Equivalent Coefficient Of Thermal Expansion Research Articles

Equivalent thermal expansion coefficients of lumped layer in laminated composites

Lumping a group of plies into a single layer to reduce the size of the problem and to increase the efficient computation is often used in thick composite structural modeling. In doing so, the use of equivalent properties for replacing the lumped heterogeneous medium by an equivalent homogenous material is required. The present study focused development of the equivalent coefficients of hygrothermal expansion of lumped layer by taking into account for induced curvature and shear deformation for an unsymmetrical and/or unbalanced layers lumping. The results of the ply stresses obtained by using the present model were almost exactly the same as the results obtained by using a full model for most of the cases studied.

Thermomechanical Properties of Nickel Silicide: Dependence on the Microstructure

Nickel monosilicide (NiSi) is a key material in microelectronics and its thermomechanical properties play an important role in determining the stress/strain field generated in a transistor structure. The Coefficient of Thermal Expansion (CTE) is of particular importance in the determination of such a field. As NiSi is used in microelectronics in its polycrystalline form, it becomes of particular interest to study the thermomechanical behaviour of the NiSi aggregate, considered as a unique macroscopic body. The grain orientation of a 120 nm polycrystalline NiSi film grown on single crystal silicon has been studied by means of electron diffraction, and the evaluation of the CTE tensor of the film in the wafer reference frame has been performed by weighted averaging the single grain contributions. The results clearly show the importance of orientation distribution in determining the value of the equivalent coefficient of thermal expansion of the aggregate.

Design, Analysis, Manufacture, and Test of APC-2/AS4 Thermoplastic Composite Pressure Vessels for Deep Water Marine Applications

A general design and analysis methodology is presented for the development of thick-wall thermoplastic composite pressure vessels for deep-water marine applications. A parametric study was performed to determine the optimum tapered radius, initial radial clearance, and plug length of the plug-supported end-caps employed here as end-closures since it was found that these optimum parameters could improve the performance of the composite pressure vessels by minimizing bending and shear stresses near the ends. Stress and buckling nonlinear finite element analyses (FEA) were performed taking hygrothermal effects into account. An equivalent coefficient of thermal expansion to model coefficient of moisture expansion for FEA software, where moisture absorption is not an input, is introduced to fully model hygrothermal effects. Based on the FEA results and taking the pressure vessel weight, ease of fabrication, mechanical and environmental performance, and cost into account APC-2/AS4 thermoplastic composite was found to be a suitable material system for the pressure vessel. An in situ thermoplastic composite filament winding/tape laying system employing infrared local and global heaters was developed in the Advanced Materials Manufacturing Laboratory of the University of Hawaii at Manoa, and was employed to manufacture the thick-wall composite pressure vessels. The manufactured pressure vessels had excellent quality, were instrumented by strain gages, and then successfully tested in the Hawaii Institute of Geophysics of the University of Hawaii at Manoa high-pressure water-filled pressure chamber. The strain gage results from the experiments were compared with those obtained from the FEA and excellent agreements were achieved.

High precision composite pipes for SOLAR-B optical structures

The authors have been developing new high thermal conductivity and low moisture absorption composite pipes for high precision space optics applications on the Japanese Institute of Space and Astronautical Science (ISAS) SOLAR-B satellite. Pitch based K13C (Mitsubishi Chemical) high modulus and high conductivity graphite fiber, and EX1515 (Bryte Technology) low moisture absorption cyanate resin, were applied to the pipes. Thermal expansion of the composite pipes was designed to be zero and more uniform in the longitudinal direction in order to obtain long term dimensional stability in the space environment. Model pipes whose length was 500 mm were fabricated and evaluated for thermal and hygroscopic deformation in a new testing apparatus. Equivalent coefficient of thermal expansion of the model pipes was essentially zero (less than 0.1 ppm/°C) and standard deviation of these coefficients was 0.05 ppm/°C. Hygroscopic deformation of the model pipes was under representative conditions 7 ppm over 3 month. The excellent thermal and hygroscopic stability were verified. In addition, thermal conductivity of the model pipes was more than 200 W/(m · K).

AN INDIRECT INTERFERENTIAL METHOD FOR MEASURING THE DEFORMATIONS OF STRUCTURES IN TEMPERATURE

The dimensional stability of a base of ceramic glass, designed to constitute a stable reference frame, has been determined with interferometric measurements in flowing air with variable temperature. An interferometric arrangement composed by one beam splitter and two mirrors was assembled directly on the base. The irradiance I(t) as a function of temperature at constant pressure was collected in the highest order of the interference pattern, I(t) shows a cyclic behavior, due to the superposition of the air refractivity variations and of the mechanical stretching of the frame. The component of the signal due to the air refractivity alone can be regarded as the reference signal, with a valuable periodicity in the inverse-temperature space, i.e. in the expansion coefficients space. The remaining component corresponding to the deformations of the supporting structure can be evaluated as a phase modulation of the reference signal. Preliminary results of measurements show that an equivalent thermal expansion coefficient of the order of magnitude of ±2·10–8 °C–1 can be probed. The theoretical and actual resolving power of the method, the unavoidable effects due to the presence of air, and some algorithms useful for noise reduction are discussed.

FPCを接着したアルミニウム積層板の熱変形解析(第2報)

This paper describes a method for eliminating thermal deformation on an aluminum laminated plate fixed to a flexible printed circuit (FPC) by adhesive. The objective of this study is to develop a head-arm for a magnetic disk storage system. Thermal deformation is calculated using the finite element method and the composite beam method. The deformation caused by temperature changes can be eliminated by making the equivalent thermal expansion coefficient of the FPC and that of the aluminum equal. Two methods for achieving this are investigated: controlling the volume of copper leaf in the FPC and controlling the volume of stainless steel inserted in the adhesive layer. The following results are found. The width ratio of copper leaf needed to eliminate thermal deformation is 0.50-0.55, and the necessary thickness of stainless steel is 10-15 μm. These results indicate that the insertion of stainless steel in the adhesive layer is the more appropriate method for application in the development of a new head-arm.