CN107977544B - Elastic strain calculation method and system for constraint test piece in temperature-stress test - Google Patents

Elastic strain calculation method and system for constraint test piece in temperature-stress test Download PDF

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CN107977544B
CN107977544B CN201711138839.1A CN201711138839A CN107977544B CN 107977544 B CN107977544 B CN 107977544B CN 201711138839 A CN201711138839 A CN 201711138839A CN 107977544 B CN107977544 B CN 107977544B
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elastic strain
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赵志方
金瑞鑫
赵志刚
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Zhejiang University of Technology ZJUT
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    • G01—MEASURING; TESTING
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    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
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    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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Abstract

The invention provides a method for calculating elastic strain of a constraint test piece in a temperature-stress test, which comprises the following steps of: a: obtaining the reset elastic strain generated by the chuck reset test piece in the reset elastic phase through a testing machine; b: calculating equivalent elastic strain caused by the development of internal stress in the reset interval time period of the equivalent elastic phase by an equivalent elastic strain calculation method; c: and (4) combining the reset elastic strain obtained in the step (A) and the equivalent elastic strain obtained in the step (B) to obtain the elastic strain of the concrete in a recovery period by an elastic strain calculation method in the recovery period, and then accumulating the elastic strains in the recovery periods to obtain the elastic strain of the constraint test piece. The invention also comprises an elastic strain calculation system in the temperature-stress test by using the method. The invention has the advantages of simple structure, accurate test result, wide applicability and the like.

Description

Elastic strain calculation method and system for constraint test piece in temperature-stress test
Technical Field
The invention belongs to the field of temperature-stress tests, and particularly relates to a method and a system for calculating elastic strain of a constraint test piece in a temperature-stress test.
Background
Concrete cracking sensitivity analysis and cracking risk evaluation have been the hot issues of concern in the concrete science research and engineering community. The cracking problem of mass concrete and modern high-performance concrete of large-scale water conservancy and hydropower projects, ports and docks, high-speed railways, bridges, nuclear power projects, wind power projects and the like has a crucial influence on the durability, structural safety and economy of the projects.
In the past 40 years, a great deal of results have been obtained in the evaluation and study of concrete cracking resistance by a temperature-stress test method, in relation to cracking caused by temperature stress of mass concrete.
The first domestic temperature stress tester (TSTM-CI) was developed earlier by the development of foreign temperature stress testers, until 2002 in China, based on the principle of the second-generation uniaxial constraint device, by the ancestor of the culture media of the university of Qinghua and the Linshihai, and the tester basically meets the indexes of a prototype on various performances and shows good performance in the aspects of measuring constraint deformation and constraint stress. A temperature stress tester closed-loop measurement and control system (TSTM-CII) is developed on the basis of TSTM-CII by billows, and a plurality of groups of thermal and mechanical models are established through temperature stress tests. On the basis, the Wuhan university of science and technology develops a humidity-controllable system which can supplement the water loss caused by wind heat and wind cold to the concrete.
In the temperature-stress test based on the domestic temperature-stress tester, the elastic strain of the main test piece (constraint test piece) given by the system is found to be obviously smaller, and the creep-shrinkage ratio obtained according to the elastic strain is even as high as 0.98, and obviously deviates from the normal range value.
Disclosure of Invention
The invention provides a high-accuracy method and a high-accuracy system for calculating the elastic strain of a constraint test piece in a temperature-stress test, aiming at overcoming the defects in the prior art.
The invention obtains the correct elastic strain of the constraint test piece in the temperature-stress test so as to determine the creep of the concrete. The invention provides a method and a system for calculating elastic strain in a temperature-stress test, which improve the calculation accuracy on the basis of data such as age, free strain, motor running times, real-time displacement and the like of concrete measured in the temperature-stress test.
In order to achieve the purpose, the invention adopts the following technical scheme:
the elastic strain calculation method in the temperature-stress test comprises the following steps:
a: obtaining the reset elastic strain generated by the reset of the chuck in the reset elastic phase through a testing machine;
b: calculating equivalent elastic strain caused by the development of internal stress in the reset interval time period of the equivalent elastic phase by an equivalent elastic strain calculation method;
c: and (4) combining the reset elastic strain obtained in the step (A) and the equivalent elastic strain obtained in the step (B) to obtain the elastic strain of the concrete in a recovery period by an elastic strain calculation method in the recovery period, and then accumulating the elastic strains in the recovery periods to obtain the elastic strain of the constraint test piece.
