Abstract: Finite element analysis of honeycomb sandwich panel has been performed by modeling the structure through three different approaches. Continuum properties are calculated through analytical solution and verified through FE analysis of bare core. In addition to that the thickness of core has also been varied in all the three approaches in order to study its effect on vibration analysis of sandwich structure.
Abstract: Bulk amorphous alloys are new class of materials with excellent mechanical and thermal properties. Bulk metallic glasses (BMGs) have wide range of application such as structural materials. Minor alloying additions play beneficial role in the production and properties of BMGs. The present study was conducted to investigate the effect of Y and Nb addition on activation energy, crystallization behavior, thermal and mechanical properties of Zr64.5Ni15.5Al11.5Cu8.5. Bulk amorphous ingots and sheets of three [Zr0.645Ni0.155Al0.115Cu0.085]100-xM2 (M = Y and Nb and x = 0, 2 at. %) alloys were produced by Cu mold casting technique. The alloys were characterized by XRD, DSC, SEM, FESEM and EDS. Activation energies were calculated. The alloy containing Y shows single stage crystallization while Nb addition shows double stage crystallization. The maximum activation energy calculated is 300 kJ/mol. Parameters describing thermal stability in these systems were determined from DSC data which improved as a result of these additives. Reduced glass transition temperature Trg and thermal parameters like g, d and b were improved by Y addition. The supercooled liquid region varies between 87-100 K. Hardness and elastic moduli were also improved. It was concluded that Y and Nb addition has beneficial effect on mechanical properties. Three phases NiZr2 and CuZr2 and Cu10Zr7 were identified by XRD and confirmed by EDS in the samples annealed at 823 K while the AlNiY ternary phase was detected in the alloy containing Y.
Abstract: Residual stresses development during manufacturing of composites depends mostly on the shrinkage behaviour of the polymer matrix from the point where stresses cannot be relaxed anymore. The matrix shrinkage may have a thermal and/or chemical origin and can leads to dimensional instability, ply cracking, delamination and fibre buckling. The approaches for measuring cure shrinkage can be classified as volume and non-volume dilatometry. Each technique has corresponding advantages and drawbacks but volume dilatometry is the one that is mostly used. In the present article, we report a home-built apparatus, named PVT-a mould, on which temperature, volume change and reaction conversion degree are measured simultaneously for an applied pressure. It can also be used to study the composite during curing and for the bulk samples having several millimetre thicknesses. The instrument is preferred over other techniques as it works in conditions close to the industrial ones. This device was used to measure cure shrinkage of resin and thermoset composite material with different fibre fractions as a function of temperature and reaction conversion degree. The heat of cure of the resin measured by PVT-a mould was compared to the results obtained by DSC.
Abstract: Composite materials are used extensively in aircraft structures, automobiles, sporting goods, and many consumer products. Thin-walled multicell beams made of composite materials, have important applications in aerospace structures. The torsion load on these beams is caused due to distance between Centre of Pressure (CP) and Centre of Gravity (CG) of aerospace vehicle in flight. Warping is a result of torsion load and its analysis is important to predict actual behavior of multicell beams. Study of warping displacements is necessary because prevention of warping leads to stress development. Enhancement in design requires design optimization generated by parametric modeling. Problem of cross-sectional distortion can be controlled through use of rigid diaphragms equally spaced along the length of beam. The aim of present study is to establish a procedure for parametric modeling in presence of rigid regions and simulate warping effects caused by torsion on multicell beams. Quasi-isotropic composite material has been used in multicell beams. Four models of multicell beams analyzed have same length and thickness, but different number of rigid regions and corresponding compatible mesh size. Warping is simulated by FEM based computational program ANSYS, and one; ten and seventy rigid regions inside beam were analyzed. Numerical simulations results show that beam with single rigid region has higher axial warping and more uniform rate of change as compared to beams with multiple rigid regions. It was found that first beam model with one rigid region has warping error 41.6%, second and third model each with ten rigid regions (but different edge size) have 2.5% error in warping, fourth model has 70 rigid regions and it has 0% error in warping. Results show that inaccurate interlaminar shear stresses do not affect the warping behavior of multicell beams. Once the parametric model is defined, then it becomes very quick and easy process to perform warping analysis of composite multicell beam with rigid regions.
Abstract: This paper presents the mathematical modelling of fatigue damage able to carry out simulation of evolution of delamination in the laminated composite structures under cyclic loadings. A new elastic fatigue damage evolution law is proposed here. A classical interface damage evolution law, which is commonly used to predict static debonding process, is modified further to incorporate fatigue delamination effects due to high cycle loadings. The proposed fatigue damage model is identified using Fracture Mechanics tests like DCB, ENF and MMB. Simulations of delamination under fatigue loading are performed and results are successfully compared with reported experimental data on HTA/6376C unidirectional material. Delamination crack growth with variable fatigue amplitude is also performed and simulation results show that the proposed fatigue damage law can also accommodate this variable amplitude phenomenon. A study of crack tip behaviour using damage variable evolution is also carried out in this paper. Finally the effect of mesh density on crack growth is also discussed.
