6.3+ 6.4 Stress, strain and Young Modulus, deforming materials Flashcards
what is stress?
the force per unit area , ( causes deformation)
tensile stress= tensile force per area
what is strain?
how much something changes shape, compared to original length
no units
what is the relationship between stress and strain?
dircetly proprtional: where constant = young’s Modulus
what does young’s modulus represent?
the stiffness of a material
the greater the constant- the more stiff
what is ultimate tensile strength?
how much stress a material can withstand before fracture
what is an elastic limit?
The value of stress or force beyond which elastic deformation becomes plastic deformation; the material will not return to its original shape and size when the stress or force is removed
what is the gradient of a stress strain graph?
young modulus ( up until limit of proportionality has been exceeded)
what is the limit of proportionality?
The value of the stress beyond which the stress is no longer proportional to the strain
what is the yield point?
the point beyond which the material extends rapidly for a small change in stress
what does it mean for a material to be brittle?
A material that distorts very little even when subject to a large stress and does not exhibit much plastic deformation; for example, concrete or glass
what does it mean for a meterial to be ductile?
has a large plastic region and so can be drawn into a wire
what does it mean for a material to be polymeric?
it experiences a high strain before breaking
draw the stress strain graph for rubber
what does area under lines represent
X = energy stored per unit volume
what is strength?
The extent to which a material resists breaking under stress; a strong material has a high Ultimate Tensile Strength and high breaking stress
what is the force extension graph for a polythene strip?
