Shell and IMechE Pakistan have taken the first step towards establishing a long-term relationship; Shell floated the ideas of stress analysis of their tank lorries as
student projects.
Two student chapters, Pakistan Navy Engineering College (PNEC-NUST) and School of Mechanical and Manufacturing Engineering of National University of Sciences and Technology (SMME-NUST) undertook to work on the project. The objective was to provide Shell with an improved design of the Tank Lorry with enhanced safety against roll over and reduced cost of operations.
CPEC and Pakistan
With the completion of the China-Pakistan Economic Corridor (CPEC) in 2018, Pakistan will experience accelerated economic growth with increased living standards. Transportation will rise exponentially throughout the country and will necessitate regular and more increased supply of fuel to different parts of the country from the oil refineries in the south. Transportation costs will therefore play an important role in the overall profitability, scalability and market share of key players like Shell.
Ladder Frame Chassis
Tank lorries are used for transporting several thousand litres of fuel between cities. The chassis frame is an integral part of the lorry as it sustains the bulk of the loading experienced by the lorry; therefore a structurally sound chassis is crucial for the lorry to perform its functions.
The chassis frame of a lorry functions not only as a support base for the entire structure, but is also, essentially, the component on which the entire loading of the vehicle is projected. The loading includes the weight of the vehicle, including body, tank (with the carried fuel) and components, to be modeled under different static and dynamic conditions for the vehicle. It is imperative, that the chassis must be structurally sound enough to withstand not only the static loading, but must also function properly in dynamic conditions, and especially off-road conditions where road bumps are considered.
Finite Element Analysis (FEA) is an important tool for the modeling and analysis of such structures. The chassis frame, isolated from the vehicle, is first modeled in appropriate CAD software. FEA software models the frame structure based on specified boundary conditions. Based on the results of the FEA, decisions regarding design changes are easily made to ensure optimum choice available. The deciding factors in this analysis are the stress distribution and the maximum deflection that the structure can withhold. FEA is often used in conjecture with experimental procedures for verification of accuracy of the results.
Three load cases were defined for initial studies from literature review of existing ladder frame chassis - bending, torsional and bump cases. Under these studies, the stresses on the entire frame were mapped and critical regions located. This was essential as it assisted in improving the designs.
Regions with very low stresses like the running gear assembly were identified to undergo reduction in weight and centre of mass. Enhancing the designs provide around a 50kg of weight reduction. However, these were only the initial studies. Further studies on changing the overall cross section can lead to weight reduction of up to 200kg.