# COMPLIANCE CONSTANT

Any one of the coefficients of the relations in the generalized Hooke's law used to express strain components as linear functions of the stress components. Also known as elastic constant.

## Related Terms

### DIELECTRIC STRENGTH

A measure of the ability of an insulating material to withstand electric stress (voltage) without failure. Fluids with high dielectric strength (usually expressed in volts or kilovolts) are good electrical insulators. (ASTM Designation D 877.)

### BULK MODULUS (OF ELASTICITY)

A ratio of normal stress to a change in volume. A term used in determining the compressibility of a fluid. Data for petroleum products can be found in the International Critical Tables.

### SCC

Stress corrosion cracking.

### POISE

A measure of viscosity (absolute viscosity) numerically equal to the force required to move a plane surface of one square centimeter per second when the surfaces are separated by a layer of fluid one centimeter in thickness. It is the ratio of the shearing stress to the shear rate of a fluid and is expressed in dyne seconds per square centimeter (DYNE SEC/CM2); 1 centipoise equals .01 poise.

### NON-NEWTONIAN FLUID

Fluid, such as a grease or a polymer-containing oil (e.g., multi-grade oil), in which shear stress is not proportional to shear rate.

### SHEAR STRESS

Frictional force overcome in sliding one layer of fluid along another, as in any fluid flow. The shear stress of a petroleum oil or other Newtonian fluid at a given temperature varies directly with shear rate (velocity). The ratio between shear stress and shear rate is constant; this ratio is termed viscosity of a Newtonian fluid, the greater the shear stress as a function of rate of shear. In a non-Newtonian fluid, such as a grease or a polymer-containing oil (e.g. multi-grade oil) - shear stress is not proportional to the rate of shear. A non-Newtonian fluid may be said to have an apparent viscosity, a viscosity that holds only for the shear rate (and temperature) at which the viscosity is determined.

### STRESS CORROSION CRACKING

Material deterioration due to cracking, by being under static stress either applied or residual.

### THERMAL SHOCK

The development of a steep temperature gradient and accompanying high stress within a material or structure.

### TENSILE STRESS

A stress that causes two parts of an elastic body, on either side of a typical stress plane, to pull apart.

### HSC

Hydrogen stress cracking.