FEM buckling analysis of quasi-isotropic symmetrically laminated rectangular composite plates with a square/rectangular cutout

A numerical study was conducted using the finite element method to determine the effects of square and rectangular cutouts on the buckling behavior of a 16-ply quasi-isotropic graphite/epoxy symmetrically laminated rectangular composite plate. The square/ rectangular cutouts were subjected to uniaxial compression loading. This study addresses the effects of the size of the square/rectangular cutout, orientation of the square/rectangular cutout, plate aspect ratio (a/b), and plate length/thickness ratio (a/t) on the buckling behavior of the symmetrically laminated rectangular composite plate under uniaxial compression loading. Buckling loads were computed for seven different quasi-isotropic laminate configurations [0°/+45°/?45°/90°]_2s, [15°/+60°/?30°/?75°]_2s, [30°/+75°/?15°/?60°]_2s, [45°/+90°/0°/?45°]_2s, [60°/?75°/+15°/?30°]_2s, [75°/?60°/+30°/?15°]_2s, [90°/?45°/+45/°0°]_2s. Results showed that the magnitudes of the buckling loads decrease with increasing cutout positioned angle as well as c/b and d/b ratios for plates with a rectangular cutout. The symmetrically laminated quasi-isotropic [0°/+45°/?45°/90°]_2s composite plate is stronger than all other symmetrically analyzed laminated quasi-isotropic composite plates. The magnitudes of the buckling loads of a rectangular composite plate with square/rectangular cutout decrease with increasing plate aspect ratio (a/b) and plate length/thickness (a/t) ratio.     

An elastic-plastic stress analysis in silicon carbide fiber reinforced magnesium metal matrix composite beam having rectangular cross section under transverse loading

In this work, an elastic-plastic stress analysis has been conducted for silicon carbide fiber reinforced magnesium metal matrix composite beam. The composite beam has a rectangular cross section. The beam is cantilevered and is loaded by a single force at its free end. In solution, the composite beam is assumed perfectly plastic to simplify the investigation. An analytical solution is presented for the elastic-plastic regions. In order to verify the analytic solution results were compared with the finite element method. An rectangular element with nine nodes has been choosen. Composite plate is meshed into 48 elements and 228 nodes with simply supported and in-plane loading condations. Predictions of the stress distributions of the beam using finite elements were overall in good agreement with analytic values. Stress distributions of the composite beam are calculated with respect to its fiber orientation. Orientation angles of the fiber are chosen as 0°, 30°, 45°, 60° and 90°, The plastic zone expands more at the upper side of the composite beam than at the lower side for 30°, 45° and 60° orientation angles. Residual stress components ofσ _x andτ _xy are also found in the section of the composite beam.     

基于Deform轴类零件台阶圆角开式冷挤压工艺有限元模拟

研究了电机轴台阶圆角开式冷挤压过程中金属的流动规律以及不同工艺组合下的变形程度值和轴向镦粗情况,并与实验结果进行对比验证,从而得到完全成形和基本成形时的变形程度和圆角半径的取值范围,给出了阶梯轴开式冷挤压成形有关过渡圆角挤压的可行范围.     

Investigation of thermal performance of SAC variables using fuzzy logic based expert system

The thermal performance of a solar air collector (SAC) is investigated experimentally under the different climatic conditions of north eastern India using fuzzy logic based expert system (FLES). The FLES based on subtractive clustering (SC) with the fuzzy logic method where here, SC is used for extraction of optimal fuzzy IF-THEN rules while a fuzzy logic is used for modeling of SAC variables. This work considered four input variables [like mass flow rate (m), collector tilt angles (θ), solar radiation (Q), temperature (T)] and the four output variables [i.e. efficiency (η), exergetic efficiency (η_II), temperature rise (∆T), and pressure drop (∆P)]. First, 272 trials of experimentation on SAC are performed by varying m from 0.0078 to 0.0118 kg/s and θ from 30 to 60°, whereas the variation of metrological data is obtained in different working days. Then modeling and parametric analysis is carried out for SAC. Experimental results reveal that the value of η increases with the increase in m, Q, T and θ up to 45°. The higher value of m results in a higher value of ∆P and that reduces the value of η_II. Also, FLES model provides comparable and acceptable values for SAC. At last, validation of the FLES model is done via published data to confirm the results.

