Cushion foam sheets, made from different blends of wheat starch, were developed with a co-rotating twin-screw extruder machine and compared to commercial plastic foam cushions. An experimental study was developed to identify the effect of three ingredients: glycerol, gluten, and sodium bicarbonate on the bulk expansion, the cellular structure and the mechanical properties of the resulted foams. The experiments showed that the properties of the resulted foams were affected by the formulation. Foams with high level of glycerol and gluten content had lower densities and higher expansion ratio, cell size area, and cell wall thickness than blends with high level of sodium bicarbonate, which had better mechanical strength but less elasticity and shock absorption. The extruded materials had shown their suitability for cushioning use by having comparable physical properties with the commercial plastic foams. The dynamic cushion curve test indicated that the starch-based foam sheets provided good shock absorption properties. They had lower and larger deceleration peak than the expandable polyethylene foams we tested.
Random vibration tests are an efficient way to simulate the mechanical vibratory effects caused by transportation. The usual method is only concerned with the frequency distribution pattern of the signal using the average power spectral density. This work offers an additional method based on detailed analysis of instantaneous acceleration levels of a real road transport, which enables modelling of the statistical distribution of these levels. Continuous recording of acceleration signal all along the journey permits confirmation that this statistical distribution is not a Gaussian distribution but a modified Gaussian distribution, for which parameters are estimated and discussed. Therefore, it is possible to evaluate the transport severity by working out the appearance probability of acceleration levels greater than a fixed threshold and also the statistical moments, i.e. second order moment which gives the root mean square value together with fourth order moment (kurtosis) which evaluates the difference between the experimental distribution and the Gaussian distribution.
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