Applied Strength of Materials for Engineering Technology

                             Applied Strength of Materials for Engineering Technology

Defnitions - 

• Allowable (stress, load, etc.)..............Permitted for safe design.

• Bending moment, M ........................Moment in a beam that is loaded in bending with transverse loads. 
• Bending stress, σ ..............................A normal stress along the length of a beam that develops due to transverse loading. 
• Buckling.............................................Collapse of a long, thin member under longitudinal compressive loading, at a load much lower than the load that causes yielding in tension.
• Density, ρ .........................................Mass density is the mass of an object or fluid divided by its volume. See specific weight entry for weight density. 
• Distributed load, w ...........................Force acting over a length (such as the weight of a beam) or area (such as a snow load on a roof). Compare point load.
•  Eccentricity, e ...................................Distance between the neutral axis of a part and the location of an applied point load. 
• Effective length of a column..............Portion of the length of a column that bows like a fully pinned column. 
• Elastic deformation.............................Temporary deformation; release the load and the part returns to its original shape. Compare plastic deformation.
•  Elastic modulus, E ...........................A measure of the stiffness of a material (the resistance to elastically deforming under a given load.) The slope of the linear elastic portion of the stress-strain curve. Also called Young's modulus or modulus of elasticity.
•  Euler critical buckling load, Pcr .......The load at which an ideal Euler column will fail, assuming perfect material and perfectly aligned loading.
•  Factor of Safety, F.S...........................The material's strength (typically yield strength) divided by the actual stress in the part. Also called “factor of ignorance” because it includes unknowns such as materials defects, improper installation, abuse by the operator, lack of maintenance, corrosion or rot, temperature variations, etc.
• Fillet weld...........................................A weld with a triangular cross section used for joining lapped plates. Unlike soldering or brazing, welding involves melting the base metal as well as the joining material. 
• General shear formula........................Equation for finding the shear stress within a beam of any shape. 
• Joint efficiency...................................The efficiency of a bolted or welded joint is the lowest allowable load divided by the allowable load of the weaker of the two plates some distance from the joint. 
• Longitudinal direction........................Along the length of a part, such as a beam or shaft. Compare transverse direction. 
• Longitudinal stress, σ .......................A normal stress that develops in a tensile or compressive member due to longitudinal loading. Modulus of elasticity, E ...................See elastic modulus.
•  Moment, M .......................................More accurately called a force moment, the product of a length and a transversely applied force. Used in beam problems. There are other types of moment (such as area moment: the product of a length and an area). 
• Moment of inertia, I .........................More accurately called “second moment of area”. Divide a shape into n tiny areas a, each at a distance y from the x-x centroidal axis, and sum the areas and distances as I x=∑1 n ai yi 2 . The larger the moment of inertia, the greater the bending load a beam can support, and the less bending deflection will occur. 
• Normal................................................Perpendicular, in the mathematical sense.
•  Normal stress, σ ...............................Force divided by area, when the force acts perpendicular to the area. Tensile and compressive stresses are normal stresses. 
• Plastic deformation.............................Permanent deformation; release the load and the part remains distorted. Compare elastic deformation. 
• Plastic section modulus, Z ................Sum of the first moments of areas above and below the neutral axis of a steel beam. Used for calculating bending stresses in structural steel beams. 
• Point load, P .....................................Force acting at a single point. Compare distributed load. 
• Poisson's ratio, ν ..............................A mechanical property of engineering materials equal to the negative of the transverse strain divided by longitudinal strain. A measure of how much a tensile member will thin during elastic deformation.
• Polar moment of inertia, J ................More accurately called “polar second moment of area”. Divide a shape into n tiny areas a, each at a distance r from the centroid, and sum the areas and distances as J =∑1 n ai ri 2 . The larger the polar moment of inertia, the greater the torque a shaft can support, and the less angular twist will be produced.
•  Pressure (of a fluid), p .....................Fluid equivalent of normal stress. A pressurized gas produces a uniform pressure perpendicular to the walls of the pressure vessel. A pressurized liquid produces a uniform pressure in a small pressure vessel; the pressure is nonuniform in a tall vessel due to gravity (lower pressure at the top, higher at the bottom).
•  Radius of curvature, R .....................If a beam segment is bent with a constant bending moment, the segment becomes a circular arc with a radius of curvature, R.
•  Radius of gyration, rG ......................Concentrate an area at a distance r from the x-x neutral axis. If the moment of inertia of the original area is the same as for the concentrated area, then rGx is the radius of gyration about the x-x axis. The larger the radius of gyration, the more resistant a column is to buckling. Calculate rG=√I / A . 
• Reaction moment, M A or M B ........Moment at reaction point A or B which supports a transversely loaded cantilever beam.
•  Reaction force, RA or RB ................Forces at reaction points A or B which support a transversely loaded beam. 
• Section modulus, S ...........................Moment of inertia divided by the distance from the neutral axis to the surface. The larger the section modulus, the more resistant a beam is to bending.
•  Shear modulus, G .............................The shear analog to Young's modulus: shear stress divided by shear strain in an elastic material.
•  Shear load, V ....................................Transverse load on a beam. 
• Shear plane.........................................In a bolted joint with two plates pulling in opposite directions, the shear plane is the transverse plane within a bolt that lies at the interface of the two plates.
•  Shear strain, γ ..................................Shear deflection divided by original unit length 
• Shear stress, τ ...................................Force divided area, when the force acts parallel to the area. 
• Specific weight, γ ............................Specific weight, a.k.a. weight density, is the weight of an object or fluid divided by its volume. The symbol, lower case gamma, is also used for shear strain. In this text, plain gamma means shear strain, while bold gamma means specific weight. See density entry for mass density. 
• Strain (normal), ε .............................Change in length of a material under normal load divided by initial length.
•  Stress..................................................See normal stress, shear stress, bending stress, torsional stress, longitudinal stress.
•  Stress concentration............................A locally high stress due to a sharp discontinuity in shape, such as a hole or notch with a small radius. While the overall stress in the part may be at a safe level, the stress at the discontinuity can exceed yield or ultimate strength, causing failure.
•  Tensile strength, σUTS .......................Maximum stress on the stress-strain diagram. Beyond this point, the material necks and soon breaks. 
• Thermal expansion coefficient, α ....Materials property that determines how much a material expands or contracts with changing temperature. 
• Torque, T ..........................................Rotational moment applied to a shaft. Units of moment and torque are the same (force × distance). 
• Torsion................................................Twisting of a shaft due to an applied torque. 
• Torsional stress, τ ............................A shear stress that develops in a shaft due to torsional loading. 
• Transfer distance, d ..........................Term used in calculating moment of inertia of a compound shape.
•  Transverse direction...........................Perpendicular (crosswise) to the length of a long part, such as a beam or shaft. Compare longitudinal direction.
•  Ultimate tensile strength, σUTS .........See tensile strength. 
• Yield strength, σYS ............................Below the yield strength, a material is elastic; above it, the material is plastic. 
• Young's modulus, E .........................See elastic modulus.