SHEAR DEFORMATION EFFECTS ON THERMALLY INDUCED INSTABILITY OF LAMINATED PLATES

A theoretical investigation of dynamics for linear elastic moderately thick structures due to uniform space- and time-dependent temperature fields is presented. The structures aredescribed by partial differential equations including a transverse inertia term for a general deformation state with interlaminar shear strains. A viscous model of external damping with a constant proportionality coefficient is assumed to describe a dissipation of the structural energy in the transverse motion. The particular problem of dynamic cylindrical bending due to the temperature with Gaussian and harmonic distributions is analyzed in detail. Dynamic thermal buckling of both symmetric alternating cross-ply composite plates and antisymmetric angle-ply composite laminates is investigated. The influence of neglecting the shear effects on dynamic stability regions is shown.     

TEMPERATURE-DEPENDENT CREEP BUCKLING OF PLATES

The Norton-Bailey power law for material creep is used to predict the time-dependent lateral deflection of flat rectangular plates. In particular, the plates considered have a through-thickness steady-state temperature distribution. This effect is considered by using Maxwell's law to modify the power creep law. The plate lateral-deflection equations are derived for creep exponents of 3 and 5, using the “sandwich plate element” frequently used to predict creep buckling of plates, ft is shown that, for one engineering material, the predictions have approximately the same degree of agreement with experimental data as have the respective creep laws.     

THERMALLY INDUCED STRESS WAVES IN FUNCTIONALLY GRADED MATERIALS WITH TEMPERATURE-DEPENDENT MATERIAL PROPERTIES

This article is concerned with the dynamic treatment of thermally induced stress waves in an infinite elastic plate subjected to impulsive electromagnetic radiation. The plate is assumed to be a functionally graded material (FGM), meaning that the material is composed of multiconstituents in ceramics and metals, the volume fractions of which distribute continuously inside the material. The mathematical problem is one of wave propagation in a typical nonhomogeneous material The radiation absorption is assumed to occur at a constant rate for the duration of the pulse and to diminish exponentially with distance from the surface of the plate, assuming negligible heat conduction. In treating problems, the nature of the stress-wave buildup in the plate is studied for the case of a temperature-dependent solid, that is, when material properties vary with temperature. The numerical procedure employs the characteristic method based on the integration of the governing equations along the characteristics. Numerical calculations are carried out for ceramic-metal FGM plates showing the influences of the temperature-dependent material properties and the volume fractions of the phases composing the FGM on the magnitude of the dynamic thermal stresses.     

TOPOLOGY OF THE FOUR-MODE STRAIN ENERGY OF THERMALLY BUCKLING PLATES

Using the Galerkin representation of heated nonlinear plate equations, we derived modal equations for the first four symmetric plate modes of a simply supported and clamped isotropic plate. The modal equations have myriad cubic amplitude terms, yet each and every one of which must account for the energy conservation; hence, the Hamiltonian property is preserved. The Hamiltonian consists of the kinetic energy and the strain (potential) energy of plate bending, membrane stretching, and thermal expansion. Since the strain energy enters into the exponent of the stationary Fokker-Planck distribution for displacement, we investigate the topological structure of strain energy under a uniform temperature plate heating. The strain energy is concave with a single zero minimum for a prebuckled plate; however, it develops a double-well potential as the plate temperature exceeds a certain critical buckling temperature for each modal coordinate. The peaks of the bimodal Fokker-Planck distribution are determined mainly by the double-well potential of the primary plate mode, which is not significantly affected by modal truncations under a uniform temperature plate heated up to five times the critical buckling temperature. Hence, this explains how the single-mode Fokker-Planck formulation was used to validate the response statistics of thermally buckled aluminum and composite plates.     

