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

In this article, to investigate the severity of damage to the helicopter pilot under the crash impact, the numerical simulation of the actual helicopter cockpit seat has been done. To limit the complexity of the problem, a fully vertical impact was considered as a reference scenario for the assembly consisting of a collapsible helicopter seat, an energy absorption section, and a humanoid dummy. For this purpose, the three-dimensional model of the chair in the laboratory was studied in two states with and without the addition of the energy absorption mechanism. A honeycomb structure was used in the seat cushion section. The results of the research showed that the use of UPVC damper to test the crash impact with a certain mass based on biomechanical criteria, an average 80 % decrease in serious injuries to the skull and spine has been achieved. Also, based on the results obtained in this research, although the aluminum honeycomb structure meets the criterion of damage to the head and is within the permissible range, it has rejected the criteria of damage to the spine and permissible acceleration range. However, compared to the case without honeycomb, it has performed much better and has been able to absorb the energy of the crash impact.

Large and/or complicated sandwich structures are often manufactured by connecting pre-fabricated sandwich panels by means of connections, adhesive or bolts. In nearly all sandwich constructions certain types of joints have to be used for assembly but little is known about their mechanical behavior. This paper deals with the investigation of the behavior of two aluminum joints with different geometries under low velocity impact tests. These two joints are used to connecting sandwich panels with glass-epoxy skins and aluminum honeycomb core. The joints and sandwich panels are connected by means of epoxy resin. After construction of the specimens, low velocity impact tests were performed on the specimens. Finite element analysis were used to simulate the behavior of sandwich panels with connection. Verification of the numerical results was performed by comparing the numerical and experimental results. There was a good compliance between numerical and experimental results. Also, the effect of increasing the length and the thickness of the connections on the behavior of the sandwich panel was done through a parametric study using the FEM model.

Cellular solids are extremely used in aerospace industries and civil infrastructures due to their low weight/strength index that leads to decrease in total weight and fuel consumption. Determination of mechanical properties of these structures is absolutely essential for structural design fulfillment. In this paper the calculation of in-plane elasticity properties of elliptical cell honeycomb composite structure is investigated. In this regard at the beginning, by using free body diagram of the smallest repeating unit of cell, the forces and moments applied on unit cell are obtained; and then by using strain energy theory and Castigliano's theory, the in-plane elastic constants are obtained. For validation of theory results, by using the ABAQUS finite element program, the elliptical honeycomb is simulated and by using normal and shear loading conditions and obtaining stresses and strains, the elastic constants are calculated and compared with theory amounts. The results show that the relation of the macroscopic Young's modulus and the macroscopic shear modulus are directly proportional to the thickness of the cell wall and inversely proportional to the small diameter of the ellipse.

In this paper deflection and free vibration of sandwich panel is studied. The core of Sandwich panels is made of hexagonal honeycomb and faces are made of two different materials of Carbon Fiber Reinforced Plastic and K-aryl/epoxy covering. The governing equations are deduced from the First order Sheer Deformation Theory (FSDT) and they are solved using Generalized Differential Quadrature Method (GDQM). The classical method in the references is used to verify the DQ method and to show that the applied GDQM method has a good results with compared to the references. Deflection of sandwich panel is investigated with two different load types. Finally natural frequency for the first 4 modes and the two different faces materials are calculated and the effect of various lengths to core thickness ratios and faces to honeycomb core thickness ratios are studied. Further, the effect of foundation stiffness coefficient on deflection and natural frequency are showed.

In this paper, a new analytical model has been presented for energy absorption of aluminum-foam sandwich panels under ballistic impact. The panels consist of hexagonal honeycomb core sandwiched between two aluminum skins. In analytical model cylindrical rigid projectile with flat ended has been considered. In the quasi-static loading, by using the springs-mass model, energy absorption of Aluminum skins with considering difference energy absorption mechanisms calculated. Energy absorption of honeycomb has been determined by wierzbicki model. Energy balancing equation has been employed for determination the ballistic limit and residual velocity of striker. The results of ballistic limit and residual velocity of striker computed by new model have good agreement with experimental results. Also the effects of projectile mass and diameter and cell diameter of honeycomb in energy absorption of sandwich panel has been investigated.

Wind tunnels generate controlled air flow which passes through the model. Thus، a series of useful data related to air flow quality are obtained. The final goal of wind tunnel design is to generate a uniform air flow with minimum turbulence intensity and low flow angle. One of the methods for decreasing the turbulence intensity is to install honeycomb and screens in the settling chamber of the wind tunnel. In this research، the effects of honeycomb and screens with specified geometric parameters on velocity distribution، turbulence intensity، skewness and flatness are investigated. A set of hot-wire anemometer is used to measure turbulence intensities. It measures flow instantaneous velocity with high frequency. The results show that the installation of honeycomb and screens، and isolation of the test section from the fan decreases the turbulence intensity of the test section about 75% and، optimizes the skewness and flatness values. Moreover، normal probability distribution of instantaneous velocity approaches the normal distribution.

