Fatigue failure, Flaking, Flowing, Foreign material, Forging marks, Fusion line, Fusion zone, Galling, Glazing

Tabel 2.1 i

DEFFECT	DESCRIPTION
Fatigue failure	Progressive yielding of one or more local areas of weakness such as tool marks, sharp indentation, minute cracks, or inclusions, under repeated stress. As working stress on piece is repeated, cracks develope, at ends of which there are high concentrations of stress. Cracks spread, usually from the surface or near surface, of the area. After a time, there is so little sound metal left the normal stress is higher than strength of remaining material, and it snaps. Failure is not due to crystallization of metal, as many believe. Appearance of a typical fatigue failure is easily explained. As failure proceeds, severed surfaces rubs and batter each other, crushing grains of material and producing full or smooth appearance, remaining unfractured portion preserves normal grain structure up to moment of failure. The progressive nature of the failure is usually indicated by several more or less concentric lines, the center or focus, of which discloses original point or line of failure. • Usual causes are tool marks, sharp corners, nicks, cracks, inclusions, galling, corrosions, or insufficient tightening of studs or bolts to obtain proper stretch.
Flaking	Breaking away of pieces of flated or painted surface. • Usual causes are incomplete bonding, excessive loading, or blistering.
Flowing	Spreading of a plated or painted surface. Usually accompanied by flaking. • Usual causes are incomplete bonding, excessive loading or blistering.
Foreign material	Any solid or liquid material not integral to a part. Such material may or may not be adherent to a surface or passage.
Forging marks	Ridges or grooves on the external surface of a part caused by foreign unwanted material or irregularities on the forming die.
Fusion line	Interface of the weld bead and parent metal.
Fusion zone	The weld bead formed by the melting of filler metal and parent metal, or of parent metal only.
Galling	A transfer of metal from one surface to the other of closely fetted surfaces causing damage to both surfaces. • Usual cause is severe chafing or fretting action caused during engine operation by a slight relative movement on two surfaces under high contact pressure.
Glazing	Development of a hard glossy surface on bearing surfaces. An often beneficial condition except on inner and outer races. • Usual cause is a combination of pressure, oil and heat.