Abstract: Resin Infusion process is an affordable process for developing composite structures but resin impregnate is made difficult by its large size of engineering products. This research demonstrates development of large structures such as body of a high performance automobile in a single step resin infusion process. Three different scaled down models of the car were developed according to user’s technical requirements focusing on minimal weight, air drag and aesthetics. Pro E and ANSYS were used to determine the optimal shape, geometry, size, aesthetics and strength. The digital model of exterior shape of car body was developed through coordinate measuring machine using selected model instead of Pro-E modeling due to time constraints. The digitized data was used for development of Pro-E model. The Pro-E model was scaled up to generate CAD drawings for tool development. Different stations were marked on the model and sliced virtually for development of pattern. After developing pattern, the mold was manufactured from carbon and glass / polyester composites for prototype manufacturing of the car body. The prototype manufacturing involved placement of specific number of carbon layers as perform on female side of the mold. The vacuum sucked the resin through a number of carefully selected entry ports. Multiple resin delivery ports ensured effective resin distribution and impregnation. After curing the cutting, trimming and drilling operations were carried out to finish car body to actual size. Polyacrylic wind shield was thermoformed in convection current oven according to streamlined geometry of car body. The car body was integrated with the compatible floor panels and accessories. The crumble zone shock absorber in the bumper was manufactured using successive layers of Nomex® honeycomb and PVC rigid foam to dampen the accidental shock. The successful test runs were made to qualify the car body according to user’s technical requirements.
Abstract: Polyurethanes with two different types of –OH backbones castor oil (CO) and hydroxyl terminated polybutadiene (HTPB) were synthesized by using moderately reactive iso-phorone diiscocayante (IPDI) as curing agent. IR spectroscopy and mechanical property evaluations were carried out to elucidate the structure-property relationship of the polymer. It was found that the polymer, intersegment bonding had significant effects on the ultimate tensile properties. The CO based polymer exhibited far better mechanical properties than that of HTPB based polymer. However, a reverse behavior was observed in the composites. Composite fabricated with HTPB based polymer matrix showed four times the tensile strength of CO based composite. SEM comparison of the fractured composites revealed better wetting and adhesion properties with HTPB. Dynamic mechanical testing results indentified a relationship between the viscoelastic parameters and frequency of the applied load.
Abstract: A high dielectric constant nano-composite was fabricated using polyurethane (PU) as matrix and poly (p-chloromethyl styrene) (PCMS) grafted with copper phthalocyanine oligomer (CuPc, a planar multiring semiconductor with dielectric constant>105) (name the grafting product as PCMS-g-CuPc) as filler. According to the TEM-observed morphologies, PCMS-g-CuPc balls (~80 nm) distribute uniformly in PU matrix, while in PCMS-g-CuPc balls the PCMS acts as “matrix” which contains dispersed CuPc particles with a average size of ca. 25nm [1/20 of that of CuPc in simple blend of PU and CuPc (PU/CuPc)]. At 100Hz, the dielectric constant of the nanocomposite reaches 345, almost 7 times higher than that of PU/CuPc. The enhanced dielectric response in the nano-composite can be explained by the remarkably strengthened interface exchange coupling effect as well as the Maxwell-Wagner-Sillars polarization mechanism due to the significantly reduced CuPc particle size in the nano-composite.
Abstract: Ni-Mn-Ga magnetic shape memory alloys are employed for applications in actuators and sensing devices. Ni-Mn-Ga single crystalline alloys exhibit ferromagnetic shape memory effect with large reproducible strains in moderate magnetic fields. The cost for producing single crystals is high and there is a requirement to investigate the polycrystalline Ni-Mn-Ga alloys for similar applications. This work presents a study of the effect of composition and heat treatment on the microstructure, in polycrystalline off-stoichiometric compositions of high Ni, Ni-Mn-Ga alloys. Cast polycrystalline alloys were homogenized and analysed using optical microscopy, X-ray diffraction, and thermal analysis. Stability of the martensitic transformation temperature was studied by aging the alloys at different temperatures. Martensitic structure was found in both the alloys (~ 54at% and 58 at%). The alloy with high Ni~58 at% content was found to be having a dual phase structure (martensite and FCC γ). Single phase Ni-Mn-Ga alloy has shown transformation at temperature >400K while the dual phase alloy with Ni ~58at% has transformed at temperature >700K thus making it suitable for high temperature applications. Martensitic stabilization effect was observed in alloy with Ni ~54 at% after aging treatment while it was absent in alloy with ~58at% Ni.