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Drop Test theoretical calculations & material selection

  1. Oct 29, 2012 #1
    Hello,

    I am currently assigned to perform a drop tests on a unit that we sell. Thing is that I am an Electronic Engineer so I am not best at mechanics.

    I am wondering whether you can calculate forces and required material strength to withstand the drop test. The reason I am asking is because one of the units I testes shattered at the corner.

    Here are the specs:

    Height - 48 inches (122cm)
    Unit weight - 5kg
    Dropped on 3 chipboard plates carpet and concrete floor.
    Every corner, bottom and sides is secured with 7mm thick rubber bumpers. The corners are rounded and bottom one form kind of rectangular with an empty space

    -------------------
    | |
    | | (diagram)
    | B |
    |\ /|
    -------------------

    B stands for battery and the corner which shattered was underneath it.

    During my test unit fell roughly flat on the chipboard and on one corner where slightly more weight is located above it (the battery) shattered to pieces despite being protected by rubber bumper.

    Now my questions are:
    1) Injection moulding - can knitlines (non are visible in the shattered area but they are present in some other areas of the case) or any other injection moulding defects contribute to that, if so what to look for?

    2) How to calculate the best material for use (current case is made from Minlon 10B140NC010 but the front cover was made from Zytel70G30HSL which seem to be stronger. Front cover do not protrude much but having said that 2 drop tests were performed (2 back covers - one damage to mounting posts inside case, one shattered corner) while only 1 front made from Zytel used without any sign of damage.

    Unfortunately I cant provide detailed pictures due to nature of the project and as such any information can be only roughly estimated but I would appreciate any help in that matter (especially calculations).

    Kind Regards
    Artur
     
  2. jcsd
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