جستجوی مقالات مرتبط با کلیدواژه « کامپوزیت » در نشریات گروه « مکانیک »

In this article, the effect of filling foam on the energy absorption capability of hybrid tubes with different thicknesses of the composite layer has been investigated experimentally. For this purpose, 10 aluminum/woven glass fiber/polyester resin hybrid tubes with 5 different thicknesses of the composite layer between 0 and 1.75 mm were produced by manual tape winding on an aluminum tube with an outer diameter of 42 mm and a thickness of 1 mm, then, 5 of these tubes were filled with polyurethane foam with free density of 40 kg/m3. Afterwards, the hybrid tubes were subjected to the quasi-static axial compression test using a universal pressure testing machine with a constant displacement rate of 10 mm/min until their complete crushing, and the specific energy absorption, crushing force efficiency, and crushing mode shapes were extracted for each tube. The results show that in the low thicknesses of the composite layers, filling the tubes with polyurethane foam effectively improves the specific energy absorption and the crushing force efficiency. However, the role of the foam becomes less effective and even negative in the high thicknesses of the composite layers.

Improving the mechanical properties of the 3D printed parts by a 3D printer based on fused filament fabrication by continuous fibers (carbon, glass, and aramid) has been the focus of many researchers. Due to the nature of additive manufacturing processes that produce the parts layer by layer, in most of the research, continuous fibers are layered on a 2D surface. Robots with high degrees of freedom have been used in cases where fibers are placed on curved surfaces. In this research, a method for deposition of the continuous glass fibers on a curved surface is presented. This method is implemented on a simple and cheap 3D printer. The presented method is based on modifying the G-code, creating a rotating axis for the nozzle, and applying and using computer-aided design and manufacturing techniques. Finally, by 3D scanning of the printed sample and comparing it with the 3D model, the amount of deviation and tolerance of the surface form is determined. The obtained experimental results indicate the effectiveness of the presented method for the deposition of continuous fibers on curved surfaces. With the presented system, continuous fibers are deposited on a curved surface that consists of paths with different degrees of curvature, by simultaneous impregnation of fiber and polymer. Comparing the scanned sample with the printed sample shows that the maximum deviation is 0.1 mm. This error is acceptable due to the nature of shrinkage and distortion of thermoplastic polymer materials in forming processes according to the DIN 16901 standard.

Nowadays, sandwich panels are used as light load-bearing structures in most aerospace structures and other industries. Smooth and uniform surfaces, excellent resistance to fatigue, low weight, and good energy absorption are the characteristics of honeycomb panels. In this article, to investigate the energy absorption and strength of sandwich panels with composite skin and the use of an elastomer layer as a layer between the composite skin and aluminum honeycomb core 5052 under quasi-static punch loading, using two mandrels with flat and spherical cross-section. The experimental form has been discussed. The failure modes in this test include wrinkling of the skin, separation of the adhesive layer between the plate and the core, tearing of the plate, crushing of the core of the sandwich panel outside the plate, bending of the core of the sandwich panel inside the plate, rupture of the core of the sandwich panel are classified. By examining the experimental results of the mandrel penetration test, it was determined that the strength and energy absorption of the sandwich panel increased by 20% using the elastomer layer, and the cohesion and adhesion of the skin of the sandwich panel to the core was greatly improved. Using the elastomer layer, in the three-point bending test, the displacement of the sample increased by 8.7 times until reaching the breaking force of the structure.

In this study, samples reinforced with continuous metal wire as both a reinforcing component and a shape memory actuator were printed via the Fused Deposition Modeling (FDM) additive manufacturing method. Shape memory materials are a significant subset of smart materials that can recover their original shape in response to a specific stimulus such as heat, magnetism, electricity, moisture, etc. The stimuli for shape memory materials are generally classified into two main categories: direct and indirect. In some cases, direct stimulation may not be possible for shape recovery, and introducing solutions for adding indirect stimulation capability to these materials can expand their application range. In this study, the chromium-nickel metal wire was used as a reinforcing agent to improve the mechanical properties and introduce indirect stimulation capability to the materials by applying voltage simultaneously using the in-situ impregnation method in the FDM process. Adding continuous fibers through the in-situ impregnation method during the printing of parts significantly enhances the mechanical properties of polymeric samples. According to the obtained results for a 0.15 mm diameter metal wire, the increase in tensile strength for 5% and 10% reinforced samples was 63% and 134%, respectively. The increase in flexural strength for samples reinforced with 5% and 10% metal wire was 10% and 105%, respectively.

