Abstract: Hyperelastic material simulation is necessary for proper testing of products functionality in cases where prototype testing is expensive or not possible. Hyperelastic material is nonlinear and more than one stress-strain response of the material is required for its characterization. The study was focused on prediction of hyperelastic behavior of rubber neglecting the viscoelastic and creep effects in rubber. To obtain the stress strain response of rubber, uniaxial and biaxial tension tests were performed. The data obtained from these tests was utilized to find the coefficients of Mooney-Rivlin, Odgen and Arruda Boyce models. Verification of the behavior as predicted by the fitted models was carried out by comparing the experimental data of a planar shear test with its simulation using the same constitutive models.
Abstract: Single-edged notched tension (SENT) specimen is used to study the fatigue crack growth rate (FCGR) behavior of AISI 50100 steel using MTS 810. Calibration tests are run to get plots of crack mouth opening displacement (CMOD) vs. Load and CMOD vs. Crack length to width ratio with the known crack lengths. FCGR of welded and un-welded specimens are plotted against stress intensity range to show the effect of welding on fatigue crack growth rate of AISI 50100 steel, initial results of the experimentation are presented.
Abstract: In this work the two epoxy composites the controlled behavior of composite material (CBCM) and the thermally activated symmetrical composite (SYMM) have been tested for their shape memory property. These composites have been heated above their glass transition temperature (Tg) and deformed to the same displacement. The activated position has been taken as the reference point for displacement measurements during the fixing cycle. During the recovery, two types of tests have been conducted: Unconstrained recovery test and constrained recovery test. It has been found that the recovery of CBCM plate is better as compared to the SYMM plate (unconstrained recovery test). Similarly, it has been found that CBCM plate produces larger forces of recovery than SYMM plates (constrained recovery test).
Abstract: The global behavior of composite materials is strongly influenced by the quality of adhesion between different components. A component can be single phase, like fibers or particles used as reinforcement in a homogenous matrix, or a multiphase material like a layer in long-fiber laminate. In the latter case the degradation of adhesion implies the separation of the layers, known as delamination. Among all different failure mechanisms, Delamination is considered to be the most prominent mode of failure in fiber-reinforced laminates as a result of their relatively weak inter-laminar strength. When laminated structures are subjected to static, dynamic or cyclic loadings, the inter-laminar adhesion strength between individual plies tends to deteriorate significantly and act as the origin of the final failure. Therefore, an efficient and reliable design tool capable of predicting delamination could improve the durability for composite laminates. There exist damage mechanics based formulations capable of simulating the delamination crack growth in carbon/glass fiber epoxy based composite laminates. The present study is focused on taking a step forward in this respect. At first, already existed local interface models effectiveness is tested and results are successfully compared with available experimental data for UD IMS/924 Carbon/fiber epoxy composite laminate. Next, a non-local integral-type regularization scheme is introduced to overcome the spurious localization problem associated to the existing local model. Basic concepts and mathematical modeling of Non-Local damage evolution law are comprehensively studied and presented in this study. Finite Element simulation results based on proposed model are discussed in detail and are compared with experimental results.
Abstract: Mechanical properties of HTPB (binder) strongly depend on its microstructure. Microstructure of HTPB consists of three major configurations cis, trans and vinyl. The contents of these configurations in the backbone of polymer chain determine the properties of end products. So it is very important to control and determine the ratios of cis, trans and vinyl in HTPB. HTPB was prepared by free radical polymerization of butadiene initiated by hydrogen peroxide in ethanol as solvent. Quantity of the initiator and polymerization time was varied in different experiments. The resulting polymers were analyzed for hydroxyl value (OH value), number average molecular weight (Mn) and viscosity (η). The results indicated that these properties were highly affected by the variation in initiator ratios and reaction time. Microstructure of the polymers was determined by FTIR spectroscopy using ATR (Attenuated Total Reflectance) assembly. Calibration curve was plotted for each functional group (cis, trans and vinyl) using corrected peak values from the spectra (corrected using cis: 804.7 to 640.1 cm-1; trans: 978.8 to 944.9 cm-1; vinyl: 927.7 to 895.2 cm-1). Cis, trans and vinyl contents of the polymers were calculated from the calibration curve. The data indicated that although the variation of initiator quantity and polymerization time affected OH value, Mn and η severely but microstructure variations were quite insignificant.
