In this video we will learn about design procedure for cotter joint, this cotter joint also known as socket and spigot joint, so here it consists of 3 parts. the red colored part is socket, inside this socket there is another part shown by green color i.e. spigot end, the third part is cotter shown by blue color, which we are using to assemble the socket and spigot, the cotter joint is used for tensile load as well as for compressive load. so the major dimension are, diameter of rod denoted as small d, here load p applied to both the sides of cotter joint, here socket is a hollow part therefore d1 is outer diameter of socket, d2 is internal diameter of socket, now this internal diameter of socket = external diameter of spigot which is d2, here d3 is the diameter of spigot collar, d4 is the diameter of socket collar, here b is the mean width of cotter, here cotter is a part which is having slope on one side and it is straight on other side. here a is the distance from end of slot to end of spigot rod and here c is thickness of socket collar and e is thickness of socket, and here thickness of cotter we denoted as small t. Now let us analyze types of failure occurs during application of cotter joint. So here i make a table of various stresses induced in cotter joint. so there are three tensile stress, four shear stress, three crushing stress, and one bending stress. here minimum area of cotter joint is diameter of rod i.e. small d. so the first failure occurs at minimum area, i.e. tensile stress in Rod which is = load p divided by cross section area of rod i.e. (pie by 4 d square). The next failure occurs due to tensile stress at diameter of spigot end, so the formula is load p divided by area of cross section i.e. (pie by 4 d2 square) minus d2 multiply by thickness small t. The next tensile stress is at outside diameter of socket end, and the formula is load p divided by area of cross section i.e. (pie by 4 d1 square minus d2 square) minus thickness small t into (d1 minus d2). so these are 3 tensile stresses in cotter joint. now the next stress is shear stress. So failure occurs due to shear stress at diameter of spigot end collar, and the formula is load p divided by area of cross section i.e. (pie d2 into thickness t1). The next failure occurs due to double shear stress at distance from end of slot to end of spigot, so the formula is load p divided by area of cross section. The next failure occurs due to double shear stress at thickness of socket collar, so the formula is load p divided by area of cross section i.e. 2 into (d4 minus d2) into thickness of socket collar i.e. capital C. The next failure occurs due to direct shear stress at width of cotter, and the formula is load p divided by area of cross section i.e. 2 into width of cotter b into thickness small t. so these are 4 shear stresses in cotter joint. now the next stress is crushing stress. So failure occurs due to crushing stress at diameter of a spigot end, and the formula is load p divided by area of cross section i.e. diameter of spigot end d2 multiply by thickness small t. next failure occurs due to crushing stress at outside diameter of spigot end collar and formula is load p divided by area of cross section i.e. (pie by 4 d3 square minus d2 square). next failure occurs due to crushing stress at outside diameter of socket collar and formula is load p divided by area of cross section i.e. d4 minus d2 multiply by thickness small t. so these are 3 crushing stresses in cotter joint. now the next stress is bending stress. so failure occurs due to bending stress in width of cotter so the formula is Load p into 2d4 plus d2 divided by 4 tb square, here t is the thickness of cotter and b is the mean width of cotter.
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