The friction stirring process is one of the new processes in the production of metal matrix composites. Choosing the right parameters for the uniform distribution of particles in this process is vital. One of the important parameters in this process is the number of processes passes and the change in the direction of the tool rotation between the process passes. In this study, the effect of the number of passes and the change in the tool rotation direction on the distribution of SIC particles in aluminum 6061 has been investigated. Aluminum 6061 is one of the hard deposit able aluminum alloys, in which magnesium and silicon are the main elements. First, samples are produced using one, two, and four process passes, with and without changing the tool rotation direction between the process passes. Then, the distribution of particles in the base metal is studied using macro- and microscopic photographs. The results showed that the number of processes passes and the change in the tool rotation direction have a significant effect on the uniform distribution of particles.

In the present work, the effect of smart shape-memory alloys on thermal buckling and post-buckling of monoclinic and unidirectional composite panels has been investigated. The aerodynamic pressure applied to the system was modeled using the piston theory method. The effect of thermal heating for ultrasonic flows was also estimated from the reference temperature method. The panel is modeled nonlinearly with large deformations based on Van Karmen's theory. The obtained results show that the shape-memory alloy was able to increase the critical temperature of thermal buckling. The effect of the arrangement of composite layers on increasing the thermal buckling temperature was also studied. The results show that the amount of thermal deflection is greatly reduced due to the use of this alloy. Also, in the higher temperature differences, the rate of reduction of the panel increases. In this work, the effects of thermal stress on buckling and thermal buckling in a rectangular composite panel with hinge-hinge boundary conditions were investigated. Also, the effect of shape retention alloy in controlling these two phenomena has been studied. The shape memory alloy wire was placed in martensitic mode to apply a compressive force to the panel to control the heating and aerodynamic forces after changing the phase to austenite. The governing equations of the system were extracted through the layer theory method to show the effects of in-plane displacements better. Investigations on the effect of different layers (symmetry effects and arrangement angle of composite sheets) were performed to investigate thermal buckling. According to the obtained results, the layer arrangement of plates (0.90 / 0.90), (-45.45), (30/60), and (0.90 / 90.0), respectively, had the greatest effect on raising the critical temperature of thermal buckling in dimensional ratios equal to or greater than one. This shows that the symmetry of the arrangements has a greater effect than the angle of the arrangements. Examining the buckling diagrams for the effect of a shape memory alloy, it can be concluded that by placing this alloy in the composite panel, in addition to raising the buckling temperature, this alloy has a greater effect on displacement control by increasing the temperature after the critical buckling temperature.

In order to produce and design parts with high adaptive, 3D printing is a novelty technology. In considering to low hardness of produced parts with PLA filament, using consolidated composite materials with carbon continues fiber, could resolve this problem and increase mechanical characteristic of mentioned produced parts. Base on defense industrial equipment’s, included aerospace industrial, in UAV production procedure, and in order to improve the efficiency of production and quality of produces, employing the 3D printing devices with ability of using the consolidated filament with continues fiber, are needed. So according to the requirement of using consolidated filament with continues fiber, designing a filament-maker device with continues fiber filament with polymer filament structure and carbon consolidator fiber production ability, had started. In order to all right using of the PLA, polymer filament melt experimental effects and extruder device velocity on produced filament surface cut endurance, is analyzed. In this study, 3K carbon fiber is used and factors such as fiber surface coarseness impregnate between fiber and matrix, impregnator temperature effective and filament output velocity are estimated. The results of this study that seen by electronic microscope images shows the coarseness incising of fiber surface in preparation step of   fiber and high-quality carbon fiber impregnate by PLA molten. Besides, by means of TAGOCHI examination design method, filament is produced and samples are tested. With TAGOCHI analysis of results, the best melt temperature is 190 centigrade and the best accumulating velocity is 1 RPM.

