Embodiments of the present invention generally relate to a fatigue testing apparatus and particularly to a direct stress fatigue testing apparatus.
Description of Related Art
[002] In modern industries, corrosion, fracture and wear are main causes of failure of mechanical parts. However, the corrosion and wear processes are slow, therefore, they can be avoided by regularly replacing the mechanical parts or repairing regularly. There are many reasons for fracture of the mechanical parts, such as overload, low temperature, brittleness, hydrogen embrittlement, stress corrosion, fatigue loading, and so forth. However, the fatigue loading is an important non-linear loading parameter resulting in failure of material that is loaded within strength limits. Therefore, it is important to determine limiting stresses applicable to the material for anticipating the failure. Direct stresses comprising of tensile and compressive stresses that play an important role in this regard, as these are the most common stresses withstand by any material used in different applications.
[003] Conventionally, a fatigue test has been performed by loading a sample into a fatigue tester. The sample is loaded using a pre-determined test stress, and then unloaded to either zero load or an opposite load. This cycle of loading and unloading is repeated until an end of the test is reached. However, this process requires a number of iterations to determine a behavior of the tested sample until the sample has failed depending on parameters of the test.
[004] There is thus a need for an advanced and more effective direct stress fatigue testing apparatus that can administer the drawbacks faced

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by the conventional approaches.
SUMMARY
[005] Embodiments in accordance with the present invention provide a direct stress fatigue testing apparatus. The apparatus comprising: a frame designed to provide a rigid support to components of the apparatus. The apparatus further comprising: a beam having a first end and a second end such that the first end of the beam is fixedly attached to a trunnion of the frame and the second end of the beam is attached to a specimen to be tested. The apparatus further comprising: an exciter motor operated at a pre-defined speed to enable a rotation of a rotor shaft, wherein a centrifugal force is exerted due to an unbalanced mass in the rotor shaft of the exciter motor, such that the centrifugal force generates a linear force applied as a load on the specimen for fatigue testing.
[006] Embodiments of the present invention may provide a number of advantages depending on its particular configuration. First, embodiments of the present application may provide an apparatus that acts as a fatigue testing machine under direct stresses.
[007] Next, embodiments of the present invention may provide a fatigue testing apparatus that measures and predicts a performance of a material under dynamic loading conditions.
[008] Next, embodiments of the present invention may provide a fatigue testing apparatus that requires a minimal change to an existing setup.
[009] These and other advantages will be apparent from the present application of the embodiments described herein.
[0010] The preceding is a simplified summary to provide an understanding of some embodiments of the present invention. This summary is neither an extensive nor exhaustive overview of the present invention and its various

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embodiments. The summary presents selected concepts of the embodiments of the present invention in a simplified form as an introduction to the more detailed description presented below. As will be appreciated, other embodiments of the present invention are possible utilizing, alone or in combination, one or more of the features set forth above or described in detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The above and still further features and advantages of embodiments of the present invention will become apparent upon consideration of the following detailed description of embodiments thereof, especially when taken in conjunction with the accompanying drawings, and wherein:
[0012] FIG. 1A illustrates a rear three-dimensional view of a direct stress fatigue testing apparatus, according to an embodiment of the present invention;
[0013] FIG. 1B illustrates a left side view of the direct stress fatigue testing apparatus, according to an embodiment of the present invention;
[0014] FIG. 1C illustrates a front view of the direct stress fatigue testing apparatus, according to an embodiment of the present invention;
[0015] FIG. 1D illustrates an isometric view of the direct stress fatigue testing apparatus, according to an embodiment of the present invention; and
[0016] FIG. 2 depicts a flowchart of a method for determining a behavior of materials under direct stress, according to an embodiment of the present invention.
[0017] The headings used herein are for organizational purposes only and

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are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word "may" is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words "include", "including", and "includes" mean including but not limited to. To facilitate understanding, like reference numerals have been used, where possible, to designate like elements common to the figures. Optional portions of the figures may be illustrated using dashed or dotted lines, unless the context of usage indicates otherwise.
DETAILED DESCRIPTION
[0018] The following description includes the preferred best mode of one embodiment of the present invention. It will be clear from this description of the invention that the invention is not limited to these illustrated embodiments but that the invention also includes a variety of modifications and embodiments thereto. Therefore, the present description should be seen as illustrative and not limiting. While the invention is susceptible to various modifications and alternative constructions, it should be understood, that there is no intention to limit the invention to the specific form disclosed, but, on the contrary, the invention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as defined in the claims.
[0019] In any embodiment described herein, the open-ended terms "comprising", "comprises", and the like (which are synonymous with "including", "having", and "characterized by") may be replaced by the respective partially closed phrases "consisting essentially of, "consists essentially of", and the like or the respective closed phrases "consisting of, "consists of", the like.
[0020] As used herein, the singular forms "a", "an", and "the" designate both the singular and the plural, unless expressly stated to designate the

