Prototype fabrication of a composite automobile body based on integrated structure

This paper describes the integrated fabrication and assembly approach used to replace a steel body cover in Samand Sarir automobile by composite one because composite could perform higher mechanical performance, i.e., strength, stiffness, and impact absorption energy at low velocity. Considering the integrated body as base design criteria, the steel cover is redesigned and fabricated by composite material. Tensile, flexural, and charpy impact tests were carried out to determine the properties of woven fabric laminated composite in [0/90°] and [±45°] fiber orientations. The selected composite laminate shows 2.9 times impact resistance; its desirability factors are improved 1.8 times for strength and 3.35 times for stiffness. Using finite element method, the impact of the composite body cover was simulated by ABAQUS for several thicknesses and fiber orientations. The FEM results indicate that finally laminated composite [0/90°]₇ can improve the crashworthiness of composite part in comparing to steel body cover. The integrated 3D preform of glass woven fabric was stitched like the shape of 3D model of body cover and placed in mold for prototype fabrication. It can be concluded that vacuum bagging as suggested fabrication method could be suitable for 3,000–5,000 annual production volume. Eventually, the fabricated composite body cover weighed 1.7 kg, which is 42% lighter than the steel body cover.     

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.     

Effect of fiber orientation on interfacial fracture toughness for adhesively bonded composite plates

In this study, interfacial fracture toughness was investigated experimentally and numerically in laminated composite plates with different fiber reinforcement angles bonded with adhesive. The composite plates are four-layered and the layer sequence is [0º/θ]_s. DCB test was applied to composite plates reinforced with epoxy resin matrix and unidirectional carbon fiber. The experimental sample model for the DCB test was made using the ANSYS finite element package program. In the numerical study, four layered composites were prepared in three dimensions. Under critical displacement value; mode I fracture toughness at the crack tip was calculated using VCC (virtual crack closure) technique. Numerical values consistent with experimental results have presented in graphical forms. At 60o and 75° the greatest fracture toughness was obtained. In addition, numerical results have shown that fiber orientation prevents the uniform distribution of stress on the interface crack tip and causes stress accumulation, especially at the edge of the plate.

     

Fracture toughness of CFRP laminated plates according to resin content

CFRP(carbon fiber reinforced plastic) has recently found wide use in different industries. The material, however, is very prone to damage from collision with foreign objects. This study aims at finding Ĵ-integral in mode II for CFRP laminated plates based on classical bar theory for dynamic conditions in consideration of inertia forces and eventually to finding dynamic inter-layer fracture toughness. Dynamic inter-layer fracture toughness was observed using an in-house ENF (End Notched Flexure) experimental facility using Split Hopkinson’s Bar (SHPB). Also the variation of the fracture toughness depending on different resin contents and fiber arrangement in the CFRP specimen ([0°3/90°3/0°6/90°3/0°3], [0°20], [0°5/90°10/0°5]) was observed. It was established that under both quasi-static and dynamic load conditions, the critical load and the inter-layer fracture toughness increased sharply following the extension of the resin content. Thus, it may be concluded that the resin content is the major factor determining the inter-layer fracture toughness in the CFRP laminated plate.     

Interlaminar stresses of a rectangular laminated plate with simply supported edges subject to free vibration

The interlaminar stresses in a laminated rectangular orthotropic plate with four sides simply supported edges during free vibration was determined by using the integration method involving the dynamic inertia terms and displacements. The approximate stresses solutions are obtained under the effect of frequencies of vibration for four-layer symmetric cross-ply laminates with the ply configurations [0°/90°]_s and [90°/0°]_s, angle-ply laminates with the ply configuration [45°/−45°]_s. Numerical results show that the natural frequency has significant effects on the dominant interlaminar stresses in the stacking sequences [0°/90°]_s, [90°/0°]_s and [45°/−45°]_s.     

On the Pressure Dependence of Shear Strengths in Sliding, Boundary-Layer Friction

Density functional theory, as implemented in a full-potential linearized augmented plane wave method, flair, is used to calculated the pressure-dependent shear strength S of KCl on a Fe(100) substrate and the results are compared to the experimental dependence given by S = S₀ + aP S = S_{0} + \alpha P , where P is the contact pressure and S ₀ = 65 ± 5 MPa and α = 0.14 ± 0.02. Calculations were performed for a KCl bilayer enclosed between two Fe(100) slabs, where the energy was found to vary harmonically as a function of the separation between the outermost layers. Thus, a simple analytical model was developed for the pressure-dependent shear strength of the film, which includes both linear and quadratic pressure dependence. However, the coefficient of the quadratic term was found to be much smaller than the linear term, leading to the linear shear-strength pressure dependence found experimentally. The calculated values of S ₀ 〈10〉 = 64 ± 9 and S ₀ 〈11〉 = 69 ± 8 MPa are in excellent agreement with experiment, while α 〈10〉 and α 〈11〉 equal 0.05 ± 0.01, somewhat lower than, but within the same range as the experimental values.     

