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High strengtj buoyancy materials, such as syntactic foam, are required to provide buoyancy for a wide variety of deep submergence vehicles and deep ocean installations. Syntactic foam of 22pcf net buoyancy is currently variable for these applications, together with suitable quality control testing procedures. Materials of 34pcf net buoyancy are achievable based on the development of composites such as aggregates of small hollow spheres embedded in a matrix of syntactic foam.

A pressure molding technique for preparing syntactic carbon foam having high compressive strength and low bulk density (> 500 lb/in2 at 0·18 g/cm3) is described. The use of hollow phenolic resin and carbon microspheres of various types, particle size, and wall thickness, along with different carbonaceous binder materials, solvents, and molding pressures prior to coking at 900°C were some of the major variables investigated in relation to compressive strength and density characteristics of the syntactic carbon foams.

The effect of hydrostatic pressure on the mechanical behavior of a syntactic foam which is composed of glass micro-spheres embeded in epoxy resin matrix was investigated up to the high pressure of 3000kg/cm2.The behavior of the syntactic foam tested under hydrostatic pressure was typically brittle, although the matrix material behaved in a ductile manner. The tensile strength increased linearly with the increase of pressure. The increasing rate of the tensile strength with pressure was larger than that for the matrix material. However, a transition of the mechanical properties occurred around the pressure of 1500kg/cm2 and above this pressure the tensile strength dropped and the elongation value increased discontinuously. This transition phenomenon was considered to be related to the breakdown of the glass micro-spheres by hydrostatic pressure. The above trends of the behavior of syntactic foam under hydrostatic pressure were not altered by the change in volume fraction of the micro-spheres, although the transition pressure was affected a little. Penetration effect of the pressure medium used was small on the mechanical properties of the syntactic foam.

Strip-beams of molded fabric-reinforced plastic, unidirectional wound glass-reinforced plastic, and polystyrene and syntactic foam have been tested in pulse bending in a modified electrodynamic testing device. The main stages of the failure process and the nature of the relation between the peak load and the number of cycles to failure have been established. For all the materials tested these relations are similar to the cyclic strength curves obtained at low loading rates. It is shown that for glass-reinforced plastics there is a correlation between the various stages of the failure process.

A failure condition is proposed for the composite material “syntactic foam” based upon an experimental program carried out under combined biaxial and triaxial stress states. The material itself is composed of hollow glass “microspheres” embedded in an epoxy resin matrix. It exhibits finite strength under hydrostatic compression, unlike any other engineering material and thus gives rise to a closed failure surface in principal stress space. In addition to loadings corresponding to radial lines starting from the origin in stress space out to the failure envelope, other load paths were also used. Some effects due to loading and unloading and then reloading to another stress state were also investigated. Under biaxial stress states it was found that the ultimate strength of the material is sensitive to its past stress history to some degree, the reason being attributed to the initially isotropic material developing weak planes perpendicular to the compressive principal stress resulting in a “latent anisotropy.”

The capability of elastomeric ablative thermal shield materials to meet the system requirements for lifting re-entry vehicles having lift-to-drag ratios of 0.5 to 1.5 when entering the earth's atmosphere from near earth orbits is investigated. Chemically blown phenyl-methyl silicone elastomeric foams are examined and compared with a representative elastomeric syntactic foam. The thermo-mechanical compatibility, high-temperature stability, environmental resistance of the chemically-blown elastomeric foam ablative, and its resistance to ablation and degradation at the relatively low-heat-flux, long-time heating conditions of lifting re-entry vehicles, are presented. Equilibrium glide trajectories, heating environments, and shear forces are shown for representative re-entry conditions. Ablation-insulation material weights are calculated from experimental data. A structural weight tradeoff is made for aluminum and titanium sheet-stringer construction. The extreme low temperature capability and compatibility of the chemically-blown phenyl methyl silicone elastomeric foam with metal structures are examined for temperatures of — 290°F. Fabrication and attachment methods are discussed.

