Claims:We claim:
1. A specimen arrangement for Biaxial Tensile testing, comprising:
three to five cruciform specimens attached and aligned one above the other;
wherein in three layers of the cruciform specimens, top and bottom layers being identical without having a gauge section while middle layer having the gauge section,
wherein in four layers of the cruciform specimens, top and bottom layers being identical without having the gauge section, while rest of the layers having the gauge section, and
wherein in five layers of the cruciform specimens, top and bottom layers being identical without having the gauge section, with middle layer having the gauge section, while rest of the layers being with or without the gauge section.
2. The specimen arrangement as claimed in claim 1, wherein arms of the layers of the cruciform specimens are slitted.
3. The specimen arrangement as claimed in claim 2, wherein the arms of the layers of cruciform specimens are slitted by Electro Discharge Machine (EDM).
4. The specimen arrangement as claimed in claim 2, wherein the arms of the layers of cruciform specimens are slitted by water jet cutting technique.
5. The specimen arrangement as claimed in claim 2, wherein the arms of the layers of cruciform specimens are slitted by laser technique.
6. The specimen arrangement as claimed in claim 1, wherein the layers of cruciform specimens are being welded together.
7. The specimen arrangement as claimed in claim 1, wherein the layers of , Description:CRUCIFORM SPECIMEN FOR BIAXIAL TENSILE TESTING
TECHNICAL FIELD
[0001] The present disclosure, in general, relates to biaxial test system to determine the mechanical properties of metal sheets. More particularly, the present disclosure relates to design a cruciform specimen, for biaxial tensile testing, with minimum variation in slit geometry and overall geometry of specimen for the biaxial test at various loading ratio under bi-axial tensile mode.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present disclosure. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed subject matter, or that any publication specifically or implicitly referenced is prior art.
[0003] Sheet metal forming operation is one of the most commonly used processes to create various parts for the automotive industry. In sheet metal forming operation, forming load prediction in press shop, strain distributions in automotive components, failure prediction and spring back prediction in sheet metal forming operations, requires extensive and accurate knowledge of plastic behavior under various stress state. This is the reason that led to development of general plasticity theory.
[0004] An experimental investigation is also important to ensure that the constitutive model accurately describes the behavior of the material under various complex loading conditions. Biaxial testing is required to calculate the parameter of various constitutive equations, known as yield function, that is used to represent material behavior for prediction of forming load and strain distribution achieved by the automotive component during the forming process.
[0005] In the biaxial testing, one of the major problems is failure of the cruciform specimen without achieving maximum strain (4 % to 5 % approximately) in a gauge section of the cruciform specimen. Failure occurs from an arm due to improper slit size and a larger hole at one of the slit ends due to excessive heating while the cruciform specimen preparation through laser cutting and no strengthening of the arm through another mechanism. The failure of the cruciform specimen less than 2 % is a major problem while conducting the biaxial testing. Also, as initial thickness of the cruciform specimen increases, it reduces the chances of preparing biaxial specimen through laser cutting. Biaxial cruciform specimen prepared through laser cutting from steel with a thickness of more than 1 mm is unable to achieve strain more than 1 % due to aforementioned problem during the cruciform specimen preparation. It impacts in the determination of constitutive parameter for various yield locus utilized during various forming process simulations.
[0006] The existing cruciform specimen prepared through the laser cutting for sheet metal thickness less than 1 mm can accurately provide biaxial stress-strain curve through the biaxial tensile test by ensuring superior homogeneity in gauge section of the cruciform specimen in terms of strain and stress. The slits provided in the arm of the cruciform specimen ensure both homogeneous stress and strain distribution in the gauge section. This cruciform specimen is used to measure elastoplastic deformation behavior at various stress or strain ratios. In this kind of cruciform specimen, only in-plane deformation takes place in comparison to the hydrostatic bulge testing method. This kind of cruciform specimen is easier to fabricate through laser cutting if the thickness of the sheet is less than 1mm. As one goes for higher thickness, a laser cutting method of preparation doesn’t work as it increases the size of the hole at the start of slit preparation in the biaxial specimen. So, the existing cruciform specimen has less probability to achieve the biaxial stress-strain curve for more than 2 % equivalent strain level during the experiment for sheet metal thickness of more than 1 mm.
[0007] Accordingly, it would be desirable to develop a cruciform (biaxial) specimen that can be used to generate biaxial stress-strain curve up to 5 % equivalent strain level by overcoming the above mentioned technical problems.
[0008] Therefore, there is a need in the art to have a new design and structured cruciform specimen which is cost effective and simple in structure to avoid the reduced level of overall equivalent plastic strain (less than 2 %) during biaxial test experiment.
[0009] 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 acknowledgment or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
OBJECTS OF THE DISCLOSURE
[0010] Some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed hereinbelow.
