Journal of Science and Technology of Composites
Year:2016 | Volume:3 | Issue:3|Papers Count:12

The impact behavior of steel– polyurea bi-layer panel and the effect of curvature is studied numerically and experimental analysis is used for numerical result verification. Numerical analysis for 12 different radius of curvature is performed. On the other hand three radius of curvature is used in experimental analysis.Simple drop weight impact test apparatus is used and the falling weight height is 30 cm. The bi-layer samples in three radius of curvature are fabricated and each sample consisted of steel layer and polyurea coating. Two important parameters measured are the maximum plastic deformation of panel and impactor acceleration history. A high speed accelerometer is used for measuring the impactor acceleration in experimental method. Also the permanent plastic deformation is measured with numerical measurement system attached to the drop test apparatus. LS-DYNA software is used in numerical analysis and explicit solution is done. The results in numerical method and test (if available) are compared together and show good agreement. The results for all cases show that, increasing the panel radius of curvature will increase impactor acceleration and will decrease plastic deformation of bi-layer panel, but if the radius of curvature is increased more and more, then the impactor acceleration will not be increased further and will be nearly constant. On the other hand plastic deformation of the panel will be constant when the panel radius of curvature is increased more.

One of the main advantages for the increasing engineering application of composites in weight-critical structural applications is their high specific stiffness and strength. Composite materials behavior is complicated more than metallic material because of different mechanisms, damage growth rate and effect of them in each other. In this paper, a continuum damage mechanics based model is developed to simulate stiffness degradation and fatigue life prediction of laminated composites under fatigue loading conditions.Damage parameters are used to estimate the degradation of elastic properties in matrix, fiber and shear direction. The material properties of the damage evolution equations are derived by testing on 0o and 90o unidirectional plies and [0/90]s cross-ply laminate. To evaluate the model under multiaxial fatigue loading, arbitrary states of stress and stress ratio available results of experiments on unidirectional 90, 0 and 30 plies under fatigue loading conditions are used. Also, to evaluate the model for composite laminates with stress concentration results of experiments of pin-loaded cross-ply [04/904]s laminate are used. The obtained results show the capability of proposed model in fatigue life prediction of unidirectional and crossply laminates under uniaxial and multiaxial fatigue loading with different states of stress.

Nowadays, using composite materials has been grown increasingly especially in aerospace and automobile manufacturing. Composite drilling is the main machining process for assembling the composite components.The damages caused by drilling process, such as delamination, fiber breakage, fiber pull out and matrix cracking around the hole can decrease the residual strength of drilled components. In this paper, the effect of drilling parameters such as feed rate, spindle speed and drill diameter on the thrust force, delamination for composite specimens with different percentages of nano fibers are discussed. Taguchi method is used for Designing of Experiment to analysis effect of machining parameters (feed rate, spindle speed, drill diameter) and percentage of nano particles on the thrust force and delamination factor. The results show that by increasing carbon nano tube up to a special percentage (about 5%) delamination and thrust force decrease. Also, by decreasing feed rate and increasing spindle speed, thrust force and delamination factor decrease.

In this study, the distribution of radial and tangential creep strains and ratio of effective stress to internal pressure in a glass/vinyl ester thick-walled cylinder for long-term time period are studied. The constants of Schapery compatibility equations have been used for different temperatures and stresses. A symmetric multilayer composite long cylinder with 0, 45 and 90 fiber orientations has been modeled. The cylinder has been loaded by internal pressure and temperature difference. Also, the classical lamination theory has been applied for solving the equations. Viscoelastic model using Prandtl-Russ relations and Mendelson’s approximation method has been analyzed. In addition, the distribution of radial and tangential creep strains and effective stress in the wall thickness for different layouts and temperatures difference in 15 years has been drawn and analyzed. The results show that the ratio of effective stress to internal pressure increases.Further, with growing the temperature in the unidirectional multilayer with 0° and 90 ° fiber orientations, the radial and tangential creep strains increase. Also, in the unidirectional multilayer with 45° fiber orientation, the ratio of effective stress to internal pressure decreases with increasing the temperature differences. In addition, the absolute values of radial and tangential creep strains in the One of them is inner and the other in outerwalls increase and decrease, respectively.

