Method for compiling equivalent acceleration spectrum of creep under variable temperatures and loads
Disclosed is a method for compiling an equivalent acceleration spectrum of creep under variable temperatures and loads. The method includes following steps: respectively carrying out a material high-temperature tensile test, material high-temperature creep tests and creep tests under two-stage variable temperatures and loads, and calculating values of a parameter p in a creep damage accumulation model under two-stage variable temperatures and loads; based on a nonlinear damage accumulation model under multi-stage variable temperatures and loads, calculating a damage D caused by a multi-stage variable temperatures and loads creep load spectrum by utilizing values of parameter p; based on the principle of consistency of damage D, transforming the multi-stage variable temperatures and loads creep load spectrum into an equivalent acceleration spectrum of a first-order maximum creep load, and finally compiling the equivalent acceleration spectrum of creep under variable temperatures and loads.
1. A method for compiling an equivalent acceleration spectrum of creep under variable temperatures and loads, comprising:
S 1 : obtaining a corresponding tensile strength σ bi at different temperatures T i through a high-temperature tensile test of materials, wherein i=1, 2, 3 . . . , n;
S 2 : obtaining a corresponding creep fracture time t fi under different stress-temperature (σ i ,T i ) combinations through high-temperature creep tests of materials;
S 3 : obtaining a creep duration t i corresponding to each stage of load through creep tests under two-stage variable temperatures and loads;
S 4 : calculating values of parameter p in the creep damage accumulation model by combining a tensile strength σ b1 and a tensile strength σ b2 obtained in S 1 , a creep fracture time t f1 and a creep fracture time t f2 obtained in S 2 and a creep duration t 1 and a creep duration t 2 obtained in S 3 based on a creep damage accumulation model under two-stage variable temperatures and loads;
wherein the creep damage accumulation model under two-stage variable temperatures and loads is
(
t
1
t
f
1
)
φ
1
,
2
+
t
2
t
f
2
=
1
,
wherein,
φ
1
,
2
=
ln
(
-
ln
(
σ
2
/
σ
b
2
)
-
p
)
/
ln
(
-
ln
(
σ
1
/
σ
b
1
)
-
p
)
;
and
S 5 : calculating a damage D caused by a creep load spectrum under multi-stage variable temperatures and loads by utilizing the values of parameter p obtained in S 4 according to a nonlinear creep damage accumulation model load under multi-stage variable temperatures and loads; converting the creep load spectrum under multi-stage variable temperatures and loads into the equivalent acceleration spectrum of a single-stage maximum creep load based on the principle of consistency of the damage D, and finally compiling the equivalent acceleration spectrum of creep under variable temperatures and loads;
wherein the nonlinear creep damage accumulation model load under multi-stage variable temperatures and loads is
D
=
(
(
(
(
t
1
t
f
1
)
φ
1
,
2
+
t
2
t
f
2
)
φ
2
,
3
+
t
3
t
f
3
)
φ
3
,
4
+
…
+
t
n
-
1
t
fn
-
1
)
φ
n
-
1
,
n
+
t
n
t
fn
,
wherein,
φ
n
-
1
,
n
=
ln
(
-
ln
(
σ
n
/
σ
b
n
)
-
p
)
/
ln
(
-
ln
(
σ
n
-
1
/
σ
bn
-
1
)
-
p
)
;
assuming a state with maximum creep load in the creep load spectrum under multi-stage variable temperatures and loads to be (σ 2 ,T 2 ), then according to the principle of the damage D equivalence represented by
D
=
(
(
(
(
t
1
t
f
1
)
φ
1
,
2
+
t
2
t
f
2
)
φ
2
,
3
+
t
3
t
f
3
)
φ
3
,
4
+
…
+
t
n
-
1
t
fn
-
1
)
φ
n
-
1
,
n
+
t
n
t
fn
=
t
equal
t
f
2
,
other states with smaller creep loads are equivalently accelerated to the state (σ 2 ,T 2 ) with maximum creep load, and a duration of the creep load spectrum of original multi-stage variable temperatures and loads could be accelerated to t equal of the equivalent acceleration spectrum of creep from t 1 +t 2 + . . . +t n , so as to compile the equivalent acceleration spectrum of creep under variable temperatures and loads.
2. The method according to claim 1 , wherein in S 1 , the high-temperature tensile test of materials is carried out on an electro-hydraulic servo fatigue tester.
3. The method according to claim 1 , wherein in S 2 , the high-temperature creep tests of materials are carried out on a creep tester, and a series of high-temperature creep tests of materials under different stress-temperature (σ i ,T i ) combinations are carried out.
4. The method according to claim 1 , wherein in S 3 , according to results of the high-temperature creep tests, the creep tests under two-stage variable temperatures and loads are carried out on a creep tester until fracture occurs, and the creep duration t i corresponding to each stage of load is recorded.
5. The method according to claim 4 , wherein in S 3 , the creep tests under two-stage variable temperatures and loads are carried out manually or by a computer to change a stress and a temperature.
6. The method according to claim 1 , wherein in S 4 , p is an average value of results obtained from multiple tests.