KR102478605B1 - A test jig for primary barrier high strain tensile test - Google Patents

Abstract

A test jig for a high strain tensile test of a primary barrier according to the present invention is a test jig used for a tensile test. The test jig includes: a tension rod formed in a hollow cylindrical shape to have a predetermined length; an insert rod which is inserted into the tension rod and combined with the tension rod to protrude a predetermined length to an upper surface of the tension rod; and a stud bolt screwed into a thread formed from a lower end of the tension rod to an inner circumferential surface at a predetermined height, wherein the length of the stud bolt protruding outward from the lower end of the tension rod by rotation is adjustable. According to the present invention having such a configuration, the test jig formed in a shape including an acceleration section so that a test can be performed with a target strain value during the high strain tensile test in a room temperature and cryogenic environment.

Description

Test jig for primary barrier high strain tensile test {A TEST JIG FOR PRIMARY BARRIER HIGH STRAIN TENSILE TEST}

The present invention relates to a test jig used in a high strain tensile test, and more particularly, to test the high strain tensile strength of primary/secondary barrier base materials considering room temperature and cryogenic environments for developing LNG CCS (Cargo Containment System). It is about the test jig used for

Natural gas is the only environmentally friendly fuel that can effectively meet the demand for low carbon emissions among fossil fuels. Expansion of shale gas development is expected to stabilize natural gas prices. Due to these characteristics, the demand for and interest in natural gas is continuously increasing in recent years. When natural gas is liquefied at -162°C, its volume can be reduced to 1/600, so it is stored and transported in a cryogenic liquefied state.

There are various storage tank structures for storing cryogenic LNG on ships, which are the main means of transporting natural gas. The material must be able to withstand static and hydrodynamic loads due to sloshing and gas loads due to LNG vaporization in storage tanks.

In the LNG cargo hold (see FIG. 1a), internal liquid flow, that is, sloshing occurs due to the movement of the ship in the six degrees of freedom, which may cause structural damage to the cargo hold due to an increase in sloshing pressure. Therefore, in order to develop domestic LNG CCS, it is necessary to evaluate the high strain tensile strength of the primary and secondary barrier materials considering room temperature and cryogenic environments. In order to realize sufficient high strain, a separate high strain tensile jig was developed, manufactured, and tested.

Flat tensile test specimens are used for dynamic testing of plates. The strain developed in the gage length of the specimen depends on both the applied displacement rate and the parallel length of the reduced section of the specimen. Specimens with short parallel lengths can have high strain. However, the parallel length Lc must be maintained so that the original gauge length Lo is in a uniaxial stress state (see Fig. 1b). Therefore, the recommended sizes of parallel length Lc, width bo, thickness ao, and transition radius r for the specimen are as follows.

To fabricate the specimens, the guidelines and descriptions for the preparation of flat tensile test specimens in ISO 6892-1:2009, Annex B were followed, with special care being taken to avoid strain hardening at the cut edges.

Spark erosion, water jet cutting, high speed machining or strain hardened edges, other processes to mitigate surface roughness and specimen warping are recommended. The surface of the sheet sample should be maintained in its original state as received, and the surface roughness of the cut surface should be minimized (see Fig. 1c).

As the test jig, a tensile jig and a grip jig are used, and the original shape of each jig is shown in Fig. 1d.

The end of the tension jig is in the form of a stud bolt for fixing the grip jig, and the wedge-shaped plate inside the grip jig serves to fix the specimen.

Republic of Korea Patent Registration No. 10-2122654 (Name: Specimen grip jig for cryogenic test and cryogenic tensile test apparatus including the same, registration date: 2020.06.08. )

The present invention was invented to improve the above problems, and an object of the present invention is to form a shape including an acceleration section so that the test can be performed at a target strain value during a high strain tensile test in a room temperature and cryogenic environment It is to provide a test jig.

Technical problems of the present invention are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

A test jig for a primary barrier high strain tensile test according to an embodiment of the present invention devised to achieve the above object is a test jig used for a tensile test, a tension rod formed in a hollow cylindrical shape to have a constant length, and a tension rod. Insert rod coupled to the tension rod to be inserted into the top surface of the tension rod and protruded by a certain length from the lower end of the tension rod to the thread formed from the lower end of the tension rod to the inner circumferential surface of a certain height, and protrudes outward from the lower end of the tension rod by rotation It is characterized in that it comprises a stud bolt whose length is adjustable.

In addition, the outer end of the insert rod included in the test jig for the primary barrier high strain tensile test according to an embodiment of the present invention is characterized in that it is coupled to the end of the grip jig to proceed with the tensile test.

In addition, the tensile rod of the test jig for the primary barrier high strain tensile test according to an embodiment of the present invention has an acceleration section formed in an internal hollow shape, and the acceleration section is formed from the lower end of the tension rod to the inner circumferential surface of a certain height. By including a portion that extends upward with the same inner diameter from the top of the screw thread to a certain height and narrows the inner diameter, to provide a space in which the insert rod can move and accelerate while maintaining the lower end of the insert rod inserted into the tension rod. characterized by the formation of

According to one embodiment of the present invention, there is an effect of being able to provide a test jig formed in a shape including an acceleration section so that the test can be performed at a target strain value during a high strain tensile test in a room temperature and cryogenic environment. .