COMPUTATION OF TRANSIENT THERMAL STRESSES IN ELASTIC-PLASTIC TUBES: EFFECT OF COUPLING AND TEMPERATURE-DEPENDENT PHYSICAL PROPERTIES

The objective of this study is to obtain the transient solution of the thermoelastic-plastic deformation of internal heat-generating tubes by considering the thermomechanical coupling effect and the temperature-dependent physical properties of the material. The previously developed steady-state model describing the elastic-plastic behavior of the tubes is modified to obtain the transient solution. The propagation of the elastic-plastic interface for a given heat load is obtained; and the corresponding stress, displacement, and plastic strain components are computed. The effect of the coupling is investigated using three different engineering materials, namely, steel, aluminum, and magnesium; and it has been found to be negligible. On the other hand, the temperature dependence of the mechanical and thermal properties affects the computed profiles significantly.     

ANALYSIS OF SUBSTRATE EFFECTS ON THE RESPONSE OF PYROELECTRIC THIN-FILM INFRARED SENSORS

An infrared (IR) sensor with a lead titanate (PbTiO₃) thin film using the technology of microelectromechanical systems (MEMS) has been designed, fabricated, and developed. Anisotropic wet etching of Si(111) orientation in ethylenediamine/pyrocatechol (EDP) solution is used to process a micromachined cantilever beam for better thermal isolation and the array form available. The major IR-sensing part on the cantilever beam consists of a 5-nm PbTiO₃ layer deposited by RF sputtering, and a gold (Au) black layer evaporated as an IR radiation absorber, with the active cantilever dimensions of 200 x 100 x 5 mu m³ formed by the etching processes. The substrate effect on the performance of the IR sensor has been studied in both experimental and theoretical analysis. The cantilever structure exhibits much superior performance in both theory and experiment to that of a traditional IR-sensing bulk structure under incident radiation at a wavelength of 970 nm.     

THERMALLY FORCED VIBRATIONS OF MODERATELY THICK POLYGONAL PLATES

Bruno A. Boley was among the first to analyze thermally induced vibrations of beams and plates, a subject of paramount importance in various fields of engineering and space technology. The present paper is concerned with moderately thick plates within the Mindlin theory. A correspondence of the solution to the simpler one of an auxiliary prestressed thin plate with effective parameters is derived. By another projection the solution of the thermal deflection can be further reduced to that of two effectively stressed membranes. The correspondence of deflections is extended to moments and shear forces in the case of neglected rotatory inertia. The class of solutions, however, is restricted to simply supported plates with straight edge elements. The representation in the frequency domain is understood and frequency response functions for the deflection of parallogram plates are presented, where a Boundary Element Technique with Green's functions of rectangular domains is used.     

溅射和硒化工艺对CIS薄膜性能的影响

采用中频交流磁控溅射方法在镀有Mo薄膜的玻璃衬底上沉积Cu-In薄膜,然后在硒气氛下硒化形成CIS薄膜.对薄膜的成分、结构、表面形貌及电学性能进行了表征和检测.测试结果表明,CIS薄膜中Cu和In的含量主要取决于Cu-In薄膜中Cu和In的成分配比.CIS薄膜的表面形貌取决于溅射沉积Cu-In薄膜的靶电流密度.硒化过程中基片温度和硒源温度对CIS薄膜中Se含量及薄膜的微观结构和电学性能影响很大.在适当的硒化工艺条件下,获得了性能优异的CIS薄膜.     

FREE VIBRATIONS OF A CONICAL SHELL WITH TEMPERATURE-DEPENDENT MATERIAL PROPERTIES

This article presents an analysis of the free vibrations of a truncated conical thin shell subjected to thermal gradients. The governing equations of the shell are based on the Donnell-Mushtari theory of thin shells. Simply supported and clamped boundary conditions are considered at both ends of truncated conical shell. Temperature loading due to supersonic flow is assumed to vary along the meridian and across the thickness of the shell Hamilton's principle is used to derive the appropriate governing equations of a conical shell with temperature-dependent material properties. The shell material has a kind of inhomogeneity due to the varying temperature load and temperature dependency of material properties. The resulting differential equations are solved numerically using the collocation method. The results are compared with certain earlier results. The influence of temperature load on the vibration characteristics is examined for the conical shells with various geometrical properties.     

