Chapter 3 Flashcards
Define: Engineering Stress
F/A ; the applied force divided by the original area of the object.
Define: Engineering Strain
Change in L / Original L (L = length)
Define: Modulus of Elasticity
Or Young’s Modulus; measure of the inherit stiffness of a material
Define: Yield Point
Change in slope at the end of a linear region on the stress-strain diagram .
Define: Yield Strength
Or yield stress; property of a material that indicates the stress associated with the yield point
Define: Ultimate Strength
Property of a material when the applied load reaches a maximum value of engineering stress; known as tensile strength or ultimate strength.
Define: Necking
After reaching the tensile strength, the object begins a process of localized elongation b
Which becomes concentrated in one small section of the specimen.
Define: Fracture Stress
The stress calculated just prior to failure (breaking)
Define: Ductility
Amount of strain a material can endure before failure; measured as elongation (EL) or area reduction (AR)
Define: Elongation
Measure of ductility; change in Length / original length
Define: Area Reduction
Measure of ductility; change in Area / original Area
Define: True Stress
Instantaneous stress found by dividing the applied load by the instantaneous value of area
Define: True Strain
Instantaneous strain found be dividing “instantaneous” elongation per unit length of the material
Define: Work Hardening
or Strain hardening; using strain to make a metal stronger.
Define: Flow Curve
Stress = (K) e^n ; approximation of the behavior of metals in the plastic region, including their capacity for strain hardening
Define: Strength Coefficient
“K” ; units of MPa; equals the value of true stress at a true strain value of 1.
Define: Strain Hardening Exponent
“n” = slope of the stress vs. strain graph
Define: Elastic Behavior
Behavior of material completely defined by its stiffness. Fractures rather than yielding to plastic flow.
Define: Perfectly Plastic Behavior
Once yield strength is reached, material plastically forms at constant stress level (Y=K) and n=0.
Define: Strain Hardening Behavior
Material obey’s Hooke’s law int heat after the yield strength, deformation requires ever-increasing stress so that K>Y and n>0.
Define: Barreling
Consequence of friction between surfaces in that middle of the specimen is permitted to increase in area much more than that at the ends. (compression test)
Define: Flexure Test
or Bending Test; where beam is supported by two supports and load is applied at its center. Measures bend.
Define: Torsion Test
Measures shear stress and strain by torquing a tube via twisting
Define: Hardness (Brinell, Rockwell)
Brinell - Mostly for nonmetals and metals of low to medium hardness; conducted with steel ball placing pressure on a specimen
Rockwell - More versatile and done with a cone-shaped indentor
Define: Viscoelasticity
Property of polymers that determines the strain a material will experience when subjected to combinations of stress and temperature over time.