     

Influence of triangular wavy baffles on heat and fluid flow characteristics in a channel

Laminar periodic flow and heat transfer in a three-dimensional channel with triangular wavy baffles (TWBs) have been numerically investigated. The baffles with three different angles of attack: 30°, 45° and 60° have been considered for Reynolds numbers ranging from 100 to 1000. For a better understanding in the heat transfer mechanisms, the pressure contour, secondary flow pattern, streamlines of impinging flow, wall streamline and iso-surface are also reported. Apparently, each wavy baffle generates two counter-rotating vortices. The 30° and 45° baffles generate vortices with comparable intensities which are considerably higher than that caused by 60° baffles. At similar conditions, the 30° and 45° baffles give comparable Nu/Nu₀ values which are considerably higher than that provided by the 60° baffles, but the 30° baffles cause lower f/f ₀ than the 45° and 60° baffles. For the range determined, the maximum thermal performances achieved by using baffles with the attack angles of 30°, 45° and 60° are 2.3, 2.2, and 1.88, respectively.     

Solid particle erosion behaviour of glass fibre reinforced boric acid filled epoxy resin composites

The tests which involved angular aluminium (Al₂O₃) particles with two different sizes of approximately 200 and 400 μm were conducted at the operating conditions namely different impact velocities of approximately 23, 34 and 53 m/s, two different fibre directions [0° (0/90) and 45° (45/−45)] and three different impingement angles of 30°, 60° and 90°. New composites with addition of Boric Acid filler material at 15% of resin exhibited upper wear than the neat materials without filler material. This means the filler material has decreased the erosion wear resistance. SEM views showing worn out surfaces of the test specimens were scrutinised.     

Influence of fiber orientation on abrasive wear of unidirectionally reinforced carbon fiber–polyetherimide composites

A composite with continuous carbon fibers (CF) (80% by vol.) and high performance thermoplastic polyetherimide (PEI) matrix was developed and evaluated for various mechanical properties as a function of fiber orientation angle (0°, 30°, 45°, 60° and 90°). It was observed that Young's modulus, Poisson's ratio, toughness and % strain decreased with the increase of fiber orientation angle with respect to loading direction. In-plane shear modulus was highest for fibers with 45°. Overall, unidirectional (UD) CF reinforcement enhanced all strength properties of PEI significantly. Composites with fibers in 0° (parallel to loading direction) proved best in almost all the properties. Tribological evaluation in abrasive wear mode under different loads and fiber orientations indicated that coefficient of friction (μ) and specific wear rate (K₀) decreased with load, in general. Comparatively low specific wear rate (K₀), (in the order of 0.7 1×10^?9 m³/Nm) was observed for 0° fiber orientation, while fibers in 90° showed almost three times higher wear rate. Overall fiber reinforcement in 0° orientations proved beneficial from both strength and tribological performance point of view. SEM proved useful to correlate wear rate with surface topography.     

基于多向挤压的超长异形轴径向挤压工艺研究

传统锻压方法成形阶梯轴,多采用轴向正挤压方法,所加工轴的长度受水压机开口高度的限制。为此,本文基于多向挤压技术提出了阶梯轴径向挤压成形方法,来加工“超长”阶梯轴,并通过数值模拟的方法对新工艺与传统工艺进行了比较,其优势为可以实现采用小吨位水压机加工“超长”异形阶梯轴;可以有效减小毛坯轴的轴肩过度体积,减少材料浪费。     

Characteristics of flow past a circular cylinder with a rectangular groove

In the present study, features of the flow past a circular cylinder with single longitudinal groove pattern placed on its surface were investigated. Six different rectangular groove sizes were tested for angular position of the groove from the forward stagnation point of the circular cylinder within 0°≤θ≤150°. The particle image velocimetry (PIV) technique were employed to measure flow field downstream of the cylinder immersed in a uniform flow field with the Reynolds number, Re=5000. Time-averaged flow data such as vorticity, 〈ω〉 streamline, 〈Ψ〉, streamwise, 〈u′u′〉 and transverse, 〈v′v′〉 Reynolds normal stresses, turbulent kinetic energy, TKE and RMS of streamwise, u_rms and transverse, v_rms velocity components were obtained from PIV data to demonstrate flow features. Moreover, frequency of Karman vortex shedding was explored using single point spectral analysis. It is concluded that presence of the groove on a cylinder surface significantly affects the near wake flow structure and turbulence statistics. Karman vortex shedding frequency, f_k strongly depends on the groove size. Moreover, the shear layer instability is induced on the grooved side with additional frequencies.     

