3.4.2 - Materials Flashcards
What is the stiffness of a spring also known as?
the spring constant, k
How to find k from a force-change in length graph?
the gradient (up to a limit)
How to find energy stored by a string from force-change in length graph?
the area
What is the limit on a force-length graph?
the plastic deformation,, the point at which the spring cannot go back to its original length
what is the stiffness of multiple springs in parallel?
the force applied will be shared between them, so the combination will extend less
What does the stiffness of a metal wire depend on?
the cross-sectional area
its length
the material it is made out of
What is stress measured in?
N/m^2 or Pa
what is the stiffness of multiple springs in series?
The tension/ force will be the same across each spring, so each spring will extend as much as one spring alone,, the total extension will be bigger, meaning it is less stiff
How to work out the Young’s Modulus of a stress-strain graph?
Use the values of stress and strain at the limit of proportionality
What is the elastic limit also called?
the yield point
What is the equation for the ultimate tensile stress/ strength?
Fmax/ Area
What does the stress-strain graph for a ductile metal look like?
straight line until it hits the limit of proportionality, with elastic deformation followed by plastic deformation
What does the stress-strain graph for a brittle/ amorphous material (e.g. glass) look like?
some elastic deformation then it quickly fractures
What does the stress-strain graph for a polymeric material (e.g. rubber) look like?
the gradient increases,, it deforms a lot as long chain molecules untangle, then it becomes much stiffer as the straightened chains are very strong
