Abstract:
A test machine for testing the physical properties of a test specimen is provided. The test machine includes a fixture that applies a first force on the test specimen in a first direction and utilizes magnetic force to bring about the rotation of a fixture to apply a second force on the test specimen in a second direction. The test machine can better simulate field applications where a material may experience, for example compression or tension at the same time it experiences a rotational moment.

Description:
BACKGROUND 
       [0001]    The present exemplary embodiment relates to a material testing apparatus and method capable of applying loads to a test specimen. More particularly, the present exemplary embodiment relates to a testing apparatus and method that utilizes a magnetic force to rotate a test specimen while a load is applied to the specimen. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications. 
         [0002]    The present material testing apparatus and method relates to the testing of elastomeric materials. Elastomeric materials may be tested for various properties. Examples of some of the properties of interest of these materials include tensile strength, hardness, compression, rebound, shear, elongation, hysteresis, etc. Unfortunately, in most cases, the evaluation of a specimen&#39;s characteristics of a particular property must be completed in isolation from other forces. This limits the usefulness of such product testing to approximate real field data for the reason that in most field applications of an elastomeric product it is difficult, if not impossible, to limit the forces being applied to an object to just one force which is applied in only one direction. 
         [0003]    Therefore, it would be advantageous for a testing apparatus to be able to apply a predetermined amount of forces on a test specimen from selected directions at the same time or at relative proximity in time to simulate the field environment which the specimen would experience. 
       BRIEF DESCRIPTION 
       [0004]    A test machine for testing a test specimen is provided. The test machine includes a fixture for contacting the specimen and applying a force to the specimen along at least one of an x-axis, y-axis, or z-axis of the test machine. At least one electromagnet for producing the at least one electromagnet being positioned such that the magnetic force produced by the at least one electromagnet is of sufficient strength and direction to cause rotation of the fixture. 
         [0005]    A method of testing the effects of applying a rotational moment to a test specimen is also provided. The method includes applying an axial force to the test specimen along an axis. The method also includes generating a predetermined non-mechanical rotational force to thereby twist the test specimen around the axis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective view of a material testing machine; 
           [0007]      FIG. 2  is a perspective view of a material testing machine which includes an embodiment of the present material testing apparatus; and 
           [0008]      FIG. 3  is a top view of the relationship of the electromagnets in one embodiment of the material testing apparatus. 
           [0009]      FIG. 4  is a top view of the relationship of the electromagnets in another embodiment of the material testing apparatus. 
           [0010]      FIG. 5  is a perspective view of a material testing machine which includes another embodiment of the present material testing apparatus. 
           [0011]      FIG. 6  is a perspective view of a material testing machine which includes a further embodiment of the present material testing apparatus. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    To test for shear, tensile or compressive characteristics of an elastomeric material, a force is typically applied to a sample or test specimen of the material in a single direction, however in order to get a more accurate prediction of how the material will perform under real world conditions, it may be desirable to apply a force to the material in a second direction during, before or after the application of the force in the first direction. For example, as a tread block of a tire comes in contact with a roadway, the tread block may experience a compressive force in a first direction. While in contact with the roadway, the same tread block may also encounter a torquing force in a second direction. The inventor has developed an apparatus and a method to apply multiple forces to an elastomeric material during testing. For example, the apparatus and method can initiate a rotational torquing force on a test specimen while applying a first compressive force to the test specimen. Alternatively, the specimen may experience the rotational moment either immediately prior to or immediately after the first force. Advantageously, when applying the second force, the method does not interfere with the ability of the apparatus to apply the first force on the test specimen. Additionally, it is preferred that the method does not mechanically engage the fixture or the test specimen. Mechanically engaged is used herein to describe at least the situation when the two items would come in physical contact. 