Damping in partially delaminated composites

A simple model was developed to predict the material damping in partially delaminated composites. First, we evaluated the damping loss factors experimentally in three kinds of specimens corresponding to various partial delamination areas. Second, the stiffness loss with delamination growth was assumed to result directly in the loss of energy from the oscillatory system because the delamination due to interlaminar stress is accompanied with stiffness loss in numerous laminated composites. By correlating the laminate stiffness reduction and the corresponding delamination area, a model for their basic material damping properties was formulated using the elastic-viscoelastic principle, the rule-of-mixtures law and modified Hashin’s Model. We predicted the damping of any partially delaminated composites with different stacking sequences based on Adams and Ni’s work and their basic damping loss factors. Numerical and experimental results demonstrate that damping is significantly influenced by the size of delamination area in laminated composites. In addition, experimental improvements in making accurate damping measurements are discussed as well.     

Effect of laser beam incidence angle on cladding morphology in laser cladding process

The change of angle θ between laser cladding powder plane and substrate plane will lead to changes in cladding layer's geometric morphology. Therefore, we established a quantitative numerical prediction model for cladding layer geometry. In this model, we consider the variation of θ, the laser energy attenuation rate and the temperature rise of the powder particles. At the same time, the simulation results were verified by experiments. The results show that when θ is in the range of 50°~90°, the initial temperature is 298 K, the scanning speed is 3.75 mm/s, and the laser spot diameter is 4.5 mm, the Fe#1 powder cladding can achieve better forming effect on Q235. In general, with the decrease of θ, the height of the cladding layer decreases and the width of the layer increases. However, when θ is less than 50°, the quality of the formed morphology significantly deteriorated. The experimental results are in good agreement with the simulation results, which verifies the validity and reliability of the model. This work provides a theoretical reference for further understanding the relationship between the laser cladding morphology and the incident angle.     

Analysis of a crack approaching a circular hole in cross-ply laminates under biaxial loading

The problem of a crack approaching a circular hole in cross-ply laminates under uniaxial and biaxial loading is investigated in this paper. The effects of material orthotropy, geometry [R/d and a/d], and loading conditions on crack tip singularity are investigated. The stress intensity factors are obtained by the modified mapping collocation method. The present results for an isotropic infinite plate show good agreement with existing solutions. The results for cross-ply laminates show that the stress intensity factors strongly depend on material orthotropy, geometry, and loading condition. The stress intensity factors for cross-ply laminates exist between those for θ=0° and those for θ=90° in the whole range of crack length and decrease as the percentage of 0° plies increases. In the range of small crack length the stress intensity factors for biaxial tension are higher than those for uniaxial tension. In the range of large crack length the stress intensity factors for uniaxial tension are higher than those for biaxial tension.     

Design of damping valve for vehicle hydro pneumatic suspension

According to the design features of a hydro pneumatic spring, the necessity of a separate damping valve is proposed. Based on a 1/4 vehicle linear suspension model, the optimum damping coefficient is worked out and the parameters of the damping valve are determined with the equivalent linearization method. A practical structure of the damping valve is proposed having a small size, high flowrate when the valve opens, and the ability of enduring high back pressure. Based on bench tests, the damping valve has been found to properly work and be suitable. The design method and damping valve structure are useful guides for hydro pneumatic suspension, especially for the design of heavy-duty vehicles. __________ Translated from Transactions of Beijing Institute of Technology, 2006, 26(4): 301–304 [译自: 北京理工大学学报]     

Linear free vibration analysis of cross-ply laminated cylindrical helical springs