In the elastic strain calculation method of the temperature-stress test, the step a and the step B may be performed synchronously or in an alternative order;
in the above method for calculating elastic strain in the temperature-stress test, in step a, the method for obtaining the return elastic strain of the testing machine is as follows:
at t by a reset elastic strain calculation method according to a stepping motor1’-t1The displacement generated by resetting in the resetting elastic stage of (2) is used for obtaining the resetting elastic strain.
In the elastic strain calculation method of the temperature-stress test, the reset elastic strain calculation method is a formula (i), namely
m1＝n/L①
Wherein, n: test piece at t1’-t1A reset limit value in the reset elasticity phase;
l: the effective length of the test piece;
m 1: at t1’-t1The strain generated by the resetting of the chuck in the resetting elastic stage is the resetting elastic strain.
In the above elastic strain calculation method for the temperature-stress test, in step B, the equivalent elastic strain calculation method includes the steps of: determining the elastic modulus of the concrete according to the equivalent age of the concrete, and then increasing the constraint stress according to the equivalent elastic stage, namely t2Stress value at time point minus t1' the constraint stress increase value obtained from the stress value at the time point is divided by the average elastic modulus at this stage to obtain the equivalent elastic strain, wherein,
t2-t1representing a reset interval time within a reply period;
t1’-t1partially indicating the elastic step of returnA segment;
t2-t1the' section represents the equivalent elastic phase.
In the elastic strain calculation method of the temperature-stress test, a concrete method for determining the elastic modulus of the concrete according to the equivalent age of the concrete comprises a formula II; namely:
Figure BDA0001471061290000031
wherein t is0: initial setting time;
te: an equivalent age;
Ect,n: tensile elastic modulus for n days;
nE: a coefficient characterizing the development of tensile elastic modulus;
s: a constant.
In the elastic strain calculation method of the temperature-stress test, the calculation method of the equivalent age of the concrete is a formula (iii), and the calculation method of the equivalent age after discretization is a formula (iv), that is:
Figure BDA0001471061290000032
Figure BDA0001471061290000041
wherein, teIs the equivalent age, h; t (tau) is the curing temperature history of the concrete, DEG C; t isiI, the corresponding curing temperature at the moment is in DEG C; Δ ti-a time interval; r is an ideal gas constant, and R is 8.314J/(mol K); eaKJ/mol is the apparent activation energy.
When T is more than or equal to 20 ℃, Ea(T)/R＝Ar；
T<At 20 ℃ Ea(T)/R＝Ar+Br(20-T)
In the formula, ArAnd BrAs parameters, obtained by experiment. The research result shows that the activation energy of the cement hydration reaction is 0 toApproximately constant between 100 c. Without experimental data, it can be assumed that the apparent activation energy of the concrete is about 33.5 KJ/mol.
In the above-mentioned method for calculating elastic strain in temperature-stress test, in step C, the method for calculating elastic strain in recovery period is represented by the formula (v), that is
S＝m1+e1 ⑤
Wherein, S: elastic strain of the concrete in one recovery period;
m 1: resetting elastic strain;
e 1: equivalent elastic strain.
The invention relates to an elastic strain calculation system in a temperature-stress test, which comprises a test system which is connected with a test piece template and has data processing and storage functions, wherein the test system comprises a parameter input module, a reset elastic strain calculation module and an equivalent elastic strain calculation module which are all connected with a recovery period elastic strain calculation module, the recovery period elastic strain calculation module is also connected with the test piece elastic strain calculation module, and the test system comprises a test piece template, a reset elastic strain calculation module and an equivalent elastic strain calculation module, wherein:
and (3) test piece template: the testing machine system is used for obtaining the elastic strain of the test piece after the prepared concrete is poured in the testing machine system;
a parameter input module: for inputting predetermined parameters;
the reset elastic hardware calculation module: the elastic strain of the test piece in the elastic phase of resetting is calculated;
equivalent elastic strain calculation module: the equivalent elastic strain calculation module is used for calculating the equivalent elastic strain of the test piece in the equivalent elastic stage;
an elastic strain calculation module in a recovery period: the elastic strain of the test piece in a recovery period is calculated;
the test piece elastic strain calculation module: used for calculating the elastic strain of the test piece in the whole age.
