Materials 3: Mechanical Flashcards
Define Stress and Strain and how they are calculated.
Stress:
Pressure due to applied load. Tension, compression, shear, torsion, and their combination
Stress is calculated by the applied force divided by area.
Strain: Response of the material to stress (i.e. physical deformation such as elongation due to tension).
Strain is calculated by the extension or change to original divided by the original length of the material.
Define Elastic Deformation
Elastic Deformation means a reversible deformation once the force is removed. this non-permanent deformation where the material completely recovers to its original state upon release of the applied stress.
Define Plastic deformation
Plastic deformation is where bonds are strenched and planes shear, beyond a materials elastic limit causing a permanent deformation.
Define Poissons’s ratio
Poisson’s ratio defines how much strain occurs in the lateral direction (x and y) when strained in the (z) direction.
This is calculated by the lateral strain divided by the longitudinal strain.
Cite the primary differences between elastic, anelastic, viscoelastic, and plastic deformation behaviors
Elastic deformation is time independent and nonpermanent, anelastic deformation is time-dependent and nonpermanent, viscoelastic deformation is both instantaneous and time dependent and is not totally recoverable, while plastic deformation is permanent.
Explain the concept of ductility.
Ductility is an important mechanical property. It is a measure of the degree of plastic deformation that has been sustained
at fracture. A material that experiences very little or no plastic deformation upon fracture is termed brittle
Explain the concept of tensile strength
After yielding, the stress necessary to continue plastic deformation in metals increases to a maximum, point M in Figure below, and then decreases to the eventual fracture, point F. The tensile strength TS (MPa or psi) is the stress at the maximum on the engineering stress–strain curve . This corresponds to the maximum stress that can be sustained by a structure in tension; if this stress is applied and maintained, fracture will result. All deformation up to this point is uniform throughout the narrow region of the tensile specimen. However, at this
maximum stress, a small constriction or neck begins to form at some point, and all subsequent deformation is confined at this neck, as indicated by the schematic specimen. This phenomenon is termed “necking,” and fracture ultimately occurs at the neck. The fracture strength corresponds to the stress at fracture.
Explain the concept of elastic deformation
Deformation in which stress and strain are proportional is called elastic deformation; a plot of stress versus strain results in a linear relationship, as shown in Figure below. The slope of this linear segment corresponds to the modulus of elasticity E. This modulus may be thought of as stiffness, or a material’s resistance to elastic deformation. The greater the modulus, the stiffer the material, or the smaller the elastic strain that results from the application of a given stress. The modulus is an important design parameter used for computing elastic deflections. Elastic deformation is nonpermanent, which means that when the applied load is released, the piece returns to its original shape. As shown in the stress–strain plot , application of the load corresponds to moving from the origin up and along the straight line. Upon release of the load, the line is traversed in the opposite direction, back to the origin.