[0011] It is a general object of the present disclosure to overcome aforementioned and other drawbacks in prior specimen/device/system/apparatus design.
[0012] It is another object of the present disclosure to provide a cruciform specimen to be used for biaxial testing of sheet metal for more than 1 mm thickness to avoid any failure in the specimen before achieving an equivalent plastic strain of 4 %.
[0013] It is another object of the present disclosure to ensure homogeneous deformation in gauge section during biaxial testing.
[0014] It is another object of the present disclosure to ensure homogeneous distribution of stress and strain in gauge section during biaxial testing
[0015] It is another object of the present disclosure to provide enough space in the gauge section so that strain gauges can be properly glued on one side along both loading directions of the cruciform specimen. On the other side of cruciform specimen, we need to use speckle pattern to measure strain through the DIC system to ensure homogeneous deformation.
[0016] It is another object of the present disclosure to provide fast and efficient fitment of the strain gauge and speckle pattern on the specimen sheet metal for obtaining strain data during testing.
[0017] It is another object of the present disclosure to provide the biaxial specimen which is cost efficient, easy to manufacture, a lesser number of parts, and achieve at least 4 % of equivalent plastic strain in the gauge section during biaxial test experiment.
[0018] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY
[0019] One or more drawbacks of the conventional cruciform specimen are overcome, and additional advantages are provided through the new cruciform specimen design as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be a part of the claimed disclosure.
[0020] The present disclosure relates to newly designed cruciform specimen that can be used to conduct a biaxial test under biaxial loading condition. The newly designed cruciform specimen has a square gauge section at center and each arm consists of equidistant slits from each other that start from the free end of the arm to one of the side of square gauge section.
[0021] In an embodiment, the present disclosure relates to a specimen arrangement for Biaxial Tensile testing. The arrangement includes three to five cruciform specimens attached and aligned one above the other, wherein in three layers of the cruciform specimens, top and bottom layers being identical without having a gauge section while middle layer having the gauge section, wherein in four layers of the cruciform specimens, top and bottom layers being identical without having the gauge section, while rest of the layers having the gauge section, and wherein in five layers of the cruciform specimens, top and bottom layers being identical without having the gauge section, with middle layer having the gauge section, while rest of the layers being with or without the gauge section.
[0022] In an aspect, arms of the layers of the cruciform specimens are slitted.
[0023] In an aspect, the arms of the layers of cruciform specimens are slitted by Electro Discharge Machine (EDM).
[0024] In an aspect, the arms of the layers of cruciform specimens are slitted by water jet cutting technique.
[0025] In an aspect, the arms of the layers of cruciform specimens are slitted by laser technique.
[0026] In an aspect, the layers of cruciform specimens are being welded together.
[0027] In an aspect, the layers of cruciform specimen are made up of steel.
[0028] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
[0029] 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 to form a further embodiment of the disclosure.
[0030] 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 DRAWINGS
[0031] It is to be noted, however, that the appended drawings illustrate only typical subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods or structure in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0032] FIG. 1 illustrates a cruciform (Biaxial Tensile) specimen according to BS ISO 16842 (2014);
[0033] FIG. 2(a) illustrates a cruciform (Biaxial Tensile) specimen according to BS ISO 16842 (2014);
[0034] FIG. 2(b) illustrates four arms of the cruciform (Biaxial Tensile) specimen after complete removal of material from gauge section (60 mm X 60 mm) of cruciform specimen shown in FIG. 2(a);
[0035] FIG. 2(c) illustrates a newly designed cruciform specimen in accordance with the present disclosure;
[0036] FIG. 2(d) illustrates an isometric view of the cruciform specimen shown in FIG. 2(c) in accordance with the present disclosure;
[0037] FIG. 3(a) illustrates a cruciform (Biaxial Tensile) with extended slits until the end of the arm;
[0038] FIG. 3(b) illustrates four arms of cruciform (Biaxial Tensile) specimen after complete removal of material from gauge section (60 mm X 60 mm) of cruciform specimen shown in FIG. 3(a);
[0039] FIG. 3(c) illustrates a newly designed cruciform specimen in accordance with the present disclosure; and
[0040] FIG. 3(d) illustrates an isometric view of the cruciform specimen shown in FIG. 3(c) in accordance with the present disclosure.
[0041] 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
[0042] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0043] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0044] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0045] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0046] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0047] Embodiments explained herein pertain to a cruciform specimen design of sheet metal under biaxial tensile loading condition. In new cruciform specimen design proposed herein, slits are extended to the end of all four arms starting from the respective sides of a square gauge section of the cruciform specimen.
[0048] FIG. 1 illustrates a cruciform (Biaxial Tensile) specimen according to BS ISO 16842 (2014). The distance between two adjacent slits is 7.5 mm. Length and width of each slit are 60 mm and 0.2 mm respectively. In an aspect, the dimension of gauge section is 60 mm X 60 mm.
