Fatigue Analysis And Life Prediction Of Honeycomb
IJSART - Volume 3 Issue 2 –FEBRUARY 2017ISSN [ONLINE]: 2395-1052Fatigue Analysis and Life Prediction of HoneycombStructures1, 21, 2Ajit Lohote1, Prof.S.S.Kelkar2Department of Mechanical EngineeringJSCOE, Pune University, Maharashtra, India.Abstract- The use of honeycomb composite structure continuesto increase rapidly due to the variety of their application, ransportation rails, etc. The sandwich composites are multilayered materials made of bonding stiff, high strength skinsfacings to low density core material. In structural componentshigh stiffness to weight ratios is the major benefit of thehoneycomb sandwich concept. In this study a honeycombstructure is evaluated. Static behavior of sandwich areinvestigated for permissible load. Then a fatigue analysis iscarried out to investigate for its life prediction. The objectiveof the project is to find number of cycles a structure sustainsat a particular load. If a structure fails at early stage, effortswill be taken to increase its stiffness and strength as designparameters.A Finite element analysis of honeycomb structuresis to be carried out with ANSYS Workbench as bothpreprocessor and post processor. The finite element analysisresults compared with the experimental results.one facing sheet is in compression, the other is in tension.Similarly honeycombcore corresponds to the I-beam web. Thecore resists the shear loads and increases the structure stiffnessby holding facing sheet apart, improving on I-beam and itgives constant support to flanges or facing sheets to make auniformly stiffened panel. The core to skin adhesive rigidlyjoins honeycomb sandwich components and permits them toact as single unit with a bending rigidity and high torsion.Keywords- Finite element analysis, Honeycomb, fatigue analysis.S. Belouettar et.al. [1] Presented work is related tostatic and fatigue behaviours of honeycomb composites usingfour point bending test, in this they found the effects of coredensity and the cell of orientation on the maximum load andon the damage processes. Craig A et.al.[2] proposed the studyof Analytical predictions are made for the three-point bendingcollapse strength of sandwich beams with composite faces andpolymer foam cores.Hualin Fan et.al. [4] Presented work isrelated to study compression behaviours of the latticecomposites and sandwich columns with different skinthicknesses.Isaac M et.al. [5] Presented work is related todetermine experimental the flexural behaviour of compositecompare the result with theoretical models.I. INTRODUCTIONSandwich panels are used for design and constructionof lightweight transportation systems such as satellites,aircraft, and missiles. Structural weight saving is the majorconsideration and the sandwich construction is frequently usedinstead of increasing material thickness, honeycomb are madeof very thin material. They reduce the weight, while providingthe structural rigidity. This type of sandwich constructionconsists of two thin facing layers separated by a core material.Potential materials for sandwich facings are aluminum alloys,high tensile steels, titanium, inconel-617 and composites withcomposites with honeycomb cores and a suitable matrixdepending on the specific mission requirement. Several typesof core shapes and core materials have been applied to theconstruction of sandwich structures. Among them, thehoneycomb core that consists of very thin foils in the form ofhexagonal cells perpendicular to the facings is the mostpopular.The facing sheets of a honeycomb sandwich panelcan compared with the flanges of I-beam, as they carry thesimilar bending stresses to like the beam is subjected. WithPage 46Fig.1 Honeycomb Sandwich panel compared with I-beam [10]The proposed work is to determine fatigue life ofhoneycomb composite panel having honeycomb structuresandwich between glass fiber panel. Fatigue life is determinedby FEA analysis and validated with experimental results.II. HONEYCOMB STRUCTUREHoneycomb sandwich construction is mostly used invarious structures, as the concept is most suitable withlightweight structures for high in- plane and flexural stiffness.Honeycomb sandwich panels consist of two thin sheets (skins)www.ijsart.com
