Patent Publication Number: US-2021190653-A1

Title: Device for Preparing Sheet Specimens

Description:
The present invention refers to a device for preparing sheet specimens to perform laboratory test for mechanical characterizations. 
     BACKGROUND OF THE INVENTION 
     For several applications, it is necessary to obtain the mechanical properties of sheet materials before its use. The performed tests allow selecting materials for given applications, check the properties for current industrial use or determine properties for material improvements, among others. 
     In practice, some of these tests require the introduction of cracks in the specimens to measure the material resistance to crack propagation under different loads and environments. 
     With the devices currently known for preparing sheet specimens, cracks are usually introduced by applying cyclic loads. These pre-cracking fatigue tests are costly and time consuming. 
     This kind of known devices for preparing sheet specimens has the drawback that the preparation is expensive because of its duration and use of costly laboratory equipment. 
     Therefore, one purpose of the present invention is to provide a device for introducing cracks in sheet specimens in which the preparation only takes a reduced time, with the consequent saving of costs. The obtained cracked specimen closely reproduces the behavior of specimen with fatigue pre-cracks or other type of cracks. 
     DESCRIPTION OF THE INVENTION 
     With the device according to the present invention it is possible to solve said drawbacks, providing other advantages that are described below. 
     The device for preparing sheet specimens according to the present invention comprises a base for placing on it a sheet specimen and a cutting punch to produce sheared cracks or sharp notches, such as sharp notches with a radius similar to a crack, at the end of the cut area in said sheet specimen. 
     Thanks to this feature, the cracks can be formed cutting directly the sheet, and not by cyclic loading, so that the preparation of the sheet specimen takes a reduced time in comparison with the conventional devices. 
     According to a preferred embodiment, said cutting punch comprises a beveled lower end and a central vertical groove. 
     Furthermore, said cutting punch also comprises two cutting portions divided by said central vertical groove, each cutting portion defining an obtuse angle with respect to the vertical axis of the cutting punch. 
     This configuration of the cutting punch permits to make cracks that are suitable for the subsequent tests to be carried out on the specimen. 
     Advantageously, the base comprises centering means for centering said sheet specimen to ensure a correct position of the sheet specimen on the base. 
     According to a preferred embodiment, said centering means comprise a plurality of holes inside which pins protruding from the base are housed. 
     Preferably, the device for preparing sheet specimens according to the present invention also comprises a press-holder element for pressing the sheet specimen against the base during the cutting of the sheet specimen for holding it. 
     Said pressing element can be preferably placed in said central vertical groove of the cutting punch. However, said pressing element can be placed in any suitable position of pressing and holding the sheet specimen. 
     Said cutting punch and said pressing element are preferably mounted on a pressing frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding the above explanation and for the sole purpose of providing an example, some non-limiting drawings are included that schematically depict a practical embodiment. 
         FIG. 1  is a perspective view of the device for preparing sheet specimens according to the present invention; 
         FIG. 2  is a cross-sectional view of the device for preparing sheet specimens according to the present invention; 
         FIG. 3  is a frontal elevation view of the cutting punch of the device for preparing sheet specimens according to the present invention; 
         FIG. 4  is a side cross-section elevation view of the cutting punch of the device for preparing sheet specimens according to the present invention; and 
         FIG. 5  is an elevation view of a detail of the contact zone between the cutting punch and the sheet specimen in the device for preparing sheet specimens according to the present invention. 
     
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     The device for preparing sheet specimens according to the present invention can be seen in  FIG. 1  in a perspective view. 
     The device according to the present invention comprises a base  1  on which a sheet specimen  2  is placed and a cutting punch  3 , which makes little cracks on the sheet specimen  2 , as will be explained hereinafter. 
     The sheet specimen  2  is conventional (it can be made e.g. from steel) and its shape can be seen in this  FIG. 1 . Preferably, the sheet specimen  2  has a rectangular shape with curved notches provided in opposite sides of the larger sides of the rectangle, e.g. in a centered position. This way, the little cracks will be made in the zone between these curved notches. 
     For granting the correct positioning of the sheet specimen  2  on the base  1 , and therefore the correct positioning of the little cracks, the base  1  comprises centering means, which can be seen in more detail in  FIG. 2 . 
     These centering means comprise a plurality of holes  11  placed in the base  1  inside which pins  12  are housed. These pins  12  protruding slightly from the base  1 , so that these pins  12  are also housed inside corresponding through holes  21  of the sheet specimens  2 . 
     These centering means permit a very simple and accurate positioning of the sheet specimen  2  in the desired position on the base  1 . 
     The configuration of the cutting punch  3  can be seen more clearly from  FIGS. 3 and 4 . 
     The cutting punch  3  comprises a beveled lower end, e.g. having a beveled portion defining an angle of about 45° with respect to the vertical axis A of the cutting punch  3 . 
     The cutting punch  3  also comprises a central vertical groove  32 . This central vertical groove  32  divides the lower end of the cutting punch  3  in two cutting portions  34 , which are symmetrical with respect the vertical axis A of the cutting punch and define an obtuse angle with said vertical axis A. The obtuse angle can range, e.g. between 100° and 120°, but can be any obtuse angle that permits a correct cutting of the little cracks in the sheet specimen  2 . 
     The device for preparing sheet specimens according to the present invention also comprises a pressing element  4  (shown in  FIG. 5 ) for holding and pressing the sheet specimen  2  against the base  1 . 
     This pressing element  4 , and preferably also the cutting punch  3 , is mounted on a pressing frame  5 , which is not shown in detail, and whose function is just lowering and raising the pressing element  4  and the cutting punch  3 , as described hereinafter. 
     The operation of the device for preparing sheet specimens according to the present invention is very simple. 
     Firstly, the sheet specimen  2  is placed on the base  1  in the correct position. To this end, the pins  12  are used, so that the pins  12  are housed inside the through holes  21  of the sheet specimen  2 . 
     Once the sheet specimen  2  is positioned in its correct position, the pressing element  4  and the cutting punch  3  are lowered by conventional means, so that little sheared cracks are cut in the zone between the notches of the sheet specimen  2 . 
     After that, the sheet specimen  2  can be removed from the base  1  and used for mechanical testing purposes. 
     Even though reference has been made to a specific embodiment of the invention, it is obvious for a person skilled in the art that the device described herein is susceptible to numerous variations and modifications, and that all the details mentioned can be substituted for other technically equivalent ones without departing from the scope of protection defined by the attached claims.