Design of joints 12-13, 12′-13′ (welded joints) — Design of Automotive Towing Devices

A. Loading diagram and design data

External loading diagram

Loading diagram of the left welded joint

Design data

External forces: F_X, F_Y, F_Z act at distances L_c (Ex.3.1), X₁, X₂, Y₁, Z₁ (Ex.1.2.2); the forces and moments at the centre of the welded joint 12-13 (12′-13′) are calculated (Calc.0):

F_Xs = F_Xd = F_X/2,

F_Ys = F_Yd = F_Y/2,

F_Zs = F_Zd = F_Z/2,

M_X13 = F_Y (L_c + Z₁)/2,

M_Y13 = F_X (L_c + Z₁)/2 + F_Z (X₁ + X₂)/2,

M_Z13 = F_X Y₁/2 + F_Y (X₁ + X₂)/2.

Note. Since the external forces may act in either direction in service, the maximum possible loads were determined (the components were added in the moment relations).

Dimensional constraints: tube 12, with dimensions h₁₂, t₁₂ (Ex.6.1), is welded to tie rod 13 of thickness g₁₃ (Ex.7.1).

Operating constraints: temperature T = (−30…40) °C; outdoor working environment with high humidity.

Design constraints: weldable materials.

B. Choice of materials and heat treatments

Elements 12 and 13 were designed assuming they are made of weldable S235 steel (Annex.M.01). This steel is not heat-treated before welding; after welding, the subassembly may undergo stress-relief annealing. For the adopted steel, the yield strengths σ₀₂ and the ultimate tensile strengths σ_r are retained for the calculations.

C. Design of the constructive shape

Constructive model

Constructive features and constraints

– the weld throat thickness a should be smaller than the wall thickness of tube 12 and of tie rod 13, a < min(t₁₂, g₁₃);

– the two elements must be perpendicular;

– a fillet weld is made along the closed contour (square section).

D. Calculation model, sizing and checking

Calculation model

The calculation model is similar to the general calculation model in Sec.3.5.

Calculation data

– loading: F_X = F_Xs, F_Y = F_Zs, F_Z = F_Ys; M_X = M_X13; M_Y = M_Z13; M_Z = M_Y13;

– shape and dimensions: the inner contour of the weld bead is a square of side h = h₁₂;

– materials: σ₀₂ – the yield strength; σ_at = σ₀₂/c – the allowable tensile stress; c = 2…3 – the safety factor; τ_afs = (0.6…0.7)σ_at – the allowable shear stress of the weld.

Sizing

Using calculation window Calc.3.5.1, the weld throat thickness a^nec is determined; a whole value a > a^nec is adopted.

E. Design of the constructive-technological shape

Constructive-technological drawing

Recommendations for choosing the dimensions and constructive-technological parameters:

– weld throat thickness, a;

– the weld is made along the closed contour (as symbolised);

– after welding, the subassembly undergoes stress-relief annealing.