Beach Marks - Also known as clam shell marks. Beachmarks represent the propagation of a crack through a material due to fatigue. These marks are visible to the eye, and may contain thousands of striations.

Boundary Conditions -The properties of a system which are externally imposed on it.

Brittle Fracture - Fracture that occurs by rapid crack propogation and without appreciable macroscopic deformation.

Case Hardening - This surface treatment may be accomplishes in many ways, most likely by exposing the material to a carbonaceous or nitrogen rich environment at elevated temperatures. The carbon or nitrogen then diffuses into the surface of the material, increasing surface strength, thus increasing resistance to scratches and other surface flaws.

Dispersion Phase - The part of he composite that is inside the matrix phase. e.g., steel rods in steel reinforced concrete.

Ductile Fracture - A mode of fracture that is attended by extensive gross plastic deformation.

Element -A section of a body obtained from dividing the body up into a finite number of regions.

Fatigue Life - The number of cycles the will cause failure at a certain stress level

Fatigue Limit - A characteristic of the material and its geometry. If a material is loaded below the fatigue limit, the material will not fail, regardless of the number of cycles it is subject to.

Fatigue Strength - The stress at which failure occurs for a given number of cycles.

Fracture toughness (Kc) - the critical value in which may be used to specify the conditions for brittle fracture.

Intergranular Fracture - Fracture of polycrystalline materials by crack prorogation along grain boundaries.

K_C - The fracture toughness of a material that has thickness less than some minmum calculated value.

K_IC - The fracture toughness of a material that has thickness greater than some minmum calculated value.

Matrix Phase - The part of the composite which completely encompasses the dispersion phase. ⁵ e.g., the matrix is the conrete in steel reinforced concrete.

Mean Stress - Average stress between maximum and minimum stress. For a reversed cyclic stress the mean stress would be zero.

Mesh -The grid of a finite element system

Node -Points at which different elements are jointed together; nodes are the locations where values of unknowns (usually displacements) are to be approximated.

Plane Strain The condition, wherein, for tensile loading, there is zero strain perpendicular to both the stress axis and the direction of crack propagation; this condition is found in thick plates, and the zero-strain direction is perpendicular to the plate surface.

Plane strain fracture toughness (K1c) - The condition, wherein, for tensile loading, there is zero strain perpendicular to both the stress axis and the direction of crack propagation; this condition is found in thick plates, and the zero-strain direction is perpendicular to the plate surface.

Plane Stress - The state that a sample of material is in if a stress is applied to it and its thickness is less than some minimum value.

Plastic Deformation - Deformation that is permanent or nonrecoverable after release of the applied load. It is accompanied by permanent atomic displacements.

Porosity - A volume fraction of a material that is empty, or without material.

Repeatrd Stress Cycle - More commonly seen in engineering applications than the reversed stress cycle, the repeated stress cycle is a sine wave that is asymmetric about the x axis. The maximum and minimum stresses are NOT equal and opposite in sign.

Reversed Stress Cycle - This type of stress cycle has an amplitude symmetric about the x axis. The maximum and minimum stresses are equal, but opposite in sign.

Shot Peening - When a material is bombarded with small, round steel shot (i.e. bb's, buckshot) at high velocities, it is termed shot peening. This process will increase the resistance to fatigue failure by adding dislocations and hardening the surface, which is where a crack may begin due to surface flaws.

Stiffness Matrix -A matrix defining the geometric and material properties of a system.

Strain Hardening - The increase in hardness and strength of a ductile metal as it is plastically deformed below its recrystallization temperature.

Stress concentration (Kt) - is the measure of the degree to which an external stress is amplified at the tip of a small crack.

Stress intensity (K) - is a function of applied stress and the size and position of crack that specifies the intensity at the tip of a crack.

Striations - These markings are thought to be the advancement of a crack through a material. Unlike Beachmarks, Striations are thought to be the advancement of a crack due to one cycle of loading.

Transgranular Fracture - Fracture of polycrystalline materials by crack propagation through the grains.

Yield strength (sigma y) - is the stress at a 0.002 strain offset on the stress/strain curve of the material. Also, is the point of transition from elastic deformation to plastic deformation.