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Hi, how to model screw joint connecting two thin plates,the screw fail by shear action.

    • Rania
      Subscriber
    • peteroznewman
      Subscriber
      Different levels of detail are put in the model depending on what you are interested in learning.
      For example, if you are designing a Sheetmetal structure and plan to use screws at specific locations, a common modeling approach is to use a Fixed Joint to connect the hole in one sheet to the hole in the other sheet. Use one Fixed Joint for each screw in the assembly. Apply the loads to the structure and Probe the forces going through each Fixed Joint. Make sure you have a coordinate system that has one axis aligned with the screw axis. After you obtain the three forces on the Fixed Joint, use vector addition to combine the two in-plane forces as the total shear force. Compare this shear force with the allowable shear force for the size and material selected for that screw.

    • Rania
      Subscriber
      thanks for your reply. please do you have any tutorial on how to create the fixed joint? in my model I have created the screw as 3D model "same as in the picture but without threading" I did not get similar load displacement curve similar to lab exp "same as in the picture shown below" I appreciate your answer.
    • peteroznewman
      Subscriber
      Since you are not designing a structure to survive design loads, but instead trying to simulate a lab tensile test to simulate the force- displacement profile, you need a different model. That means you don't need a Fixed Joint. You need to provide more detail about the screws and sheets.
      Please reply with the screw geometry dimensions. What is the solid shaft diameter, below the threads? What is the screw material? What is the Yield Strength and Ultimate Tensile Strength of the screw material?
      Please reply with the sheet geometry dimensions. What is the sheet thickness, width, length from the clamp edge to the free edge? I don't care how much length is in the clamp. What is the size of the hole in the sheet? What is the dimension from the free edge to the center of the hole? What is the Yield Strength and Ultimate Tensile Strength of the sheet material?
      In Engineering Data, did you insert any type of Plasticity into the material model for the screw and the sheet materials? You must insert that to see a nonlinear force-displacement curve.
      Do you have a photograph of the sheets and screw pieces before and after the test? If so, please insert those images into your reply.
    • Rania
      Subscriber
      Screw Geometry: dia=5.5 mm;L=20mm; the screw material is stainless steel. but I do not have material properties. but I used these form google; yield strength =600;tensile strength=800;
      Sheet geometry: plate thickness 1=2 mm ;plate thickness 2=3 mm ; length=100; width=40 mm; material properties: yield strength =250;tensile strength=320;
      screw placed at 30 mm from the edges of the two plates,hole in the plates=5.5 mm Dia
      I do not have pictures for the one screw test but here is picture of the 2 screws test,as shown below the screw failed by shear,
      I want to find a simple method to model these screws,
      I appreciate your reply

    • peteroznewman
      Subscriber
      One simple way to build this model is to take the shaft of the screw and split that face at two planes of the thin sheet. Use bonded contact to connect that thin cylindrical surface to the cylindrical surface of the hole in the thin sheet.
      Use Frictional Contact between the head of the screw and the top of the thick sheet. Use Frictional contact between the cylindrical surface at the top of the shaft (above the thin sliced face) and the cylindrical face of the hole.
      Use Frictional Contact between the two strips.
    • Rania
      Subscriber
      Dear i FOLLOWED what you've mentioned above, pictures below showed the unreformed shape and deformed shape, the stiffness of the FEA is different to the lab test? Do you have any comments? Thanks a lot


    • peteroznewman
      Subscriber
      Are the plates solid elements or shell elements?
      If the plates are solid elements, then you need to have four quadratic or eight linear elements through the thickness. A single solid element is stiffer than multiple solid elements through the thickness. That will shift the curve closer to the lab curve.
      What part of Australia are you in?
    • Rania
      Subscriber
      I have changed the no of elements but it did not make any difference thanks
    • peteroznewman
      Subscriber
      Check the value of the material Young's modulus for the units you used in your model. Is the value correct?
      Did you insert any type of Plasticity into the material model for the screw and the sheet materials? For example, bilinear kinematic hardening. What value and what units did you use?
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