Stress
How is engineering stress calculated, and what does it represent?
internal resistance of a material to deformation under applied force (F/A0)
What is engineering strain?
The deformation of a material due to stress.
What is the formula for Hooke's Law?
stress = elastic modulus * strain
(σ= Ε * ε)
What does the coefficient of thermal expansion tell us about a material?
How much it expands/contracts due to a change in its temperature (heating/cooling).
A metal wire with an original cross-sectional area of 0.5 cm² is subjected to a force of 100 N. What is the engineering stress on the wire?
100N/(5x10-5 m2)= 2x106 Pa = 2MPa
What is axial strain?
Strain to the object in the direction of the axis that the force was applied.
Which is the formula for Poisson's Law?
= -εx / εz
= -lateral strain / axial strain
How is a material’s safety factor calculated?
N = (Stressyield)/(Stressworking)
Where N is the safety factor
Is shear stress caused by forces that are parallel or perpendicular to the material’s surface?
parallel
What is the equation to find engineering strain?
Engineering strain=(ΔL)/L0
The change in length divided by the initial length.
If the Elastic modulus of a material is 200 Gpa, what is its strain when it experiences a stress of 400 Mpa?
(400*106)/(200*109) =
0.002
How is a material’s coefficient of thermal expansion calculated?
αL = (ΔL)/L0ΔT
If a constant force is applied to two wires, one with radius r and the other with radius 2r, which wire experiences a larger tensile stress, and by how much?
tensile stress in wire with radius r is 4x larger
What is the difference between axial strain and lateral strain?
Axial strain is strain to the object along the axis of the force. Lateral strain is strain orthogonal to the axis of the force.
(a) If a specimen expands axially and experiences a strain of 0.03, and has a Poisson's ratio of 0.33, what is the value of its lateral strain?
(b) if its initial diameter is 12 mm, what is the change of diameter? (△d)
(a) v * (axial) = lateral = -0.0099
(b) lateral*d0 = -0.1188 mm
If a material has a yield stress of 3000 psi, and a safety factor of 3, what is the working stress?
1000 psi