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singular only.
[0021] FIG. 1A illustrates a rear three-dimensional view of a direct stress fatigue testing apparatus 100 (hereinafter referred to as the apparatus 100), according to an embodiment of the present invention. According to embodiments of the present invention, the apparatus 100 may be a mass-spring-damper system that may be used for carrying out experiments based on forced vibrations. In an embodiment of the present invention, the apparatus 100 may comprise a frame 102 that may be designed to provide a rigid support to components of the apparatus 100.
[0022] Further, in an embodiment of the present invention, the frame 102 may comprise an l-section 104 that may be designed to provide a structural rigidity to the apparatus 100. In an embodiment of the present invention, the apparatus 100 may comprise a damper 106 that may be attached to the l-section 104. In an embodiment of the present invention, the damper 106 may be employed to change a stiffness of the apparatus 100.
[0023] FIG. 1B illustrates a left side view of the apparatus 100, according to an embodiment of the present invention. In an embodiment of the present invention, a left view of the frame 102 may be illustrated that may be composed of any material such as, but not limited to, a steel, an aluminum, a wood, and alike. Embodiments of the present invention are intended to include or otherwise cover any type of the material of the frame 102, including known, related art, and/or later developed technologies.
[0024] FIG. 1C illustrates a front view of the apparatus 100, according to an embodiment of the present invention. The apparatus 100 may comprise a beam 108 that may be supported by the damper 106, in an embodiment of the present invention. Further, the beam 108 may be having a first end 110a and a second end 110b. In an embodiment of the present invention,

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the beam 108 may be extended horizontally and fixedly attached to a trunnion 112 from the first end 110a. In an embodiment of the present invention, the beam 108 may be fixedly attached to the trunnion 112 from the first end 110a, so that the fixed end of the beam 108 may not move transversely or rotate. As used herein, the term "trunnion 112" may refer to a protrusion that may be used as a mounting or pivoting point.
[0025] The beam 108 may be, but not limited to, a simple beam, and so forth. In a preferred embodiment of the present invention, the beam 108 may be a cantilever beam. Embodiments of the present invention are intended to include or otherwise cover any type of the beam 108, including known, related art, and/or later developed technologies.
[0026] Further, the apparatus 100 may comprise a specimen 114 that may be a sample to be tested under a fatigue loading, in an embodiment of the present invention. In an embodiment of the present invention, a first side of the specimen 114 may be removably attached to the frame 102 and a second side of the specimen 114 may be removably attached to the second end 110b of the beam 108. In an embodiment of the present invention, the specimen 114 may be attached from both sides by using a fastening means 116a-116b (hereinafter referred to as the fastening means 116). The fastening means 116 may be, but not limited to, pipe clamps, C clamps, and so forth. In a preferred embodiment of the present invention, the fastening means 116 may be screw clamps. Embodiments of the present invention are intended to include or otherwise cover any type of the fastening means 116, including known, related art, and/or later developed technologies. Further, in an embodiment of the present invention, the specimen 114 may be of any shape such as, but not limited to, a flat shape, a round bar type shape, and so forth. Embodiments of the present invention are intended to include or otherwise cover any shape of the specimen 114, including known, related art, and/or later developed technologies.

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[0027] FIG. 1D illustrates an isometric view of the apparatus 100, according to an embodiment of the present invention. The apparatus 100 may further comprise an exciter motor 118 that excites a disc 120 giving a fatigue load onto the specimen 114. The exciter motor 118 may be operated at a pre-defined to speed to enable a rotation of a rotor shaft 122, in an embodiment of the present invention. The exciter motor 118 may be, but not limited to, a Direct Current (DC) exciter motor, an Alternate Current (AC) exciter motor, and so forth. Embodiments of the present invention are intended to include or otherwise cover any type of the exciter motor 118, including known, related art, and/or later developed technologies. In an embodiment of the present invention, the exciter motor 118 may comprise the rotor shaft 122 that may rotate due to an interaction between windings and magnetic fields which produces a torque around an axis of the rotor shaft 122. In an embodiment of the present invention, the rotor shaft 122 may vibrate due to an unbalanced mass 124 on the rotor shaft 122 of the exciter motor 118. In such embodiment of the present invention, the vibration or a centrifugal force may be produced by an interaction of the unbalanced mass 124 with a radial acceleration due to rotation of the rotor shaft 122. In an embodiment of the present invention, the centrifugal force that may be exerted by the unbalanced mass 124 may generate a linear force that may be applied as a load on the specimen 114. This may result in buckling of the specimen 114. In an embodiment of the present invention, the load may be changed by increasing a speed of the exciter motor 118. In another embodiment of the present invention, the load may be changed by placing more weight on the disc 120. In an embodiment of the present invention, the unbalanced mass 124 may be attached to the disc 120 that may be mounted on the rotor shaft 122 of the exciter motor 118.
[0028] Further, in an embodiment of the present invention, the specimen 114 that may be used for the fatigue loading may act as a cantilever that

