نشریه مهندسی مکانیک مدرس
سال نوزدهم شماره 9 (شهریور 1398)

This paper presents a novel severe plastic deformation method entitles modified friction assisted tube straining for producing ultrafine-grained cylindrical tubes. Using friction power generates heat to locally increase temperature of the deformation area and creates severe combined strains and lower pressing force. Experimental tests were executed on Cu/30Zn alloy to investigate applicability of the presented method. The optimum process parameters, 710Rev/min rotary speed and 0.08mm/Rev feed rate were found, applying experimental test to process tubs fault free.  Microstructure study of processed specimens showed a significant grain refinement from the initial value of 76μm to 9μm and 7μm in longitudinal and peripheral directions, respectively. Yield stress and ultimate tensile strength of processed specimens increased to 325 and 202MPa from the initial values of 160MPa in peripheral and longitudinal directions, respectively. Also, hardness significantly increased to 72Hv from the initial value of 48Hv.

The cold roll bonding (CRB) is a type of bonding process between similar and/or dissimilar metals that is bonded through plastic deformation via rolling process at room temperature. In addition, the accumulative roll bonding (ARB) process is considered as one of the methods for applying severe plastic deformation (SPD) with the ability to achieve ultra-fine grains (UFG) structure and improved mechanical properties. In this research, a combined method was suggested consisting of ARB and CRB processes in order to fabricate UFG copper strip with simultaneous increase of strength and electrical conductivity. Microstructure, mechanical properties, and electrical conductivity of copper specimen fabricated via combined method and ARB processes were investigated. Field emission scanning electron microscope (FESEM) micrographs showed in the crystalline structure of the specimen fabricated via combined method, a large amount of the UFG with uniform distribution are observable. Also tensile strength and hardness of strips increased with increasing the number of rolling passes. Finally, investigation the electrical conductivity of the specimens by four-point probes test showed electrical conductivity decreases with increasing the number of ARB cycles, while the specimen fabricated via combined method increased simultaneously strength, hardness, and high electrical conductivity.

A wind turbine airfoil was analysed, using computational fluid dynamics (CFD) to study the oscillating effects and slip boundary conditions. The slip boundary condition is due to applying superhydrophobic surface. Fluids on these surfaces are repelled. The superhydrophobic surface can delay the icing on blades. The surfaces is assumed at the leading edge; the icing can occur on this region. The chosen oscillation parameters was enough for modelling dynamic stall. The dynamic stall cause a severe loading on the blade. This phenomenon is depicted by two vortices: leading edge vortex and trailing edge vortex. Three reduced frequencies are considered:  in a range of  slip lengths. In this regard, the Transition-SST model is applied for SD7037 airfoil with. The results showed that applying a superhydrophobic surface with low values of the slip length cannot be appropriate during the oscillating motion; but at the slip lengths larger than 100 microns, the aerodynamic coefficients are significantly changed. At the highest reduced frequency, the lift and drag coefficients are reduced about 12% and 40%, respectively. Increasing the slip length postponed the vortex formation and stall angle.

In this paper, the thermal conductivity coefficient of multi-walled boron nitride nanotubes has been investigated, using molecular dynamics simulation based on the Tersoff and Lenard Jones potential functions. The effects of diameter, length, and temperature on the thermal conductivity of double-walled boron nitride nanotubes have been studied. Also, by considering the 2, 3, 4, and 5-wall nanotubes, the effect of number of walls on the thermal conductivity of boron nitride nanotubes were studied. Finally, by considering of zigzag and armchair nanotubes, the effect of chirality has been investigated. The results showed that the thermal conductivity coefficient of double-walled boron nitride nanotubes increases by increasing the diameter of nanotubes and decreases by increasing temperature. It had been demonstrated that with 73% and 82% increase in the outer diameter of nanotubes, the thermal conductivity increases 93% and 98%, respectively. Furthermore, regarding to the chirality, the armchair nanotubes have a higher thermal conductivity than the zigzag ones. Also, the simulation results showed that thermal conductivity coefficient increases by increasing the length of boron nitride nanotubes and 50% increase of effective nanotube length increases the thermal conductivity by 25% approximately. Finally, by studying the effect of the number of walls, it is concluded that in the same length and temperature, nanotubes with higher number of walls have higher thermal conductivity coefficient in comparison.