IJSART - Volume 3 Issue 2 –FEBRUARY 2017and Da lightweight thicker core. Usually materials used forface sheets are composite laminates and metals, while coresare made by metallic and non-metallic honeycombs, cellularfoams, balsa wood or trusses. The flexural stiffness and outof-plane shear and compressive strength is provided by thecore. Important issues in honeycomb sandwich structures arefailure mechanisms, the quality of structure that are developedunder different loading conditions and effects of geometricnonlinearities, effects of nonlinear material behavior.ISSN [ONLINE]: 2395-1052subject to alternating stressesfor a long period of time fatigueoccurs. e.g. airplane wings, turbine blades and bones.There are three steps that can be viewed in material failurebecause of fatigue on a microscopic level:1. Crack Initiation: Initial crack occurs in this stage. Thatcrack may be caused by surface scratches caused byhandling, or tooling of the material; threads as in a screw,slip bands /dislocations intersecting the surface as aneffect of previous cyclic loading or work hardening.2. Crack Propagation: Crack continues to grow atthis stagedue to continuous application of stresses3. Failure: Failure is occurred when the material that hasn’tbeen affected by the crack can’t withstand the stress. Thishappens very quickly.III. FATIGUE ANALYSISFig.2 Exploded view of honeycomb core sandwich structure[11]In materials science, fatigue is the weakening of amaterial caused by repeatedly applied loads. It is theprogressive and localized structural damage that occurs whena material is subjected to cyclic loading. The nominalmaximum stress values that cause such damage may be muchless than the strength of the material typically quoted as theultimate tensile stress limit, or the yield stress limit.Fatigue failure of Honeycomb StructuresOne of the common causes of Honeycomb Structuresfailure is due to fatigue. Repeated cycling of the load causesfatigue. It is continuous damage due to both fluctuatingstresses as well as strains on material. Cracks are initiated andpropagated in the regions where strain is more severe.Fig.3 S-N curveThe concept of fatigue is not difficult, when motionis repeated; the object becomes weak. For example, while youare running, your leg and other muscles of your body becomeweak, not always to the point where you can't move themanymore, but there is aconsiderable decrease in quality output.This same principle is seen in materials. When the material isPage 47Fatigue is generally understood as the gradualdeterioration of a material which is subjected to cyclic loads.In fatigue testing, a specimen is subjected to periodicallyvarying constant amplitude stress. The applied stresses mayalternate between equal positive and negative value from zeroto maximum positive or negative value, or between equalpositive and negative values or between unequal positive andnegative values.A series of fatigue tests are made on a number ofspecimens of the material at different stress levels. The stressendured is then plotted against the number of cycle sustained.By choosing lower and lower stresses, a value may be foundwhich will not produce failure, regardless of the number ofapplied cycle. This stress value is called the fatigue limit ofthe material or the endurance limit. The plot of the two termsis called stress-cycle diagram or S-N diagram. The fatiguelimit may be established for most steels be-tween 2 and 10million cycles. Non-ferrous metals such as aluminum usuallyshow no clearly defined fatigue limit. Survey of the variousaspects of fatigue of structures.IV. FINITE ELEMENT ANALYSISThe CAD model is imported to ANSYS Workbench.The appropriate element size is selected according to thewww.ijsart.com
IJSART - Volume 3 Issue 2 –FEBRUARY 2017geometry features. Then using Shell element the aluminumhoneycomb is meshed and then the composite platesmaintaining the connectivity. The meshed model is checkedfor element criteria. Shell 63 element type is used for meshing.Number of nodes and elements are 50165 and 41630respectively.ISSN [ONLINE]: 2395-1052Results of fatigue analysis of honeycomb structurewith and without composite material for 1 kN load are shownin following figures.The composite panel is made of 6 layers of Glassfiber sheets arranged with different degree of orientation. Thelayers of thickness 0.2083 mm are arranged as 45o, -45o, 45o,-45o, 45o, -45o.The top and bottom layers are arranged as inthe order by total 12 layers. The Aluminum core issandwiched between the layers. Material properties ofaluminum core and glass fiber are given in following tables.Table 1: Material properties Aluminum core [10]Fig.4 Fatigue life of specimen without composite for 1 kNload.log10(St)Without composite321034567log10(N)Graph .1 S-N Curve results of specimen without composite.Table 2: Material properties of Glass fibres [10]Fig.5 Fatigue life of specimen with composite for 1 kN load.log10(St)With composite321034567log10(N)Graph 2S-N Curve results of specimen with composite.Page 48www.ijsart.com
