Page 1 Design of a cotter joint If the allowable stresses in tension, compression and shear for the socket, rod and cotter be t s , c s and t respectively, assuming that they are all made of the same material, we may write the following failure criteria: 1. Tension failure of rod at diameter d 2 t dP 4 p s= 4.2.2.1F- Tension failure of the rod (Ref.[6]). 2. Tension failure of rod across slot 2 11 t ddt P 4 p?? -s= ?? ?? 4.2.2.2F- Tension failure of rod across slot (Ref.[6]). t Page 2 Design of a cotter joint If the allowable stresses in tension, compression and shear for the socket, rod and cotter be t s , c s and t respectively, assuming that they are all made of the same material, we may write the following failure criteria: 1. Tension failure of rod at diameter d 2 t dP 4 p s= 4.2.2.1F- Tension failure of the rod (Ref.[6]). 2. Tension failure of rod across slot 2 11 t ddt P 4 p?? -s= ?? ?? 4.2.2.2F- Tension failure of rod across slot (Ref.[6]). t 3. Tensile failure of socket across slot 22 21 2 1 t (d d ) (d d )t P 4 p?? -- - s= ?? ?? 4.2.2.3F- Tensile failure of socket across slot. 4. Shear failure of cotter 2bt P t= 4.2.2.4F- Shear failure of cotter. 5. Shear failure of rod end 11 2d P t= l 4.2.2.5F- Shear failure of rod end d 2 t Page 3 Design of a cotter joint If the allowable stresses in tension, compression and shear for the socket, rod and cotter be t s , c s and t respectively, assuming that they are all made of the same material, we may write the following failure criteria: 1. Tension failure of rod at diameter d 2 t dP 4 p s= 4.2.2.1F- Tension failure of the rod (Ref.[6]). 2. Tension failure of rod across slot 2 11 t ddt P 4 p?? -s= ?? ?? 4.2.2.2F- Tension failure of rod across slot (Ref.[6]). t 3. Tensile failure of socket across slot 22 21 2 1 t (d d ) (d d )t P 4 p?? -- - s= ?? ?? 4.2.2.3F- Tensile failure of socket across slot. 4. Shear failure of cotter 2bt P t= 4.2.2.4F- Shear failure of cotter. 5. Shear failure of rod end 11 2d P t= l 4.2.2.5F- Shear failure of rod end d 2 t 6. Shear failure of socket end () 31 2d d P -t= l 4.2.2.6F- Shear failure of socket end 7. Crushing failure of rod or cotter 1c dt P s= 4.2.2.7F- Crushing failure of rod or cotter 8. Crushing failure of socket or rod () 31 c dd t P -s= 4.2.2.8F- Crushing failure of socket or rod d Page 4 Design of a cotter joint If the allowable stresses in tension, compression and shear for the socket, rod and cotter be t s , c s and t respectively, assuming that they are all made of the same material, we may write the following failure criteria: 1. Tension failure of rod at diameter d 2 t dP 4 p s= 4.2.2.1F- Tension failure of the rod (Ref.[6]). 2. Tension failure of rod across slot 2 11 t ddt P 4 p?? -s= ?? ?? 4.2.2.2F- Tension failure of rod across slot (Ref.[6]). t 3. Tensile failure of socket across slot 22 21 2 1 t (d d ) (d d )t P 4 p?? -- - s= ?? ?? 4.2.2.3F- Tensile failure of socket across slot. 4. Shear failure of cotter 2bt P t= 4.2.2.4F- Shear failure of cotter. 5. Shear failure of rod end 11 2d P t= l 4.2.2.5F- Shear failure of rod end d 2 t 6. Shear failure of socket end () 31 2d d P -t= l 4.2.2.6F- Shear failure of socket end 7. Crushing failure of rod or cotter 1c dt P s= 4.2.2.7F- Crushing failure of rod or cotter 8. Crushing failure of socket or rod () 31 c dd t P -s= 4.2.2.8F- Crushing failure of socket or rod d 9. Crushing failure of collar 22 41 c (d d ) P 4 p?? -s= ?? ?? 4.2.2.9F- Crushing failure of collar. 10. Shear failure of collar 11 dt P pt= 4.2.2.10F- Shear failure of collar. Cotters may bend when driven into position. When this occurs, the bending moment cannot be correctly estimated since the pressure distribution is not known. However, if we assume a triangular pressure distribution over the rod, as shown in figure-4.2.2.11 (a), we may approximate the loading as shown in figure- 4.2.2.11 (b) Page 5 Design of a cotter joint If the allowable stresses in tension, compression and shear for the socket, rod and cotter be t s , c s and t respectively, assuming that they are all made of the same material, we may write the following failure criteria: 1. Tension failure of rod at diameter d 2 t dP 4 p s= 4.2.2.1F- Tension failure of the rod (Ref.[6]). 2. Tension failure of rod across slot 2 11 t ddt P 4 p?? -s= ?? ?? 4.2.2.2F- Tension failure of rod across slot (Ref.[6]). t 3. Tensile failure of socket across slot 22 21 2 1 t (d d ) (d d )t P 4 p?? -- - s= ?? ?? 4.2.2.3F- Tensile failure of socket across slot. 4. Shear failure of cotter 2bt P t= 4.2.2.4F- Shear failure of cotter. 5. Shear failure of rod end 11 2d P t= l 4.2.2.5F- Shear failure of rod end d 2 t 6. Shear failure of socket end () 31 2d d P -t= l 4.2.2.6F- Shear failure of socket end 7. Crushing failure of rod or cotter 1c dt P s= 4.2.2.7F- Crushing failure of rod or cotter 8. Crushing failure of socket or rod () 31 c dd t P -s= 4.2.2.8F- Crushing failure of socket or rod d 9. Crushing failure of collar 22 41 c (d d ) P 4 p?? -s= ?? ?? 4.2.2.9F- Crushing failure of collar. 10. Shear failure of collar 11 dt P pt= 4.2.2.10F- Shear failure of collar. Cotters may bend when driven into position. When this occurs, the bending moment cannot be correctly estimated since the pressure distribution is not known. However, if we assume a triangular pressure distribution over the rod, as shown in figure-4.2.2.11 (a), we may approximate the loading as shown in figure- 4.2.2.11 (b) (a) (b) 4.2.2.11F- Bending of the cotter This gives maximum bending moment = 31 1 dd d P 26 4 -?? + ?? ?? and The bending stress, 31 31 11 b 3 2 dd dd dd Pb 3P 26 42 6 4 tb tb 12 -- ?? ? ? ++ ?? ? ? ?? ? ? s= = Tightening of cotter introduces initial stresses which are again difficult to estimate. Sometimes therefore it is necessary to use empirical proportions to design the joint. Some typical proportions are given below: 1 d 1.21.d = 2 d 1.75.d = d 3 = 2.4 d 4 d1.5.d = t0.31d = b 1.6d = 1 l l 0.75d == 1 t0.45d = s= clearance d 3 b d 1 P/2 P/2 P/2 P/2 - + 31 1 dd d 64 31 1 dd d 64 - + 1 d 4 1 4 dRead More

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