Finite element analysis (FEA) is a computerized method of predicting how a product design reacts to real-world forces. FEA shows if a product will break, wear out, or work the way it is designed, before it is made.
We worked with Evotech to conduct a series of tests on the steering pivot box and front of the bike assembly. Our aim was to prove the structural layout of the design and determine where it needed more work, rather than define detailed design solutions.
The FEA models successfully predicted how the structure would respond to the relevant ISO stress tests (load cases), and their results fed in to the build of real prototypes.
Evotech’s FEA models showed us that the steering pivot box, which eliminates the conventional fork steerer-tube, was efficient. Though requiring further development work, it offered a viable development path.
They showed exactly where we needed to focus our effort — most importantly, the handlebar connection design, which did not work well under either static or rocking loads. (Think of a rider sprinting, rocking the bike from side to side.) This was down to the narrowed section at the bolted fork interface.
HANDLEBAR TO FORK UPPER JOINT EVOLUTION
Snapshots of how we used FEA to test and refine the radical design of the TF1 interface between the handlebar and the steering pivot box.
The FEA testing predicted this region of the design would fail in the real world. We redesigned it before prototyping, and it became a key focus for prototype testing and development, with several iterations of the joint’s geometry. Figures above show revisions 1–4 of this critical region of the design.
FEA Assessment of KÚ Cycle BAR / Fork
Assembly under ISO 4210 Load Cases
Hybrid shell/solid FEA model of the geometry, with the appropriate connections between discrete components (CQUAD4/CTRIA3 shell, CTETRA10 solid element types).
Materials –‘standard’ Woven/UD mixed laminate developed for a similar application (10 plies/1.58 and 18 plies/3 mm thick), based on a T800 system for both materials, aligned , where possible, with the key axes (along tubes etc. ). Draping effects not considered.
ISO 4210 loading definition for forks and bars to be defined as follows;
BS EN ISO 4210 5:2015 (Steering Test Methods)
Test 4.3 ‘Handlebar and stem assembly Lateral bending test’
Test 4.9 ‘Handlebar and stem assembly Fatigue test’
BS EN ISO 4210 6:2015 (Frame and Fork Test Methods)
Test 5.4 ‘Front fork Rearward impact test’
Test ‘5.5 Front fork Bending fatigue test and rearward impact test’
Overall structure represented by shell elements for thin walled sections (PCOMP ply based laminate definition) using appropriate mesh density and quality for stiffness assessment. Thick sections are modelled but not considered in the Max Strain Failure Index strength calculation.
Composite shell structure using laminate offset (PCOMP Z0) to reflect Outer Mould Surface build direction.
Idealised connections (reflecting the appropriate degrees of freedom) used to represent assembly interfaces and test structure. Local features simplified so that the overall effects/laminate strength can be assessed.
In the absence of composite fatigue data, a static to fatigue ‘knock down’ of 2.0 is applied , based on aerospace industry best practise.
Post processing of FEA output performed to allow generation of;
Calculation of laminate failure indices, based on Max Strain criteria.
Models will be built and post processed using MSC Apex/MSC Patran and solved using MSC Nastran.
The following FEA solution sequences considered.
Linear Static Analysis (SOL101) for static and fatigue load cases.
Linear Modal Dynamic Analysis (SOL103) to determine critical frequencies and down stream time steps for impact load case.
Linear Transient Dynamic Analysis (SOL112) for impact load case (strain rate effects not considered).
Model and Output check using standard approach, based on numerical response and ‘fit for purpose’ assessment.