Thermal characteristics of an ammonia-charged closed-loop pulsating heat pipe

At this age, engineering applications are demanding effective ways of heat recovery and energy savings for their optimum performance. Among other cooling techniques, pulsating heat pipes have emerged as a convenient and cost effective thermal design solution due to its excellent heat transfer capability, high thermal efficiency and structural simplicity. The paper presents an experimental study on the operational limit of an aluminum closed-loop pulsating heat pipe (CLPHP) charged with ammonia. It consists of total 14 turns of aluminum pipe with 3 mm inner and 4 mm outer diameter. Ammonia was used as working fluid with 3 different filling ratios such as 0.4, 0.6 and 0.8. Operation orientations were vertical, 30°, 45°, 60°, 90° and 180° inclinations. Constant electric heat input of 36 W was applied to the heating block and temperature rise in various sections was monitored till steady state was reached. Temperature was measured at different locations of the CLPHP by using thermocouples. The effects of operational orientations and filling ratios were investigated on heat transfer by working fluid Q̇_php (Watt), overall heat transfer coefficient U (W/m² °C) and thermal resistance R (°C/W) considering the measured temperature. The result shows that, 0.4 and 0.6 fill ratios and inclination angle of 30º give better result than any other arrangements for CLPHP.

     

Numerical and experimental modelling of flow at Tyrolean weirs

In this study, a small-scaled Tyrolean weir model was constructed in the laboratory environment and a series of experiments were conducted on it, for two different rack inclinations (θ₁ = 18° and θ₂ = 25°) and three different bar spacings (e₁ = 3 mm, e₂ = 6 mm and e₃ = 10 mm) for a range of upstream flow discharges. The flow rates passing through the racks and going downstream over the racks were measured. Empirical equations for the discharge coefficient and water capture capacity of the Tyrolean weirs were determined by applying dimensional analysis to the parameters involved in the phenomenon. The related dimensionless parameters were presented with graphs and empirical equations for discharge coefficients were derived, coefficient of determination R² of equations for θ₁ = 18° and θ₂ = 25° are found 0.838 and 0.825 respectively. According to results obtained from experimental data, C_d increases as the Froude number ((F_r)_e) between bars increases and water capture capacity [(q_w)_i/(q_w)_T] of the racks decreases with increasing ((F_r)_e). Also, a numerical model of the Tyrolean weir was generated by using Flow-3D software and it was shown that the results of the numerical analysis were very consistent with the physical model results at large bar spacing such as e = 10 mm. As the bar spacing (e) reduces, the success of the numerical model giving consistent results with physical model is decreasing.     

Pressure measurement technique and installation effects on the performance of wafer cone design

The present study explores novel pressure averaging technique for wafer cone flowmeter design and its robustness in the presence of double 90° bend (out-of-plane) and gate valve as a source of upstream flow disturbance. The wafer cone flowmeter is tested in a circular pipe (inside diameter of 101 mm) with water as the working medium for the flow Reynolds number ranging from 1.19×10⁵ to 5.82×10⁵. Influence of the half cone angle (α) on the coefficient of discharge (C_d) of wafer cone flowmeter is studied with this new pressure averaging technique. Half cone angles considered in this study are 30° and 45° with a constant constriction ratio (β) of 0.75. The upstream static pressure tap is located at 1D upstream of the wafer cone. The downstream pressure averaging technique comprises eight circumferential holes of diameter 2 mm on the maximum diameter step of the wafer cone. The pressure taps are communicated through the support strut which serves as a downstream static pressure tap. The disturbance causing elements are individually placed at 1.5D, 5.5D, 9.5D and 13.5D upstream to the wafer cone flowmeter. The wafer cone flowmeter is also tested with gate valve opening of 25%, 50% and 75% for all the arrangements considered. The 30° cone is found to be better than 45° cone for the range of Reynolds number covered in the present study. The results show that the 30° wafer cone flowmeter with novel downstream pressure averaging technique is insensitive to the swirl flow created by a double 90° bend (out-of-plane) and requires an upstream length of 9.5D with a gate valve as a source of flow disturbance.     

Vibration characteristics of orthotropic shaft–disk system with different constrained damping layers: experimental and numerical study

This paper reports the results of an investigation carried out to study the effect of various constrained layers (viscoelastic layer (VEL), electrorheological fluid, and magnetorheological fluid) on natural frequency and damping factor. The different fiber orientations (0°, 30°, 45°, 60°, and 90°) were considered for glass/epoxy (G/E) and graphite/epoxy (GR/E) shaft–disk systems. Experimental evaluation and finite element technique are employed to investigate the natural frequency and damping factor for various combinations. The vibrational characteristics of the composite sandwich shaft–disk system are also compared in this present study. From the study, it is evident that the VEL core shows excellent frequency and damping loss factor performances, and the 90° fiber-oriented composites are dominant in vibration damping performances. The GR/E shaft–disk system outperforms the G/E shaft–disk system.     

