Testing Materials Flashcards
What is stress?
Force per unit area.
What does stress depend on?
Materials as opposed to specimen.
What is the yield stress?
The stress at which a material begins to deform plastically.
What is the breaking stress?
The stress at which a material fractures.
What is the formula for stress?
Stress (ō) = F / A
On a force-extension graph, what is happening when the graph is linear?
When the spring is stretched the extension is proportional to the force applied for a spring constant.
What’s the Hooke’s Law formula?
F = kx
What happens at the edge of the linear part of the Hooke’s Law graph? What happens when it curves?
This is the elastic limit. When the graph curves, plastic deformation takes place - a permanent response to a temporary force. This section of the graph is the plastic region.
On a Hooke’s Law graph what happens when the line cuts off?
This is the fracture point.
When you pull a spring you are applying a f….e and w…k is done on the spring. This transfers e….y which is transferred to …. energy when the force is removed.
Force, work, energy, kinetic.
What is the formula for energy transferred when Hooke’s Law applies?
E = 1/2 fx = 1/2 (kx)x = 1/2 kx^2
What does strain allow us to do?
Compare, fairly, materials of varying lengths.
What is the formula for strain?
E = x/l
G….s experiences little extension. This is because glass experiences lots of c….k propagation and little p…..c deformation. It is brittle.
Glass, crack, plastic.
In mild steel, the metal first experiences e….c deformation before reaching the p….c region where extension is u….m along the rod. The material begins to n….k where the edges become thinner until it fractures.
elastic, plastic, uniform, neck.
Why do materials get round edges when they are bended?
They are tougher and experience more plastic deformation before fracture.
What is the Young Modulus formula?
E = stress/strain = F/A / x/l
the Young Modulus is usually very l….e
Large.
Young Modulus measures …
Stiffness.
Why may the graph for Young Modulus not have a line through the origin?
Could be :
- Systematic error
- If the bottom line is for length that would be the starting length.
