Nonmetallic Materials and Composites at Low Temperatures

Frontmatter

Thermal Properties of Crystalline Polymers at Low Temperatures

Thermal Properties of Crystalline Polymers at Low Temperatures

Abstract

In comparison with inorganic solids there have been few studies of the low temperature thermal properties of polymers, even though these properties are of considerable interest in scientific research and cryogenic technology. From the three important thermal quantities, heat capacity Cp, thermal conductivity K and thermal expansion α, the heat capacities of polymers have been most widely studiedi¹. Most of the studies on thermal conductivity of polymers are confined to the range between liquid nitrogen and room temperature. Recently, however, the situation has improved and thermal conductivity data² for polymers are now available in the temperature range 0.1 to 300K. In contrast, there is a lack of data on thermal expansion measurements at low temperatures. On the other hand there has been a growing theoretical interest in the lattice dynamics of polymers representing a rather extreme form of anisotropy in the crystalline state³.

I Engeln, M Meissner

Thermal Conductivity at Low Temperatures in Semicrystalline Polymers

Thermal Conductivity at Low Temperatures in Semicrystalline Polymers

Abstract

Over the past few years we have studied in detail the influence of (i) crystallinity and (ii) crystallite orientation in determining the thermal conductivity, κ, of semicrystalline polymers.^1–3 Between about 2K and room temperature the variations in κ with these two parameters are completely different above and below about 25K. At the higher end of the range the conductivity increases both with crystallinity and with orientation, the latter being brought about by drawing or extruding the isotropic polymer. At low temperatures, on the other hand, the specimens with the greatest crystallinity have the lowest conductivity with values in a 50% crystalline specimen at ∿ 1.5K roughly an order of magnitude lower than those found “universally” for amorphous solids.⁴ These low values, furthermore, are found to be more or less independent of crystallite orientation. The overall behaviour just described is shown schematically in figure 1.

D Greig, N D Hardy

Elastic Nonlinearity of Vitreous Silica at Low Temperatures

Elastic Nonlinearity of Vitreous Silica at Low Temperatures

Abstract

Low-temperature anomalies in the thermal, acoustic and dielectric properties of amorphous solids have found increasing attention in recent years.¹ Compared with crystals, these materials exhibit an anomalously high specific heat and low thermal conductivity². This behaviour can be explained by the existence of low-energy excitations with a nearly constant density of states in an energy range extending at least between 10 mK and 10 K. More detailed information has been obtained by ultrasonic and dielectric measurements³ which demonstrate that these excitations are best described as two-level systems. According to a generally accepted model they originate from small groups of atoms, which are energetically nearly equivalent, tunnelling between two positions in the amorphous matrix.⁴ About the physical nature of the tunnelling “particles”, however, not much has previously been known.

M v Schickfus, S Hunklinger, K Dransfeld

Ultrasonic Absorption in Polymethylmethacrylate at Low Temperatures

Ultrasonic Absorption in Polymethylmethacrylate at Low Temperatures

Abstract

In a series of experiments performed at low temperatures it has been demonstrated that amorphous solids exhibit thermal, acoustic and dielectric properties which are not observed in perfect crystals.¹ These anomalies are caused by a broad distribution of low-energy excitations which have their microscopic origin in structural rearrangements of small groups of atoms via quantum mechanical tunnelling.² These tunnelling states interact strongly with phonons resulting in a strong ultrasonic absorption and a temperature dependent sound velocity even at temperatures of a few mK.³

G Federle, S Hunklinger

Radiation Damage in Thin Sheet Fibreglass Insulators

Radiation Damage in Thin Sheet Fibreglass Insulators

Abstract

The term “radiation damage”, as applied to structural behaviour, can be defined as the reduction in load-carrying ability resulting from exposure to radiation. It has been observed that the radiation induced loss in strength of a material could depend upon the type of load to be resisted.^1–4 The data in this paper indicate that the structural configuration could be of major importance.

Elena A Erez, Herbert Becker

Epoxide Resins for Use at Low Temperatures

Epoxide Resins for Use at Low Temperatures

Abstract

Materials based on epoxide resins are frequently used in the manufacture of nuclear physics apparatus, such as bubble chambers, superconducting magnets and ancillary equipment. In such applications, these materials are required to operate under high stress at temperatures below 20 Kelvin.

D Evans, J T Morgan

Dynamic Mechanical Properties of Poly (Methacrylates) at Low Temperatures

Dynamic Mechanical Properties of Poly (Methacrylates) at Low Temperatures

Abstract

The application of plastics in aerospace and cryogenic technology is becoming more and more important. At TNO we had available a series of systematically chemically modified poly(methacrylates) for which the dynamic-mechanical properties had been measured down to liquid nitrogen temperature^1–6 At CEN, equipment was available to measure dynamic-mechanical properties from liquid helium temperature upwards⁷. In view of the importance of low temperature properties we decided to cooperate.