The nacelle cover and nose cones of most megawatt wind turbines are made of composite sheets. Due to the complex shapes, geometries, and large dimensions of these components, they are composed of several parts that must be assembled using non-permanent mechanical joints, such as bolts. Therefore, it is very important to consider all the effective parameters that affect composite joints. One of the most critical design parameters for bolt connections is the amount of bolt preload or tightening torque. However, increasing the preload without caution is not feasible due to the composite material present on both sides of the joint, as this can potentially damage the composite sheets. As a result, this paper aims to evaluate experimentally the effect of bolt preload or tightening torque on composite joints. To achieve this, identical specimens were fabricated, each with a different bolt tightening torque ranging from 2 Nm to 50 Nm. These specimens were then subjected to a tensile load. After determining the optimal preload force, four different types of arrangements were experimentally tested to find the best bolt arrangement. Finally, by examining various aspects, the best arrangement for connecting different parts of the nacelle cover and nose cone was determined.

In this research, the influence of the parameters of metallic wires in the foam cores of sandwich panels as a reinforcement to improve the bending properties of sandwich panels has been investigated. In this regard, the three parameters including the number of wires (on a scale of 1, 2, and 3 wires), wire material (aluminum, iron, and steel) and their diameter (0.75, 1, and 1.5 mm) as the effective input parameters and specific bending strength and modulus of the structure have been selected as the output parameters of the design of experiment. In order to evaluate the parameters after validating the numerical model using the built prototype, an experiment has been designed using the Mini Tab software (Taguchi method) and simulation of the proposed tests has been carried out using the Abaqus software.The results showed that the optimal sample with priority of strength to weight includes three steel wires on each side, with the diameter of one millimeter. Also, with the increase in the number and diameter of the wires, the strength has increased, but this relationship is not always correct when assessing the strength to the weight of the sample. Increasing the mechanical properties of the wire increases the overall strength of the structure, so that the bending strength of the sandwich panel reinforced with three steel wires rises by about 43%, the bending modulus by about 80%, the specific strength by weight by 21%, and the special bending modulus by about 54%.

Flanges are parts that provide the possibility of connection, change of direction, access for repairs and inspection between large and main parts of equipment and structures. In this research, due to the importance of maximum lightening while maintaining the strength of parts in aerospace structures, composite flanges and shells were made, which are used in aeronautical structures such as bossting rockets and satellite carriers. They are responsible for connecting the parts and large shells of the structure. The material of the flanges used in these structures is aluminum in the lightest state, and in this research, with the aim of lightening as much as possible, 4 flanges and 4 shells were made in 2 sets, each set includes 2 flanges and 2 shells. After connecting the flanges and shells to each other, experimental modal analysis and tensile tests were performed. Also numerical simulation of the modal and tensile test was performed with ANSYS software. The results of experimental tests and numerical analysis on the manufactured parts show that the specific frequency of the composite flange is higher than that of the steel and aluminum flange (in low frequency range). Also, the delamination factor in the composite flange blade has more effect on increasing the length of the structure due to the tensile force, rather than the failure of the matrix and fibers.

In this research, energy absorption in sandwich panel structures with honeycomb core and skin made of glass-epoxy multi-layer composite, aluminum, and two-dimensional glass fabrics impregnated with shear-thickening fluid under low-velocity impact loading has been investigated. Polyethylene glycol 400 and hydrophilic fumed silica with nanometer dimensions were used to make the shear thickening fluid, and then a rheometer was used to verify the rheological properties of the fluid. The test was carried out at two heights of 100 and 500 mm with a drop weight device. The sandwich panel honeycomb core has been tested once filled with shear thickening fluid and again empty of shear thickening fluid. The results of the rheology test show that the viscosity value increases with the increase of the shear rate. The impact test results show an increase in energy absorption in the structure of sandwich panels filled with shear thickening fluid compared to empty sandwich panels. At the drop height of 500 mm, the absorption of specific energy in the sandwich panel structure with a skin made of two-dimensional glass fabrics impregnated with shear thickening fluid, the ratio of sandwich panel with a skin made of aluminum and composite increased by 27.93, and 9.47%, respectively, and energy absorption in The sandwich panel with composite skin has increased by 16.86% compared to the sandwich panel with aluminum skin.

