Journal of Science and Technology of Composites
Year:2016 | Volume:2 | Issue:4|Papers Count:8

Indentation test is a method in which the behavior of a material, in response to the indentation can provide a variety of information. Residual stresses within the body and modulus of elasticity are of the most important information that can be obtained from this response. A composite material is a combination of two or more different materials and due to this difference and heterogeneity a residual stress occurs in them. Considering the destructive effects of this kind of stresses on performance of composite structures, it is necessary to determine the magnitudes and distribution of them. Currently there are some mechanical experimental methods for determining macro residual stresses in laminated composites. However, there is no mechanical experimental method for determination of micro residual stresses in a unidirectional ply. In this research, a finite element simulation of the indentation test for determining the modulus of elasticity and micro-residual stresses of a unidirectional composite ply is presented. For this purpose, an appropriate representative volume element of the unidirectional composite ply has been considered and a virtual indentation has been applied on it. The results show that the estimated modulus of elasticity for the fiber in this way depends on the penetration depth, while the estimated residual stresses are independent of the penetration depth. To evaluate the effect of matrix on the results of the indentation in fibers, an isotropic material with similar properties to the glass fiber, has been modeled and the results were compared with the results of indentation on composites.

In this paper, the effective diameter of the punch and the speed of loading and geometry penetrating properties of quasi-static punching (QS-PS) laminate composites has been studied experimentally. The composites have 12 layers of 2D woven glass fiber with area density of 200 g/m2, is manufactured by Hand lay-up method. Epoxy resin systems is made of a diglycidyl ether of bisphenol A (DGEBA), Epon 828, as the epoxy prepolymer and Epikure F-205 as the curing agent. In this study, of two ratio of span 5 and 10 and three strain rate 5, 250 and 500 mm/min as well as three indenters with flat, conical and ogival used. The results of investigation ratio of span show that with decrease half size in the ratio of span, deform the target page lower and contact force 20% increases. Results punching shear at different strain rates shows that with increasing strain rate, composite strength increases. In comparing the results of indenter with different geometries indicate that the flat indenter has higher contact force and maximum of the absorbed energy is by the cone indenter.

In this research, distribution of residual stresses in three-phase representative volume element (RVE) consisting of carbon fiber, carbon nanotube and matrix, as three dimensional has been determined. Finite element analysis and cylinder analytical model have been used to determination of residual stresses in every phase. Cylinder analytical model has been developed to three-phase RVE. Coefficient of thermal expansion has been considered differently at various directions in carbon fiber and carbon nanotube phases. Placement of carbon nanotubes has been considered parallel to carbon fiber and as ring around carbon fiber using electrophoresis method. Different volume fraction of carbon nanotube has been considered as 0%, 1%, 2%, 3%, 4% and 5% and distribution of residual stresses of different volume fraction was compared together, but volume fraction of carbon fiber is considered as constant equal 60%. Radial residual stress, tangential residual stress, axial residual stress and residual stress invariant have been determined in different phases. Results of residual stress invariant of two different analysis as finite element and cylinder analytical model have been compared in different phases that are in good agreement together.

Friction stir processing (FSP) is a novel process for refinement of microstructure, improvement of material’s mechanical properties and production of surface layer composites. In this investigation via friction stir processing, metal matrix composite (MMC) was fabricated on surface of 5083 aluminum sheets by means of 5 mm SiC particles. First combination of rotational speed and travelling speeds were performed. Optimum condition was selected due to highest tensile strength. It was seen that sample which fabricated by 1000rpm and 28mm/min had improvement in tensile strength in comparison to other conditions. After that the effect of multipass on the optimum sample were investigated. The friction processed surface composite layer was analyzed through optical and scanning electron microscopical studies. Mechanical properties of the friction stir processed surface composites were evaluated through microhardness and universal tensile tests. The results were compared with the properties of the base metal. The surface composite layer resulted in that change of tool rotational direction between FSP four passes exhibited better properties in hardness, tensile behavior and wear resistance compared to the behavior of the base metal. The microhardness and tensile strength of the as-received alloy, and surface composite after that change of tool rotational direction between four passes specimens were about 85Hv and 285 MPa, 118Hv and 316 MPa, respectively.

