Identification of the mechanical properties of tires for wheelchair simulation.

The development of high performance wheelchairs and wheelchair simulators requires dynamic models taking into account the properties of tires. In this paper the properties of two wheelchair tires are measured by means of a rotating disc testing machine and are compared with the properties of bicycle tires, which have similar dimensions and structure. Tests are carried out considering variations in speed, inflation pressure and load. The possibility of fitting experimental results with the Magic Formula, the Dugoff formula and a linear model is discussed. A dynamic model of a wheelchair is developed, which includes a linear tire model derived from experimental results. Steady turning and slalom manoeuvres are simulated. Numerical results show the effect of tire properties on the handling characteristics of the wheelchair.N/

Processing and Properties of Melt Processable UHMW‐PE Based Fibers Using Low Molecular Weight Linear Polyethylene's

The rheology, solid state drawability, morphology, and mechanical properties of polyethylene blends containing ultrahigh molecular weight polyethylene (UHMW-PE) and linear-low molecular weight polyethylene waxes (PEwax) are explored. Addition of PEwax enables melt processing of UHMW-PE and improves solid state drawability, providing opportunities in recycling of UHMW-PE waste. Small angle X-ray scattering results show that both PEwax and UHMW-PE align fully in the drawing direction, irrespective whether the PEwax has an Mn below or above the critical molecular weight at which entanglements can form (Mc). Tensile moduli of drawn specimen are in accordance to the Irvine–Smith model confirming that both UHMW-PE and PEwax align in the drawing direction and no chain slip occurs toward zero strain and both UHMW-PE and PEwax fractions, irrespective of their molecular weight, contribute fully to the modulus. Tensile strength of the blends scales according to the rule of mixtures where PEwax below Mc scale toward zero and those above Mc do contribute to the tensile strength. Modulus hence can be regarded as insensitive to the molecular weight of the PEwax used, whereas strength does show to be sensitive to the molecular weight of the PEwax

Fast, light-responsive, metal-like polymer actuators generating high stresses at low strain

Producing lightweight polymeric actuators able to generate high stresses typical of hard metals and/or ceramics remains challenging. The photo-mechanical responses of ultra-drawn ultra-high molecular weight polyethylene (UHMWPE) actuators containing azobenzene photo-switches with symmetrically attached polyethylene (PE) side chains are reported. Long PE side chains promote dispersion within the apolar UHMWPE matrix, and the ultra-drawn films are highly aligned. The ultra-drawn azobenzene-doped UHMWPE films have high Young's moduli (∼100 GPa) and are viscoelastic at room temperature at strains below 1%. The photo-mechanical response of the films is fast (6 × 104 Pa (kg m−3)−1) to UV or visible light at a low strain (∼0.06%). The actuator responds to rotating linearly polarized light, causing a photo-induced stress wave response. Such rapid, high-stress, low-strain, photo-mechanical responses are unique in soft polymer systems with physical values approaching hard metals/ceramics