In this research, influence of foam filling technique in honeycomb cores by using lightweight rigid polyurethane foam is investigated. Plastic mechanical behaviors of honeycomb cores are studied by mean of numerical method. Four types of Aluminum honeycombs (Al 5052 alloy) both bare and foam-filled were subjected to unidirectional compression. Analyses were carried out for different impact velocities to survey quasi-static and dynamic crushing response of the honeycomb cores. Crushing strengths and specific absorbed energy were obtained for honeycomb cores which have different relative densities. FEM results showed that foam filling technique can increase crushing strength of honeycomb core up to 24 times, and its specific absorbed energy up to 11 times. However, it was found that in heavier honeycombs the effect of foam filling technique decreases significantly. Furthermore, it was found that in quasi-static situation, foam filling technique can enhance desired core mechanical properties’. Meanwhile, in dynamic states of impact it was illustrated that polyurethane foam have not significant role in improving crushing strength and specific absorbed energy of honeycomb cores. For instance, in crushing with impact velocity of 100 m/s, amount of specific absorbed energy for bare and foam-filled cores were approximately equal.

In this paper, a new analytical model has been presented for energy absorption of aluminum-honeycomb sandwich panels under high velocity impact. In high velocity impact, striker with initial velocity penetrates into target and perforates it completely and exits by residual velocity. The panels consist of hexagonal honeycomb core sandwiched between two aluminum skins. In analytical model cylindrical projectile with flat ended have been considered. It is supposed that aluminum skins failure by mean resistive pressure. Energy absorption of honeycomb has been determined by wierzbicki model. Energy balancing equation has been employed for determination the ballistic limit and residual velocity of striker. The results of ballistic limit and residual velocity of striker computed by new model have good agreement with experimental results. Also the effects of projectile mass and diameter and cell diameter of honeycomb in energy absorption of sandwich panel has been investigated.

In this paper, ballistic impact on sandwich panel with composite face sheet made of Glass/Epoxy and aluminum honeycomb core has been studied. The solution is derived from a wave propagation model. At first both analytical and numerical solutions were clarified and their results were compared with experimental results. Some deformation patterns, failure modes and energy absorption mechanisms were identified by observation, such as: dynamic movement of the target, stretching, bending deformation, delamination, debonding, shear fracture honeycomb, tensile fracture of Glass/Epoxy and plug and petal formation in composite facings. The solution involves a four-stage and effective masses of the face sheets and core as the shock waves travel through sandwich panel are derived using Lagrangian mechanics. The resulting non-linear differential equation of motion was solved considering the local damage effects and corresponding energy absorptions. Also numerical model, analysis of the penetration process was performed by a nonlinear explicit finite element code, LSDYNA. The results of analytical solution and numerical simulation are compared with experimental tests. Ballistic impact tests is carried out on the samples by flat-ended projectile with 8/5 gr mass and 10 mm diameter in difference velocities.

this paper، ballistic impact on sandwich panel with composite facesheet made of Glass/Epoxy and aluminum honeycomb core has been investigated experimentally. Ballistic impact test also carried out on Honeycomb and composite and the effect absorption energy by adding composite on two sides honeycomb is studied. By this model the influence of the components on the behavior of the sandwich panel under impact load was evaluated. Ballistic impact tests is carried out on the samples by flat-ended projectile with 8/5 gr mass and 10 mm diameter in difference velocities. Also، the contribution of the failure mechanisms to the energy absorption of the projectile kinetic energy was determined. The results show that honeycomb sandwich has more energy than when alone ballistic tests conducted on has absorbed and front cover compared with back cover sandwich structure has lower energy absorption. Also bigger than ballistic limit velocity absorbed the maximum amount of energy.

Solar panels are used in satellites to absorb solar energy and supply the power needed for space missions. Mission definition and satellite lifetime is restricted by the way and the amount of energy that can be supplied for satellite subsystems. Therefore, the design of satellite solar panels as a unique source for power supply in satellites is very sensitive and important. In this paper, an efficient design for solar panels of a GEO communication satellite is proposed considering the maximum strength to weight ratio and minimum deflection. For this purpose different space structures including Iso Grid structures, honeycomb and composite plates are studied. Several structural analyses are performed on the models in order to assurance from the strength and durability of the model in space working environments. The design according to composite-honeycomb is introduced as the best model for solar panel structure. The proper configuration of layers is also presented by developing a code based on an optimization algorithm.

Honeycomb is one of the major components of a wind tunnel, which is used to make the air flow uniform and reduce the flow angle. A honeycomb is installed upstream of the nozzle in the settling chamber. As high costs are incurred for construction of honeycomb in large vertical wind tunnels, and in view of the difficulties in installation of these units, it is necessary to reduce the ratio of length to hydraulic diameter of the honeycomb. However, reduction of this ratio may affect the honeycomb performance. In this paper, various honeycomb designs have presented and flow quality has been experimentally investigated for each case. A hot wire anemometer (HWA) and a device for measurement of flow angle (yaw head) have been used to study the flow downstream of the honeycomb. Results show that with decrease in length to hydraulic diameter ratio from 7 to 2, the honeycomb performance is adequate for change in flow angle from -20 to 20º. These results have been used in the design of a vertical wind tunnel, namely Tofan Vertical Wind Tunnel, which will be used for the simulation of skydiving. Based on these results a square honeycomb of length to hydraulic diameter ratio of 2 has been selected, which has resulted in a reduction of up to 60% in the construction cost of the honeycomb.