Today, one of the useful methods of flow control, especially external aerodynamics, is plasma DBD actuators. In this study, the effect of plasma DBD actuators on cylinders in tandem arrangement is investigated. The actuators are considered on upstream cylinder. The cylinders are placed in distance (L/D) relative to each other. Investigation is done at two Reynolds number (100 and 200) with two different conditions of applying actuators. Cases with Vp-p=55kv and Vp-p=1kv are selected from references. The results of the present study are validated against the previous available experimental and numerical data and close agreement is found. Finite volume method is applied to solve equation of motion. Plasma actuators caused downstream cylinder experience upper values of drag coefficient and Nusselt number in all cases of study. Also, the growth of drag coefficient and Nusselt number are decreased by rising the Reynolds number, so that increasing the Nusselt number is 2% more at cases with Re=100 compared to cases with Re=200.

Fuel sloshing is one of the most important factors in disturb attitude of the spacecraft from desire in orbital maneuver. So, controlling this phenomenon is a critical problem in attitude control. There are active and passive control methods to control fuel sloshing. Active method has better responses to control fuel sloshing and its effect on attitude of the spacecraft in the same time; so, mostly this method is used. For this aim, it is necessary to model slosh dynamic. In this paper, slosh dynamic is modeled by a multi-pendulum model, and, then, coupled equations of the spacecraft and fuel slosh dynamic are derived. In the presented model, pendulums can move freely in 3D atmosphere, and this matter makes presented model closer to real. Coupled equations of the spacecraft and fuel slosh dynamic are nonlinear. Therefore, nonlinear control methods should be used to attitude control in more realistic mode. In this paper, two candidate Lyapunov functions are proposed; then, using these functions, controllers are obtained. The effectiveness of these controllers on attitude of the spacecraft and pendulums is described by a simulation. Although, there are some little differences in time responses based on two controllers, results of simulation illustrate good responsibility of controllers to control aims.

In this paper, the effects of particles size of Magnetorheological Carbonyl iron powder on damping force and energy dissipation capacity for a Magnetorheological double ended type damper is investigated experimentally. Despite of the considerable researches on the effects of particles size on the viscosity of Magnetorheological fluids, sedimentation of fluids and electromagnetic field intensity in damper, there is no a published work about the effects of iron particles size on the damping force amplitude and energy dissipation capacity of double-ended Magnetorheological damper. Therefore, in the present research, two different Magnetorheological fluids were prepared with the same volumetric percentage of % 35 from two different sizes of Iron particles i.e. 40 µm and 63µm and filled into a double ended type damper. The double-ended damper had three electric coils and was tested in different frequencies, different electric currents and 15 mm displacement stroke. The effects of Magnetorheological fluid particles on produced damping force and energy dissipation capacity were analyzed by extracting force-displacement and force-time curves from experiments. The results showed that the maximum amplitude of damping force is increased with increasing the applied electric current on the damper and the amount of this force for fluid with 63µm particles size is slightly higher than that for the fluid with 40µm particles size. However, the energy dissipation capacity of the investigated damper in all excitation frequencies with the all applied electrical currents for fluid with 63µm particles size was considerably higher than that for fluid with 40µm particles size.

The equations of nonlinear motion of clamped-hinged beam with an open crack were extracted and through solving them, the internal resonance in the cracked beam was studied. To this end, the crack was modeled as a torsional spring and the cracked beam was considered as two beam segments connected by a torsional spring. The equations of motion of the cracked beam were extracted considering the geometrical nonlinearity. Then, using the Galerkin’s method, these equations were changed to a set of nonlinear differential equations for vibration modes which were solved by the perturbation method. Since the mechanical energy of the beam in each mode depends on the instantaneous amplitude of vibration of the beam at the corresponding mode, so to analyze the influence of the crack on the energy exchange between the modes, the instantaneous amplitudes of the vibration modes were obtained. The results show that in the cracked beam the magnitude of the energy exchanged between the modes is less and the frequency is more than that in the intact beam. Also, by increasing the crack depth the frequency of energy exchange between the modes increases. The Vibration response obtained for the cracked beam with various amounts of the damping ratios shows that the frequency and the amplitude of energy exchange between the modes are independent of the system damping. To validate the results by the perturbation method, the equations of motions are also solved by a numerical method and the obtained results are in agreement with the results of the analytical method.