Through the technical scheme, the elastic strain is divided into 'the strain generated by chuck reset' + 'the equivalent elastic strain caused by the development of the internal stress in the reset interval time period' so as to provide a more accurate elastic strain calculation method.
Compared with the prior art, the invention has the following advantages: 1. the principle is simple, and the calculation is quick; 2. the operation is convenient, and the framework is simple; 3. the test result is accurate and the applicability is wide.
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FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a system block diagram of a system using the method of the present invention;
FIG. 3 is a schematic diagram of the present invention illustrating the stress of a constrained test piece during a recovery cycle;
FIG. 4 is a schematic diagram of the stress and strain of a constrained test piece obtained during the operation of the temperature-stress testing machine of the present invention;
FIG. 5 is a graph showing the elastic strain development of two types of concrete in the adiabatic mode according to the present invention;
FIG. 6 is the elastic strain development curves of two concretes in TMC mode according to the invention;
FIG. 7 is a creep-shrinkage ratio development curve for two concretes of the invention in adiabatic mode;
FIG. 8 is a creep-shrinkage ratio development curve for two concretes in TMC mode according to the invention.
In the figure, a test piece template 1; a parameter input module 22; a reset elastic strain calculation module 21; an equivalent elastic strain calculation module 23; an elastic strain calculation module 25 in a recovery period; the specimen elastic strain calculation module 24.
Detailed Description
The following are preferred embodiments of the present invention and are further described with reference to the accompanying drawings, but the present invention is not limited to these embodiments.
As shown in FIG. 1, the method for calculating the elastic strain of the constrained test piece in the temperature-stress test comprises the following steps, wherein the step A and the step B can be synchronously performed;
or, firstly, carrying out the step A and then carrying out the step B;
or, firstly, carrying out the step B, and then carrying out the step A;
in this embodiment, step a is performed first, and then step B is performed to describe specifically:
a: obtaining the reset elastic strain generated by the reset of the chuck in the reset elastic phase through a testing machine;
the method for obtaining the reset elastic strain of the testing machine is as follows:
as shown in fig. 3 and 4, at t from the stepping motor by the reset elastic strain calculation method1’-t1The displacement generated by resetting in the resetting elastic stage of (2) to obtain the resetting elastic strain, and the calculation method of the resetting elastic strain is a formula ①, namely
m1＝n/L ①
Wherein, n: test piece at t1’-t1A reset limit value in the reset elasticity phase;
l: the effective length of the test piece;
m 1: at t1’-t1The strain generated by the resetting of the chuck in the resetting elastic stage is the resetting elastic strain.
B: calculating equivalent elastic strain caused by the development of internal stress in the reset interval time period of the equivalent elastic phase by an equivalent elastic strain calculation method;
the equivalent elastic strain calculation method comprises the following steps: determining the elastic modulus of the concrete according to the equivalent age of the concrete, and then increasing the constraint stress according to the equivalent elastic stage, namely t2Stress value at time point minus t1' the constraint stress increase value obtained from the stress value at the time point is divided by the average elastic modulus at this stage to obtain the equivalent elastic strain, wherein,
t2-t1representing a reset interval time within a reply period;
t1’-t1part of the representation of the elastic phase of reset;
t2-t1the' section represents the equivalent elastic phase.
The concrete method for determining the elastic modulus of the concrete according to the equivalent age of the concrete comprises a formula II; namely:
Figure BDA0001471061290000071
wherein t is0: initial setting time;
te: an equivalent age;
Ect,n: tensile elastic modulus for n days;
nE: a coefficient characterizing the development of tensile elastic modulus;
s: a constant.
Wherein the tensile modulus of elasticity E for n daysct,nMeasured by mechanical experiments, and the coefficient nE and the constant s for representing the development of the tensile elastic modulus are obtained by combining the measured tensile elastic modulus with the common knowledge.