The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

Figure 1a is a photograph of an LNG cargo hold that has reached a manufacturing completion stage according to the prior art.
Figure 1b is a schematic diagram showing the characteristics of the specimen dimensions used in the high strain tensile test of the present invention.
Figure 1c is a schematic diagram showing the shape and dimensions of the specimen used in the high strain tensile test of the present invention.
1d is a photograph and a part of a design drawing of a basic form of a test jig for a primary barrier high strain tensile test according to the prior art.
Figure 2 is a cross-sectional view of a modified form of a test jig for a primary barrier high strain tensile test according to an embodiment of the present invention and a photograph taken to show behavior during the test.
3 is a view for explaining installation of a specimen and a test jig before performing a test to which a test jig for a primary barrier high strain tensile test is applied according to an embodiment of the present invention.
4 is a graph showing temperature changes of a chamber and a specimen during a test using a test jig for a primary barrier high strain tensile test according to an embodiment of the present invention.
5 is a graph showing a stress-strain curve after performing a test using a test jig for a primary barrier high strain tensile test according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings to the extent that those skilled in the art to which the present invention pertains can easily practice the present invention.

In describing the embodiments, descriptions of technical contents that are well known in the technical field to which the present invention pertains and are not directly related to the present invention will be omitted. This is to more clearly convey the gist of the present invention without obscuring it by omitting unnecessary description.

For the same reason, in the accompanying drawings, some components are exaggerated, omitted, or schematically illustrated. Also, the size of each component does not fully reflect the actual size. In each drawing, the same reference number is given to the same or corresponding component.

Figure 2 is a cross-sectional view of a modified form of a test jig for a primary barrier high strain tensile test according to an embodiment of the present invention and a photograph taken to show behavior during the test.

Referring to FIG. 2 , a tensile jig among test jigs for a primary barrier high strain tensile test according to an embodiment of the present invention is designed to have a cross-sectional shape as shown in FIG. 2 (a).

The test jig for the primary barrier high strain tensile test according to the present invention is a test jig used for a tensile test, and is inserted into the tension rod 1 formed to have a constant length in a hollow cylindrical shape and the tension rod (1). The insert rod 2 coupled to the tension rod 1 so that it can protrude a certain length to the upper surface of 1) and the screw thread formed from the lower end of the tension rod 1 to the inner circumferential surface of a certain height, and the tension rod by rotation It is characterized in that it includes a stud bolt 3 capable of adjusting the length protruding outward from the lower end of (1).

In addition, in the tension rod 1, an acceleration section is formed among the inner hollow shapes, and the acceleration section is upward with the same inner diameter from the top of the screw thread formed from the lower end of the tension rod 1 to the inner circumferential surface of a certain height to a certain height. By including a part that extends and narrows the inner diameter, the lower end of the insert rod 2 is formed to provide a space in which the insert rod 2 can move and accelerate while maintaining the insertion inside the tension rod 1. to be characterized

In the case of the existing jig, the equipment specification satisfies the test speed specification, but the test is completed immediately because it is a high strain tensile test. The test is performed at a target high strain value by forming an acceleration section so that the test can be performed at the target strain value.

As experimental equipment, a tensile tester (UTM) with a load capacity of ±50 kN and a cryogenic chamber capable of cooling the space containing the tensile tester to minus 170 ° C were used.

Unless otherwise specified, tests are conducted at room temperature between 10°C and 35°C, and the test temperature can be recorded if required. Tests performed under controlled conditions shall be performed at a temperature of (23 ± 5) °C.

The speed of the actuator is selected prior to the high strain test to obtain the desired strain in the parallel length of the specimen. The initial displacement rate allows an estimate of the achievable nominal engineering strain using the equation below.

In the above equation, Lc is the parallel length of the specimen.

Material behavior is determined by the parallel longitudinal strain of the specimen during testing. Therefore, the purpose of the test procedure is to perform the test at a constant strain rate on the parallel length of the specimen, not necessarily the speed of the actuator.

The test speed is determined by referring to the table below to obtain the target strain.

3 is a view for explaining installation of a specimen and a test jig before performing a test to which a test jig for a primary barrier high strain tensile test is applied according to an embodiment of the present invention.

Referring to Figure 3, Figure 3 (a) is a design drawing showing the test piece 10, Figure 3 (b) shows the adjusting connector bolt 30, Figure 3 (c) is an insert rod setup, Figure 3 ( d) represents the tension rod setup, respectively.

Displacements and forces must be zero offset before the specimen 10 is installed in the testing machine. When mounting the specimen on the grip jig 20, it must be well aligned so that only axial force is applied.

After inserting the test piece 10 between the wedge-shaped plates of the upper grip jig 20, turn the adjustment connector bolt clockwise to fix the test piece (see FIG. 3(a)).

The role of the adjusting connector bolt is to fix the test piece 10 by pushing the wedge plate into the grip jig 20 (see Fig. 3(b)).