J Heijboer, M Pineri

Dielectric Loss Due to Antioxidants in Polyolefins

Dielectric Loss Due to Antioxidants in Polyolefins

Abstract

Thomas and King¹ reported in 1975 that the presence in polyethylene of certain antioxidants of the substituted phenol type caused a dielectric relaxation at 4.2 K. Although peak loss factor occurred at several kHz, the loss enhancement at 50–60 Hz was significant in view of the possible use of polyethylene tapes for the insulation of a superconducting power transmission line. It has now been found that all antioxidants that are derivatives of 2,6 di-tert-butyl phenol (“DBF” - see figure 1) cause such a relaxation, but that any other phenol or non-phenol antioxidant may be used without causing significant loss enhancement at cryogenic temperatures.² DBF and its derivatives cause similar relaxations when added to polyethylene, polypropylene or other polyolefins, or dissolved in paraffin or decalin.³ By an appropriate isotopic substitution it has been demonstrated that the effect is due to the hindered rotation of the hydroxyl groups of the molecules,⁴ so in fact it is now clear that Thomas and King rediscovered at cryogenic temperatures a dielectric relaxation which had been known since 1957. Davies and Meakins⁵ then reported that a solution of 2, 4, 6 tri-tert-butyl phenol in decalin had two resolved relaxations, and were able to identify the faster one (30 GHz loss peak at ambient temperature) with hydroxyl group rotations and the slower one with rotations of entire molecules.

R Isnard, G Frossati, J Gilchrist, H Godfrin

Low Temperature Fracture Measurements on Polyethylene in Comparison with Epoxide Resins

Low Temperature Fracture Measurements on Polyethylene in Comparison with Epoxide Resins

Abstract

The mechanical properties of several epoxide resins (EP), linear high-molecular isotropic polyethylenes (HDPE) and stretched HDPE were determined between 2 and 293 Kelvin. This paper will concentrate on the tensile strength σ_B, the critical stress intensity factor K_1c and the energy of fracture γ.

Bernhard Kneifel

Fatigue Test of Epoxide Resin at Low Temperatures

Fatigue Test of Epoxide Resin at Low Temperatures

Abstract

In the various large scale projects concerned with energy resources, superconducting magnet technology becomes increasingly important; for example, in magnetic confined fusion reactor SC magnets are believed to be necessary from power balance. In the case of the Tokamak reactor both toroidal and poloidal magnets should be constructed as SC magnets. The former type magnet is to produce a large and intense magnetic field (DC mode), but the latter is to generate a pulsating field (AC mode). In these magnets, the materials are exposed to complex stress/strain states in a complicated dynamic and time dependent manner.

S Nishijima, S Ueta, T Okada

Lap Test of Epoxide Resin at Cryogenic Temperatures

Lap Test of Epoxide Resin at Cryogenic Temperatures

Abstract

The reasons why the expected performance of superconducting magnets is not easily achieved are because of instabilities such as training and degradation. Impregnation or potting techniques have been employed in order to modify such instabilities. Epoxide resin has been selected in this work from the range of impregnating materials (eg woods metal,¹ epoxy^{2 5} and wax⁶) because epoxide resins have been shown to possess excellent adhesive strength and satisfactory mechanical properties at cryogenic temperatures.

S Nishijima, T Okada

Cohesive Strength of Amorphous Polymers at Low and High Temperatures

Cohesive Strength of Amorphous Polymers at Low and High Temperatures

Abstract

A force of 6 nN is required to break a carbon-to-carbon bond¹. It therefore follows that polycarbonate in which an area of 1 mm² is traversed by about 10¹² molecular chains ought to survive a stress of 2000 MNm⁻² assuming one chain out of three parallels the direction of the applied load. However, the tensile yield strength of polycarbonate² is 62 MNm⁻². Obviously, the initial assumption is a fallacy. It can not be the right way to get an answer to the question - How strong are polymers really?

M Fischer

The Thermal Conductivity and Thermal Expansion of Non-Metallic Composite Materials at Low Temperatures

The Thermal Conductivity and Thermal Expansion of Non-Metallic Composite Materials at Low Temperatures

Abstract

This paper presents a short review of the behaviour of the thermal conductivity and the thermal expansion of non-metallic particle-filled and fibre-filled composite materials from room temperature down to liquid helium temperatures. A brief discussion of the physical mechanisms which are involved and the possibility of predicting the thermal properties of a composite is also given.

