Australian Multiple Combinations test truck components to their limits, and a new initiative is setting up a real world coupling testing program, to assess the forces exerted on the connections between road train elements.
The project is an initiative of the ARTSA Institute as lead, alongside the Australian Trucking Association (ATA), Truck Industry Council (TIC) and Heavy Vehicle Industry Australia (HVIA) and is funded by the Commonwealth Government through the National Heavy Vehicle Regulator’s (NHVR) Heavy Vehicle Safety Initiative.
The project will be doing field testing on quad combinations, in the Northern Territory. The vehicles will be fitted with an array of instrumentation to make a series of measurements. Most of the equipment will be concentrated around the dolly and its connections the fifth wheel and the pin coupling.
“We are going to model that road and combination, virtually, within a program called MSC Adams Multibody Dynamics,” says Rob Smedley, Director and Senior Engineer, Smedley Engineers. “Then, we are able to virtually reconfigure the combination that was tested, and calibrate that model to the on road values we have measured. From there, we will be able to rearrange that virtual vehicle into a number of different combinations, such as AB-triples, quins and other types of combinations.
“From this data we will develop a new formula, which can be used to determine coupling forces in all sorts of different combinations.”
Parallel to the on road testing the team will also be setting up a couple of projects in which laboratory testing of components, emulating the kind of forces at play on the road, are carried out in more controlled conditions. This will further validate the field testing results.
The D-value is simply a shorthand coupling specification that relates to the dynamic force between the vehicles in a combination. The value increases with higher the masses are either side of any connection.
The D-value requirement between the prime mover and the first trailer in a quad set-up, at the fifth wheel, is relatively low because the prime mover is a lot lighter than the trailers behind. The connection that requires the highest D-value is the one in the middle, with high masses in the trailers in front of it and behind. This is the coupling which appears to be undergoing forces higher than the notional design limits of the couplings.
“The vehicle we have selected for the project, we believe is going to be the worst case,” says Rob. “We are going to model other combinations to confirm it is the worst case, when we have calibrated it. Then we will be able to do many more combinations, even down to singles and doubles, to make sure we aren’t over-estimating the forces.
“We should come up with a formula, which will be able to be used for all combination designers come up with. That’s the goal.”
The formula may not be one single calculation for all combinations. it may well turn out there is a different formula for each distinct configuration. The initial results of this research should be available in around 18 month’s time.
The next stage will be to incorporate the findings in the Australian Standard for these couplings. Once it is in the standards, that will feed back through the system, via relevant ADRs and the National Heavy Vehicle Standards.
The process of updating the Australian Standard is expected to be a relatively simple process, for this kind of change, because the decision-makers in this field are looking for a sound evidence base to provide clarity for the standard.
The whole process should provide engineers, road users and managers with confidence to design increasingly innovative combinations, with the benefit of a more precise knowledge of the forces being exerted on couplings within Australia’s heaviest combinations.
