Project Evo II Avanti Chrono Evo II - Our Fastest Bike. Ever.
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Structure

Composite Lay-up

A carbon frame’s stiffness is essentially
determined by two things; firstly its surface geometry
and secondly the mechanical
properties and orientation of its composite lay-up.

Composite lay-up is the process of choosing not only how the carbon fibres are oriented but also the selection of different carbon fibre types to optimise strength and stiffness. Some areas require stiffer carbon which is typically more brittle and other areas require high strength carbon which may be more flexible. Optimisation of the weight and strength of the frame is about a compromise between these two requirements.

For a bike designed predominantly for speed, the shape of the frame and its aerodynamic performance is fundamental. This means the geometrical stiffness comes secondary to the aerodynamic performance and it is within these aerodynamic shape parameters that the carbon laminate must operate to create both a fast and stiff structure.

FEA Simulation

Finite Element Analysis (FEA) is the process whereby a CAD designed 3D computer model of a frame is created. The physical properties of the materials and the orientation and locations of the fibres are simulated. Using mathematical equations, the frame is stressed and analysed for a predetermined set of load parameters.

What does that mean? The ADT team can very accurately test if the proposed design will perform to the level that they expect from it without having to build actual models of the bike.

The ADT team can very accurately test if the proposed design will perform to the level that they expect from it without having to build actual models of the bike.

How Does FEA Work?

The proposed shape is broken down into thousands of points called nodes which in turn constitute a mesh. The mesh is in 3d and is in the shape of the frame. It is then programmed with the properties of the materials and also the material arrangements.

Certain areas deemed to be of high stress, such as the bottom bracket and head tube in particular, contain more densely compacted nodes for deeper analysis and, likewise, areas of lower stress contain fewer.

Different restraints and loads are applied to the model dependant on the mode of loading. These could be for head tube stiffness, bottom bracket stiffness, torsional stiffness or other selected loadcases.

Analyse, Repeat, Amend

Every part of the frame is then reviewed for stress and stiffness/deflection. It is at this point that optimisation of the laminate is carried out. Areas where material can be removed are modified and areas which may need more material or different arrangement of fibres are changed and the model is re-solved.

This process is repeated until stiffness and weight requirements are met. This process also removes any stress concentrations close to or above the limit set by the team. These are either completely removed or reduced to within the tolerances the ADT team have set. At all times the overall aerodynamic shape is taken into consideration and prioritised.

All the information gathered is then put through a series of mathematical programs that solve the data accrued. The results of the stress and deformation are then displayed to be pored over by the ADT team.

Prototypes

When all is said and done, no amount of computer modelling can compare with the raw data amassed from real-world testing. This is where a number of prototypes are manufactured from the final optimised design solution and tested.

The prototypes are placed into a number of jigs specifically designed to test bike parts. These jigs analyse all the same data the computer models were testing.

How does it work? To measure bottom bracket stiffness the frame is anchored at both the headtube and the chain stays, then a weight is placed through the bottom bracket at an offset and the amount of deflection is measured. This data is then used to calculate the stiffness of the bottom bracket area.

The same process is used to measure stiffness at both the head tube and the chain stays, with the frame being anchored at different points depending on what is being measured.

For fatigue testing the frame is placed on separate specific jigs and the different areas such as the bottom bracket, head tube etc. are subjected to the same forces that are applied in the real world, but at much higher loads.

These forces are applied through 100,000 cycles whilst the frame is being tested for any changes in feedback which may inform the team of any weaknesses that may exist.

If anything is found to be beyond the limits set by the team then it is re-designed and re-analysed through precisely the same processes and the information gathered is stored for future test models.