FORM 2
THE PATENT ACT 1970
[39 OF 1970]
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
[See Section 10 and Rule 13]
"SPLIT HOPKINSON PRESSURE BAR APPARATUS AND METHOD THEREOF"
Name and Address of the Applicant: TATA MOTORS LIMITED, Bombay House, 24 Homi Mody Street, Hutatma Chowk, Mumbai -400001, Maharashtra, India.
Nationality: Indian
The following specification particularly describes the nature of the invention and the manner in which it is to be performed.

TECHNICAL FIELD
The present disclosure relates to a Split Hopkinson bar arrangement and more particularly relates to an apparatus to calculate the dynamic stress strain response of the materials.
BACKGROUND OF DISCLOSURE
A split Hopkinson pressure bar is an apparatus to calculate the dynamic stress strain response of the materials. The main use of the split Hopkinson pressure bar is to measure stress pulse propagation in a metal bar.
The analysis and behavior of mechanical structures under various load conditions are done by Computer Aided Engineering (CAE). During Computer Aided analysis (CAE) the mechanical properties of materials used are provided as inputs for the computation. These material properties are generated as per the loading conditions in the actual use of the material. The Computer Aided Analysis (CAE) during crash testing, it is necessary to establish the material characteristics at high strain rates. To achieve high strain rates Split Hopkinson bar set up is used for testing high strain rate properties of the materials in use.
The Split Hopkinson bar mechanism consists of a piston cylinder arrangement which propels an impact striker to the required impact speed. An incident bar and a transmitting bar are positioned in front of the impact striker and are aligned with the axis of the striker. This helps in complete transmission of impact force from the impact striker to the incident bar without any retardation of impact force. The specimen material to be tested is positioned between the incident bar and the transmitting bar. The impact force is transmitted to the transmitting bar through the specimen; a stress wave is created which propagates through the bar toward the specimen. This wave is referred to as the incident wave, and upon reaching the specimen, splits into two smaller waves. One of the waves is, the transmitted, which travels through the specimen and into the transmitted bar, causing plastic deformation in the specimen. The other wave, called the reflected wave, is reflected away from the specimen and travels back down the incident bar. Here, the specimen is exposed to high strain rate of pulse and its characteristics are acquired through special instrumentation.
The conventional split Hopkinson bar mechanism is designed for generating the mechanical properties in compressive direction. In case if the specimen has to be tested in tensile direction, the piston cylinder arrangement needs changes such that the impact striker is

propelled in the opposite direction. This change leads to two different arrangements for testing the specimen in compression as well as in tensile direction which makes the test apparatus very cumbersome and costly.
Hence, there is a need to develop a single split Hopkinson bar apparatus that can be used for both tensile as .well as compressive directions which is simple in construction and cost effective.
OBJECTS OF THE DISCLOSURE
An objective of the present disclosure is to provide a split Hopkinson bar apparatus which can be used for tensile as well as compressive direction.
One objective of the present disclosure is to provide a split Hopkinson bar apparatus having different specimen holding within the incident and transmitting bars.
One objective of the present disclosure is to provide a split Hopkinson bar apparatus which is simple in construction and cost effective.
SUMMARY OF THE DISCLOSURE
The shortcomings of the prior art are overcome and additional advantages are provided through the provision as claimed in the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.
In an embodiment of the disclosure a split Hopkinson pressure bar apparatus is disclosed comprising; a propeller unit consisting of a piston cylinder arrangement to propel a striker a guide barrel fixed to an end of the propeller unit, wherein said guide barrel accommodates the striker. An incident bar whose one end of the incident bar is placed proximal to the guide barrel and the other end of the incident bar is fixed to a specimen gripper. A transmitting bar whose one end of the transmitting bar is fixed to a specimen gripper and the other end of the transmitting bar is free to move upto a predetermined distance parallel to the axis of the apparatus. At least one fork having plurality of extended arms is connected to each of the specimen grippers to secure a test specimen at either ends.

In an embodiment of the disclosure a split Hopkinson pressure bar apparatus is disclosed wherein the forks provided on incident bar and transmitting bar are detached in order to generate a compressive stress wave in the specimen.
In an embodiment of the disclosure a split Hopkinson pressure bar apparatus is disclosed, wherein one end of the test specimen is fixed to a specimen gripper provided on the incident bar and the other end of the test specimen is gripped to a specimen gripper provided on the transmitting bar to generate compressive stress wave.
In an embodiment of the disclosure a split Hopkinson pressure bar apparatus is disclosed wherein the striker moves within the guide barrel and impacts the incident bar at impact velocities.
In an embodiment of the disclosure a split Hopkinson pressure bar is disclosed, wherein a pressure chamber provided within the propelling unit generates thrust to propel the striker at impact velocities.
In an embodiment of the disclosure a split Hopkinson pressure bar is disclosed, wherein the forks are oriented mutually perpendicular to each other.
In an embodiment of the disclosure a split Hopkinson pressure bar is disclosed, wherein the test specimen is connected to the extended arms of the fork by pins.
In an embodiment of the disclosure a split Hopkinson pressure bar is disclosed, wherein the fork with extended arms provided on the incident bar is fixed to one end of the test specimen which is proximal to the transmittal bar.
In an embodiment of the disclosure a split Hopkinson pressure bar is disclosed, wherein the fork with extended arms provided on the transmittal bar is fixed to other end of the test specimen which is proximal to the incident bar.
In an embodiment of the disclosure the fork with extended arms can be of a straight beam which secures the test specimen using pins and generates the same tensile stress wave in the specimen with the impact of the striker.

