Claims:
1. A method of preparing a sample (3) for bi-axial tensile testing, the method comprising:
deforming, a portion of the sheet metal (1) by a stamping process to define a stamped portion (2);
wherein deforming the sheet metal (1) by stamping process, pre-strains the stamped portion (2);
cutting the sample (3) in a cruciform shape from the stamped portion (2) of the sheet metal (1), wherein the cruciform shape is defined by a plurality of arms (4) extending away from a center (5b) equidistantly.

2. The method as claimed in claim 1, wherein the sheet metal (1) is stamped to deform into a dome shaped portion (2).

3. The method as claimed in claim 1, wherein the stamped portion (2) of the sheet metal (1) is defined with at least one of a flat surface and a convex surface for cutting the sample (3).

4. The method as claimed in claim 1, wherein the sample (3) from the stamped portion (2) is pre-strained by stamping to a strain ranging from 5 % to 10 %.

5. The method as claimed in claim 1, wherein the strain in the stamped portion (2) increases with an increase in depth of the stamped portion (2).

6. The method as claimed in claim 1 comprises, defining a plurality of slits (5) along the base section (5a) in each of the plurality of arms (4) of the sample (3) for distribution of stress and strain in the base section (5a) during tensile testing.

7. The method as claimed in claim 6 wherein, width of each of the plurality of slits (5) ranges from 0.2 mm to 0.3 mm.

8. The method as claimed in claim 1 wherein, the pre-strained sample (3) achieves biaxial stress strain curve under plane strain condition beyond 10 % equivalent plastic strain.

9. A sample (3) for biaxial tensile testing produced by the method as claimed in claim 1, the sample comprising:
the sample (3) defined by a cruciform shape with a plurality of arms (4) extending away from a center (5b) equidistantly;
wherein the sample (3) is pre-strained by stamping to a strain ranging from 5 % to 10 %.

10. The sample (3) as claimed in claim 9 comprises, a plurality of slits (5) defined along a base section (5a) in each of the plurality of arms (4) of the sample (3) for distribution of stress and strain in the base section (5a) during tensile testing.

11. The sample (3) as claimed in claim 9 wherein, width of each of the plurality of slits (5) ranges from 0.2 mm to 0.3 mm.
, Description:TECHNICAL FIELD

Present disclosure relates in general to a field of metal testing. Particularly, but not exclusively, the present disclosure relates to a sheet metal used for conducting a bi-axial tensile test. Further, embodiments of the disclosure, disclose a method of preparing a sample from the sheet metal and subjecting the sample to bi-axial tensile testing.

BACKGROUND OF THE DISCLOSURE

Sheet metals are generally manufactured by processing metallic slabs. Metallic slabs may be manufactured by processes such as casting including but not limiting to continuous casting, and then the metal is formed into various shapes depending on the application. One such application is converting metallic slabs into sheet metal by series of metal forming processes. During drawing of the metallic sheet from metallic slabs, processes such as hot rolling and cold rolling are carried out.

Generally, hot rolling may be performed in a Hot Strip Mill (HSM). The primary objective of HSM is to make sheets from slabs and acquire intended properties in the sheets. Typically, HSM has two sections- Roughing Mill and Finishing Mill. Roughing Mill is essentially a single strand reversing mill whose function is to reduce the thickness of the slabs as well as break the cast structure. After roughing, strips go into the finishing mill. The job of a finishing mill is to reduce the thickness of the sheets and incorporates requisite properties into the sheets. The sheets may be used for producing various products like cutting saws, automotive components (Circlips, Washers, Springs, and Recliner, Driven and disc plate), gardening tools, surgical blade, springs, measuring devices, wire rods, tire bead wires, deep drawn high strength wires, wires for suspension bridges, and others.

Further, before processing the sheet metal into the required product, the sheet metal may be tested for various mechanical properties including tensile test, elongation test, etc. A bi-axial tensile test is one such test carried out on the sheet metal for recording various stress and strain paths. The bi-axial tensile test is conducted to understand the plastic behavior of the sheet metal under these stress and strain paths and to design the formed component accordingly. Various tests are performed to evaluate constitutive parameters for various material models required for forming load prediction in press shop, strain distribution in various components during forming processes, necking, failure prediction and accurate prediction of spring back. Specifically, plastic anisotropy of sheet metals could influence forming processes and related defects. Generally, a cruciform shaped sample is cut from the formed sheet metal and the cruciform shaped sample is subjected to bi-axial tensile testing to estimate and calculate the parameters of sheet metal.