In the present study, the properties of polymeric nanocomposite foams investigated in variant multi-walled carbon nanotubes (MWCNTs) content and under various processing parameters. For this purpose, polyamide 6 (PA6) selected as matrix and melt compounded with MWCNT in variant weight percentages (i.e.0, 0.5, 1 and 1.5%) using a twin-screw extruder. Then, the prepared nanocomposites were foamed using Azodicarbonamide as blowing agent by injection molding machine based on Design of Experiments (DOE) using Taguchi method according to L16 orthogonal array. Influence of weight percentage of MWCNTs and injection molding processing parameters including holding pressure and holding pressure time (all in four levels) investigated on mechanical and structural properties of nanocomposite foam samples. Specific tensile strength investigated as mechanical property and for investigation of structural properties of nanocomposite foam samples, SEM test has been done that the results of this test showed that a well microcellular structure achieved. According to the results of signal to noise ratio (S/N) weight percentage of MWCNTs is the most effective parameter on specific tensile strength and structural properties of nanocomposite foam samples. The results demonstrated that by adding 1 wt% of MWCNTs, specific tensile strength of samples increased about 147%. Also, the results indicated that by addition of MWCNTs, cell density increased and mean cell size decreased that means providing optimal conditions for foaming.

Nowadays, two-layer metallic sheets have become as a useful solution to produce multi-functional products. Generally, two-layer metallic sheets can have advantageous characteristics such as increasing formability of the low formable component, improving the corrosion and wear resistance and reducing weight and cost of manufactured products. Therefore, understanding the forming limit behavior of a two-layer metallic sheet has an essential role in the design of sheet metal forming processes. Forming limit diagram (FLD) is a suitable method to predict the formability of metallic sheets in sheet metal forming operations. The aim of this research was to determine the forming limit diagram in Aluminum-Copper two-layer metallic sheets experimentally. The forming limit diagram can be used as a criterion in order to predict necking initiation which may cause tearing in sheet metal forming processes. In this paper, the forming limit diagrams of Aluminum-Copper two-layer metallic sheets have been obtained through an experimental procedure for the first time.

Carbon fiber-reinforced polymer composites (CFRP) due to the ratio high strength to weight down day by day growing in various industries, such as aerospace and automotive. Due to the different thermal expansion coefficient between the fibers and resin polymer composite drilling materials difficult to create one of the final parts. The helical milling method in the recent years due to the force reduction in machining and holes at once (no need to pre drill) is one of the new methods for drilling CFRP. In this study, amount delaminate to be explored according to force and machining parameters. For determine the amount of the feed, cutting speed and screw pitch the several tests was conducted and Therefore three cutting speed, four speeds feed and one screw pitch was determined. After the experimental results showed that amount delaminate has a direct relationship with the axial force during machining operations. Also diameter hole is produced factors influencing on the delamination factor (Fd). That increasing cutting speed and reduce feed production of the hole causes with to higher precision and reduced delamination factor.

In this study, the bending behavior of pure and intra-ply hybrid composites reinforced with brittle and ductile fibers were simulated based on a finite element method. For this purpose, a four-ply composite with the unidirectional stacking sequence was designed by using the dimensional, physical and mechanical properties. In this way, the three point bending test was simulated on the model composites by using Abaqus software. In these models, the mechanical properties of composite layers were defined base on nonlinear (elastic-plastic) behaviors. In order to validate the simulated model; the theoretical results were compared with the experimental ones. The results reveal that the model can predict the bending force at different deflection, accurately. As can be seen, the maximum difference between numerical and experimental results for fracture bending load is about 9.7%. In addition, the results distribution analysis at each layer of hybrid composites show that at the yield stress point, the outer layers of composites bear the longitudinal stress up to maximum strength but at this point the inner layers just used 30 percent of their maximum longitudinal stress.