THERMAL EFFECTS ON FLOW PROPERTIES OF ALUMINUM ALLOYS

The flow properties of aluminum alloys under hot working conditions can be studied by hot torsion testing. However, the properties obtained may be severely affected by the thermal effects generated during testing. In this paper thermal analysis is made by a finite element analysis (FEA) to evaluate the temperature distribution over the test specimen, and the predictions of the flow stresses of an aluminum alloy AA5252 are modified by taking into account the temperature changes. It has been shown that the further flow softening at high strain rates, as a result of heat accumulation during testing can be predicted by the method presented.     

掺杂对FeS2薄膜光电性能的影响

采用磁控溅射淀积合金膜和纯铁膜,通过离子注入掺杂,研究了不同条件下FeS2薄膜的晶体结构,光吸收系数、电阻率、载流子浓度等光电性能,并用正电子湮灭谱研究了膜内的空位缺陷。结果表明,掺杂提高了薄膜的导电性能。离子注入使薄膜光吸收系数增加,禁带宽度上升,霍尔迁移率提高;合金溅射导致光吸收系数降低,禁带宽度下降,载流子浓度升高。注入Zn2 退火前空位浓度较大,退火后空位浓度低于纯FeS2膜。     

低能量质子辐照对背场硅太阳电池电性能影响的研究

研究了在模拟空间质子辐照环境条件下,质子能量分别为60 keV、150 keV,辐照剂量为1×1013～2×1016cm-2时,背场硅太阳电池的电性能的变化。试验表明,电池的开路电压Voc、短路电流Isc、最大输出功率Pmax随着质子能量和辐照剂量的增加出现了大幅衰降。随着能量的增大Voc和Pmax衰降幅度明显大于Isc,而随辐照剂量的增加短路电流Isc衰降幅度要比Voc和Pmax大得多,并且随着质子能量的增大短路电流,Isc与辐照剂量呈明显的线性关系。当质子能量为60keV,辐照剂量为1.2×1013cm-2时,Pmax/P。衰降到75％。通过深能级瞬态能谱X射线激发光电子能谱和红外光谱,初步分析了能量小于200 keV质子辐照导致电池电性能衰降的原因。     

酸洗预处理对生物质热解焦物理化学特性的影响

选用松木、杨木、玉米秸秆和稻壳4种生物质为原料,采用3%（体积分数）乙酸溶液进行洗涤除灰后,进行快速热解实验,对比研究酸洗预处理对4种生物质热解焦物理化学特性的影响。结果表明：乙酸酸洗可有效去除松木、杨木、玉米秸秆和稻壳灰分中的大部分无机元素,从而促进热解过程中挥发分的释放、显著改善热解焦的表面化学特性。酸洗可促进热解焦孔隙结构的形成,提高比表面积和总孔容积,但会使平均孔径减小,这表明酸洗主要提高微孔率,对微孔的形成有较大的促进作用。同时,酸洗使得更多的含氧官能团保留在生物质热解焦表面,这种影响对玉米秸秆和稻壳尤为明显。气化焦油的吸附实验结果表明酸洗后热解焦的吸附能力有所增加。     

THERMAL STRESS ANALYSIS OF THERMOVISCOELASTIC HOLLOW CYLINDER WITH TEMPERATURE-DEPENDENT THERMAL PROPERTIES

ABSTRACT

We analyzed the thermal stress on a thermoviscoelastic hollow cylinder with temperature-dependent thermal properties with the finite difference method. It was gradually heated at the inner surface and the outer surface was kept at the initial temperature. The cylinder material was thermorheologically simple and had a temperature-dependent coefficient of linear thermal expansion, thermal conductivity, and thermal diffusivity (and/or specific heat). A bisphenol A–type epoxy resin was chosen as the thermoviscoelastic material of the cylinder for numerical analysis. Based on these results, we discuss the effects of thermoviscoelasticity and temperature-dependent thermal properties on the stress field.     