H M Rosenberg

Nonlinear Stresses and Displacements of the Fibres and Matrix in a Radially Loaded Circular Composite Ring

Nonlinear Stresses and Displacements of the Fibres and Matrix in a Radially Loaded Circular Composite Ring

Abstract

The mechanical behaviour and failure mechanism of the reinforcing fibres and the polymer matrix of a circular composite ring, subjected to radial pressure and cryogenic thermal loading, and the design of a thick composite arch, are studied using nonlinear finite element analysis. The rings are sections of a pultruded 0.203 m × 0.0065 m (8 in × ¼ in) diameter × thickness, polyester-glass pipe, reinforced in both the axial and circumferential directions. The arch is 1.0 m in radius, 0.1 m thick and 0.065 m wide. Circular rings of pultruded polyester-glass may be used at the tips of the composite radial structures, supporting the round aluminum rippled conductors of superconductive energy storage magnets.

Samaan George Ladkany

The Strain Energy Release Rate of a Glass Fibre Reinforced Polyester Composite

The Strain Energy Release Rate of a Glass Fibre Reinforced Polyester Composite

Abstract

A superconductive energy storage magnet requires a large quantity of low-thermal-conductive, high-load-carrying supporting structures to carry the radial and axial compressive loads from the 1.8 K magnet coils to room temperature bedrock.^1–3 Engineering data is needed on low cost commercial composites for struts to be used in the superconductive energy storage magnet designs at the University of Wisconsin-Madison. The main properties are compressive strengths, delamination strengths, shear properties and compressive fatigue properties at cryogenic temperatures and room temperatures.^4–7

Kyung S Han, James Koutsky

Recent European Work on the Nondestructive Testing of Composite Materials

Recent European Work on the Nondestructive Testing of Composite Materials

Abstract

Fibre-reinforced composite materials, notably GRP and CFRP are now finding increasing use in structural applications including shipping, aircraft and aerospace as well as in large cryogenic items. This development has revived interest in the special problems associated with the testing and inspection of such materials and it is therefore an appropriate time to survey existing methods in relation both to their scientific background and their practical shortcomings. Much work on the NDT of composites has, of course, taken place in the USA but this paper aims to discuss only the main European contributions.

W N Reynolds

Physical Properties of Epoxide Resin/Glass Fibre Composites at Low Temperatures

Physical Properties of Epoxide Resin/Glass Fibre Composites at Low Temperatures

Abstract

The versatility of epoxide resins may be regarded as both an asset and a disadvantage in terms of low temperature applications. An asset because the vast range of materials available, together with all the formulating variables possible, enables most problems to be overcome. A disadvantage because this bewildering choice often leads to the selection of the wrong material with consequent processing/manufacturing problems or mismatched physical properties in the cured state.

D Evans, J T Morgan

Charpy Impact Test of Cloth Reinforced Epoxide Resin at Low Temperature

Charpy Impact Test of Cloth Reinforced Epoxide Resin at Low Temperature

Abstract

Extremely large superconducting magnets have been recognised as essential in projects such as energy storage or fusion. The increase in size and pulsative operation of such magnets makes applied forces in components complex and varied. It is important, therefore, to elucidate the behaviour of each magnet component against the various forces at cryogenic temperature.

S Nishijima, T Okada

Nonmetallic and Composite Materials as Solid Superleaks

Nonmetallic and Composite Materials as Solid Superleaks

Abstract

There are two types of superleaks, namely: the undesirable and the desirable. The former corresponds to, for instance, a crack in a Dewar containing He II and through which a super flow is established, ie, it leaks the so-called superfluid component of the He II. The latter is a device through which one needs, at given circumstances, a flow of superfluid He II. Summarising, the first is an accident and the second a device. This paper deals only with the devices, in general solid porous materials in which the so-called diameter of the pores, gaps, inter-crystalline spaces, or small channels, etc, are equal or smaller than 100 Å. Of course, the type of slits and capillaries used by Kapitza¹ and by Allen and Misener² when they discovered the superfluidity are also superleaks. However, the small channels they considered differed by approximately two orders of magnitude to those considered in this paper.

J M Goldschvartz

Low Temperature Properties of Carbon Fibre Reinforced Epoxide Resins

Low Temperature Properties of Carbon Fibre Reinforced Epoxide Resins

Abstract

In recent years Carbon Fibre Reinforced Epoxide resins have been used for applications in the aerospace industry. The high ratios of strength and stiffness to specific weight are important in structures such as satellites and space vehicles. For applications at room temperature the material properties were also studied with care. The test equipment, the specimens and the manufacturing procedures were controlled at a high standard. A high tensile or a high modulus carbon fibre is used according to the particular requirement. As many structures will work at low temperatures in the future, the material properties at these temperatures are required for design purposes. The most important properties are strength, stiffness and thermal characteristics.

