Design of joint 8-9 (welded joint) — Design of Automotive Towing Devices

A. Loading diagram and design data

External loading diagram

Loading diagram of the welded joint 8-9

Design data

External forces: F_X, F_Y, F_Z act at distances L_c (Ex.3.1), X₁, Z₁ (Ex.1.2.2), h₆ (Ex.4.1) and a (Ex.5.1); the moments at the centre of the square section are calculated (Calc.0):

M_X9 = F_Y (L_c + Z₁),

M_Y9 = F_X (L_c + Z₁) + F_Z (X₁ + h₆/2 + a),

M_Z9 = F_Y (X₁ + h₆/2 + a).

Dimensional constraints: the lower column body 8 is welded to flange 9, with dimensions h₈, t₈, g (Ex.4.3).

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

Design constraints: weldable materials for elements 8 and 9.

B. Choice of material and heat treatment

Element 8 was designed in weldable steel (Annex.M.01). A weldable steel is also adopted for element 9. These steels are not heat-treated before welding; after welding, the subassembly may undergo stress-relief annealing. For the adopted steels, 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 t₈ of tube 8 and the thickness g of flange 9 (a < min(t₈, g));

– the two elements must be perpendicular;

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

D. Calculation model and sizing

Calculation model

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

Calculation data

– loading: F_Xs = F_Z, F_Ys = F_X, F_Zs = F_Y; M_Xs = M_Z9; M_Ys = M_X9; M_Zs = M_Y9;

– shape and dimensions: the inner contour of the weld bead is a square of side h = h₈;

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

Sizing

The weld throat thickness a^nec is determined with calculation window Calc.3.5.1; a whole value a > a^nec is adopted.

E. Design of the constructive-technological shape

Constructive-technological drawing

Recommendations for choosing the dimensions and technological parameters:

– weld throat thickness, a;

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

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