In an embodiment of the disclosure a split Hopkinson pressure bar is disclosed, wherein the tensile stress wave and compressive stress wave is propagated through the incident bar, test specimen and transmitting bar.
In an embodiment of the disclosure a split Hopkinson pressure bar is disclosed, wherein the specimen grippers are provided with threading means to fix onto the end of incident bar and transmitting bar respectively.
In an embodiment of the disclosure a method for generating tensile stress wave on a test specimen by split Hopkinson pressure bar apparatus is disclosed, said method comprises steps of; connecting a fork with extended arms fixed on a specimen gripper of a incident bar to one end of a test specimen which is proximal to a transmitting bar, and fixing other end of the test specimen by connecting a fork with extended arms fixed on a specimen gripper of the transmittal bar. Generating pressure in a pressure chamber to propel a striker, wherein said striker impacts the incident bar and impact load applied on the incident bar is transmitted to a test specimen by the fork to generate tensile stress waves in the specimen.
The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The novel features and characteristic of the disclosure are set forth in the appended claims. The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:
Figure 1 illustrates a split Hopkinson pressure bar used for a compressive specimen according to prior art.
Figure 2 illustrates a split Hopkinson pressure bar used for a tensile specimen according to prior art.

Figure 3 illustrates a split Hopkinson pressure bar in accordance with the present disclosure.
Figure 3 A illustrates a perspective view of a split Hopkinson pressure bar in accordance with the present disclosure.
Figure 4 illustrates the incident bar, transmitting bar, the test specimen and the striker used for tensile characterization in comparison with prior art and present disclosure.
Figure 5 illustrates Specimen gripping arrangement in accordance with the present disclosure.
Figure 6 illustrates split Hopkinson pressure bar for compression testing of the test specimen in accordance to the present disclosure.
The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAILED DESCRIPTION OF DISCLOSURE
The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the disclosure as set forth in the appended claims. The novel features which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.

Referring now to the drawings wherein the drawings are for the purpose of illustrating an exemplary embodiment of the disclosure only, and not for the purpose of limiting the same.
Figure 1 illustrates a prior art of a split Hopkinson pressure bar used for testing a specimen under compression. The apparatus as shown in the figure consists of a propelling unit (T) consisting of a pressure chamber (2'), wherein the pressure required to propel the striker (3') is generated by a piston cylinder arrangement. The amount of pressure required to propel the striker (3') can be effectively controlled based on the requirement of the experiment. A guide barrel (4') is fixed to the propeller unit (1') which houses the striker (3r), wherein the striker (3') moves within the guide barrel (4') concentrically. The said striker (3') is a solid striker and capable of withstanding high pressure stresses and shocks. An incident bar (5') is placed proximal to the end of the guide barrel (4'), but the striker (3:) is not in contact with the incident bar (5'). A test specimen (6:) is placed in between the incident bar (5') and the transmitting bar (7'), wherein both the incident bar (5') and the transmitting bar (7') are free to move parallel to the axis of the apparatus. During testing the pressure chamber (2') is pressurized upto a desired requirement to propel the striker (3') to impact onto the target for testing. The accelerated striker (3') strikes the incident bar (5') placed at the end of the guide barrel (4') at the required velocity. After the impact of the striker (3') with the said incident bar (5'), the force of impact of the striker (3') on the incident bar (5') propels the incident bar (5') in that direction and the said movement is transmitted to the said transmitting bar (7') through the said test specimen (6') placed in between the incident bar (5') and transmitting bar (7'). By this process a stress wave is generated in the assembly of the said incident bar (5'), test specimen (6') and the transmitting bar (7'). The stresses generated due to the impact force of the striker (3') can be calculated and tabulated using special instrumentation and the values for the compression test wave is achieved.
Figure 2 illustrates a prior art split Hopkinson pressure bar used for testing a specimen under tensile loading. The apparatus for tensile testing varies from that of compression testing apparatus as disclosed in Figure 1. The propelling unit (T) consists of a hollow striker (8') placed on the said extended incident bar (9J). An incident bar (5') extends into the propelling unit (1!) and the said incident bar (5') is provided with a flange/anvil (10') at the end of the propelling unit (T). The said pressure chamber (2') is reoriented such that it would propel the said hollow striker (8') towards the flange/anvil (10'). At the start of the experiment, the said hollow striker (8:) is located inside the extension of the said pressure chamber (2'). When the pressure chamber (2') is pressurized to the required pressure, the hollow striker (8') is pushed

