CN113029832B

CN113029832B - Medium-high strength titanium alloy cyclic loading test method

Info

Publication number: CN113029832B
Application number: CN202110228593.7A
Authority: CN
Inventors: 于翔宇; 徐强; 陈凤林; 皇甫文珠
Original assignee: 702th Research Institute of CSIC
Current assignee: 702th Research Institute of CSIC
Priority date: 2021-03-02
Filing date: 2021-03-02
Publication date: 2023-05-12
Anticipated expiration: 2041-03-02
Also published as: CN113029832A

Abstract

The invention relates to the technical field of titanium alloy, in particular to a cyclic loading test method of a medium-high strength titanium alloy, which comprises the following steps: a. processing a required initial sample; b. placing the initial sample on a material testing machine for compression loading test, displaying a load-displacement curve by matching software on the material testing machine, and converting the load-displacement curve into a stress-strain curve by a conversion formula; c. machining the compressed initial sample to obtain a tensile test piece; d. carrying out a tensile test on the obtained tensile test piece to reach a preset strain quantity, and obtaining a stress-strain curve under the loading condition; e. if the cyclic loading test is needed, the compression test is machined from the tensile test piece, the compression test is continued, and the steps c and d are repeated, so that the required cyclic loading test amount is finally achieved.

Description

Medium-high strength titanium alloy cyclic loading test method

Technical Field

The invention relates to the technical field of titanium alloy, in particular to a cyclic loading test method for a medium-high strength titanium alloy.

Background

The medium-high strength titanium alloy is an advanced structural material widely applied to the fields of ship manufacture, pressure vessels, aerospace and the like, and has the advantages of high specific strength, good corrosion resistance, good high-temperature performance and the like. The titanium alloy component usually has an alternating loading process in the service process, and the performance and the change of the material performance of the titanium alloy material in the cyclic loading process are directly related to whether the component can finish the work or not.

The Babylonian effect of the material means that a small amount of plastic deformation is generated by pre-loading the metal material, and the metal material is loaded in the same direction after being unloaded, so that the specified residual stress is increased; reverse loading, prescribes a phenomenon of residual stress reduction. The Babyloning effect is a common phenomenon of metal materials, and has adverse effects on normal-temperature plastic deformation, dimensional stability and service performance of the materials. Knowledge of the bosch effect helps build up a structural model of the material under complex cyclic plastic deformation, thereby essentially studying the work hardening of the material. The Boschierd effect of materials is generally studied in a cyclic loading manner, namely, the materials are unloaded after being positively loaded to a certain degree of plastic deformation, and are further reversely loaded to the same or different degrees of plastic deformation, and then unloaded, and the materials are positively loaded to the same or different degrees of plastic deformation for the second time. This process is repeated one or more times to test the material for continuous changes in the stress-strain curve.

When the cyclic loading performance of the titanium alloy material is measured, the tensile loading test is easy to realize, but when the reverse compression test is carried out, the compression instability phenomenon often occurs, and even more so, for a plate, before the plastic deformation degree for use is reached, a material sample is bent due to the instability of a compression rod, so that the measured test data cannot be used. The method is required to be improved in the aspects of sample shape design, sample preparation and test flow, and can ensure that complete and accurate experimental data of normal-temperature cyclic loading of the material can be obtained, so that normal-temperature plastic deformation, dimensional stability, service performance and the like of the medium-high-strength titanium alloy material can be evaluated reliably.

Disclosure of Invention

Aiming at the defects in the prior art, the applicant provides a medium-high strength titanium alloy cyclic loading test method, which can obtain complete and more accurate experimental data of normal-temperature cyclic loading of materials and is convenient for researching the Bashenger effect of the materials.

The technical scheme adopted by the invention is as follows: a cyclic loading test method for a medium-high strength titanium alloy comprises the following steps:

a. initial sample required for processing: determining the specification of an initial sample to be prepared according to the elongation percentage of the medium-high strength titanium alloy and the expected number of cyclic loading;

b. placing the initial sample on a material testing machine for compression loading test, displaying a load-displacement curve by matching software on the material testing machine, and converting the load-displacement curve into a stress-strain curve by a conversion formula;

c. machining the compressed initial sample to obtain a tensile test piece;

d. carrying out a tensile test on the obtained tensile test piece to reach a preset strain quantity, and obtaining a stress-strain curve under the loading condition;

e. if the cyclic loading test is needed, machining a compression sample from the tensile test piece, continuing the compression test, and repeating the steps c and d to finally reach the required cyclic loading test amount.

As a further improvement of the above technical scheme:

the diameter of the initial sample is D, the height of the initial sample is H, and D is more than or equal to 0.5H and less than or equal to 2H.

When a tensile test piece is obtained in an initial sample, a plurality of tensile test pieces are obtained in the initial sample at uniform intervals.

