Design of joint 7-8 (pin joint) — example

Design data

External forces: F_X = 1500 N.

Dimensional constraints: the square tube 7, of side h₇ = 50 mm and thickness t₇ = 5 mm, is assembled with the square tube 8, of side h₈ = 60 mm and thickness t₈ = 5 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 7 and 8.

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

Material properties

Allowable shear stress τ_af = 60 MPa.

Allowable steel-on-steel crushing stress σ_as = 70 MPa.

Sizing and checking

Sizing

From the sizing relation obtained from the crushing strength conditions of the pin joint, with F = F_X = 1500 N, t_i = t₇ = 5 mm, t_e = t₈ = 5 mm and σ_as = 70 MPa, the required pin diameter is

D_b = 10 mm is adopted.

Checking

The shear stress in the pin, with F = 1500 N and D_b = 10 mm, is

and the check τ_f ≤ τ_af becomes 9.55 ≤ 60 MPa (satisfied).

Constructive-technological shape

Constructive-technological drawing

Adopted constructive-technological parameters

– dimensions: h₇ = 50 mm, t₇ = 5 mm, h₈ = 60 mm, t₈ = 5 mm, L₇ = 105 mm, L₈ = 95 mm, l = 30 mm; D_b = 10 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 joint components

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

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