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基于修正单层梁理论的夹层梁最大弯曲正应力计算 总被引:1,自引:0,他引:1
目的计算夹层梁横截面的最大弯曲正应力。方法将夹层梁等效成等截面均质单层梁,进而推导出了理论计算公式,并在此基础上进行了三点弯曲试验的算例研究。结果当破坏载荷与夹层梁横截面的尺寸一定时,随着芯层与总厚度比的增加,修正单层梁理论计算的最大正应力值逐渐增加,而单层梁理论计算的结果为恒定值。对于同样结构的夹层梁,随着芯层弹性模量与表层模量比的增加,修正单层梁理论计算的最大正应力与单层梁理论的差异值越来越小。结论修正单层梁理论与层合梁理论计算的结果是一致的,该方法可有效进行最大弯曲正应力的预测与计算。 相似文献
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负泊松比蜂窝夹层板作为一种特殊的复合材料结构,目前对其动态行为尚缺乏认识。应用Reddy剪切板理论分析了对边简支负泊松比蜂窝夹层板的弯曲振动。将内凹六边形胞元的蜂窝芯层等效为一正交异性层,芯层的等效弹性参数由修正后的Gibson公式得出。由具体算例可知经典叠层板理论和一阶剪切板理论不适合用于蜂窝夹层板的振动分析。应用Reddy剪切板理论研究了蜂窝夹层板板厚比、芯层板厚及胞元角度对弯曲振动频率的影响,并绘出相应的曲线图。结果表明:对于对边简支负泊松比蜂窝夹层板,当板厚比小于某一值时,固有频率参数随板厚比的增加而增加;但当板厚比大于该值时,固有频率参数随板厚比的增加呈现复杂的变化形式。本文得到的结果为蜂窝夹层板的设计和实际应用提供了理论依据和数值参考。 相似文献
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提出了一种由齿板-玻璃纤维(TP-GF)混合面板和聚氨酯(PU)泡沫芯材组成的新型TP-GF/PU泡沫夹层梁,结构中金属板通过齿钉压入GF与内部芯材连接,该夹层梁采用真空导入模压工艺制作。通过低速冲击试验,研究了不同冲击能量、纤维厚度和泡沫密度下TP-GF/PU泡沫夹层梁的冲击响应和损伤模式,并与普通的夹层梁进行了对比分析;通过双悬臂梁试验研究了混合夹层梁的界面性能,计算了夹层梁的应变能释放率。结果表明:在22 J、33 J、44 J能量冲击下,泡沫芯材密度为150 kg/m3的TP-GF/PU泡沫夹层梁的最大接触力较普通夹层梁分别提高了31.2%、48.6%、33.3%,冲击能量吸收分别增加了17.2%、11.3%、15.5%;随着冲击能量、面板纤维层数及芯材密度的增加,TP-GF/PU泡沫夹层梁最大接触力增大,密度较低的TP-GF/PU泡沫夹层梁损伤形式主要为面板的局部弯曲,而芯材密度较高的TP-GF/PU泡沫夹层梁则以穿透损伤为主;增加泡沫芯材密度和面板纤维厚度能够提高TP-GF/PU泡沫夹层梁的抗冲击性能,随着芯材密度的增大TP-GF/PU泡沫夹层梁的应变能释放率峰值越高,界面性能越好。 相似文献
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提出了一种齿板-玻璃纤维混合面板和泡沫芯材组成的新型混合夹层结构,齿板通过齿钉与泡沫芯材相连。该结构采用真空导入成型工艺制备,通过三点弯曲试验研究该结构在不同跨度以及不同芯材密度情况下的破坏模式和弯曲性能,并与普通泡沫夹层结构进行对比分析,同时探究了齿板对该结构界面性能的影响。结果表明:在泡沫芯材密度为35kg/m~3、80kg/m~3和150kg/m~3情况下,齿板-玻璃纤维混合泡沫夹层梁弯曲承载能力与普通泡沫夹层梁相比分别提高了168%、211%和258%,其界面剪切强度依次为0.09 MPa、0.21 MPa和0.45 MPa;随着芯材密度和跨度的变化,该结构主要产生芯材剪切和芯材凹陷两种破坏形态,齿板的嵌入有效抑制界面的剪切失效。另外,利用理论公式估算了试件受弯极限承载能力,理论值与实测值吻合较好。 相似文献
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基于高阶剪切弯曲理论,对含有软质芯材的复合材料格栅夹层板的弯曲特性进行了理论研究。基于能量法,推导了含有软质芯材的复合材料格栅的等效弹性参数计算式;基于高阶剪切弯曲理论,推导了夹层板的弯曲平衡微分方程,并采用Navier方法,给出了分布载荷作用下四边简支、上下表层为对称正交铺层的夹层板弯曲问题的理论解;用算例对典型格栅夹层板的理论解和有限元仿真解进行了对比,两者误差为7.1%,验证了本文理论方法的正确性;并分析了夹层板跨厚比、格栅厚度、格栅复合材料铺层角度、格栅间距等参量对含有软质芯材的典型复合材料格栅夹层板弯曲挠度的影响规律。 相似文献
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设计并制备了双向纤维腹板增强复合材料夹层梁,对其受弯性能进行了四点弯曲试验研究,开展单、双向格构夹层梁性能对比分析,研究不同腹板高度、厚度对夹层梁受弯性能的影响,基于经典夹层梁理论及简支梁受弯基本理论,研究夹层梁破坏模式和机理。试验结果表明:双向格构腹板增强形式能有效提高该夹层结构的极限变形能力与受弯极限承载力,且随着试件厚度加大提高作用更明显;保持夹层梁基本参数不变,增加试件高度有利于提高刚度,增强夹层梁极限承载力;单一增加腹板厚度有益于提高该夹层梁的极限变形能力,但不能明显提高其极限承载力。理论分析表明:采用铁木辛柯梁理论求得的挠度理论值与实验值吻合较好。 相似文献
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泡沫铝层合梁的三点弯曲变形 总被引:20,自引:0,他引:20
研究了泡沫铝层合梁三点弯曲的载荷(P)-位移(δ)曲线、变形过程及面板破坏、夹芯剪切破坏、凹陷破坏等破坏模式。用极限载荷公式得到的计算值与实验值符合良好。实验所得的加载和卸载刚度(P/δ)与计算结果吻合较好。泡沫铝层合梁具有较低的密度((0.42~0.92)×10~3kg/m~3)和很高的弯曲比刚度(E~(1/2)/ρ)。利用极限载荷公式建立了破坏模式图。 相似文献
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In recent years the use of composite materials as reinforcement in concrete beams has increased whenever durability is the main controlling parameter. Many studies have been performed on the behaviour of concrete beams but few have analysed the structural behaviour of plane elements like slabs or grids. The paper analyses the experimental flexural behaviour of a concrete beam grid reinforced with CFRP bars. An one-third scale experimental model of a real concrete floor, was tested in bending. The experimental results show the flexural behaviour in terms of cracking phases and deflection until the failure. The experimental model was affected by the cracking of concrete even under low loads. The experimental model is analysed both by elastic theory of orthotropic plate and a FEM code. An approximate method of calculation, based on an orthotropic plate model, is developed that considers modified bending rigidities for orthogonal directions. 相似文献