The beneficial effects of the invention are as follows: the invention can acquire accurate cyclic loading test data by combining with digital image related equipment, has the characteristics of flexibility, simplicity and convenience, can acquire various cyclic loading modes, does not need to modify a material testing machine, can avoid bending of a material sample due to instability of a compression bar, and is convenient for researching the Basheng effect of the material.

Drawings

FIG. 1 is a schematic diagram of the Boschierge effect;

FIG. 2 is a diagram showing the structure of an initial state of an initial sample;

FIG. 3 is a schematic diagram of a sample structure of a compressed initial sample;

FIG. 4 is a schematic illustration of a tensile test piece as it is stretched;

FIG. 5 is a schematic illustration of a tensile test piece in which a compressed test piece is obtained;

FIG. 6 is a schematic diagram of a compressed sample as it is compressed;

FIG. 7 is a schematic illustration of a tensile specimen obtained from a compressed specimen;

fig. 8 is a schematic diagram of a tensile specimen when stretched.

Wherein: 10. an initial sample; 20. a tensile test piece; 30. the sample is compressed.

Detailed Description

The following describes specific embodiments of the present invention with reference to the drawings.

As shown in fig. 1 to 8, the cyclic loading test method for the medium-high strength titanium alloy in the embodiment comprises the following steps:

a. initial sample 10 required for processing: determining the specification of an initial sample 10 to be prepared according to the elongation of the medium-high strength titanium alloy and the expected number of cyclic loading;

b. placing the initial sample 10 on a material testing machine for compression loading test, displaying a load-displacement curve by matching software on the material testing machine, and converting the load-displacement curve into a stress-strain curve by a conversion formula;

c. machining on the compressed initial specimen 10 to obtain a tensile specimen 20;

d. carrying out a tensile test on the obtained tensile test piece 20 to reach a preset strain amount, and obtaining a stress-strain curve under the loading condition;

e. if further cyclic loading test is required, the compressed test specimen 30 is machined from the tensile test specimen 20, the compression test is continued, and steps c and d are repeated to finally achieve the desired cyclic loading test amount.

The diameter of the initial sample 10 is D, and the height of the initial sample 10 is H, wherein D is more than or equal to 0.5H and less than or equal to 2H.

When the tensile test pieces 20 are obtained in the initial test piece 10, a plurality of tensile test pieces 20 are obtained at uniform intervals in the initial test piece 10.

The invention combines the digital image related equipment to obtain the accurate cyclic loading test data, the invention has the characteristics of flexibility, simplicity and convenience, can obtain various cyclic loading modes, does not need to modify a material testing machine, leads the compression rod to be unstable and generally bends when the slender rod-shaped sample is subjected to compression experiments, adopts the method of integrally compressing the short and thick sample and then sampling, and obtains a pre-deformation on the premise of avoiding sample bending, namely, the invention can avoid bending of the material sample due to compression rod instability, wherein the initial sample 10, the tensile test piece 20 and the compression test piece 30 are collectively called as the material sample.

The above description is intended to illustrate the invention and not to limit it, the scope of which is defined by the claims, and any modifications can be made within the scope of the invention.

Claims

1. A cyclic loading test method for a medium-high strength titanium alloy comprises the following steps:

a. initial sample (10) required for processing: determining the specification of an initial sample (10) to be prepared according to the elongation of the medium-high strength titanium alloy and the number of expected cyclic loading;

b. placing an initial sample (10) on a material testing machine for compression loading test, displaying a load-displacement curve by matching software on the material testing machine, and converting the load-displacement curve into a stress-strain curve by a conversion formula;

c. machining the compressed initial sample (10) to obtain a tensile test piece (20);

d. carrying out a tensile test on the obtained tensile test piece (20) to reach a preset strain amount, and obtaining a stress-strain curve under loading conditions reaching the preset strain amount;

e. further performing a cyclic loading test, machining a compression sample (30) from the tensile test piece (20), continuing the compression test, repeating steps c and d, and finally achieving the required cyclic loading test amount,

the initial test piece and the tensile test piece adopt cylindrical pieces,

the diameter of the initial sample (10) is D, and the height of the initial sample (10) is H, wherein D is more than or equal to 0.5H and less than or equal to 2H;

the axis of the sampling position of the tensile test piece is parallel to the axis of the initial test piece, and the tensile test piece intercepts a section of the tensile test piece to be used as a test piece for a subsequent compression test; the test piece compressed in the previous step intercepts the concentric position to be used as a second tensile test piece.

2. The cyclic loading test method for the medium-high strength titanium alloy according to claim 1, wherein the method comprises the following steps of: when a tensile test piece (20) is obtained from an initial sample (10), a plurality of tensile test pieces (20) are obtained from the initial sample (10) at uniform intervals.