Short Definitions / Explanations
Relative Density – Relative density is the density of foam divided by the density of the solid parent material of the struts. In other words, it is the mass of real material in a block of foam compared to what it would be if it were a solid block of the same material. Typical relative densities for Duocel® foams run from about 2% to 15% depending on the material being foamed and the application. Due to the physics of small-scale structures, the majority of Duocel® foams are manufactured in the 3-10% density range. For actually foam density you would use (parentDensity x relativeDensity = foamDensity). To find Relative density use (foamDensity/parentDensity = relativeDensity).
Foam Compression – This a method in which we press the foam to reduce pore size and increase relative density beyond our normal foaming limitations
PPI – This is the amount of pores per inch of foam.
Isotropic Load Response – This is the ability of a material to have equal compression strengths no matter the direction of force
Tensile Strength – The pressure required to deform the foam when pulled in opposite directions.
Shear Strength – The pressure required to deform the foam when force is applied in a parallel direction to the foam.
Modulus of Elasticity – A description of deformation that is not permanent in a mathematical fashion
Compression – Pressure that is applied inward on an object
Tension –Pressure that is applied outward on an object
Shear Modulus – An object's tendency to shear
Vickers Hardness – The material's resistance to plastic deformation by a standardized object. The unit HV is equal to force applied over the surface area of the indent.
Specific Heat – The heat capacity per unit mass of material
Bulk Thermal Conductivity – The ability of the material to transfer thermal energy
Coefficient of Thermal Expansion – The tendency of the volume of an object to change as the temperature changes
Bulk Resistivity – The electrical resistance in ohms of a given material.
Mohs Hardness – The ability of a harder material to scratch a softer material. The unit is on a scale of 1-10 where Talc is 1 and Diamond is 10. Since this test was developed materials have been found that fall out side of this scale.
Compression Strength – The pressure required to deform the material with forces pushing inward on the object
Sublimation point – This is the temperature at a given pressure at which the material will go directly from a solid to a gas. The pressure must be below the triple point in the phase diagram for the material.
Oxidation Resistance – The ability of a material to resist the direct and indirect attack of oxygen.
Flexural Strength The ability of a brittle material to resist deformation under load.
Young’s Modulus – The stiffness of an isotropic material
Knoop Hardness – The micro hardness test that is mostly used for brittle materials or very thin sheets of ductile material
Poisson’s Ratio – Is the ratio between the contraction or expansion of a material in direction perpendicular to the force being applied over the contraction or expansion in the direction of force.
Pore – Each bubble structure in the open-celled foam generally consists of 14 reticulated windows or facets. The polygonal opening through each open window is referred to as a "pore". In any given bubble, the polygonal pores actually are of two or three different characteristic sizes and shapes, but for material designation purposes, they are simplified to an average size and circular shape. The number of these pores that would subtend one inch then designates the foam "pore size". Duocel® metal foams are generally manufactured from 5 to 40 pores per inch, while Duocel® carbon and ceramic foams are manufactured from 5 to 100 pores per inch. An average pore diameter is about 50% to 70% the diameter of its parent bubble, thus a 10 pore per inch (PPI) foam would have roughly 5 to 7 bubbles per inch.
Cell – The cell is each individual bubble. The “cell” is made up of 14 pores
Primary Foam – Standard Duocel® foams are referred to as "primary" foams. In this case, the base material to be foamed is simply resolved to a liquid state, foamed directly, and then reticulated. The resulting foam strut or ligament then consists of a solid beam of roughly triangular section that is made of the solid, homogeneous base material chosen. While there is porosity in the bubble structure due to the foaming process, there are no porosities or discontinuities within the individual ligaments.
Secondary Foam – "Secondary" foams are generally produced on custom order for special applications. These foams are made by post-processing the primary foam to upgrade it for a specific function that cannot be technically provided by the primary foam. Typical secondary foams may have an aluminum foam core (primary foam), that has been uniformly coated with platinum, as the secondary foam, for use as a high surface area catalytic reactor element. While it is technically possible to make platinum the primary foam, there would be a significant added cost of establishing new foaming equipment specifically for platinum. In addition, there would be a major cost in the platinum metal itself. Since only the surface of the platinum is functional as a catalyst, the bulk of the material in the primary platinum foam would be wasted. By using a readily available primary foam as the skeletal substrate, and applying a thin, catalytically active platinum surface coating, a high specific surface area catalyst component can be produced much more rapidly, and at a much lower development and production cost. While some secondary foams, as discussed above, are produced purely for economic reasons, others are produced, like composites, for technical purposes to combine the best characteristics of two or more materials.
Trabecular – Small rod like structure.
Cancellous Bone – Spongy bone