CHap 2-Tensile Testing

8/16/2019 CHap 2-Tensile Testing

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Chap : 2

Tensile Test


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Introduction

• Tensile properties are used in selecting

materials for various applications.

• Tensile properties are also used inresearch and development to compare

new materials or processes.• tensile stress–strain curves can be used

to predict a

material’s behavior under forms of loading


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Introduction

• Tensile Test permit todetermine

–Strength

–Ductilit

– Toughness

–!lastic "odulus

–Strain#hardening capabilit


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Introduction

• The level of stress that causesappreciable

plastic deformation of a material iscalled its ield stress

• The ma$imum tensile stress that amaterial carries is called its tensilestrength %or ultimate strength orultimate tensile strength&

• Ductilit is a measure of how much

the material can deform before it


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Tensile Specimens


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"echanical Testing "achine


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Stress–Strain Curve


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–'inear elastic: elongation in thespecimen that is proportional tothe applied load.

–!ngineering stress: the ratio of theapplied load () to the originalcross#sectional area) *o) of the

specimen.

• !ngineering stress e+uation: , -(*o

• !n ineerin strain e uation: e -


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•

/ield Stress: the stress at which permanent%plastic& deformation occurs.

• (ermanent %plastic& deformation: stressand strain are no longer proportional.

• 0ltimate tensile strength %0TS&: thema$imum engineering stress.

• If the specimen is loaded beond its 0TS it

begins to 1nec.3• 4racture stress: the engineering stress at

fracture.


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• "odulus of elasticit: ration of stressto strain in the elastic region. – "odulus of elasticit e+uation: ! - ,e

• This linear relationship is nown as5ooe’s 'aw.

• (oisson’s 6atio: the ratio of thelateral strain to the longitudinalstrain.


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True#Stress and True#Strain

• True#stress: ratio of the load) () tothe instantaneous cross#sectionalarea) *) of the specimen.

• True#strain: the sum of all theinstantaneous engineering strains. – True#stress e+uation: , - (*

– True#strain e+uation: e - ln%llo&


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Ductilit

• Ductilit: e$tent of plasticdeformation that the material

undergoes before fracture.• Two measures of ductilit:

– Total elongation: %lf #lo&lo $ 7889

–6eduction of *rea: %*o#*f &*o $7889


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Temperature !ects

*s temperatureincreases:

Ductilit andtoughnessincrease.

/ield stressand themodulus of

elasticit


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!ect of Strain 6ate on0ltimate Tensile Strength

*s the temperature

increases) theslopes of the curvesincrease; thus)strength becomes

more and moresensitive to strainrate astemperatureincreases


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Sample problem 7


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Sample problem 2

• 4orce and length change data are given intable below for the tension test of *ISI


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solution


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Sample problem A


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Sample problem B

!ngineering stress–strain data from a tension teston *ISI B7B8 steel tempered at 28BC %B884&are listed in Table below. The diameter beforetesting was ?.>7 mm) and after fracture theminimum diameter in the neced region was ?mm.

Determine the following:

!lastic modulus) 8.29 oset ield strength)ultimate tensile strength) percent elongation)and percent

reduction in area.


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Sample problem B


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Sample problem =

Stress–strain data are plotted in 4ig. below for the initialportion of a tension test on *ISI B7B8 steel temperedat =AC %78884&. Eote that data points * and F arelabeled with their stress–strain coordinates.

)a(Determine the elastic modulus E.)b(If a bar of this material 100mm long is

strained to point A and then unloaded, what isits length at point A and also after unloading

)c(If a sample of this material is strained to point B andthen unloaded, what is the plastic (permanent) strain thatremains after unloading?


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Sample (roblem =


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Sample (roblem >• 4orce and length change data are given in Table

below for the initial portion of a tension test on*ISI B7B8 steel tempered at =AC %78884&.

The diameter before testing was ?.77 mm) andthe gage length 'i for the length change

measurement was =8 mm.(a) Calculate corresponding values of

engineering stress and display thesevalues on a stressstrain plot!

(b) Calculate corresponding values of Truestress and strain!

)c(Determine the yield strength for a plastic strainoset of 0.002, that is, 0.2%, and percent

elongation percent reduction in area.


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Sample (roblem >

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CHap 2-Tensile Testing