A linear free vibration analysis of symmetric cross-ply laminated cylindrical helical springs is performed based on the first-order shear deformation theory. Considering the rotary inertia, the shear and axial deformation effects, governing equations of symmetric laminated helical springs made of a linear, homogeneous, and orthotropic material are presented in a straightforward manner based on the classical beam theory. The free vibration equations consisting of 12 scalar ordinary differential equations are solved by the transfer matrix method. The overall transfer matrix of the helix is computed up to any desired accuracy. The soundness of the present results are verified with the reported values which were obtained theoretically and experimentally. After presenting the non-dimensional graphical forms of the free vibrational characteristics of (0°/90°/90°/0°) laminated helical spring made of graphite-epoxy material (AS4/3501-6) with fixed–fixed ends, a non-dimensional parametric study is worked out to examine the effects of the number of active turns, the shear modulus in the 1–2 plane (G₁₂), the ratio of the cylinder diameter to the thickness (D/d), and Young's moduli ratio in 1 and 2 directions (E₁/E₂) on the first six natural frequencies of a uniaxial composite helical spring with clamped-free, clamped-simple, and clamped–clamped ends.     

Turbulent natural convection flow and heat transfer in an inclined square enclosure

Numerical analysis was performed for the two-dimensional turbulent natural convection in an inclined enclosure. The enclosure has two walls which one is heated and the other cooled, and has the other two walls of the linear temperature distributions. The inclined angle is equal to zero when the wall of linear temperature was horizontal and increases counter-clockwise. The mean continuity, mean momentum and mean energy equations have been obtained by using the conventional time-averaging procesure. The turbulent model has been applied ak-ε two equation model of turbulence similar to the one proposed by the Launder and Spalding. Numerical results were studied for a series of inclined angle, ranging from 0° to 60° and for a Grashof number range of 6×10⁶∼10⁸. The average heat transfer rate on hot wall is shown maximum value at 30° regardless of Grashof number taken here. When Gr≥5×10⁷ and θ≥45°, the flow region of whole enclosure became a significant turbulence. This paper was presented at the International Symposium on the Refined Flow Modeling and Turbulent Measurement. Iowa City, Iowa, U.S.A., 1985     

复合材料层合板阻尼特性有限元数值模拟

应用耗散能原理建立了复合材料层合板的阻尼预测分析模型,对复合材料层合板进行三维有限元模态分析,求出各个模态下的应力、应变分量。根据模态分析结果,从单向复合材料的阻尼性能参数出发,利用层合板应变能、耗散能和结构模态阻尼的关系求出各个模态对应的模态阻尼损耗因子。利用该方法,分别计算了单向层合板和对称层合板的结构模态阻尼损耗因子。数值计算结果与已有的理论分析和试验结果相比吻合较好,从而验证了该方法的合理性,该方法还可以比较三维应力分量对阻尼的贡献。     

Low-velocity impact-induced delamination detection by use of the S0 guided wave mode in cross-ply composite plates: A numerical study

Finite element method based numerical simulations are performed to identify low-velocity impact-induced asymmetrically-located delamination in the [0/90₃]_S and [0/90]_2S composite plates, respectively, using a fundamental symmetric guided wave mode (S₀). The wave attenuation effect due to the viscoelasticity of the composite material is modeled by calculating the Lamb wave attenuation constants and using the Rayleigh proportional damping model. The estimated sizes and locations of the delamination in both plates were in good agreement with the experimental measurements. Moreover, the analysis of wave structure of the impacted plates shows that when the S₀ mode propagates through the damaged region, the delamination mouth opens up due to the presence of standing waves, which are generated as a consequence of multiple reflections of trapped waves with the delamination boundaries.     

Development and application of an ultra-precision lathe

This paper deals with the detailed development of an ultraprecision lathe for the purpose of machining magnetic disks. The rotational and feed accuracy and stiffness of the air bearing and the air slide were tested, respectively. A microcutting device using a piezoelectric material was also developed in order to maintain a uniform and precise depth of cut. Experiments machining a magnetic disk were carried out.Nomenclature A [m²] Area of piezoelectric actuator - C _o [mF] Capacitance of PZT - d ₃₃ [m V^–1] Piezoelectric constant - K _f [N V^–1] Equivalent force constant - K _m [N m^–1] Coefficient of force feedback - k _h [N m^–1] Stiffness of hinge - l [m] Length of PZT - M [kg] Mass of PZT system - r [mm] Radius of notch - U [m] Displacement of piezoelectric - ₃ [F m^–1] Dielectric constant of PZT - b [mm] Width of hinge - D _e [N s^–1] Equivalent damping coefficient - F _l [N] External load - K _e [N m^–1] Equivalent stiffness of PZT - k [m² N^–1] Elastic compliance of PZT - L [mm] Distance between hinge holes - M _e [kg] Equivalent mass of PZT - R _o [W] Output impedance of amp. - t [mm] Thickness between hinge holes - V _i [V] Input voltage - [g cm^–3] Density of PZT     