towards the said flange/anvil (10') of the said incident bar (5') under pressure causing a pulling action on the said test specimen (6') fixed in between the incident bar (5') and the transmitting bar (7'). With the strike of the said hollow striker (8'), the said incident bar (5') is pulled towards the anvil (10) and the said transmitting bar (7') is also pulled in the same direction by the said test specimen (65). A tensile stress wave is generated and is propagated along the incident bar (5'), test specimen (6') and transmitting bar (7') and the values can be calculated and tabulated using special instrumentation.
Figure 3 illustrates a split Hopkinson pressure bar in accordance with the present disclosure. In accordance with the present disclosure the said test specimen (10) is loaded in tensile direction and tensile loading is generated on the test specimen (10) by the impact of the striker (2) on the incident bar (4). The propelling unit (1) consists of a pressure chamber (11) wherein the pressure within the pressure chamber (11) is generated by piston cylinder arrangement to propel the striker (2) to strike the required target. A guide barrel (3) is fixed to the propelling unit which houses the striker (2) and the guide barrel (3) guides the striker (2) to strike the incident bar (4). The striker (2) propulsion takes place in concentric movements. The incident bar (4) is placed proximal to the guide barrel (3) and the other end of the incident bar (4) has a specimen gripper (5. 7) fixed to it by threading means. The transmitting bar (6) placed in line with the incident bar (4) and is free to move parallel to the axis of the apparatus. One end of the transmitting bar (6) is fixed with a specimen gripper (5, 7) by threading means. At least one fork (8) having plurality of extended arms (9) is gripped to the specimen gripper (5, 7) provided on incident bar (4) and transmitting bar (6). The forks (8) are mutually perpendicular to each other as shown in the figure. The extended arms (9) of the forks (8) are used to secure the test specimen (10) through pins (12). The test specimen (10) is suitably modified to secure firmly onto the extended arms (9) using pins (12) to perform tensile testing. When the striker (2) is impacted onto the said incident bar (4), the stress wave is transmitted to the said transmitting bar (6) through the test specimen (10) and a tensile stress wave is generated.
Figure 3 A illustrates a perspective view of a split Hopkinson pressure bar in accordance with the present disclosure. The test specimen (10) to generate tensile stress wave is slightly modified in order to connect the said forks (8) through pins (12). Atleast one fork (8) with extended arms (9) is fixed to a specimen gripper (5, 7) provided at the end of the incident bar (4) and at least one fork (8) with extended arms (9) is fixed to a specimen gripper (10) provided on the transmitting bar (6). The forks (8) with extended arms (9) are oriented

mutually perpendicular to each other. During testing, when the striker (2) strikes the incident bar (4), the fork (8) with extended arms (9) secured onto the test specimen (10) generates a tensile pulling effect on the test specimen. The stress wave is transmitted to the said transmitting bar (6) with the said modified specimen in tensile loads.
Figure 4 illustrates the incident bar, transmitting bar, the test specimen used for tensile characterization in the present disclosure. The incident bar (4) of the present disclosure has threads and are provided at one end for incident bar (4) to accommodate easy threading of specimen gripper (5) onto the incident bar (4). Similarly the transmitting bar (6) of the present disclosure has threads provided at one end of the transmitting bar (6). The test specimen (10) of the present disclosure has been modified in order to secure the pins (12) of the forks (8) with extended arms (9) for tensile testing of the specimen. The test specimen (10) is preferably of I section shape having plurality of pin holes (13) for easy mating of the pins (12).
Figure 5 illustrates Specimen gripper arrangement in accordance with the present disclosure. The specimen gripper (5, 7) provided on the incident bar (4) and transmitting bar (6) are provided with threading means which is threaded onto the ends of the incident bar (4) and transmitting bar (6) as shown in the figure. The fork (8) with extended arms (9) are gripped onto the specimen gripper (5, 7) and the ends of the extended arms (9) are provided with pins (12) for securing the test specimen (10) during tensile testing conditions. The fork (8) with extended arms (9) provided on the incident bar (4) is fixed horizontal to the axis of the split Hopkinson pressure bar apparatus and the fork (8) with extended arms (9) provided on the transmitting bar (6) is fixed vertical to the axis of the split Hopkinson pressure bar apparatus. This arrangement forms a mutually perpendicular orientation of the said forks (8) and extended arms (9) which generates tensile stress on the test specimen (10) with the impact from the striker (2) onto the incident bar (4).
Figure 6 illustrates split Hopkinson pressure bar for compression testing of the test specimen according the present disclosure. The said incident bars (4) and transmitting bars (6) are provided with threads on either ends to mount the specimen grippers (5. 7) by threading means respectively. The test specimen (10) held in between the incident bar (4) and the transmitting bar (6) undergoes compression stress wave with the impact of the striker (2) onto the incident bar (4). The compression stress wave propagates through the incident bar (4), test

specimen (10) and transmitting bar (6). The compression stress wave values can be calculated and tabulated using special instrumentation.
REFERENCE NUMERALS

