Claims:CLAIMS:

1. Fixture assembly for tensile testing machine comprises a top fixture and a bottom fixture wherein the each top and bottom fixture includes cylindrical clamp heads and coupling shafts and said coupling shaft with knurling on its surface; the clamp head is provided with centrally position bore and collar opening disposed centrally and are aligned from the center of the collar with the center bore; said clamp heads of the top and bottom fixtures are configured to hold a specified test sample through a C –shaped collar (C-Holder)and wherein the central bore depth is adapted to hold the test sample head centrally.

2. Fixture assembly for tensile testing machine as claimed in claim 1, wherein the said clamp head and the coupling shaft are aligned coaxially.

3. Fixtures assembly for tensile testing machine as claimed in claim 1, wherein said clamp head coupling shaft are constituted by a cylinder.

4. Fixtures assembly for tensile testing machine as claimed in claim 1, wherein the said clamp head and shaft are made of 50CrMo4 alloy special steel.

5. Fixture assembly for tensile testing machine as claimed in claim 4, wherein the alloy possess a good combination of ultra-high strength and cold bending among other properties.

6. Fixture assembly for tensile testing machine as claimed in claim 1, wherein the top and bottom fixture and the test sample are configured for testing each sample range, as in ASTM 770M (Type D, E & F).

7. Fixture assembly for tensile testing machine as claimed in claim 1, wherein the fixture components after heat treatment are checked for retained austenite content.

8. Fixture assembly for tensile testing machine as claimed in claim 1, wherein the coupling shaft of the fixture is knurled to avoid any accidental slippage during loading.

9. Fixture assembly for tensile testing machine as claimed in claim 1, wherein the dimensions for

each fixture is calculated based on bending moment calculations and practicality.

10. Fixture assembly for tensile testing machine as claimed in claim 1, wherein the fixture assembly is adapted to align the test sample axis with the axis of the machine.

Dated: this 19th day, December, 2016.

(N. K. Gupta)
Patent Agent,
Of NICHE,
For SAIL.

To,
The Controller of Patents,
The Patent Office, Kolkata.

, Description:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)

COMPLETE SPECIFICATION
(Section 10 and rule 13)

TITLE

FIXTURE FOR TENSILE TESTING MACHINE

APPLICANT

STEEL AUTHORITY OF INDIA LIMITED,
A GOVT. OF INDIA ENTERPRISE,
Rourkela Steel Plant
Rourkela - 769011, Orissa, India

The following specification particularly describes the nature of the
invention and the manner in which it is to be performed

FIXTURE FOR TENSILE TESTING MACHINE

FIELD OF THE INVENTION

The present invention relates to a set of fixtures for tensile testing machine. More particularly, the present invention provides additional Mechanical Testing capabilities in Steel Industries in assessing the resistance of a steel plate to lamellar tearing.

BACKGROUND OF THE INVENTION

Rourkela Steel plant produces long products with wide and thicker plates as the prime product in its product mix. Various grades of Plates and Slabs are produced at the plant. The Research and Control laboratory Department is responsible for process and quality control of the production. All the grades meeting the quality requirement are certified acceptable by the laboratory. But failures to meet the quality requirement became frequent at the customer end. All these have to be taken care of and uplifting the plant’s pride became the prime objective.

The Test House does Mechanical Testing of Steel Samples, as a part of its Certification Process for various products produced at Rourkela Steel Plant. Owing to competition from other steel producers of the market, the plant required a stringent quality control. Additional quality requirements mandated additional Testing amidst costly equipment purchase. The need for extending the functions of already existing legacy machines is found to be the only remedial measure.

One such extension of facility is Micro-Tensile Testing of samples along the Through Thickness with our legacy Tensile Testing Machine. The testing of the sample has to be in accordance with an ASTM Standard for necessary appreciation from the customer. With all these in mind, a sturdy common fixture has been devised which is capable of testing all the grades at RSP. The fixture is capable of testing Through-Thickness Tensile Samples, As per ASTM 770M.

OBJECTS OF THE INVENTION

The present invention provides Through-Thickness Tensile testing as an extended facility to already existing legacy Tensile Testing Machine by means of a sturdy fixture. The present invention is directed to provide additional Mechanical Testing capabilities in Steel Industries in assessing the resistance of a steel plate to lamellar tearing. In addition to lamellar tearing, this innovation will help ensure low Sulphur in Steel Making, Minimum segregation of inclusions, Inclusion Shape Control as a part of its quality control without the need for extra equipment.

The present invention solves the technical problems existing in the known art and to provide an easy processing and durable, and is suitable for a certain range of thickness tensile testing fixture.

Herein disclosed are fixtures for tensile testing machine head, comprises a clamp and the coupling shaft, said coupling shaft in in the shape of cylinder with knurling on its surface, the clamp head is provided with an upper portion of the center of the coupling shaft with the center hole, said clamp head through the center hole coupling link, the lower part is provided with a central aperture U-shaped central opening, the central opening of the U-shaped lower portion has a lower U-shaped opening and the central opening is larger than the lower portion of the U-shaped opening.

In an embodiment, there is provided a jig head which is composed of a cylinder and the jig head and the coupling shaft are coaxial.

SUMMARY OF THE INVENTION

Therefore such as herein described there is provided a fixture assembly for tensile testing machine comprises a top fixture and a bottom fixture wherein the each top and bottom fixture includes cylindrical clamp heads and coupling shafts and said coupling shaft with knurling on its surface; the clamp head is provided with centrally position bore and collar opening disposed centrally and are aligned from the center of the collar with the center bore; said clamp heads of the top and bottom fixtures are configured to hold a specified test sample through a C –shaped collar (C-Holder)and wherein the central bore depth is adapted to hold the test sample head centrally.

