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DIMENSIONAL STABILITY INVESTIGATION OF LOW CTE MATERIALS AT TEMPERATURES FROM 140 K TO 250 K USING A HETERODYNE INTERFEROMETER
Abstract
Light weight materials with excellent dimensional stability are increasingly needed in space based applications such as telescopes, optical benches, and optical resonators. Glass-ceramics and composite materials can be tuned to reach very low coefficient of thermal expansion (CTE) at certain temperatures, including room temperature and cryogenics, where a growing number of instruments in scientific and earth observation space missions are operated. Very accurate setups are needed to determine the CTE of such materials. With our laser-interferometric dilatometer setup we are able to measure CTEs of a large variety of materials in the temperature range of 140 K to 250 K. Special mirror mounts with a thermally compensating design enable measurements of the expansion of cylindrical tube-shaped samples using a heterodyne interferometer with demonstrated noise levels in the order of 10 pm/ p Hz. The temperature variation of the sample is obtained by a two stage controlled heating/cooling setup where a pulse tube cooler and electric heaters apply small amplitude temperature signals to cool/heat the sample radiatively in order to reach a homogeneous temperature over the whole sample. A carbon fiber reinforced polymer (CFRP) sample was selected to run CTE measurements, achieving results in the 10^8 K^1 range including all known uncertainties. The limitations of our setup have been identified and the largest uncertainty contribution has been determined to be tilt-to-length coupling of the sample due to temperature variations. Several improvements are currently underway to minimize our uncertainty budget. New results with the enhanced setup will be presented
n the framework of the momentless theory of cylindrical thin shells, the elastic deformation of multilayer pipes and pressure vessels is investigated. It is assumed that the pipes and pressure vessels are made by two-way spiral winding of carbon fiber reinforced plastic tape on a metal mandrel.
The analysis of the dependences of elastic deformations on the reinforcement angles is performed. The relations for axial and circumferential deformations of the wall, depending on the structure of the layer package, reinforcement angles under static loading are obtained. The separate and combined effect of internal pressure and temperature is considered. For the separate effect of loads, the graphs of deformations against the winding angle are plotted.
Composite pipes made of KMU-4L carbon fiber reinforced plastic, as well as composite metal-composite pipes, are investigated. The results obtained for thermal loads are in good agreement with the data of the known experiment and solution. Depending on the load parameters, composite and metal-composite structures with dimensionally stable properties are determined.
It is shown that dimensionally stable structures can be used to solve the problem of compensation of elastic deformations of pipelines. For this purpose, using the ASCP software package, the variant analysis of model structures is performed. By the comparative analysis of the three versions of the structure, layer package structures and reinforcement schemes, ensuring a significant reduction of loads on the supporting elements are obtained. On the example of a pipeline with a flowing fluid, it is shown that the use of dimensionally stable multilayer pipes makes it possible to eliminate bending deformations and significantly reduce the level of working forces and stresses.
Dimensionally stable composite multilayer pipes open up new approaches to the design of pipelines and pressure vessels. It is possible to create structures with predetermined (not necessarily zero) displacement fields, consistent with the fields of the initial technological displacements, as well as with the displacements of conjugate elastic elements and equipment when the operating mode changes. The scope of such structures is not limited to "hot" pipes. The results can be used in cryogenic engineering
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