         [0013]    Non-limiting examples of mechanical testing equipment to which the present apparatus may be applicable are described in the following U.S. patents, which are incorporated herein by reference, in their entirety: U.S. Pat. Nos. 4,478,086, 4,869,112, 5,005,424, 5,361,640, 5,425,276, 5,693,890, 5,719,339, 6,058,784, 6,526,837, and 6,679,124. A commercially available example of such an apparatus is the MTS 831 available from MTS Systems Corporation of Eden Prairie, Minn. 
         [0014]    With respect to the first force, in  FIG. 1 , the invention is illustrated with an apparatus for applying a compressive or tensile force to the test specimen. This is not meant to limit the invention to only an apparatus which may apply a force to the test specimen along the vertical axis of the test specimen. 
         [0015]      FIG. 1  illustrates an exemplary material testing apparatus  10  for applying loads to a test specimen. The apparatus  10  includes an upper fixture  14 A and a lower fixture  14 B that hold the test specimen (T) along a longitudinal axis  15 . The lower fixture  14 B is connected to an actuator  16  through which loads are applied to the test specimen (T) and reacted against a reaction structure generally indicated at  18 . Optionally, the apparatus  10  may include more than one actuator. For example, a second actuator may be located proximate of fixture  14 B. Alternatively, fixtures  14 A and  14 B may be capable of retaining the test specimen for either tensile or compressive testing. 
         [0016]    In the embodiment illustrated, the material testing apparatus  10  includes a frame  20  having a base  22 . A pair of support members  24  extends upwardly from the base  22  and is joined together by a crossbeam  26 , which provides a stable support surface. A pair of stationary support columns  28  extends upwardly from the crossbeam  26  to an adjustable crosshead  30 . A fixed support  36  extends from crossbeam  30  to a load cell  32 . Load cell  32  joins the upper fixture  14 A to support  36  and crosshead  30 . The load cell  32  provides a representative signal indicative of tension/compressive forces applied to test specimen. Alternatively, the load cell may be located in communication with fixture  14 B (not shown) instead of fixture  14 A, as shown. A further alternative is that apparatus  10  may include more than one load cell. In one of the various embodiments of apparatus  10 , the actuator or actuators are aligned with an upper or lower fixture and that the load cell or load cells are aligned with the fixture which the actuator is not aligned. 
         [0017]    Apparatus  10  further includes an actuator  16 . Actuator  16  may be powered by any type of drive system such as an electrical system, a pneumatic system, or a hydraulic system. Support  38  extends from actuator  16  to lower fixture  14 B. Preferably actuator  16  is in communication with fixture  14 B and actuator  16  may be used to move fixture  14 B to apply a tensile force or compressive force to a test specimen. 
         [0018]    As appreciated by those skilled in the art, the upper fixture  14 A and lower fixture  14 B, of apparatus  10  can take many forms and are not limited to fixtures  14 A and  14 B illustrated in  FIG. 1 . Any suitable fixture may be used to practice the invention. Examples of other such fixtures are illustrated in the aforementioned U.S. patents. The fixture is able to retain a portion of the test specimen (T) during the desired testing. 
         [0019]    Optionally apparatus  10  may include a control system that provides control signals along a signal line to the actuator  16  (or actuators if the system includes more than one actuator) and receives signals along a control line from load cell  32  which are proportional to the forces measured by the load cell (or load cells if the system includes more than one load cell.) Examples of suitable commercially available control systems are the various FLEXTEST® control systems available from MTS Systems Corporation. FLEXTEST is a registered trademark of MTS Systems Corporation. 
         [0020]    With respect to the apparatus  10 , just as it is advantageous to displace the test specimen (T) in a desired tensile state or compressed state; it is also advantageous to be able to apply a torque to the test specimen (T) as part of the tensile or compression testing. Such a rotational moment may be applied to the test specimen prior to, during, or after the application of the first force. It would further be advantageous that the rotation is performed to a predetermined degree and at a predetermined rate. 
