| Lap joint |
A riveted, welded, or bonded connection between two plates made by overlapping one plate above the other. Lap joints having plates above and below a butt joint avoid the bending moment associated with a simple lap joint. |
| Laser hardening |
Hardening of steel by a moving CO2 or Nd:YAG laser beam focussed down to a few mm in diameter. A point in the surface of an object is rapidly heated into the austenite range and then rapidly cooled to form tempered martensite. |
| Laser hardening |
A surface-hardening process which uses a laser to quickly heat a surface. Heat conduction into the interior of the part will quickly cool the surface, leaving a shallow martensitic layer. |
| Laser sintering |
A manufacturing technique by which parts are built layer by layer (each typically 20 μm thick) from plastic or metal (Direct Metal Laser Sintering, DMLS) material in powder form, each layer being sintered by a scanning laser. |
| Latent heat |
Thermal energy absorbed or released when a substance undergoes a phase change. |
| Lathe |
A machine tool in which work, gripped in the headstock, is rotated against the cutting tool to produce turned, bored, faced, or threaded components. |
| Lead angle |
The angle of the helix of a screw thread or worm thread. It is the measure of the inclination of a screw thread from a plane perpendicular to the axis of the screw. |
| Lead of thread |
On a single threaded screw, the distance the screw or nut advances in one complete revolution. |
| Lead screw |
The master screw running along the length of the bed of a lathe from which all screws threads on that machine are cut. |
| Lead screw |
Master screw used for cutting a screw thread in a lathe. |
| Least count |
The smallest value that can be read from an instrument having a graduated scale. Except on instruments provided with a vernier, the least count is that fraction of the smallest division which can be conveniently and reliably estimated; this fraction is ordinarily one-fifth or one-tenth, except where the graduations are very closely spaced. |
| Left hand screw |
One that screws into the mating part or advances when turned to the left or counter clockwise. |
| Length of engagement |
It is the axial measurement within which the external and internal threads have theoretical contact. |
| Linear (tensile or compressive) strain |
The change per unit length due to force in an original linear dimension. An increase in length is considered positive. |
| Linear-elastic fracture mechanics |
A method of fracture analysis that can determine the stress (or load) required to induce fracture instability in a structure containing a cracklike flaw of known size and shape. |
| Liquation temperature |
The lowest temperature at which partial melting can occur in an alloy that exhibits the greatest possible degree of segregation. |
| Liquid carburizing |
Surface hardening of steel by immersion into a molten bath consisting of cyanides and other salts. |
| Liquid nitriding |
A method of surface hardening in which molten nitrogen-bearing, fused-salt baths containing both cyanides and cyanates are exposed to parts at subcritical temperatures. |
| Load |
For testing machines, a force applied to a test piece that is measured in units such as pound-force, newton, or kilogram-force. |
| Load and resistance factor design |
A design procedure developed for the AISC by the Research Council on Structural Connections. Assigns uncertainties in the strength of (i.e., resistance of) and in the service loads to be placed on a shear joint to estimate the probable strength of the joint. It is a recently defined alternative to the Allowable stress design procedure. |
| Load factor (F) |
The ratio between an increase in bolt tension and the external load which has caused the increase. |
| Load factors |
Factors reflecting the probability of an increase in load in a shear joint. Used in load and resistant factor design. |
| Load range, P |
In fatigue, the algebraic difference between the maximum and minimum loads in a fatigue cycle. |
| Load ratio, R |
In fatigue, the algebraic ratio of the minimum to maximum load in a fatigue cycle, that is, R = Pmin/Pmax. Also known as stress ratio. |
| Lobe |
The projecting part such as rotor lobe or the cam lobe. |
| Lock nut |
A nut which provides extra resistance to vibration loosening (beyond that produced by proper Preload ), either by providing some form of Prevailing torque, or, in free-spinning lock nuts, by deforming, cramping, or biting into mating parts when fully tightened. |
| Lock nut |
A type of nut that is prevented from loosening under vibration. The locking action is accomplished by squeezing, gripping or jamming against the bolt threads. |
| Lockbolt |
A fastener which bears a superficial resemblance to a bolt, but which engages a collar (instead of a nut) with annular grooves (instead of threads). The collar is swaged over the grooves on the male fastener to develop preload. |
| Locknut |
1. A thin auxiliary nut tightened against another nut to prevent loosening. 2. A single nut with special features that prevent loosening. |
| Lock-nut pipe thread |
The lock-nut pipe thread is a straight thread of the largest diameter which can be cut on a pipe. Its form is identical with that of the American or Briggs standard taper pipe thread. In general, “Go” gages only are required. These consist of a straight-threaded plug representing the minimum female lock-nut thread, and a straight-threaded ring representing the maximum male lock-nut thread. This thread is used only to hold parts together, or to retain a collar on the pipe. It is never used where a tight threaded joint is required. |
| Longitudinal direction |
The principal direction of flow in a worked metal. See also normal direction and transverse direction. |
| Low-E coating |
(low-emittance coating) A thin metallic or metal-oxide coating on a glass sheet to absorb and reflect infrared radiation. The coating is applied either by a pyrolytic chemical vapour-deposition process (hard coat), or by sputtering (soft coat). |
| Lubricant |
Any substance interposed between two surfaces for the purpose of reducing the friction or wear between them. |
| Lüders lines |
Elongated surface markings or depressions, often visible with the unaided eye, that form along the length of sheet metal or a tension specimen at an angle of approximately 45° to the loading axis. Caused by localized plastic deformation, they result from discontinuous (inhomogeneous) yielding. Also known as Lüders bands, Hartmann lines, Piobert lines, or stretcher strains. |