Conventional cruciform samples were prepared through laser cutting of sheet metal. A plurality of slits is provided on the arms of cruciform specimen to ensure homogeneous stress and strain distribution in a gauge section. This sample may be further used to measure elastic-plastic deformation behavior at various stress or strain ratios by bi-axial tensile testing. The cruciform shaped samples accurately provide biaxial stress strain curve under plane strain condition up to 4 % equivalent plastic strain through biaxial tensile test. However, in the biaxial testing, the sample often tends to fail after achieving maximum equivalent plastic strain of 4 % approximately. The parameter estimation of the yield functions in the sheet metal is thus influenced by availability of biaxial stress-strain data in limited range. Further, failure of the sample after achieving maximum equivalent plastic strain of 4 % often indicates towards a pre-mature failure of the sample. For instance, the sample or sheet metal may be able to withstand greater plastic strain before undergoing failure. However, the sample often tends to fail at equivalent plastic strain of 4 % due to the shape of the sample used in bi-axial tensile testing. Failure in testing of the cruciform specimen is due to the specimen design and thus availability of accurate data on plastic behavior of sheet metal is low. Therefore, the results obtained by subjecting the cruciform shaped sample to bi-axial tensile test is often inaccurate. In some scenarios, though the sheet metal may be capable of withstanding greater plastic strains, the premature failure of the sheet metal often causes the manufacturer to further invest in improving the strength of the sheet metal by adding various alloying elements or by altering the manufacturing processes.

Present disclosure is directed to solve one or more limitation stated above or any other limitations associated with the conventional arts.

The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

SUMMARY OF THE DISCLOSURE

One or more shortcomings of the prior art are overcome by a method as disclosed and additional advantages are provided through the method as described 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 a non-limiting embodiment of the disclosure, a method of preparing a sample for bi-axial tensile testing is disclosed. The method involves deforming a portion of the sheet metal by a stamping process to define a stamped portion where deforming the sheet metal by stamping process, pre-strains the stamped portion. The next step involves cutting the sample in a cruciform shape from the stamped portion of the sheet metal, where the cruciform shape is defined by a plurality of arms extending away from a center equidistantly.

In an embodiment of the disclosure, the sheet metal is stamped to deform into a dome shaped portion and the stamped portion of the sheet metal is defined with at least one of a flat surface and a convex surface for cutting the sample.

In an embodiment of the disclosure, the sample from the stamped portion is pre-strained by stamping to a strain ranging from 5 % to 10 % and the strain in the stamped portion increases with an increase in depth of the stamped portion.

In an embodiment of the disclosure, a plurality of slits are defined along the base section in each of the plurality of arms of the sample for distribution of stress and strain in the base section during tensile testing. Further, each of the plurality of slits are defined with a width ranging from 0.2 mm to 0.3 mm.

In an embodiment of the disclosure, the pre-strained sample achieves biaxial stress strain curve under plane strain condition beyond 10 % equivalent plastic strain.
It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the disclosure.

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 FIGURES

The novel features and characteristics 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:

Fig. 1 illustrates a schematic top view of a sheet metal, in accordance with some embodiments of present disclosure.

Fig. 2 is a flowchart illustrating method of manufacturing the sample, in accordance with some embodiments of present disclosure.

Fig. 3 illustrates a top view and side view of the sheet metal after stamping, in accordance with some embodiments of present disclosure.

Fig. 4 illustrates a perspective view of the sheet metal with the deformed part and the cruciform shaped sample cut from the deformed part, in accordance with some embodiments of present disclosure.
Fig. 5a shows a simulation of strain distribution on the stamped portion subjected to bi-axial tensile test, in accordance with some embodiments of present disclosure.