A failure condition recently proposed for the composite material syntactic foam is applied to the inhomogeneous state of stress which occurs in a layered sphere exposed to external pressure. The sphere is composed of syntactic foam which surrounds an assumed perfectly elastic hollow inclusion of higher strength than the syntactic foam. In addition to the establishment of the stress level at which the syntactic foam begins to crush, an analysis similar to that of perfect plasticity theory is carried out to find the ultimate collapse pressure of the syntactic foam. The results are found to compare favorably with experimental data. This problem is of importance in the further development of buoyancy materials for deep submergence vehicles.

The mechanical behavior of three kinds of organic foams, each at two different densities, was experimentally investigated under conditions of pulsed one-dimensional strain shock loading. The input pulse width in each experiment was nominally 0.1 μsec, and the input stress level (as referenced to quartz) was varied between 10 and 23 kbar. The materials studied were polyurethane foam at bulk densities of 0.33 and 0.21 g/cc, syntactic foam (phenolic microballoons dispersed in a resin binder) at 0.66 and 0.23 g/cc, and polystyrene bead foam at 0.091 and 0.049 g/cc. Specimen thicknesses varied between 1.0 and 6.5 mm. It was found that the pulse duration was greatly lengthened and that the peak stress was decreased (accounting for both impedance mismatch and attenuation effects) by factors of between about 8 and 500, depending upon the type of foam, its thickness, and its density.

Most deep submersible vehicles make use of a buoyancy material known as syntactic foam. This material is a composite made up of closely packed hollow glass microspheres embedded in a resin matrix. Typically the microspheres have diameters in the range 50–150μ. They are relatively expensive to manufacture and it is principally their cost which determines the cost of the syntactic foam. The ash from generating stations which burn pulverized coal contains a small proportion of hollow glassy microspheres, known as cenospheres, and these have about the right size distribution for use in syntactic foam. The ash disposal method used in certain British generating stations is such that the cenospheres can readily be collected as a useful lightweight product. Some preliminary pressurization experiments on a syntactic foam made with cenospheres have been carried out and these suggest that cenospheres will probably perform as well as the manufactured microspheres for at least some applications.

Syntactic foam is a composite light weight material consisting of a low density hollow microsphere filler embedded in a resin matrix. The resulting curved material is a solid which was either cast or machined into the desired shape. Syntactic foams have a wide variety of buoyancy and structural applications in the deep ocean where light weight, high strength and resistance to water absorption are important criteria. The physical properties of a family of syntactic foam materials as well as variables which permit foam properties to be adjusted to meet specific requirements are analyzed. The behavior of syntactic foam under hydrostatic exposure and its stability after exposure are reported. Nondestructive (NDT) test procedures for quality control and estimated material costs are reviewed.

The use of foams or porous solids in a variety of applications such as energy absorbers. buoyancy materials, etc. has renewed interest in the accurate representation of the properties of these materials. In particular, a “compressive constitutive law” or equation of state is needed in the calculation of the dynamic response of the material to suddenly applied loads. Static testing to provide such data is appealing because of its simplicity; however, the importance of rate effects cannot be determined bv this one method alone. Therefore, additional but numerically limited elevated strain-rate tests must be run for this purpose.

This paper deals with three major problems in packaging a complex logic module: mechanical layout; interconnection techniques; and encapsulation. The first two sections independently consider mechanical layout and interconnection techniques. The third section combines information from the first two, and derives a method for design evaluation. The fourth and final section develops and applies encapsulation methods.

Hollow glass spheres, 10 inches in diameter, were exposed to implosions of nearby spheres at 7,000, 10,000, and 21,000 ft depths in the ocean. Coatings of butyl and neoprene rubber, and syntactic foam increased the damage resistance at depth slightly; no significant differences among the three coatings nor between 1/2-inch and 1-inch thicknesses were found. Liminted data indicate that resistance to implosions increases with depth.

This work has been carried out under Contract Nonr-3484(00), NR 260-107 with the Office of Naval Research.

The sound velocity of 16 plastics, two low‐sound‐velocity elastomers, and three types of syntactic foam have been measured at a frequency of 500 kHz in the temperature range 0°–30°C. Sound velocity values in the range 872–2836 m/sec and thermal coefficient of sound velocity in the range −0.93 to −9.55 m/sec°C are reported.