Design of joint 5-6 (pin joint) — example

Design data

External forces: F_Z = 700 N.

Dimensional constraints: the square tube 5, of size h₅ = 50 mm and thickness t₅ = 5 mm, is assembled with the square tube 6, of size h₆ = 50 mm and thickness t₆ = 5 mm; Z₁ = 180 mm.

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

Design constraints: dimensional interchangeability.

Materials and heat treatments

A weldable material, S235 steel according to SR EN 10025-2 (STAS 500/2), was chosen for elements 5 and 6.

The pin is made of a steel for mechanical construction, e.g. E295 (SR EN 10025/2005).

Material properties

Allowable tensile stress of the pin material: σ_at = σ₀₂/c = 295/(2…3) = (97.66…147.5) MPa, σ_at = 100 MPa adopted; allowable shear stress of the pin material: τ_af = (0.6…0.8)σ_at = (0.6…0.8)·100 = (60…80) MPa, τ_af = 70 MPa adopted.

Allowable steel-on-steel crushing stress: σ_asț = 70 MPa.

Sizing and checking

Sizing

From the sizing relation obtained from the crushing strength conditions of the pin joint, with F = F_Z = 700 N, t_i = t₅ = 5 mm and t_e = t₆ = 5 mm, the required pin diameter is

D_b = 10 mm is adopted.

Checking

The shear stress in the pin, with F = 700 N and D_b = 10 mm, is

and the check τ_f ≤ τ_af becomes 4.45 ≤ 70 MPa (satisfied).

Constructive-technological shapes

Constructive-technological drawings

Adopted dimensions and constructive-technological parameters:

– dimensions: h₅ = 50 mm, t₅ = 5 mm, h₆ = 60 mm, t₆ = 5 mm, L₆ = 70 mm, D_b = 10 mm, l₁ = 15 mm, l₂ = 20 mm, L₅ = 205 mm;

– technological operations: milling the tube ends, drilling/reaming the pin holes;

– roughness of the machined surfaces: R_a1 = 12.5 µm, R_a2 = 6.3 µm;

– sharp edges are chamfered 1×45°;

– the position of the pin hole (and, if needed, of the adjustment pin hole) is set when drawing the assembly.

Adopted dimensions of the joint components:

– spring-type (safety) split pin, d = 2.5 mm;

– washer for pins: d₁ = 10 mm, D = 20 mm, h = 2.5 mm.