Leed titanate as an ionic Perovskite is ferroelectric at the lower of the below 766 K, which is called the transition temperature (Curie temperature), and at the above of this temperature is in the paraelectric phase. Studying the influence of mechanical parameters on the ferroelectric properties of PbTiO3 is important in the industrial application (such as RAM) of PbTiO3. In this study, using the molecular dynamics simulation method, the stress-strain effects on the polarization of lead titanate in the ferroelectric phase have been investigated. For modeling the atomic potential and interactions between ions in the ferroelectric phase, the short-range Buckingham potential and long-range coulombic potential, and, in addition, the fourth-order potential of oscillatory springs using a shell model (a model for calculating the polarization of a system) has been used. In this study, the effects of mechanical stress-strain action in the ferroelectric phase were investigated in two tensile and compression uniaxial stress-strain. In tensile stress-strain mode, the application of external stress leads to an increase in the polarization of the system, while applying compression stress-strain results in the decrease of the polarization of the system, so that by applying stress-strain, the polarization of the system reaches zero.

Curing process of composites results in the formation of residual stress and distortion. According to costs of composites fabrication, simulation of the fabrication process in order to avoid wasting investment is important. A common and simple method of composite fabrication is hand lay-up. In this research plane stress due to temperature change of composite laminates has been investigated and its resultant curvature has been analyzed. So, two symmetric and un-symmetric laminates with eight plies are subjected to 100-degree centigrade temperature change and normal and shear stresses have been calculated. First, by classical lamination theory which is the most important theory in stress analysis of composites, mechanical properties of glass/epoxy composite with 70 percent volume fraction, temperature change and stacking sequence are input variables of the written program. Three in-plane stress component is read and the amount of curvature has achieved that shows it is negligible for the symmetric sample. To validate the residual stress field, finite element simulation for both samples has been done that resulted in finding the same results with negligible errors. Assumptions are considered in finite element modeling and classical lamination theory which result in deviation of outputs from reality. In spite of these assumptions, the thermal simulation of composite laminations in ABAQUS software can have the desired prediction of reality. The innovation of the research is the use of this software and the verification of code.

Polymeric foams are one of the best candidates for thermal insulation. Accordingly, to investigate the thermal insulation properties of polymeric foams has attracted the attention of scientific communities in recent years. In this study, optimization of thermal insulation properties of polymeric foams is performed from solid and radiation thermal conductivities points of view. In this regard, a theoretical model based on cell size and foam density is developed. The results of the developed theoretical model are verified in comparison to various experimental results. Based on the results, the error of the theoretical model is lesser than 5%. Decreasing the foam density increases and decreases the solid and radiation thermal conductivity, respectively. Also, the radiation thermal conductivity is decreased by reducing the cell size. Response surface method (RSM) is applied in order to optimize the solid and radiation thermal conductivities. The results illuminate that the foam density of 23.5 kg.m-3 and cell size of 53 μm are the optimum conditions. At the optimum conditions, both of the solid and radiation thermal conductivities are lesser than 3 mW/mK. According to the results, the data obtained from developed theoretical model and RSM are in a good agreement. The total thermal conductivity is 30 mW/mK at optimum conditions which is a desirable value at aforementioned cell size range.

Hypoeutectic Al-Ni alloys are extensively used in automotive and aerospace industries due to their excellent castability and appropriate high-temperature specific strength. The addition of Mn to the composition of these alloys promotes the formation of Mn-rich precipitates and improves their strength and hardness, especially at high temperatures. However, if the Mn content exceeds 2 wt. %, increasing the size and volume fraction of Mn-rich compounds adversely affects the mechanical properties, especially the ductility and toughness of the alloys. On this basis, the current study was aimed to control the negative impact of high Mn content on tensile properties of hypoeutectic Al-Ni alloys by increasing the solidification rate and friction stir processing. For this purpose, the Al-4Ni-4Mn samples, prepared under different solidification rates of 3.5 and 10.4 °C/s, were subjected to friction stir processing (12 mm/min, 1600 rpm). Microstructural characterization and image analysis results show the substantial refinement of Mn-rich particles and their distribution in the matrix, refinement of grains, and elimination of casting defects such as gas/shrinkage porosities and entrained oxide bifilms. According to the results, increasing the solidification rate and applying of friction stir processing improved the tensile strength, yield strength, fracture strain, toughness, and microhardness of alloy by 63, 55, 123, 188 and 58%, respectively.