W Weiss

The Use of Graphite/Epoxy Composites in Aerospace Structures Subject to Low Temperatures

The Use of Graphite/Epoxy Composites in Aerospace Structures Subject to Low Temperatures

Abstract

This paper will briefly describe two graphite/epoxy structures and the critical performance parameters and properties related to each of them. The programmes are (1) Applications Technology Satellite (ATS) Reflector Support Truss, and (2) Side Brace for the A37B Aircraft Main Landing Gear. The first programme was sponsored by NASA Goddard and the second programme was sponsored by Air Force Flight Dynamics Laboratory (AFFDL) of Wright Patterson Air Force Base, Ohio, USA. Hercules conducted the design, development, fabrication, and testing of the structures in cooperation with Fairchild Industries, and AFFDL.

K A Philpot, R E Randolph

Standardizing Nonmetallic Composite Materials for Cryogenic Applications

Standardizing Nonmetallic Composite Materials for Cryogenic Applications

Abstract

The technology of composite materials is presently at the state that metals technology was before being systematized by the establishment of industry standards. It is difficult to imagine working in metals technology in the United States without the ability to associate performance with designations such as 304L for stainless steel or 2024-T4 for aluminium. It would be equally difficult for individuals in other countries to perform effectively without similar national metal and alloy coding systems that transcend proprietary designations, but this is the situation presently confronting those working in the composite materials area, in the United States and elsewhere.

M B Kasen

Special Applications of Nonmetallic Materials in Low Temperature Technology

Special Applications of Nonmetallic Materials in Low Temperature Technology

Abstract

In large scale superconducting technical devices, it is often necessary to transmit large forces from low temperature to room temperature. The thermal losses caused by the cryogenic structure essentially determine, in some cases, the efficiency of the total superconducting system. Therefore these losses have to be minimised. This can be done in two ways:

(1)

constructively: with distances between the temperature levels as large as possible and a thermal conducting cross-section compatible with operating stresses; for compressive loads, buckling has to be avoided without enlarging the thermal cross-section;

 

(2)

using structural materials with a low ratio of thermal conductivity to strength.

 

W Elsel

Machined GRP Laminates for Components in Heavy Electrical Engineering and Their Use at Very Low Temperatures

Machined GRP Laminates for Components in Heavy Electrical Engineering and Their Use at Very Low Temperatures

Abstract

The size of components produced from machined GRP laminates varies from a few grams up to several tens of kilograms (Figs 1 and 2).

Heinz Fuchs

Mass Transport into a Three-Component Composite Subjected to a Temperature Gradient

Mass Transport into a Three-Component Composite Subjected to a Temperature Gradient

Abstract

If considered on the basis of cellular structure alone, rigid polyurethane foams (PUF) consisting entirely of closed cells are ideal materials for thermal insulation applications. However, the low load-bearing capacity of the material and the vulnerability of the cell membranes make it virtually impossible for the foam to be used on its own. Therefore, technical insulations are usually based on composites consisting of (a) a substrate, which by virtue of its superior engineering properties supports the insulant (PUF), (b) A liner, which reduces ingress of species which might damage the insulant if they were to come into contact with it, and (c) the insulant itself. Examples of such composites are the insulation panels used in the building industry.

A Cervenka

Panel Discussion

Fundamentals of Nonmetallic Materials at Low Temperatures: Panel Discussion Summary

Abstract

The purpose of the panel discussion was to review large scale applications of structural components which would be suitable for fabrication from nonmetallic materials and composites. The author was the moderator of the panel which consisted of the following members:

• G. Hartwig Karlsruhe Nuclear Research Centre, FRG
• A. Nyilas KfK, Karlsruhe, FRG
• W. Elsel Siemens AG, Erlangen, FRG
• A. Cervenka Shell Chemical, Amsterdam, Holland
• R. Schmid Ciba-Geigy AG, Basel, Suisse
• J. Schmidtchen BASF, Ludwigshafen, FRG
• W. Wicke Ruhrchemie, Oberhausen, FRG
• Mr. Hesselt Messerschmitt-Bolkow-Blohm,Ottobrunn, FRG
• H. Hacker Siemens AG, Erlangen, FRG
• R. Randolph Hercules Inc., Salt Lake City, Utah, U.S.A.

R L Kolek

Conference Summary: Fundamental Aspects and Applications of Non-Metallic Materials at Low Temperatures

Abstract

This second conference devoted entirely to the properties of non-metallic materials at low temperatures, was sponsored by the International Cryogenic Materials Conference Board. It took place in hot summer weather at the European Organisation for Nuclear Research (CERN) in Geneva on August 4–5 1980.

J T Morgan

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