Composites are a class of advanced materials in which simple material combinations are used to create new materials with superior mechanical and physical properties. The use of composites in vessels has several advantages such as weight loss, improvement of radar and magnetic properties, resistance to chemical corrosion and mechanical corrosion and fatigue, vibration absorption and noise, high strength-to-weight ratio, good resistance to underwater shocks. Replacing steel components with composite components can save 60 to 80 percent on component weight and 20 to 50 percent weight savings by replacing aluminum and composite components. In this study, the pin joints used in marine composite equipment were investigated in multilayer monodirectional composite made of glass and epoxy fibers. For this purpose, a model was considered for the problem and the parameters of the center of the pin from the free edge of the multilayer to the pin diameter (w/d) and the ratio of multilayer width to pin diameter (e/d) were defined as the variables of the problem. Then, to obtain the rupture force and rupture mode, the samples were subjected to tensile loading. The results showed that the maximum force tolerance and rupture mode were significantly affected by w/d and e/d parameters and with increasing the w/d ratio, the force tolerant increased and the mode of the rupture changed from shear to the mode of shear to the crush mode, and for each e/d ratio, there is an optimal limit for w/d.

The use of common adhesive methods in metal-composite bonding leads to weak joints that are separated with the least load. The purpose of this research is to investigate the increase in the tensile strength of aluminum metal to glass fibers reinforced with epoxy resin using a new combined method that includes the advantages of both adhesive and mechanical (pinning) methods. In this method, the pins embedded in the structure are used as an interface for load transfer, and the aim is to investigate the amount of strength changes with different types of interface pins. Therefore, the pins are passed through them during the layering of composite fibers and then the curing process is completed. Therefore, a part of the metal structure has penetrated between the warp and weft of the composite and it is expected that the strength will increase. Four connection models without pin (pure adhesive), pin with a diameter of 1.2 mm, pin with a diameter of 1.6 mm and pin with a claw with a diameter of 1.2 mm have been evaluated and the results of the strength of the connections have been compared. Tensile test results have shown that this type of connection has a significant increase in strength compared to the sample without pins, and in three types of connections with different characteristics, 335%, 609%, and 421% increase in strength has been observed, respectively. Also, failure occurred gradually in samples with pins and suddenly in samples without pins.

This paper investigates the free vibrations of a sandwich panel with metal/composite hybrid face sheets reinforced with carbon and glass fibers and a soft core with simply-support boundary conditions. To derive the governing equations, with third shear deformation theory (TSDT) of multilayers and Hamilton's principle have been used for a rectangular sandwich panel with a metal/composite hybrid top and bottom face sheets. It is assumed full connection of the face sheets to the softcore and linear displacement. After comparing the results of the present research with similar and ensuring the correctness of the extracted equations, the parameters effective, volume fraction metal layer and composite with angular layering, the ratio of length to thickness and thickness of the core to the face sheet, length sandwich panel to width and the layup (0,90) and (45, -45) for two types of glass and carbon fibers hybridized with AL 2024 T3 aluminium investigated. The results showed that the carbon/aluminium hybrid with the volume of the composite (Vc) equal to 0.5 has the highest natural frequency value in the first five mode shapes with layup AL/-45/45/core/45/-45/AL. Also, by increasing the thickness of the softcore to the surface and the ratio of length sandwich panel to total thickness, the effect of the aluminium layer decreases.

Here the healing process of glass/epoxy composites is studied experimentally. The healing agent is composed of ML506 epoxy resin and HA-11 hardner which is charged into microtubes. The microtubes are interleaved between the first and the second and the fifth and the sixth layers. The initial damage is introduced to the samples by drop weight impact tests and the recovery percentage of the tensile strength due to healing process is measured by tensile test. The effects of healing time (without thermal cycles), number of healing units and thermal cycles are investigated on the recovery of the tensile strength. Composite samples containing 8, 16 and 32 healing units are studied in the periods of 1, 6 and 12 days after the initial damage. Also, some damaged samples are set to 1, 3, 5 and 7 thermal cycles and after one day, tensile tests are carried out. The results show that without thermal cycles the healing process is almost completed after 6 days with an 83% recovery. In addition, the maximum amount of tensile strength recovery is equal to 86% which is related to the samples with 32 healing units after 12 days. This amount of healing efficiency can also be achieved by means of 5 thermal cycles. This is also true for thermal cycles where the effect of thermal cycles is tangible up to 5 cycles.

