RESULT 50 mm
500 mm
Specimen W, load
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
X Y x Z section
Creep specimen Y = width Z = thickness
Table 1
Length, mm Thickness,
31.91
Experiment 1
28.50
Experiment 2
31.91
Experiment 3
31.60
Experiment 4
mm Width, mm Thickness, mm Width, mm Thickness, mm Width, mm Thickness, mm Width, mm
5.050 5.050 5.027 5.027 5.090 5.090 5.084 5.084
Experiment 1 : ( Table 2 )
Temperature : 80 ⁰C Load : 2 N Time ( minute )
Deflection ( mm )
0 1 2 3 4 5 6 7 8
1.91 2.10 2.29 2.42 2.48 2.56 2.61 2.64 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 Experiment 1 : ( Table 3 ) Temperature : 80 ⁰C Load : 2 N Time ( minute ) 0 1 2 3 4 5 6 7 8
Deflection ( mm ) 1.91 2.10 2.29 2.42 2.48 2.56 2.61 2.64 2.69
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
Length,L0 (mm) 31.91 31.91 31.91 31.91 31.91 31.91 31.91 31.91 31.91
Creep Strain,ε 0.060 0.066 0.072 0.076 0.078 0.080 0.082 0.083 0.084
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 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08
0.060 0.066 0.072 0.076 0.078 0.080 0.082 0.083 0.084
1.33 1.21 1.11 1.05 1.02 1.00 0.98 0.96 0.95
Time (minute ) = 0 0.08 / 0.060 =1.33 N / mm Time (minute ) = 2 0.08 / 0.072 = 1.11 N / mm
Time (minute ) = 4 0.08 / 0.078 = 1.02 N / mm
Time (minute ) = 1 0.08 / 0.066 = 1.21 N / mm Time (minute ) = 3 0.08 / 0.076 = 1.05 N / mm
Time (minute ) = 5 0.08 / 0.080 = 1.00N / mm
Time (minute ) = 6
Time (minute ) = 7
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
Experiment 2 : ( Table 4 )
Temperature : 100 ⁰C Load : 2 N
Time ( minute )
Deflection ( mm )
0 1 2 3 4 5 6 7 8
4.38 5.40 5.90 6.10 6.38 6.52 6.66 6.91 7.14
Calculation :
Specimen cross section area :
(A) = Y x Z
(A) = 5.027 mm x 5.027 mm
= 25.27 mm² Stress act on the specimen : (σ) = F/A = 10 W/A
(σ) = 2N /25.27 mm² = 0.08 N / mm²
Creep strain:
(ϵ) = elongation of current time / original length
= L’ / x Experiment 2 : ( Table 5 ) Temperature : 100 ⁰C Load : 2 N Time ( minute ) 0 1 2 3 4 5 6 7 8
Deflection ( mm ) 4.38 5.40 5.90 6.10 6.38 6.52 6.66 6.91 7.14
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
Length,L0 (mm) 28.50 28.50 28.50 28.50 28.50 28.50 28.50 28.50 28.50
Creep Strain,ε 0.154 0.189 0.207 0.214 0.224 0.229 0.234 0.242 0.251
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
Modulus of elasticity :
(E) = stress / strain =σ/ϵ Stress, N / mm²
Creep Strain,ε
Modulus of elasticity, (E)
0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08
0.154 0.189 0.207 0.214 0.224 0.229 0.234 0.242 0.251
0.519 0.423 0.386 0.374 0.357 0.349 0.342 0.331 0.319
Time (minute ) = 0
Time (minute ) = 1
0.08/ 0.154 =0.519 N / mm Time (minute ) = 2 0.08/0.207 = 0.386 N / mm
Time (minute ) = 4 0.08 / 0.224 = 0.357 N / mm Time (minute ) = 6 0.08 / 0.234 = 14.29 N / mm
0.08 /0.189 = 0.423 N / mm Time (minute ) = 3 0.08 / 0.214 = 0.374N / mm
Time (minute ) = 5 0.08 / 0.229 =0.349N / mm Time (minute ) = 7 0.08 /0.242=0.331 N / mm
Time (minute ) = 8 0.08 / 0.251 = 0.319 N / mm
Experiment 3 : ( Table 7 )