MODELING OF BUOYANCY-DRIVEN FLOW AND HEAT TRANSFER FOR AIR IN A HORIZONTAL ANNULUS: EFFECTS OF VERTICAL ECCENTRICITY AND TEMPERATURE-DEPENDENT PROPERTIES

In this article fluid dynamic and thermal fields are presented for numerical simulations of laminar, steady, two-dimensional buoyancy-driven flows in an annulus between two vertically eccentric pipes using the penalty finite element method. The simulations were accomplished for Rayleigh numbers between 10 3 and 10 5 and radius ratio of 2.6, with various eccentricities. For most of the work, the usual Boussinesq approximation was made. However, in order to demonstrate the effects of temperature-dependent physical properties for natural convection in a concentric annulus, a modified Boussinesq approximation with temperature-dependent viscosity and thermal conductivity has been used. The formulation was based on primitive variables. Numerical results are presented in terms of isotherms, streamlines, and Nusselt numbers. The results are compared with recent publications and excellent agreement has been found. Stable solutions were obtained when the model was modified to incorporate temperature-dependent viscosity and thermal conductivity and applied to the case of a concentric annulus. The varying viscosity had the most effect on the fluid velocity, while the effects of varying thermal conductivity were most noticeable in the temperature profiles and local Nusselt numbers.     

相变蓄热板材用于电加热地板采暖的节能效果研究

采用等效比热法和全隐式有限差分格式,编程对影响相变蓄热板材(PCTSP)作为电加热地板采暖系统填充层节能效果的因素(加热方式、相变温度、相变半径、潜热及热导率)进行参数化研究。结果表明:将20mm厚的PCTSP用作填充层,相对于40mm厚碎石混凝土作为填充层来说:①当PCTSP的热物性给定时,采用不同的加热模式,基于总能耗的节能率是完全不同的,同时能够取得节能效果的相变温度范围也不同;②对于第一种加热模式,热导率、相变半径和潜热越大,能够取得节能效果的相变温度范围越宽,即相变材料的选择自由度越大。     

活化剂种类对生物质活性炭理化特性的影响

采用KOH、K2CO3和ZnCl2为活化剂,椰壳、竹子、杨木和棉秆为原材料制备活性炭,研究不同活化剂对生物质热解活化产物及活性炭理化特性的影响.结果表明,KOH活化时,生物质的固液气三相比例均衡,CO体积产量最高,活性炭的表面官能团稳定性最好,骨架破碎,微孔结构发达,微孔面积可达749.90 m2/g.K2CO3活化时...     

INFLUENCE OF DAMAGE ON THE THERMAL RESPONSE OF GRAPHITE-EPOXY LAMINATES

A “constrained ” displacement finite element approach for studying the influence of transverse cracks and delaminations on the thermal response of laminated composites is presented. Typical results are given in the form of percent retention curves for the coefficient of thermal expansion as a function of crack density. Cross-ply and quasi-isotropic T300/5208 graphite-epoxy laminates are considered. It is shown that transverse cracks can have a significant influence on the coefficient of thermal expansion, but delaminations located symmetrically about the laminate mid-plane have no influence on thermal expansion.     

DYNAMICS AND ACTIVE BENDING VIBRATION CONTROL OF TURBOMACHINERY ROTATING BLADES FEATURING TEMPERATURE-DEPENDENT MATERIAL PROPERTIES

The problem of bending vibration, dynamic response, and actively dynamic control of rotating beams of nonuniform cross section, operating in a temperature field and impacted by a blast, is addressed. The structural model is in the form of a thin-walled beam whose material properties are considered to be temperature dependent. The implemented vibration control methodology is based on the piezoelectric strain actuation. In this context, a system of piezo actuators bonded to the structure surface that are spread over the entire span of the beam and actuated out of phase is considered. As a result, a control bending moment is piezoelectrically induced at the beam tip. In the context of this paper, to control the free and forced vibration, velocity feedback control is implemented. The considered control methodology is also useful toward counteracting the deleterious effects induced by the thermal degradation of material properties of blade structure. Results highlighting the effects of the blade taper on bending natural frequencies, as well as of the temperature and time-dependent external excitation on the open/closed-loop bending dynamic response are presented, and pertinent conclusions are drawn.