Operational sensitivities of military air craft, deterrent measures in aircraft design to prevent the accumulation of static charge on the surface of the aircraft or Electrostatic Discharge, is very necessary and important. These include antistatic coatings, flame spraying, the use of carbon fiber composites and nanocomposites in aircraft fuselage design, and electrostatic dischargers. The aim of this study was to investigate, simulate and compare the effect of electrostatic discharge (ESD) in military aircraft with all-metal, all-composite body and the combined state of several structures. In this paper, by selecting the military Aircraft body of composite, metal and combined mode, the effects and surface of induced electric field, surface currents due to electrostatic flux and Radiation electromagnetic fields from the transient state of surface current will be compared and examined in different parts of the military air craft, including: radar system, cabin and electronic telecommunication systems, internal and external fuel tank.

In this research, the mechanical properties including bending strength and impact resistance for steel composite beams with high performance concrete are discussed. In the construction of the steel part of the specimens, the shield cross-section grade 4 is used in the tensile part of the sheet with a thickness of 5 mm and two widths of 30 and 40 mm and a length of 70 cm. It should be noted that the compression wing of some specimens is made of concrete with Different steel reinforced fibers. Self-compacting concrete with 3 percent of different steel fibers, which are 0, 0.5, and 1 percent, was used in making the concrete of the specimens. The results of the impact tests showed that the amount of energy absorption as well as the initial maximum force increased with the increase in the fibers percentage that the highest energy absorption is related to the w4hc4sf1 beam, which has increased by 0.09% compared to the specimen without concrete. Regarding the results of the bending test, the resistance value increased intermittently with the increase of fibers. The w4hc4sf1 beam had the best performance, and its strength increase compared to the same specimen without concrete was equal to 204%.

A nanoparticle or an infinitesimal particle is usually defined as a particle of matter that has a diameter between 1 and 100 nanometers (nm). The properties of nanoparticles often differ significantly from larger particles of matter. Nanoparticles show different dislocation mechanics, which together with their unique surface structure, lead to different mechanical properties from bulk materials. Nowadays, by adding nanoparticles, the mechanical properties of composites are improved. Due to their small size, nanoparticles increase the surface area between the base material and the reinforcement and therefore improve the mechanical properties. The type of nanoparticle used, dimensions, weight percentage and the way of nanoparticle distribution are determining factors in improving mechanical properties. In the present study, while presenting the concepts related to nanocomposite, the effect of five different nanoparticles on the common mechanical properties considered by structural designers is investigated. The results show that the addition of nanoparticles up to a certain weight percentage improves the properties, and more than that amount sometimes has the opposite effect, one of the reasons for which is the clumping of nanoparticles.

The aim of the present study was to investigate the adhesion and thermal resistance of epoxy / Novalac glass composite. Due to the use of phenolic resins, the pre-impregnation method has been used by combining different percentages of epoxy and novac resin. The two-piece composite samples of epoxy glass and novac glass were bonded once without glue and once with glue. In the following, the effect of different compounds of two types of epoxy resins and Novalak on adhesion and heat resistance has been investigated and evaluated. Using the results of differential scanning calorimeter test and gelling time, the sintering cycle of the samples is predicted. The results showed that the presence of curing agent of both epoxy and novac resin in the composition is essential. The results of interlayer shear strength test and three-point bending showed that the presence of phenolic resin in the samples reduced the mechanical strength of the sample. In the connection of two composites of epoxy glass and Novalac glass, the presence of exon adhesive has increased the strength of the samples compared to the direct connection of epoxy by 2.48%. Finally, the results of the oxyacetylene test indicate the need for pre-baking and a gradual increase in temperature in the cooking cycle.

The applications of reinforced composites and heterogeneous solid materials have been widely developed in different fields of aerospace and mechanical engineering. In this research, the necessity of using non-destructive methods in identifying possible damages in composite materials is pointed out. In addition, the acoustic emission method is described and compared with other non-destructive evaluation methods. It is stated that acoustic emission is a dynamic diagnosis method which can instantly show discontinuities in a structure under tension. The nature of acoustic emission signals is mentioned as an electrical signal. Finally, it is concluded that the best method to check the delamination and fiber damage in composite laminates is the acoustic emission method.