1' Propelling Unit (Prior Art)
2' Pressure chamber (Prior Art)
3' Guide Barrel (Prior Art)
4' Striker (Prior Art)
5' Incident bar (Prior Art)
6' Test Specimen (Prior Art)
7' Transmitting bar (Prior Art)
8' Hollow Striker (Prior Art)
9' Extended Incident bar (Prior Art)
10' Flange/anvil (Prior Art)
1 Propelling unit
2 Striker
3 Guide Barrel
4 Incident Bar
5 Specimen gripper (Incident Bar)
6 Transmitting Bar
7 Specimen Gripper (Transmittal bar)
8 Fork

9 Extended Arms
10 Test Specimen
10A One end of test specimen
10B Other end of test specimen
11 Pressure Chamber
12 Pin
13 Pin holes
EQUIVALENTS
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of

an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."
In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.
While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

WE CLAIM:
1. A split Hopkinson pressure bar apparatus comprising;
a propeller unit (1) consisting of a piston cylinder arrangement to propel a striker (2);
a guide barrel (3) fixed to an end of the propeller unit (1). wherein said guide barrel (3) accommodates the striker (2);
a incident bar (4), wherein one end of the incident bar (4) is placed proximal to the guide barrel (3) and the other end of the incident bar (4) is fixed to a specimen gripper (5);
a transmitting bar (6), wherein one end of the transmitting bar (6) is fixed to a specimen gripper (7) and the other end of the transmitting bar (6) is free to move upto a predetermined distance parallel to the axis of the apparatus;
at least one fork (8) having plurality of extended arms (9) is connected to each of the specimen grippers (5 , 7) to secure a test specimen (10) at either ends.
2. The apparatus as claimed in claim 1, wherein the forks (8) provided on incident bar (4) and transmitting bar (6) are detached in order to generate a compressive stress wave.
3. The apparatus as claimed in claim 1, wherein one end of the test specimen (10) is fixed to a specimen gripper (5) provided on the incident bar (4) and the other end of the test specimen (10) is gripped to a specimen gripper (7) provided on the transmitting bar (6) to generate compressive stress wave.

4. The apparatus as claimed in claim 1. wherein the striker (2) moves within the guide barrel (3) and impacts the incident bar (4) at impact velocities.
5. The apparatus as claimed in claim 1, wherein a pressure chamber (11) provided within the propelling unit (1) generates thrust to propel the striker (2) at impact velocities.
6. The apparatus as claimed in claim 1. wherein the forks (8) are oriented mutually perpendicular to each other.

7. The apparatus as claimed in claim 1, wherein the test specimen (10) is connected to the extended arms (9) of the fork (8) by pins (12).
8. The apparatus as claimed in claim 1, wherein the fork (8) with extended arms (9) provided on the incident bar (4) is fixed to one end (10A) of the test specimen (10) which is proximal to the transmittal bar (6).
9. The apparatus as claimed in claim 1, wherein the fork (8) with extended arms (9) provided on the transmittal bar (6) is fixed to other end (10B) of the test specimen (10) which is proximal to the incident bar (4).
10. The apparatus as claimed in claim 1, wherein the tensile stress wave and compressive stress wave are propagated through the incident bar (4), test specimen (10) and transmitting bar (6)
11. The apparatus as claimed in claim 1, wherein the specimen grippers (5 , 7) are provided with threading means to fix onto the end of incident bar (4) and transmitting bar (6) respectively.
12. A method for generating tensile stress wave on a test specimen by split Hopkinson pressure bar apparatus, said method comprises steps of;
connecting one end (10A) of the test specimen (10) which is proximal to a transmitting bar (6) to a fork (8) with extended arms (9) fixed on a specimen gripper (5) of a incident bar (4) and fixing other end (10B) of the test specimen (10) by connecting a fork (8) with extended arms (9) fixed on a specimen gripper (7) of the transmittal bar (6); and
generating pressure in a pressure chamber (11) to propel a striker (2), wherein said striker impacts the incident bar (4) and impact load applied on the incident bar (4) is transmitted to a the test specimen (10) by the fork (8) to generate tensile stress waves.