A Study into How to Assess Low Cycle Fatigue Behaviour of an Aluminium Conical Lighting Column
Fatigue failure of lighting columns, as a result of wind and traffic induced vibration, has received particular attention in recent years with the increased number of premature lighting failures on exposed sites. Designs involving welds are particularly at risk due to changes in material structure. Aluminium Lighting Company (ALC) are market leaders in the UK of fully extruded Aluminium lighting columns. Eliminating the use of welds within their columns could potentially give superior fatigue performance and extended life of the columns.
Challenges
The present study will investigate how to characterise low cycle fatigue behaviour of the aluminium lighting columns via Finite Element Analysis (FEA) underpinned by low cycle fatigue testing and supported by the microstructural evaluation of the columns. In addition, ASTUTE will assist the company with the set-up and data analyses on actual field tests of columns under wind-loading to provide real-time fatigue data for FEA analysis.
The collaborative work looking at using FEA, fatigue test data and microstructural evaluation demonstrated the feasibility of this approach for robust structural loading behaviour evaluation for ALC’s columns. The FEA modelling has illustrated regions of the column where fatigue could be an issue. However, after metallurgical inspection it was found that the fully extruded columns exhibited a uniform microstructure, along with the FEA demonstrating stresses well below the fatigue limit threshold. As a result, the ALC columns show good resistance to fatigue cracking over the lifetime of the column.
Impact
FE analysis has highlighted that pressed stressed columns show superior fatigue resistance to welded columns. The stresses simulated in the column have demonstrated that the fatigue life of the column will exceed the desired lifetime of the column. This enables these columns to be placed in the most demanding of environments with safety the number one consideration. ALC will also have confidence in employing this approach in the future.
