Stress strain curve

Stress strain curve

1. Stress-strain curve
Dr. RisalahA. Mohammed

6. stress–straincurve
stress–straincurveforamaterialgivesthe
relationshipbetweenstressandstrain.Itis
obtainedbygraduallyapplyingloadtoa
testcouponandmeasuringthedeformation,
fromwhichthestressandstraincanbe
determined(seetensiletesting).These
curvesrevealmanyofthepropertiesofa
material,suchastheYoung'smodulus,
theyieldstrengthandtheultimatetensile
strength.

7. Elastic Limit
The elastic limit is the limit beyond which the material will no longer go back to its original shape when the load is
removed, or it is the maximum stress that may e developed such that there is no permanent or residual deformation
when the load is entirely removed.
Point A, This is the proportionality limit, which represents the maximum value of stress at which the
stress-strain curve is linear.

8. yield point
Yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of
plastic behavior.
Yield point is the point at which the material will have an appreciable elongation or yielding without any
increase in load.
Yieldstressishow
muchforceneedstobe
appliedtoanobjectto
causeittochangefrom
elasticdeformationto
plasticdeformation.

9. OffsetMethod
Insomematerials,thestressatwhich
thematerialchangesfromelasticto
plasticbehaviorisnoteasilydetected.
Inthiscase,theoffsetyieldstrengthis
determined.Alineisconstructed
paralleltotheinitialportionofthe
stress-straincurvebutoffsetby0.002
L/L(0.2%)fromtheorigin.The0.2%
offsetyieldstrengthisthestressat
whichtheconstructedlineintersects
thestress-straincurveasshown

10. *Oncethematerialyields,itbeginstostrain
hardenwhichincreasesthestrengthofthe
material.Inthestress-straincurvesbelow,the
strengthofthematerialcanbeseentoincrease
betweentheyieldpointYandtheultimate
strengthatpointU.Thisincreaseinstrengthis
theresultofstrainhardening.
Ultimate Strength
The maximum ordinate in the stress-strain diagram is the
ultimate strength or tensile strength.
Plasticdeformationisthepermanent
distortionthatoccurswhenamaterialis
subjectedtotensile,compressive,bending,or
torsionstressesthatexceeditsyieldstrengthand
causeittoelongate,compress,buckle,bend,or
twist.

11. Rapturestrengthisthestrengthof
thematerialatrupture.Thisisalso
knownasthebreakingstrength.
Instressstraincurvewhenthe
specimenreachesitsultimate
stressthendiameterofportion
startdecreasingbecauseoflocal
instability.Thisphenomenais
callednecking
Fracture (Rupture)Strength