In the current study, low velocity off-center impacts of glass/epoxy laminates considering different impact locations are investigated experimentally and numerically. Low velocity impact tests are performed using an instrumented drop-weight machine and the composite specimens are formed through the use of the vacuum infusion process. To simulate low velocity impact properties of the composite, the finite element software ABAQUS/Explicit is employed. The damage model is implemented in the FE code by a user-defined material subroutine (VUMAT). In order to effectively describe the progressively intralaminar damage for composite laminates, two three-dimensional progressive damage models are presented exponentially and linearly and for predicting damage initiation of composite plates, 3D Hashin’s failure criterion is chosen.Both damage models are established as functions of energy dissipated by damage in addition to introducing the characteristic length for each three dimensional solid element. The contact force-time histories and peak loads are obtained to compare the numerical and the experimental results at several impact energy levels and three different impact locations of the composite plates. In addition to these achievements, the comparison of the numerically predicted damage pattern and damage size and those observed experimentally can verify the efficiency of the present models.

In this study, a brass alloy-based (Cu-30%Zn) composite was fabricated by Graphite particles with initial size of 7μm reinforcement via friction stir processing. Groove with the Width and depth of 0.3mm & 2.5 mm were made on the surface of a brass specimen, respectively and filled by Graphite powder. Friction stir processing was carried out with transverse and rotational speeds of 100mm/min and 800rpm, respectively and the tilt angle of 1o. Single pass and three-pass FSP were conducted on the samples. The microstructure and mechanical properties before and after FSP were investigated. Optical and scanning electron microscope observations revealed that increasing the number of passes exhibits homogeneous distribution of Graphite particles. The wear behavior was examined without lubricant and at room temperature using a pin-on-disc device. The results showed that the wear resistance of composite layers containing MoS2 particles has increased to about 1.5 times the substrate. Maximum hardness in the stir zone was 141 Vickers, while the hardness of base metal was 84 Vickers. TOEFL test results also showed that the corrosion potential layer composite with graphite particles near to the values of the base metal had no significant change. While the corrosion potential in the processed layer without reinforcing particles of the base metal is approximately 48 Mv.

In this article, interface characteristics of aluminum and cast iron bimetal has been investigated. To reach an acceptable composite products, from two materials, interface characteristics needs to be investigated. Aluminum melt was poured, at 700 and 750oC, around cylindrical cast iron bars having melt/solid volume ratios of 3, 5 and 8, respectively. Optical and SEM microscopic observations showed that a reaction layer may form at the interface. This layer is composed of Fe2Al5 intermetallic which forms initially at the rough surface of the insert after making contact with molten metal. Microstructural analysis showed the increasing of temperature and the Vm/Vs ratio leads to formation of a thicker and more uniform intermetallic layer. Microhardness of the Fe2Al5 was 824 HV and the thickness of interaction layer varied from 5μm, for the sample produced at 700oC and 3 Vm/Vs, up to 20μm for the sample poured at 750oC and 8 Vm/Vs. A mechanism is suggested for nucleation and growth of this intermetallic layer and also graphite engulfment of gray cast iron, by aluminum melt, at the interface of two metals.

Composite lattice structures, due to their advantages such as high strength, light weight and resistance to corrosion are recently employed in various industrial applications including aerospace and marine structures. These structures are usually composed of two major parts: the shell and the lattice structure.The lattice part is made of a system of Helical, Hoop or axial ribs. During loading, the loads are transferred to the ribs and the ribs distribute the loads throughout the structure. In the present paper, first the fabrication of the semi-cylindrical lattice structure is explained. Then, the buckling behavior of the semicylindrical lattice structure is investigated using the ABAQUS finite element software. The effect of various parameters such as the thickness and ply angles in the shell laminate were studied. Moreover, the effect of rib parameters such as different patterns and the rib thicknesses were obtained by finite element analysis.In addition, in order to validate the results, a comparison between the experimental and finite element results was performed.

