Chapter 3: Key Terms

toughness

The energy absorbed (as by the helmet) up to the failure point on the stress-strain diagram is the __ of the material.

Mechanical properties

__ are a subgroup of physical properties. Mechanical properties describe a material's ability to resist forces. Mechanical properties are dependent on the amount of material and on the size and shape of the object. Examples are strength and stiffness.

Physical properties

__ are based on the laws of physics that describe mass, energy, force, light, heat, electricity, and other physical phenomena.

Shear

__ (slip) stress occurs when parts of an object slide by one another. For example, if the front and back covers of a book are pushed in opposite directions, the pages slide or "shear" by each other.

Wetting

__ a surface with an adhesive material, such as a sealant, brings the material into intimate association with the surface so that chemical and micromechanical bonding can occur.

force

A __ is a weight or load applied to an object.

load

A force is a weight or __ applied to an object.

ultimate tensile strength

If the test is a tensile test, it is then called the __.

plastic deformation

If we take all the charms off the spring, the spring does not return to its original length. It has become permanently stretched out. This condition is termed __ or permanent deformation.

shade guide

In dentistry, esthetic materials have their own set of color tabs or shades, called a __.

abrasion resistance

In dentistry, we are interested in the __(wear resistance) of dental restorations to food, opposing teeth, and other dental materials such as ceramic crowns or porcelain denture teeth.

ultimate compressive strength

Likewise, if the test is a compressive test, it is then called the __.

fatigue

Many things fail after being stressed repetitively for a long time, and such failure is called __.

galvanic shock

Occasionally, a new amalgam filling will hurt when it is touched with a metal fork. This __ is the result of electricity flowing from the fork to the amalgam and through the pulp.

elasticity

Scientists and engineers have extensively investigated this phenomenon of change in shape and return to the original shape. This phenomenon is called __.

water sorption

Some materials absorb water. This property is termed __.

stress concentration

Stress increases around defects. This phenomenon is called __.

resilience

Such an ability to absorb energy and not become deformed is called __.

coefficient of thermal expansion

The __ is a measure of this change in volume in relation to the change in temperature.

heat of vaporization

The __ is the amount of energy required to boil a material.

heat of fusion

The __ is the amount of energy required to melt a material.

heat capacity

The __ of a material is a measure of the amount of thermal energy that a material can hoard.

viscosity

The __ of a material is its ability to flow.

specific heat capacity

The __ of a material is the amount of energy needed to raise the temperature of one unit of mass of that material by 1°C.

density

The amount or mass of a material in a given volume is the __ of the material.

elastic limit

The point on the stress-strain plot at which the line starts to curve and plastic deformation begins is called the __, the proportional limit, or the yield point,

percolation

The process of heating and cooling, and the accompanying opening and closing of the gap, is called __.

modulus of elasticity

The proportionality constant, or the slope of a graph of stress versus strain, is called the __, or Young's modulus: modulus of elasticity = stress/strain

elastic deformation

When a stress is removed and the object returns to its original length, the initial change in length is called __.

ultimate strength

We have exceeded the strength of the spring. The stress at that point is called the __.

Bending

__ is a common stress and is actually a combination of several types of stresses, as illustrated in Figure 3.6. When an object is bent, one side is compressed, but the opposite side is stretched. In addition to these compressive and tensile forces, shear forces also occur inside the object. A variety of bending tests are used to examine the ability of materials to resist bending.

Color

__ is a complex phenomenon that is a psychological response to a physical stimulus. The physical stimulus is the light reaching the rods and cones of the eye.

Vapor pressure

__ is a measure of a liquid's tendency to evaporate and become a gas.

Fracture toughness

__ is a measure of the energy required to fracture a material when a crack is present.

Poisson's ratio

__ is a mechanical property that is the ratio of the strain in the direction of the stress to the strain in a direction perpendicular to the stress.

Hardness

__ is a property that is measured by scientific instruments that press a special tip into the surface of the test material.

Tension

__ is a pulling stress.

Stress relaxation

__ is similar to creep. Both occur slowly, over time. Creep is a slow change in shape, but stress relaxation is a slow decrease in force over time.

Solubility

__ is the amount of a material that dissolves in a liquid, such as water.

Strain

__ is the change in length divided by the original length.

Stress

__ is the load (force) divided by the cross-sectional area of the object:

Thermal conductivity

__ is the rate of heat flow through a material.

Creep

__ is the small change in shape that results when an object is under continuous compression.

Biologic properties

__ of materials are the effects the materials have on living tissue. For example, a crown should not irritate the gingiva, tongue, or buccal mucosa.

Torsion

__ stress is a twisting force. Turning a doorknob is an example of a torsional stress.

Compression

is a pushing or crushing stress.

Goldilocks principle

not too hard, not too soft, just right.