Charpy impact test. Method for determining behavior of materials under conditions favorable to brittle fracture. Used where results of a tension impact test would not be significant. It is the most popular impact test. Test is performed by striking a notched specimen supported as simple beam with a falling weight. Results are reported as energy absorbed in fracture and a description of the fracture. ASTM E-23 describes test for metals, ASTM A 327 for cast iron, ASTM D-256 for plastics and ASTM D-758 for plastics at subnormal and elevated temperatures.

Clash-Berg test. Method for determining stiffness of plastics as a function of temperature by a torsion test (ASTM D-1043). Test consists of direct measurements of apparent modulus of rigidity over wide temperature range.

Cleavage strength. Tensile load (lb/in. of width) required to cause separation of a 1-in. long metal-to-metal adhesive bond under the conditions set in ASTM D-1062.

Climbing drum peel test. Method for determining peel resistance of adhesive bond between a relatively flexible and rigid material. (ASTM D1781).

Coefficient of elasticity. Alternate term for modulus of elasticity.

Cohesive strength. Theoretical stress that causes fracture in tension test if material exhibits no plastic deformation.

Cold crushing strength. Load required to produce fracture in refractory bricks and shapes divided by average cross section area of specimen. (ASTM C-133).

Cold flow. Permanent deformation of plastics remaining after load applied at temperature below distortion temperature is removed. It is an alternate term for creep in plastics (ASTM D-674) and rubber (ASTM D-530).

Complex modulus. Measure of dynamic mechanical properties of material taking into account energy dissipated as heat during deformation and recovery. It is equal to the sum of static modulus of a material and its loss modulus. In the case of shear loading it is called dynamic modulus. See also damping capacity.

Compressibility. Extent to which material is compressed in test for compressibility and recovery of gasket materials (ASTM F-36). It is usually reported with recovery.

Compressibility and recovery test. Method for measuring behavior of gasket materials under short time compressive loading at room temperature. ASTM F-36 outlines a standard procedure. Test is not designed to indicate long term (creep) behavior and should not be confused with the plastometer test.

Compression-deflection test. Nondestructive method for determining relationship between compressive load and deflection under load for vulcanized rubber. (ASTM D-575). Compression fatigue. Ability of rubber to sustain repeated fluctuating compressive loads. (ASTM D-623).