铺设角度对层合板结构声功率的影响分析*

针对层合板结构铺设角度对前二阶声辐射模态幅值和辐射声功率的影响进行分析。利用分层理论结合有限元模型求解层合板的铺设角度与振动速度信息之间关系。通过声辐射模态理论,以某12层层合板结构为例,研究固定边界条件下的层合板辐射模态数、对称铺设角度、单向铺设角度以及激励力位置对声辐射模态幅值和辐射总声功率的影响。计算结果表明,在相同角度下,对称铺设层合板结构最大声功率值要小于单向角度铺设层合板结构最大声功率值;另外在低频时,对层合板结构辐射声功率起主要贡献的是前两阶辐射模态。并以某16层零度铺设的固定边界条件下的层合板结构为例,对复合材料层合板结构的声辐射模态幅值及声功率进行试验分析。     

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.     

Temperature measurement in orthogonal metal cutting

Orthogonal cutting experiments were carried out on steel at different feedrates and cutting speeds. During these experiments the chip temperatures were measured using an infrared camera. The applied technique allows us to determine the chip temperature distribution at the free side of the chip. From this distribution the shear plane temperature at the top of the chip as well as the uniform chip temperature can be found. A finite-difference model was developed to compute the interfacial temperature between chip and tool, using the temperature distribution measured at the top of the chip.Nomenclature contact length with sticking friction behaviour [m] - c specific heat [J kg^–1 K^–1] - contact length with sliding friction behaviour [m] - F _P feed force [N] - F _V main cutting force [N] - h undeformed chip thickness [m] - h _c deformed chip thickness [m] - i,j denote nodal position - k thermal conductivity [W m^–2 K^–1] - L chip-tool contact length [m] - p defines time—space grid, Eq. (11) [s m^–2] - Q _C heat rate entering chip per unit width due to friction at the rake face [W m^–1] - Q _T total heat rate due to friction at the rake face [W m^–1] - Q _% percentage of the friction energy that enters the chip - q ₀ peak value ofq(x) [W m^–2] - q _e heat rate by radiation [W] - q(x) heat flux entering chip [W m^–2] - t time [s] - T temperature [K] - T _C uniform chip temperature [°C] - T _max maximum chip—tool temperature [°C] - T _mean mean chip—tool temperature [°C] - T _S measured shear plane temperature [°C] - x,y Cartesian coordinates [m] - V cutting speed [m s^–1] - V _C chip speed [m/s] - rake angle - ,, control volume lumped thermal diffusivity [m² s^–1] - emmittance for radiation - exponent, Eq. (3) - density [kg m^–3] - Stefan-Boltzmann constant [W m^–2 K⁴] - (x) shear stress distribution [N m^–2] - shear angle     

金属橡胶-硅橡胶叠层复合材料阻尼器动态性能试验与建模

通过对金属橡胶-硅橡胶叠层复合材料阻尼器的动力学特性进行试验和理论研究,发现金属橡胶-硅橡胶叠层复合阻尼材料具有明显的非线性迟滞特征,迟滞回线并非椭圆,含有多种阻尼成分.在此基础上,用理论和试验相结合的手段研究金属橡胶-硅橡胶叠层复合材料阻尼器的动力学建模,提出各恢复力成分、物理意义明确的非对称弹性粘性阻尼双折线迟滞恢复力模型.模型中的参数由试验数据辨识,用所建模型重构恢复力-位移迟滞回线,结果表明该模型能很好描述这类非线性振动系统的特性.     

Local pool boiling coefficients on horizontal tubes

Local pool boiling on the outside and inside surfaces of a 51 mm diameter tube in horizontal direction has been studied experimentally in saturated water at atmospheric pressure Much variation in local heat transfer coefficients was observed along the tube periphery On the outside surface the maximum and the minimum are observed at θ=45° and 180°, respectively However, on the inside surface only the minimum was observed at θ=0° Major mechanisms on the outside surface are liquid agitation and bubble coalescence while those on the inside surface are micro layer evaporation and liquid agitation As the heat flux increases liquid agitation gets effective both on outside and inside surfaces The local coefficients measured at θ=90° can be recommended as the representative values of both outside and inside surfaces