Creep Test

Y x Z section

X

RESULT

With applying load W, the specimen will sustain a stress.

At point O,

∑M = 0

500 x W = F x 50

F = 10 W

Where F = the actual load will apply on the specimen, N

Creep specimen

Y = width

Z = thickness

500 mm50 mm

Specimen

W, load

Table 1

Length, mm

Experiment 1 31.91

Thickness,

mm5.050

Width, mm 5.050

Experiment 2 28.50

Thickness,

mm5.027

Width, mm 5.027

Experiment 3 31.91

Thickness,

mm5.090

Width, mm 5.090

Experiment 4 31.60

Thickness,

mm5.084

Width, mm 5.084

Experiment 1 : ( Table 2 )

Temperature : 80 ⁰C

Load : 2 N

Time ( minute ) Deflection ( mm )

0 1.91

1 2.10

2 2.29

3 2.42

4 2.48

5 2.56

6 2.61

7 2.64

8 2.69

Calculation :

Specimen cross section area :

(A) = Y x Z

(A) = 5.050 mm x 5.050 mm

=25.50 mm²

Stress act on the specimen :

(σ) = F/A = 10 W/A

(σ) = 2N / 25.50 mm²

= 0.08 N / mm²

Creep strain:

(ϵ ) = elongation of current time / original length

= L’ / x



Load : 2 N

Time ( minute ) Deflection ( mm ) Length,L0 (mm) Creep Strain,ε

0 1.91 31.91 0.060

1 2.10 31.91 0.066

2 2.29 31.91 0.072

3 2.42 31.91 0.076

4 2.48 31.91 0.078

5 2.56 31.91 0.080

6 2.61 31.91 0.082

7 2.64 31.91 0.083

8 2.69 31.91 0.084

Time (minute ) = 0

1.91 mm / 31.91 mm = 0.060 mm

Time (minute ) = 1

2.10mm /31.91 mm = 0.066mm

Time (minute ) = 2

2.29mm / 31.91mm = 0.072 mm

Time (minute ) = 3

2.42mm / 31.91mm = 0.076 mm

Time (minute ) = 4

2.48mm / 31.91mm = 0.078 mm

Time (minute ) = 5

2.56mm / 31.91mm = 0.080 mm

Time (minute ) = 6

2.61mm / 31.91mm = 0.082 mm

Time (minute ) = 7

2.64mm /31.91 mm = 0.083 mm

Time (minute ) = 8

2.69mm / 31.91mm = 0.084mm

Modulus of elasticity :

(E) = stress / strain

= σ / ϵ

Stress, N / mm² Creep Strain,ε Modulus of elasticity, (E)

0.08 0.060 1.33

0.08 0.066 1.21

0.08 0.072 1.11

0.08 0.076 1.05

0.08 0.078 1.02

0.08 0.080 1.00

0.08 0.082 0.98

0.08 0.083 0.96

0.08 0.084 0.95

Time (minute ) = 0 Time (minute ) = 1

0.08 / 0.060 =1.33 N / mm 0.08 / 0.066 = 1.21 N / mm


0.08 / 0.072 = 1.11 N / mm 0.08 / 0.076 = 1.05 N / mm


0.08 / 0.078 = 1.02 N / mm 0.08 / 0.080 = 1.00N / mm


0.08 / 0.082 = 0.98 N / mm 0.08 / 0.083 = 0.96 N / mm

Time (minute ) = 8

0.08 / 0.084 = 0.95 N / mm



Load : 2 N


0 4.38

1 5.40

2 5.90

3 6.10

4 6.38

5 6.52

6 6.66

7 6.91

8 7.14

Calculation :


(B) = Y x Z

(B) = 5.027 mm x 5.027 mm

= 25.27 mm²


(σ) = F/A = 10 W/A

(σ) = 2N /25.27 mm²

= 0.08 N / mm²

Creep strain:


