2 Replies Latest reply on May 14, 2012 9:35 AM by Vijayendra Srinivasa Rao

    Stress analysis on Bracket

    Vijayendra Srinivasa Rao
    Vijayendra Srinivasa Rao May 10, 2012 9:56 AM

      Hi,

       

      I have a concern regarding the stress analysis on the bracket I have designed.

       

      The bracket is carrying Horn Antenna Assy which is then fixed to the Master Block . Then the entire Assy is purely under Gravity due to its own Mass.

       

      The weight of the Assy is 3.5Kg including Bracket.

       

      I have done some analysis on this assy applying gravity as loading condition and providing the Fasteners from the Connector facility in solidworks.

       

      I have used AISI 304 Steel Alloy for the Fastener Material.

       

      I am veryfing whether the Bolt assy is within the defined Factor of safety or not.

       

      In case1: I have applied preload strength data in solidworks for bolts as 2.5Nm torque with deifned FOS of 2. In this case I got a factor of safety of ~5. Which is a good sign of strength.

       

      In case2: I have applied preload strength data in solidworks for bolts as 4.2Nm torque with deifned FOS of 2. In this case I got a factor of safety of < 2. Which is not acceptable within this very small increase of torque value.

       

      Can some give me some explanation whether I am performing the correct method for the analysis or not.

       

      Appreciate the feedback.

       

      Thanks

      Vijay

        • Re: Stress analysis on Bracket
          Mikael Martinsson
          Mikael Martinsson May 11, 2012 7:57 AM (in response to Vijayendra Srinivasa Rao)

          Hi.

          A picture of the problem would of course be nice to understand it better. (dimension of the bolts, bolt direction and distances compared to the COG-load to understand axial, shear and bending moments).

           

          My knowledge is poor on how to properly use the safety factor and the "safety check plot" with bolt connectors in SW Simulation. Since you normally preload the bolts, lets say up to 75-90% of its proof load strength it is kind of hard to reach a FOS of 2 or 3 on each bolt. Especially if you use yield limit as "bolt strength" and have other loads that imposes shear, bending moment or additional axial loading to the bolt. I always set FOS = 1 as the limit for each bolt in the "strength data" section and then look at the combined FOS for the bolt pattern. Hand calculation is also a good idea.

            • Re: Stress analysis on Bracket
              Vijayendra Srinivasa Rao
              Vijayendra Srinivasa Rao May 14, 2012 9:35 AM (in response to Mikael Martinsson)

              Hello Mikael,

               

              Thanks for your reply. Now I have uploaded the image which I am doing some analysis.

               

              Bracket Assy with Horn Antenna.JPG

              As you mentioned some point in the above, I have calculated the Torque preload condition manually (which is 4.5Nm) and applied on each bolts. Also I have used the Yield strength as the strength of the fastener Assy.

               

              During the simulation I have defined the FOS of 1.5. The combined Fos on each bolt is greater than 1.5 and I have verified with hand calculation as well.

               

              When I define a Fos of 2 o each bolt, the result shows less than Fos 2. I was confused about this result. Can you please give some information regarding this result?

               

              Also, can't we do the analysis by defining higher Fos on each Bolt, because the strength of the 1/4-20 Hexagonal Headed bolt with A2 ST/ST has to withstand higher load.

               

              Thanks

              Vijay