Damping capacity. Measure of the ability of a material to absorb vibration by converting mechanical energy in to heat. It is equal to the area of the elastic hysteresis loop divided by the deformation energy of a vibrating material. It can be calculated by measuring the rate of decay of vibrations induced in a material. For details see "Mechanical Properties of Polymers," L. E. Niel son, Reinhold Publishing Corp.; "Nondestructive Testing," W. y. Mc Gonnagle, McGraw-Hill Book Co. and "Mechanical Testing of Materials," A. J. Fenner, Philosophical Library Inc.

Deflection temperature. Temperature at which a plastic specimen deforms a specified amount under a specified load. It is not a direct guide to the high temperature limit of a plastic for a specified application, but rather a means for comparing the relative heat resistance of plastics. (ASTM D-648).

Deformation energy. Energy required to deform a material a specified amount. It is the area under the stress-strain diagram up to a specified strain.

Deformation under load. Measure of the ability of rigid plastics to with stand permanent deformation and the ability of nonrigid plastics to return to original shape after deformation. Standard test methods for determining both types of deformation under load are given in ASTM D-621. For rigid plastics deformation (which can be flow or flow and shrinkage) is reported as % change in height of specimen after 24 hr under a specified load. For nonrigid plastics results are reported as % change in height after 3 hr under load and recovery in the 11/2 hr period following removal of the load. Recovery is % increase in height calculated on basis of original height.

Delamination strength. Measure of the node-to-node bond strength of honeycomb core materials. It is equal to the tensile load applied to a honeycomb panel at fracture divided by its width times thickness. (ASTM C-363).

De Mattia flexing machine test. Method for measuring the cracking resistance (ASTM D-430) and crack growth resistance of rubber (ASTM D-813).

Diamond pyramid hardness number (DPHN). Measure of the indentation hardness of a material. It is the amount of plastic deformation caused by a 136 deg pyramidal diamond indentor under a specified load. (ASTM E-92). Also known as Vickers hardness.

Dissipation factor. Ratio of the loss modulus to static modulus of a material under dynamic loading. It is proportional to damping capacity. An alternate term is loss tangent.

Drop ball impact test. Method for determining the energy absorption characteristics of a material subjected to shock loading. Metal ball of known weight is dropped on specimen from regularly increasing heights and height of drop, producing failure is reported. Test is used for hard metals, ceramics and plastics.

Drop weight test. Method for determining the nil-ductility transition temperature of steel. Results are reported as temperature above which specimens no longer show brittle fracture after specified shock loadings. (ASTM E-208).

Dry strength. Strength of an adhesive joint determined immediately after drying or after a period of conditioning in a specified atmosphere. (ASTM D-1144).

Ductile-to-brittle transition temperature. Indication of temperature range in which metals undergo transition from ductile to brittle behavior. It is an indication of the minimum temperature at which metals have sufficient ductility for forming. For some refractory metals ductile-to-brittle transition temperatures are well above room temperature.

Ductility. Extent to which a material can sustain plastic deformation without rupture. Elongation and reduction of area are common indices of ductility.

Du Pont flexing machine test. Method for determining the cracking resistance of rubber (ASTM D-430). Rubber specimens are mounted to a fabric base and subjected to tensile and compressive flexing until failure occurs. Results are reported as a comparison of the severity of cracking in various samples, and number of cycles required to produce specified severity of cracking in the material.

Durometer hardness. Measure of the indentation hardness of plastics and rubber. It is tze extent to which a spring loaded steel indentor protrudes beyond a pressure foot into the material. Standard procedures are given in ASTM D-1706 (plastics) and ASTM D-2240 (plastics and rubber).

Dynamic creep. Creep that occurs under fluctuating load or temperature.

Dynamic ductility test. Method for determining ductility of zinc strip or sheet. A series of cups are formed by a plunger and depth of deepest nonruptured cup is reported. (ASTM B-69).

Dynamic modulus. Complex modulus of material under dynamic shear loading. It is equal to the sum of static shear modulus and loss modulus. Dynamic modulus takes into account energy dissipated as heat when material is deformed.

Dynamic modulus, effective. Indication of the vibration absorption characteristics of elastomers. It is determined in the Yerzley mechanical oscillograph test (ASTM D-945). It is not an actual physical modulus, but an extension of dynamic modulus beyond the straight line portion of the load-deformation curve.