In general, the method for calculating the equivalent age of concrete is a formula (iii), and the method for calculating the equivalent age after discretization is a formula (iv), that is:
Figure BDA0001471061290000072
Figure BDA0001471061290000073
wherein, teIs the equivalent age, h; t (tau) is the curing temperature history of the concrete, DEG C; t isiI, the corresponding curing temperature at the moment is in DEG C; Δ ti-a time interval; r is an ideal gas constant, and R is 8.314J/(mol K); eaKJ/mol is the apparent activation energy.
When T is more than or equal to 20 ℃, Ea(T)/R＝Ar；
T<At 20 ℃ Ea(T)/R＝Ar+Br(20-T)
In the formula, ArAnd BrAs parameters, obtained by experiment. Research results show that the activation energy of the cement hydration reaction is approximately constant between 0 and 100 ℃. Without experimental data, it can be assumed that the apparent activation energy of the concrete is about 33.5 KJ/mol.
The relation between the equivalent age and the actual age of the concrete corresponding to standard curing at 20 ℃ can be obtained by adopting the formula.
C: combining the elastic strain of the concrete obtained in the step A and the equivalent elastic strain obtained in the step B to obtain the elastic strain of the concrete in a recovery period by an elastic strain calculation method in the recovery period, and then accumulating the elastic strains in the recovery periods to obtain the elastic strain of the constraint test piece, wherein the elastic strain calculation method in the recovery period is a formula (v), namely
S＝m1+e1 ⑤
Wherein, S: elastic strain of the concrete in one recovery period;
m 1: resetting elastic strain;
e 1: equivalent elastic strain.
As shown in fig. 2, an elastic strain calculation system based on the elastic strain calculation method for constraining a test piece in a temperature-stress test, which applies the method of the present invention, includes a test system 2 connected to a test piece template 1 and having data processing and storing functions, the test system 2 includes a parameter input module 22, a reset elastic strain calculation module 21 and an equivalent elastic strain calculation module 23 which are all connected to a recovery period elastic strain calculation module 25, the recovery period elastic strain calculation module 25 is further connected to a test piece elastic strain calculation module 24, and the parameter input module 22 is connected to the equivalent elastic strain calculation module 23 and the reset elastic strain calculation module 21. Wherein:
and (3) test piece template: the testing machine system is used for obtaining the elastic strain of the test piece after the prepared concrete is poured in the testing machine system;
parameter input module 22: for inputting predetermined parameters;
the reset elastic strain calculation module 21: the elastic strain of the test piece in the elastic phase of resetting is calculated;
equivalent elastic strain calculation module 23: the equivalent elastic strain calculation module is used for calculating the equivalent elastic strain of the test piece in the equivalent elastic stage;
elastic strain in recovery period calculation module 25: the elastic strain of the test piece in a recovery period is calculated;
the test piece elastic strain calculation module 24: the elastic strain of the constrained specimen for the temperature-stress test over the entire age was calculated.
As shown in fig. 5 to 8, the following is a test procedure for concrete:
1. test raw materials and mixing ratio
In the test, two kinds of concrete are prepared, wherein the 'reference concrete' adopts the raw materials and the mixing proportion of dam concrete of the hyperbolic arch dam A, and the 'reference concrete' (35% of fly ash mixing amount) and the 'ultra-high concrete' (80% of fly ash mixing amount) of the concrete with different fly ash mixing amounts. The raw materials used in the test are the raw materials used in the hyperbolic arch dam A: huaxin ordinary 42.5 portland cement, Jingmen grade III fly ash, fine aggregate of artificial sand and coarse aggregate of artificial macadam with the maximum aggregate particle size of 40 mm. The mixing ratio is shown in table 1:
TABLE 1 mixing ratio of two kinds of fly ash concrete
Figure BDA0001471061290000091
2. Mixing two kinds of concrete mixed with fly ash in a laboratory, pouring the mixed concrete into a template of a test piece, inputting predetermined parameters, starting a test, ensuring that the test is normally carried out until the test is finished, and exporting measured data.
