**6.5 Stress and failure**

Shear stress is the stress that attempts to tear something separate. It is characterized as the shear force divided by the area over which the force is acting. In a wheelchair hub, its value is low and is rather higher in the X-brace pivot of a wheelchair. The modulus of elasticity (E) is a material property that tells how much a material make an effort not to distort when it is under stress. Strain is the proportion of how a lot of a material twists when under pressure.

Looking at the most extreme bending stress in a wheelchair axle with the limit elastic of the material used, it is possible to know whether the hub is sufficiently strong enough to hold up under the individual user's weight and other external forces applied on it. The weight of the person should not exceed 212.33 kg.
