FEM CALCULATION
Designers should do strength analysis from early concept level and throughout the design design process
FEM analysis, especially of the simple static type, became cheap and practical several years ago. When working in for example Solidworks or NX, the structural strength of a concept can be analyzed for strength from very early on and at several times throughout the design process.
Being able to analyze strength is vital when designing structures that need to optimize size due to aesthetics, weight and price. Using this as input to conceptual decisions is highly benificial for both team work, risk reduction, and the design process as a whole.
Worst cases: Situation where user applies load to an extension of the chair, creating a large moment in the floor base structure. This case may happen when the monitor is used as a handle support as a user falls down.
Aluminium structures: A static FEM analysis of a welded aluminium structure, consisting of casted and sheetmetal parts welded and screwed together.
Only the flexing 1/4 segment of the whole structure was analyzed in order to save time.
Sandcasted aluminium: Sand casted aluminium can work very well as load bearing structures and handling dynamic loads, as the casted material is usually less porous and can be made quite thick. Attention must be paid to localized stresses in analysis, as fluctuating loads from vibrations and shocks can lead to fatigue failures even though the stress lies below yield limit. Note the large wall thickness and edge fillets that help distribute the forces.
Die-casted aluminium: A part design before and after strength optimization. This armrest column was analyzed for torsional strength and stiffness, which comes into play whenever a user lifts themselves up or rests their hips on an armrest.
Strength analysis helps in designing the stiffenning rib pattern, and deciding on edge fillet sizes to better distribute the bending forces from the top joint and downwards.
Mechanical evaluation: A very early mock-up for a heavy-duty armrest joint in order to make a strength analysis before deciding on the correct path. In this case, the linked mechanism distributes a sideways 100kg load on the armrest tip evenly on the lighter areas.