3. Elastic phase (t 1' -t 1):
if the reset limit of the test piece at t 1' -t1 is n micrometers, the corresponding test piece strain is m1(m1 is n/1.5, and the effective length of the test piece is 1.5 m); then the elastic strain to return of the test piece at the stage t 1' -t1 is m1。
4. Equivalent elastic phase:
the modulus of elasticity of concrete can be determined from its maturity (equivalent age). First, the equivalent age t is calculatedeThen t is calculated by the formula ②1Equivalent modulus of elasticity at the stage' to t2, through which the constraint stress increases (i.e. t2Stress of minus t1Stress of') divided by the average modulus of elasticity to calculate the equivalent elastic strain e1. The invention adopts Kanstad improved elastic modulus development model, which comprises the following steps:
Figure BDA0001471061290000101
wherein t is0: initial setting time;
te: an equivalent age;
Ect,28: tensile elastic modulus for 28 days;
nE: representing the coefficient of the development of tensile elastic modulus, and taking 0.4;
s: and constant, the reference concrete is 0.25, and the ultra-high fly ash concrete is 0.35.
The 28-day elastic modulus of the reference concrete and the ultra-high fly ash-doped concrete is measured by a mechanical test and respectively 24.0GPa and 27.8 GPa.
The equivalent age calculation formula of the concrete is formula (III), and the formula (IV) is changed into formula (IV) after discretization treatment:
Figure BDA0001471061290000102
Figure BDA0001471061290000103
wherein, teIs the equivalent age, h; t (tau) is the curing temperature history of the concrete, DEG C; t isiI, the corresponding curing temperature at the moment is in DEG C; Δ ti-a time interval; r is an ideal gas constant, and R is 8.314J/(mol K); eaKJ/mol is the apparent activation energy.
When T is more than or equal to 20 ℃, Ea(T)/R＝Ar；
T<At 20 ℃ Ea(T)/R＝Ar+Br(20-T)
In the formula, ArAnd BrAs parameters, obtained by experiment. Research results show that the activation energy of the cement hydration reaction is approximately constant between 0 and 100 ℃. Without experimental data, it can be assumed that the apparent activation energy of the concrete is about 33.5 KJ/mol.
5. Elastic strain in one recovery period
The elastic strain of the concrete in one adjustment period is equal to the elastic part m of the concrete1Plus its equivalent elastic part e1。
6. Elastic strain calculation throughout age
And accumulating the elastic strains of all the adjustment periods to obtain the elastic strain of the constraint test piece.
Creep-shrinkage ratio is expressed as the ratio of tensile creep to free shrinkage deformation, creep being the free strain of the free specimen minus the elastic strain of the constrained specimen. The creep-shrinkage ratio can describe the stress relaxation degree in concrete, and the larger the ratio is, the larger the stress relaxation degree in the constrained test piece is, and the stress relaxation degree is generally within 0.5-0.8. In the temperature-stress test of the HYPY-TSTM-I type temperature-stress tester produced by Navig ocean company, the elastic strain of a constraint test piece given by the system is obviously smaller, and the creep-shrinkage ratio obtained according to the elastic strain is even as high as 0.98, so that the deviation is too large. The invention can provide a relatively accurate elastic strain calculation method based on data measured by a HYPY-TSTM-I type temperature-stress tester produced by the aircraft-sourced ocean company and the existing theory, and the creep-shrinkage ratio of the concrete obtained according to the invention is within 0.5-0.8, and the test shows that the application is good. Of course, the new elastic strain calculation method provided by the invention is not only suitable for HYPY-TSTM-I type temperature-stress testing machines produced by the Naoyuan ocean company, but also suitable for other types of temperature-stress testing machines.
The invention only needs to add the elastic phase of the concrete in the temperature-stress test and the equivalent elastic phase to obtain the elastic strain in a recovery period, and then adds the elastic strains in the recovery periods to obtain the elastic strain of the constraint test piece.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
The embodiments described in this specification are merely illustrative of implementations of the inventive concept and the scope of the present invention should not be considered limited to the specific forms set forth in the embodiments but rather by the equivalents thereof as may occur to those skilled in the art upon consideration of the present inventive concept.