         [0021]      FIG. 2  shows one embodiment of the material testing apparatus. The apparatus  10  includes one or more electromagnets  40  and  42 . The embodiment of  FIG. 2  includes one electromagnet each on each support column  28  with electromagnets  40  and  42  extending along support columns  28  at least a distance of the displacement of fixture  14 B. As shown, fixture  14 B is capable of rotating and is not fixed. Various techniques may be used to allow fixture  14 B to rotate. In one embodiment actuator  16  may rotate and, in turn, the rotation of actuator  16  may thereby bring about the rotation of fixture  14 B. In another embodiment, support  38  may include a rotational joint, such as, but not limited to, a ball joint. In a further embodiment, the rotational joint may be integral to fixture  14 B or separate from fixture  14 B and support  38 . The invention is not limited to the aforementioned techniques to bring about the rotation of fixture  14 B. 
         [0022]    As illustrated, magnets  40  and  42  are arranged in a “push-pull” arrangement. Push-pull is used herein to describe a pair a magnets which the magnetic forces exerted by each magnet is exerted along the same axis, be it the x, y, or z-axis; however the forces are exerted in opposite directions along the chosen axis. Therefore, the magnets are aligned to rotate the test specimen (T) in the fixture by applying its forces in opposite directions. The magnetic forces are applied to structure  48 , which is attached to fixture  14 B. Structure  48  is made of a material capable of reacting to a magnetic force. Examples of such a material include metallic compounds such as, but not limited to, steel, iron, and alloys of each. As illustrated, the magnetic force of magnet  40  is directed in the direction of arrow F 1  and the magnetic force of magnet  42  is directed in the direction of arrow F 2 . Any known technique to power magnets  40  and  42  may used to supply power to magnets  40  and  42 , to generate the magnetic force, such as applying a current to the magnets to generate the magnetic force. 
         [0023]    With respect to magnets  40  and  42 , they may have the same strength or different strengths. Also, the embodiment may include more than two (2) magnets. The magnets may be present in pairs, such as one (1), two (2), and three (3) or more pairs of magnets. However it is not to be implied that an odd number of magnets may not be used. 
         [0024]    Furthermore, the magnets do not need to have a uniform size. The size of any two particular magnets may vary. In one particular embodiment, the heights of the magnets may be adjusted to alter the angle of rotation of the test specimen. Also, it is not required that the magnets are straight up and down as one or more of the magnets may be aligned at an angle relative to columns  28 . Additionally, the current provided to each magnet does not have to be uniform. Another optional aspect of the invention is that amplification may be used to alter the signal to the magnet and to control the size of the magnetic force exerted by the magnet. In this way, the amplification is ultimately being used to control the degree of rotation. In one embodiment, the degree of rotation is a function of the vertical displacement of fixture  14 B. The degree of rotation may be measured by any type of angle sensor. Amplification is not limited to just controlling the degree of rotation. In alternate embodiments, amplification may be used to control other aspects of the testing to be preformed by apparatus  10 . 
         [0025]      FIG. 3  shows a top view of the embodiment shown in  FIG. 2 . Electromagnets  40  and  42  are located on each support column  28  respectively. Preferably electromagnets  40  and  42  extend along support columns  28  at least a distance of the displacement of fixture  14 B. As illustrated, magnets  40  and  42  are arranged in a “push-pull” arrangement. Therefore, the magnets are aligned to rotate the test specimen in the fixture by applying their forces in opposite directions. The magnetic forces are applied to structure  48 , which is attached to fixture  14 B. Structure  48  is made of a material capable of reacting to a magnetic force. As illustrated, the magnetic force of magnet  40  is directed in the direction of arrow F 1  and the magnetic force of magnet  42  is directed in the direction of arrow F 2 . 