Abstract: The dissimilar metals components of duplex stainless steels are more and more used in engineering fields recently. But the welding of dissimilar metals is more a challenge than that of similar metals. The joints of dissimilar metals between 2205 duplex stainless steel and 304 austenitic stainless steel were produced by tungsten inert gas arc welding (GTAW) with welding wire ER2209 and ER309, respectively. The microstructural characterization of welded joints is systematically analyzed by using optical microscope and X-ray diffractometer. The pitting corrosion resistance of the joints is evaluated by electrochemical test. Results show that the microstructure of joint consists of austenite and ferrite, and no detrimental phases precipitate in the weldment. The biphase ratio of austenite (γ) / ferrite (α) is adequate both in weld metal and heat-affected zone (HAZ), which is advantageous to the performance of welded joints. The weld metals have relatively lower pitting corrosion resistance compared with the 2205 base metal, and the pitting corrosion resistance of the joint produced with ER2209 is better than that of the joint with ER309 in chloride solution.
Abstract: Internally pressurized tape wound composite shells of revolution with plugged ends are immensely utilize in commercial and aerospace applications. The focus of present endeavor is the realistic design of composite shells. A balanced symmetric stacking sequence of glass/epoxy has been considered. Its mechanical properties are determined from the experimental testing of flat plate samples as per ASTM standards. Netting analysis is then performed to find out the winding angles and hoop/helical layers contribution for optimum structural performance and higher efficiencies. The winding kinematics has been comprehended from the developed surface of the composite cylindrical shell and it has elucidated that each helical layer results from the interlacing of two plies with alternate angles of + θ and θ to the shell meridian. These helically interlaced layers are responsible for the creation of triangular shaped flip flop patterns which run both across the circumference as well as along the shell meridian. These characteristic patterns of helical winding known as mosaic patterns are not generally incorporated in the design calculations which are normally based on mechanics of composite laminates. Their pronounce effect in altering the transverse fiber stress is presented in the present study. The influence of mosaics in the presence of hoop layers is targeted for the first time hence the laminate that has been analyzed comprise of both hoop layers and helical layers with mosaic patterns. A software code has been developed in MATLAB using classical laminate plate theory (CLPT) incorporated with different failure criteria. Range of burst pressures based on different failure criteria has been plotted. Results of MATLAB code and FEA based ANSYS software, are in close agreement.
Abstract: An investigation based on experimental and analytical approaches was conducted to evaluate the behavior of the stitched laminates under hygrothermal conditions. Tensile strength of laminates under different environmental conditions was predicted using FEM model. Effects of stitching parameters upon strength performance of laminates were studied using FEM model and validity of results was checked by comparing with the experimental results. Test results have shown that hygrothermal environment condition has no significant effect on the tensile strength of unstitched laminates, but improved the strength of stitched laminates significantly. Stitching decreased the tensile strength of laminates under 20°C dry environment; however, it improved the tensile strength under 20°C wet environment. It was also found from analytical results that, the failure strength of stitched laminates is higher for smaller thread radius (R<0.25) and relatively greater (5~6mm) stitching distance (5~6mm).
Abstract: Structural health monitoring based on Lamb wave attracts great attention in large-span structures. Lamb wave propagation in complex structures is very complicated due to multiple reflection and mode conversion at geometrical and material features. For effectively inspecting structural integrity, numerical simulation is employed to for extract damage features. It is essential to develop fast and low-cost simulating methods to study Lamb wave propagation in damaged structures. Spectral element method (SEM) is one of the most attractive methods, which is employed to study wave propagation in damaged structures. A massless spring, coupling the longitudinal and rotational vibration, is proposed to model a transverse crack and analyze wave propagation in a composite cracked beam based on SEM. Cracked spectral element formulation is derived by modeling the crack as the spring, whose stiffness is obtained from laws of fracture mechanics. Due to asymmetry of the crack, extensional and flexural wave modes are reflected and transmitted from an incident flexural wave mode. The proposed model is verified by comparing with conventional finite element analysis. Power reflection and transmission varying with the crack depth is also calculated. The results indicate that power reflection/transmission ratio of a single mode is monotonic, which may provide some quantitative foundations for structural health monitoring.