The challenge is to perform a feasibility study aiming at replacing the single-sided swing-arm for high performance MV Agusta F4 1000R and “Brutale” 990R/1090RR motorcycles made in aluminum alloy with a Resin Transfer Molding (RTM) carbon composite one. Injection-based technologies for long fiber reinforcement, such as RTM, have been found particularly rewarding for motorsport cars and motorbikes.
After an initial re-assessment of shape and design of the part to make it more suitable to be manufactured with RTM technologies, Nexus has been used to guide an Abaqus® FE model toward the identification of optimal solutions.
A proper design of the swing-arm requires defining constraints on structural strength (maximum level of stresses/strain) and on structural stiffness (vertical, lateral and more important torsional). This will be done launching a Abaqus® FE model of the swing-arm and reading relevant results from within Nexus. Additional manufacturing constraints have been defined to control change in thickness between different areas of the laminate while changing local lamination, i.e. number of plies and orientations.
A multi-objective approach is followed: solutions that guarantee minimum weigh for a given torsional stiffness and meet all the other requirements are searched for by minimizing the weight while maximising the torsional stiffness. Due to the relatively large number of discrete variables such as number of plies in the composite laminates, Genetic Algorithms seem the preferred choice for this particular application. Accordingly NSGA-II algorithm has been selected from within Nexus, even is different procedures can be used with just few clicks of the mouse.
The optimisation process involves 60 design variables, used to describe composite laminate evolution in the swing-arm, together with 18 constraint functions, including ramp-rate manufacturing constraint overall the structure.
Advantages in using Nexus:
Main advantages of using Nexus to guide the optimisation process are:
- easy integration of external FEM and CFD solvers among which Nastran, Abaqus, Radioss, Fluent, Ansys and Adams;
- parallel and concurrent evaluations to exploit your hardware and software resources in the best possible way. A scalable architecture you can tune application by application;
- access to all your the results via organised tables and SQL extern databases;
- advanced Design of Experiment (DoE) and statistical tools to explore and analyse your results;
- state-of-the-art libraries for single- and multi-objective optimisations, Design of Experiments and response surfaces modelling.
The obtained Pareto’s frontier shows that the torsional stiffness increases together with the weight, this being along the line of common engineering understanding. However, the Pareto’s frontier well define this relation showing that a composite Swing-Arm will lead to a reductions of twisting angle up to 19 % . Alternatively, if the original torsional is preserved, a weight reduction of about 18% can be achieved.
The stress analysis of the optimized configurations shows that stress levels are below the imposed constraint values, i.e. 100 MPa in absolute value. Accordingly, strength and damage tolerance requirements are fulfilled for the selected configuration.
(*)Accepted for publication on Applied Composite Materials.
Airoldi A., Bertoli M.D., Lanzi L, Sirna M, Sala G,
“Design of a motorcycle composite swing-arm by means of multi-objective optimisation”.