         [0026]      FIG. 4  shows a top view of an alternative embodiment. Electromagnets  40  and  46  are located on one support column  28 , and electromagnets  42  and  44  are located on the other support column  28 . Preferably electromagnets  40 ,  42 ,  44 , and  46  extend along support columns  28  at least a distance of the displacement of fixture  14 B. Magnets  50  are attached to fixture  14 B such that they interact with electromagnets  40 ,  42 ,  44 , and  46 . As illustrated, diagonally opposed electromagnets  42  and  46  are arranged to push magnets  50 , and diagonally opposed electromagnets  40  and  44  are arranged to pull magnets  50 . Therefore, the electromagnets are aligned to rotate the test specimen in the fixture by applying their forces to magnets  50 . As illustrated, the magnetic force of electromagnet  40  is directed in the direction of arrow F 1 , the magnetic force of electromagnet  42  is directed in the direction of arrow F 2 , the magnetic force of electromagnet  44  is directed in the direction of arrow F 3 , and the magnetic force of electromagnet  46  is directed in the direction of arrow F 4  thus creating a circular torquing force or rotational moment F c  on fixture  14 B during, before or after the application of a compressive or other directional force applied to the test specimen by apparatus  10 . 
         [0027]    With reference to  FIG. 5 , a third embodiment of the invention is illustrated. In this embodiment, an electromagnetic motor is incorporated into the testing machine. In this embodiment, support  38  extends from actuator  16 , through crossbeam  26  to fixture  14 B in a manner that will allow support  38  to rotate. Electromagnetic motor  52  is located near one end of support  38 . The motor includes a plurality of electromagnets  54 . Upon the application of an electrical current to motor  52 , magnets  54  produce a magnetic field in the direction of arrow A of sufficient strength to cause support  38  to rotate and thereby rotate fixture  14 B. 
         [0028]      FIG. 6  illustrates a fourth embodiment of the invention. In this embodiment, magnet  56  is attached to support columns  28  and is oriented diagonally between support columns  28 . Magnet  56  can be either a permanent magnet or an electromagnet. Structure  48  is attached to test fixture  14 B. Structure  48  is made of a material capable of reacting to the magnetic force exerted by magnet  56 . As fixture  14 B is moved along axis  15 , the magnetic force is exerted onto structure  48  at localized points, i.e. the place on structure  48  that is the closest to magnet. Thus, as fixture  14 B is moved along axis  15 , the localized magnetic force exerted on structure  48  moves along structure  48  in a perpendicular relationship to axis  15 . This causes fixture  14 B to rotate as it is moved along axis  15 , which in turn causes the test specimen to rotate. Angle α may be modified to change the rate of rotation relative to the amount of displacement of fixture  14 B. A smaller angle α will create a very low rate of rotation relative to the amount of displacement of fixture  14 B, while a larger angle α will create a large rate of rotation relative to the amount of displacement of fixture  14 B. One advantage of this embodiment is that it allows for modification of the rate of rotation without the need to change amplification of an electromagnet as a function of the linear displacement of fixture  14 B. 
         [0029]    Optionally, a thickness monitor such as a laser may be added to the testing machine to determine how the thickness of the test specimen is changing as the various forces are applied to the test specimen. The above alternate/optional embodiments of the invention may be practiced in any combination thereof. 
         [0030]    The invention also includes a method of testing the effects of applying a rotational moment to a test specimen. The method includes the step of securing at least one end of the test specimen in a fixture. In one embodiment, the test specimen is held securely enough that the desired test may be accomplished on the test specimen, but not so rigidly that the retention of the test sample interferes with the testing. In various embodiments, two opposing ends of the test specimen will be secured. 
         [0031]    Preferably, the fixture includes a rotatable element at an end of the fixture attached to one of the opposing ends of the test specimen. The method also includes the step of applying a force to the test specimen along one of x-axis, y-axis, or z-axis of the test specimen. A predetermined non-mechanical rotational moment is applied to thereby rotate the fixture, and twist the test specimen. 
         [0032]    Optionally the method may include the step of monitoring the twisting of the test specimen. Furthermore, the method may include adjusting the non-mechanical rotational force in response to the monitoring. Another optional step may be adjusting the linear force applied to the specimen in response to the monitoring. 
         [0033]    The description has been provided with reference to exemplary embodiments of the electromagnetic rotation and stability apparatus. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiments be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.