BOA creates custom mechanical bellows designs to meet the requirements of specific automotive, on-road and off-road applications for exhaust, on-engine and intercooler systems. The company uses finite element analysis software to simulate the ability of proposed bellows designs to decouple the engine motion from the rest of the system. The company then builds a prototype of the proposed design that the customer installs on a vehicle for testing at the proving grounds, capturing data from accelerometers, strain gauges and displacement sensors.
The primary purpose of physical testing for BOA is to validate the critical tradeoff between static manufacturing/assembly offset and dynamic range. The exhaust flex joint has a certain amount of flexibility, or dynamic range, which is needed to accommodate the relative motion of the engine and the exhaust system. However, the initial variation in alignment between the engine and exhaust system, called the static offset, takes up a certain amount of that dynamic range. Physical testing is needed to determine the dynamic range required by the vehicle’s operating envelope to ensure it is within the flex hose’s dynamic range.
Physical testing is also performed to determine the fatigue life of the flex joint on this particular vehicle. The required life of the flex joint might be 150,000 miles, yet there is rarely time to drive the prototype for this full distance. In any case, the life of the flex joint is determined not by how many miles the vehicle is driven but by the number and magnitude of severe loads it receives, such as when the vehicle goes over a pothole. The amount of damage produced by these events is estimated by driving a prototype with the flex joint installed over potholes, Belgian blocks, or other hazards designed to generate severe loads on the flex joint. The loads from each event are recorded by the sensors.
The damaging events are converted to stresses and strains. The vehicle OEM determines a duty cycle that defines how many of each of these damaging events the vehicle is expected to see during its warranty life. The test data is compressed and accelerated to generate a damage profile that corresponds to the OEM’s duty cycle and is used as input for a fatigue analysis that predicts the life of the flex joint.