Temperature : 80 ⁰C Load : 3 N Time ( minute )
Deflection ( mm )
0 1 2 3 4 5 6 7 8
2.90 3.55 4.30 6.10 6.99 7.30 7.32 7.34 7.38
Calculation :
Specimen cross section area :
(A) = Y x Z
(A) = 5.09 mm x 5.09 mm
= 25 ,91 mm² Stress act on the specimen : (σ) = F/A = 10 W/A
(σ) = 3N / 25.91 mm² = 0.12 N / mm²
Creep strain:
(ϵ) = elongation of current time / original length = L’ / x Experiment 3 : ( Table 8 ) Temperature : 80 ⁰C Load : 3 N Time ( minute ) 0 1 2 3 4 5 6 7 8
Deflection ( mm ) 2.90 3.55 4.30 6.10 6.99 7.30 7.32 7.34 7.38
Time (minute ) = 0 2.90 mm / 31.91 mm = 0.091 mm
Time (minute ) = 1
Length,L0 (mm) 31.91 31.91 31.91 31.91 31.91 31.91 31.91 31.91 31.91
Creep Strain,ε 0.091 0.111 0.135 0.191 0.219 0.229 0.229 0.230 0.231
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
Modulus of elasticity :
(E) = stress / strain =σ/ϵ Stress, N / mm²
Creep Strain,ε
Modulus of elasticity, (E)
0.12 0.12 0.12 0.12 0.12 0.12 0.12
0.091 0.111 0.135 0.191 0.219 0.229 0.229
1.319 1.081 0.889 0.628 0.548 0.524 0.524
0.12 0.12
0.230 0.231
Time (minute ) = 0 0.12 / 0.091 =1.319 N / mm Time (minute ) = 2 0.12/ 0.135 = 0.889 N / mm
Time (minute ) = 4 0.12 / 0.219 = 0.548 N / mm Time (minute ) = 6 0.12 / 0.229 = 0.524 N / mm
0.522 0.519 Time (minute ) = 1 0.12/ 0.111=1.081 N / mm Time (minute ) = 3 0.12/ 0.191 = 0.628 N / mm
Time (minute ) = 5 0.12 / 0.229 = 0.524 N / mm Time (minute ) = 7 0.12 / 0.230 = 0.522 N / mm
Time (minute ) = 0.12 /0.231 = 0.519 N / mm
Experiment 4 : ( Table 9 )
Temperature : 100 ⁰C Load : 3 N Time ( minute )
Deflection ( mm )
0 1 2 3 4 5 6 7 8
4.90 6.22 7.30 7.34 7.42 7.50 7.54 7.60 7.63
Calculation :
Specimen cross section area :
(A) = Y x Z
(A) = 5.084 mm x 5.084 mm
= 25.85 mm²
Stress act on the specimen : (σ) = F/A = 10 W/A
(σ) = 3N / 25.85 mm² = 0.12 N / mm²
Creep strain:
(ϵ) = elongation of current time / original length = L’ / x Experiment 4 : ( Table 10 ) Temperature : 100 ⁰C Load : 3 N Time ( minute ) 0 1 2 3 4 5 6 7 8
Deflection ( mm ) 4.90 6.22 7.30 7.34 7.42 7.50 7.54 7.60 7.63
Time (minute ) = 0 4.90 mm / 31.60 mm = 0.155 mm
Length,L0 (mm) 31.60 31.60 31.60 31.60 31.60 31.60 31.60 31.60 31.60
Creep Strain,ε 0.155 0.197 0.231 0.232 0.235 0.237 0.239 0.241 0.241
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 Modulus of elasticity :
(E) = stress / strain =σ/ϵ Stress, N / mm²
Creep Strain,ε
Modulus of elasticity, (E)
0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.12
0.155 0.197 0.231 0.232 0.235 0.237 0.239 0.241 0.241
0.774 0.609 0.519 0.517 0.511 0.506 0.502 0.498 0.498
Time (minute ) = 0 0.12/ 0.155 =0.774 N / mm Time (minute ) = 2 0.12/ 0.231 = 0.519 N / mm
Time (minute ) = 4 0.12 / 0.235 = 0.511 N / mm Time (minute ) = 6 0.12 / 0.239 = 0.502 N / mm Time (minute ) = 8 0.12 / 0.241 = 0.498 N / mm
Time (minute ) = 1 0.12 / 0.197 = 0.609 N / mm Time (minute ) = 3 0.12 / 0.232 = 0.517 N / mm
Time (minute ) = 5 0.12 / 0.237 = 0.506 N / mm Time (minute ) = 7 0.12 / 0.241 =0.498 N / mm
GRAF
DISCUSSIONS 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.