Claims (2)

1. A method for calculating elastic strain of a constraint test piece in a temperature-stress test comprises the following steps:
a: obtaining the reset elastic strain generated by the test piece when the chuck is reset through a testing machine; the method specifically comprises the following steps:
the method for obtaining the reset elastic strain of the testing machine is as follows: at t by a reset elastic strain calculation method according to a stepping motor1’-t1In the reset elastic phase of (2), the reset elastic strain of the test piece, i.e. the strain produced by the reset of the chuck, is obtained, the value of which is t1' and t1Strain difference of two points;
the reset elastic strain calculation method is a formula (I):
m1＝n/L ①
wherein, n: test piece at t1’-t1A reset limit value in the reset elasticity phase;
l: the effective length of the test piece;
m 1: at t1’-t1In the resetting elastic stage, the strain of the test piece generated by resetting the chuck is the resetting elastic strain;
b: calculating equivalent elastic strain caused by the development of internal stress by an equivalent elastic strain calculation method;
the equivalent elastic strain calculation method comprises the following steps: determining the elastic modulus of the concrete according to the equivalent age of the concrete, and then increasing the constraint stress according to the equivalent elastic stage, namely t2Stress value at time point minus t1' the constraint stress increase value obtained from the stress value at the time point is divided by the average elastic modulus at this stage to obtain the equivalent elastic strain, wherein,
t2-t1indicating a reply within a reply periodA bit interval time;
t1’-t1part of the representation of the elastic phase of reset;
t2-t1' part represents the equivalent elastic phase;
the concrete method for determining the elastic modulus of the concrete according to the equivalent age of the concrete comprises a formula II; namely:
Figure FDA0002457845660000021
wherein t is0: initial setting time;
te: an equivalent age;
Ect,n: tensile elastic modulus for n days;
nE: a coefficient characterizing the development of tensile elastic modulus;
s: a constant;
the calculation method of the equivalent age of the concrete is formulas III and IV, namely:
Figure FDA0002457845660000022
Figure FDA0002457845660000023
wherein, teIs the equivalent age, h; t (tau) is the curing temperature history of the concrete, DEG C; t isiThe curing temperature at the moment i is controlled at the temperature of △ ti-a time interval; r is an ideal gas constant, and R is 8.314J/(mol K); eaKJ/mol as apparent activation energy;
when T is more than or equal to 20 ℃, Ea(T)/R＝Ar；
T<At 20 ℃ Ea(T)/R＝Ar+Br(20-T)
In the formula, ArAnd BrAs a parameter, obtained by experiment; research results show that the activation energy of the cement hydration reaction is approximately constant between 0 and 100 ℃; without test dataIt can be assumed that the apparent activation energy of the concrete is about 33.5 KJ/mol;
c: combining the reset elastic strain obtained in the step A and the equivalent elastic strain obtained in the step B to obtain the elastic strain of the concrete in a recovery period by an elastic strain calculation method in the recovery period, and then accumulating the elastic strains in the recovery periods to obtain the elastic strain of the constraint test piece;
the calculation method of the elastic strain in the recovery period is a formula (c), namely
S＝m1+e1 ⑤
Wherein, S: elastic strain of the concrete in one recovery period;
m 1: resetting elastic strain;
e 1: equivalent elastic strain.
2. A calculation system based on the method for calculating elastic strain of a constrained test piece in a temperature-stress test according to claim 1, wherein the method comprises the following steps: including linking to each other and having test system (2) of data processing and memory function with test piece template (1), test system (2) including all connecting in parameter input module (22), the elastic strain calculation module that resets (21) and equivalent elastic strain calculation module (23) of reply cycle elastic strain calculation module (25), reply cycle elastic strain calculation module (25) still be connected with test piece elastic strain calculation module (24), wherein:
test piece template (1): the testing machine system is used for obtaining the elastic strain of the test piece after the prepared concrete is poured in the testing machine system;
parameter input module (22): for inputting predetermined parameters;
a reset elastic strain calculation module (21): the elastic strain of the test piece in the elastic phase of resetting is calculated;
equivalent elastic strain calculation module (23): the equivalent elastic strain calculation module is used for calculating the equivalent elastic strain of the test piece in the equivalent elastic stage;
an elastic strain calculation module (25) in a recovery period: the elastic strain of the test piece in a recovery period is calculated;
a test piece elastic strain calculation module (24): used for calculating the elastic strain of the test piece in the whole age.
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