Nick Jordan, technical engineering manager at a well-known military steering specialist, addresses the need for data-driven design in the manufacture of military vehicles
Data is a critical asset for military organisations, but it is only valuable if it’s meaningful and used effectively. This may explain why the military vehicle industry is proactively responding to evolving security threats and upgraded technologies.
It starts with real life military vehicles. Strain gauging equipment is added to test vehicles to calculate forces and collect meaningful design data for steering and suspension systems. By using data generated from real-life vehicles, design engineers can make more informed decisions on how to best manufacture a military vehicle.
It is not necessarily the static values of the load or frequency data that
is of most concern in the design process, considering that most military vehicles are designed to go above and beyond the actual loads and frequencies they will face. Rather, it’s the dynamic nature of the vehicle’s activity - the varying loads, changeable frequencies and irregular abusive loads that occur during the vehicle’s life that should be a fundamental consideration.
This use of real-life data takes this dynamism from the qualitative realm, so engineers can use this when developing a vehicles design.
It goes without saying that the current considerations for human-driven military vehicles will also need to be brought into the new paradigm of autonomous combat vehicles. For instance, adverse weather conditions, such as sandstorms, black ice and dust can challenge even the best military vehicles in the industry. Without an expert steering system, suspension system and chassis, you cannot leverage the new autonomous
Take just the steering system as an example. If the parts used aren’t bespoke to the vehicle and the conditions it will face, it will be severely limited in action, even with the most intelligent insight on far ahead objects. Thankfully, rigorous physical and environmental testing in the steering industry now means steering components can take on the debris, moisture and temperature variation that is faced in service, without resulting in water ingression or awkward high torque steering.
Testing of steering systems is primarily about replicating as near to the same conditions that would be encountered on the road. Theoretical testing using calculations is a good start, but nothing gets closer to reality than physical testing. Using an on-site test facility with purpose-built test rigs, it is possible to test a subassembly of the entire steering system, presenting the whole structure with ‘like for like’ conditions that match the final application.
One of the most important parameters to test for a military vehicle and its parts is the maximum load. With this information you can observe how much force a part can endure, in both tensile and compression, before a failure occurs. Using different rigs to test a range of force applications, forces up to ±400kN can be applied both statically and dynamically.
Moreover, with enough data, you can compile a multitude of loads at their respective frequencies and cycles as part of a dynamic block testing programme. This programme effectively mirrors the real-life data that is gathered from the vehicle to accurately assess the true fatigue life of the part.
With a variety of loads and frequencies in place, engineers can measure the number of cycles that the parts can endure over time, performing 1,000,000 load cycles in only one week. That’s enough to replicate infinite life for a part on a vehicle.
Validating light- weighted parts
Recently Pailton Engineering contributed to the development of a high-tech, well-armoured and incredibly agile military vehicle. The vehicle OEM asked for a small, lightweight steering drag link assembly that would allow the personnel carrier
to remain light and nimble, but also have the strength to handle the maximum load values the vehicle may face out in service.
Pailton’s team of designers analysed the loading information, selected
the right joints by carrying out theoretical calculations on all aspects of the assembly. However, this standard way of working wasn’t sufficient for such a non-standard request.
As the customer wanted such a small, light joint, just carrying out a theoretical calculation wasn’t enough. The team undertook a variety of physical testing to find a small enough part to fit the brief - which was incredibly challenging. They then took a different path to get around this problem, keeping the same geometry of the drag link but changing the material to a lightweight, yet strong, alternative.
The company designed, manufactured and continually tested this non-standard drag link throughout the design process to very accurate loads, to generate detailed findings.
To successfully navigate through water, the components underneath military vehicles must be completely sealed off to external elements to keep dust, grit and salt out of components, and lubrication in.
This is where environmental testing comes in. For military applications, this testing is arguably just as important as the physical testing. It is vital that every part of the steering system is able to handle water exposure, changes to temperature and humidity variance.
Military vehicles endure extreme conditions during their lifetime, taking on temperatures as low as -40ºC, without resulting in high torque steering.
Every test is designed to replicate the real conditions a vehicle will face, to ensure the vehicle is fit for purpose. While all military vehicles can differ, when it comes to the environmental testing of military-grade steering components, there are some crucial parameters to consider.
Pailton Engineering uses a salt spray test rig, where up to six steering parts at a time can be tested dynamically against salt spray, at varying temperatures. This rig is a large container with a rotary arm that controls the movement of steering components, normally at a rate of one cycle every three seconds - one cycle representing one turn of the steering wheel.
The test can use varying concentrations of salt, with higher concentrations being for the more extreme applications, as often seen in the military vehicle industry.
So, what can you expect to see from a test like this? The results will illustrate changes in torque, rate of corrosion, overall effect of grit on the vehicle and its steering system, as well as any potential for water ingress. Of course, the best possible result for this test to show is that these parts are capable of working in these conditions at low temperatures.
The same test rig can also be used to test the system against other factors, such as deep water. During rotary submersion, the parts are fully submerged in water. Ultimately, if a part can endure underwater movement at one cycle every three seconds, at varying temperatures, without corroding or failing, then the vehicle manufacturer can be confident in putting those steering parts in a military vehicle for use in the end environment.
There are alternatives that can be explored to improve the performance of a part. From different finishes, to upgraded sealing and greases, there has been plenty of scope for development in recent years. With steering components taking on new and improved design features and passing rotary submersion testing, comes new opportunities for high-performance extreme vehicles taking on deep water wading.
One customer’s request led to the production of the next generation of bevel boxes, needed for vehicles carrying out long journeys at low temperatures with high levels of moisture and grit. Bevel boxes are a pivotal component of a steering system, transmitting torque through 90° in order to provide a compact steering system package.
After improving on the design features of the previous bevel box, with a serration cover and alternative grease, the bevel box took on a 56 week long environmental test programme. Operated at a rate of one rotary cycle every three seconds continuously and submitted to salt exposure and temperatures of -40°C for four hours every week, the new design features were validated.
External validation showed the generation three bevel box conformed with ingress protection codes IP66 and IP67, which is great news for the military industry.
What does the future hold?
Warfare is changing, and governments are being forced to adapt their military vehicle fleets to keep up. The next five years will see the rapid adoption and adaptation of intelligent technology and applying this to disruptive military applications.
Some military vehicle manufacturers are receiving orders worth more than $195 million from the US army, take the Joint light Tactical Vehicle (JLTV) program for example. These vehicles will displace one third of the Marine Corps high mobility multipurpose wheeled vehicles (HMMWV) in 2019.
The impressive payload, miles range and high-speed military vehicles in general explains why this industry is generating so much interest. Some of these large vehicle orders are set to have planned operating capability by the end of 2020.
New technology could improve the survival rates of personnel - whether as a result of increased agility, autonomous resupply or high-performance steering, and it’s this notion that makes the implementation of such technology incredibly important.
Nick Jordan is Technical Engineering Manager at Pailton Engineering