Due to higher demands for tailor welded blanks (TWBs) applications in the transportation industry, it is important to understand their forming characteristics in manufacturing processes, especially the deep drawing, in order to produce products with higher qualities. Due to differences between the base materials strength as well as the existence of the welding zone, the formability of TWBs is frequently less than the base metals. The aim of this study is the comparison of weld line displacement and drawing depth in TWBs designed and produced by laser welding and friction stir welding. Laser welding is more appropriate for TWBs production comparing to the other welding processes because of the creation of limited heat affected zone and suitable keyhole. The parameters of the friction stir welding process are very important due to having a high influence on complicated plastic zone variation, the material flow pattern and temperature distribution in TWBs sheets. In this paper, by design experiments, the effect of blank holder force and linear welding velocity on drawing depth and weld line displacement of TWBs have been investigated. Moreover, the harnesses of the weld zone in both processes have been examined. Results show that by increasing the linear velocity of laser welding, the amount of weld line displacement and drawing depth will be increased. Furthermore, the higher linear velocity of friction stir welding will result in the higher weld line displacement and drawing depth. Likewise, the harnesses of the laser welding zone are higher than those ones for friction stir welding zone.

In this paper, finite element analysis with combined (nonlinear isotropic/AF kinematic hardening model) and chaboche hardening models are employed to investigate ratcheting behavior in stainless steel branch pipes under dynamic moments and internal pressure. Obtained results show that the maximum value of ratcheting strain takes place in the junction of branch pipes in the hoop stress direction. In this case, the rate of progressive strains increases with the increase of the bending moment levels in constant internal pressure. Furthermore, this study reveals that the geometry and dimensions of branch pipes have a significant impact on the rate of progressive strains. The bending moment levels to initiate strain accumulation phenomena will be increased with the increase of the dimensions of branch pipes. In the BSS1 sample, comparison between results obtained using progressive strains with combined and chaboche hardening models are much better than those of Armstrong-Fredrick hardening model and are near to the experimental data. Of course, in BSS2 sample, the behavior of ratcheting with combined hardening model is near the experimental results. For the BSS3 sample, the prediction of ratcheting with the chaboche hardening model is better than using the other strain hardening models and are near to the experimental data. Like the carbon steel samples studied in the recent paper, compared to the Armstrong-Frederick hardening model, the chaboche and combined hardening models exhibit an appropriate prediction and similar to experimental results in stainless steel samples.

In this paper, the dynamic stability of a moderately thick rectangular plate carrying an orbiting mass and lying on a visco-elastic foundation is studied. Considering all inertial terms of the moving mass and using plate first-order shear deformation theory, the governing equations on the dynamic behavior of the system are derived. The Galerkin’s method on the basis of trigonometric shape functions is applied to change the coupled governing partial differential equations to a system of ordinary differential equations. Due to the alternative motion of the mass along the circular path over the plate’s surface, the governing equations are the equations with the periodic constant. Applying the semi-analytical incremental harmonic balance method, the influences of the relative thickness of the plate, radius of the motion path, and stiffness and damping of the visco-elastic foundation on the instability conditions of the system are investigated. A good agreement can be observed by comparing the predicted results of the incremental harmonic balance method with the numerical solution results. Based on the findings, increasing the radius of the motion path broadens the instability regions. Moreover, increasing the stiffness and damping of the foundation cause the system more stable.

This paper introduces the initiation and evolution of interlaminar and intralaminar damage in the laminated composite plate under high-velocity impact with the finite element model. Damage in composite layers and delamination between layers are defined based on progressive damage model and cohesive zone modeling. Interlaminar and intralaminar damage initiation are predicted with Hashin criterion and traction-separation law and the damage evolution is predicted with reducing the value of stiffness based on fracture toughness energy that is available in ABAQUS. In this study, needed parameters for the finite element model such as fracture toughness energy are measured experimentally with some tests such as CT and DCB. The finite element model is valid with a velocity comparison of the impactor after impact in experimental impact test with 160J and the numerical simulation. The low percent difference between the experimental and numerical impact results is achieved and thus the needed parameters for simulation is extracted correctly. The present paper introduces a validated, accurate and low-cost finite element model with damage consideration and perforation of impactor for a laminated composite under the high-velocity impact that needed parameters could be measured experimentally.

