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.
Packaging systems always endure some type of damage during transportation, and Wöhler curves are typically used to determine the mechanical wear evolution of a packaging system. Damage estimations can be performed using a Rainflow method, but continuous stress recording is required. However, this recording is not always possible, so global transportation vibrations are represented by the power spectral density (PSD). In this paper, the damage of a system according to the Wöhler curve was studied. The Basquin model was used to determine the mechanical wear evolution of the system, and the mechanical behaviour was established by extracting the Basquin coefficient b and the constant system C from the Wöhler curves. A Wöhler curve was further realized for a packaging system, and its Basquin coefficient b and system constant C were also extracted. Damage is estimated by the accumulation of the stress cycles using the PalmgrenMiner rules. In this paper, the maximum peaks of the cycle were detected in a signal. The density probability of the maximum stress apparition was also constructed from a multivariate Gaussian model. PSDs have the same statistical properties as the corresponding temporal events, so these statistical properties were extracted by the spectral moment method. Furthermore, a damage equation was proposed using the PSD, and the damage induced by different PSDs was determined from the damage equation and compared with the actual duration on a vibration table.
INTRODUCTIONThe global road network is growing each year, and it is composed of millions of kilometres. Various types of roads or road conditions are often encountered with longer travel distances with countless stress possibilities. The study of these stresses is a crucial point for determining the viability of products. It is also important to design product packaging with transportation in mind.Many packaging solutions exist to protect goods against transportation hazards, but these stresses induce some modifications to the mechanical properties of these systems by damage accumulation. If the damage accumulation is too important, then the packaging system cannot properly protect the packaged goods.Some damage measurement approaches were proposed in the literature, but they are mainly based on continuous acceleration recording 1 or on the consideration of a particular parameter or phenomenon of a packaging system. 2,3 This method uses continuous signal recording. The most widely used method to estimate damage from a continuous recording is based on the study of the evolution of the mechanical properties by accumulating the cycle stress. This method uses the Wöhler curves.These curves describe the damage wear evolution of a system by counting the number of stress cycles for a particular magnitude until the cycle breaks. The system mechanical wear evolution knowledge is based on a temporal cycle extraction method, such as Rainflow, for determining the global damage.In transportation studies, power spectrum densities (PSDs) are traditionally used to ...
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