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On a geometrically exact curved/twisted beam theory under rigid cross-section assumption 总被引:3,自引:0,他引:3
A geometrically exact curved/ twisted beam theory, that assumes that the beam cross-section remains rigid, is re-examined
and extended using orthonormal frames of reference starting from a 3-D beam theory. The relevant engineering strain measures
with an initial curvature correction term at any material point on the current beam cross-section, that are conjugate to the
first Piola-Kirchhoff stresses, are obtained through the deformation gradient tensor of the current beam configuration relative
to the initially curved beam configuration. The stress resultant and couple are defined in the classical sense and the reduced
strains are obtained from the three-dimensional beam model, which are the same as obtained from the reduced differential equations
of motion. The reduced differential equations of motion are also re-examined for the initially curved/twisted beams. The corresponding
equations of motion include additional inertia terms as compared to previous studies. The linear and linearized nonlinear
constitutive relations with couplings are considered for the engineering strain and stress conjugate pair at the three-dimensional
beam level. The cross-section elasticity constants corresponding to the reduced constitutive relations are obtained with the
initial curvature correction term. Along with the beam theory, some basic concepts associated with finite rotations are also
summarized in a manner that is easy to understand.
Received: 17 June 2002 / Accepted: 21 January 2003
The work was partly sponsored by a grant (CDAAH04-95-1-0175) from the Army Research Office with Dr. Gary Anderson as the
grant monitor. We would also like to thank Prof. Raymond Plaut of Dept. of Civil and Environmental Engineering at Virginia
Polytechnic Institute and State University for his technical help. 相似文献
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New accurate two-noded shear-flexible curved beam elements 总被引:2,自引:0,他引:2
There are two purposes of this work. One is to present two accurate two-noded finite elements which are derived from the
potential energy principle and the Hellinger–Reissner functional principle respectively. The second is to show the successful
application of the internal displacement parameters in developing a high-order related displacement-rotation interpolation
field. Because the derived interpolation field is capable of accurately modeling deformation modes in extreme thin curved
beams and nearly straight beams, both shear locking and membrane shocking are avoided. Several standard numerical tests display
superior behaviors of the present elements.
Received: 5 February 2002 / Accepted: 16 September 2002 相似文献
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In this work we consider solutions for the Euler-Bernoulli and Timoshenko theories of beams in which material behavior may
be elastic or inelastic. The formulation relies on the integration of the local constitutive equation over the beam cross
section to develop the relations for beam resultants. For this case we include axial, bending and shear effects. This permits
consideration in a direct manner of elastic and inelastic behavior with or without shear deformation.
