Issue 30

N. Petrone et alii, Frattura ed Integrità Strutturale, 30 (2014) 226-236; DOI: 10.3221/IGF-ESIS.30.29 227 development of customized load cells to be applied to the vehicle components for the complete measurement of loads acting on the vehicle interfaces with the ground [5,6] or with the rider [7]. On the basis of this set of information, engineers can develop methods for the virtual assessment of main components of the motorcycle such as frames and suspensions [7-9] by using multibody codes for the prediction of vehicle dynamics or finite element analysis for the assessment of frame stiffness properties and fatigue life of casted, CNC machined and welded components. The use of laboratory tests has always been supported by manufacturers as a tool for ensuring experimentally the durability of their product, despite the lack of mandatory regulation from an international body. Manufacturers are responsible for any damage that customers can encounter during the supposed use of their vehicle, therefore they have to ensure the degree of safety of the product under their responsibility. Laboratory tests however, as we can find in the manufacturers or research centers laboratory, can range from simple single channel constant amplitude fatigue tests [8,10], to multiple channels variable amplitude fatigue tests [11-15] of the full vehicle [11,15] or of its components [12,13]. Within the different experiences developed throughout the world, further distinction can be made between the benches involving a dummy in the tests, therefore using inertial forces to reproduce the actions stressing the vehicle [3,11], and the benches involving a reaction frame around the component [10,12,13,14]. Variable amplitude testing of full motorcycles, despite its appealing ability of reproducing exactly the load histories measured in the field, require acceleration procedures to ensure that the mileage demanded from the component assessment may be reproduced in a reasonable and industrially sustainable amount of time. Very few information are available in the literature regarding these acceleration procedures [14,15] as this may be the bottleneck of the procedure or the real know-how that companies tend to protect. Aim of the present work was the instrumentation of a maxi scooter for the field collection of service loads acting on the scooter’s main components such as frame, fork, handlebar, rear frame and suspension. Service loads collected during a representative amount of field tests were used to develop an accelerated test procedure for the accelerated bench fatigue testing of a new model prototype comparison. O VERALL METHOD DESCRIPTION he method adopted for the study was defined starting from the request of a motorcycle manufacturer for the fatigue assessment of a new prototype of maxi-scooter that was under development (prototype P1), whose final version was not yet equipped for road tests. The manufacturer wanted to make sure that the prototype P1, supposed to be used for the early design stage road tests, would ensure to test drivers the proper fatigue durability and survive a 50’000 km drive test campaign without any failure on main safety components. The study then was based on a service loads collection campaign using an existing maxi-scooter produced by a competitor, chosen by the prototype manufacturer as similar in dimensions and performances. The scooter was a Yamaha Tmax, 500 cc: two samples of this motorcycle were available for the study. The first sample, named TmaxS was instrumented and calibrated for the field data collection. The instrumented scooter TmaxS was also used to tune the fatigue test bench and to verify the amount of fatigue damage that was applied by the accelerated test load histories on the bench with respect to the target fatigue damage as collected from the field tests. The second sample, named TmaxD, was used for the fatigue testing of the commercial scooter. The prototype sample P1 underwent the same fatigue tests of the TmaxD to verify its ability to survive to the assumed target life. V EHICLE I NSTRUMENTATION he maxi-scooter TmaxS was prepared for the application of a large number of channels, in order to have a certain degree of redundancy in the evaluation of loads and solicitations acting on the scooter. The full list of applied channels, their name and units, the type of sensor used are listed in Tab. 1. The location and sign convention of most of them are presented in Fig. 1. As it can be appreciated, most of the channels were strain gauge channels directly applied to the motorcycle components: as a measuring principle, the intrinsic compliance of the component under single load components was used to obtain a channel calibrated in the assembled configuration of the scooter. T T