Fig. 5b is a graphical representation of plastic strain v/s time for the stamped portion subjected to bi-axial tensile test, in accordance with some embodiments of 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 method of preparing a sample for bi-axial tensile testing illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION

The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the 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 disclosure. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other devices 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 scope of the disclosure. The novel features which are believed to be characteristic of the disclosure, as to its organization, 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.

In the present disclosure, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

While the disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will be described below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a system that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such mechanism. In other words, one or more elements in the device or mechanism proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the mechanism.

Embodiments of the present disclosure discloses a method of preparing a sample for bi-axial tensile testing. Conventionally, in the biaxial testing, the sample often tends to fail after achieving maximum equivalent plastic strain of 4 % approximately. The sample often tends to fail at equivalent plastic strain of 4 % due to the shape of the sample used in bi-axial tensile testing. Failure in testing of the cruciform specimen is due to the specimen design and thus availability of accurate material data in biaxial stress state for plastic behavior to a high strain level is low. Therefore, the results obtained by subjecting the cruciform shaped sample to bi-axial tensile test is often in accurate. In some scenarios, though the sheet metal may be capable of withstanding greater plastic strain, the premature failure of the sheet metal often causes the manufacturer to further invest in improving the strength of the sheet metal by adding various alloying elements or by altering the manufacturing processes.

Accordingly, the present disclosure discloses a method of preparing a sample for bi-axial tensile testing. The method includes aspects of deforming a portion of the sheet metal by a stamping process to define a stamped portion. The stamped portion is obtained by deforming the sheet metal by a stamping process, thereby pre-straining the stamped portion. Preferably, the sheet metal is stamped to deform into a dome shaped portion and the stamped portion of the sheet metal is defined with at least one of a flat surface and a convex surface for cutting the sample. The sample from the stamped portion is pre-strained by stamping to a strain ranging from 5 % to 10 % and the strain in the stamped portion increases with an increase in depth of the stamped portion. The next step involves cutting the sample in a cruciform shape from the stamped portion of the sheet metal, where the cruciform shape is defined by a plurality of arms extending away from a center (5b) equidistantly. Further, a plurality of slits are defined along the base section in each of the plurality of arms of the sample for distribution of stress and strain in the base section during tensile testing. Each of the plurality of slits are defined with a width ranging from 0.2 mm to 0.3 mm. The pre-strained sample achieves biaxial stress strain curve under plane strain condition beyond 10 % equivalent plastic strain.

The following paragraphs describe the present disclosure with reference to Figs. 1 to 5.

Fig. 1 illustrates a top view of a sheet metal (1) and Fig. 2 shows a flowchart illustrating the method of manufacturing the sample (3) and Fig. 3 illustrates a top view and side view of the sheet metal (1) after stamping. The first step [101] of preparing the sample (3) involves stamping of the sheet metal (1) to deform a part of the sheet metal (1). Initially, the sheet metal (1) is chosen to have a flat profile and the same maybe subjected to a stamping operation. The sheet metal (1) may be stamped by a stamping unit known in the art, which may be defined with a cavity, for receiving the sheet metal (1) that is to be compacted. The stamping unit or the a punch is defined with a dome shaped punch or stamp, which may not be considered as a limitation, as the stamping unit may include any other geometrical shapes such as but not limiting to square, cylindrical and the like. Further, the system may include a plurality of stamping members). The plurality of stamping members may be configured to apply pressure on to the sheet metal for conforming or forcing the sheet metal (1) into the cavity. As an example, the stamping members may be but not limiting to mechanical hammers, pneumatic hammers, hydraulic hammers or presses and the like. In an embodiment, during stamping process, the plurality of stamping members may apply pressure on to the sheet metal (1) within the stamping unit. Due to the application of pressure onto the sheet metal (1) in the stamping unit, the sheet metal (1) deforms and conforms to the shape of the cavity in the stamping unit. As the sheet metal (1) is stretched or conforms to the shape of the cavity during the stamping operation, the strain in the sheet metal (1) increases. The strain increases particularly in the region that is being deformed by the stamping member. This deformed region is herein referred to as the stamped portion (2). Further, a deeper cavity causes the stamping member to force or conform the sheet metal (1) into the cavity with greater plastic strain. The strain in the stamped portion (2) is directly proportional to a depth of the stamped portion (2). For instance, if the depth to which the stamped portion (2) is deformed is low, then the strain in the stamped portion (2) is also low. Further, if the depth to which the stamped portion is high, the plastic strain that the stamped portion has undergone is also greater. Thus, the depth of the cavity in the stamping unit and the depth to which the sheet metal (1) is stamped to define the stamped portion (2) directly corelates to the strain in the stamped portion (2). In an embodiment, the sheet metal (1) may be stamped to define the stamped portion (2) with the strain in the stamped portion (2) ranging from 3 % to 10 %. The dome shape of the stamped portion (2) may be of a convex curvature. The dome shape of the stamped portion (2) may also be a flat area to cut a sample (3) form the stamped portion (2). The dome shape of the stamped portion (2) may be achieved by a process selected from a set of drawing, punching, and embossing process. The dome shape of the stamped portion (2) may be of different heights and may be prepared to achieve various levels of equivalent plastic strain.