The lower part is also fixed to the test piece (10) in the same way as the upper part. At this time, the insert rod goes up from the tension rod (see FIG. 3(c)).

In a state where the test piece 10 is fixed to the lower grip jig 20, the tension rod is raised using a displacement regulator so that the insert rod is sufficiently inserted into the tension rod. At this time, care is taken not to apply a compressive load to the test piece 10 (see FIG. 3(d)).

Liquid nitrogen (LN2) is injected into the chamber to maintain a cryogenic state using a cryogenic chamber for cryogenic testing. Temperature sensors are attached to the top/bottom of the chamber and to the specimen 10 to check the temperature in real time. For uniform temperature distribution of the test piece 10, after the temperature sensor attached to the test piece 10 reaches the target temperature and maintains it for more than 60 minutes, a high strain tensile test is performed.

Attach the temperature recording device in a way that does not affect the dynamic response of the test piece (10). The temperature of the specimen 10 should be monitored, and the frequency should be kept low enough to avoid significant temperature changes unless this is a factor to be studied in the test.

4 is a graph showing temperature changes of a chamber and a test piece during a test using a test jig for a primary barrier high strain tensile test according to an embodiment of the present invention.

After mounting the test piece 10 and inputting information for test execution, such as strain rate, sample rate, and high strain tensile test, the test equipment should have the following performance.

A force sensor must be fixed to one of the mechanical plates in order to measure the force generated by the specimen 10 reacting to the plate during the test. This sensor must be negligible compared to the self-deformation being measured during the measurement operation and must also be capable of continuous measurement of the force at any point in time with an accuracy of ±1%.

The measuring device and, where applicable, the device that graphically records the forces and displacements produced by the testing machine shall be checked periodically. The device shall be tested using a set of standard weights known to an accuracy of ±1% or better and corresponding to the force applied during the test. To verify the device, a spacer of known thickness should be used with an accuracy of ±0.5% or ±0.1mm, whichever is more restrictive.

The sample rate should be such that sufficient data can be obtained during the test.

)와 공학적 변형률 (

)은 다음 식과 같이 계산된다.engineering strain (

) and the engineering strain (

) is calculated as follows.

,

,

Here, the meaning of each component is as follows.

: n+1 단계에서의 공학적 변형률,

: Engineering strain at step n+1,

: n 단계에서의 공학적 변형률,

: Engineering strain at step n,

: n 단계와 n+1 단계 사이의 시간 증가분.

: Time increment between step n and step n+1.

In addition, the engineering stress (σ) is calculated as follows, and the meaning of each component is as follows.

σ=F/A

σ = Stress (Pa), F = force (N), A = area (mm2).

)은 아래 수식과 같이, 1%(0.01)와 10%(0.1)의 변형률을 평균으로 구합니다. In addition, the mean strain rate (

) is obtained by averaging strains of 1% (0.01) and 10% (0.1), as shown in the formula below.

From here,

는 평균 변형률(

),

is the average strain (

),

은 1%의 변형률에서의 시간,

is the time at 1% strain,

은 10% 변형률에서의 시간이다.

is the time at 10% strain.

If the strain at break is less than 10%, calculate the average strain between the 1% strain and the measured strain at break. By agreement, the upper limit of the strain range can be changed from 10% to another specified value, such as strain at maximum force.

5 is a high strain tensile test result graph showing a stress-strain curve after performing a test using a test jig for a primary barrier high strain tensile test according to an embodiment of the present invention.

The table below is a comparison of target speed and measured speed.

On the other hand, in the present specification and drawings, preferred embodiments of the present invention are disclosed, and although specific terms are used, they are only used in a general sense to easily explain the technical content of the present invention and help understanding of the present invention. It is not intended to limit the scope of the invention. It is obvious to those skilled in the art that other modifications based on the technical idea of the present invention can be implemented in addition to the embodiments disclosed herein.

1: tension rod
2: insert rod
3 : stud bolt
10: test piece
20 : grip jig
30: adjustment connector bolt
40: Insert rod setup
50: Tension rod setup

Claims (3)

As a test jig used for tensile testing of tank barrier base materials exposed to cryogenic environments of -162 ° C or lower,
A tension rod formed in a hollow cylindrical shape to have a certain length;
an insert rod inserted into the tension rod and coupled to the tension rod so as to protrude a predetermined length toward the top surface of the tension rod; and
A stud bolt screwed into a screw thread formed from the lower end of the tension rod to an inner circumferential surface of a certain height and having an adjustable length protruding outward from the lower end of the tension rod by rotation,
The tension rod,
An acceleration section is formed among the hollow shapes inside,
The acceleration section,
By including a portion extending upward with the same inner diameter from the upper end of the screw thread formed from the lower end of the tension rod to the inner circumferential surface of a certain height to a certain height and narrowing the inner diameter,
A test jig for a primary barrier high strain tensile test, characterized in that the lower end of the insert rod is formed to provide a space in which the insert rod can move and accelerate while maintaining the insertion inside the tension rod.
According to claim 1,
The outer end of the insert rod,
Test jig for the primary barrier high strain tensile test, characterized in that coupled to the end of the grip jig to proceed with the tensile test.
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