A finite element solution method is presented from a three-field variational form based on an extension of the Hu–Washizu
principle to permit inelastic material behavior. The approximation for beams uses equilibrium satisfying axial force and bending
moments in each element combined with discontinuous strain approximations. Shear forces are computed as derivative of bending
moment and, thus, also satisfy equilibrium. For quasi-static applications no interpolation is needed for the displacement
fields, these are merely expressed in terms of nodal values. The development results in a straight forward, variationally
consistent formulation which shares all the properties of so-called flexibility methods. Moreover, the approach leads to a
shear deformable formulation which is free of locking effects – identical to the behavior of flexibility based elements.
The advantages of the approach are illustrated with a few numerical examples.
Dedicated to the memory of Prof. Mike Crisfield, for his cheerfulness and cooperation as a colleague and friend over many
years. 相似文献
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Control of the electron beam active zone position in electron beam welding processes 总被引:1,自引:0,他引:1
It is known that charged particles emitted from the region of electron beam (EB) interaction with the material being processed, are an important source of information for the understanding of EB welding processes. Measurements for the three largest groups of charged particles, namely, backscattered electrons, true secondary electrons and ions are presented here. It was estimated that only the signals of the direct component amplitude of these particles’ currents, processed by neural networks, could be used to effectively control the EB welding process. Computer simulations of various models of neural networks are described. The best result was obtained for a network that determines an optimal value of focusing current for the weld being made, based on the amplitude of signals measured with a moderately defocused EB. 相似文献
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A mixed formulation for Timoshenko beam element on Winkler foundation has been derived by defining the total curvature in
terms of the bending moment and its second order derivation. Displacement and moment have been chosen as primary variables,
while slope and first derivation of moment have been chosen as secondary variables. The behaviour matrix for Timoshenko beam
element has been obtained in mixed form by using weak formulation with equilibrium and compatibility equations. The presented
formulation makes the analysis of beams free of shear locking.
Received: 10 July 2002 / Accepted: 14 January 2003 相似文献
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对分别加入4 种稀释剂的双酚A 环氧树脂和酚醛环氧树脂的电子束辐射固化性能进行了研究。分析了稀释剂种类及含量对环氧树脂体系辐射产物的固化度、固化均匀性、固化区域大小及其动态力学性能的影响规律。结果表明: 电子束固化环氧树脂体系中加入稀释剂后, 辐射产物的固化度、玻璃化转变温度及储能模量有所下降, 但固化均匀性得到提高; 加入稀释剂的环氧树脂电子束固化区域的厚度均小于未加稀释剂树脂, 而底面直径却大于未加稀释剂树脂; 随着树脂中实际稀释剂含量的增加, 电子束固化环氧树脂固化度逐渐降低, 固化层厚度减小, 固化区域的底面直径先增加后减小。 相似文献
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Propagation properties of astigmatic sinh-Gaussian beams (ShGBs) with small beam width in turbulent atmosphere are investigated. Based on the extended Huygens–Fresnel integral, analytical formulae for the average intensity and the effective beam size of an astigmatic ShGB are derived in turbulent atmosphere. The average intensity distribution and the spreading properties of an astigmatic ShGB propagating in turbulent atmosphere are numerically demonstrated. The influences of the beam parameters and the structure constant of atmospheric turbulence on the propagation properties of astigmatic ShGBs are also discussed in detail. In particular, for sufficiently small beam width and sinh-part parameter as well as suitable astigmatism, we show that the average intensity pattern converts into a perfect dark-hollow profile from initial two-petal pattern when ShGBs with astigmatic aberration propagate through atmospheric turbulence. 相似文献
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Properties of indium tin oxide films deposited on unheated polymer substrates by ion beam assisted deposition 总被引:1,自引:0,他引:1
The optical, electrical and mechanical properties of indium tin oxide (ITO) films prepared on polyethylene terephthalate (PET) substrates by ion beam assisted deposition at room temperature were investigated. The properties of ITO films can be improved by introducing a buffer layer of silicon dioxide (SiO2) between the ITO film and the PET substrate. ITO films deposited on SiO2-coated PET have better crystallinity, lower electrical resistivity, and improved resistance stability under bending than those deposited on bare PET. The average transmittance and the resistivity of ITO films deposited on SiO2-coated PET are 85% and 0.90 × 10− 3 Ω cm, respectively, and when the films are bent, the resistance remains almost constant until a bending radius of 1 cm and it increases slowly under a given bending radius with an increase of the bending cycles. The improved resistance stability of ITO films deposited on SiO2-coated PET is mainly attributed to the perfect adhesion of ITO films induced by the SiO2 buffer layer. 相似文献