平纹编织碳纤维/Kevlar纤维增强混杂复合材料微-宏观切削去除机理研究

由于碳纤维和Kevlar纤维力学性能相差迥异,在C-K纤维混杂增强复合材料(Carbon-Kevlar fiber hybrid composite,CKFH)加工中易产生加工缺陷,比单种纤维复合材料的加工缺陷更难控制。由此,从微观和宏观角度,构建CKFH三维有限元切削模型,分析CKFH的切削去除机理及平纹编织结构对切削过程的影响机制。结果表明,在不同纤维取向下,Kevlar纤维均易产生抽丝拉毛现象,尤其当纤维取向θ=0°/180°时最为明显;纤维取向θ=0°/180°时,切屑多为卷曲片状切屑,纤维取向θ=45°、90°、135°时,两种纤维的断裂相互影响,切削表面、切屑形态均与切削方向存在密切关系,当纤维取向θ=45°时,多为细小片状切屑,纤维取向θ=90°时,切屑多为絮状块状切屑,纤维取向θ=135°时,切屑多为成块状切屑;从碳纤维切向Kevlar纤维时,Kevlar纤维出现松散、抽丝拉毛现象明显,从Kevlar纤维切向碳纤维时,在Kevlar纤维的韧性弯曲区碳纤维发生弯曲脆断、碎裂,易出现凹坑;平纹编织结构对切削应力的传递具有明显的阻断作用,有限元仿真结果与试验观测结果基本吻合。     

Influence of cone angle on the performance of a wafer cone flowmeter

The present study explores the effect of upstream disturbances like a single 90°bend, double 90° bends (in plane and out of plane) on the performance of wafer cone flowmeters with same beta ratio (β) of 0.77 but different half cone angles (α) of 30° and 45°. The influence of these disturbances on the upstream and downstream axial velocity (u) profiles are studied experimentally. The orientation effects, if any, are also studied experimentally. The minimum upstream distances required to get a fully developed flow for these disturbances vary with type of upstream disturbance, beta ratio (β) and half cone angle (α) of the wafer cone flowmeter. The study is carried out for a single phase flow with air as working medium at high Reynolds number (Re_D = 144000). From the results obtained from this study, it may be concluded that the wafer cone flowmeter with a beta ratio (β) of 0.77 and a cone angle of 30° requires less upstream distance compared to the wafer cone flowmeter with a beta ratio (β) of 0.77 with a cone angle of 45° for all the disturbances under consideration.     

Investigations on mechanical and structural aspects of ultrasonic hybrid polymer mixture welding for industrial applications

Two-dimensional C_f/Al composites were fabricated by liquid-solid extrusion following vacuum infiltration technique (LSEVI), and defects were studied and analyzed through optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope(TEM), and the tests of ultimate tensile strength (UTS). Through research, it was found that gas impurities were the main factors to generate hole defects within the 2D-C_f/Al composites, so vacuum level of the test system should be higher than 0.09 MPa. The infiltration of composites would not be sufficient and uniform under the low squeeze pressure of 50 MPa and low squeeze temperature of 590 °C. However, when squeeze pressure was larger than 90 MPa, fiber damage appeared, and macro internal cracks even occurred if it was over 100 MPa. Poor tensile behavior of composites between carbon fibers and matrix might arise because of the inappropriate process parameters. Brittle tensile fracture of composites was observed under the higher preform preheating temperature of 640 °C, and Al₄C₃ was found. Separated fibers and aluminum alloy of tensile fracture might occur under the lower preheating temperature of 580 °C. These defects hindered the improvement of property of C_f/Al composites greatly, and they should be avoided. Through contrast of UTS, internal cracks and poor tensile behavior were the most detrimental factors. Their UTSs were 45 and 117 MPa, respectively, which were less than 120 MPa of matrix. Improved process parameters were used to prepare the 2D-C_f/Al composite, and its defects were seldom found, so UTS of composite was improved 93.3 % than that of matrix.     