[0049] FIG. 2(a) illustrates a cruciform (Biaxial Tensile) specimen according to BS ISO 16842 (2014). The distance between two adjacent slits is 7.5 mm. Length and width of each slit are 60 mm and 0.2 mm respectively. The dimension of gauge section is 60 mm X 60 mm.
[0050] FIG. 2(b) four arms of Cruciform (Biaxial Tensile) specimen after complete removal of material from gauge section (60 mm X 60 mm) of cruciform specimen shown in FIG. 2(a).
[0051] FIG. 2(c) illustrates a newly designed cruciform specimen in accordance with the present disclosure. In the newly designed cruciform specimen, one cruciform (Biaxial Tensile) specimen according to BS ISO 16842 (2014) is sandwiched between two identical geometrical features as shown in FIG. 2(b) arms of identical geometrical features as shown in FIG. 2(b) are joined through laser welding to the respective arms of Cruciform (Biaxial Tensile) specimen according to BS ISO 16842 (2014).
[0052] FIG. 2(d) illustrates an isometric view of the cruciform specimen shown in FIG. 2(c) in accordance with the present disclosure
[0053] FIG. 3(a) illustrates a cruciform (Biaxial Tensile) with extended slits until the end of the arm. The distance between two adjacent slits is 7.5 mm. Length and width of each slit are 100 mm and 0.2 mm respectively. The dimension of gauge section is 60 mm X 60 mm.
[0054] FIG. 3(b) illustrates four arms of Cruciform (Biaxial Tensile) specimen after complete removal of material from gauge section (60 mm X 60 mm) of cruciform specimen shown in Fig.3. (a).
[0055] FIG. 3(c) illustrates a newly designed cruciform specimen in accordance with the present disclosure. In the newly designed cruciform specimen, one cruciform (Biaxial Tensile) specimen is sandwiched between two identical geometrical features as shown in FIG. 3(b). Arms of identical geometrical features as shown in FIG. 3(c) are joined through laser welding to the respective arms of cruciform (Biaxial Tensile) specimen.
[0056] FIG. 3(d) illustrates an isometric view of the cruciform specimen shown in FIG. 3(c) in accordance with the present disclosure.
[0057] In new cruciform specimen design, three to five cruciform specimens of similar size are taken according to cruciform specimen design. Gauge section of two cruciform specimens is cut out in such a way so that only arm portion of the specimen remains. Now respective arms of the cut-out specimens are kept in such a way so that one cruciform specimen having the gauge section according to cruciform specimen design can be sandwiched between the cut-out specimens. Respective arms of the cut-out cruciform specimens are welded using laser or any other suitable welding technique so that sandwiched specimen having gauge section remains intact with welded arms of the cut-out cruciform specimens during biaxial testing.
[0058] In an aspect, in case of three layers of the cruciform specimens, top and bottom layers being identical without having a gauge section while middle layer having the gauge section.
[0059] In another aspect, in case of four layers of the cruciform specimens, top and bottom layers being identical without having the gauge section, while rest of the layers having the gauge section.
[0060] In another aspect, in case of five layers of the cruciform specimens, top and bottom layers being identical without having the gauge section, with middle layer having the gauge section, while rest of the layers being with or without the gauge section.
[0061] Slits of all these above-designed specimens can be prepared through laser or EDM (Electro Discharge Machine) or water jet cutting technique.
[0062] Further, the newly designed cruciform specimen ensures homogeneous deformation in the gauge section during biaxial testing.
[0063] Yet further, the newly designed cruciform specimen ensures homogeneous distribution of stress and strain in gauge section during biaxial testing
[0064] Yet further, the newly designed cruciform specimen provides enough space in the gauge section so that strain gauges can be properly glued on one side along both loading directions of the cruciform specimen. On the other side of the cruciform specimen, speckle pattern can be used to measure strain through the DIC technique.

TECHNICAL ADVANTAGES
[0065] The present disclosure prevents failure of the cruciform specimen from arm section without achieving at least 4 % equivalent strain in gauge section.
[0066] The present disclosure provides cruciform specimens that can be of any thickness.
[0067] The present disclosure provides a cruciform specimen design in which the gauge can achieve an equivalent plastic strain up to a level of at least 8 % during biaxial testing.
[0068] The present disclosure proposes that the geometry is prepared either through EDM (Electro discharge machine) or water jet cutting technique so that the geometry ensures proper slit size with no variation in its width.
[0069] Furthermore, those skilled in the art can appreciate that the above description does not provide specific details of the manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art can choose suitable manufacturing and design details.
[0070] It should be understood, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise, as apparent from the discussion herein, it is appreciated that throughout the description, discussions utilizing terms such as “oxidizing,” or “cutting,” or “purifying,” or “dialyzing,” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.
[0071] Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0072] It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.