In an embodiment, the strain may be imparted to the sheet metal (1) by any other methods known in the art including but not limited to methods such as stretch forming. The strained part of the sheet metal (1) may further be used to cut out a sample (3).

Step [102] involves cutting the stamped portion (2) of the sheet metal in the cruciform shaped sample (3). Fig. 4 illustrates a perspective view of the sheet metal (1) with the stamped portion (2) and the sample (3) cut from the stamped portion (2). The cruciform shape may be defined by a plurality of arms (4) extending away from a center (5b) of the sample (3), equidistantly. The plurality of arms (4) may be equal dimensions. Further, each of the plurality of arms (4) may be defined with a base section (5a). The base section (5a) may be the region where the stress and strain is concentrated during the bi-axial tensile test. The base section (5a) may extend for a pre-determined length from the center (5b) of the sample (3) in each of the plurality of arms (4). Further the sample (3) from the stamped portion (2) may be cut by any of the methods including but not limited to electro discharge machine, water jet cutting technique, and laser cutting process.

Step [103] involves the aspect of defining a plurality of slits (5) along the base section (5a) of each of the plurality of arms (4). The plurality of slits (5) may be defined along the base section (5a) in each of the plurality of arms (4) of the sample (3) for equal or homogenous distribution of stress and strain in the base section (5a) during tensile testing. Also, each of the plurality of slits (5) may be defined with a width ranging from 0.2 mm to 0.3 mm. The plurality of slits (5) may extend longitudinally along each of the plurality of arms (4).

Fig. 5a shows a simulation of strain distribution on the stamped portion (2) subjected to bi-axial tensile test and Fig. 5b is a graphical representation of plastic strain v/s time for the stamped portion (2) subjected to bi-axial tensile test. As seem from the Fig. 5a and Fig. 5b, the stamped portion (2) is strained or plastically deformed during the stamping process. Consequently, the strain the stamped portion (2) already reaches an equivalent plastic strain of around 4 %. Thus, the sheet metal (1) is pre-strained before cutting the sample (3). The sample (3) obtained from the above-mentioned method may further be subjected to bi-axial tensile test. It is observed that the sample (3) prepared by above-mentioned method can be further tested in balanced biaxial straining mode to achieve additional equivalent plastic strain of 5%. Thus, more than 10% of equivalent plastic strain could be achieved for the sample (3) of the sheet metal (1). In an embodiment, the sample (3) prepared from the above-mentioned method ensures a homogeneous deformation in base section (5a) during stretching or stamping and during biaxial testing under plane strain conditions. In an embodiment, the sample (3) prepared form the above-mentioned method is already pre-strained by the stamping process. Consequently, the sample (3) achieves an equivalent plastic strain greater than 10 % before undergoing failure. Thus, the sample (3) subjected to bi-axial tensile tests provides accurate results of the stress and strain the sample (3) may withstand before undergoing failure.

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, 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 description 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, 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."

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 in the description.

Referral Numerals:

Referral numeral Description
1 Sheet metal
2 Stamped portion of the sheet metal
3 Sample
4 Arms
5 Slits
5a Base section of the sample
5a Central section of the sample