= L’ / x



Load : 2 N


0 4.38 28.50 0.154

1 5.40 28.50 0.189

2 5.90 28.50 0.207

3 6.10 28.50 0.214

4 6.38 28.50 0.224

5 6.52 28.50 0.229

6 6.66 28.50 0.234

7 6.91 28.50 0.242

8 7.14 28.50 0.251

Time (minute ) = 0

4.38 mm / 28.50 mm = 0.154 mm

Time (minute ) = 1

5.40 mm / 28.50 mm = 0.189 mm

Time (minute ) = 2

5.90 mm / 28.50 mm = 0.207 mm

Time (minute ) = 3

6.10 mm / 28.50 mm = 0.214 mm

Time (minute ) = 4

6.38 mm / 28.50 mm = 0.224 mm

Time (minute ) = 5

6.52 mm / 28.50 mm = 0.229mm

Time (minute ) = 6

6.66 mm / 28.50 mm = 0.234 mm

Time (minute ) = 7

6.91 mm / 28.50 mm = 0.242 mm

Time (minute ) = 8

7.14 mm / 28.50 mm = 0.251 mm



= σ / ϵ


0.08 0.154 0.519

0.08 0.189 0.423

0.08 0.207 0.386

0.08 0.214 0.374

0.08 0.224 0.357

0.08 0.229 0.349

0.08 0.234 0.342

0.08 0.242 0.331

0.08 0.251 0.319


0.08/ 0.154 =0.519 N / mm 0.08 /0.189 = 0.423 N / mm


0.08/0.207 = 0.386 N / mm 0.08 / 0.214 = 0.374N / mm


0.08 / 0.224 = 0.357 N / mm 0.08 / 0.229 =0.349N / mm


0.08 / 0.234 = 14.29 N / mm 0.08 /0.242=0.331 N / mm

Time (minute ) = 8

0.08 / 0.251 = 0.319 N / mm



Load : 3 N


0 2.90

1 3.55

2 4.30

3 6.10

4 6.99

5 7.30

6 7.32

7 7.34

8 7.38

Calculation :


(C) = Y x Z

(C) = 5.09 mm x 5.09 mm

= 25,91 mm²


(σ) = F/A = 10 W/A

(σ) = 3N / 25.91 mm²

= 0.12N / mm²

Creep strain:


= L’ / x



Load : 3 N


0 2.90 31.91 0.091

1 3.55 31.91 0.111

2 4.30 31.91 0.135

3 6.10 31.91 0.191

4 6.99 31.91 0.219

5 7.30 31.91 0.229

6 7.32 31.91 0.229

7 7.34 31.91 0.230

8 7.38 31.91 0.231

Time (minute ) = 0

2.90 mm / 31.91 mm = 0.091 mm

Time (minute ) = 1

3.55mm / 31.91 mm = 0.111 mm

Time (minute ) = 2

4.30 mm / 31.91 mm = 0.135 mm

Time (minute ) = 3

6.10 mm / 31.91 mm = 0.191 mm

Time (minute ) = 4

6.99 mm / 31.91 mm = 0.219 mm

Time (minute ) = 5

7.30 mm / 31.91 mm = 0.229 mm

Time (minute ) = 6

7.32 mm / 31.91 mm = 0.229 mm

Time (minute ) = 7

7.34 mm / 31.91 mm = 0.0.230 mm

Time (minute ) = 8

7.38 mm / 31.91 mm = 0.231 mm



= σ / ϵ


0.12 0.091 1.319

0.12 0.111 1.081

0.12 0.135 0.889

0.12 0.191 0.628

0.12 0.219 0.548

0.12 0.229 0.524

0.12 0.229 0.524

0.12 0.230 0.522

0.12 0.231 0.519


0.12 / 0.091 =1.319 N / mm 0.12/ 0.111=1.081 N / mm


0.12/ 0.135 = 0.889 N / mm 0.12/ 0.191 = 0.628 N / mm


0.12 / 0.219 = 0.548 N / mm 0.12 / 0.229 = 0.524 N / mm


0.12 / 0.229 = 0.524 N / mm 0.12 / 0.230 = 0.522 N / mm

Time (minute ) =

0.12 /0.231 = 0.519 N / mm



Load : 3 N


0 4.90

1 6.22

2 7.30

3 7.34

4 7.42

5 7.50

6 7.54

7 7.60

8 7.63

Calculation :


(D) = Y x Z

(D) = 5.084 mm x 5.084 mm

= 25.85 mm²


(σ) = F/A = 10 W/A

(σ) = 3N / 25.85 mm²

= 0.12 N / mm²

Creep strain:


= L’ / x



Load : 3 N


0 4.90 31.60 0.155

1 6.22 31.60 0.197

2 7.30 31.60 0.231

3 7.34 31.60 0.232

4 7.42 31.60 0.235

5 7.50 31.60 0.237

6 7.54 31.60 0.239

7 7.60 31.60 0.241

8 7.63 31.60 0.241

Time (minute ) = 0

4.90 mm / 31.60 mm = 0.155 mm

Time (minute ) = 1

6.22mm / 31.60 mm = 0.197 mm

Time (minute ) = 2

7.30 mm / 31.60 mm = 0.231 mm

Time (minute ) = 3

7.34 mm / 31.60 mm = 0.232 mm

Time (minute ) = 4

7.42 mm / 31.60 mm = 00.235 mm

Time (minute ) = 5

7.50 mm / 31.60 mm = 0.237mm

Time (minute ) = 6

7.54 mm / 31.60 mm = 0.239 mm

Time (minute ) = 7

7.60 mm / 31.60 mm = 0.241 mm

Time (minute ) = 8

7.63 mm / 31.60 mm = 0.241 mm



= σ / ϵ


0.12 0.155 0.774

0.12 0.197 0.609

0.12 0.231 0.519

0.12 0.232 0.517

0.12 0.235 0.511

0.12 0.237 0.506

0.12 0.239 0.502

0.12 0.241 0.498

0.12 0.241 0.498


0.12/ 0.155 =0.774 N / mm 0.12 / 0.197 = 0.609 N / mm


0.12/ 0.231 = 0.519 N / mm 0.12 / 0.232 = 0.517 N / mm


0.12 / 0.235 = 0.511 N / mm 0.12 / 0.237 = 0.506 N / mm


0.12 / 0.239 = 0.502 N / mm 0.12 / 0.241 =0.498 N / mm

Time (minute ) = 8

0.12 / 0.241 = 0.498 N / mm

GRAF

0 1 2 3 4 5 6 7 80

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

Creep Strain vs Time curves for exp. 1

Time(minute)

Cree

p S

trai

n

0 1 2 3 4 5 6 7 80

0.05

0.1

0.15

0.2

0.25

0.3

Creep Strain vs Time Curves for exp.2

Time(minute)

Cre

ep s

trai

n

0 1 2 3 4 5 6 7 80

0.05

0.1

0.15

0.2

0.25

Creep Strain vs Time Curves for exp.3

Time(minute)

Cree

p St

rain

DISCUSSIONS

0 1 2 3 4 5 6 7 80

0.05

0.1

0.15

0.2

0.25

0.3

Creep Strain vs Time Curves for exp. 4

Time(minute)

Cree

p S

trai

n

Creep is high temperature progressive deformation at constant stress. "High

temperature" is a relative term dependent upon the materials involved. Creep rates are used in

evaluating materials for boilers, gas turbines, jet engines, ovens, or any application that

involves high temperatures under load. Understanding high temperature behaviour of metals

is useful in designing failure resistant systems.

When a material like steel is plastically deformed at ambient temperatures its strength

is increased due to work hardening. This work hardening effectively prevents any further

deformation from taking place if the stress remains approximately constant. Annealing the

deformed steel at an elevated temperature removes the work hardening and restores the steel

to its original condition.

However, if the steel is plastically deformed at an elevated temperature, then both

work hardening and annealing take place simultaneously. A consequence of this is that steel

under a constant stress at an elevated temperature will continuously deform with time, that is,

it is said to "creep”.

To determine creep properties, material is subjected to prolonged constant tension or

compression loading at constant temperature. Deformation is recorded at specified time

intervals and a creep vs. time diagram is plotted. Slope of curve at any point is creep rate. If

failure occurs, it terminates test and Time for Rupture is recorded.

Like the Creep Test, Stress Rupture Testing involves a tensile specimen under a

constant load at a constant temperature. The difference being, Stress Rupture Testing uses

higher stresses and is always continued until failure of the material occurs. The Stress

Rupture test is used to determine the time to failure and elongation.

If specimen does not fracture within test period, creep recovery may be measured. To

determine stress relaxation of material, specimen is deformed a given amount and decrease in

stress over prolonged period of exposure at constant temperature is recorded. Standard creep

testing procedures are detailed in ASTM E-139, ASTM D-2990 and D-2991 (plastics) and

ASTM D-2294 (adhesives).

A creep test involves a tensile specimen under a constant load maintained at a

constant temperature. Measurements of strain are then recorded over a period of time. Creep

occurs in three stages: Primary, or Stage I; Secondary, or Stage II: and Tertiary, or Stage III.

Stage I, or Primary creep occurs at the beginning of the tests, and creep is mostly transiently,

not at a steady rate.

Resistance to creep increases until Stage II is reached. In Stage II, or Secondary

creep, the rate of creep becomes roughly steady. This stage is often referred to as steady state

creep. In Stage III, or tertiary creep, the creep rate begins to accelerate as the cross sectional

area of the specimen decreases due to necking or internal voiding decreases the effective area

of the specimen. If stage III is allowed to proceed, fracture will occur.

The creep test is usually employed to determine the minimum creep rate in Stage II.

Engineers need to account for this expected deformation when designing systems. A creep

test is carried out by applying a constant load to a specimen and observing the increase in

strain (or extension) with time.

Documents

Creep Test