In an embodiment, the clamp head and the coupling shaft are aligned coaxially and are constituted from a cylinder and further the fixture assembly is adapted to align the test sample axis with the axis of the machine.

In another embodiment the components of the said fixtures assembly are made of 50CrMo4 alloy special steel which possesses a good combination of ultra-high strength and cold bending among other properties. The top and bottom fixture and the test sample are configured for testing each sample range, as in ASTM 770M (Type D, E & F).

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

Figure 1 illustrates the Engineering Drawing of the Fixture Made in accordance with the present invention;
Figure 2 illustrates the Schematic Diagram of the Micro Tensile Test Sample for plates that are 45-64 mm thick in accordance with the present invention.
Figure 3 illustrates Time-Temperature Transformation Diagram of 50CrMo4
Figure 3 illustrates Contineous Cooling Curves with various cooling rates and Hardness
(Courtesy of Vấclav Kotlan et al.)

DESCRIPTION OF THE INVENTION

The Figure 1 illustrates a tensile testing fixture to be used with a testing machine, including the jig head and the coupling shaft. Fixtures for tensile testing machine head comprises a clamp and the coupling shaft, said coupling shaft in in the shape of cylinder with knurling on its surface, the clamp head is provided with an upper portion of the center of the coupling shaft with the center hole. The said clamp head possess the center hole coupling link, the lower part is provided with a central aperture U-shaped central opening, the central opening of the U-shaped lower portion has a lower U-shaped opening and the central opening is larger than the lower portion of the U-shaped opening.. Whether the use of a threaded connection, or pins connected by the same large-diameter cylindrical upper portion of the center-hole diameter and the holder coupling shaft of the head, and the sample is of 45-64 mm thickness.

In an exemplary embodiment, there is provided three fixtures as shown in Figure 1 devised for each of the specimen of ASTM 770 (Type D, E & F). The lip dimensions for each fixture have been calculated based on bending moment calculations and practicality.

The fixture is has to be made of a sturdy material which doesn’t undergo any deformation compared to the material being tested. In view of this 50CrMo4¬ (DIN 17200-86, Nº 1.7228)¬ grade of ¬¬¬Steel is chosen, because of its vide availability and data available on it. The Time-Temperature Transformation Diagram of 50CrMo4 is shown in fig 3. Three numbers of fixtures are made for testing each sample range, as in ASTM 770M. The fixture after heat treatment is checked for retained austenite content and is found well within the norms. The holding part of the fixture is knurled to avoid any accidental slippage during loading.

The ideal lip geometry is found to be of the closed cantilever type (as shown in the figure) and care has been taken to align the specimen axis with the axis of the machine.

JUSTIFICATION FOR THE MATERIAL CHOSEN AND THE HT PARAMETERS

50CrMo4 is an alloy special steel, direct hardenable with a good hardenability and a cooling curve for it is readily available. Moreover, it possess a good combination of ultra-high strength and cold bending among other properties. From the cooling curve, heat treatment parameters have been optimized. 50CrMo4 steel having the following composition as shown in the below mentioned table. Optical Emission Spectroscopy is done on the purchased material to verify the composition. The results along with the specification data is as shown below.

C Si Mn P S Cr Mo Fe
Spcification 0.46-0.54 ≤ 0.4 0.5-0.8 ≤0.025 ≤0.035 0.9-1.2 0.15-0.3 (rest)
OES Data 0.51 0.35 0.71 0.011 0.012 1.2 0.3

The cooling curve for the composition is as shown in the figure 4 from which the parameters are decided for the heat treatment of the fixture. The transformation temperatures are verified with Andrews formula and are as shown in the figure 4.

The cooling curve is based on the work of Vấclav Kotlan et al. in their publication “Modelling of laser heating with induction pre-heating and post-heating and its experimental verification, 2015/11/9, Industrial Electronics Society, IECON 2015-41st Annual Conference of the IEEE, p: 002852-002857”.

After making the fixture with dimensions as shown in the figure 1, Hardening Treatment is to be done at a temperature 860 ºC. After soaking for a time period of 40 minutes, the fixtures are then immediately quenched in water kept at a temperature of 4 ºC. This is done to achieve a minimum quenching rate of 40 ºC per second. The water bath had been continuously stirred to achieve uniform cooling rate. After quenching, the fixtures are to be tempered at 540 ºC for the formation of Bainitic (upper) in the microstructure. A Quench hardness of around 63 HRC backs the Heat-Treatment and microstructure justification.

The amount of retained austenite, when components of such composition are Heat-Treated, is measured by comparing the integrated intensity of austenite peak to integrated intensity of ferrite/martensite peak. Following austenite and ferrite/martensite peak with CrKα radiation are used for testing.
hkl 2θ
Ferrite/martensite 200 106.1
211 156.4
Austenite 200 79.0
220 128.3

Retained Austenite content is calculated using the principle below is found to be well less than 1.2% proving the sound phase and structure stability of the fixture.

BEST MODE OF THE WORKING OF THE INVENTION

• The fixtures work best, if ASTM 770 samples are being tested. As an example figure 2 illustrates a Micro Tensile Test Sample for plates that are 45-64 mm thick.
• The maximum Yield Stress of the materials being tested should not exceed 1000 Mpa.
• The legacy machine should have the top and bottom axis aligned to the direction of loading.
• The machine should be capable of holding round samples. (C-Holders)

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.