Soft tissues exhibit viscoelastic behavior, which includes time-dependent creep and stress relaxation, and hysteresis in a loading cycle. Changes in the viscoelastic properties of soft tissues such as spinal ligaments under dynamic loading can cause the damages. In this study viscoelastic behavior of spinal ligaments is investigated by considering two different quasi-linear viscoelastic models under dynamic loading for creep and stress relaxation. After developing equations, the results of formulation were compared with the results of experimental data in the literature and finally, the viscoelastic model that had more accurate behavior to the results of experiments, was choose as the appropriate model of spinal ligament. For this purpose, obtained data by Hingoryani in an experimental study (related to creep and relaxation tests on rabbit medial ligament) were plotted in a log-log graph. According to the graphs, it was found that the strain rate decreased with higher levels of stress and relaxation rate decreased with higher levels of strain. According to the results, present formulation and the obtained constants of the equations had acceptable accordance with the experimental results, and therefore these equations can be used for spinal ligaments with acceptable accuracy.

This study presents a new numerical analysis of thermal behavior and flow of filling gas in inclined double plane windows by considering radiation effects of fluid, as a gray, absorbing, emitting, and scattering medium. In recent years, the installation of inclined double pane windows from the vertical to horizontal sense, especially in the new architecture, is more used. The main goal is to verify the effect of window's inclination angle on the performance of double pane windows in decreasing the rate of heat transfer via this part of the building. The governing equations include the continuity, momentum, and energy, are discretized by using the finite volume method and they are solved with the SIMPLE algorithm. In order to compute the radiative term in the gas energy equation, the radiative transfer equation is solved numerically by the discrete ordinate method. Results are shown as contours of streamlines, isotherms, and distributions of horizontal and vertical components of velocity in the whole cavity of the window and filling gas in different incline angles. The results illustrated that by increasing in incline angle, the rate of flow vortices is decreased. The flow of gas is rotational and the recirculated flow inside the window breaks down to many smaller vortices at a specified inclination angle so it influences the amount of total heat transfer coefficient of the window.

The present study is an attempt to analyze the yield threshold in a rotating variable-thickness disk made of functionally graded material (FGM) based on the Tresca yield criterion. The analysis was performed based on the small deformation theory and for the plane stress state. The modulus of elasticity, density and yield stress were assumed to be a power function of the radial coordinate. The Poisson’s ratio due to slight variations in engineering materials is assumed constant, and the equilibrium equation governing the rotating disk was solved analytically. In addition to the type of material, the disk cross section profile can affect the distribution of stress fields. The thickness of the disk cross-section varies in the radial direction by a power function. In the present analysis, various states are considered for onset yield and commencement of plastic flow. For evaluation and validation, the results of the study are compared to similar results related to specific states (homogeneous and functionally graded constant-thickness disk) investigated in previous references. The results show that considering variable thickness for disk section has a significant effect on the stress level and the prediction of onset yield point.

This paper examines the design, manufacture, and analysis a Gamma-type Stirling engine using the solar parabolic collector. The calculation base for designing is so that the size of the solar parabolic collector needed to start the engine is not too large. After finishing the design and manufacturing of the parts, the assembled Stirling engine was initially initiated by a 550W electric heater tested in two non-insulated and insulated conditions for different input power. In the non-insulated state, the Stirling engine has a maximum power of about 68.69W with an output of 12.66%; and insulated mode of Stirling engine maximum watts with an output of 15.72% was obtained. Then we constructed a solar parabolic collector based on the power of the heater used. Designing the collector is such that it has the ability to reflect around 550W. Thus, the diameter of the collector is 1m and its depth is 12cm. This solar parabolic collector provides the power needed by the engine to work during the day. The maximum output power of the solar Stirling engine is about 30W.

In the present study, the effect of graphite nano platelet (GNP) as a filler on the vibrational properties of the epoxy EP411 DSM matrix was studied. For this purpose, GNP-epoxy composites samples were fabricated with 0-5 wt.% of GNPs using the solution mixing method. Free and forced vibrations tests on the cantilever composite specimens were conducted. Based on the free vibration results, the structural damping loss factor η was obtained as a function of the GNP loading. It was found that η   decreases as the GNP wt.% increases and reaches to the lowest value at 0-3 wt.% of GNP content, and  increases as the GNP loading increases and reaches to the value at 3-5 wt.% of GNP. Also, the frequency response function (FRF) around the second vibration mode was obtained for the neat epoxy. The Rayleigh damping coefficients were calculated employing the free and forced vibration results. The results revealed a nonlinear dependence of damping ratio η on the natural frequency of the neat epoxy. A representative volume element (RVE) incorporating 0-5 wt.% of GNPs was generated and the vibrational properties were numerically simulated. The modeling results were compared with those obtained from the experiment to verify whether the basic assumptions had been chosen properly.