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may be fixed the frame 102 from the first side and supported by the beam 108 from the second side. Therefore, a value of direct stress for the specimen 114 may be calculated by using below defined equations:
YAB=((Fbx2)/ (12En3)) [3l(b2-l2) +x(3l2-b2)] — (1)
R=((Fa2)/ (2I3)) (3l-a) (2)
Yo=((Fba2)/ (12E|~|3)) [3l(b2-l2) +a(3l2-b2)] (3)
ko=F/Yo=(12En3)/ (a2b [31 (b2-l2) +a(3l2-b2)]) — (4)
T=V(1+(2^U/UJn)2)/V ((l-U^/Wn2)2 + (2^/UJn)2) —- (5)
Ftr=kxV(1 +(2^U/UJn)2) (6)
=k/M(mue)(cJo2/cJOn2V(1 +(2^u/cjUn)2))/V((1 w2/wn2) +(2^u/cjUn)2) where X=mue/M
Ftr=mueCJ02V(1+(2^CJ0/CJ0n)2)/V((1-CJ02/CJ0n2)2+(2^CJ0/CJ0n)2) — (7)
where Y is a deflection at a given point, R is a reflection at free end, ko is a stiffness, T is transmissivity, Ftr is transmitted force, w is angular velocity of rotating mass, ujn is angular velocity corresponding to natural frequency, M is mass of rotating object, mu is the unbalanced mass 124, e is an eccentricity, E is Young's Modulus, and I is a moment of inertia.
[0029] FIG. 2 depicts a flowchart of a method 200 for determining a behavior of material under the direct stress by using the apparatus 100, according to an embodiment of the present invention.
[0030] At step 202, the apparatus 100 may be provided with the specimen 114 that may act as the cantilever as the specimen 114, may be attached to the frame 102 from the first side and supported by the beam 108 from the second side.

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[0031] At step 204, the apparatus 100 may be provided with the exciter motor 118 that may be operated at the pre-defined speed and enables the rotation of the rotor shaft 122.
[0032] At step 206, the centrifugal force may be exerted due to the unbalanced mass 124 on the rotor shaft 122 of the exciter motor 118.
[0033] At step 208, the exerted centrifugal force may provide the linear force that may be imparted on the specimen 114 as the load.
[0034] At step 210, the value of the direct stress for the specimen 114 may be calculated for determining the behavior upon imparted the load onto the specimen 114.
[0035] While the invention has been described in connection with what is presently considered to be the most practical and various embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
[0036] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope the invention is defined in the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements within substantial differences from the literal languages of the claims.

CLAIMS
I/We Claim:

1. A direct stress fatigue testing apparatus (100), the apparatus (100)
comprising:
a frame (102) designed to provide a rigid support to components of the apparatus (100);
a beam (108) having a first end (110a) and a second end (110b) such that the first end (110a) of the beam (108) is fixedly attached to a trunnion (112) and the second end (110b) of the beam (108) is removably attached to a specimen (114) to be tested; and
an exciter motor (118) operated at a pre-defined speed to enable a rotation of a rotor shaft (122), wherein a centrifugal force is exerted due to an unbalanced mass (124) in the rotor shaft (122) of the exciter motor (118), such that the centrifugal force generates a linear force applied as a load on the specimen (114) for fatigue testing.
2. The apparatus (100) as claimed in claim 1, wherein the frame (102) comprises an l-section (104) designed to provide a structural rigidity to the apparatus (100).
3. The apparatus (100) as claimed in claim 1, wherein the specimen (114) act as a cantilever as the specimen (114) is attached to the frame (102) from a first side and supported by the beam (108) from a second side.
4. The apparatus (100) as claimed in claim 2, wherein the specimen (114) is attached to the frame (102) and the beam (108) through a fastening means (116a-116b).
5. The apparatus (100) as claimed in claim 4, wherein the fastening means (116a-116b) are screw clamps.

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6. The apparatus (100) as claimed in claim 1, wherein the unbalanced mass (124) is attached to a disc (120) such that the disc (120) is mounted on the rotor shaft (122) of the exciter motor (118).
7. The apparatus (100) as claimed in claim 1, wherein the load applied on the specimen (114) is changed by increasing a speed of the exciter motor (118).
8. The apparatus (100) as claimed in claim 1, wherein the load applied on the specimen (114) is changed by placing more weight on a disc (120).
9. The apparatus (100) as claimed in claim 1, wherein the rotor shaft (122) vibrates due to the unbalanced mass (124) on the rotor shaft (122) of the exciter motor (118).
10. The apparatus (100) as claimed in claim 1, wherein a value of direct stress for the specimen (114) is calculated upon applying the linear force as the load onto the specimen (114).