compression tests. Commercially available ANSYS FE code with parametrical inputs and shell elements has been selected for particular task. Transverse isotropic wood mechanical properties were assigned for a cellular wood frame and corresponding properties for plywood or MDF (medium density fibreboard) cover skins.
Special attention has been devoted to experimental testing of DendroLight® core structure and sandwich application. Bending and compression tests were performed on ZWICK Z100 testing machine. Bending set-up has been used to test sandwich beams with dimensions of 30x50x300 mm (Fig. 1). Compression tests were performed on specimens with dimensions 40x200x200 – according to EN789 standard [2]. For recording the strain distribution during the tests, the strain gauges alongside the non-contact optical measuring system ARAMIS has been used. Obtained accuracy of computer simulation model do not exceed 20 % scatter comparing with experimental results within the elastic zone. Taking into account original scatter of wood mechanical properties it may be concluded as good basis for scaling up and delivering the design guidelines for the sandwich panel application with DendroLight® core
FEM Strategies for Numerical Modeling of Dendrolight Cellular Wood Material Core
No full textDendroLight is a novel wood material primarily used as core material for furniture industry. The manufacturing of this material was started at the year 2010 in Ventspils. It is made from profiled/perforate wood boards stacked in perpendicular layers and then sliced once more in plates perpendicularly to the board’s layers. The main advantage of such a solution is significant reduction of structural weight (up to 40 %) comparing to conventional timber. Material properties are not fully assessed jet, however first experimental test runs demonstrate that it has sufficient stiffness for the use as core material in wood sandwich panels in load bearing structures like walls and floors[1]. For further development of load bearing structures with DendroLight core, reliable design methodology is needed, able to assess detailed geometry component (like profiled board web thickness) influence over the stiffness for large scale structure.
In current research several numerical modeling techniques have been compared including numerical models from shell and solid elements in ANSYS and ABAQUS software. The aim is to elaborate an accurate numerical model for prediction of DendroLight structure mechanical behavior. Precision of numerical model is estimated comparing displacements of experimentally tested small scale specimens in compression and bending with mechanical responses of numerical model
Investigaton of Wood Based Panels with Plywood and GFRP Composite Components
No full textThe current research aims to extend the existing knowledge about weight reduction of wood based panels with plywood faces and glass fibre reinforced plastic (GFRP) stiffeners, where experimental prototypes have been analysed and optimized utilizing ANSYS finite element code and design of computer experiments. The initial study demonstrated that replacing homogeneous core of plywood boards with corrugated glass fibre composite hollow core it is possible to reach up to 65 % weight reduction at the same time keeping stiffness unchanged
Bending Stiffness and Weight Optimization of Plywood Sandwich Panels
No full textSandwich structures and rib stiffened panels from metal, fiber materials and plastics has been recognized as efficient and material saving solutions for applications requiring lightweight design elements, like ships, trains and aircrafts[1]. In addition to weight reduction, sandwich structures also allow to integrate addition properties for the panel like insulation and wave damping layers.
Wood is now widely used in sandwich design for building walls and floors, where insulation properties is most important than weight reduction. However excellent mechanical properties of plywood are suitable for manufacturing of lightweight sandwich panels for heavy duty load applications like floors in passenger transport. Mechanical properties of single plywood layer (veneer) in longitudinal direction are close to GFRP fabric ~ 17 GPa. Changing orientation of layers is possible to create tailored solutions for specific load conditions. Plywood sandwich panels with rib stiffener cores are not widely studied, thus there is potential to create more weight efficient solution than traditional plywood boards.
The aim of current research is to find most effective cross section design for plywood sandwich panels with rib stiffened and corrugated core as well as to develop overall methodology for assessing efficiency of sandwich panel, taking stiffness and volume of full plywood board as reference