Heat transfer of polymeric foams is consisting of three different mechanisms including heat transfer through a solid phase, gas phase, and thermal radiation. Thermal insulation properties of polymeric foams are affected by different structural properties. Also, these structural properties have a different influence on the different heat transfer’s mechanisms. Therefore, it is necessary to use theoretical models. Several theoretical models have been presented so far, meanwhile, providing theoretical models that can estimate the thermal conductivity using the easiest measurable properties along with sufficient accuracy and reliability can be very helpful. In this regard in the present study, a theoretical model based on cell size and foam density is developed in order to predict the thermal properties of polymeric foams. It was concluded that the error of the developed theoretical model is lower than 8% in comparison to the experimental results. In the following, the effect of most important structural parameters i.e. foam density and cell size on the thermal conductivity is investigated. Based on the results, determining the optimum density is necessary to achieve the lowest thermal conductivity. Also, the gas thermal conduction has the most contribution to the overall thermal conductivity and achieving the nanometer cell sizes can be useful in order to decrease it.

In the present study, a parametric study has been carried out to investigate the influence of ice accretion on the aerodynamic performance of NACA0012 airfoil through numerical simulations using FENSAP-ICE. The results reveal that at zero angle of attack the ice profile created on the leading edge of the airfoil is symmetric. The most dominant feature in the flow-field of an iced airfoil is a recirculation zone that forms due to concavity regions created on both upper and lower surfaces of the airfoil. The numerical simulations show that the appearance of the recirculation zone alters significantly the aerodynamic coefficients. At the angle of attack 12°, lift coefficient decreases by %20.58 and the drag coefficient increases by %15.92 in comparison with the clean airfoil. The effects of temperature and air flow velocity on the ice accretion created on the NACA0012 were investigated for glaze ice and rime ice. The thickness of ice increases with decreasing temperature, and glaze ice with the sharp horn is created at the temperatures ranging from 0°C to -14°C. Making the transition from glaze ice to rime ice occurs at temperatures varied from -14°C to -16°C and at temperatures below -16°C rime ice is created. In order to eliminate the ice accretion, a thermal de-icing system is simulated. By applying a heat power of 30 watts, the melting of 21.41 gr horn ice starts and the created ice on the airfoil surface is completely melted. It should be noted that with the introduction of thermal de-icing system the runback water flow on the airfoil’s surface occurs.

The ring inside the one-way valve has an important role in the reciprocating compressor. In this article, two different materials for rings were considered; stainless steel with the material number 1.5022 and sign 38si6, and carbon-peek composite. These two rings were prepared in valves with identical conditions in design and manufacturing and were used in reciprocating compressors with the same applications. The results of this experiment showed that the life of the valve with a steel ring was 145 days, while the valve with a carbon-peek ring was intact after 210 days. The most important reason for early failure in the steel ring is an inappropriate distribution of forces due to the springs below the ring. Another common cause of failure in these valves is the stresses on walls in the location of springs. Therefore, in this paper, the stresses in the chamber of springs, which are critical points in the design and construction of the valves, are also discussed. By using robust business codes like Abaqus software, the design and analysis stages of the valve are carried out in quasi-static conditions. The stresses and tensions on the chamber of spring and the ring are much stronger in the steel ring than the carbon-peek composite ring. The results obtained from numerical simulations are consistent with experimental observations. In addition, accurate thickness for the ring was determined by use of flow relations.

In the wind tunnels, the balance measurement instrument is used to measure six components of force and moment on an airplane model. The balance of measurement consists of two parts of the balance structure and electronic equipment. In this research, a mechanism with flexible hinges is designed to achieve the desired configuration of the balance structure. In the process of designing the geometric structure of this mechanism, an effective arrangement has been implemented for the six load cell - flexure columns. The advantages of flexible hinges in comparison to conventional hinges are the absence of friction, compactness and its linear behavior. The reaction effects of the components of force and moment on each six load cell - flexure columns created the coupling errors. One of the main sources of this kind of error is related to the structure of the balance mechanism. The reason for this type of error is the inadequacy of the axial flexibility to the lateral flexibility of the columns. The aim of this research is to optimize the design of the flexible mechanism in order to achieve the minimum coupling error of the structure. For this purpose, hinge design considerations and analytical equations of the flexible mechanism have been extracted. The design of the balance mechanism is optimized by creating a structure coupling error matrix. To validate the analytic equations and results, the problem is compared with the finite element analysis. The results indicated that the measurement errors decrease in the measurement of six components of force and moment of balance.