In this research, the fabrication of in situ Al-Mn-Al2O3 composite samples from different composition of Al-MnO2 as starting materials have been made by stir casting method. For this purpose, a mixture of Al and MnO2 powders with weight ratio 1: 7 was ball-milled. Then 1, 3, 4 and 7wt% of this mixture along with 5%wt Mg (to improve wettability) have been added to melted aluminum at 900oC. The disperstion of added materials in molten of Al was made by using graphite stirrer during 8 minutes. The molten of composite was casted into a preheated steel mold. Differential thermal analysis (DTA) was conducted on starting powder mixtures to study the aluminothermic reaction and the possible other reaction or phase changes. XRD analysis and scanning electron microscopy (SEM) were used to investigate the microstructure and phase composition of composite samples. The results show that the final phase composition for all composites is solid solution of Al-Mn, ceramic phase of alumina and MnAl6 intermetallic compound. The amount of MnAl6 and Al2O3 particles in composite samples were increased by adding higher quantity of MnO2 into molten of Al. Moreover there is an optimal amount of MnO2 in which haighest mechanical properties such as hardness, strength and toughness is obtained for composite samples.

In the case of presence of deep micro-cracks within the composite structures, they must be replaced. The self-healing phenomenon which is inspired from the biological systems such as vascular networks in plants or capillary networks in animals is an appropriate strategy to control the defects and micro-cracks. In the present research, by taking accounts the advantages of self-healing concept, an attempt has been made to control the micro-cracks and damages which were created in composite structures. To do so, a series of micro glass tubes were employed to provide a self-healing system. These micro-tubes were filled with epoxy resin+anhydride as a healing agent. When the structure is subjected to loading conditions, some damages or micro-cracks are created. In this situation, the micro glass tubes will rupture and the healing agent flows in the damage area, leading to the elimination of the defects over a time span. The aim of this study is to find out the appropriate micro glass tubes volume fraction and healing time to obtain an efficient healing. For this purpose, glass micro-tubes containing various anhydride agent loadings of 2, 4 and 6 vol. % were incorporated in epoxy-carbon fibers composites and the bending behavior of the specimens were assessed during different time span from defect creation. The highest bending strength recovery of 84% was observed for the specimen with 4% healing agent after 8 days.

Due to the wide applications of polymeric materials, it is necessary to develop a dynamic constitutive model to investigate their strain rate dependent mechanical behavior. In this study, the generalized strain rate dependent constitutive model was developed based on the experimental results of polymers. The experimental data of thermoset and thermoplastic polymers were used to evaluate the model. The present model includes three main components; the first component expresses the elastic stress-strain behavior of polymers. The second component models the nonlinear stress-strain behavior of the material using the Johnson-Cook model and the third component predicts the ultimate strength of polymers. Then, by combining the generalized strain rate dependent constitutive model and the plasticity micromechanical model of Huang, the shear behavior of glass/epoxy composites is predicted. This model, called dynamic constitutive-micromechanical model, removed dependency of composite mechanical behavior to the fiber volume fraction and the strain rate. Therefore, experimental characterization was reduced significantly.Finally, it was shown that the generalized strain rate dependent constitutive model and the dynamic constitutive-micromechanical model predicted the mechanical behavior of neat polymers and glass/epoxy composites respectively, with good accuracies.

In this study, an exact analytical solution of steady heat conduction problem in exponentially graded inhomogeneous materials with temperature-dependent heat conductivity is presented. The FGM properties are assumed to depend exponentially on spatial coordinates whereas the temperature dependency is taken to be a linear function. The proposed method is based on an integral transformation of the temperature field, which transforms the nonlinear heat equation into a linear one for the transformed temperature. The boundary conditions are to be transformed as well. Once the linear equation is solved and the transformed temperature is obtained, the inverse transform is used to calculate the physical temperature field. The boundary conditions are enforced on the transformed temperature. Finally, in order to demonstrate the application of the proposed method, two numerical examples are worked out, i.e. nonlinear heat conduction in the radial direction of cylindrical and spherical thick-walled shells. In order to check the validity of the proposed solution scheme, a numerical solution of the problems has been performed and an excellent agreement has been established.