Investigate on milling force of cryogenic cooling processing aluminum honeycomb treated by ice fixation

Aerospace metal honeycomb materials with low stiffness had often the deformation, burr, collapse, and other defects in the mechanical processing. They were attributed to poor fixation method and inapposite cutting force. This paper presented the improvement of fixation way. The hexagonal aluminum honeycomb core material was treated by ice fixation, and the NC milling machine was used for a series of cryogenic machining. Considering the similar structure of fiber-reinforced composite materials, the milling force prediction model of ice fixation aluminum honeycomb was established, considering tool geometry parameters and cutting parameters. Meanwhile, the influence rule on milling force was deduced. The results show that compared with the conventional fixation milling method, the honeycomb processing effect is improved greatly. The machining parameters affect order on milling forces: the cutting depth is the most important, followed by the cutting width, then the spindle speed and the feed. Moreover, too small cutting depth (a_p?=?0.5 mm) will cause insufficient cutting force, while a_p?>?2 mm with higher force will reduce the processing quality of honeycomb. Simultaneously, the honeycomb orientation (θ) has a great influence on processing quality. Using the model, the predicted and measured error values of the feed and main cutting force are all small in θ?<?90°. But, the rate is 33 and 26% for the main cutting force and feed force error in θ?>?90°, respectively, while they all exhibit the smallest error in θ?=?60°. This bigger error mainly is due to unstable cutting force with obtuse angle. In addition, the tool rake angle has little influence on cutting quality in θ?<?90°, but bigger on that in θ?>?90°. Furthermore, the calculation model successfully conforms to the main deformation mechanism and influences parameters of the cutting force in the milling process, and it can accurately predict the cutting force in θ?<?90° and guide the milling process.     

The effect of bridging on fatigue crack growth behavior in Aramid Patched Aluminum Alloy(APAL)

A new hybrid composite (APAL: Aramid Patched Aluminum Alloy), consisting of a 2024-T3 aluminum alloy plate sandwiched between two aramid/epoxy laminate (HK 285/RS 1222), was developed. Fatigue crack growth behavior was examined at stress ratios of R=0.2, 0.5 using the aluminum alloy and two kinds of the APAL with different fiber orientation (0°/90° and 45° for crack direction). The APAL showed superior fatigue crack growth resistance, which may be attributed to the crack bridging effect imposed by the intact fibers in the crack wake. The magnitude of crack bridging was estimated quantitatively and determined by a new technique on basis of compliances of the 2024-T3 aluminum alloy and the APAL specimens. The crack growth rates of the APAL specimens were reduced significantly as comparison to the monolithic aluminum alloy and were not adequately correlated with the conventional stress intensity factor range(ΔK). It was found that the crack growth rate was successfully correlated with the effective stress intensity factor range (ΔK _eff =K _br -K _ct ) allowing for the crack closure and the crack bridging. The relation between da/dN and theΔK _eff was plotted within a narrow scatter band regardless of kind of stress ratio (R=0.2, 0.5) and material (2024-T3 aluminum alloy, APAL 0°/90° and APAL±45°). The result equation was as follow:da/dN=6.45×10⁻⁷(ΔK _eff )^2.4.     

非零迎流角半球缺群无阀泵流场及流量特性

理论研究了以半球缺群作为无移动部件阀的无阀压电泵的液体输送和混合搅拌功能,针对半球缺群迎流角的变化对该压电泵的泵送性能及混合搅拌效果的影响进行了仿真分析与试验验证。围绕迎流角θ在0°≤θ≤90°的变化,建立多组有限元模型,模拟了半球缺群迎流角变化引起的速度场、压强差、阻力系数及仿真流量的变化规律,并进行了试验验证。结果表明,0°≤θ≤45°时,仿真流量随θ的增加而增加;45°θ≤90°时,仿真流量随θ的增加而减小;θ≈45°时取得最大流量96.13mL/min。此外,研究显示旋涡的大小及强度具有与仿真流量相同的变化趋势。泵流量试验验证了仿真研究及其结果的正确性:在θ≈45°时,试验流量达到67.90mL/min;0°θ≤360°时,试验流量与仿真流量的变化趋势一致,并且θ在一个周期的变化中泵流量及旋涡强度出现2次正向最大值和2次反向最大值。本研究为优化无阀压电泵的泵送性能和混合功能奠定了基础。     

Bending properties for composites with wrinkled and overlapped fabric preform

The fiber fabric layers in a preform can be wrinkled or overlapped during a preform loading of the resin transfer molding and thermoforming processes of thermoplastic composites. These fabric discontinuities affect both the mechanical properties and failure mechanisms of those composites. Based on the energy method, the analytical bending modulus is considered and compared to the experimental data for several wrinkling and overlapping patterns. Also, those effects on the bending properties are described through the effective parameters, α, which are the wrinkled parameter and overlapped parameter. It is found that the large fiber content and stress concentrations near discontinuity are the reasons for the larger bending moduli of the wrinkled and overlapped models. As a function of the wrinkled length to the span length (L _W /L) and the overlapped length to the span length (L _O /L), respectively, the bending strengths and failure mechanisms show the two stages. This is due to not only the failure modes but also the geometrical structures of the fiber fabric preform.