IJSART - Volume 3 Issue 2 –FEBRUARY 2017ISSN [ONLINE]: 2395-1052Fatigue analysis of honeycomb structure withoutcomposite has shows1,60,000life cycles and for honeycombstructure with composite shows 2,30,000 life cycles for 1kNload.VI. RESULTS AND DISCUSSIONSV. EXPERIMENTAL VALIDATIONEquipment Make : Instron Structural Testing System(Country-Germany)Test Equipment used: Instron Actuator 25KN (AC/MC/059)Controller: 8800 Instron Make2.5Comparison between FEA Analysis andExperimental validationFEA Resultlog10(St)2ExperimentalResult1.510.504 log10(N) 536Graph 4S-N Curve comparison between FEA Analysis andExperimental validationFig.6 Experimental setupFrom the above graph it can be seen that FEA resultsand experimental result are closely matching.VII. CONCLUSION1.2.Fig.7 Testing specimenExperimental : with composite3.log10(St)32Fatigue testing in three point bending were performed onhoneycomb structure. It shows that at 1kN load &frequency 10Hz, Crack observed after 1,80,936 cycles ofhoneycomb structure with composite.Fatigue analysis has been performed for honeycombstructure without composite life cycle is 1,60,000 cyclesand honeycomb structure with composite life cycle is2,30,000 cycles for 1kN load.3.Based on the results it can be used in some applicationslike automotive and aerospace where the structure canundergo repeated or complete reverse fatigue load.1APPENDIX034567Journal Paper submittedlog10(N)Graph 3S-N Curve results for experimental validation ofspecimen with compositePage 49Ajit T. Lohote, Prof. S. S. Kelkar,”Fatigue Analysisand Life Prediction of Honeycomb Structure”, MECHPGCON2016.www.ijsart.com
IJSART - Volume 3 Issue 2 –FEBRUARY 2017ACKNOWLEDGEMENTI would like to thank my guide Prof. S. S. Kelkar forguiding and providing necessary help as and when required.Thanks also to HOD of mechanical department and its stafffor providing the necessary help.ISSN [ONLINE]: 2395-1052bending”, Elsevier, Nanyang Technological University,Singapore 639798, Singapore (2014).[10] N. Gir, A. Patel, A. Ghalke, “FEA and Experimentationevaluation of Composite Sandwich panel under StaticThree Point Bending Load” IPASJ, ISSN 2321-6441,Volume 4 (April 2014).REFERENCES[1] Belouettar, S., Abbadi, A., Azari, Z., Belouettar, R.,&Freres, P. (2009). Experimental investigation of staticand fatigue behavior of composites honeycomb materialsusing four point bending tests. Composite Structures,87(3), 265-273.[11] K. Kantha Rao, K. Jaytirtha Rao, “Heat InsulationAnalysis of an Aluminium Honeycomb SandwichStructure”, IPASJ, ISSN 2321-6441, Volume 2 (August2014).[2] Craig A. Steeves, Norman A. Fleck, “Collapsemechanisms of sandwich beams with composite faces anda foam core, loaded in three-point bending”, InternationalJournal of Mechanical Sciences 46 (2004) 561–583.[3] Herranen, H., Pabut, O., Eerme, M., Majak, J., Pohlak,M., Kers, J., &Aruniit, A. (2012). Design and testing ofsandwich structures with different core materials.Materials Science, 18(1), 45-50.[4] Hualin Fan, Lin Yang, Fangfang Sun, DainingFangFan,H., Yang, L., Sun, F., & Fang, D. (2013). Compressionand bending performances of carbon fiber reinforcedlattice-core sandwich composites. Composites Part A:Applied Science and Manufacturing, 52, 118-125.[5] Isaac M. Daniel, Jandro L. Abot, J. L. (2000). Fabrication,testing and analysis of composite sandwich beams.[6] Jin Zhang, Peter Supernak, Simon Mueller-Alander, ChunH. Wang “Improving the bending strength and energyabsorption of corrugated sandwich composite structure”Elsevier, Materials and Design 52 (2013) 767–773.[7] KavehKabir, Tania Vodenitcharova, Mark Hoffman,“Response of aluminium foam-cored sandwich panels tobending load” Elsevier,Composites: Part B 64 (2014) 24–32.[8] V. Crupi, G. Epasto, E. Guglielmino, “Comparison ofaluminium sandwiches for lightweight ship structures:Honeycomb vs. foam”, Elsevier, Marine Structures 30(2013) 74–96.[9] A. Rajaneesh, I. Sridhar ,S. Rajendran, “Failure modemaps for circular composites sandwich plates underPage 50www.ijsart.com
Fatigue failure of Honeycomb Structures Fatigue is generally understood as the gradual One of the common causes of Honeycomb Structures failure is due to fatigue. Repeated cycling of the load causes fatigue. It i
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Fatigue Life Prediction in . Composite Materials . Predicting fatigue life in composites is challenging because even simple load states lead to complex behavior in the individual fiber and matrix constituents. Furthermore, the effects of frequency and load history can only be
4. Significantly better S-N fatigue resistance of the forged steel was observed, as compared with the two cast materials (see Figure 4). Comparison of long-life fatigue strength (defined as the fatigue strength at 106 cycles) shows that the fatigue limit of cast aluminum and cast iron are only 35% and 72% of the forged steel, respectively.
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